Medical  Lib ran/  Exchange 


Medical  Society  of  the 
County  of  Kings 


Plate  1. 


FIG.   1. 


FIG.  2. 

FIG.  i. — Human  blood-corpuscles,  fresh ;  magnified  840  diameters,  -jV  inch  homogeneous  oil- 
immersion-objectivc  by  Zeiss,  original  negative  amplified  twice  (Stratford). 

FIG.  2. — Blood  of  Guinea-pig,  spread  and  dried  on  glass  cover;  magnified  1,450  diameters,  ^ 
inch  homogeneous  oil-immersion-objective  by  Zeiss,  and  Tolles's  amplifier  (Sternberg). 


A  TEXT-BOOK  OF 


HUMAN    PHYSIOLOGY 


BY 

AUSTIN  FLINT,   M.  D.,   LL.  D. 

PROFESSOR   OF   PHYSIOLOGY  AND   PHYSIOLOGICAL  ANATOMY   IN  THE    BELLEVUE   HOSPITAL   MEDICAL  COLLEGE 

NEW   YORK  I   VISITING   PHYSICIAN  T6  BELLEVUE    HOSPITAL  ;    FELLOW  OF  THE   NEW   YORK  STATE 

MEDICAL  ASSOCIATION  ;    CORRESPONDENT    OF    THE    ACADEMY    OP   NATURAL   SCIENCES 

OF  PHILADELPHIA  ;    MEMBER  OF  THE  AMERICAN  PHILOSOPHICAL  SOCIETY,  ETC. 


WITH  TUREE    'HUNDRED  AND  SIXTEEN  FIGURES  IN  THE  TEXT,  AND  THREE  PLATES 


FOURTH   EDITION,   ENTIRELY   REWRITTEN 


NEW    YORK 
D.    APPLE TON    AND    COMPANY 

1889 


COPYRIGHT,  1875,  1879,  1881,  1888, 
D.   APPLETON  AND  COMPANY. 


PREFACE. 


THE  present  edition  of  this  treatise  has  been  rewritten  ;  and  while  the 
general  arrangement  of  subjects  is  retained,  but  little  remains  of  the 
original  text.  Although  the  third  edition,  published  in  1880,  is  still 
much  used  as  a  text-book,  for  several  years  I  have  not  been  able  to  follow 
it  closely  in  public  teaching ;  and  its  defects  have  become  so  important 
that  it  has  seemed  to  me  impossible  to  remedy  them  without  making  a 
new  book. 

I  have  thought  it  advisable  to  curtail  still  more  the  historical  refer- 
ences contained  in  former  editions.  At  the  present  day  it  is  not  possible 
to  give  even  a  brief  account  of  the  literature  of  physiology  within  the 
limits  of  a  single  volume  of  convenient  size.  I  have  avoided,  also,  as  far 
as  practicable,  discussions  of  unsettled  and  disputed  questions,  as  un- 
profitable and  confusing. 

I  have  adopted  the  new,  chemical  nomenclature,  which  is  now  almost 
universally  accepted,  but  have  not  attempted  to  give  a  full  account  of  the 
chemistry  of  the  body.  Physiological  chemistry  has  now  become  a  sci- 
ence by  itself ;  and  while  it  has  contributed  very  largely  to  exact,  physio- 
logical knowledge,  its  full  consideration  is  properly  confined  to  special 
treatises. 

Recent  advances  in  the  knowledge  of  minute  anatomy,  due  largely  to 
improved  instruments  and  methods,  have  had  an  important  share  in  the 
progress  of  physiology.  These  have  been  considered  incidentally,  and 
they  now  form  an  essential  part  of  all  complete  works  on  anatomy. 

One  who  has  long  been  a  student  and  teacher  of  physiology  can 
hardly  fail  to  have  an  idea,  more  or  less  definite,  of  what  a  text-book 
should  be,  however  imperfectly  he  may  carry  out  this  idea  in  his  own 
work.  I  shall  be  more  than  satisfied  if  I  have  been  able  to  give  concise 
and  connected  statements  of  well-established  facts,  in  such  a  form  that 
they  can  easily  be  acquired  by  students  and  in  language  that  can  not  be 
misunderstood.  Peculiar  views  and  theories,  whether  of  the  author  or  of 
others,  have  no  proper  place  in  a  text-book,  which  should  represent  facts 
generally  recognized  and  accepted,  and  not  the  ideas  of  any  one  individual, 

8 


iv  PEEFACE. 

It  does  not  seem  to  me  that  the  value  of  a  text-book  is  materially  en- 
hanced by  elaborate  descriptions  of  apparatus  and  methods,  except  as 
they  involve  principles  susceptible  of  general,  physiological  application ; 
nor  does  it  seem  profitable  to  follow  out  the  details  of  intricate,  mathe- 
matical calculations  involved  in  certain  studies,  such  as  physiological 
optics  and  acoustics,  the  results  of  which  are  universally  accepted.  It  is 
sufficient  to  teach  by  text-books  the  science  of  physiology.  The  art  of 
investigation  and  the  methods  employed  in  physiological  research  are  to 
be  learned  in  the  laboratory  and  from  special  treatises  and  monographs. 

To  those  who,  by  early  education  and  common  usage,  have  long  been 
accustomed  to  English  weights  and  measures,  the  metric  system  frequently 
fails  to  convey  a  definite  idea,  without  a  mental  reduction  to  the  familiar 
standard ;  but  the  metric  system  is  now  very  generally  used  in  scientific 
works.  In  the  text,  the  English  weights  and  measures  and  the  Fahren- 
heit scale  of  the  thermometer  have  been  retained,  and  their  equivalents  in 
the  metric  system  are  given  in  parentheses.  In  microscopic  measure- 
ments the  micromillimetre  (ToV<F  °f  a  millimetre,  or  3-5-5-^  of  an  inch), 
indicated  by  the  Greek  letter  //,,  is  frequently  employed. 

The  form  and  typography  of  the  book  have  been  changed,  it  is  hoped 
for  the  better.  One  new  plate  and  sixty-one  new  figures  have  been  intro- 
duced. Two  plates  and  sixty-three  figures  have  been  discarded.  The  old 
illustrations  which  remain  have  been  carefully  examined  and  all  remedi- 
able defects  have  been  corrected.  For  most  of  the  illustrations  that  have 
been  retained,  new  electrotypes  have  been  taken  from  the  originals,  and 
thirty  cuts  have  been  re-engraved.  A  few  engravings,  however,  taken 
from  classical  authorities,  though  defective  from  an  artistic  point  of  view, 
have  been  retained  in  their  original  form.  It  is  due  to  the  publishers  to 
make  these  statements,  and  to  say  that  they  have  spared  nothing  in  the 
mechanical  execution  of  the  work. 

AUSTIN  FLINT. 

NEW  YORK,  August,  1888. 


I  HAVE  taken  advantage  of  the  opportunity  afforded  by  the  printing 
of  a  second  impression  of  this  edition,  to  introduce  a  new  description  of 
the  anatomy  of  the  human  ovum,  with  a  lithographic  plate,  in  accord- 
ance with  the  very  recent  studies  of  the  normal,  human  ovum,  by  Nagel 
(1888).  These  observations  appeared  after  the  fourth  edition  had  been 
completed.  I  have  also  introduced  three  new  figures  in  the  text,  and 
have  revised  the  descriptions  of  fecundation  of  the  ovum  and  segmenta- 
tion of  the  vitellus. 

A.  F. 
March,  1889. 


CONTENTS. 


CHAPTER  I. 

THE  BLOOD. 

PAGE 

Quantity  of  blood— General  characters  of  the  blood— Blood-corpuscles— Development  of  the  blood- 
corpuscles — Leucocytes — Development  of  leucocytes — Blood-plaques — Composition  of  the  red  cor- 
puscles— Globuline — Hwmaglobine — Composition  of  the  blood-plasma — Inorganic  Constituents — 
Organic  saline  constituents — Organic  non-nitrogenized  constituents — Excrcmentitious  constituents 
— Organic  nitrogenized  constituents — Plasmine,  fibrin,  metalbumen,  serine — Peptones — Coloring 
matter— Coagulation  of  the  blood— Conditions  which  modify  coagulation— Coagulation  of  the  blood 
in  the  organism — Cause  of  the  coagulation  of  the  blood ....  1 

CHAPTER   II. 
CIRCULATION  OF  THE  BLOOD-ACTION  OF  THE  HEART. 

Discovery  of  the  circulation— Physiological  anatomy  of  the  heart— Valves  of  the  heart— Movements  of 
the  heart — Impulse  of  the  heart — Succession  of  the  movements  of  the  heart — Force  of  the  heart — 
Action  of  the  valves — Sounds  of  the  heart — Causes  of  the  sounds  of  the  heart — Frequency  of  the 
heart's  action — Influence  of  age  and  sex — Influence  of  digestion — Influence  of  posture  and  muscu- 
lar exertion— Influence  of  exercise  etc. — Influence  of  temperature — Influence  of  respiration  on  the 
action  of  the  heart — Cause  of  the  rhythmical  contractions  of  the  heart — Accelerator  nerves — Direct 
inhibition  of  the  heart — Reflex  inhibition  of  the  heart — Summary  of  certain  causes  of  arrest  of  the 
action  of  the  heart 29 

CHAPTER  III. 
CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

Physiological  anatomy  of  the  arteries — Course  of  blood  in  the  arteries — Locomotion  of  the  arteries  and 
production  of  the  pulse— Pressure  of  blood  in  the  arteries— Pressure  in  different  parts  of  the  arterial 
system— Depressor  nerve— Influence  of  respiration  on  the  arterial  pressure— Rapidity  of  the  current 
of  blood  in  the  arteries— Rapidity  in  different  parts  of  the  arterial  system— Circulation  of  the  blood 
in  the  capillaries— Physiological  anatomy  of  the  capillaries— Pressure  of  blood  in  the  capillaries- 
Relations  of  the  capillary  circulation  to  respiration— Causes  of  the  capillary  circulation — Influence 
of  temperature  on  the  capillary  circulation — Influence  of  direct  irritation  on  the  capillary  circulation 
— Circulation  of  the  blood  in  the  veins — Physiological  anatomy  of  the  veins — Course  of  the  blood  in 
the  veins — Pressure  of  blood  in  the  veins — Rapidity  of  the  venous  circulation — Causes  of  the  venous 
circulation — Air  in  the  veins — Uses  of  the  valves — Conditions  which  impede  the  venous  circulation 
— Regurgitant  venous  pulse — Circulation  in  the  cranial  cavity — Circulation  in  erectile  tissues — 
Derivative  circulation — Pulmonary  circulation — Circulation  in  the  walls  of  the  heart — Passage  of 
the  blood-corpuscles  through  the  walls  of  the  vessels  (diapedesis) — Rapidity  of  the  circulation — 
Phenomena  in  the  circulatory  system  after  death 60 

CHAPTER  IV. 

RESPIRA  TION-RESPIRA  TOR  Y  MO  VEMENTS. 

General  considerations — Physiological  anatomy  of  the  respiratory  organs — Movements  of  respiration — 
Inspiration— Muscles  of  inspiration— Expiration— Muscles  of  expiration — Types  of  respiration— 


vi  CONTENTS. 


PAGE 


Frequency  of  the  respiratory  movements— Relations  of  inspiration  and  expiration  to  each  other 
—Respiratory  sounds— Capacity  of  the  lungs  and  the  quantity  of  air  changed  in  the  respiratory 
acts— Residual  air— Reserve  air— Tidal,  or  breathing  air — Complemental  air— Extreme  breathing 
capacity— Relations  in  volume  of  the  expired  to  the  inspired  air— Diffusion  of  air  in  the  lungs  .  .  108 

CHAPTER   V. 
CHANGES  WHICH  THE  AIR  AND   THE  BLOOD   UNDERGO  IN  RESPIRATION. 

Composition  of  the  air— Consumption  of  oxygen— Exhalation  of  carbon  dioxide— Relations  between  the 
quantity  of  oxygen  consumed  and  the  quantity  of  carbon  dioxide  exhaled— Sources  of  carbon 
dioxide  in  the  expired  air— Exhalation  of  watery  vapor— Exhalation  of  ammonia — Exhalation  of 
organic  matter— Exhalation  of  nitrogen— Changes  of  the  blood  in  respiration  (hteinatosis)— Difference 
in  color  between  arterial  and  venous  blood— Comparison  of  the  gases  in  venous  and  arterial  blood- 
Analysis  of  the  blood  for  gases— Nitrogen  of  the  blood— Condition  of  the  gases  in  the  blood— Rela- 
tions of  respiration  to  nutrition  etc.— The  respiratory  sense— Sense  of  suffocation— Respiratory 
efforts  before  birth — Cutaneous  respiration— Breathing  in  a  confined  space— Asphyxia  .  .  .135 

CHAPTER  VI. 

ALIMENTATION. 

General  considerations— Hunger— Seat  of  the  sense  of  hunger— Thirst— Seat  of  the  sense  of  thirst- 
Duration  of  life  in  inanition— Classification  of  alimentary  substances— Nitrogenized  alimentary 
substances— Non-nitrogenized  alimentary  substances— Inorganic  alimentary  substances— Alcohol 
— Coffee— Tea— Chocolate— Condiments  and  flavoring  articles— Quantity  and  variety  of  food  neces- 
sary to  nutrition— Necessity  of  a  varied  diet 1G4 

CHAPTER  VII. 

DIGESTION— MASTICATION,  INSALIVATION  AND  DEGLUTITION. 

Prehension  of  food— Mastication— Physiological  anatomy  of  the  teeth— Anatomy  of  the  maxillary  bones 
— Temporo-maxillary  articulation— Muscles  of  mastication— Action  of  the  tongue,  lips  and  cheeks 
in  mastication— Parotid  saliva— Submaxillary  saliva — Sublingual  saliva— Fluids  from  the  smaller 
glands  of  the  mouth,  tongue  and  fauces— Mixed  saliva — Quantity  of  saliva— General  properties 
and  composition  of  the  saliva— Action  of  the  saliva  on  starch— Uses  of  the  saliva— Physiological 
anatomy  of  the  parts  concerned  in  deglutition — Mechanism  of  deglutition — First  period  of  degluti- 
tion—Second period  of  deglutition — Protection  of  the  posterior  nares  during  the  second  period  of 
deglutition— Protection  of  the  opening  of  the  larynx  and  uses  of  the  epiglottis  in  deglutition— Third 
period  of  deglutition — Deglutition  of  air 188 

CHAPTER   VIII. 
GASTRIC  DIGESTION. 

Physiological  anatomy  of  the  stomach  —  Glands  of  the  stomach — Closed  follicles— Gastric  juice- 
Gastric  fistula  in  the  human  subject  in  the  case  of  St.  Martin— Secretion  of  the  gastric  juice- 
Properties  and  composition  of  gastric  juice— Action  of  the  gastric  juice  in  digestion — Peptones — 
Action  of  the  gastric  juice  upon  fats,  sugars  and  amylaceous  substances — Duration  of  gastric  diges- 
tion—Conditions which  influence  gastric  digestion — Movements  of  the  stomach 211 

CHAPTER   IX. 

INTESTINAL  DIGESTION. 

Physiological  anatomy  of  the  small  intestine— Glands  of  Brunner— Intestinal  tubules,  or  follicles  of 
Lieberkuhn—  Intestinal  villi— Solitary  glands,  or  follicles,  and  patches  of  Peyer— Intestinal  juice — 
Action  of  the  intestinal  juice  in  digestion— Pancreatic  juice — Action  of  the  pancreatic  juice  upon 
starches  and  sugars— Action  upon  nitrogenized  substances— Action  upon  f;its— Action  of  the  bile 
in  digestion— Biliary  fistula— A7ariations  in  the  flow  of  bile— Movements  of  the  small  intestine- 
Peristaltic  and  antiperistaltic  movements— Uses  of  the  gases  in  the  small  intestine— Physiological 
anatomy  of  the  large  intestine— Processes  of  fermentation  in  the  intestinal  canal— Contents  of  the 
large  intestine— Composition  of  the  faeces— Excretine  and  excretoleic  acid— Stercorine— Indol,  skatol, 
phenol  etc.— Movements  of  the  large  intestine— Defalcation— Gases  found  in  the  alimentary  canal  .  233 


CONTENTS.  vii 

PAGE 

CHAPTER   X. 

ABSORPTION-LYMPH  AND   CHYLE. 

Absorption  by  blood-vessels — Absorption  by  lacteal  and  lymphatic  vessels— Physiological  anatomy  of 
the  lacteal  and  lymphatic  vessels— Lymphatic  glands— Absorption  by  the  lacteals—  Absorption  by 
the  skin — Absorption  by  the  respiratory  surface — Absorption  from  closed  cavities,  reservoirs  of 
glands,  etc.— Absorption  of  fats  and  insoluble  substances— Variations  and  modifications  of  ab- 
sorption—Mechanism of  the  passage  of  liquids  through  membranes— Lymph  and  chyle— Properties 
and  composition  of  lymph— Origin  and  uses  of  the  lymph— Composition  of  the  chyle— Microscopical 
characters  of  the  chyle— Movements  of  the  lymph  and  chyle 272 

CHAPTER   XI. 
SECRETION. 

Classification  of  the  secretions — Mechanism  of  the  production  of  the  true  secretions— Mechanism  of 
the  production  of  the  excretions — Influence  of  the  composition  and  pressure  of  the  blood  on  se- 
cretion— Influence  of  the  nervous  system  on  secretion— Anatomical  classification  of  glandular 
organs — Classification  of  the  secreted  fluids — Synovial  membranes  and  synovia — Mucous  mem- 
branes and  mucus— Physiological  anatomy  of  the  sebaceous,  ceruminous  and  Meibomian  glands- 
Ordinary  sebaceous  matter— Smegma  of  the  prepuce  and  of  the  labia  minora— Vernix  caseosa — 
Cerumen— Meibomian  secretion— Mammary  secretion— Physiological  anatomy  of  the  mammary 
glands— Mechanism  of  the  secretion  of  milk— Conditions  which  modify  the  lacteal  secretion- 
Quantity  of  milk— Properties  and  composition  of  milk— Microscopical  characters  of  milk— Composi- 
tion of  milk— Variations  in  the  composition  of  milk— Colostrum— Lacteal  secretion  in  the  newly- 
born— Secretory  nerve-centres 306 

CHAPTER  XII. 

EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

Differences  between  the  secretions  proper  and  the  excretions— Physiological  anatomy  of  the  skin — 
Physiological  anatomy  of  the  nails — Physiological  anatomy  of  the  hairs — Sudden  blanching  of  the 
hair — Perspiration — Sudoriparous  glands — Mechanism  of  the  secretion  of  sweat — Properties  and 
composition  of  the  sweat— Peculiarities  of  the  sweat  in  certain  parts — Physiological  anatomy  of  the 
kidneys— Mechanism  of  the  production  and  discharge  cf  urine— Influence  of  blood-pressure,  the 
nervous  system  etc.,  upon  the  secretion  of  urine— Physiological  anatomy  of  the  urinary  passages 
—Mechanism  of  the  discharge  of  urine— Properties  and  composition  of  the  urine— Influence  of 
ingcsta  upon  the  composition  of  the  urine  and  upon  the  elimination  of  nitrogen — Influence  of  mus- 
cular exercise  upon  the  elimination  of  nitrogen — Water  regarded  as  a  product  of  excretion — Varia- 
tions in  the  composition  of  the  urine 341 

CHAPTER   XIII. 

USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

Physiological  anatomy  of  the  liver— Distribution  of  the  portal  vein,  the  hepatic  artery  and  the  hepatic 
duct— Structure  of  a  lobule  of  the  liver— Arrangement  of  the  bile-ducts  in  the  lobules— Anatomy  of 
the  excretory  biliary  passages— Nerves  and  lymphatics  of  the  liver — Mechanism  of  the  secretion  and 
discharge  of  bile— Quantity  of  bile— Uses  of  the  bile— Properties  and  composition  of  the  bile— Biliary 
salts— Cholesterine — Tests  for  bile — Excretory  action  of  the  liver— Formation  of  glycogen  in  the 
liver— Change  of  glycogen  into  sugar — Conditions  which  influence  the  quantity  of  sugar  in  the 
blood— Summary  of  the  glycogenic  action  of  the  liver — Probable  office  of  the  ductless  glands- 
Physiological  anatomy  of  the  spleen— Suprarenal  capsules— Addison's  disease— Thyroid  gland— 
Myxoedema— Thymus— Pituitary  body  and  pineal  gland 392 

CHAPTER   XIV. 

NUTRITION-ANIMAL  HEAT  AND  FORCE. 

Nature  of  the  forces  involved  in  nutrition— Life,  as  represented  in  development  and  nutrition— Sub- 
stances which  pass  through  the  organism— Metabolism— Substances  consumed  in  the  organism- 
Conditions  which  influence  nutrition— Animal  heat  and  force— Estimated  quantity  of  heat  produced 
by  the  body— Limits  of  variation  in  the  normal  temperature  in  man— Variations  with  external  tem- 
perature—Variations in  different  parts  of  the  body— Variations  at  different  periods  of  life  etc.— 


viii  CONTENTS. 

PAGE 

Influence  of  exercise  etc.,  upon  the  heat  of  the  body— Influence  of  the  nervous  system  upon  the 
production  of  animal  heat  (heat-centres)— Mechanism  of  the  production  of  animal  heat— Equaliza- 
tion of  the  animal  temperature— Relations  of  heat  to  force 420 

CHAPTER   XV. 

MOVEMENTS-VOICE  AND  SPEECH. 

Amorphous  contractile  substance  and  amoeboid  movements— Ciliary  movements— Movements  due  to 
elasticity— Elastic  tissue— Muscular  movements — Physiological  anatomy  of  the  involuntary  muscu- 
lar tissue— Contraction  of  the  involuntary  muscular  tissue— Physiological  anatomy  of  the  voluntary 
muscular  tissue— Connective  tissue — Connection  of  the  muscles  with  the  tendons — Chemical  com- 
position of  the  muscles— Physiological  properties  of  the  muscles— Muscular  contractility,  or  excita- 
bility— Muscular  contraction — Electric  phenomena  in  muscles — Muscular  effort — Passive  organs  of 
locomotion — Physiological  anatomy  of  the  bones — Physiological  anatomy  of  cartilage — Voice  and 
speech — Sketch  of  the  physiological  anatomy  of  the  vocal  organs — Mechanism  of  the  production  of 
the  voice— Laryngeal  mechanism  of  the  vocal  registers— Mechanism  of  speech — The  phonograph  .  460 

CHAPTER   XVI. 

PHYSIOLOGICAL  DIVISIONS,  STRUCTURE  AND   GENERAL  PROPERTIES  OF  THE 

NERVOUS  SYSTEM. 

Divisions  and  structure  of  the  nervous  tissue— Medullated  nerve-fibres— Simple,  or  non-medullated 
nerve-fibres— Gelatinous  nerve-fibres  (fibres  of  Remak)— Accessory  anatomical  elements  of  the 
nerves — Termination  of  the  nerves  in  the  muscular  tissue — Termination  of  the  nerves  in  glands — 
Modes  of  termination  of  the  sensory  nerves — Corpuscles  of  Vater,  or  of  Pacini — Tactile  corpuscles 
—End-bulbs— Structure  of  the  nerve-centres— Nerve-cells— Connection  of  the  cells  with  the  fibres 
and  with  each  other— Accessory  anatomical  elements  of  the  nerve-centres— Composition  of  the 
nervous  substance— Degeneration  and  regeneration  of  the  nerves— Motor  and  sensory  nerves— Mode 
of  action  of  the  motor  nerves — Associated  movements — Mode  of  action  of  the  sensory  nerves — 
Physiological  differences  between  motor  and  sensory  nerve-fibres— Nervous  excitability— Different 
means  employed  for  exciting  the  nerves— Rapidity  of  nervous  conduction— Personal  equation- 
Action  of  electricity  upon  the  nerves— Law  of  contraction— Induced  muscular  contraction— Electro- 
tonus,  anelectrotonus  and  catelectrotonus— Negative  variation 501 

CHAPTER  XVII. 

SPINAL  AND  CRANIAL  NERVES. 

Spinal  nerves— Cranial  nerves— Anatomical  classification— Physiological  classification— Motor  oculi 
communis  (third  nerve) — Physiological  anatomy — Properties  and  uses— Influence  upon  the  move- 
ments of  the  iris— Patheticus,  or  trochlearis  (fourth  nerve)— Physiological  anatomy — Properties  and 
uses— Motor  oculi  externus,  or  abducens  (sixth  nerve)— Physiological  anatomy— Properties  and  uses 
— Nerve  of  mastication  (the  small,  or  motor  root  of  the  fifth)— Physiological  anatomy— Properties 
and  nses — Facial,  or  nerve  of  expression  (seventh  nerve) — Physiological  Anatomy — Intermediary 
nerve  of  Wrisberg — Alternate  paralysis — General  properties — Uses  of  the  chorda  tympani — Influence 
of  various  branches  of  the  facial  upon  the  movements  of  the  palate  and  uvula— Spinal  accessory 
(eleventh  nerve)— Physiological  anatomy— Uses  of  the  internal  branch  from  the  spinal  accessory  to 
the  pneumogastric— Influence  of  the  spinal  accessory  upon  the  heart— Uses  of  the  external,  or  mus- 
cular branch  of  the  spinal  accessory — Sublingiial,  or  hypoglossal  (twelfth  nerve)— Physiological 
anatomy — Properties  and  uses— Trifacial,  or  trigeminal  (fifth  nerve)— Physiological  anatomy— Prop- 
erties and  nses— Pneumogastric  (tenth  nerve)— Physiological  anatomy— Properties  and  uses— Gen- 
eral properties  of  the  roots — Properties  and  uses  of  the  auricular  nerves — Properties  and  uses  of  the 
pharyngeal  nerves— Properties  and  uses  of  the  superior  laryngeal  nerves— Properties  and  nses  of  the 
inferior,  or  recurrent  laryngeal  nerves— Properties  and  uses  of  the  cardiac  nerves— Depressor  nerve 
of  the  circulation — Properties  and  uses  of  the  pulmonary  nerves— Properties  and  uses  of  the  ceso- 
phageal  nerves— Properties  and  uses  of  the  abdominal  nerves 53D 

CHAPTER  XVI  [I. 

THE  SPINAL    CORD. 

General  arrangement  of  the  cerebro-spinal  axis— Membranes  of  the  encephalon  and  spinal  cord— Cephalo- 
rachidian  fluid— Physiological  anatomy  of  the  spinal  cord— Columns  of  the  cord— Direction  of  the 
nerve-fibres  in  the  cord— General  properties  of  the  spinal  cord— Motor  paths  in  the  cord— Sensory 


CONTENTS.  ix 

PAGE 

paths  in  the  cord — Relations  of  the  posterior  white  columns  of  the  cord  to  muscular  co-ordination — 
Nerve-centre*  in  the  spinal  cord — Reflex  action  of  the  spinal  cord — Exaggeration  of  reflex  excitability 
by  decapitation,  poisoning  with  strychnine  etc.— Reflex  phenomena  observed  in  the  human  subject  586 

CHAPTER   XIX. 

THE  ENCEPHALIC  GANGLIA. 

Physiological  divisions  of  the  encephalon— Weights  of  the  encephalon  and  of  certain  of  its  parts— The 
cerebral  hemispheres— Cerebral  Convolutions— Basal  ganglia— Corpora  striata,  optic  thalami  and 
internal  capsule — Tubercular  quadrigemina — Pons  Varolii — Directions  of  the  fibres  in  the  cerebrum 
—Cerebral  localization — General  uses  of  the  cerebrum— Extirpation  of  the  cerebrum — Facial  angle- 
Pathological  observations— Reaction-time — Centre  for  the  expression  of  ideas  in  language — The 
cerebellum — Physiological  anatomy — Extirpation  of  the  cerebellum — Pathological  observations — 
Connection  of  the  cerebellum  with  the  generative  function — Medulla  oblongata  (Bulb) — Physiologi- 
cal anatomy — .Uses  of  the  medulla  oblongata — Respiratory  nerve-centre — Cardiac  centres — Vital 
point  (so  called)— Rolling  and  turning  movements  following  injury  of  certain  parts  of  the  encephalon  601 

CHAPTER   XX. 

SYMPATHETIC  NERVOUS  SYSTEM— SLEEP. 

General  arrangement  of  the  sympathetic  system— General  properties  of  the  sympathetic  ganglia  and 
nerves— Direct  experiments  on  the  sympathetic— Vaso-motor  centres  and  nerves— Reflex  vaso-motor 
phenomena — Vaso-inhibitory  nerves — Trophic  centres  and  nerves  (so-called) — Sleep — Condition  of 
the  brain  and  nervous  system  during  sleep— Anaesthesia  and  sleep  produced  by  pressure  upon  the 
carotid  arteries— Differences  between  natural  sleep  and  stupor  or  coma— Regeneration  of  the  brain- 
substance  during  sleep — Condition  of  the  organism  during  sleep  ......  633 

CHAPTER   XXI. 
SPECIAL  SENSES— TOUCH,  OLF ACTION  AND  GUSTATION. 

General  characters  of  the  special  senses— Muscular  sense  (so  called) — Sense  of  touch — Variations  in 
tactile  sensibility  in  different  parts  (sense  of  locality  of  impressions)— Table  of  variations  measured 
by  the  festlu'siometer — Appreciation  of  temperature — Tactile  centre — Olfaction — Nasal  fossae — 
Schneiderian  and  olfactory  membranes— Olfactory  (first  nerve)— Physiological  anatomy — Olfactory 
bulbs— Olfactory  cells  and  terminations  of  the  olfactory  nerve-fibres— Properties  and  uses  of  the 
olfactory  nerves — Mechanism  of  olfaction — Relations  of  olfaction  to  the  sense  of  taste — Reflex  acts 
through  the  olfactory  nerves — Olfactory  centre — Gustation — Savors — Nerves  of  taste — Chorda  tym- 
pani — QloBSO-pharyngea]  (ninth  nerve)— Physiological  anatomy — General  properties  of  the  glosso- 
pharyngeal— Relations  of  the  glosso-pharyngeal  nerves  to  gustation— Mechanism  of  gustation- 
Physiological  anatomy  of  the  organ  of  taste— Papillae  of  the  tongue— Taste-beakers— Connections  of 
the  nerves  with  the  organs  of  taste— Taste-centre  .  652 


CHAPTER   XXII. 
VISION. 

General  considerations— Optic  (second  nerve) — General  properties  of  the  optic  nerves— Physiological 
anatomy  of  the  eyeball— Sclerotic  coat — Cornea— Choroid  coat— Ciliary  mnscle— Iris— Pupillary 
membrane— Retina—  Crystalline  lens— Aqueous  humor — Chambers  of  the  eye— Vitreous  humor — 
Summary  of  the  anatomy  of  the  globe— The  eye  as  an  optical  instrument— Certain  laws  of  refrac- 
tion, dispersion  etc.,  bearing  upon  the  physiology  of  vision — Refraction  by  lenses — Visual  purple 
and  visual  yellow  and  accommodation  of  the  eye  for  different  degrees  of  illumination— Formation  of 
images  in  the  eye— Mechanism  of  refraction  in  the  eye — Astigmatism— Movements  of  the  iris— Di- 
rect action  of  light  upon  the  iris— Action  of  the  nervous  system  upon  the  iris— Mechanism  of  the 
movements  of  the  iris— Accommodation  of  the  eye  for  vision  at  different  distances— Changes  in 
the  crystalline  lens  in  accommodation — Changes  in  the  iris  in  accommodation— Erect  impressions 
produced  by  images  inverted  upon  the  retina— Field  of  indirect  vision— The  perimeter— Binocular 
vision— Corresponding  points— The  horopter— Duration  of  luminous  impressions  (after-images)— 
Irradiation— Movements  of  the  eyeball— Muscles  of  the  eyeball— Centres  for  vision— Parts  for  the 
protection  of  the  eyeball — Conjunctiva!  mucous  membrane— Lachrymal  apparatus— Composition  of 
the  tears  .  .  .671 


x  CONTENTS. 

PAGE 

CHAPTER   XXIII. 
AUDITION. 

Auditory  (eighth  nerve)— General  properties  of  the  auditory  nerves— Topographical  anatomy  of  the 
parts  essential  to  the  appreciation  of  sound— The  external  ear— General  arrangement  of  the  parts 
composing  the  middle  ear — Anatomy  of  the  tympanum — Arrangement  of  the  ossicles  of  the  ear — 
Muscles  of  the  middle  ear— Mastoid  cells— Eustachian  tube— Muscles  of  the  Eustachian  tube— Gen- 
eral arrangement  of  the  bony  labyrinth— Physics  of  sound— Noise  and  musical  sounds— Pitch  of 
musical  sounds— Musical  scale— Quality  of  musical  sounds— Harmonics,  or  overtones— Resultant 
tones— Summation  tones— Harmony— Discords— Tones  by  influence— Uses  of  different  parts  of  the 
auditory  apparatus— Structure  of  themembrana  tympani— Uses  of  themembrana  tympani— Mechan- 
ism of  the  ossicles  of  the  ear — Physiological  anatomy  of  the  internal  ear — General  arrangement  of 
the  membranous  labyrinth — Liquids  of  the  labyrinth — Distribution  of  nerves  in  the  labyrinth — Or- 
gan of  Corti— Uses  of  different  parts  of  the  internal  ear— Centres  for  audition  .  .  .  .728 

CHAPTER   XXIV. 
ORGANS  AND  ELEMENTS  OF  GENERATION. 

General  considerations — Female  organs  of  generation — General  arrangement  of  the  female  organs — 
The  ovaries — Graafian  follicles — The  parovariuin — The  uterus — The  Fallopian  tubes — Structure  of 
the  ovum — Discharge  of  the  ovum — Passage  of  ova  into  the  Fallopian  tubes — Puberty  and  menstrua- 
tion— Changes  in  the  Graafian  follicle  after  its  rupture  (corpus  luteum) — Male  organs  of  genera- 
tion—The testicles — Vesiculse  seminales— Prostate— Glands  of  the  urethra — Male  elements  of  gen- 
eration—Spermatozoids  ............  765 

CHAPTER  XXV. 

FECUNDATION  AND  DEVELOPMENT  OF  THE  OVUM. 

General  considerations— Fecundation— Changes  in  the  fecundated  ovum— Segmentation  of  the  vitell- 
us— Primitive  trace— Blastodermic  layers— Formation  of  the  membranes— Amniotic  fluid— Umbilical 
vesicle— Formation  of  the  allantois  and  the  permanent  chorion— Umbilical  cord— Membranes  de- 
cidua;— Formation  of  the  placenta— Uses  of  the  placenta— Development  of  the  ovum— Development 
of  the  cavities  and  layers  of  the  trunk  in  the  chick— Vertebral  column— Development  of  the  skele- 
ton—Development of  the  muscles— Development  of  the  skin— Development  of  the  nervous  system 
— Development  of  the  organs  of  special  sense— Development  of  the  digestive  apparatus— Develop- 
ment of  the  respiratory  apparatus— Development  of  the  face — Development  of  the  teeth — Develop- 
ment of  the  genito-urinary  apparatus— Development  of  the  circulatory  apparatus — Description  of 
the  foetal  circulation  ............  793 

CHAPTER  XXVI. 

FCETAL  LIFE-DEVELOPMENT  AFTER  BIRTH— DEATH. 

Enlargement  of  the  uterus  in  pregnancy— Duration  of  pregnancy — Size,  weight  and  position  of  the 
foetus  — The  foetus  at  different  stages  of  intraiiterine  life— Multiple  pregnancy— Cause  of  the  first 
contractions  of  the  uterus,  in  normal  parturition— Involution  of  the  uterus— Meconium— Dextral 
pre-eminence— Development  after  birth— Ages— Death— Cadaveric  rigidity  (rigor  mortis)  .  .  843 


LIST  OF  ILLUSTRATIONS. 


Plate     I,  Fig.  1.   Human  blood-corpuscles  (Stratford)  ) 

"     2.   Blood  of  Guinea-pig  (Sternberg) ...  f Frontispiece. 

Plate    II,  Fig.  1.   Deutoplasm-forming  ovum  from  a  Graafian  fol-'j 

licle  of  a  woman  twenty-seven  years  old. .  .  .  I  (Nagel).  .facing  m 
1     2.    Fresh  ovum  from  a  Graafian  follicle  of  a  woman 

thirty  years  old J 

Plate  III,  Fig.  1.   Human  embryon  at  the  ninth  week. .  j  (Erdl)                      _  fadng  page  g()5 
"     2.   Human  embryon  at  the  twelfth  week  ) 

FIGURE  PAGE 

1.  Human  blood-corpuscles  (Sternberg) 6 

2.  Human  red  blood-corpuscles  arranged  in  rows  (Funke) 7 

3.  Blocd-corpuscles  of  the  frog  (United  States  Army  Medical  Museum) 8 

4.  Artificial  capillary  filled  with  a  sanguineous  mixture,  seen  under  a  micrometer  (Malas- 

sez) 9 

5.  Human  blood-corpuscles,  showing  post-mortem  alterations  (Funke) 9 

6.  Human  leucocytes,  showing  amoeboid  movements  (Landois) 12 

7.  Human  red  blood-corpuscles  and  two  leucocytes  (Sternberg) 14 

8.  Blood-plaques  and  their  derivatives  (Landois) 16 

y.  Crystallized  haemaglobine  (Gautier) 18 

10.  Coagulated  fibrin  (Robin) '. 28 

11.  Heart  in  situ  (Dalton) 32 

12.  Course  of  the  muscular  fibres  of  the  left  auricle  (Landois) 33 

13.  Heart,  anterior  view  (Bonamy  and  Beau) 33 

14.  Left  cavities  of  the  heart  (Bonamy  and  Beau) 34 

15.  Right  cavities  of  the  heart  (Bonamy  and  Beau) 35 

16.  Muscular  fibres  of  the  ventricles  (Bonamy  and  Beau) 36 

17.  Branched  muscular  fibres  from  the  heart  (Landois) 37 

18.  Valves  of  the  heart  (Bonamy  and  Beau) 37 

19.  Diagram  showing  shortening  of  the  ventricles  during  systole 40 

20.  Side  view  of  the  heart  (Landois) 40 

21.  Cardiograph  (Chauveau  and  Marey) 41 

22.  Scheme  of  the  course  of  the  accelcrans  fibres  (Stirling) 55 

23.  Small  artery  from  the  mesentery  of  the  frog  (United  States  Army  Medical  Museum). . .  63 

24.  Sphygmograph  of  Marey 67 

25.  Sphygmograph  applied  to  the  arm  (Marey) 68 

26.  Trace  of  the  pulse  (Vierordt) 68 

27.  Portions  of  four  traces  taken  in  different  conditions  of  the  pulse  (Marey) 68 

28.  Cardiometer  of  Magcndie  (Bernard) 72 

29.  Compensating  instrument  of  Marey 73 

30.  Chauvcau's  instrument  for  measuring  the  rapidity  of  the  flow  of  blood  in  the  arteries.  76 

31.  Capillary  blood-vessels  (Landois) 78 

32.  Small  artery  and  capillaries  (United  States  Army  Medical  Museum) 80 

33.  Web  of  the  frog's  foot  (Wagner) 81 

34.  Circulation  in  the  web  of  the  frog's  foot  (Wagner) 82 


xii  LIST  OF  ILLUSTRATIONS. 

FIGURE  PAGE 

35.  Small  artery  and  capillaries  from  the  lung  of  the  frog  (United  States  Army 'Medical 

Museum) 83 

36.  Portion  of  the  lung  of  a  live  triton  (Wagner) 84 

37.  Venous  radicles  uniting  to  form  a  small  vein  (United  States  Army  Medical  Museum). .  88 

38.  'Small  blood-vessel  of  the  mesentery  of  the  frog,  showing  diapedesis  of  leucocytes 

(Landois) „ .  105 

39.  Trachea  and  bronchial  tubes  (Sappey) 110 

40.  Lungs,  anterior  view  (Sappey) 112 

41.  Bronchia  and  lung.-;,  anterior  view  (Sappey) 113 

42.  Mould  of  a  terminal  bronchus  and  a  group  of  air-cells  (Robin) 114 

43.  Section  of  the  parenchyma  of  the  human  lung,  injected  through  the  pulmonary  artery 

(Schultze) 115 

44.  Thorax,  anterior  view  (Sappey) 116 

•   45.  Thorax,  posterior  view  (Sappey) • 116 

46.  Diaphragm  (Sappey) .- 118 

47.  Action  of  the  diaphragm  in  inspiration  (Hermann) 118 

48.  Elevation  of  the  ribs  in  inspiration  (Beclard) 120 

49.  Arrowroot  starch-granules  (United  States  Army  Medical  Museum) 172 

50.  Crystals  of  palmitinc  and  palmitic  acid  (Funke) 173 

51.  Crystals  of  stearine  and  stearic  acid  (Funke) 173 

52.  Tooth  of  the  cat  (\Valdeyer).. : 190 

53.  Inferior  maxilla  (Sappey) 192 

54.  Salivary  glands  (Tracy) 195 

55.  Cavities  of  the  mouth,  pharynx  etc.  (Sappey) 203 

56.  Muscles  of  the  pharynx,  etc.  (Sappey) 204 

57.  Longitudinal  fibres  of  the  stomach  (Sappey) 212 

58.  Fibres  seen  with  the  stomach  everted  (Sappey) 213 

59.  Pits  in  the  mucous  membrane  of  the  stomach,  and  orifices  of  the  glands  (Sappey) 213 

60.  Goblet-cells  from  the  stomach  (Landois) 214 

61.  Glands  of  the  greater  pouch  of  the  stomach  (Heidenhain) 215 

62.  Pyloric  glands  (Ebstein) 215 

63.  Gastric  fistula  in  the  case  of  St.  Martin  (Deaumont) 216 

64.  Dog  with  a  gastric  fistula  (Beclard) 217 

.  65.  Matters  taken  from  the  pyloric  portion  of  the  stomach  (Bernard) 224 

66.  Stomach,  liver,  small  intestine  etc.  (Sappey) 234 

67.  Gland  of  Brunner  (Frey) 235 

68.  Intestinal  tubules  (Sappey) 236 

69.  Intestinal  villus  (Leydig) 238 

70.  Capillary  net-work  of  an  intestinal  villus  (Frey) 238 

71.  Epithelium  of  the  small  intestine  of  the  rabbit  (Funke) 238 

72.  Patch  of  Peyer  (Sappey) 240 

73.  Patch  of  Peyer,  seen  from  its  attached  surface  (Sappey) 240 

74.  Gall-bladder,  ductus  choledochus  and  pancreas  (Le  Bon) 243 

75.  Canula  fixed  in  the  pancreatic  duct  (Bernard) 244 

76.  Pancreatic  fistula  (Bernard) 245 

77.  Dog  with  a  biliary  fistula 251 

78.  Stomach,  pancreas,  large  intestine  etc.  (Sappey) 258 

79.  Opening  of  the  small  intestine  into  the  caecum  (Le  Bon) 259 

80.  Micro-organisms  of  the  largo  intestine  (Landois) 264 

81.  Stercorine  from  the  human  faeces 266 

82.  Origin  of  lymphatics  (Landois) 274 

83.  Lymphatic  plexus,  showing  endothelium  (Bclaieff) 276 

84.  Superficial  lymphatics  of  the  skin  of  the  palmar  surface  of  the  finger  (Sappey) 277 


LIST  OF  ILLUSTRATIONS.  xiii 

rlGTTKE  PAGE 

85  Deep  lymphatics  of  the  skin  of  the  finger  (Sappey) 277 

86.  Same  finger,  lateral  view  (Sappe} ) 277 

87.  Superficial  lymphatics  of  the  arm  (Sappey) 278 

88.  Superficial  lymphatics  of  the  leg  (Sappey) '. 278 

89.  Lacteals  (Asellius) 280 

90.  Thoracic  duct  (Mascagni) 281 

91.  Valves  of  the  lymphatics  (Sappey) 282 

92.  Lymphatics  and  lymphatic  glands  (Sappey) 283 

93.  Different  varieties  of  lymphatic  glands  (Sappey) 284 

94.  Epithelium  of  the  small  intestine  of  the  rabbit  (Funke) 289 

95.  Epithelium  filled  with  fat,  from  the  duodenum  of  the  rabbit  (Funke) 289 

96.  Villi  filled  with  fat,  from  the  small  intestine  of  an  executed  criminal  (Funke) 289 

97.  Egg  prepared  so  as  to  illustrate  cndosmotic  action 293 

98.  Chyle  from  the  lacteals  and  thoracic  duct  (Funke) 298 

99.  Sebaceous  glands  (Sappey) 321 

100.  Ceruminous  glands  (Sappey) 322 

101.  Meibomian  glands  (Sappey) 323 

102.  Mammary  gland  of  the  human  female  (Lie'geois) 329 

103.  Human  milk-globules  (Funke) 334 

104.  Colostrum  (Funke) 338 

105.  Anatomy  of  the  nails  (Sappey) 346 

106.  Section  of  the  nail,  etc.  (Sappey) 347 

107.  Hair  and  hair-follicle  (Sappey) 349 

108.  Root  of  the  hair  (Sappey) 349 

10y.  Human  hair  (United  States  Army  Medical  Museum) 351 

110.  Transverse  section  of  a  human  hair  (United  States  Army  Medical  Museum) 351 

111.  Surface  of  the  palm  of  the  hand  (Sappey) 354 

1 1 2.  Sudoriparous  glands  (Sappey) 355 

113.  Vertical  section  of  the  kidney  (Sappey) 359 

114.  Longitudinal  section  of  the  pyramidal  substance  of  the  kidney  (Sappey) 360 

115.  Longitudinal  section  of  the  cortical  substance  of  the  same  kidney  (Sappey) 360 

1 1 6.  Structure  of  the  kidney  (Landois) 363 

117.  Blood-vessels  of  the  kidney  (Sappey) 365 

118.  Diagram  showing  the  mechanism  of  micturition  (Kiiss) 372 

119.  Crystals  of  urea  (Funke) 376 

120.  Crystals  of  uric  acid  (Funke) 380 

121.  Sodium  urate  (Funke) 380 

122.  Crystals  of  hippuric  acid  (Funke) 382 

123.  Crystals  of  creatine  (Funke) 382 

1 24.  Crystals  of  crcatinine  (Funke) 382 

125.  Crystals  of  calcium  oxalate  (Funke) 383 

126.  Crystals  of  leucine  (Funke). 383 

127.  Crystals  of  tyrosine  (Funke) 384 

128.  Crystals  of  taurine  (Funke) 384 

1 29.  Crystals  of  sodium  chloride  (Funke) 385 

130.  Lobules  of  the  liver,  intcrlobular  vessels  and  intralobular  veins  (Sappey) 394 

131.  Transverse  section  of  a  single  hepatic  lobule  (Sappey) 395 

132.  Liver-cells  from  a  human,  fatty  liver  (Funke) 396 

133.  Portion  of  a  transverse  section  of  an  hepatic  lobule  of  the  rabbit  (Kolliker) 396 

134.  Racemose  glands  attached  to  the  biliary  ducts  (Sappey) 397 

135.  Gall-bladder,  hepatic,  cystic  and  common  ducts  (Sappey) 398 

136.  Cholesterine  extracted  from  the  bile 404 

137.  Instrument  for  puncturing  the  floor  of  the  fourth  ventricle  (Bernard) 411 


xiv  LIST  OF  ILLUSTRATIONS. 

FIGURE  PAGE 

138.  Operation  of  puncturing  the  floor  of  the  fourth  ventricle  (Bernard) 412 

139.  Malpighian  corpuscle  of  the  spleen  of  the  cat  (Cadiat) 415 

140.  Section  of  a  human,  suprarenal  capsule  (Cadiat) 420 

141.  Thyroid  and  thymus  glands  (Sappey) 424 

142.  Amoeba  diffluens  (Longet) 460 

143.  Ciliated  epithelium  (Landois) 461 

144.  Small  elastic  fibres  (Kolliker) 463 

145.  Larger  elastic  fibres  ( Robin) 463 

146.  Large  elastic  fibres — i'enestrated  membrane — (Kollikcr) 463 

147.  Muscular  fibres  from  the  urinary  bladder  (Sappey) 465 

148.  Muscular  fibres  from  the  aorta  (Sappey) 465 

149.  Muscular  fibres  from  the  uterus  (Sappey) 465 

150.  Striated  muscular  fibres  (United  States  Army  Medical  Museum) 467 

151 .  Striated  muscular  fibres  (Sappey) .   468 

152.  Fibres  of  tendon  from  the  human  subject  (Rollett) 468 

153.  Net-work  of  connective  tissue  (Rollett) 469 

154.  Frog's  leg  prepared  so  as  to  show  the  effects  of  curare  (Bernard)   473 

155.  Diagram  of  the  myograph  of  Hel-.nholtz  (Landois) 479 

156.  Curve  of  a  single,  muscular  contraction  (Landois) 479 

157.  Muscular  current  in  the  frog  (Bernard) 480 

158.  Longitudinal  section  of  bone  (Sappey) 482 

159.  Longitudinal  section  of  bone  (United  States  Army  Medical  Museum) 482 

160.  Transverse  section  of  bone  (Sappey) 483 

161.  Transverse  section  of  bone  (United  States  Army  Medical  Museum) 484 

162.  Bone-corpuscles  (Rollett) 484 

163.  Section  of  cartilage  (United  States  Army  Medical  Museum) 486 

164.  Section  of  diarthrodial  cartilage  (Sappey) 486 

165.  Section  of  the  cartilage  of  the  ear  (Rollett) 487 

166.  Longitudinal  section  of  the  human  larynx  (Sappey) 488 

167.  Posterior  view  of  the  muscles  of  the  larynx  (Sappey) 489 

168.  Lateral  view  of  the  muscles  of  the  larynx  (Sappey) 490 

169.  Glottis  seen  with  the  laryngoscope  (Lc  Bon) 492 

170.  Appearance  of  the  vocal  chords  in  the  production  of  the  chest-voice  (Griitzner) 497 

171.  Appearances  of  the  vocal  chords  in  the  production  of  the  falsetto-voice  (Mills) 498 

172.  Nerve  fibres  from  the  human  subject  (Kolliker) 508 

173.  Nodes  of  Ranvier  and  lines  of  Fromann  (Ranvier) 5C9 

1 74.  Fibres  of  Remak  (Kolliker) 509 

175.  Mode  of  termination  of  the  motor  nerves  (Rouget) 511 

176.  Intrafibrillar  terminations  of  a  motor  nerve  in  striated  muscle  (Landois) 512 

177.  Termination  of  nerves  in  non-striated  muscle  (Cadiat) 512 

178.  Termination  of  the  nerves  in  the  salivary  glands  (Pflugcr) 513 

179.  Corpuscle  of  Vater  (Sappey) 514 

]  80.  Papillae  of  the  skin  (Sappey) 515 

181.  End-bulbs,  or  corpuscles  of  Krause  (Ludden) 516 

182.  Unipolar  cell  from  the  Gasserian  ganglion  (Schwalbe) 517 

183.  Unipolar  nerve-cell  with  a  spiral  fibre  (Landois) 518 

184.  Bipolar  nerve-cell  (Landois) 518 

185.  Multipolar  nerve-cell  (Landois) 518 

186.  Gray  matter  of  the  spinal  cord,  treated  with  silver  nitrate  (Grandry) 519 

187.  Electric  forceps  (Liegeois). . .   535 

188.  Frog's  leg  prepared  so  as  to  show  induced  contraction  (Liegeois) 535 

189.  Method  of  testing  the  excitability  in  elcctrotonus  (Landois) 537 

190.  Cervical  portion  of  the  spinal  cord  (Hirschfeld) 540 


LIST  OF  ILLUSTRATIONS.        .  xv 


191.  Dorsal  portion  of  the  spinal  cord  (HirschfeM) jfc 540 

192.  Inferior  portion  of  the  spinal  cord,  and  cauda  equina  (Ilirschfeld) 540 

193.  Roots  of  the  cranial  nerves  (Ilirschfeld) 541 

194.  Distribution  of  the  motor  oculi  communis  (Ilirschfeld) 542 

195.  Distribution  of  the  patheticus  (Ilirschfeld) 546 

196.  Distribution  of  the  motor  oculi  externus  (Hirschfeld) 547 

197.  Distribution  of  the  small  root  of  the  fifth  nerve  (Ilirschfeldj 548 

198.  Incisors  of  the  rabbit,  before  and  after  section  of  the  nerve  of  mastication  (Bernard)..    549 

199.  Superficial  branches  of  the  facial  and  the  fifth  (Ilirschfeld) 551 

200.  Chorda  tympani  nerve  (Ilirschfeld) 554 

201-206.  Expressions  of  the  face,  produced  by  contractions  of  the  muscles  under  electrical 

excitation  (Le  Bon,  after  Duchenne) 556 

207.  Spinal  accessory  nerve  (Ilirschfeld) 557 

208.  Sublingual  nerve  (Sappey) 563 

209.  Principal  branches  of  the  large  root  of  the  fifth  nerve  (Robin) 564 

210.  Ophthalmic  division  of  the  fifth  (Ilirschfeld) 5(55 

211.  Superior  maxillary  division  of  the  fifth  (Hirschfeld) 566 

212.  Inferior  maxillary  division  of  the  fifth  (Ilirschfeld) 567 

213.  Cutaneous  distribution  of  sensory  nerves  to  the  face,  head  and  neck  (Beclard) 668 

214.  Anastomoses  of  the  pneumogastric  (Hirsclifcld) 574 

215.  Distribution  of  the  pneumogastric  (Hirschfeld)   575 

216.  Transverse  section  of  the  spinal  cord  (Gerlach) 590 

217.  Columns  and  conducting  paths  in  the  spinal  cord 593 

218.  Frog  poisoned  with  strychnine  (Liegeois) 599 

219.  Structures  displayed  upon  the  right  side  in  a  median  longitudinal  section  of  the  brain 

semi-diagrammatic 602 

220.  Vertical  section  of  the  third  cerebral  convolution  in  man  (Meynert) 604 

221.  Diagram  of  the  external  surface  of  the  left  cerebral  hemisphere 605 

222.  Diagram  of  the  internal  surface  of  the  right  cerebral  hemisphere 605 

223.  Horizontal  section  of  the  hemispheres  at  the  level  of  the  cerebral  ganglia  (Dalton). . .  607 

224.  Diagram  of  the  human  brain  in  a  transverse  vertical  section  (Palton) 608 

225.  Direction  of  some  of  the  fibres  in  the  cerebrum  (Le  Bon) 612 

226.  Motor  cortical  zone  on  the  outer  surface  of  the  cerebrum  (Exner) 613 

227.  Paracentral  lobule  (Exner) 614 

228.  Lateral  view  of  the  human  brain  with  certain  motor  cortical  areas 614 

229.  Inner  surface  of  the  right  cerebral  hemisphere  (Schafcr  and  Horsley) 616 

230.  Cerebellum  and  medulla  oblongata  (Hirschfeld) 623 

231.  Anterior  view  of  the  medulla  oblongata  (Sappey) 628 

232.  Floor  of  the  fourth  ventrical  (Hirschfeld) 629 

233.  Cervical  and  thoracic  portion  of  the  sympathetic  (Sappey) , 636 

234.  Lumbar  and  sacral  portions  of  the  sympathetic  (Sappey) 687 

235.  Olfactory  ganglion  and  nerves  (Hirschfeld) 659 

236.  Terminal  filaments  of  the  olfactory  nerves  (Kolliker) 660 

237.  Glosso-pharyngeal  nerve  (Sappey) 666 

238.  Papillae  of  the  tongue  (Sappey) 668 

239.  240.  Varieties  of  papillse  of  the  tongue  (Sappey) 669 

241.  Taste-beakers  (Engelmann) 670 

242.  Optic  tracts,  commissure  and  nerves  (Hirschfeld) 672 

243.  Diagram  of  the  decussation  at  the  optic  commissure 672 

244.  Choroid  coat  of  the  eye  (Sappey) 676 

245.  Ciliary  muscle  (Sappey) 678 

246.  Rods  of  the  retina  (Schultze) 682 

247.  Vertical  section  of  the  retina  (H.  Miiller) 683 


xvi  LIST  OF  ILLUSTRATIONS. 

FIGITKE  PAGE 

248.  Connection  of  the  rods  and  cones  of  the  retina  with  the  nervous  elements  (Sappey) . . .   683 

249.  Blood-vessels  of  the  retina  (Loring) 685 

250.  Crystalline  lens,  anterior  view  (Babuchin) 686 

251.  Section  of  the  crystalline  lens  (Babuchin) 686 

252.  Zone  of  Zinn  (Sappey) 687 

253.  Section  of  the  human  eye 689 

254.  Refraction  by  convex  lenses , 694 

255.  Achromatic  lens 697 

256.  Section  of  the  lens,  etc.,  showing  the  mechanism  of  accommodation  (Fick) 710 

257.  Field  of  vision  (Nettleship,  after  Landolt) 712 

258.  Binocular  field  of  vision  (Nettleship,  after  Forster) 714 

259.  Muscles  of  the  eyeball  (Sappey) 718 

260.  Diagram  illustrating  the  action  of  the  muscles  of  the  eyeball  (Fick) 720 

261.  Lachrymal  and  Meibomian  glands  (Sappey) 726 

262.  Lachrymal  canals,  lachrymal  sac  and  nasal  canal  (Sappey) ' 727 

263.  General  view  of  the  organ  of  hearing  (Sappey) 732 

264.  Ossicles  of  the  tympanum  (Arnold) 733 

265.  Ossicles,  seen  from  within  (Riidinger) 734 

266.  Bony  labyrinth  (Rudinger) 736 

267.  Resonators  of  Helmholtz 744 

268.  Membrana  tympani  (Rudinger) 749 

269.  Diagram  of  the  labyrinth — vestibule  and  semicircular  canals  (Rudinger) 756 

270.  Otoliths  from  various  animals  (Riidinger) 757 

271.  Section  of  the  first  turn  of  the  spiral  canal — section  of  the  cochlea  (Rudinger) 758 

272.  Distribution  of  the  cochlear  nerve  in  the  spiral  canal  (Sappey) ....  760 

273.  The  two  pillars  of  the  organ  of  Corti  (Sappey) 761 

274.  Vertical  section  of  the  organ  of  Corti  (Waldeyer) 761 

275.  Uterus,  Fallopian  tubes  and  ovaries  (Sappey) 767 

276.  Section  of  the  ovary  (Waldeyer) 770 

277.  Virgin  uterus  (Sappey) '. 771 

278.  Muscular  fibres  of  the  uterus  (Sappey) 772 

279.  Superficial  muscular  fibres  of  the  uterus  (Liegeois) 773 

280.  Inner  layer  of  muscular  fibres  of  the  uterus  (Liegeois) 773 

281.  Blood-vessels  of  the  uterus  and  ovaries  (Rouget) 775 

282.  Section  through  the  right  Fallopian  tube  (Richard) 776 

283.  External  erectile  organs  of  the  female  (Liegeois) 777 

284.  Primordial  ovum  with  two  germinal  vesicles  (Nagel) 778 

285.  Sections  of  two  corpora  lutea  (Kolliker) 783 

286.  Testicle  and  epididymis  (Arnold) 786 

287.  Vas  deferens,  vesiculae  seminales  and  ejaculatory  ducts  (Liegeois) 788 

288.  Spermatozoids,  spermatic  crystals,  leucocytes  etc.  (Peyer)  791 

289.  Human  spermatozoids  (Landois) 791 

290.  Spermatogenesis,  semi-diagrammatic  (Landois) 792 

291.  Ovum  of  the  rabbit,  showing  penetration  of  spermatozoids  and  retraction  of  the  vitel- 

lus  (Hensen) 706 

292.  Mulatto  woman  with  twins,  one  white  and  the  other  black 798 

293.  Formation  of  the  blastodermic  vesicle  (Van  Beneden) 800 

294.  Primitive  trace  of  the  embryon  (Liegeois) 802 

295.  Formation  of  the  membranes  (Kolliker) 804 

296.  Villi  of  the  chorion  (Haeckel) 808 

297.  Placenta  and  deciduae  (Liegeois) 811 

298-300.  Development  of  the  chick  (Briicke) 814,  815 

301.  Development  of  the  nctochord  (Robin) 816 


LIST  OF  ILLUSTRATIONS.  xvii 


302.  Human  embryon  one  month  old  (Dalton) 816 

303.  Development  of  the  nervous  system  of  the  chick  (Longet,  after  Wagner) 819 

304.  Development  of  the  spinal  cord  and  brain  of  the  human  subject  (Longet,  after  Tiedc- 

mann) 820 

305.  Foetal  pig,  showing  umbilical  hernia  (Dalton) 822 

306.  Development  of  the  bronchial  tubes  and  lungs  (Longet,  after  Kathkc  and  Miiller) 825 

307-309.  Development  of  the  face  (Coste) 826,  827 

310.  Temporary  and  permanent  teeth  (Sappey) 829 

311.  Foetal  pig,  showing  the  Wolffian  bodies  (Dalton) 831 

312.  Diagrammatic  representation  of  the  genito-urinary  apparatus  (Henle) 833 

313.  Area  vasculosa  (Bischoff) 835 

314.  Aortic  arches,  in  the  mammalia  (Von  Baer) 837 

315.  Diagram  of  the  foetal  circulation 840 

316.  Cholesterine  extracted  from  meconium 847 


HUMAN   PHYSIOLOGY. 


CHAPTER  I. 

THE  BLOOD. 

Quantity  of  blood— General  characters  of  the  blood— Blood-corpuscles— Development  of  the  blood-corpus- 
cles— Leucocytes— Development  of  leucocytes — Blood-plaques — Composition  of  the  red  corpuscles— 
Globuline— Haemaglobine— Composition  of  the  blood-plasma — Inorganic  Constituents— Organic  saline 
constituents — Organic  non-nitrogenized  constituents— Excrementitious  constituents — Organic  nitrogen- 
ized  constituents — Plasmine,  fibrin,  metalbumen,  serine — Peptones — Coloring  matter— Coagulation  of 
the  blood— Conditions  which  modify  coagulation— Coagulation  of  the  blood  in  the  organism — Cause  of 
the  coagulation  of  the  blood. 

AViTH  the  progress  of  knowledge  and  the  accumulation  of  facts  in  physi- 
ology, the  importance  of  the  blood  in  its  relations  to  the  phenomena  of  ani- 
mal life  becomes  more  and  more  thoroughly  understood  and  appreciated. 
The  blood  is  the  most  abundant  and  highly  organized  of  the  fluids  of  the 
body,  providing  materials  for  the  regeneration  of  all  parts,  without  excep- 
tion, receiving  the  products  of  their  waste  and  conveying  them  to  proper 
organs,  by  which  they  are  removed  from  the  system.  These  processes  require, 
on  the  one  hand,  constant  regeneration  of  the  nutritive  constituents  of  the 
blood,  and  on  the  other,  its  constant  purification  by  the  removal  of  effete 
matters. 

Those  tissues  in  which  the  processes  of  nutrition  are  active  are  supplied 
with  blood  by  vessels ;  but  some,  less  highly  organized,  like  the  epidermis, 
hair,  cartilage  etc.,  which  are  called  extra-vascular  because  they  are  not  pene- 
trated by  vessels,  are  none  the  less  dependent  upon  the  blood,  as  they  imbibe 
nutritive  material  from  the  blood  of  adjacent  parts. 

The  importance  of  the  blood  in  the  processes  of  nutrition  is  evident ; 
and  in  animals  in  which  nutrition  is  active,  death  is  the  immediate  result  of 
its  abstraction  in  large  quantity.  Its  importance  to  life  can  be  readily  dem- 
onstrated by  experiments  upon  the  inferior  animals.  If,  in  a  small  dog,  a 
canula  adapted  to  a  syringe  be  introduced  through  the  right  jugular  vein 
into  the  right  side  of  the  heart,  and  a  great  part  of  the  blood  be  suddenly 
withdrawn  from  the  circulation,  immediate  suspension  of  all  the  so-called 
vital  processes  is  the  result ;  and  if  the  blood  be  then  returned  to  the  system, 
the  animal  is  as  suddenly  revived. 

Certain  conditions,  one  of  which  is  diminution  in  the  force  of  the  heart's 
action  after  copious  haemorrhage,  prevent  the  escape  of  all  the  blood  from 
the  body,  even  after  division  of  the  largest  arteries ;  but  after  the  arrest  of 


2  THE  BLOOD. 

the  functions,  which  follows  copious  discharges  of  this  fluid,  life  may  be 
restored  by  injecting  into  the  vessels  the  same  blood  or  the  fresh  blood  of 
another  animal.  This  observation,  which  was  first  made  on  the  inferior  ani- 
mals, has  been  applied  to  the  human  subject ;  and  it  has  been  ascertained 
that  in  patients  sinking  under  haemorrhage  the  introduction  of  even  a  few 
ounces  of  fresh  blood  may  restore  the  functions  for  a  time,  and  sometimes 
permanently. 

Quantity  of  Blood. — The  determination  of  the  entire  quantity  of  blood 
contained  in  the  body  has  long  engaged  the  attention  of  physiologists,  with- 
out, however,  any  absolutely  definite  results.  The  fact  that  physiologists 
have  not  succeeded  in  determining  definitely  the  entire  quantity  of  blood 
shows  the  extent  of  the  difficulties  to  be  overcome  before  the  question  can  be 
entirely  settled.  The  chief  difficulty  lies  in  the  fact  that  all  the  blood  is  not 
discharged  from  the  body  after  division  of  the  largest  vessels,  as  after  decapi- 
tation ;  and  no  perfectly  accurate  means  have  been  devised  for  estimating 
the  quantity  which  remains.  The  estimates  of  experimenters  present  the 
following  wide  differences :  Allen-Moulins,  who  was  one  of  the  first  to  study 
this  question,  estimated  the  quantity  of  blood  at  one  twentieth  the  weight  of 
the  entire  body.  The  estimate  of  Herbst  was  a  little  higher.  Hoffmann 
estimated  the  quantity  at  one  fifth  the  weight  of  the  body.  These  observers 
estimated  the  quantity  remaining  in  the  system  after  opening  the  vessels,  by 
mere  conjecture.  Valentin  was  the  first  to  attempt  to  overcome  this  diffi- 
culty by  experiment.  For  this  purpose  he  employed  the  following  process : 
He  took  first  a  small  quantity  of  blood  from  an  animal  for  purposes  of  com- 
parison ;  then  he  injected  into  the  vessels  a  known  quantity  of  a  saline  solu- 
tion, and  taking  another  specimen  of  blood  some  time  after,  he  ascertained 
by  evaporation  the  proportion  of  water  which  it  contained,  and  compared  it 
with  the  proportion  in  the  first  specimen.  He  reasoned  that  the  excess  of 
water  in  the  second  specimen  over  the  first  would  give  the  proportion  of  the 
water  which  had  been  added  to  the  whole  mass  of  blood ;  and  as  the  entire 
quantity  of  water  introduced  was  known,  the  entire  quantity  of  blood  could 
be  deduced  therefrom. 

The  following  process  was  employed  by  Lehmarin  and  Weber,  and  was  ap- 
plied directly  to  the  human  subject  in  the  cases  of  two  decapitated  criminals : 
These  observers  estimated  the  blood  remaining  in  the  body  after  decapita- 
tion, by  injecting  the  vessels  with  water  until  it  came  through  nearly  color- 
less. The  liquid  was  carefully  collected,  evaporated  to  dryness,  and  the  dry 
residue  was  assumed  to  represent  a  certain  quantity  of  blood,  the  proportion 
of  dry  residue  in  a  definite  quantity  of  blood  having  been  previously  ascer- 
tained. If  it  were  certain  that  only  the  solid  matter  of  the  blood  was  thus 
removed,  such  an  estimate  would  be  tolerably  accurate. 

The  process  just  described  gives  an  idea  of  the  probable  quantity  of  blood 
in  the  body;  but  the  most  serious  objection  to  it  is  the  possibility  that 
certain  solid  constituents  of  the  tissues  are  washed  out  by  the  water  passing 
through  the  vessels,  and  it  is  generally  thought  that  the  estimate  by  Leh- 
manii  and  Weber,  that  the  quantity  of  blood  is  equal  to  about  one  eighth  of 


GENERAL  CHARACTERS.  3 

the  weight  of  the  body,  is  too  high.  More  recent  observations  have  been 
made  upon  the  inferior  animals,  by  various  methods,  which  are  all  more  or 
less  open  to  objection,  and  which  it  is  not  necessary  to  describe  in  detail ; 
but  the  results  of  nearly  all  of  the  experiments  made  within  the  last  few 
years  show  a  less  proportion  of  blood  than  was  estimated  by  Lehmann  and 
Weber.  Remembering  that  all  estimates  must  be  regarded  as  approxi- 
mate, it  may  be  assumed  that  in  a  person  of  ordinary  adipose  and  mus- 
cular development  the  proportion  of  blood  to  the  weight  of  the  body  is 
about  one  to  ten.  The  relative  quantity  of  blood  is  less  in  the  infant  than 
in  the  adult  and  is  diminished  in  old  age.  It  has  been  found,  also,  in 
observations  on  the  inferior  animals,  to  be  greater  in  the  male  than  in  the 
female. 

Prolonged  abstinence  from  food,  except  when  large  quantities  of  liquid 
are  ingested,  has  a  notable  effect  in  diminishing  the  mass  of  blood,  as  indi- 
cated by  the  small  quantity  which  can  be  removed  from  the  body,  under  this 
condition,  with  impunity;  and  it  has  been  experimentally  demonstrated  that 
the  entire  quantity  of  blood  is  considerably  increased  during  digestion.  Ber- 
nard drew  from  a  rabbit  weighing  about  two  and  a  half  pounds  (1,134 
grammes),  during  digestion,  ten  and  a  half  ounces  of  blood  (300  grammes) 
without  producing  death ;  while  he  found  that  the  removal  of  half  that 
quantity  from  an  animal  of  the  same  size,  fasting,  was  fatal.  Wrisberg  re- 
ported a  case  of  a  female  criminal,  very  plethoric,  from  whom  nearly  twenty- 
one  and  a  half  pounds  of  blood  (9,745  grammes)  flowed  after  decapitation. 
As  the  relations  of  the  quantity  of  blood  to  digestion  are  so  important,  it  is 
unfortunate  that  the  conditions  in  this  respect  were  not  noted  in  the  obser- 
vations of  Lehmann  and  Weber.  It  is  evident  that  the  quantity  of  blood 
in  the  body  must  be  considerably  increased  during  digestion ;  but  as  regards 
the  extent  of  this  increase,  it  is  not  possible  to  form  any  very  definite  idea. 
It  is  shown  only  that  there  is  a  marked  difference  in  the  effects  of  haemor- 
rhage in  animals  during  digestion  and  fasting. 

GENERAL  CHARACTERS  OF  THE  BLOOD. 

Opacity. — The  opacity  of  the  blood  depends  upon  the  fact  that  it  is  not 
a  homogeneous  fluid,  but  is  composed  of  two  distinct  elements,  a  clear  plasma 
and  corpuscles,  which  are  both  nearly  transparent  but  which  have  each  a 
different  refractive  power.  If  both  of  these  elements  had  the  same  refrac- 
tive power,  the  mixture  would  present  no  obstacle  to  the  passage  of  light ; 
but  as  it  is,  the  rays,  which  are  refracted  in  passing  from  the  air  to  the 
plasma,  are  again  refracted  when  they  enter  the  corpuscles,  and  again,  when 
they  pass  from  the  corpuscles  to  the  plasma,  so  that  they  are  lost,  even  in  a 
thin  layer  of  the  fluid. 

Odor,  Taste,  Reaction  and  Specific  Gravity. — The  blood  has  a  faint  but 
characteristic  odor.  This  may  be  developed  so  as  to  be  very  distinct,  by  the 
addition  of  a  few  drops  of  sulphuric  acid,  when  an  odor  peculiar  to  the  ani- 
mal from  which  the  blood  has  been  taken  becomes  very  marked. 

The  taste  of  the  blood  is  faintly  saline,  on  account  of  the  presence  of  a 


4  THE  BLOOD. 

considerable  proportion,  three  or  four  parts  per  thousand,  of  sodium  chloride 
in  the  plasma. 

The  reaction  of  the  blood  is  always  distinctly  alkaline.  It  is  not  easy, 
however,  to  demonstrate  the  alkalinity  of  the  blood,  on  account  of  the  red 
color  of  the  blood-corpuscles;  but  the  difficulty  may  be  avoided  by  using 
certain  precautions.  The  following  method,  employed  by  Schafer,  is  quite 
satisfactory  :  A  drop  of  blood  is  put  upon  a  piece  of  glazed,  reddened  litmus- 
paper.  After  a  few  seconds  the  blood  is  lightly  wiped  off  with  a  damp  cloth, 
leaving  a  spot  of  a  distinctly  blue  color.  According  to  Zuntz,  the  alkalinity 
diminishes  rapidly  after  the  blood  is  drawn  from  the  vessels.  The  alkaline 
reaction  is  due  to  the  presence  of  sodium  carbonate  and  sodium  phosphate  in 
the  plasma. 

The  specific  gravity  of  defibriuated  blood  is  between  1052  and  1057 
(Robin),  being  somewhat  less  in  the  female  than  in  the  male.  The  density 
varies  greatly  under  different  conditions  of  digestion. 

Temperature. — The  temperature  of  the  blood  is  generally  given  as  between 
98°  and  100°  Fahr.  (36-67°  and  37-78°  C.) ;  but  experiments  have  shown  that 
it  varies  considerably  in  different  parts  of  the  circulatory  system,  independ- 
ently of  exposure  to  the  refrigerating  influence  of  the  atmosphere.  By  the 
use  of  very  delicate  registering  thermometers,  Bernard  succeeded  in  estab- 
lishing the  following  facts  with  regard  to  the  temperature  in  various  parts  of 
the  circulatory  system,  in  dogs  and  sheep  : 

1.  The  blood  is  warmer  in  the  right  than  in  the  left  cavities  of  the  heart. 

2.  It  is  warmer  in  the  arteries  than  in  the  veins,  with  a  few  exceptions. 

3.  It  is  generally  warmer  in  the  portal  vein  than  in  the  abdominal  aorta, 
independently  of  the  digestive  act. 

4.  It  is  constantly  warmer  in  the  hepatic  than  in  the  portal  veins. 

He  found  the  highest  temperature  in  the  blood  of  the  hepatic  vein,  where 
it  ranged  between  101°  and  107°  Fahr.  (38-33°  and  41-67°  C.).  In  the  aorta, 
it  ranged  between  99°  and  105°  Fahr.  (37'22°  and  40-55°  C.).  It  may  be 
assumed,  then,  in  general  terms,  that  the  temperature  of  the  blood  in  the 
deeper  vessels  is  between  100°  and  107°  Fahr.  (37'78°  and  41-67°  C.). 

Color. — The  color  of  the  blood  is  due  to  the  corpuscles.  In  the  arterial 
system  it  is  uniformly  red.  In  the  veins  it  is  generally  dark  blue  and  some- 
times almost  black.  The  color  in  the  veins,  however,  is  not  constant.  Many 
years  ago,  John  Hunter  observed,  in  a  case  of  syncope,  that  the  blood  drawn 
by  venesection  was  bright  red ;  and  more  recently,  Bernard  has  demonstrated 
that  in  some  veins,  the  blood  is  nearly  if  not  quite  as  red  as  in  the  arterial 
system.  The  color  of  the  venous  blood  depends  upon  the  condition  of  the 
organ  or  part  from  which  it  is  returned.  The  red  color  was  first  noticed  by 
Bernard  in  the  renal  veins,  where  it  contrasts  very  strongly  with  the  black 
blood  in  the  vena  cava.  He  afterward  observed  that  the  redness  existed  only 
during  the  activity  of  the  kidneys ;  and  when,  from  any  cause,  the  secretion 
of  urine  was  arrested,  the  blood  became  dark.  He  was  led,  from  this  obser- 
vation, to  examine  the  venous  blood  from  other  glands ;  and  directing  his 
attention  to  those  which  he  was  able  to  examine  during  their  activity,  par- 


ANATOMICAL  ELEMENTS.  5 

ticularly  the  salivary  glands,  he  found  the  blood  red  in  the  veins  during 
secretion,  but  becoming  dark  as  soon  as  secretion  was  arrested.  In  the  sub- 
maxillary  gland,  by  Faradization  of  a  certain  nerve,  called  the  motor  nerve  of 
the  gland,  Bernard  was  able  to  produce  secretion,  and  by  stimulating  another 
nerve,  to  arrest  it ;  in  this  way  changing  at  will  the  color  of  the  blood  in  the 
vein.  It  was  found  by  the  same  observer  that  division  of  the  sympathetic  in 
the  neck,  which  dilates  the  vessels  and  increases  the  supply  of  blood  to  one 
side  of  the  head,  produced  a  red  color  of  the  blood  in  the  jugular.  He  also 
found  that  paralysis  of  a  member  by  division  of  the  nerve  had  the  same 
effect  on  the  blood  returning  by  the  veins. 

The  explanation  of  these  facts  is  evident  in  view  of  the  reasons  why  the 
blood  is  red  in  the  arteries  and  dark  in  the  veins.  Its  red  color  depends  upon 
the  presence  of  oxygen  in  the  corpuscles ;  and  as  the  blood  passes  through 
the  lungs  it  loses  carbon  dioxide  and  the  corpuscles  gain  oxygen,  changing 
from  black  to  red.  In  its  passage  through  the  capillaries  of  the  system,  in 
the  ordinary  processes  of  nutrition,  the  blood  loses  oxygen  and  gains  carbon 
dioxide,  changing  from  red  to  black.  During  the  intervals  of  secretion,  the 
glands  receive  just  enough  blood  for  their  nutrition,  and  the  ordinary  inter- 
change of  gases  takes  place,  with  the  consequent  change  of  color ;  but  dur- 
ing secretion,  the  blood  is  supplied  to  the  glands  in  greatly  increased  quan- 
tity. Under  these  conditions,  it  does  not  lose  oxygen  and  gain  carbon 
dioxide  in  any  great  quantity,  as  has  been  demonstrated  by  actual  analysis, 
and  consequently  there  is  no  marked  change  in  color.  When  filaments  of 
the  sympathetic  are  divided,  the  blood-vessels  are  dilated,  and  the  supply  of 
blood  is  increased  to  such  an  extent  that  a  certain  proportion  passes  through 
without  parting  with  its  oxygen — a  fact  which  has  also  been  demonstrated 
by  analysis — and  consequently  it  retains  its  red  color.  The  explanation  in 
cases  of  syncope  is  probably  the  same,  although  this  is  merely  a  supposition, 
Even  during  secretion,  a  certain  quantity  of  carbon  dioxide  is  formed  in  the 
gland,  which,  according  to  Bernard,  is  carried  off  in  solution  in  the  secreted 
fluid. 

It  may  be  stated,  then,  in  general  terms,  that  the  color  of  the  blood  in  the 
arteries  is  bright  red ;  and  in  the  ordinary  veins,  like  the  cutaneous  or  mus- 
cular, it  is  dark  blue,  almost  black.  It  is  red  in  the  veins  coming  from  glands 
during  secretion,  and  dark  during  the  intervals  of  secretion. 

ANATOMICAL  ELEMENTS  IN  THE  BLOOD. 

In  1661,  Malpighi,  in  examining  the  blood  of  the  hedgehog,  with  the  im- 
perfect lenses  at  his  command,  discovered  little  floating  particles  which  he 
mistook  for  granules  of  fat,  but  which  were  the  blood-corpuscles.  He  did 
not  extend  his  observations  in  this  direction;  but  a  few  years  later  (1673), 
Leeuwenhoek,  by  the  aid  of  simple  lenses  of  his  own  construction,  ranging  in 
magnifying  power  between  forty  and  one  hundred  and  sixty  diameters,  first 
saw  the  corpuscles  of  human  blood,  which  he  minutely  described  in  a  paper 
published  in  the  Philosophical  Transactions,  in  1674.  To  Leeuwenhoek  is 
generally  ascribed  the  honor  of  the  discovery  of  the  blood-corpuscles.  About 


THE  BLOOD. 


a  century  later,  William  Hewson  described  another  kind  of  corpuscles  in  the 
blood,  much  less  abundant  than  the  red,  which  are  now  known  under  the 
name  of  white  globules,  or  leucocytes. 

Without  following  the  progress  of  microscopical  investigations  into  the 
constitution  of  the  blood,  it  may  be  stated  that  it  is  now  known  to  be  com- 
posed of  a  clear  fluid,  the  plasma,  or  liquor  sanguinis,  holding  certain  corpus- 
cles in  suspension.  These  corpuscles  are  of  three  kinds : 

1.  lied  corpuscles ;  by  far  the  most  abundant,  constituting  a  little  less 
than  one-half  of  the  mass  of  blood. 

2.  Leucocytes,  or  white  corpuscles ;  much  less  abundant,  existing  only  in 
the  proportion  of  1  to  750  or  1,000  red  corpuscles. 

3.  Blood-plaques ;  varying  in  size,  shape  and  number. 

Red  Corpuscles. — These  little  bodies  give  to  the  blood  its  red  color  and 
its  opacity.  They  are  organized  structures,  containing  organic  nitrogenized 
and  inorganic  matters  molecularly  united  and  a  little  fatty  matter  in  union 
with  the  organic  constituents.  They  constitute  a  little  less  than  one-half  the 

mass  of  blood,  and  according  to  the 
observations  of  all  who  have  investi- 
gated this  subject,  are  more  abun- 
dant in  the  male  than  in  the  female. 
The  form  of  the  blood-corpuscles 
is  peculiar.  They  are  flattened,  bi- 
concave, circular  disks,  with  a  thick- 
ness of  one-fourth  to  one-third  of 
their  diameter.  Their  edges  are 
rounded,  and  the  thin,  central  por- 
tion occupies  about  one-half  of  their 
diameter.  Their  consistence  is  not 
much  greater  than  that  of  the  plas- 
ma. They  are  very  elastic,  and  if 
deformed  by  pressure,  immediately 
resume  their  original  shape  when 
containing  four  the  pressure  is  removed.  Their  spe- 
cific gravity  is  between  1088  and 
1105,  considerably  greater  than  the  specific  gravity  of  the  plasma,  which  is 
about  1028. 

When  the  blood  has  been  drawn  from  the  vessels  and  coagulates  slowly, 
the  greater  density  of  the  red  corpuscles  causes  them  to  gravitate  to  the  lower 
portions  of  the  clot,  leaving  the  white  corpuscles  and  fibrin  at  the  surface.  If 
coagulation  be  prevented  by  the  addition  of  a  small  quantity  of  sodium  sul- 
phate, there  is  quite  a  marked  gravitation  of  red  corpuscles  after  standing 
for  some  hours. 

The  peculiar  form  of  the  blood-corpuscles  gives  them  a  very  characteris- 
tic appearance  under  the  microscope.  Examined  with  a  magnifying  power 
of  between  three  hundred  and  five  hundred  diameters,  those  which  present 
their  flat  surfaces  have  a  shaded  centre  when  the  edges  are  exactly  in  focus. 


FIG.  1. — Human  blood-cormudet ;  magnified  1,450 

diameters  (Sternberg). 
This  figure  also 


ANATOMICAL  ELEMENTS. 


This  appearance  is  an  optical  effect  due  to  the  form  of  the  corpuscles  ;  their 
biconcavity  rendering  it  impossible  for  the  centre  and  edges  to  be  exactly  in 
focus  at  the  same  instant,  so  that  when  the  edges  are  in  focus,  the  centre  is 
dark,  and  when  the  centre  is  bright,  the  edges  are  shaded. 

As  the  blood-corpuscles  are  examined  with  the  microscope,  by  transmitted 
light,  they  are  nearly  transparent  and  of  a  pale-amber  color.     It  is  only  when 
they  are  collected  in  masses  that  they  present  the  red  tint  characteristic  of 
blood  as  it  appears  to  the  naked 
eye.     This  yellow  or  amber  tint  is 
quite   characteristic.      An   idea  of 
the  color  may  be  obtained  by  large- 
ly diluting  blood  in  a  test-tube  and 
holding  it  between  the  eye  and  the 
light. 

In  examining  blood  under  the 
microscope,  the  corpuscles  are  seen 
in  many  different  positions,  and 
this  assists  in  the  recognition  of 
their  peculiar  form. 


It  has  long  been  observed  that 


the  blood-corpuscles  have  a  remark- 
able tendency  to  arrange  them- 
selves in  rows  like  rouleaux  of  coin. 
This  appearance  is  due  to  the  fol- 
lowing conditions : 

Shortly  after  removal  from  the  vessels,  there  exudes  from  the  corpuscles 
an  adhesive  substance  which  causes  them  to  stick  together.  Of  course  the 
tendency  is  to  adhere  by  their  flat  surfaces  (Robin).  This  phenomenon  is 
due  to  a  post-mortem  change ;  but  it  occurs  so  soon,  that  it  presents  itself 
in  nearly  every  specimen  of  fresh  blood,  and  is  therefore  mentioned  in  con- 
nection with  the  normal  characters  of  the  blood -corpuscles. 

The  diameter  of  the  blood-corpuscles  has  a  more  than  ordinary  anatomi- 
cal interest;  for,  varying  perhaps  less  in  size  than  other  anatomical  ele- 
ments, they  are  often  taken  as  the  standard  by  which  an  idea  is  formed  of 
the  size  of  other  microscopic  objects.  The  diameter  usually  given  is  -^^  of 
an  inch  (?•!?  /*).  The  exact  measurement  given  by  Robin  is  -j^Vr  of  an 
inch  (7*3  p.).  Very  few  corpuscles  are  to  be  found  which  vary  from  this 
measurement.  Kolliker,  who  gives  their  average  diameter  as  36166  of  an 
inch  (7  /x),  states  that  "at  least  ninety-five  out  of  every  hundred  corpuscles 
are  of  the  same  size." 

Measurements  of  the  blood-corpuscles  of  different  animals  are  important, 
from  the  fact  that  it  often  becomes  a  question  to  determine  whether  a  given 
specimen  of  blood  be  from  the  human  subject  or  from  one  of  the  inferior 
animals.  Comparative  measurements  also  have  an  interest  on  account  of  a 
relation  which  seems  to  exist  in  the  animal  scale  between  the  size  of  the 
blood-corpuscles  and  muscular  activity.  In  all  the  mammalia,  with  the 


FIG.  2.— Human  red  blood-corpuscles,  arranged  in 
rows  (Funke). 


THE  BLOOD. 


exception  of  the  camel  and  llama,  in  which  the  corpuscles  are  oval,  the 
blood  has  nearly  the  same  anatomical  characters  as  in  the  human  subject. 
In  only  two  animals,  the  elephant  and  sloth,  are  the  red  corpuscles  larger 
than  in  man;  and  in  all  others,  they  are  smaller  or  of  nearly  the  same 
diameter.  In  some  animals,  the  corpuscles  are  very  much  smaller  than  in 
man,  and  by  accurate  measurements,  their  blood  can  be  distinguished  from 
the  blood  of  the  human  subject ;  but  in  forming  an  opinion  on  this  subject, 

it  must  be  remembered  that  there  is 
some  variation  in  the  size  of  the  cor- 
puscles of  the  same  animal.  The 
blood  of  the  human  subject  or  of  the 
mammals  generally  can  be  readily  dis- 
tinguished from  the  blood  of  birds, 
fishes  or  reptiles;  for  in  these  ani- 
mals, the  corpuscles  are  oval  and  con- 
tain a  granular  nucleus. 

Milne-Edwards  has  attempted  to 
show,  by  a  comparison  of  the  diameter 
of  the  blood  -  corpuscles  in  different 
species,  that  their  size  bears  an  inverse 
ratio  to  the  muscular  activity  of  the 
,  animal.  This  relation  holds  good  to 

FIG.  3.—  Blood-corpuscles  of  the  frog  ;  magnified 

370  diameters  (from  a  photograph  taken  at   some  extent,  Avhile  there  certainly  ex- 

the  United  States  Army  Medical  Museum). 

ists  none  between  the  size  of  the  cor- 
puscles and  the  size  of  the  animal.  In  deer,  animals  remarkable  for 
muscular  activity,  the  corpuscles  are  very  small,  -g-^-y  of  an  inch  (5  p.) ; 
while  in  the  sloth  they  are  -g-g1^  (8'9  /i),  and  in  the  ape,  which  is  com- 
paratively inactive  -^^  (7'7  /x).  On  the  other  hand,  in  the  dog,  which  is 
quite  active,  the  corpuscles  measure  ^-gVir  of  an  inch  (7'17  /*),  and  in  the  ox, 
which  is  certainly  not  so  active,  the  diameter  of  the  corpuscles  is  ^-jV^r  °^  an 
inch  (6  fi).  Although  this  relation  between  the  size  of  the  blood-corpuscles 
and  muscular  activity  is  not  invariable,  it  is  certain  that,  the  higher  the 
animal  in  the  scale,  the  smaller  are  the  blood-corpuscles ;  the  largest  being 
found  in  the  lowest  orders  of  reptiles,  and  the  smallest,  in  the  mammalia. 
The  blood  of  the  invertebrates,  with  a  few  exceptions,  contains  no  colored 
corpuscles. 

Enumeration  of  the  Blood- Corpuscles. — In  most  of  the  quantitative  analy- 
ses of  the  blood,  the  proportion  of  moist  corpuscles  to  the  entire  mass  of  blood 
is  stated  to  be  a  little  less  than  one-half.  This  estimate  is  necessarily  rather 
rough;  and  it  would  be  useful  to  ascertain,  if  possible,  the  normal  varia- 
tions in  the  proportion  of  corpuscles,  under  different  conditions  of  the  sys- 
tem, particularly  as  these  bodies  play  so  important  a  part  in  many  of  the 
functions  of  the  organism.  Actual  enumerations  of  the  blood  -corpuscles 
have  been  made  by  Vierordt,  Weckler,  Malassez  and  others.  It  is  stated  by 
Malassez  that  the  error  in  his  calculations  is  not  more  than  two  or  three  per 
cent.  The  process  employed  by  Malassez  is  the  following : 


ANATOMICAL  ELEMENTS. 


9 


The  blood  to  be  examined  is  diluted  with  ninety-nine  parts  of  a  liquid  com- 
posed of  one  volume  of  a  solution  of  gum-arabic  of  a  specific  gravity  of  1020 
with  three  volumes  of  a  solution  of  equal  parts  of  sodium  sulphate  and  of  so- 
dium chloride,  also  of  a  specific  gravity  of  1020.  The  mixture,  containing  one 
part  of  blood  in  one  hundred,  is  introduced  into  a  small  thermometer-tube 
with  an  elliptical  bore,  the  sides  of  the  tube  being  ground  flat  for  convenience 
of  microscopical  examination.  The 
capacity  of  the  tube  is  to  be  calcu- 
lated by  estimating  the  weight  of  a 
volume  of  mercury  contained  in  a 
given  length.  The  tube  is  then  filled 
with  the  diluted  blood,  and  the  num- 
ber of  corpuscles  in  a  given  length  of 
the  tube  is  counted  by  means  of  a  mi- 
croscope fitted  with  an  eye-piece  mi- 
crometer. In  this  way,  the  number 
of  corpuscles  in  a  given  volume  of 
blood  can  be  readily  estimated.  In 
man,  the  number  in  a  cubic  millime- 


tre of  blood — a  millimetre  =  about 
-fa  of  an  inch — is  estimated  to  be  be- 
tween four  and  a  half  and  five  mill- 
ions. 


FIG.  4. — Artificial  capillary,  filled  with  a  sanguin- 
*    eous  mixture,  seen  under  a  quadrilateral  mi- 
crometer (Malassez). 


According  to  the  observations  of  Malassez,  the  proportion  of  corpuscles  is 
about  the  same  in  all  parts  of  the  arterial  system.  In  the  veins,  the  cor- 
puscles are  more  abundant  than  in  the  arteries.  In  the  venous  system,  the 
blood  of  the  splenic  veins  presents  the  largest  proportion  of  corpuscles,  and 

the  proportion  is  smallest  in  the 
blood  of  the  hepatic  veins.  These 
results  favor  the  idea  that  the  red 
corpuscles  are  formed,  to  a  certain 
extent,  in  the  spleen  and  that  some 
are  destroyed  in  the  liver  ;  but  far- 
ther observations  are  necessary  to 
render  this  view  certain. 

Post-mortem  Changes  in  the 
Blood-Corpuscles.  —  In  examining 
the  fresh  blood  under  the  micro- 
scope, after  the  specimen  has  been 
under  observation  a  short  time,  the 
corpuscles  are  observed  to  assume  a 
peculiar  appearance,  from  the  de- 

FIG.  5.— Human  blood-corpuscles,  showing  post-mor-     velopment,  On  their  Surface,  of  Very 
tern  alterations  (Funke).  .        .  , . , 

minute,  rounded  projections,  like 

the  granules  of  a  raspberry.     A  little  later,  when  they  have  become  partly 
desiccated,  they  present  a  shrunken  appearance  and  their  edges  are  more  or 


10  THE  BLOOD. 

less  serrated.  Under  these  conditions,  their  original  form  may  be  restored 
by  adding  to  the  specimen  a  liquid  of  about  the  density  of  the  serum.  When 
they  have  been  completely  dried,  as  in  blood  spilled  upon  clothing  or  on  a 
floor,  they  can  be  made  to  assume  their  characteristic  form  by  carefully  moist- 
ening them  with  an  appropriate  liquid.  This  property  is  taken  advantage 
of  in  examinations  of  old  spots  supposed  to  be  blood ;  and  if  the  manipula- 
tions be  carefully  conducted,  the  corpuscles  may  be  recognized  without  diffi- 
culty by  means  of  the  microscope. 

If  pure  water  be  added  to  a  specimen  of  blood  under  the  microscope,  the 
corpuscles  swell  up,  become  spherical  and  are  finally  dissolved.  The  same 
effect  follows  almost  instantaneously  on  the  addition  of  acetic  acid. 

Structure. — The  blood-corpuscles  are  perfectly  homogeneous,  presenting, 
in  their  normal  condition,  no  nuclei  or  granules,  and  are  not  provided  with 
an  investing  membrane.  The  appearances  presented  upon  the  addition  of 
iodine  to  blood  previously  treated  with  water,  which  have  been  supposed  to 
indicate  the  presence  of  shreds  of  ruptured  vesicles,  are  not  sufficiently  dis- 
tinct to  demonstrate  the  existence  of  a  membrane.  The  great  elasticity  of 
the  corpuscles,  the  persistence  with  which  they  preserve  their  biconcave  form, 
and  their  general  appearance,  rather  favor  the  idea  that  they  are  homogene- 
ous bodies  of  a  definite  shape,  than  that  they  have  a  cell- wall  with  semi-fluid 
contents ;  especially  as  the  existence  of  a  membrane  has  been  only  inferred 
and  not  positively  demonstrated.  » 

Development  of  the  Blood- Corpuscles. — Very  early  in  the  development  of 
the  ovum,  the  blood-vessels  appear,  constituting  what  is  called  the  area  vascu- 
losa.  At  about  the  same  time,  the  blood-corpuscles  are  developed,  it  may  be 
before,  or  it  may  be  just  after  the  appearance  of  the  vessels,  for  this  point  is 
undetermined.  The  blood  becomes  red  when  the  embryon  is  about  one-tenth 
of  an  inch  (2-5  mm.)  in  length.  From  this  time  until  the  end  of  the  sixth 
or  eighth  week,  they  are  thirty  to  one  hundred  per  cent,  larger  than  in  the 
adult.  Most  of  them  are  circular,  but  some  are  ovoid  and  a  few  are  globular. 
At  this  time,  nearly  all  of  them  are  provided  with  a  nucleus ;  but  from  the 
first,  there  are  some  in  which  this  is  wanting.  The  nucleus  is  ^gVo  to  ToVzr 
of  an  inch  (3*1  p.  to  3'6  /*)  in  diameter,  globular,  granular  and  insoluble  in 
water  and  acetic  acid.  As  development  advances,  these  nucleated  corpuscles 
are  gradually  lost ;  but  even  at  the  fourth  month,  a  few  remain.  After  this 
time,  they  do  not  differ  anatomically  from  the  blood-corpuscles  in  the  ad  ult. 

In  many  works  on  physiology  and  general  anatomy,  accounts  are  given  of 
the  development  of  the  red  corpuscles  from  the  colorless  corpuscles,  or  leuco- 
cytes, which  are  supposed  to  become  disintegrated,  their  particles  becoming 
developed  into  red  corpuscles;  but  there  seems  to  be  no  positive  evidence 
that  such  a  process  takes  place.  The  red  corpuscles  appear  before  the  leu- 
cocytes are  formed  ;  and  it  is  mainly  the  fact  that  the  two  varieties  co-exist  in 
the  blood-vessels  which  has  given  rise  to  such  a  theory.  It  is  most  reasonable 
to  consider  that  the  first  red  corpuscles  are  formed  in  the  area  vasculosa  in 
the  same  way  that  other  anatomical  elements  make  their  appearance  at  that 
time,  the  exact  process  not  being  understood.  In  the  later  periods  of  devel- 


ANATOMICAL  ELEMENTS.  11 

opment  of  the  foetus  and  in  the  adult,  it  is  probable  that  the  red  marrow  of 
the  bones  and,  perhaps,  to  a  certain  extent,  the  spleen  have  important  uses  in 
connection  with  the  development  of  the  red  blood-corpuscles.  The  observa- 
tions of  Neumann,  of  Konigsburg,  and  of  Bizzozero,  of  Turin,  about  the 
year  1868,  have  been  extended  and  confirmed  by  others,  and  show  that  there 
is  a  generation  of  red  corpuscles  in  the  red  marrow  of  the  bones,  which  is 
now  regarded  as  the  most  important  of  the  so-called  corpuscle-forming  organs. 
In  the  foetus  and  in  the  young  infant,  the  marrow  of  nearly  all  the  bones  is 
red,  or  of  the  kind  called  lymphoid.  In  the  adult,  the  marrow  of  the  long 
bones  is  yellow,  or  fatty,  the  red  marrow  being  confined  to  the  cancellated 
structure  of  the  short  and  the  flat  bones.  Although  the  researches  with  re- 
gard to  the  spleen  are  less  positive  and  definite  in  their  results,  it  is  proba- 
ble that  this  organ  also  contributes  to  the  development  of  the  red  blood- 
corpuscles. 

The  exact  mode  of  development  of  the  red  corpuscles  in  the  marrow  and 
in  the  spleen  has  not  been  very  satisfactorily  described  and  is  still  a  question 
concerning  which  there  is  much  difference  of  opinion  among  histologists. 
A  full  discussion  of  this  question  would  be  out  of  place  in  this  work,  which 
is  intended  to  embrace  only  those  points  in  histology  that  have  been  defi- 
nitely settled. 

It  is  probable  that  the  red  corpuscles  are,  in  certain  number,  destroyed 
in  the  passage  of  the  blood  through  the  liver  and  perhaps,  also,  in  the  spleen, 
the  coloring  matter  contributing  to  the  formation  of  the  biliary  and  the  urin- 
ary pigmentary  matters.  If  this  view  be  accepted,  the  spleen  is  concerned 
in  both  the  formation  and  the  disintegration  of  blood-corpuscles. 

In  the  present  state  of  knowledge,  the  following  seem  to  be  the  most 
rational  views  with  regard  to  the  development  and  destination  of  the  red 
blood-corpuscles. 

1.  At  the  time  of  their  first  appearance  in  the  ovum,  the  blood-corpuscles 
are  formed  by  no  special  organs,  for  no  special  organs  then  exist. 

2.  In  the  foetus,  after  the  development  of  the  marrow  of  the  bones  and  of 
the  spleen,  and  in  the  adult,  these  parts  have  important  uses  in  the  forma- 
tion of  the  red  corpuscles,  especially  the  red  marrow  of  the  bones. 

3.  It  is  probable  that  the  red  blood-corpuscles  are  constantly  undergoing 
destruction,  and  that  their  coloring  matter  contributes  to  the  formation  of 
other  pigmentary  matters.    As  the  corpuscles  are  thus  destroyed,  and  as  they 
are  diminished  in  number  in  disease  or  by  haemorrhage,  they  are  probably 
replaced  by  new  corpuscles  formed  in  greatest  part  in  the  red  marrow  of  the 
bones. 

4.  Pathological  observations  seem  to  show  that  in  certain  cases  of  ane- 
mia, when  there  is  an  abnormal  destruction  of  red  corpuscles,  the  activity  of 
the  corpuscle-forming  office  of  the  marrow  is  increased,  compensating,  to  a 
certain  extent,  the  conditions  which  involve  the  abnormal  destruction  of  the 
corpuscles. 

Uses  of  the  Red  Blood- Corpuscles. — Although  the  albuminoid  constitu- 
ents of  the  plasma  of  the  blood  are  essential  to  nutrition,  the  red  corpuscles 


12 


THE  BLOOD. 


are  the  parts  most  immediately  necessary  to  life.  It  is  well  known  that  life 
may  be  restored  to  an  animal  in  which  the  functions  have  been  suspended 
by  haemorrhage,  by  the  introduction  of  fresh  blood ;  and  while  it  is  not  neces- 
sary that.this  blood  should  contain  the  fibrin-factors,  it  has  been  shown  by 
the  experiments  of  Prevost  and  Dumas  and  others,  that  the  introduction  of 
serum,  without  the  corpuscles,  has  no  permanent  restorative  effect.  When  all 
the  arteries  leading  to  a  part  are  tied,  the  tissues  lose  their  properties  of 
contractility,  sensibility  etc.,  which  may  be  restored,  however,  by  supplying 
it  again  with  blood.  It  will  be  seen,  in  treating  of  respiration,  that  one  great 
distinction  between  the  corpuscular  and  fluid  elements  of  the  blood  is  the 
great  capacity  which  the  former  have  for  absorbing  gases.  Direct  observa- 
tions have  shown  that  blood  will  absorb  ten  to  thirteen  times  as  much  oxygen 
as  an  equal  bulk  of  water ;  and  this  is  dependent  almost  entirely  on  the  pres- 
ence of  the  red  corpuscles.  As  all  the  tissues  are  constantly  absorbing 
oxygen  and  giving  off  carbon  dioxide,  a  very  important  office  of  the  corpus- 
cles is  to  carry  oxygen  to  all  parts  of  the  body.  In  the  present  state  of 
knowledge,  this  is  the  only  well  defined  use  which  can  be  attributed  to  the 
red  corpuscles,  and  it  undoubtedly  is  the  principal  one.  They  have  an  affin- 
ity, though  not  so  great,  for  carbon  dioxide  which,  after  the  blood  has  cir- 
culated in  the  capillaries  of  the  system,  takes  the  place  of  the  oxygen.  In  a 
series  of  experiments  on  the  effects  of  haemorrhage  and  the  seat  of  the  "  sense 
of  want  of  air,"  it  was  demonstrated  that  one  of  the  results  of  removal  of 
blood  from  the  system  was  a  condition  of  asphyxia,  dependent  upon  the 
absence  of  these  respiratory  elements  (Flint,  1861). 

Leucocytes,  or  White  Corpuscles  of  the  Blood. — In  addition  to  the  red  cor- 
puscles of  the  blood,  this  fluid  always  contains  a  number  of  colorless  bodies, 

globular  in  form,  in  the  substance 
of  which  are  embedded  a  greater  or 
less  number  of  minute  granules, 
forming  a  nucleus  of  irregular  shape. 
These  have  been  called  by  Eobin, 
leucocytes.  This  name  seems  more 
appropriate  than  that  of  white  or 
colorless  blood-corpuscles,  inasmuch 
as  these  bodies  are  not  peculiar  to 
the  blood,  but  are  found  in  the 
lymph,  chyle,  pus  and  various  other 
fluids,  in  which  they  were  formerly 
known  by  different  names.  The 
description  which  will  be  given  of 
the  white  corpuscles  of  the  blood, 
and  the  effects  of  reagents,  will  an- 
swer, in  the  main,  for  all  the  cor- 
puscular bodies  that  are  grouped  together  under  the  name  of  leucocytes. 

Leucocytes  are  normally  found  in  the  blood,  lymph,  chyle,  semen,  colos- 
trum and  vitreous  humor.     Pathologically,  they  are  found  in  the  secretion 


FIG.  6. — Human  leucocytes,  showing  amoeboid  move 
ments  (Landois). 


ANATOMICAL  ELEMENTS.  13 

of  mucous  membranes,  following  irritation,  and  in  inflammatory  products, 
when  they  are  called  pus-corpuscles.  They  are  globular,  with  a  smooth  sur- 
face, somewhat  opaque  from  the  presence  of  more  or  less  granular  matter, 
white,  and  larger  than  the  red  corpuscles.  In  examining  the  circulation 
under  the  microscope,  the  adhesive  character  of  the  leucocytes  as  compared 
with  the  red  corpuscles  is  readily  noted.  The  latter  circulate  with  great 
rapidity  in  the  centre  of  the  vessels,  while  the  leucocytes  have  a  tendency  to 
adhere  to  the  sides,  moving  along  slowly,  and  occasionally  remaining  sta- 
tionary for  a  time,  until  they  are  swept  along  by  a  change  in  the  direction  or 
force  of  the  current. 

The  size  of  the  leucocytes  varies  somewhat,  even  in  any  one  fluid,  such  as 
the  blood.  Their  average  diameter  may  be  stated  as  g6*o0  of  an  inch  (10  ft). 
It  is  in  pus,  where  they  exist  in  greatest  abundance,  that  their  microscopical 
characters  may  be  studied  with  most  advantage.  In  this  fluid,  after  it  is 
discharged,  the  corpuscles  sometimes  present  remarkable  changes  in  form. 
They  become  polygonal  in  shape,  and  sometimes  ovoid,  occasionally  present- 
ing projections  from  their  surface,  which  give  them  a  stellate  appearance. 
These  alterations,  however,  are  only  temporary ;  and  after  twelve  to  twenty- 
four  hours,  they  resume  their  globular  shape.  On  the  addition  of  acetic  acid 
the.y  swell  up,  become  transparent,  with  a  delicate  outline,  and  present  in 
their  interior  one,  two,  three  or  even  four  rounded,  nuclear  bodies,  generally 
collected  in  a  mass.  This  appearance  is  produced,  though  more  slowly,  by 
the  addition  of  water.  In  some  corpuscles  a  nucleus  may  be  seen  without  the 
addition  of  any  reagent. 

Leucocytes  vary  considerably  in  their  external  characters  in  different  situ- 
ations. Sometimes  they  are  very  pale  and  almost  without  granulations, 
and  sometimes  they  are  filled  with  fatty  granules  and  are  not  rendered  clear 
by  acetic  acid.  As  a  rule,  they  increase  in  size  and  become  granular  when 
confined  in  the  tissues.  In  colostrum,  where  they  are  called  colostrum-cor- 
puscles, they  generally  undergo  this  change.  As  the  result  of  inflammatory 
action,  when  they  are  sometimes  called  inflammatory  or  exudation-corpuscles, 
leucocytes  frequently  become  much  hypertrophied  and  are  filled  with  fatty 
granules. 

The  deformation  of  the  leucocytes  to  which  allusion  has  already  been 
made  is  sometimes  so  rapid  and  changeable  as  to  produce  creeping  move- 
ments, due  to  the  projection  and  retraction  of  portions  of  their  substance. 
These  movements  are  of  the  kind  called  amoaboid  and  are  supposed  to  be 
important  in  the  process  of  migration  of  the  corpuscles. 

The  relative  number  of  leucocytes,  can  only  be  given  approximately.  It 
has  been  estimated  by  counting  under  the  microscope  the  red  corpuscles  and 
leucocytes  contained  in  a  certain  space.  The  average  proportion  in  man  is 
probably  1  to  750  or  1000.  It  has  been  found  by  Hirt,  whose  observations 
have  been  confirmed  by  others,  that  the  relative  quantity  of  leucocytes  is 
much  increased  during  digestion.  He  found,  in  one  individual,  a  proportion 
of  1  to  1800  before  breakfast ;  an  hour  after  breakfast,  which  was  taken  at 
8  o'clock,  1  to  700;  between  11  and  1  o'clock,  1  to  1500;  after  dining,  at  1 
3 


THE  BLOOD. 


FIG.  7. — Human  red  blood-corpuscles  and  two  leuco- 
cytes (Sternberg). 


o'clock,  1  to  400 ;   two  hours  after,  1  to  1475 ;   after  supper,   at  8  P.  M., 
1  to  550 ;  at  11£  P.  M.,  1  to  1200.     The  leucocytes  are  much  lighter  than  the 

red  corpuscles,  and  when  the  blood 
coagulates  slowly,  they  are  frequent- 
ly found,  with  a  certain  quantity  of 
colorless  fibrin,  forming  a  whitish 
layer  on  the  surface  of  the  clot. 
Their  specific  gravity  is  about  1070. 
Development  of  Leucocytes. — 
These  corpuscles  appear  in  the 
blood  -  vessels  very  early  in  foetal 
life,  before  the  lymphatics  can  be 
demonstrated.  They  appear  in 
lymphatics  before  these  vessels  pass 
through  the  lymphatic  glands,  in 
the  foetus  anterior  to  the  develop- 
ment of  the  spleen,  and  also  on  the 
surface  of  mucous  membranes;  so 
that  they  can  not  be  considered  as 
produced  exclusively  by  the  lymphatic  glands,  as  has  been  supposed.  Al- 
though they  frequently  appear  as  a  result  of  inflammation,  this  process  is  by 
no  means  necessary  for  their  production.  Kobin  has  observed  the  phenom- 
ena of  their  development  in  recent  wounds.  The  first  exudation  consists 
of  clear  fluid,  with  a  few  red  corpuscles.  There  appears  afterward,  a  finely 
granular  blastema.  In  a  quarter  of  an  hour  to  an  hour,  pale,  transparent 
globules,  -g-oVrr  to  -g-gVrr  °f  an  in°h  (3  p-  to  4  /«,)  in  diameter,  make  their  ap- 
pearance, which  soon  become  finely  granular  and  present  the  ordinary 
appearance  of  leucocytes. 

Histological  researches  show  that  in  the  adult,  the  number  of  leucocytes 
in  the  lymph  is  increased  during  the  passage  of  this  fluid  through  the  lym- 
phatic glands.  The  blood,  also,  in  passing  through  the  spleen  has  been 
shown  to  gain  largely  in  these  corpuscles.  These  facts  are  important  in  con- 
nection with  the  pathology  of  leucocythaemia.  This  disease,  which  is  char- 
acterized by  an  excess  of  leucocytes  in  the  blood,  is  now  generally  regarded 
as  having  a  close  relation  to  certain  changes  in  the  spleen,  the  lymphatic 
glands  and  the  marrow  of  the  bones.  There  is,  indeed,  a  variety  of  the  dis- 
ease, known  as  lymphatico-splenic  leucocythgemia,  in  which  the  spleen  and 
certain  of  the  lymphatic  glands  are  enlarged,  and  another  form,  called 
medullo-lymphatic  leucocythaemia,  in  which  changes  have  been  noted  in  the 
lymphatic  glands  and  in  the  marrow.  The  anatomical  changes  which  have 
been  observed  in  the  spleen,  lymphatic  glands  and  marrow,  in  leucocythaemia, 
are  largely  hyperplastic ;  that  is,  the  normal  structure  of  these  parts  is 
increased  in  extent.  On  the  other  hand,  a  disease  called  pseudo-leucocy- 
thaemia,  presenting  the  anatomical  characters  and  general  symptoms  of  leu- 
cocythaemia, without  an  increase  in  the  leucocytes  of  the  blood,  has  been 
accurately  described.  Pathological  observations,  therefore,  are  not  entirely 


ANATOMICAL  ELEMENTS.  15 

in  accord  with  the  theory  that  the  spleen,  lymphatic  glands  and  the  bone- 
marrow  are  always  directly  concerned  in  the  production  of  leucocytes. 

Taking  into  consideration  the  histological  and  pathological  observations 
bearing  on  the  question,  the  following  seems  to  be  the  most  reasonable  view 
with  regard  to  the  mode  of  development  of  leucocytes  : 

1.  In  early  foetal  life  the  leucocytes  of  the  blood  are  developed  without 
the  intervention  of  any  special  organs,  and  perhaps,  also,  these  bodies  are 
multiplied  by  division. 

2.  In  adult  life  the  same  processes  of  development  probably  occur  in  the 
blood  and  lymph  and  in  other  situations. 

3.  It  is  probable,  though  by  no  means  certain,  that  the  spleen,  lymphatic 
glands  and  the  red  marrow  of  the  bones  are  more  or  less  actively  concerned 
in  the  production  of  leucocytes,  both  under  physiological  and  pathological 
conditions ;  but  it  is  certain  that  these  organs  and  parts  are  not  the  exclusive 
seat  of  development  of  the  so-called  white  blood-corpuscles  and  lymph-cor- 
puscles. 

Uses  of  the  Leucocytes. — It  is  impossible,  in  the  present  state  of  physi- 
ological knowledge,  to  assign  any  definite  use  to  the  leucocytes  of  the  blood 
and  lymph.  These  bodies  may  be  concerned  to  some  extent  in  the  develop- 
ment of  the  red  blood-corpuscles,  but  this  view,  which  is  held  by  many  physi- 
ologists, has  no  absolutely  positive  basis  in  fact.  All  that  can  be  said  is  that 
the  office  of  the  leucocytes  has  not  been  ascertained.  Their  action,  however, 
is  important  in  the  process  of  coagulation  of  the  blood,  lymph  and  chyle. 

Blood- Plaques. — The  so-called  blood-plaques,  described  quite  elaborately 
by  Bizzozero  and  others,  have  been  long  known  to  histologists,  under  a  vari- 
ety of  names,  such  as  globulins,  elementary  corpuscles,  granular  debris,  gran- 
ule masses,  haematoblasts  etc.  Until  within  a  few  years  these  bodies  have 
not  been  thought  to  be  of  much  importance,  and  even  now  little  is  known  of 
their  physiological  and  pathological  relations. 

The  blood-plaques  in  human  blood  may  be  easily  observed,  preparing  the 
blood  by  the  following  method  (Osier) : 

"  Upon  the  thoroughly  cleansed  finger- pad  a  single  drop  of  the  solution 
is  placed,  and  with  a  sharp  needle,  or  pricker,  the  skin  is  pierced  through 
the  drop,  so  that  the  blood  passes  at  once  into  the  fluid,  which  is  then  received 
upon  a  slide  and  covered.  The  withdrawal  of  the  corpuscles  into  the  solu- 
tion prevents  the  plaques  from  aggregating,  and  they  remain  as  isolated  and 
distinct  elements.  The  amount  of  blood  allowed  to  flow  into  the  drop  must 
not  be  large,  and  should  be  quickly  mixed.  In  many  respects  the  most  suit- 
able medium  is  osmic  acid,  one-half  to  one  per  cent.,  which  has  the  advantage 
that  by  its  use  permanent  preparations  can  be  obtained." 

The  plaques  are  thin,  circular  discs,  homogeneous  or  very  faintly  granu- 
lar and  of  a  pale,  grayish  tint.  They  measure  T7^06  to  Tiro^Tr  (1°^  ^°  ^  /*) 
in  diameter,  about  one-sixth  of  the  diameter  of  the  red  blood-corpuscles. 
They  exist  in  the  blood  in  the  proportion  of  one  to  about  eighteen  or  twenty 
red  corpuscles. 

In  the  circulating  blood,  the  plaques  are  distinct ;  but  when  the  blood  is 


16 


THE  BLOOD. 


drawn  from,  the  vessels,  they  adhere  together  and  are  usually  collected  into 
masses.     The  plaques  quickly  undergo  change  out  of  the  body,  becoming 


FIG.  8. — Blood-plaques  and  their  derivatives,  partly  after  Bizzozero  and  Laker  (Landois). 
1,  red  blood-corpuscles  on  the  flat;  2,  from  the  side;  3,  unchanged  blood-plaques  ;  4,  a  lymph-corpuscle 
surrounded  with  blood-plaques  ;  5,  blood-plaques  variously  altered  ;  6,  a  lymph-corpuscle  with  two 
masses  of  fused  blood-plaques  and  threads  of  fibrin;  7,  group  of  blood-plaques  fused  or  run  together; 
8,  a  similar  small  mass  of  partially  dissolved  blood-plaques  with  fibrils  of  fibrin. 

ovoid,  elongated  or  pointed.     They  sometimes  send  out  processes  which  give 
them  a  stellate  appearance. 

Physiologists  have  no  knowledge  of  the  uses  of  the  blood-plaques.  The 
relations  which  have  been  supposed  to  exist  between  these  bodies  and  the 
development  of  the  other  corpuscular  elements  of  the  blood,  the  phenomena 
of  coagulation,  etc.,  are  as  yet  indefinite  and  uncertain. 

COMPOSITION  OF  THE  BLOOD-CORPUSCLES. 

The  red  corpuscles  of  the  blood  contain  an  organic  nitrogenized  substance, 
called  globuline,  combined  with  inorganic  salts  and  a  coloring  matter. 
The  composition  of  the  leucocytes  has  not  been  accurately  determined,  and 
nothing  is  known  of  the  composition  of  the  blood-plaques.  The  inorganic 
matters  contained  in  the  red  corpuscles  are  in  a  condition  of  intimate  union 
with  the  other  constituents,  and  can  be  separated  only  by  incineration.  It 
may  be  stated,  in  general  terms,  that  most,  if  not  all  of  the  various  inorganic 
constituents  of  the  plasma  exist  also  in  the  corpuscles,  which  latter  are  par- 
ticularly rich  in  the  salts  of  potassium.  Iron  exists  in  the  coloring  matter  of 
the  corpuscles.  In  addition,  the  corpuscles  contain  cholesterine,  lecethine,  a 
certain  quantity  of  fatty  matter  and  probably  some  of  the  organic  saline 
constituents  of  the  blood. 

Globuline. — Rollett,  by  alternately  freezing  and  thawing  blood  several 
times  in  succession  in  a  platinum  vessel,  has  succeeded  in  separating  the  col- 
oring matter  from  the  red  corpuscles.  When  the  blood  is  afterward  warmed 
and  liquefied,  the  fluid  is  no  longer  opaque  but  is  dark  and  transparent. 
Microscopical  examination  then  reveals  the  corpuscles,  entirely  decolorized 
and  floating  in  a  red,  semi-transparent  serum.  Denis  extracted  the  organic 


COMPOSITION  OF  THE  BLOOD-PLASMA.  17 

constituent  of  the  corpuscles  by  adding  to  defibrinated  blood  about  one-half  its 
volume  of  a  solution  of  sodium  chloride  containing  one  part  in  ten  of  water. 
Allowing  this  to  stand  for  ten  to  fifteen  hours,  there  appears  a  viscid  mass, 
which  is  very  carefully  washed  with  water  until  all  the  coloring  matter 
and  the  salt  added  have  been  removed.  The  whitish,  translucid  mass  which 
remains  is  called  globuline.  Globuline  is  readily  extracted  from  the  blood  of 
birds  but  is  obtained  with  difficulty  from  the  blood  of  the  human  subject. 

Hmmaglobine. — This  is  the  coloring  matter  of  the  red  corpuscles.  It  has 
been  called  by  different  writers,  hasmaglobuline  or  hasmatocrystalline ;  but 
the  crystals  called  hasmatine  and  hsematosine  are  derivatives  of  hasmaglobine 
and  are  not  normal  constituents  of  the  blood.  Hgemaglobine  maybe  ex- 
tracted from  the  red  corpuscles  by  adding  to  them,  when  congealed,  ether, 
drop  by  drop.  A  jelly-like  mass  is  then  formed,  which  is  passed  rapidly 
through  a  cloth,  crystals  soon  appearing  in  the  liquid,  which  may  be  sepa- 
rated by  filtration  (Gautier). 

The  crystals  of  haemaglobine  extracted  from  human  blood  are  in  the  form 
either  of  four-sided  prisms,  elongated  rhomboids  or  rectangular  tablets,  of  a 
purplish-red  color.  They  are  composed  of  carbon,  hydrogen,  oxygen,  nitrogen, 
sulphur  and  a  small  quantity  of  iron.  They  are  soluble  in  water  and  in  very 
dilute  alkaline  solutions,  and  the  haemaglobine  is  precipitated  from  these 
solutions  by  potassium  ferrocyanide,  mercuric  nitrate,  chlorine  or  acetic  acid. 
The  proportion  of  this  coloring  matter  to  the  entire  mass  of  blood  is  about 
one  hundred  and  twenty-seven  parts  per  thousand.  It  constitutes  ^  to 
\\  of  the  dried  corpuscles.  A  solution  of  haemaglobine  in  one  thousand 
parts,  examined  with  the  spectroscope,  gives  two  dark  bands  between  the  let- 
ters D  and  E  in  Frauenhofer's  scale. 

Treated  with  oxygen  or  prepared  in  fluids  in  contact  with  the  air,  there 
occurs  a  union  of  oxygen  with  the  coloring  matter,  forming  what  has  been 
called  oxyhasmaglobine.  There  can  be  no  doubt  that  the  oxygen  enters 
into  an  intimate,  though  rather  unstable  combination  with  haemaglobine,  and 
this  is  an  important  point  to  be  considered  in  connection  with  the  absorption 
of  oxygen  by  the  blood  in  respiration.  A  solution  of  oxyhaemaglobine  pre- 
sents a  different  spectrum  from  that  produced  by  a  solution  of  pure  hasma- 
globine. 

COMPOSITION  OF  THE  BLOOD-PLASMA. 

Assuming  that  the  blood  furnishes  matters  for  the  nourishment  of  all  the 
tissues  and  organs,  there  should  be  found  entering  into  its  composition  all 
the  constituents  of  the  body  which  undergo  no  change  in  nutrition,  like 
the  inorganic  salts,  and  organic  matters  capable  of  being  converted  into  the 
organic  constituents  of  every  tissue.  Farthermore,  as  the  products  of  waste 
are  all  taken  up  by  the  blood  before  their  final  elimination,  these  also  should 
enter  into  its  composition. 

Most  of  the  constituents  of  the  blood  are  found  both  in  the  corpuscles 
and  plasma.  It  is  difficult  to  determine  all  of  the  different  constituents  of 
these  two  parts  of  the  blood.  It  has  been  shown,  however,  that  the  phos- 


18 


THE  BLOOD. 


phorized  fats  are  more  abundant  in  the  globules,  while  the  fatty  acids  are 
more  abundant  in  the  plasma.     The  salts  of  potassium  exist  almost  entirely 

in  the  corpuscles,  and  the  sodium  salts 
are  four  times  more  abundant  in 
the  plasma  than  in  the  corpuscles 
(Schmidt).  In  addition  to  the  nutri- 
tive matters,  the  blood  contains  urea, 
cholesterine,  sodium  urate,  creatine, 
creatinine,  and  other  substances,  the 
characters  of  which  are  not  yet  fully 
determined,  belonging  to  the  class  of 
excrementitious  matters.  Their  con- 
sideration comes  more  appropriately 
under  the  head  of  excretion. 

The  following  table  gives  approxi- 
mately the  quantities  of  the  differ- 
ent constituents  of  the  blood-plasma. 
These  may  be  divided  into  the  follow- 
ing classes  :  1.  Inorganic  constituents ; 
2.  Organic  saline  constituents;  3.  Or- 
ganic non  -  nitrogenized  constituents ; 
4.  Excrementitious  constituents ;  5.  Or- 
ganic nitrogenized  constituents.  This 
table  will  be  taken  as  a  guide  for  the 
study  of  the  individual  constituents 
of  the  blood-plasma.  As  regards  gases, 
in  addition  to  carbon  dioxide,  which 
is  classed  with  the  excrementitious  con- 
stituents, the  blood  contains  oxygen,  nitrogen  and  hydrogen.  The  nitrogen 
and  hydrogen  are  not  important,  and  the  relations  of  oxygen  will  be  fully 
considered  in  connection  with  the  physiology  of  respiration.  Most  of  the 
coloring  matter  of  the  blood  exists  in  the  red  corpuscles,  which  contain  a 
peculiar  substance  that  has  already  been  considered  in  connection  with  the 
chemical  constitution  of  these  bodies. 

In  studying  the  composition  of  the  blood,  as  well  as  the  composition  of 
food,  the  tissues,  secreted  fluids  etc.,  it  is  convenient  to  divide  its  constituents 
into  classes,  and  this  has  been  done  in  the  simplest  manner  possible. 

It  is  evident,  the  blood  receiving  all  the  products  of  disassimilation  as 
well  as  the  nutritive  matters  resulting  from  digestion,  that  there  should  be 
a  division  of  its  constituents  into  nutritive  and  excrementitious.  The  ex- 
crementitious matters  are  the  products  of  disassimilation  of  the  organism, 
which  are  taken  up  by  the  blood  or  conveyed  to  the  blood-vessels  by  the 
lymphatics,  exist  in  the  blood  in  small  quantity,  and  are  constantly  being 
separated  from  the  blood  by  the  different  excreting  organs.  Their  constant 
removal  from  the  blood  is  the  explanation  of  the  minute  proportion  in  which 
they  exist  in  this  fluid. 


FIQ.  9.— Crystallized  hcemaglobine  (Gautier). 
a,  b,  crystals  from  the  venous  blood  of  man  ;  c, 
blood  of  the  cat ;  d,  blood  of  the  Guinea  pig; 
e,  blood  of  the  marmot ;  /,  blood  of  the  squir- 
rel.   (Gautier.) 


COMPOSITION  OF  THE  BLOOD-PLASMA.  19 


CONSTITUENTS   OF   THE   BLOOD-PLASMA. 

Specific  gravity,  1028. 

Water,  779  parts  per  1,000  in  the  male;  791  parts  per  1,000  in  the  female. 
Sodium  chloride,  3  to  4  parts  per  1,000. 
Potassium  chloride,  0'359  parts  per  1,000. 
Ammonium  chloride,  proportion  not  determined. 
Potassium  sulphate,  0'288  parts  per  1,000. 
Sodium  sulphate,  proportion  not  determined. 
Potassium  carbonate,  proportion  not  determined. 
Sodium  carbonate  (with  sodium  bicarbonate),  1*200  parts  per  1,000. 
Magnesium  carbonate,  proportion  not  determined. 
Calcium  phosphate  of  the  bones,  and  neutral  phosphate,  ") 
Magnesium  phosphate, 

Potassium  phosphate,  >  1'500  parts  per  1,000. 

Ferric  phosphate  (probable), 
Basic  phosphates  and  neutral  sodium  phosphate, 
Silica,  copper,  lead,  and  magnesia,  traces  occasionally. 

f  Sodium  lactate,  proportion  not  determined. 
Calcium  lactate  (probable),  proportion  not  determined. 
Sodium  oleate, 


tn 

E 

o 


palmitatc, 

stearate, 

valerate, 


valerate, 

butyrate,     '  r475  Parts  Per  1^W0' 


g        I"  Oleine, 


Palmitine, 

Stearine, 

Lecethine,  containing  nitrogen  and  called  phosphorized  fatty  matter,  0'400  parts  per  1,000. 

Glucose,  0-002  parts  per  1,000. 

Glycogen,  proportion  not  determined. 

Inosite,  proportion  not  determined. 

Carbon  dioxide  in  solution. 

Urea,  0'177  parts  per  1,000,  in  arterial  blood;  0*088,  in  the  blood  of  the  renal  vein. 

Sodium  urate,  proportion  not  determined. 

Potassium  urate  (probable),  proportion  not  determined. 

Calcium  urate,  "  "  "  " 

Magnesium  urate,      "  "  "  " 

Ammonium  urate,      "  "  "  " 

Sodium  sudorates,  etc.,  "          "  " 

Inosates,  "          •'  " 

Oxalates,  "  "  " 

Creatinine,  "  "  " 

Leucine,  "  "  " 

Hypoxanthine,  "  "  " 

Cholesterine,  0-455  to  0'751  parts  per  1,000,  in  the  entire  blood. 

(  Fibrin,  3  parts  per  1,000. 

g    (  Plasmme,  25  parts  (dried)  per  1,000.  ]  Xf  .     '      .      ot.  ,  AAA 

.2  ,N  ^  Metalbumm,  22  parts  per  1,000. 

fj.  §  J  Serine,  53  parts  (dried)  per  1,000. 

O  g    I  Peptones,  4  parts  (dried)  and  28  parts  (racist)  per  1,000. 

•5    I  Coloring  matters  of  the  plasma,  proportion  and  characters  not  determined. 


20  THE  BLOOD. 

Excluding  for  the  present,  all  consideration  of  the  products  of  dis- 
assimilation,  there  remain  the  various  constituents  of  the  blood  that  are 
more  or  less  directly  concerned  in  nutrition. 

Physiological  chemists  recognize  certain  chemical  constituents  of  the 
organism,  which  may  be  elementary  substances,  but  which  are  more  fre- 
quently compounds.  Sodium  chloride  is  spoken  of  as  a  constituent  of 
the  blood,  because,  as  sodium  chloride,  it  gives  to  the  blood  certain  proper- 
ties. The  chemical  elements,  chlorine  and  sodium,  are  not  regarded  as  con- 
stituents of  the  blood,  because  they  do  not  exist  uncombined  in  the  blood. 
Still,  a  chemical  constituent  may  be  a  chemical  element,  as  in  the  case  of 
oxygen,  which,  as  oxygen,  has  certain  important  uses  in  the  economy; 
although  even  oxygen  probably  is  loosely  combined  in  the  body  with  other 
matters. 

A  chemical  constituent  of  the  blood  or  of  any  of  the  animal  tissues  or 
fluids  may  be  defined  as  a  substance  extracted  from  the  body,  which  can  not 
be  subdivided  without  chemical  decomposition  and  loss  of  certain  character- 
istic properties.  This  definition  will  apply  to  all  classes  of  chemical  con- 
stituents of  the  body,  organic  as  well  as  inorganic.  The  chemical  elements 
of  which  the  constituents  are  composed  are  properly  the  ingredients  of 
the  body. 

The  constituents  of  the  blood,  and,  indeed,  of  the  entire  organism,  may 
be  classified  as  follows  : 

I.  Inorganic  Constituents. — This  class  is  of  inorganic  origin,  definite 
chemical  composition  and  crystallizable.  The  substances  included  in  this 
class  are  all  introduced  from  without  and  are  all  discharged  from  the  body  in 
the  same  form  in  which  they  entered.  They  never  exist  alone,  but  are  always 
combined  with  the  organic  constituents,  and  form  a  part  of  the  organized 
fluids  or  solids.  This  union  is  so  intimate  that  they  are  taken  up  with  the 
organic  matters,  as  the  latter  are  worn  out  and  become  effete,  and  are  dis- 
charged from  the  body,  although  themselves  unchanged.  To  supply  the  place 
of  the  constituents  thus  thrown  off,  a  fresh  quantity  is  deposited  in  the  pro- 
cess of  nutrition.  They  give  to  the  various  organs  important  properties ;  and 
although  identical  with  substances  in  the  inorganic  world,  in  the  interior  of 
the  body  they  behave  as  organic  substances.  They  require  no  special  prepara- 
tion for  absorption,  but  are  soluble  and  taken  in  unchanged.  They  are  re- 
ceived into  the  body  in  about  the  same  proportion  at  all  periods  of  life,  but 
their  discharge  is  notably  diminished  in  old  age,  giving  rise  to  calcareous  in- 
crustations and  deposits  and  a  considerable  increase  in  the  calcareous  matter 
entering  into  the  composition  of  the  tissues.  Water,  sodium  chloride,  the 
carbonates,  sulphates,  phosphates  and  other  inorganic  salts  may  be  cited  as 
examples  of  this  class  of  constituents. 

The  uses  of  water  in  the  blood  are  sufficiently  evident.  It  acts  as  a 
solvent  for  the  inorganic  salts,  the  organic  salts  and  the  excrementitious 
matters.  In  conjunction  with  the  nitrogenized  matters,  it  constitutes  a 
medium  in  which  the  corpuscles  are  suspended  without  solution. 

The  various  salts  enumerated  in  the  table  exist  in  solution  in  water  and  are 


COMPOSITION  OF  THE  BLOOD-PLASMA.  21 

more  or  less  intimately  combined  with  the  coagulable  organic  matters.  Of 
these,  the  sodium  chloride  is  the  most  abundant.  It  undoubtedly  has  an  im- 
portant use  in  giving  density  to  the  plasma  and  in  regulating  the  processes  of 
endosmosis  and  exosmosis.  In  connection  with  the  organic  salts  and  crystal- 
lizable  excrementitious  matters,  it  may  be  stated,  in  general  terms,  that  the 
blood  contains  14  to  16  parts  per  1,000  of  matters  in  actual  solution,  of  which 
6  to  8  parts  consist  of  inorganic  salts.  The  presence  of  these  substances  in 
solution,  with  the  organic  coagulable  matters,  prevents  the  solution  of  the 
corpuscular  elements  of  the  blood.  The  presence  of  the  chlorides  and  the 
alkaline  sulphates  assists  in  dissolving  the  sulphates,  carbonates  and  the  cal- 
careous phosphates.  The  carbonates  and  phosphates  are  in  part  decomposed 
in  the  system  and  furnish  bases  for  certain  of  the  organic  salts,  such  as  the 
lactates,  urates  etc. 

2.  Organic  Saline  Constituents. — These  substances  are  in  greatest  part 
formed  in  the  organism  and  they  exist  in  the  blood  in  very  small  quantity. 
The  lactates  are  probably  produced  by  decomposition  of  a  portion  of  the 
bicarbonates  and  the  union  of  the  bases  with  lactic  acid,  the  lactic  acid 
resulting,  possibly,  from  a  change  of  a  portion  of  the  saccharine  matter  in 
the  blood.     The  physiological  relations  of  these  substances  are  little  under- 
stood.    The  salts  formed  by  the  union  of  fatty  acids  with  bases  are  probably 
produced  by  decomposition  of  fatty  matters,  a  great  part  of  which  is  de- 
rived from  the  food. 

3.  Organic  Non-nitrogenized  Constituents. — These  usually  exist  in  the 
blood  in  small  quantity  and  are  derived  mainly  from  the  food.     Lecethine, 
although  it  contains  nitrogen,  is  included  in  this  class  because  it  presents 
many  of   the  properties   of   the   fats.     It   exists   in   the   blood,  bile,  nerv- 
ous substance  and  the  yelk  of  egg.      Its  chemical  properties  and  physio- 
logical relations  are  not  well  understood.     The  saccharine  matters  and  glyco- 
gen  are  derived  in  part  from  the  food  and  in  part  from  the  liver,  where 
glycogen  is  formed.     They  are  of  organic  origin,  definite  chemical  compo- 
sition and  crystallizable.     The  fats  and  sugars  are  distinguished  from  other 
organic  substances  by  the  fact  that  they  are  composed  of  carbon,  hydrogen 
and  oxygen.     In  the  sugars,  the  hydrogen  and  oxygen  exist  in  the  propor- 
tion to  form  water,  which  fact  has  given  them  the  name  of  carbohydrates. 
The  constituents  of  this  class  play  an  important  part  in  development  and 
nutrition.     One  of  them,  sugar,  appears  very  early  in  foetal  life,  formed 
first  in  the  placenta  and  afterward  in  the  liver,  its  formation  by  the  lat- 
ter organ  continuing  during  life.      Fat  is  a  necessary  constituent  of  food 
and  is  also  formed  in  the  interior  of  the  body.     The  exact  influence  which 
these  substances  have  on  development  and  nutrition  is  not  known ;  but  ex- 
periments and   observation   have   shown   that   this   influence  is  important. 
They  will  be  considered  more  fully  in  connection  with  the  physiology  of 
nutrition. 

4.  Excrementitious    Constituents. — A  full   consideration   of  these  sub- 
stances, which  are  all  formed  by  the  process  of  disassimilation  of  the  tissues 
and  are  taken  up  by  the  blood  to  be  eliminated  by  the  proper  organs,  be- 

V 


22  THE  BLOOD. 

longs  to  the  physiology  of  excretion.  The  relations  of  carbon  dioxide  to  the 
system  will  be  fully  considered  in  connection  with  the  physiology  of  res- 
piration. 

5.  Organic  Nitrogenized  Constituents. — This  class  of  constituents  is  of 
organic  origin,  indefinite  chemical  composition  and  non-crystallizable.  The 
constituents  included  in  this  class  are  apparently  the  only  matters  that  are  en- 
dowed with  so-called  vital  properties,  taking  materials  for  their  regeneration 
from  the  nutritive  fluids  and  appropriating  them  to  form  part  of  their  own 
substance.  Considered  from  this  point  of  view,  they  are  different  from  any 
substances  met  with  out  of  the  living  body.  They  are  all,  in  the  body, 
in  a  state  of  continual  change,  wearing  out  and  becoming  effete,  when  they 
are  transformed  into  excrementitious  substances.  The  process  of  repair  in 
this  instance  is  not  the  same  as  in  inorganic  substances,  which  enter  and  are 
discharged  from  the  body  without  undergoing  any  change.  The  analogous 
substances  which  exist  in  food  undergo  elaborate  preparation  by  digestion, 
before  they  can  even  be  absorbed  by  the  blood-vessels;  and  still  another 
change  takes  place  when  they  are  appropriated  by  the  various  tissues.  They 
exist  in  all  the  solids,  semi-solids  and  fluids  of  the  body,  never  alone,  but  al- 
ways combined  with  inorganic  substances.  As  a  peculiarity  of  chemical  con- 
stitution, they  all  contain  nitrogen,  which  has  given  them  the  name  of 
nitrogenized  or  azotized  matters. 

Of  the  different  classes  of  constituents  of  the  blood,  it  is  at  once  apparent 
that  the  organic  nitrogenized  matters  are  more  complex  in  their  constitution, 
properties  and  uses  than  the  other  classes.  These  substances,  as  they  exist  in 
the  blood,  possess  certain  peculiar  and  characteristic  properties. 

Plasmine,  Fibrin,  Metalbumin,  Serine. — The  name  plasmine  was  given 
by  Denis  to  a  substance  which  he  extracted  from  the  blood  by  the  following 
process  :  The  blood  drawn  directly  from  an  artery  or  vein  is  received  into  a 
vessel  containing  one-seventh  part  of  its  volume  of  a  concentrated  solution  of 
sodium  sulphate,  which  prevents  coagulation ;  in  a  short  time  the  corpuscles 
gravitate  to  the  bottom  of  the  vessel,  and  the  plasma  may  be  separated  by 
decantation ;  to  the  plasma  is  added  an  excess  of  pulverized  sodium  chloride, 
when  a  soft,  pulpy  substance  is  precipitated,  which  is  plasmine.  This  sub- 
stance, after  desiccation,  bears  a  proportion  of  about  twenty-five  parts  per 
thousand  of  blood.  It  is  soluble  in  ten  to  twenty  parts  of  water,  when 
a  portion  of  it  coagulates  and  may  be  removed  by  stirring  with  twigs  or  a 
bundle  of  broom-corn,  in  the  way  in  which  fibrin  is  separated  from  the  blood. 
The  fibrin  thus  separated  is  called  by  Denis  concrete  fibrin,  and  the  substance 
which  remains  in  solution,  dissolved  fibrin.  By  most  writers  of  the  present 
day,  the  dissolved  fibrin  of  Denis  is  called  metalbumin. 

According  to  Denis,  plasmine  is  a  proper  constituent  of  the  blood,  and 
after  extraction  by  the  process  just  described,  it  is  decomposed  into  concrete 
fibrin  and  dissolved  fibrin,  or  metalbumiu.  Having  removed  the  concrete 
fibrin  from  the  solution  of  plasmine,  the  metalbumin  is  coagulated  by  the 
addition  of  magnesium  sulphate,  which  does  not  coagulate  ordinary  albumin. 
The  proportion  of  dried  metalbumin  in  the  blood  is  about  twenty-two  parts 


COAGULATION  OF  THE  BLOOD.  23 

per  thousand.  The  proportion  of  dried  fibrin  is  about  three  parts  per 
thousand. 

After  the  extraction  of  plasmine  from  the  blood,  another  coagulable  sub- 
stance remains,  which  is  called  serine.  This  is  coagulated  by  heat,  the  strong 
mineral  acids  or  absolute  alcohol,  but  is  not  coagulated  by  ether,  which 
coagulates  egg-albumen.  Serine  bears  a  close  resemblance  to  ordinary  albu- 
min but  is  much  more  osmotic.  Its  proportion,  desiccated,  in  the  blood  is 
about  fifty-three  parts  per  thousand. 

Peptones  etc. — A  certain  quantity  of  nitrogenized  matter,  distinct  from 
the  constituents  just  described,  has  been  extracted  from  the  blood,  which  is 
analogous  to  peptone.  This  is  separated  by  coagulating  the  serum  of  the 
blood  with  hot  acetic  acid  and  filtering,  when  the  peptones  pass  through  in 
the  filtrate.  These  substances  are  probably  derived  from  the  food.  Their 
proportion  in  the  plasma  is  about  four  parts,  dried,  per  thousand,  or  twenty- 
eight  parts  before  desiccation. 

A  small  quantity  of  coloring  matter  exists  in  the  plasma.  If  the  corpus- 
cles be  separated  as  completely  as  possible,  the  clear  liquid  still  has  a  reddish- 
amber  color.  This  coloring  matter  has  never  been  isolated  and  studied.  It 
is  analogous  to  the  coloring  matter  of  the  red  corpuscles,  the  bile  and  the 
urine. 

In  addition  to  the  organic  nitrogenized  constituents  which  have  just  been 
described,  some  physiological  chemists  recognize  a  substance  called  para- 
globuline,  or  fibrinoplastic  matter,  and  fibrinogenic  matter.  These  are  sup- 
posed to  be  factors  of  fibrin,  which  come  together  in  the  coagulation  of  the 
blood.  They  will  be  considered  in  connection  with  the  theories  of  coagula- 
tion. The  so-called  sodium  and  potassium  albuminates  have  not  been  posi- 
tively established  as  normal  constituents  of  the  blood. 

COAGULATION  OF  THE  BLOOD. 

The  blood  retains  its  fluidity  while  it  remains  in  the  vessels  and  circula- 
tion is  not  interfered  with,  and  is  then  composed  of  a  clear  plasma  holding 
corpuscles  in  suspension.  Soon  after  the  circulation  is  interrupted  or  after 
blood  is  drawn  from  the  vessels,  it  coagulates  or  "  sets  "  into  a  jelly-like  mass. 
In  a  few  hours,  contraction  will  have  taken  place,  and  a  clear,  straw-colored 
fluid  expressed,  the  blood  thus  separating  into  a  solid  portion,  the  crassa- 
mentum,  or  clot,  and  a  liquid  which  is  called  serum.  The  serum  contains 
all  the  constituents  of  the  blood  except  the  corpuscles  and  fibrin-factors, 
which  together  form  the  clot.  Coagulation  takes  place  in  the  blood  of  all 
animals,  beginning  a  variable  time  after  its  removal  from  the  vessels.  In  the 
human  subject,  when  the  blood  is  received  into  a  moderately  deep,  smooth 
vessel,  the  phenomena  of  coagulation  present  themselves  in  the  following 
order : 

First,  a  gelatinous  pellicle  forms  on  the  surface,  which  occurs  in  one 
minute  and  forty-five  seconds  to  six  minutes ;  in  two  to  seven  minutes,  a 
gelatinous  layer  has  formed  on  the  sides  of  the  vessel ;  and  the  whole  mass 
becomes  of  a  jelly-like  consistence,  in  seven  to  sixteen  minutes.  Contraction 


24:  THE  BLOOD. 

then  begins,  and  little  drops  of  clear  serum  make  their  appearance  on  the 
surface  of  the  clot.  This  fluid  increases  in  quantity,  and  in  ten  or  twelve 
hours  separation  is  complete  (Nasse).  The  clot,  which  is  heavier,  sinks  to 
the  bottom  of  the  vessel,  unless  it  contain  bubbles  of  gas  or  the  surface  be 
very  concave.  In  most  of  the  warm-blooded  animals,  the  blood  coagulates 
more  rapidly  than  in  man.  Coagulation  is  particularly  rapid  in  blood  taken 
from  birds,  and  sometimes  it  takes  place  almost  instantaneously.  Coagula- 
tion is  more  rapid  in  arterial  than  in  venous  blood.  In  the  former,  the  pro- 
portion of  fibrin  formed  is  notably  greater  and  the  characters  of  the  fibrin 
are  somewhat  different.  A  solution  of  sodium  chloride  dissolves  the  fibrin 
of  venous  blood,  but  does  not  dissolve  the  fibrin  of  an  arterial  clot. 

The  relative  proportions  of  the  serum  and  clot  are  very  variable,  unless 
that  portion  of  the  serum  which  is  retained  between  the  meshes  of  the  coag- 
ulated mass  be  included  in  the  estimate.  As  the  clot  is  composed  of  corpus- 
cles and  fibrin,  and  as  these  in  their  moist  state  represent,  in  general  terms, 
about  one-half  of  the  blood,  it  may  be  stated  that  after  coagulation,  the 
actual  proportions  of  the  clot  and  serum  are  about  equal.  Simply  taking  the 
serum  which  separates  spontaneously,  there  is  a  large  quantity  when  the  clot 
is  densely  contracted,  and  a  very  small  quantity,  when  it  is  loose  and  soft. 
Usually  the  clot  retains  about  one-fifth  of  the  serum. 

On  removing  the  clot,  after  the  separation  of  the  serum  is  complete,  it  pre- 
sents a  gelatinous  consistence,  and  is  more  or  less  firm  according  to  the  degree 
of  contraction  which  has  taken  place.  As  a  general  rule,  when  coagulation  has 
been  rapid,  the  clot  is  soft  and  but  slightly  contracted.  When,  on  the  other 
hand,  coagulation  has  been  slow,  the  clot  contracts  for  a  long  time  and  is  much 
denser.  When  coagulation  is  slow,  the  clot  frequently  presents  what  is  known 
as  the  cupped  appearance,  having  a  concave  surface,  a  phenomenon  which  de- 
pends merely  on  the  degree  of  its  contraction.  It  also  presents  a  marked  dif- 
ference in  color  at  its  upper  portion.  The  blood  having  remained  fluid  for 
some  time,  the  red  corpuscles  settle,  by  reason  of  their  greater  weight,  leaving  a 
colorless  layer  on  the  top.  This  is  the  buffy-coat  spoken  of  by  some  authors. 
Examined  microscopically,  the  buffy-coat  presents  fibrils  of  coagulated  fibrin 
with  some  of  the  white  corpuscles  of  the  blood.  On  removing  a  clot  of  ve- 
nous blood  from  the  serum,  the  upper  surface  is  florid  from  contact  with  the 
air,  while  the  rest  of  it  is  dark ;  and  on  making  a  section,  if  coagulation  have 
not  been  too  rapid,  the  gravitation  of  the  red  corpuscles  is  apparent.  If 
the  clot  be  cut  into  small  pieces,  it  will  undergo  farther  contraction  and  ex- 
press a  part  of  the  contained  serum.  If  the  clot  be  washed  under  a  stream  of 
water,  at  the  same  time  kneading  it  with  the  fingers,  nearly  all  the  red  cor- 
puscles may  be  removed,  leaving  the  meshes  of  fibrin. 

After  coagulation,  if  the  serum  be  carefully  removed,  it  is  found  to  be  a  fluid 
of  a  color  varying  between  a  light  amber  and  a  clear  red.  This  color  de- 
pends upon  a  peculiar  coloring  matter  which  has  never  been  isolated.  The 
specific  gravity  of  the  serum  is  about  1028,  somewhat  less  than  that  of 
the  entire  mass  of  blood.  It  presents  all  the  constituents  of  the  plasma,  or 
liquor  sanguinis,  with  the  exception  of  the  fibrin-factors.  It  can  hardly 


COAGULATION  OF  THE  BLOOD.  25 

be  called  a  physiological  fluid,  as  it  is  -formed  only  after  coagulation  of  the 
blood. 

Coagulation  of  the  blood  is  due  to  the  formation  of  fibrin.  Coagulation 
of  this  substance  first  causes  the  whole  mass  of  blood  to  assume  a  gelatinous 
consistence ;  and  by  reason  of  its  contractile  properties,  it  soon  expresses  the 
serum,  while  the  red  corpuscles  are  retained.  One  of  the  causes  which  oper- 
ate to  retain  the  corpuscles  in  the  clot  is  the  adhesive  matter  which  covers 
their  surface  after  they  escape  from  the  vessels. 

Conditions  which  modify  Coagulation. — Blood  flowing  slowly  from  a  small 
orifice  is  more  rapidly  coagulated  than  when  it  is  discharged  in  a  full  stream 
from  a  large  orifice.  If  it  be  received  into  a  shallow  vessel,  it  coagulates 
much  more  rapidly  than  when  received  into  a  deep  vessel.  If  the  vessel  be 
rough,  coagulation  is  more  rapid  than  if  it  be  smooth  and  polished.  If  the 
blood,  as  it  flows,  be  received  on  a  cloth  or  a  bundle  of  twigs,  it  coagulates 
almost  instantaneously.  In  short,  it  appears  that  all  conditions  which  favor 
exposure  of  the  blood  to  the  air  hasten  its  coagulation.  The  blood  will 
coagulate  more  rapidly  in  a  vacuum  than  in  the  air. 

Coagulation  of  the  blood  is  prevented  by  rapid  freezing,  but  it  takes  place 
afterward  when  the  fluid  is  carefully  thawed.  Between  32°  and  140°  Fahr. 
(zero  and  60°  C.),  elevation  of  temperature  increases  the  rapidity  of  coagula- 
tion. Agitation  of  the  blood  in  closed  vessels  retards,  and  in  open  vessels, 
hastens  coagulation. 

Various  chemical  substances  retard  or  prevent  coagulation.  Among  them 
may  be  mentioned  the  following:  solutions  of  potassium  or  of  sodium 
hydrate  ;  sodium  carbonate ;  ammonium  carbonate ;  potassium  carbonate ; 
ammonia;  sodium  sulphate.  In  the  menstrual  flow,  the  blood  is  kept 
fluid  by  mixture  with  the  abundant  secretions  of  the  vaginal  mucous  mem- 
brane. 

Coagulation  of  the  Blood  in  the  Organism. — The  blood  coagulates  in  the 
vessels  after  death,  though  less  rapidly  than  when  removed  from  the  body. 
As  a  general  proposition,  it  may  be  stated  that  this  takes  place  between 
twelve  and  twenty-four  hours  after  circulation  has  ceased.  Under  these 
conditions,  the  blood  is  found  chiefly  in  the  venous  system,  as  the  arte- 
ries are  usually  emptied  by  post-mortem  contraction  of  their  muscular 
coat;  but  in  the  veins,  coagulation  is  slow  and  imperfect.  Coagula  are 
found,  however,  in  the  left  side  of  the  heart  and  in  the  aorta,  but  they 
are  much  smaller  than  those  in  the  right  side  of  the  heart  and  in  the  large 
veins.  These  coagula  present  the  general  characters  already  described. 
They  are  frequently  covered  by  a  soft,  whitish  film  and  are  dark  in  their 
interior. 

It  was  supposed  by  John  Hunter  that  coagulation  of  the  blood  did  not 
take  place  in  animals  killed  by  lightning,  or  by  prolonged  muscular  exertion, 
as  when  hunted  to  death ;  but  it  appears  from  the  observations  of  others  that 
this  view  is  not  correct.  J.  Davy  reported  a  case  of  death  by  lightning,  in 
which  a  loose  coagulum  was  found  in  the  heart  twenty-four  hours  after.  In 
this  case  decomposition  was  very  far  advanced,  and  it  is  probable  that  the 


26  THE  BLOOD. 

coagulum  had  become  less  firm  from  that  cause.  His  observations  also  show 
that  coagulation  occurs  after  poisoning  by  hydrocyanic  acid  and  in  animals 
hunted  to  death. 

Coagulation  in  different  parts  of  the  vascular  system  is  by  no  means  un- 
usual during  life.  In  the  heart,  coagula  which  bear  evidence  of  having  existed 
for  some  time  before  death  are  sometimes  found.  These  were  called  polypi 
by  some  of  the  older  writers  and  are  often  formed  of  fibrin  almost  free  from 
red  corpuscles.  They  generally  occur  when  death  is  very  gradual  and  when 
the  circulation  continues  for  some  time  with  greatly  diminished  activity.  It 
is  probable  that  a  small  coagulum  is  first  formed,  from  which  the  corpuscles 
are  washed  away  by  the  current  of  blood ;  and  that  this  becomes  larger  by 
farther  depositions,  until  large,  vermicular  masses  of  fibrin  are  found  attached, 
in  some  instances,  to  the  chordae  tendineae.  Bodies  projecting  into  the  caliber 
of  a  blood-vessel  soon  become  coated  with  a  layer  of  fibrin.  Rough  concre- 
tions about  the  orifices  of  the  heart  frequently  lead  to  the  deposition  of  little 
masses  of  fibrin,  which  sometimes  become  detached  and  are  carried  to  various 
parts  of  the  circulatory  system,  as  the  lungs  or  brain,  plugging  up  one  or  more 
of  the  smaller  vessels.  Blood  generally  coagulates  when  effused  into  the 
areolar  tissue  or  into  any  of  the  cavities  of  the  body ;  although,  effused  into  the 
serous  cavities,  the  tunica  vaginalis  for  example,  it  has  been  known  to  remain 
fluid  for  days  and  even  weeks,  and  coagulate  when  let  out  by  an  incision. 
Coagulation  thus  takes  place  in  the  vessels  as  the  result  of  stasis  or  of  very 
great  retardation  of  the  circulation,  and  in  the  tissues  or  cavities  of  the  body, 
whenever  it  is  accidentally  effused.  In  the  latter  case,  it  is  generally  removed 
in  the  course  of  time  by  absorption. 

The  property  of  the  blood  under  consideration  has  an  important  office  in 
the  arrest  of  haemorrhage.  The  effect  of  an  absence  or  great  diminution  of 
the  coagulability  of  the  circulating  fluid  is  exemplified  in  instances  of  Avhat 
is  called  the  hasmorrhagic  diathesis,  or  haemophilia;  a  condition  in  which 
slight  wounds  are  likely  to  be  followed  by  alarming,  and  it  may  be  fatal 
hasmorrhage.  This  condition  of  the  blood  is  not  characterized  by  any 
peculiar  symptoms  except  the  obstinate  flow  of  blood  from  slight  wounds ; 
and  it  may  continue  for  years. 

Conditions  which  accelerate  coagulation  have  a  tendency  to  arrest  haemor- 
rhage. It  is  well  known  that  exposure  of  a  bleeding  surface  to  the  air  has 
this  effect.  The  way  in  which  the  vessel  is  divided  has  an  important  influ- 
ence. A  clean  cut  will  bleed  more  freely  than  a  ragged  laceration.  In  divis- 
ion of  large  vessels,  this  difference  is  sometimes  very  marked.  Cases  are  on 
record  in  which  the  arm  has  been  torn  off  at  the  shoulder-joint,  and  yet  the 
haemorrhage  was,  for  a  time,  spontaneously  arrested ;  while  it  is  well  known 
that  division  of  an  artery  of  comparatively  small  size,  if  it  be  cut  across,  would 
be  fatal  if  left  to  itself.  Under  these  conditions,  the  internal  coat  is  torn  in 
shreds  which  retract,  their  curled  ends  projecting  into  the  caliber  of  the  ves- 
sel and  having  the  same  effect  on  the  coagulation  of  blood  as  a  bundle  of 
twigs.  In  laceration  of  such  a  large  vessel  as  the  axillary  artery,  the  arrest 
can  not  be  permanent,  for  as  soon  as  the  system  recovers  from  the  shock, 


COAGULATION  OF  THE  BLOOD.  27 

the  contractions  of  the  heart  force  out  the  coagulated  blood  which  has  closed 
the  opening. 

From  the  foregoing  considerations,  it  is  evident  that  coagulation  of  the 
blood  has  for  its  chief  office  the  arrest  of  haemorrhage.  Coagulation  never 
takes  place  in  the  organism  unless  the  blood  be  in  an  abnormal  condition 
with  respect  to  circulation.  Here  its  operations  are  mainly  conservative ; 
but  as  almost  all  conservative  processes  are  sometimes  perverted,  clots  in  the 
body  may  be  productive  of  injury,  as  in  the  instances  of  cerebral  apoplexy, 
clots  in  the  heart  occurring  before  death,  the  detachment  of  emboli  etc. 

Cause  of  the  Coagulation  of  the  Blood. — Alex.  Schmidt,  in  1861,  proposed 
a  theory  of  coagulation,  which  involves  the  coming  together  of  certain  mat- 
ters called  fibrin-factors.  This  theory,  which  had  been  indicated  by  Buch- 
anan, in  1845,  has  been  adopted  and  more  or  less  modified  by  Kiihne,  Yirchow 
and  others.  If  blood-plasma,  rendered  neutral  with  acetic  acid,  be  diluted 
with  ten  times  its  volume  of  water  at  32°  Fahr.  (zero  C.),and  then  be  treated 
with  a  current  of  carbon  dioxide,  a  flocculent  precipitate  is  formed,  which 
has  been  called  paraglobuline,  or  fibrinoplastic  matter.  This  substance  may 
be  dissolved  in  water  containing  air  or  oxygen  in  solution.  .  After  this  pre- 
cipitate has  been  separated,  if  the  clear  liquid  be  diluted  with  about  twice  its 
volume  of  ice-cold  water  and  be  treated  for  two  or  three  hours  with  a  current 
of  carbon  dioxide,  a  viscid  scum  is  produced,  which  has  been  called  fibrino- 
gen.  More  recently,  a  third  principle,  a  ferment,  has  been  described  by 
Schmidt,  which  he  considers  necessary  to  the  formation  of  fibrin.  This 
ferment  is  produced  in  some  way  by  the  leucocytes  of  the  blood,  probably 
by  partial  decomposition  of  these  bodies. 

In  view  of  the  results  of  recent  investigations  with  regard  to  the  cause  of 
the  coagulation  of  the  blood,  which,  unfortunately,  are  not  as  positive  and 
definite  as  could  be  desired,  some  physiologists  have  adopted  the  following  as 
a  provisional  theory  of  the  mechanism  of  this  process : 

There  exists,  probably  in  small  quantity  in  the  circulating  blood  and  in 
considerable  quantity  in  blood  drawn  from  the  vessels  or  arrested  in  its  cir- 
culation, a  peculiar  ferment  which  is  produced  in  some  way  by  changes  in 
the  leucocytes.  This  ferment  may  be  concerned  in  the  decomposition  of 
plasmine.  It  is  certainly  thrown  down  with  plasmine  when  plasmine  is  pre- 
cipitated by  the  action  of  reagents.  The  action  of  this  ferment  either  in- 
duces or  hastens  the  separation  of  plasmine  into  the  so-called  fibrin-factors, 
paraglobuline  and  fibrinogen.  Of  these  two  substances,  fibrinogen  is  the 
more  important  in  the  formation  of  fibrin,  a  small  quantity  of  fibrin,  only 
about  three  parts  per  thousand  of  blood,  being  formed.  A  large  quantity  of 
paraglobuline  is  not  used  in  the  formation  of  fibrin  and  remains  in  the  serum. 
It  is  possible,  indeed,  that  no  part  of  the  paraglobuline  is  concerned  in  coagu- 
lation. If  the  latter  be  true,  paraglobuline  may  be  regarded  as  identical  with 
metalbumin,  a  view  which  was  advanced  by  Robin  many  years  ago  and  is 
now  adopted  by  some  physiologists. 

Adopting  these  views,  the  mechanism  of  coagulation  may  be  succinctly 
described  as  follows : 


28 


THE  BLOOD. 


1.  As  a  condition  preliminary  to  coagulation,  there  is  either  an  increase 
in  the  formation  of  fibrin-ferment  or  an  appearance  of  ferment  in  the  blood, 
due  to  changes  in  certain  of  the  leucocytes.     The  red  corpuscles  are  probably 
not  directly  concerned  in  coagulation,  and  there  is  nothing  definite  known  of 
the  action  of  the  blood-plaques  in  this  process. 

2.  The  fibrin-ferment  unites  with  fibrinogen  and  forms  fibrin,  which  is 
the  coagulating  substance.     Paraglobuline  (or  metalbumin)  is  little  if  at  all 
concerned  in  this  process. 

3.  The  processes  described  as  incident  to  the  coagulation  of  blood  take 
place  also  in  the  coagulation  of  lymph  and  chyle. 

In  accordance  with  the  views  stated  in  connection  with  the  composition 
of  blood-plasma,  paraglobuline,  or  metalbumin,  fibrinogen  and,  finally,  fibrin 
are  products  of  decomposition,  are  abnormal  formations,  and  are  not  normal 
constituents  of  the  blood. 

It  is  possible  that  the  statement  just  given  of  the  mechanism  of  the  coagu- 
lation of  the  blood  may  be  modified  in  the  future  in  accordance  with  the  most 
recent  views  of  Schmidt,  who  claims  that  all  the  so-called  fibrin-factors  result 
from  decomposition  of  the  leucocytes,  a  great  number  of  which,  it  is  said, 
are  dissolved  soon  after  blood  is  drawn  from  the  vessels.  There  are,  in- 
deed, many  experimental  and  pathological  facts  in  support  of  this  view ;  but 
it  can  not  be  adopted  without  reserve,  until  the  experiments  of  Schmidt  shall 
have  been  supplemented  by  more  extended  observations.  Schmidt  maintains 
that  in  certain  classes  of  animals,  dissolved  red  corpuscles  are  also  concerned 
in  the  production  of  fibrin-factors. 

Leech-drawn  blood  remains  fluid  in  the  body  of  the  animal.  Richardson 
has  observed,  also,  that  the  blood  flowing  from  a  leech-bite  presents  the  same 
persistent  fluidity,  which  explains  the  well-known  fact  that  the  insignificant 
wound  gives  rise  to  considerable  haemorrhage. 

The  existence  of  projections  into  the  caliber  of  vessels,  or  the  passage  of 

a  fine  thread 
through  an  ar- 
tery or  vein,  will 
determine  the 
formation  of  a 
small  coagulum 
upon  the  foreign 
substance,  while 
the  circulation  is 
neither  inter- 
rupted nor  re- 

Fio.  10.— Coagulated  fibrin  (Robin).  tai'ded          In    the 

Fibrinous  clot,  without  red  corpuscles,  and  containing:  leucocytes,  thrown  off 

in  the  form  of  a  whitish  pseudo-membrane  in  a  case  of  ulceration  of  the     present     state    of 
neck  of  the  uterus  with  haemorrhage. 

knowledge,  ex- 
planation of  these  facts  is  difficult  if  not  impossible.  The  process,  under 
these  conditions,  can  not  be  subjected  to  direct  experiment  as  in  the  case 
of  blood  coagulating  out  of  the  body. 


DISCOVERY  OF  THE  CIRCULATION.  29 

During  coagulation,  fibrin  assumes  a  filamentous  form,  presenting,  under 
the  microscope,  the  appearance  of  rectilinear  fibrillas.  These  fibrillae 
gradually  increase  in  number,  and  as  contraction  of  the  clot  occurs,  they  be- 
come irregularly  crossed.  They  are  always  straight,  however,  and  never 
assume  the  wavy  appearance  characteristic  of  true  fibrous  tissue. 

The  blood  of  the  renal  and  hepatic  veins,  capillary  blood  and  the  blood 
which  passes  from  the  capillary  system  into  the  veins  after  death  generally 
does  not  coagulate  or  coagulates  very  imperfectly ;  in  other  words,  these  varie- 
ties of  blood  do  not  readily  form  fibrin.  The  reason  of  this  peculiarity  is  not 
known ;  but  the  fact  affords  a  partial  explanation  of  the  normal  fluidity  of 
the  blood  ;  for  this  fluid,  passing  over  the  entire  course  of  the  circulation  in 
about  thirty  seconds,  seems  to  be  constantly  losing  its  coagulability  in  its  pas- 
sage through  the  liver,  kidneys  and  the  general  capillary  system,  as  fast  as 
its  coagulability  is  increased  in  the  other  parts.  Taking  into  consideration 
the  rapidity  of  the  circulation,  it  is  evident  that  coagulation  can  not  take 
place  while  the  normal  circulation  is  maintained  and  while  the  blood  is 
undergoing  the  constant  changes  incident  to  general  nutrition. 


CHAPTER   II. 

CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

Discovery  of  the  circulation— Physiological  anatomy  of  the  heart — Valves  of  the  heart — Movements  of 
the  heart — Impulse  of  the  heart — Succession  of  the  movements  of  the  heart — Force  of  the  heart — Action 
of  the  valves — Sounds  of  the  heart — Causes  of  the  sounds  of  the  heart— Frequency  of  the  heart's  action 
— Influence  of  age  and  sex— Influence  of  digestion — Influence  of  posture  and  muscular  exertion— In- 
fluence of  exercise  etc. — Influence  of  temperature — Influence  of  respiration  on  the  action  of  the  heart 
— Cause  of  the  rhythmical  contractions  of  the  heart — Accelerator  nerves — Direct  inhibition  of  the  heart 
—Reflex  inhibition  of  the  heart — Summary  of  certain  causes  of  arrest  of  the  action  of  the  heart. 

HAKVEY  "  set  forth  for  the  first  time  his  discovery  of  the  circulation," 
in  his  public  lectures  in  1616,  and  in  1628  published  the  "  Exercitatio  Ana- 
tomica  de  Motu  Cordis  et  Sanyuinis  in  Animalibiis."  This  discovery,  from 
the  isolated  facts  bearing  upon  it  which  were  observed  by  anatomists  to  its 
culmination  in  the  experiments  of  Harvey,  so  fully  illustrates  the  gradual 
development  of  most  physiological  truths,  that  it  does  not  seem  out  of  place 
to  begin  the  study  of  the  circulation  with  a  brief  sketch  of  its  history. 

The  facts  bearing  upon  the  circulation  developed  before  the  time  of 
Harvey  were  chiefly  anatomical.  The  writings  of  Hippocrates  are  very 
indefinite  upon  all  points  connected  with  the  circulatory  system;  and  no 
clear  and  positive  statements  are  to  be  found  in  ancient  works  before  the 
time  of  Aristotle.  The  work  of  Aristotle  most  frequently  quoted  by  physi- 
ologists is  his  "  History  of  Animals ; "  and  in  this  occurs  a  passage  which 
seems  to  indicate  that  he  thought  that  air  passed  from  the  lungs  to  the 
heart;  but  in  his  work,  De  Partibus  Animalium,  it  is  stated  that  there  are 
4 


30  CIRCULATION  OF  THE  BLOOD. 

two  great  blood-vessels,  the  vena  cava  and  aorta,  arising  from  the  heart,  and 
that  the  aorta  and  its  branches  carry  blood.  Galen,  however,  demonstrated 
experimentally  the  presence  of  blood  in  the  arteries,  by  including  a  portion 
of  one  of  these  vessels  between  two  ligatures,  in  a  living  animal ;  but  his 
ideas  of  the  communication  between  the  arteries  and  veins  were  erroneous, 
for  he  believed  in  the  existence  of  small  orifices  in  the  septum  between  the 
ventricles  of  the  heart,  a  mistake  that  was  corrected  by  Vesalius,  at  about 
the  middle  of  the  sixteenth  century. 

In  1553,  Michael  Servetus,  who  is  generally  regarded  as  the  discoverer  of 
the  passage  of  the  blood  through  the  lungs,  or  the  pulmonary  circulation, 
described  in  a  work  on  theology  the  course  of  the  blood  through  the  lungs, 
from  the  right  to  the  left  side  of  the  heart.  This  description,  complete  as 
it  is,  was  merely  incidental  to  the  development  oif  a  theory  with  regard  to 
the  formation  of  the  soul  and  the  development  of  what  were  called  animal 
and  vital  spirits  (spiritus). 

A  few  years  later,. Colombo,  professor  of  anatomy  at  Padua,  and  Cesal- 
pinus,  of  Pisa,  described  the  passage  of  the  blood  through  the  lungs,  though 
probably  without  any  knowledge  of  what  had  been  written  by  Servetus.  To 
Cesalpinus  is  attributed  the  first  use  of  the  expression  circulation  of  the 
blood ;  and  he  also  remarked  that  after  ligature  or  compression  of  veins,  the 
swelling  is  always  below  the  point  of  obstruction. 

The  history  of  the  discovery  of  the  valves  in  the  veins  is  quite  obscure, 
although  priority  of  observation  is  almost  universally  conceded  to  Fabricius. 
As  regards  this  point,  only  the  dates  of  published  memoirs  are  to  be  con- 
sidered, notwithstanding  the  assertion  of  Fabricius  that  he  had  seen  the 
valves  in  1574.  In  1545,  Etienne  described,  in  branches  of  the  portal  vein, 
"  valves,  which  he  called  apophyses,  and  which  he  compared  to  the  valves  of 
the  heart."  In  1551,  Amatus  Lusitanus  published  a  letter  from  Cannanus, 
in  which  it  is  stated  that  he  had  found  valves  in  certain  of  the  veins.  In 
1563,  Eustachius  published  an  -account  of  the  valves  of  the  coronary  vein. 
In  1586,  a  clear  account,  by  Piccolhominus,  of  the  valves  of  the  veins  was 
published.  Fabricius  gave  the  most  accurate  descriptions  and  delineations 
of  the  valves,  and  his  first  publication  is  said  to  have  appeared  in  1603.  He 
demonstrated  the  valves  to  Harvey,  at  Padua ;  and  it  is  probable  that  this 
was  the  origin  of  the  first  speculations  by  Harvey  on  the  mechanism  of  the 
circulation. 

In  the  work  of  Harvey  are  described,  first  the  movements  of  the  heart, 
which  he  exposed  and  studied  in  living  animals.  He  described  minutely  all 
the  phenomena  which  accompany  its  action ;  its  diastole,  when  it  is  filled 
with  blood,  and  its  systole,  when  the  fibres  of  which  the  ventricles  are  com- 
posed contract  simultaneously,  and  "by  an  admirable  adjustment  all  the 
internal  surfaces  are  drawn  together,  as  if  with  cords,  and  so  is  the  charge  of 
blood  expelled  with  force."  From  the  description  of  the  action  of  the 
ventricles,  he  passed  to  the  auricles,  and  showed  how  these,  by  their  con- 
traction, filled  the  ventricles  with  blood.  By  experiments  upon  serpents  and 
fishes,  he  proved  that  the  blood  fills  the  heart  from  the  veins  and  is  sent  out 


DISCOVERY  OF  THE  CIRCULATION.  31 

into  the  arteries.  Exposing  the  heart  and  great  vessels  in  these  animals,  he 
applied  a  ligature  to  the  veins,  which  had  the  effect  of  cutting  off  the  supply 
from  the  heart  so  that  it  became  pale  and  flaccid ;  and  by  removing  the 
ligature  the  blood  could  be  seen  flowing  into  the  organ.  When,  on  the 
contrary,  a  ligature  was  applied  to  the  artery,  the  heart  became  unusually 
distended,  which  continued  so  long  as  the  obstruction  remained.  When 
the  ligature  was  removed,  the  heart  soon  returned  to  its  normal  condition. 
Harvey  completed  his  description  of  the  circulation,  by  experiments  showing 
the  course  of  the  blood  in  the  arteries  and  veins  and  the  uses  of  the  valves 
of  the  veins. 

By  these  simple  experiments,  the  chain  of  evidence  establishing  the  fact 
of  the  circulation  of  the  blood  was  completed.  Truly  it  is  said  that  here 
began  an  epoch  in  the  study  of  physiology;  for  then  scientific  observers 
began  to  emancipate  themselves  from  the  ideas  of  the  ancients,  which  had 
controlled  opinions  for  two  centuries,  and  to  study  Nature  for  themselves  by 
means  of  experiments. 

Although  Harvey  described  so  perfectly  the  course  of  the  blood  and  left 
no  doubt  as  to  the  communication  between  the  arteries  and  veins,  it  was  left 
to  others  to  actually  see  the  blood  in  movement  and  follow  it  from  one  sys- 
tem of  vessels  to  the  other.  In  1661,  Malpighi  saw  the  blood  circulating  in 
the  vessels  of  the  lung  of  a  living  frog,  examining  it  with  magnifying  glasses ; 
and  a  little  later,  Leeuwenhoek  saw  the  circulation  in  the  wing  of  a  bat. 
These  observations  completed  the  discovery  of  the  circulation. 

In  man  and  in  the  warm-blooded  animals,  the  organism  requires  blood 
that  has  been  oxygenated  in  the  lungs,  and  to  meet  this  demand  fully,  the 
circulatory  system  is  divided  into  pulmonic  and  systemic.  The  heart  is 
double,  having  a  right  side  and  a  left  side,  which  are  entirely  distinct  from 
each  other.  The  right  heart  receives  the  blood  as  it  is  brought  from  the  gen- 
eral system  by  the  veins  and  sends  it  to  the  lungs ;  the  left  heart  receives  the 
blood  from  the  lungs  and  sends  it  to  the  general  system.  It  must  be  borne  in 
mind,  however,  that  although  the  two  sides  of  the  heart  are  distinct  from 
each  other,  their  action  is  simultaneous ;  and  in  studying  the  motions  of  the 
heart,  it  will  be  found  that  the  blood  is  sent  simultaneously  from  the  right 
side  to  the  lungs  and  from  the  left  side  to  the  system.  It  will  not  be  neces- 
sary, therefore,  to  separate  the  two  circulations  in  the  study  of  their  mechan- 
ism ;  for  the  simultaneous  action  of  both  sides  of  the  heart  renders  it  possi- 
ble to  study  its  action  as  a  single  organ,  and  the  constitution  and  operations 
of  the  two  kinds  of  vessels  do  not  present  any  material  differences. 

For  convenience  of  study,  the  circulatory  system  may  be  divided  into 
heart  and  vessels,  the  latter  being  of  three  kinds :  the  arteries,  which  carry 
blood  from  the  heart  to  the  general  system ;  the  capillaries,  which  distribute 
the  blood  more  or  less  abundantly  in  different  parts  of  the  general  system ; 
and  the  veins,  which  return  the  blood  from  the  general  system  to  the  heart. 
The  three  kinds  of  blood-vessels  present  certain  anatomical  as  well  as 
physiological  distinctions,  which  will  be  noted  in  connection  with  the 
description  of  the  vascular  system. 


32 


CIECULATION  OF  THE  BLOOD. 


PHYSIOLOGICAL  ANATOMY  OF  THE  HEART. 

The  heart  of  the  human  subject  is  a  pear-shaped,  muscular  organ,  situ- 
ated in  the  thoracic  cavity,  with  its  base  in  the  median  line  and  its  apex  at 
the  fifth  intercostal  space,  three  inches  (7*6  centimetres)  to  the  left  of  the 
median  line,  or  one  inch  (2'5  centimetres)  within  the  line  of  the  left  nipple. 

Its  weight  is  eight  to 
ten  ounces  (227  to  283 
grammes)  in  the  female, 
and  ten  to  twelve  ounces 
(283  to  340  grammes) 
in  the  male.  It  has 
four  distinct  cavities ;  a 
right  and  a  left  auricle, 
and  a  right  and  a  left 
ventricle.  Of  these, 
the  ventricles  are  the 
more  capacious.  The 
heart  is  held  in  place 
by  the  attachment  of 
the  great  vessels  to  the 
posterior  wall  of  the 
thorax;  while  the  apex 
is  free  and  capable  of 
a  certain  degree  of  mo- 

FIG.  11.— Heart  in  situ  (Dalton,  in  Flint,  "  on  the  heart ").  tion.      The  whole  Organ 

a,  6,  c  etc.,  ribs  ;  1,  2,  3  etc.,  intercostal  spaces  :  vertical  line,  median    •          ,rQlr>iWl  ii    a  fll-»w 
line;  triangle,  superficial  cardiac  region;  x  on  the  fourth  rib,    1 

mpple'  sac   called  the  pericar- 

dium. This  sac  is  lined  by  a  serous  membrane,  which  is  attached  to  the 
great  vessels  at  the  base  and  reflected  over  its  surface.  The  membrane  is 
lubricated  by  about  a  drachm  (3'7  c.  c.)  of  fluid,  so  that  the  movements  of 
the  heart  are  normally  accomplished  without  any  friction.  The  serous  peri- 
cardium does  not  present  any  differences  from  serous  membranes  in  other 
situations.  The  cavities  of  the  heart  are  lined  by  a  smooth  membrane  called 
the  endocardium,  which  is  continuous  with  the  lining  membrane  of  the 
blood-vessels. 

The  right  auricle  receives  the  blood  from  the  venae  cavae  and  empties  it 
into  the  right  ventricle.  The  auricle  presents  a  principal  cavity,  or  sinus,  as 
it  is  called,  with  a  little  appendix,  called,  from  its  resemblance  to  the  ear  of 
a  dog,  the  auricular  appendix.  It  has  two  large  openings  for  the  vena  cava 
asceiidens  and  the  vena  cava  descendens  respectively,  with  a  small  opening 
for  the  coronary  vein  which  brings  the  blood  from  the  substance  of  the  heart 
itself.  It  has,  also,  another  large  opening,  called  the  auriculo-ventricular 
opening,  by  which  the  blood  flows  into  the  ventricle.  The  walls  of  this  cav- 
ity are  quite  thin  as  compared  with  the  ventricles,  measuring  about  one  line 
(2*1  mm.).  They  are  composed  of  muscular  fibres  arranged  in  two  layers, 


PHYSIOLOGICAL  ANATOMY  OF  THE  HEART. 


33 


FIG.  12.— Course  of  the  muscular  fibres  of  the  left 
auricle  (Landois). 


one  of  which,  the  external,  is  common  to  both  auricles,  and  the  other,  the 
internal,  is  proper  to  each.  These  muscular  fibres,  although  involuntary  in 
their  action,  belong  to  the  striated  variety,  and  are  similar  in  structure  to  the 
fibres  of  the  ventricles.  The  fibres  of  the  auricles  are  much  fewer  than  those 
of  the  ventricles.  Some  of  them  are 
looped,  arising  from  a  cartilaginous 
ring  which  separates  the  auricles  and 
ventricles  and  passing  over  the  auri- 
cles; and  others  are  circular,  sur- 
rounding the  auricular  appendages 
and  the  openings  of  the  veins,  ex- 
tending, also,  a  short  distance  along 
the  course  of  these  vessels.  One  or 
two  valvular  folds  are  found  at  the 
orifice  of  the  coronary  vein,  prevent- 
ing a  reflux  of  blood,  but  there  are  no  valves  at  the  orifices  of  the  venae  cavse. 
The  left  auricle  receives  the  blood  which  comes  from  the  lungs  by  the 

pulmonary  veins.  It  does 
not  differ  materially  in  its 
anatomy  from  the  right. 
It  is  a  little  smaller,  and 
its  walls  are  thicker, 
measuring  about  a  line 
and  a  half  (3-15  mm.). 
It  has  four  openings  by 
which  it  receives  the 
blood  from  the  four  pul- 
monary veins.  These 
openings  are  not  provid- 
ed with  valves.  Like  the 
right  auricle,  it  has  a 
large  opening  by  which 
blood  flows  into  the  cor- 
responding ventricle.  The 
arrangement  of  the  mus- 
cular fibres  is  essentially 
the  same  as  in  the  right 
auricle.  In  adult  life,  the 
cavities  of  the  auricles  are 
entirely  distinct  from  each 
other.  Before  birth,  they 
communicate  by  a  large 
opening,  the  foramen 

FIG.  IB.— Heart,  anterior  view  (Bonamy  and  Beau).  OVale,    and    the   Orifice   of 

1,  right  ventricle  ;  2,  left  ventricle;  3,4,  right  auricle  ;  5,6,  left  au-  ,-,        in-fpvinr  vprm    Pflvfl    is 

ride  ;  7,  pulmonary  artery;  8,  aorta;   9,  superior  vena  cava  ;  10,  I 

anterior  coronary  artery;  11,  branch  of  the  coronary  vein  ;  12,  .      ~,,,'Jr,,l 

12,  12,  lymphatic  vessels.  plO\  Idea 


34    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 


16  J 


16 


branous  fold,  the  Eustachian  valve,  which  serves  to  direct  the  blood  from  the 
lower  part  of  the  body  through  the  opening  into  the  left  auricle.  After 
birth,  the  foramen  ovale  is  closed  and  the  Eustachian  valve  gradually  disap- 
pears. 

The  ventricles,  in  the  human  subject  and  in  warm-blooded  animals,  con- 
stitute the  bulk  of  the  heart.  They  have  a  capacity  somewhat  greater  than 
that  of  the  auricles  and  are  provided  with  thick,  muscular  walls.  It  is  by 
the  powerful  action  of  this  portion  of  the  heart  that  the  blood  is  forced,  on 

the  one  hand,  to  the  lungs  and 
back  to  the  left  side  of  the  heart, 
and  on  the  other,  through  the  en- 
tire system  of  the  greater  circula- 
tion, to  the  right  side. 

The  capacity  of  the  cavities  on 
the  right  side  of  the  heart  is  one- 
tenth  to  one-eighth  greater  than 
that  of  the  corresponding  cavities 
on  the  left  side.  The  capacity  of 
the  ventricles  exceeds  that  of  the 
auricles  by  one-fourth  to  one- third. 
The  absolute  capacity  of  the  left 
ventricle,  when  distended  to  its 
utmost  (Robin  and  Hiffelsheim), 
is  4-8  to  7  ounces  (143  to  212  c.  c.). 
This  is  much  greater  than  most 
estimates,  which  place  the  capacity 
of  each  of  the  various  cavities, 
moderately  distended,  at  about  two 
ounces  (59-1  c.  c.) ;  but  the  ob- 
servations of  Robin  and  Hiffel- 
sheim, upon  the  human  heart, 
were  made  evidently  with  the 
greatest  accuracy,  either  before 

FIG.  U.-Left  cavities  of  the  heart  (Bonamy  and  Beau.)     cadaveric    rigidity    had    Set    in    or 

1      10ft  tif>t^'f''rjftti1rty    ffttiitti   '    O.     vniivnl    iirtltia   •    $     A     f*r\lti>ni-  "  * 


after  it  had  disappeared. 

Notwithstanding  the  disparity 


1,  left  ventricular  cavity ;  2,  mitral  valve  ;  3,  4,  colum- 
nce  carneae, ;  5,  aortic  opening ;  6,  aorta ;  7,  8,  9, 
aortic  valves ;  10,  right  ventricular  cavity ;  il,  in- 
terventricular  septum  ;  12,  pulmonary  artery  ;  13, 
14,  pulmonic  valves;  15,  left  auricular  cavity:  16,  , 

16,  right  pulmonary  veins,  with  17,  17,  openings  of     111  the  extreme  Capacity  01    the  Va- 
the  veins  ;  18,  section  of  the  coronary  vein.  .  .   .          ,  . 

nous  cavities,  the  quantity  01  blood 

which  enters  these  cavities  is  necessarily  equal  to  that  which  is  expelled. 
This  has  been  stated  to  be  a  little  more  than  two  ounces  (about  GO  c.c.). 
There  are,  however,  no  means  of  estimating  with  exactness  the  quantity  of 
blood  discharged  with  each  ventricular  contraction ;  and  the  question  seems 
to  be  rather  avoided  in  many  works  on  physiology.  Judging,  however,  from 
observations  on  the  heart  during  its  action,  it  never  seems  to  contain  much 
more  than  half  the  quantity  in  all  its  cavities  that  it  does  when  fully  dis- 
tended by  injection ;  but  the  right  cavities  are  more  dilatable  than  the  left, 


PHYSIOLOGICAL  ANATOMY   OF  THE  HEART. 


35 


8 12 


11 


and  probably  the  ordinary  quantity  of  blood  in  the  left  ventricle  is  four- 
fifths  to  five-sixths  of  its  extreme  capacity,  or  five  to  six  ounces  (120  to 
170  c.c.). 

The  cavities  of  the  ventricles  are  triangular  or  conoidal,  the  right  being 
broader  and  shorter  than  the  left,  which  latter  extends  to  the  apex.  The 
inner  surface  of  both  cavities  is  marked  by  ridges  and  papillas,  which 
are  called  columnar  carneae.  Some  of  these  are  fleshy  ridges  projecting 
into  the  cavity ;  others  are  columns  attached  by  each  extremity  and  free  at 
the  central  portion ;  and  others  are  papillse  giving  origin  to  the  chordae 
tendineae,  which  are  attached  to  the  free  edges  of  the  auriculo-ventricular 
valves.  These  fleshy  columns  interlace  in  every  direction  and  give  the  inner 
surface  of  the  cavities  a  reticulated  appearance.  This  arrangement  facilitates 
the  complete  emptying  of  the  ventricles  during  their  contraction. 

The  walls  of  the  left  ventricle  are  uniformly  much  thicker  than  those  of 
the  right  side.  The  average  thick- 
ness of  the  right  ventricle  at  the 
base  is  two  and  a  half  lines  (5-25 
mm.),  and  the  thickness  of  the 
left  ventricle  at  the  corresponding 
part  is  seven  lines  (14'7  mm.),  or 
a  little  more  than  half  an  inch 
(Bouillaud). 

The  arrangement  of  the  mus- 
cular fibres  constituting  the  walls 
of  the  ventricles  is  more  regular 
than  in  the  auricles,  and  their 
course  affords  an  explanation  of 
some  of  the  phenomena  which 
accompany  the  heart's  action. 
The  direction  of  the  fibres  can 
not  be  well  made  out  unless  the 
heart  have  been  boiled  for  a  num- 
ber of  hours,  when  part  of  the 
intermuscular  tissue  is  dissolved 
out,  and  the  fibres  can  be  easily 
separated  and  followed.  Without 
entering  into  a  minute  descrip- 
tion of  their  direction,  it  is  suffi- 
cient to  state,  in  this  connection, 
that  they  present  two  principal 
layers ;  a  superficial  layer  com- 
mon to  both  ventricles,  and  a 
deep  layer  proper  to  each  ventri- 
cle. The  superficial  fibres  pass 
obliquely  from  right  to  left  from  the  base  to  the  apex ;  here  they  take  a 
spiral  course,  become  deep,  and  pass  into  the  interior  of  the  organ,  to  form 


FIG.  15.— Right  cavities  of  the  heart  (Bonamy  and  Beau). 

1,  right  ventricular  cavity ;  2,  posterior  curtain  of  the 
tricuspid  valve  ;  3.  right  auricular  cavity  ;  4,  colum- 
nce  carnece  of  the  right  auricle  ;  5,  section  of  the  cor- 
onary vein ;  6,  Eus'tachian  valve ;  7,  ring  of  Vieus- 
sens  ;  8,  fossa  ovalis  ;  9.  superior  vena  cava  ;  10,  infe- 
rior vena  cava;  11,  aorta;  12,  12,  right  pulmonary 
veins. 


36     CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 


the  columnae  carneae.  These  fibres  envelop  both  ventricles.  They  may  be 
said  to  arise  from  cartilaginous  rings  which  surround  the  auriculo- ventricular 
orifices.  The  external  surface  of  the  heart  is  marked  by  a  little  groove  which 
indicates  the  division  between  the  two  ventricles.  The  deep  fibres  are  circu- 
lar, or  transverse,  and  surround  each  ventricle  separately. 

The  muscular  tissue  of  the  heart  is  of  a  deep-red  color  and  resembles,  in 
its  gross  characters,  the  tissue  of  ordinary  voluntary  muscles ;  but  as  already 

intimated,  it  presents  certain  pe- 
culiarities in  its  minute  anatomy. 
The  fibres  are  considerably  small- 
er and  more  granular  than  those 
of  ordinary  muscles.  They  are, 
moreover,  connected  with  each 
other  by  short,  inosculating 
branches.  (See  Fig.  17.)  The 
muscular  fibres  of  the  heart  have 
no  sarcolemma.  These  peculiari- 
ties, particularly  the  inosculation 
of  the  fibres,  favor  the  contrac- 
tion of  the  ventricular  walls  in 
every  direction  and  the  complete 
expulsion  of  the  contents  of  the 
cavities  with  each  systole. 

The  distribution  of  the  nerves 
to  the  heart  and  the  arrangement 
of  the  ganglia  and  nerve-termi- 
nations in  its  substance  will  be 
described  in  connection  with  the 
influence  of  the  nervous  system 
upon  the  circulation. 

FIG.  16.-Muscular  fibres  of  Me  ventricles  (Bonamy  and  Each   ventricle    has    two   OH- 

1,  superficial  fibres  common  to  both  ventricles ;  2,  fibres  fices  :     One   by  which   it    receives 
of  the  left  ventricle  ;  3.  deep  fibres  passing  upward  to- 
ward the  base  of  the  heart ;  4,  fibres  penetrating  the  the  blood   irom   the   auricle,   and 
left  ventricle.  ' 

the  other  by  which   the    blood 

passes  from  the  right  side  to  the  lungs  and  from  the  left  side  to  the  general 
system.  All  of  these  openings  are  provided  with  valves,  which  are  so  ar- 
ranged as  to  allow  the  blood  to  pass  in  but  one  direction. 

Tricuspid  Valve. — This  valve  is  situated  at  the  right  auriculo-ventricular 
opening.  It  has  three  curtains,  formed  of  a  thin  but  resisting  membrane, 
which  are  attached  around  the  opening.  The  free  borders  are  attached  to 
the  chordae  tendineae,  some  of  which  arise  from  the  papillae  on  the  inner  sur- 
face of  the  ventricle,  and  others,  directly  from  the  walls  of  the  ventricle. 
When  the  organ  is  empty,  these  curtains  are  applied  to  the  walls  of  the 
ventricle,  leaving  the  auriculo-ventricular  opening  free ;  but  when  the  ventri- 
cle is  completely  filled  and  the  fibres  contract,  they  are  forced  up,  their  free 
edges  become  applied  to  each  other,  and  the  opening  is  closed. 


4 


MOVEMENTS  OF  THE  HEART. 


37 


17.  —  Branched 
muscular  fibres 
from  the  heart  of 
a  mammal  (Lan- 
dois). 


Pulmom'c  Valves.—  These  valves,  also  called  the  semilunar,  or  sigmoid 
valves  of  the  right  side,  are  situated  at  the  orifice  of  the  pulmonary  artery. 
They  are  strong,  membranous  pouches,  with  their  convex- 
ities, when  closed,  looking  toward  the  ventricle.  They  are 
attached  around  the  orifice  of  the  pulmonary  artery  and 
are  applied  very  nearly  to  the  walls  of  the  vessel  when  the 
blood  passes  in  from  the  ventricle;  but  at  other  times 
their  free  edges  meet  in  the  centre,  opposing  the  regurgi- 
tation  of  blood.  At  the  centre  of  the  free  edge  of  each 
valve  is  a  little  corpuscle  called  the  corpuscle  of  Arantius; 
and  just  above  the  margins  of  attachment  of  the  valves, 
the  artery  presents  three  little  dilatations,  or  sinuses,  called 
the  sinuses  of  Valsalva.  The  corpuscles  of  Arantius  prob- 
ably aid  in  the  adaptation  of  the  valves  to  each  other  and 
in  the  effectual  closure  of  the  orifice. 

Mitral  Valve. — This  valve,  sometimes  called  the  bicus- 
pid, is  situated  at  the  left  auriculo-ventricular  orifice.  It  is  called  mitral 
from  its  resemblance,  when  open,  to  a  bishop's  mitre.  It  is  attached  to  the 
edges  of  the  auriculo-ventricular  opening,  and  its  free  borders  are  held  in 

place,  when  closed,  by 
the  chordae  tendineae  of 
the  left  side.  It  presents 
no  material  difference 
from  the  tricuspid  valve, 
with  the  exception  that  it 
is  divided  into  two  cur- 
tains instead  of  three. 

Aortic  Valves. — These 
valves,  also  called  the  sem- 
ilunar, or  sigmoid  valves 
of  the  left  side,  present 
no  difference  from  the 
valves  at  the  orifice  of 
the  pulmonary  artery. 


FIG.  18. — Valves  of  the  heart  (Bonamy  and  Beau). 


1,  right  auriculo-ventricular  orifice,  closed  by  the  tricuspid  valve  ;  ml  • , 

2,  fibrinous  ring  ;  3,  left  auriculo-ventricular  orifice,  closed  by  1  h6V  are    Situated   at    the 
the  mitral  valve  ;  4,  fibrinous  ring  :  5,  aortic  orifice  and  valves  ;  •/. 

6,  pulmonic  orifice  and  valves  ;  7,  8,  9,  muscular  fibres.  aortic  Ormce. 

MOVEMENTS  OF  THE  HEART. 

The  dilatation  of  the  cavities  of  the  heart  is  called  the  diastole,  and  the 
contraction  of  the  heart,  the  systole.  When  these  terms  are  used  without  any 
qualification,  they  are  understood  as  referring  to  the  ventricles ;  but  they  are 
also  applied  to  the  action  of  the  auricles,  as  the  auricular  diastole  and  systole, 
which  are  distinct  from  the  action  of  the  ventricles. 

A  complete  revolution  of  the  heart  consists  in  the  filling  and  emptying  of 
all  its  cavities,  during  which  they  present  an  alternation  of  repose  and  activity. 
As  these  phenomena  occupy,  in  many  warm-blooded  animals,  a  period  of  time 


38     CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

less  than  one  second,  it  will  be  appreciated  that  the  most  careful  study  is  ne- 
cessary in  order  to  ascertain  their  exact  relations  to  each  other.  When  the 
heart  is  exposed  in  a  living  animal,  the  most  prominent  phenomenon  is  the 
alternate  contraction  and  relaxation  of  the  ventricles  ;  but  this  is  only  one  of 
the  operations  of  the  organ.  In  all  the  mammalia,  the  anatomy  and  action  of 
the  vascular  system  are  practically  the  same  as  in  the  human  subject ;  and 
although  the  exposure  of  the  heart  by  opening  the  chest  modifies  somewhat 
the  force  and  frequency  of  its  pulsations,  the  various  phenomena  follow  each 
other  in  their  natural  order  and  present  essentially  their  normal  characters. 
Having  opened  the  chest,  keeping  up  artificial  respiration,  the  heart,  en- 
veloped in  its  pericardium,  is  observed,  contracting  regularly ;  and  on  slitting 
up  and  removing  this  covering,  the  various  parts  are  completely  exposed. 
The  right  ventricle  and  auricle  and  a  portion  of  the  left  ventricle  can  be 
seen  without  disturbing  the  position  of  the  parts ;  but  the  greater  part  of  the 
left  auricle  is  concealed.  As  both  auricles  and  ventricles  act  together,  the 
parts  of  the  heart  which  are  exposed  are  sufficient  for  purposes  of  study. 

Action  of  the  Auricles. — Except  the  short  time  occupied  in  the  contrac- 
tion of  the  auricles,  these  cavities  are  continually  receiving  blood,  on  the  right 
side  from  the  general  system,  by  the  venae  cavae,  and  on  the  left  side  from  the 
lungs,  by  the  pulmonary  veins.  This  continues  until  the  cavities  of  the  au- 
ricles are  completely  filled,  the  blood  coming  in  by  a  steady  current;  and 
during  the  repose  of  the  heart,  the  blood  is  also  flowing  through  the  auriculo- 
ventricular  orifices  into  the  ventricles.  When  the  auricles  have  become  fully 
distended,  they  contract  quickly  and  with  considerable  power  (the  auricular 
systole),  and  force  the  blood  into  the  ventricles,  producing  complete  diastole 
of  these  cavities.  During  this  contraction,  the  blood  not  only  ceases  to  flow 
in  from  the  veins,  but  some  of  it  is  regurgitated,  as  the  orifices  by  which  the 
vessels  open  into  the  auricles  are  not  provided  with  valves.  The  size  of  the 
auriculo- ventricular  orifices  is  one  reason  why  the  greater  portion  of  the  blood 
is  made  to  pass  into  the  ventricles;  and  farthermore,  during  the  auricular 
systole,  the  muscular  fibres  which  are  arranged  around  the  orifices  of  the 
veins  constrict  them  to  a  certain  extent,  which  tends  to  diminish  the  reflux 
of  blood.  There  can  be  no  doubt  that  some  regurgitation  takes  place  from 
the  auricles  into  the  veins,  but  this  prevents  the  possibility  of  over-distention 
of  the  ventricles. 

It  has  been  shown  that  the  systole  of  the  auricles  is  not  immediately  neces- 
sary to  the  performance  of  the  circulation ;  and  the  contractility  of  the  auri- 
cles may  be  temporarily  exhausted  by  repeated  and  prolonged  stimulation, 
the  ventricles  continuing  to  act,  keeping  up  the  circulation  of  blood. 

Action  of  the  Ventricles. — Immediately  following  the  contraction  of  the 
auricles,  by  which  the  ventricles  are  completely  distended,  there  is  contrac- 
tion of  the  ventricles.  This  is  the  chief  active  operation  performed  by  the 
heart  and  is  generally  spoken  of  as  the  systole.  The  contraction  of  the  ven- 
tricles is  very  much  more  powerful  than  that  of  the  auricles.  By  their  ac- 
tion, the  blood  is  forced  from  the  right  side  to  the  lungs,  by  the  pulmonary 
artery,  and  from  the  left  side  to  the  general  system,  by  the  aorta.  Regurgita- 


MOVEMENTS  OF  THE  HEART.  39 

* 

tion  into  the  auricles  is  prevented  by  the  closure  of  the  tricuspid  and  mitral 
valves.  This  act  accomplished,  the  heart  has  a  period  of  repose,  the  blood 
flowing  into  the  auricles,  and  from  them  into  the  ventricles,  until  the  auricles 
are  filled  and  another  contraction  takes  place. 

Locomotion  of  the  Heart. — The  position  of  the  heart  after  death  or  during 
the  repose  of  the  organ  is  with  its  base  directed  slightly  to  the  right  and  its 
apex  to  the  left  side  of  the  body.  With  each  ventricular  systole,  the  apex 
is  sent  forward  and  is  moved  slightly  from  left  to  right.  The  movement 
from  left  to  right  is  a  necessary  consequence  of  the  course  of  the  superficial 
fibres.  The  fibres  on  the  anterior  surface  of  the  organ  are  longer  than  those 
on  the  posterior  surface,  and  pass  from  the  base,  which  is  comparatively  fixed, 
to  the  apex,  which  is  movable.  As  a  consequence  of  this  anatomical  ar- 
rangement, the  heart  is  moved  upward  and  forward  during  its  systole.  The 
course  of  the  fibres  from  the  base  to  the  apex  is  from  right  to  left ;  and  as 
they  shorten,  the  apex  is  of  necessity  slightly  moved  from  left  to  right. 

The  locomotion  of  the  heart  takes  place  in  the  direction  of  its  axis  and  is 
due  to  the  sudden  distention  of  the  great  vessels  at  its  base.  These  vessels 
are  elastic,  and  as  they  receive  the  charge  of  blood  from  the  ventricles,  they 
become  enlarged  in  every  direction  and  consequently  project  the  entire  organ 
against  the  walls  of  the  chest.  This  movement  is  aided  by  the  recoil  of  the 
ventricles  as  they  discharge  their  contents. 

Twisting  of  the  Heart. — The  spiral  course  of  the  superficial  fibres  involves 
another  phenomenon  accompanying  its  contraction;  namely,  twisting.  By 
attentively  watching  the  apex,  especially  when  the  action  of  the  heart  is 
slow,  there  is  observed  a  palpable  twisting  of  the  point  upon  itself  from  left 
to  right  with  the  systole,  and  an  untwisting  with  the  diastole. 

Hardening  of  the  Heart. — If  the  heart  of  a  living  animal  be  grasped  by 
the  hand,  it  will  be  observed  that  at  each  systole  it  becomes  hardened.  The 
fact  that  it  is  composed  almost  exclusively  of  fibres  resembling  very  closely 
those  of  the  voluntary  muscles,  explains  this  phenomonen.  Like  any  other 
muscle,  it  is  sensibly  hardened  during  contraction. 

Shortening  of  the  Ventricles. — The  point  of  the  heart  is  protruded  during 
the  ventricular  systole,  but  this  protrusion  is  not  due  to  elongation  of  the  ven- 
tricles. By  suddenly  cutting  the  heart  out  of  a  warm-blooded  animal  and 
watching  the  phenomena  which  accompany  the  few  regular  movements  which 
follow,  it  is  seen  that  the  ventricles  invariably  shorten  as  they  contract.  This 
can  easily  be  appreciated  by  the  eye,  but  more  readily  if  the  point  of  the  or- 
gan be  brought  just  in  contact  with  a  plane  surface  at  a  right  angle,  when,  at 
each  contraction,  it  is  unmistakably  observed  to  recede.  During  the  inter- 
vals of  contraction,  the  great  vessels,  particularly  the  aorta  and  pulmonary  ar- 
tery, which  attach  the  base  of  the  heart  to  the  posterior  wall  of  the  thorax, 
are  filled  but  not  distended  with  blood ;  at  each  systole,  however,  these  ves- 
sels are  distended  to  their  utmost  capacity ;  their  elastic  coats  admit  of  con- 
siderable enlargement,  as  can  be  seen  in  the  living  animal,  and  this  enlarge- 
ment, taking  place  in  every  direction,  pushes  the  whole  organ  forward.  It  is 
for  this  reason  that,  in  observing  the  heart  in  situ,  the  ventricles  seem  to  elon- 


40     CIECULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 


FIG.  19. — Diagram  of  the  shortening  of 

the  ventricles  during  systole. 
The  dotted  lines  show  the  position  of  the 
heart  during  contraction. 


gate.  It  is  only  when  the  heart  is  firmly  fixed  or  is  contracting  after  it  has  been 
removed  from  the  body,  that  the  actual  changes  which  occur  in  the  length  of 

the  ventricles  can  be  appreciated.  During 
the  systole,  the  ventricles  are  shortened  and 
are  narrowed  in  their  transverse  diameter, 
but  their  antero-posterior  diameter  is  slight- 
ly increased. 

In  addition  to  the  marked  changes  in 
form,  position  etc.,  which  the  heart  under- 
goes during  its  action,  on  careful  examina- 
tion it  is  seen  that  the  surface  of  the  ventri- 
cles becomes  marked  with  slight,  longitudinal 
ridges  during  the  systole. 

Impulse  of  the  Heart. — Each  movement 
of  the  heart  produces  an  impulse,  which  can 
be  readily  felt  and  sometimes  seen  in  the 
fifth  intercostal  space  a  little  to  the  right  of  the  perpendicular  line  of  the  left 
nipple.  This  impulse  is  synchronous  with  the  contraction  of  the  ventricles. 
If  the  hand  be  introduced  into  the  chest  of  a  living  animal  and  the  finger  be 
placed  between  the  point  of  the  heart  and  the  walls  of  the  thorax,  every  time 
that  there  is  a  hardening  of  the 
point,  the  finger  will  be  pressed 
against  the  side.  If  the  impulse  of 
the  heart  be  felt  while  the  finger  is 
on  the  pulse,  it  is  evident  that  the 
heart  strikes  against  the  thorax  at 
the  time  of  the  distention  of  the  ar- 
terial system.  The  impulse  is  due 
to  the  locomotion  of  the  ventricles. 
In  the  words  of  Harvey,  "  the  heart 
is  erected,  and  rises  upward  to  a 
point  so  that  at  this  time  it  strikes 
against  the  breast  and  the  pulse  is 
felt  externally." 

Succession  of  the  Movements  of 
the  Heart. — The  main  points  in  the 
succession  of  the  movements  of  the 
heart  are  readily  observed  in  cold- 
blooded animals,  in  which  the  pul- 
sations are  very  slow.  In  examining 

the    heart    Of  the  frog,  turtle  Or   alii-  FIG.  HO.-Side  view  of  the  heart  (landois). 

cratnr  tVip  a Ifprni firms  nf  rp-nn«p  anrl  A,  apex  during  diastole  ;  A',  the  same  during  systole. 
&al0r'  "  (Modified  from  Ludwig  and  Henke.) 

activity  are  very   strongly   marked. 

During  the  intervals  of  contraction,  the  whole  heart  is  flaccid  and  the  ven- 
tricle is  comparatively  pale ;  the  auricles  then  slowly  fill  with  blood ;  when 
they  have  become  fully  distended,  they  contract  and  fill  the  ventricle,  which 


MOVEMENTS  OF  THE  HEART. 


41 


in  these  animals  is  single ;  the  ventricle  immediately  contracts,  its  action 
following  upon  the  contraction  of  the  auricles  as  if  it  were  propagated  from 
them.  When  the  heart  is  filled  with  blood,  it  has  a  dark-red  color,  which 
contrasts  strongly  with  its  appearance  after  the  systole.  These  phenomena 
may  occupy  ten  to  twenty  seconds,  giving  an  abundance  of  time  for  ob- 
servation. The  case  is  different,  however,  with  the  warm-blooded  animals, 
in  which  the  anatomy  of  the  heart  is  nearly  the  same  as  in  man.  Here  a 
normal  revolution  may  occupy  less  than  a  second ;  and  it  is  evident  that  the 
varied  phenomena  just  mentioned  are  followed  with  more  difficulty.  In  spite 
of  this  rapidity  of  action,  it  can  be  seen  that  a  rapid  contraction  of  the  auri- 
cles precedes  the  ventricular  systole,  and  that  the  latter  is  synchronous  with 
the  cardiac  impulse. 

The  experiments  of  Marey,  with  reference  to  the  relations  between  the 
systole  of  the  auricles^  the  systole  of  the  ventricles  and  the  impulse  of  the 
heart,  were  performed  upon  horses,  in  the  following  way : 

A  sound  is  introduced  into  the  right  side  of  the  heart  through  the  jugu- 
lar vein.  This  sound  is  provided  with  two  initial  bags,  one  of  which  is 
lodged  in  the  right  auricle,  while  the  other  passes  into  the  ventricle.  The 
bags  are  connected  with  distinct  tubes  which  pass  one  within  the  other  and 
are  connected  by  elastic  tubing  with  the  registering  apparatus.  At  each  sys- 
tole of  the  heart,  the  bags  in  its  cavities  are  compressed  and  produce  corre- 
sponding movements  of  the  levers,  which  may  be  registered  simultaneously. 


FIG.  21. — Curdioyriiph  (C'hauveau  and  Marey). 

"  The  instrument  is  composed  of  two  principal  elements  :  A  E,  the  registering  apparatus,  and  A  S,  the 
sphygmographic  apparatus,  that  is  to  say,  which  receives,  transmits,  and  amplifies  the  movements 
which  are  to  be  studied."  The  compression  exerted  upon  the  bag  c,  which  is  placed  over  the  apex 
of  the  heart,  between  the  intercostal  muscles,  is  conducted  by  the  tube  t  c.  which  is  filled  with  air.  to 
the  first  lever.  The  compression  exerted  upon  the  bags  o  and  v,  in  the  double  sound,  is  conducted 
by  the  tubes  t  o  and  t  v  to  the  two  remaining  levers.  The  movements  of  the  levers  are  registered 
simultaneously  by  the  cylinder  A  E. 

To  register  the  impulse  of  the  heart,  an  incision  is  made  through  the  skin 
and  the  external  intercostal  muscle  over  the  point  where  the  apex-beat  is  felt. 


42    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

A  little  bag,  stretched  over  two  metallic  buttons  separated  by  a  central  rod, 
is  then  secured  in  the  cavity  thus  formed  and  is  connected  by  an  elastic  tube 
with  the  registering  apparatus.  All  the  tubes  are  provided  with  stop-cocks, 
so  that  each  initial  bag  may  be  made  to  communicate  with'its  lever  at  will. 
When  the  operation  is  completed  and  the  sound  is  firmly  secured  in  place  by 
a  ligature  around  the  vein,  the  animal  experiences  no  inconvenience,  is  able 
to  walk  about,  eat  etc.,  and  there  is  every  evidence  that  the  circulation  is 
not  interfered  with.  The  cylinder  which  carries  the  paper  destined  to  receive 
the  traces  is  arranged  to  move  by  clock-work  at  a  given  rate.  The  paper 
may  also  be  ruled  in  lines,  the  distances  between  which  represent  certain  frac- 
tions of  a  second.  Fig.  21  represents  the  apparatus  reduced  to  one-sixth  of 
its  actual  size.  Two  of  the  levers  are  connected  with  the  double  sound  for 
the  right  auricle  and  ventricle,  and  one  is  connected  with  the  bag  destined  to 
receive  the  impulse  of  the  heart.  In  an  experiment  upon  a  horse,  the  move- 
ments of  the  three  levers  produced  traces  upon  the  paper  which  were  inter- 
preted as  follows : 

The  auricular  systole,  marked  by  the  first  lever,  immediately  preceded  the 
ventricular  systole  and  occupied  about  two-tenths  of  a  second.  The  eleva- 
tion of  the  lever  indicated  that  it  was  much  more  feeble  than  the  ventricu- 
lar systole,  and  sudden  in  its  character ;  the  contraction,  when  it  had  arrived 
at  the  maximum,  being  immediately  followed  by  relaxation. 

The  ventricular  systole,  marked  by  the  second  lever,  immediately  followed 
the  auricular  systole  and  occupied  about  four-tenths  of  a  second.  The  almost 
vertical  direction  of  the  trace  and  the  degree  of  elevation  showed  that  it  was 
sudden  and  powerful  in  its  character.  The  abrupt  descent  of  the  lever 
showed  that  the  relaxation  was  almost  instantaneous. 

The  impulse  of  the  heart,  marked  by  the  third  lever,  was  shown  to  be  ab- 
solutely synchronous  with  the  ventricular  systole. 

Condensing  the  general  results  obtained  by  Marey,  which  are  of  course 
subject  to  some  variation,  and  dividing  the  action  of  the  heart  into  ten  equal 
parts,  three  distinct  periods  are  observed,  which  occur  in  the  following 
order : 

Auricular  Systole. — This  occupies  two-tenths  of  the  heart's  action.  It 
is  feeble  as  compared  with  the  ventricular  systole,  and  relaxation  immediately 
follows  the  contraction. 

Ventricular  Systole. — This  occupies  four-tenths  of  the  heart's  action. 
The  contraction  is  powerful  and  the  relaxation  is  sudden.  It  is  absolutely 
synchronous  with  the  impulse  of  the  heart. 

Auricular  Diastole. — This  occupies  four-tenths  of  the  heart's  action. 

Force  of  the  Heart. — Hales  (1733)  was  the  first  to  investigate  experiment- 
ally the  question  of  the  force  exerted  by  the  heart,  by  the  application  of  the 
cardiometer.  He  showed  that  the  pressure  of  blood  in  the  aorta  could  be 
measured  by  the  height  to  which  the  fluid  would  rise  in  a  tube  connected 
with  that  vessel,  and  estimated  the  force  of  the  left  ventricle  by  multiplying 
the  pressure  in  the  aorta  by  the  area  of  the  internal  surface  of  the  ventricle. 
The  cardiometer  has  since  undergone  various  improvements  and  modifica- 


ACTION  OF  THE  VALVES.  43 

tions,  but  the  above  is  the  principle  made  use  of  at  the  present  day  in  esti- 
mating the  pressure  of  the  blood  in  different  parts  of  the  circulatory  system. 

Hales  estimated,  from  experiments  upon  living  animals,  the  height  to 
which  the  blood  would  rise  in  a  tube  connected  with  the  aorta  of  the  human 
subject,  at  7  feet  6  inches  (228-6  centimetres),  and  gave  the  area  of  the  left 
ventricle  as  15  square  inches  (96*67  square  centimetres).  From  this  he  cal- 
culated the  force  of  the  left  ventricle  as  equal  to  51 -5  pounds  (about  23  kilos). 
This  estimate,  however,  does  not  satisfy  all  the  physical  conditions,  and  it 
can  not  be  accepted,  even  as  an  approximation. 

The  apparatus  of  Marey  for  registering  the  contractions  of  the  different 
cavities  of  the  heart  enabled  him  to  ascertain  the  comparative  force  of  the 
two  ventricles  and  the  right  auricle ;  the  situation  of  the  left  auricle  pre- 
cluding the  possibility  of  introducing  a  sound  into  its  cavity.  By  first  sub- 
jecting the  bags  to  known  degrees  of  pressure,  the  line  of  elevation  of  a 
lever  may  be  graduated  so  as  to  represent  the  degrees  of  the  cardiometer.  In 
analyzing  traces  made  by  the  left  ventricle,  the  right  ventricle  and  right 
auricle,  in  the  horse,  Marey  found  that  as  a  general  rule,  the  comparative 
force  of  the  right  and  left  ventricles  is  as  one  to  three.  The  force  of  the 
right  auricle  is  comparatively  insignificant,  being  in  one  case,  as  compared 
with  the  right  ventricle,  only  as  one  to  ten. 

Action  of  the  Valves. — In  man  and  the  warm-blooded  animals,  there  are 
no  valves  at  the  orifices  by  which  the  veins  open  into  the  auricles.  As  has 
already  been  seen,  compared  with  the  ventricles,  the  force  of  the  auricles  is 
insignificant ;  and  it  has  f arthermore  been  shown  that  the  ventricles  may  be 
filled  with  blood  and  the  circulation  continue  when  the  auricles  are  entirely 
passive.  Although  the  orifices  are  not  provided  with  valves,  the  circular 
arrangement  of  the  fibres  about  the  veins  is  such,  that  during  the  contraction 
of  the  auricles  the  openings  are  considerably  narrowed  and  regurgitation  can 
not  take  place  to  any  great  extent.  The  force  of  the  blood  flowing  into  the 
auricles  likewise  offers  an  obstacle  to  its  return.  There  is  really  no  valvu- 
lar apparatus  which  operates  to  prevent  regurgitation  from  the  heart  into 
the  veins ;  for  the  valvular  folds,  which  are  so  abundant  in  the  general  venous 
system  and  particularly  in  the  veins  of  the  extremities,  do  not  exist  in  the 
venae  cavas.  The  continuous  flow  of  blood  from  the  veins  into  the  auricles, 
the  feeble  character  of  the  auricular  contractions,  the  arrangement  of  the 
fibres  around  the  orifices  of  the  vessels,  and  the  great  size  of  the  auriculo- ven- 
tricular openings,  are  conditions  which  provide  sufficiently  for  the  flow  of 
blood  into  the  ventricles. 

Action  of  the  Auriculo  -  Ventricular  Valves. — After  the  ventricles  have 
become  completely  distended  by  the  auricular  systole,  they  take  on  their  con- 
traction, which  is  very  many  times  more  powerful  than  the  contraction  of 
the  auricles.  They  force  open  the  valves  which  close  the  orifices  of  the  pul- 
monary artery  and  aorta  and  empty  their  contents  into  these  vessels.  To 
accomplish  this,  at  the  moment  of  the  ventricular  systole,  there  is  a  complete 
closure  of  the  auriculo- ventricular  valves,  leaving  only  the  auriculo- ventricu- 
lar opening  through  which  the  blood  can  pass.  That  these  valves  close  at 


44    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

the  moment  of  contraction  of  the  ventricles,  was  demonstrated  by  the  experi- 
ments of  Chauveau  and  Faivre,  who  introduced  the  finger  through  an  open- 
ing into  the  auricle  and  actually  felt  the  valves  close  at  the  instant  of  the 
ventricular  systole.  This  tactile  demonstration,  and  the  fact  that  the  first 
sound  of  the  heart,  which  is  produced  in  part  by  the  closure  of  the  auriculo- 
ventricular  valves,  is  synchronous  with  the  ventricular  systole,  leave  no  doubt 
as  to  the  mechanism  of  the  closure  of  these  valves.  It  is  probable  that  as 
the  blood  flows  into  the  ventricles,  the  valves  are  slightly  floated  out,  but  they 
are  not  closed  until  the  ventricles  contract. 

If  a  bullock's  heart  be  prepared  by  cutting  away  the  auricles  so  as  to 
expose  the  mitral  and  tricuspid  valves,  securing  the  nozzles  of  a  double 
syringe  in  the  pulmonary  artery  and  aorta  after  having  destroyed  the  semi- 
lunar  valves,  and  if  fluid  be  injected  simultaneously  into  both  ventricles,  the 
play  of  the  valves  will  be  exhibited.  The  mitral  valve  effectually  prevents 
the  passage  of  fluid,  its  edges  being  so  accurately  adapted  that  not  a  drop 
passes  between  them ;  but  when  the  pressure  is  considerable,  a  certain  quan- 
tity of  fluid  passes  the  tricuspid  valve  (T.  W.  King).  There  is,  indeed,  a 
certain  degree  of  insufficiency  of  the  tricuspid  valve,  which  does  not  exist  on 
the  opposite  side ;  but  it  is  very  questionable  whether  there  can  be  sufficient 
force  exerted  by  the  right  ventricle  to  produce  regurgitation  of  blood  at  the 
right  auriculo-ventricular  orifice. 

Action  of  the  Aortic  and  Pulmonic  Valves. — The  action  of  the  semilunar 
valves  is  nearly  the  same  upon  both  sides.  In  the  intervals  of  the  ventricular 
contractions,  they  are  closed  and  prevent  regurgitation  of  blood  into  the  ven- 
tricles. The  systole,  however,  overcomes  the  resistance  of  these  valves  and 
forces  the  contents  of  the  ventricles  into  the  arteries.  During  this  time,  the 
valves  are  applied,  or  nearly  applied,  to  the  walls  of  the  vessel ;  but  so  soon 
as  the  ventricles  cease  their  contraction,  the  constant  pressure  of  the  blood, 
which  is  very  great,  closes  the  openings. 

The  action  of  the  semilunar  valves  can  be  studied  by  cutting  away  a  por- 
tion of  the  ventricles  in  the  heart  of  a  large  animal,  securing  the  nozzles  of  a 
double  syringe  in  the  aorta  and  pulmonary  artery  and  forcing  water  into  the 
vessels.  It  has  been  observed  that  while  the  aortic  semilunar  valves  oppose 
the  passage  of  the  liquid  so  effectually  that  the  aorta  may  be  ruptured  before 
the  valves  will  give  way,  a  certain  degree  of  insufficiency  exists,  under  a  high 
pressure,  at  the  orifice  of  the  pulmonary  artery  (Flint,  1864).  A  slight  in- 
sufficiency of  the  pulmonic  valves  was  observed  by  John  Hunter,  in  1794.  It 
is  not  probable,  however,  that  the  pressure  of  blood  in  the  pulmonary  artery 
is  ever  sufficient  to  produce  regurgitation  when  the  valves  are  normal. 

It  is  probable  that  the  corpuscles  of  Arantius,  which  are  situated  in  the 
middle  of  each  valvular  curtain,  assist  in  the  accurate  closure  of  the  orifice. 
The  sinuses  of  Valsalva,  situated  in  the  artery  behind  the  valves,  are  regarded 
as  facilitating  the  closure  of  the  valves  by  allowing  the  blood  to  pass  easily 
behind  them. 

Sounds  of  the  Heart. — The  appreciable  phenomena  which  attend  the 
heart's  action  are  connected  with  the  systole  of  the  ventricles.  It  is  this 


SOUNDS  OF  THE  HEART.  45 

which  produces  the  impulse  against  the  walls  of  the  thorax,  and  as  will  be 
seen  farther  on,  the  dilatation  of  the  arterial  system,  indicated  by  the  pulse. 
It  is  natural,  therefore,  in  studying  these  phenomena,  to  take  the  systole  as  a 
point  of  departure,  instead  of  the  action  of  the  auricles ;  and  the  sounds, 
which  are  two  in  number,  have  been  called  first  and  second,  with  reference  to 
the  ventricular  systole. 

The  first  sound  is  absolutely  synchronous  with  the  apex-beat.  The  second 
sound  follows  the  first  with  scarcely  an  appreciable  interval.  Between  the 
second  and  the  first  sound,  there  is  an  interval  of  silence. 

Some  writers  have  attempted  to  represent  the  sounds  of  the  heart  and 
their  relations  to  each  other,  by  certain  syllables,  as  "  lubb-dup  or  lubb-tub  "  ; 
but  it  seems  unnecessary  to  attempt  to  make  such  a  comparison,  which  can 
only  be  appreciated  by  one  who  is  practically  acquainted  with  the  heart- 
sounds,  when  the  sounds  themselves  can  be  so  easily  studied. 

Both  sounds  are  generally  heard  with  distinctness  over  the  entire  prgecor- 
dial  region.  The  first  sound  is  heard  with  its  maximum  of  intensity  over 
the  body  of  the  heart,  a  little  below  and  within  the  nipple,  between  the 
fourth  and  fifth  ribs,  and  is  propagated  with  greatest  intensity  downward, 
toward  the  apex.  The  second  sound  is  heard  with  its  maximum  of  intensity 
at  the  base  of  the  heart,  between  the  nipple  and  the  sternum,  at  about  the 
third  rib,  and  is  propagated  upward,  along  the  course  of  the  great  vessels.  If 
the  stethoscope  be  placed  between  the  point  of  the  apex-beat  and  the  left 
nipple,  the  first  sound  will  be  heard  strongly  accentuated,  and  presenting  a 
certain  quality  in  its  valvular  element,  due  to  the  closure  of  the  mitral  valve. 
If  the  stethoscope  be  then  removed  to  a  point  a  little  to  the  left  of  the  ensi- 
form  cartilage,  the  element  due  to  the  closure  of  the  tricuspid  valve  will 
predominate,  and  a  slight  but  distinct  difference  in  quality  may  frequently 
be  noted.  An  analogous  difference  in  the  valvular  elements  of  the  second 
sound  may  also  be  observed.  When  the  stethoscope  is  placed  at  the  base  of 
the  heart,  just  to  the  right  of  the  sternum  and  near  the  aortic  valves,  the 
character  of  the  second  sound  is  often  notably  different  from  the  character  of 
the  sound  heard  with  the  stethoscope  placed  just  to  the  left  of  the  sternum, 
over  the  pulmonic  valves.  In  this  way  the  valvular  elements  of  the  two 
sounds  of  the  heart  may  be  separated,  each  one  into  two,  one  produced  by 
closure  of  the  valves  on  the  left  side,  and  one  by  closure  of  the  valves  of  the> 
right  side.  A  recognition  of  these  nice  distinctions  is  useful  in  physical, 
examinations  of  the  heart  in  disease. 

The  rhythm  of  the  sounds  bears  a  definite  relation  to  the  rhythm  of.:  the> 
heart's  action.  Laennec  was  the  first  to  direct  special  attention  to  the  rhythm' 
of  the  heart-sounds,  although  the  sounds  themselves  were  recognized  by  Har- 
vey, who  compared  them  to  the  sounds  made  by  the  passage  of  fluids  along' 
the  oesophagus  of  a  horse  when  drinking.  Laennec  divided  a  single  revolution 
of  the  heart  into  four  equal  parts:  the  first  two  parts,  occupied  by  the  first 
sound;  the  third  part,  by  the  second  sound;  and  the  fourth  part,  with  no; 
sound.  He  regarded  the  second  sound  as  following  immediately  after-  the 
first.  Some  authors  have  described  a  "  short  silence  "  as  occurring  after  the 


46    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

first  sound,  and  a  "  long  silence/'  after  the  second  sound.  The  short  silence, 
if  appreciable  at  all,  is  so  indistinct  that  it  may  practically  be  disregarded. 

Most  physiologists  regard  the  duration  of  the  first  sound  as  a  little  less 
than  two-fourths  of  the  heart's  action,  and  the  second  sound  as  a  little  more 
than  one-fourth.  When  the  mechanism  of  the  production  of  the  two  sounds 
is  considered,  it  will  be  seen  that  if  the  views  on  that  point  be  correct,  the 
first  sound  should  occupy  the  period  of  the  ventricular  systole,  or  four-tenths 
of  the  heart's  action.  The  second  sound  occupies  about  three-tenths,  and 
the  repose,  three-tenths. 

The  first  sound  is  relatively  dull,  low  in  pitch,  and  is  made  up  of  two  ele- 
ments ;  one,  a  valvular  element,  in  which  it  resembles  in  character  the  second 
sound,  and  the  other,  an  element  which  is  directly  due  to  the  action  of  the 
heart  as  a  muscle.  It  has  been  ascertained  that  all  muscular  contraction  is 
attended  with  a  certain  sound.  To  this  is  added  an  impulsion  element,  which 
is  produced  by  the  striking  of  the  heart  against  the  walls  of  the  thorax. 

The  second  sound  is  relatively  sharp,  high  in  pitch,  and  has  but  one  ele- 
ment, which  is  purely  valvular. 

Causes  of  the  Sounds  of  the  Heart. — There  is  now  scarcely  any  difference 
of  opinion  with  regard  to  the  cause  of  the  second  sound  of  the  heart.  The 
experiments  of  Rouanet  (1832)  settled  beyond  a  doubt  that  it  is  due  to 
closure  of  the  aortic  and  pulmonic  semilunar  valves.  In  these  experiments, 
the  second  sound  was  imitated  by  producing  sudden  closure  of  the  aortic 
valves  by  a  column  of  water.  In  the  experiments  of  the  British  Commission, 
the  semilunar  valves  were  caught  up  by  curved  hooks  introduced  through  the 
vessels  of  a  living  animal  (the  ass),  with  the  result  of  abolishing  the  second 
sound  and  substituting  for  it  a  hissing  murmur.  When  the  instruments 
were  withdrawn  and  the  valves  permitted  to  resume  their  action,  the  normal 
sound  returned. 

The  cause  of  the  first  sound  of  the  heart  has  not  been  so  well  understood. 
It  was  maintained  by  Rouanet  that  this  sound  was  produced  by  the  closure 
of  the  auriculo- ventricular  valves ;  but  the  situation  of  these  valves  rendered 
it  difficult  to  demonstrate  this  by  actual  experiment.  While  the  second  sound 
is  purely  valvular  in  its  character,  the  first  sound  is  composed  of  a  certain 
number  of  different  elements ;  but  auscultatory  experiments  have  been  made 
by  which  all  but  the  valvular  element  are  eliminated,  when  the  first  sound 
assumes  a  purely  valvular  quality.  These  observations  were  made  in  1858  by 
the  late  Dr.  Austin  Flint : 

If  a  folded  handkerchief  be  placed  between  the  stethoscope  and  in- 
tegument, the  first  sound  is  divested  of  some  of  its  most  distinctive  feat- 
ures. It  loses  the  quality  of  impulsion  and  presents  a  well  marked  valvular 
quality. 

In  many  instances,  when  the  stethoscope  is  applied  to  the  praecordia  while 
the  subject  is  in  a  recumbent  posture  and  the  heart  is  removed  by  force  of 
gravity  from  the  anterior  wall  of  the  thorax,  the  first  sound  becomes  purely 
valvular  in  character  and  as  short  as  the  second. 

When  the  stethoscope  is  applied  to  the  chest  a  little  distance  from  the 


SOUNDS  OF  THE  HEART.  47 

point  where  the  first  sound  is  heard  with  its  maximum  of  intensity,  it  pre- 
sents only  its  valvular  element. 

These  observations,  taken  in  connection  with  the  fact  that  the  first  sound 
occurs  when  the  ventricles  contract  and  necessarily  accompanies  the  closure 
of  the  auriculo-ventricular  valves,  show  that  these  valves  produce  at  least  one 
element  of  the  sound.  In  farther  support  of  this  opinion,  is  the  fact  that  the 
first  sound  is  heard  with  its  maximum  of  intensity  over  the  site  of  the  valves 
and  is  propagated  downward  along  the  ventricles,  to  which  the  valves  are 
attached.  Actual  experiments  are  not  wanting  to  confirm  this  view.  Chauveau 
and  Faivre  succeeded  in  abolishing  the  first  sound  by  the  introduction  of 
a  wire  ring  into  the  auriculo-ventricular  orifice  through  a  little  opening  in 
the  auricle,  so  as  to  prevent  the  closure  of  the  valves.  When  this  is  done, 
the  first  sound  is  lost ;  but  on  taking  it  out  of  the  opening,  the  sound  returns. 
These  observers  also  abolished  the  first  sound  by  introducing  a  small  curved 
tenotomy-knife  through  the  auriculo-ventricular  orifice  and  dividing  the 
chordae  tendineae.  In  this  experiment  a  loud  rushing  murmur  took  the  place 
of  the  sound.  These  observations  and  experiments  seem  to  settle  the  fact 
that  the  closure  of  the  auriculo-ventricular  valves  produces  one  element  of 
the  first  sound. 

The  other  elements  which  enter  into  the  composition  of  the  first  sound 
are  not  so  prominent  as  the  one  just  mentioned,  although  they  serve  to  give 
it  its  prolonged  and  "booming"  character.  These  elements  are  a  sound 
like  that  produced  by  any  large  muscle  during  its  contraction,  called  by  some 
the  muscular  murmur,  and  the  sound  produced  by  the  impulse  of  the  heart 
against  the  walls  of  the  chest. 

There  can  be  no  doubt  that  the  muscular  murmur  is  one  of  the  elements 
of  the  first  sound ;  and  it  is  this  which  gives  to  the  sound  its  prolonged  char- 
acter when  the  stethoscope  is  applied  over  the  body  of  the  organ,  as  the  sound 
produced  in  muscles  continues  during  the  whole  period  of  their  contraction. 
Admitting  this  to  be  an  element  of  the  first  sound,  its  duration  must  neces- 
sarily coincide  with  that  of  the  ventricular  systole. 

The  impulse  of  the  heart  against  the  walls  of  the  thorax  also  has  a  share 
in  the  production  of  the  first  sound.  This  is  demonstrated  by  noting  the 
difference  in  the  sound  when  the  subject  is  lying  upon  the  back,  and  when 
he  is  upright,  by  interposing  any  soft  substance  between  the  stethoscope  and 
the  chest,  or  by  auscultating  the  heart  after  the  sternum  has  been  removed. 
Under  these  conditions,  the  first  sound  loses  its  booming  character,  retaining, 
however,  the  muscular  element  when  the  instrument  is  applied  to  the  exposed 
organ. 

The  observations  showing  the  valvular  character  of  one  of  the  elements 
of  the  first  sound  have  been  so  definite  and  positive  in  their  results  that  one 
can  hardly  regard  them  as  entirely  controverted  by  the  recent  experiments 
(1885)  of  Yeo  and  Barrett,  upon  the  hearts,  cut  from  the  body,  of  cats  and 
dogs,  which  show,  it  is  claimed,  that  "  a  definite  and  characteristic  tone  sim- 
ilar in  quality  to  the  first  sound  is  produced  by  the  heart-muscle  under  cir- 
cumstances that  render  it  impossible  for  any  tension  of  the  valves  to  contrib- 


4:8     CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

ute  to  its  production."  It  will  be  assumed,  therefore,  that  the  sounds  of  the 
heart  have  a  mechanism  that  may  be  summarized  as  follows  : 

The  first  sound  of  the  heart  is  a  compound  sound.  It  is  produced  by  the 
closure  of.  the  auriculo-ventricular  valves  at  the  beginning  of  the  ventricular 
systole,  to  which  are  superadded,  the  muscular  sound,  due  to  the  contraction 
of  the  muscular  fibres  of  the  heart,  and  the  impulsion-sound,  due  to  the 
striking  of  the  heart  against  the  walls  of  the  thorax. 

The  second  sound  is  a  simple  sound.  It  is  produced  by  the  sudden  clos- 
ure of  the  aortic  and  pulmonic  semilunar  valves,  immediately  following  the 
ventricular  systole. 

It  is  of  importance,  with  reference  to  pathology,  to  have  a  clear  idea  of 
the  currents  of  blood  through  the  heart,  with  their  exact  relations  to  the 
sounds  and  intervals.  At  the  beginning  of  the  first  sound,  the  blood  is  for- 
cibly thrown  from  the  ventricles  into  the  pulmonary  artery  on  the  right  side 
and  the  aorta  on  the  left,  and  the  auriculo-ventricular  valves  are  closed. 
During  the  period  occupied  by  this  sound,  the  blood  is  flowing  through  the 
arterial  orifices,  and  the  auricles  are  receiving  blood  slowly  from  the  venae 
cavae  and  the  pulmonary  veins.  "When  the  second  sound  occurs,  the  ventri- 
cles having  become  relaxed,  the  recoil  of  the  arterial  walls,  acting  upon  the 
column  of  blood,  immediately  closes  the  semilunar  valves  upon  the  two  sides. 
The  auricles  continue  to  dilate,  and  the  ventricles  are  slowly  receiving  blood. 
Immediately  following  the  second  sound,  during  the  first  part  of  the  interval, 
the  auricles  become  fully  dilated ;  and  in  the  last  part  of  the  interval,  imme- 
diately preceding  the  first  sound,  the  auricles  contract  and  the  ventricles  are 
fully  dilated,  This  completes  a  single  revolution  of  the  heart. 

Frequency  of  the  Heart's  Action. — The  number  of  pulsations  of  the  heart 
is  not  far  from  seventy  per  minute  in  an  adult  male  and  is  between  seventy 
and  eighty  in  the  female.  There  are  individual  cases,  however,  in  which  the 
pulse  is  normally  much  slower  or  more  frequent  than  this,  a  fact  which  must 
be  remembered  when  examining  the  pulse  in  disease.  It  is  said  that  the 
pulse  of  Napoleon  I.  was  only  forty  per  minute.  Dunglison  mentioned  a 
case  which  came  under  his  own  observation,  in  which  the  pulse  presented  an 
average  of  thirty-six  per  minute.  The  same  author  stated  that  the  pulse  of 
Sir  William  Congreve  was  never  less  than  one  hundred  and  twenty-eight  per 
minute,  in  health.  It  is  by  no  means  unfrequent  to  find  a  healthy  pulse  of  a 
hundred  or  more  a  minute ;  but  in  the  cases  reported  in  which  the  pulse 
has  been  found  to  be  forty  or  less,  it  is  possible  that  every  alternate  beat  of 
the  heart  Avas  so  feeble  as  to  produce  no  perceptible  arterial  pulsation.  In 
such  instances,  the  fact  may  be  ascertained  by  listening  to  the  heart  while 
the  finger  is  placed  upon  the  artery. 

Influence  of  Age  and  Sex. — In  both  the  male  and  female,  observers  have 
constantly  found  a  great  difference  in  the  rapidity  of  the  heart's  action  at 
different  periods  of  life.  The  pulsations  of  the  heart  in  the  foetus  are  about 
140  per  minute.  At  birth  the  pulse  is  136.  It  gradually  diminishes  during 
the  first  year  to  about  128.  The  second  year,  the  diminution  is  quite  rapid, 
107  being  the  mean  frequency  at  two  years  of  age.  After  the  second  year, 


FEEQUENCY  OF  THE  HEART'S  ACTION.  49 

the  frequency  progressively  diminishes  until  adult  life,  when  it  is  at  its  min- 
imum, which  is  about  70  per  minute.  At  the  later  periods  of  life  the  move- 
ments of  the  heart  become  slightly  accelerated,  ranging  between  75  and  80 


During  early  life  there  is  no  marked  and  constant  difference  in  the  rapid- 
ity of  the  pulse  in  the  sexes  ;  but  near  the  age  of  puberty,  the  development 
of  the  peculiarities  relating  to  sex  is  accompanied  with  an  acceleration  of  the 
heart's  action  in  the  female,  which  continues  even  into  old  age. 

Influence  of  Digestion.  —  The  condition  of  the  digestive  system  has  a 
marked  influence  on  the  rapidity  of  the  pulse,  and  there  is  generally  an 
increase  in  the  pulse  of  between  five  and  ten  beats  per  minute  after  each 
meal.  Prolonged  fasting  diminishes  the  frequency  of  the  pulse  by  about 
twelve  beats.  Alcohol  first  diminishes  and  afterward  accelerates  the  pulse. 
Coffee  is  said  to  accelerate  the  pulse  in  a  marked  degree.  It  has  been  ascer- 
tained that  the  pulse  is  accelerated  to  a  greater  degree  by  animal  than  by 
vegetable  food. 

Influence  of  Posture  and  Muscular  Exertion.  —  It  has  been  observed  that 
the  position  of  the  body  has  a  very  marked  influence  upon  the  rapidity  of  the 
pulse.  In  the  male,  there  is  a  difference  of  about  ten  beats  between  standing 
and  sitting,  and  fifteen  beats  between  standing  and  the  recumbent  posture. 
In  the  female,  the  variations  with  position  are  not  so  great.  The  average  is, 
for  the  male  standing,  81  ;  sitting,  71  ;  lying,  66  ;  —  for  the  female  :  standing, 
91  ;  sitting,  84  ;  lying,  80.  This  is  given  as  the  average  of  a  large  number 
of  observations.  There  were  a  few  instances,  however,  in  which  there  was 
scarcely  any  variation  with  posture,  and  some  in  which  the  variation  was 
much  greater  than  the  average.  In  the  inverted  posture,  the  pulse  was  found 
to  be  reduced  about  fifteen  beats  (Guy). 

The  question  at  once  suggests  itself  whether  the  acceleration  of  the  pulse 
in  sitting  and  standing  may  not  be  due,  in  some  measure,  to  the  muscular 
effort  required  in  making  the  change  of  posture.  This  is  answered  by  the 
experiments  of  Guy,  in  which  the  subjects  were  placed  on  a  revolving  board 
and  the  position  of  the  body  was  changed  without  any  muscular  effort.  The 
same  results  as  those  cited  above  were  obtained  in  these  experiments,  showing 
that  the  difference  is  due  to  the  position  of  the  body  alone.  In  a  single  obser- 
vation, the  pulse,  standing,  was  89;  lying,  77;  difference,  12.  With  the  post- 
ure changed  without  any  muscular  effort,  the  results  were  as  follows  :  stand- 
ing, 87  ;  lying,  74  ;  difference,  13.  Different  explanations  of  these  variations 
have  been  offered  by  physilogists  ;  but  Guy  seems  to  have  settled  experi- 
mentally the  fact  that  the  acceleration  is  due  in  part  to  the  muscular  effort 
required  to  maintain  the  body  in  the  sitting  and  standing  positions.  The 
following  are  the  results  of  experiments  bearing  on  this  point,  in  which 
it  is  shown  that  when  the  body  is  carefully  supported  in  the  erect  or  sitting 
posture,  so  as  to  be  maintained  without  muscular  effort,  the  pulse  is  less 
frequent  than  when  the  subject  is  standing  ;  and  farthermore,  that  the  pulse 
is  accelerated,  in  the  recumbent  posture,  when  the  body  is  imperfectly  sup- 
ported : 


50    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

"  1.  Difference  between  the  pulse  in  the  erect  posture,  without  support, 
and  leaning  in  the  same  posture,  in  an  average  of  twelve  experiments  on  the 
writer,  12  beats ;  and  on  an  average  of  eight  experiments  on,  other  healthy 
males,  8  beats. 

"  2.  Difference  in  the  frequency  of  the  pulse  in  the  recumbent  posture, 
the  body  fully  supported,  and  partially  supported,  14  beats  on  an  average  of 
five  experiments. 

"  3.  Sitting  posture  (moan  of  ten  experiments  on  the  writer),  baok  sup- 
ported, 80 ;  unsupported,  87 ;  difference,  7  beats. 

"  4.  Sitting  posture  with  the  legs  raised  at  right  angles  with  the  body 
(average  of  twenty  experiments  on  the  writer),  back  unsupported,  86 ;  sup- 
ported, 68 ;  difference,  18  beats.  An  average  of  fifteen  experiments  of  the 
same  kind  on  other  healthy  males  gave  the  following  numbers :  back  unsup- 
ported, 80  ;  supported,  68 ;  a  difference  of  12  beats." 

Influence  of  Exercise  etc. — Muscular  exertion  increases  the  frequency  of 
the  pulsations  of  the  heart ;  and  the  experiments  just  cited  show  that  the 
difference  in  rapidity,  which  is  by  some  attributed  to  change  in  posture — some 
positions,  it  is  fancied,  offering  fewer  obstacles  to  the  current  of  blood  than 
others — is  mainly  due  to  muscular  exertion.  According  to  Bryan  Eobinson 
(1734),  a  man  in  the  recumbent  position  has  64  pulsations  per  minute; 
sitting,  68  ;  after  a  slow  walk,  78  ;  after  walking  four  miles  in  an  hour,  100  ; 
and  140  to  150  after  running  as  fast  as  he  could.  This  general  statement, 
which  has  been  repeatedly  verified,  shows  the  important  influence  of  the 
muscular  system  on  the  heart. 

The  influence  of  sleep  upon  the  action  of  the  heart  reduces  itself  almost 
entirely  to  the  proposition  that  during  this  condition,  there  is  usually  en- 
tire absence  of  muscular  effort,  and  consequently  the  number  of  beats  is  less 
than  when  the  individual  is  aroused.  It  has  been  found  that  there  is  no 
difference  in  the  pulse  between  sleep  and  perfect  quiet  in  the  recumbent  post- 
ure. This  fact  obtains  in  the  adult  male  ;  but  there  is  a  marked  difference 
in  females  and  young  children,  the  pulse  being  always  slower  during  sleep 
(Quetelet). 

Influence  of  Temperature. — The  influence  of  extremes  of  temperature 
upon  the  heart  is  very  decided.  The  pulse  may  be  doubled  by  remaining  a 
very  few  minutes  exposed  to  extreme  heat.  Bence  Jones  and  Dickinson  have 
ascertained  that  the  pulse  may  be  very  much  reduced  in  frequency,  for  a 
short  time,  by  the  cold  douche.  It  has  also  been  remarked  that  the  pulse  is 
habitually  more  rapid  in  warm  than  in  cold  climates. 

Although  many  circumstances  materially  affect  the  rapidity  of  the  heart's 
action,  they  do  not  complicate,  to  any  great  extent,  examinations  of  the  pulse 
in  disease.  In  cases  which  present  considerable  febrile  movement,  the  pa- 
tient is  generally  in  the  recumbent  posture.  The  variations  induced  by  vio- 
lent exercise  are  easily  recognized,  while  those  dependent  upon  temperature, 
the  condition  of  the  digestive  system,  etc.,  are  so  slight  that  they  may  prac- 
tically be  disregarded.  It  is  necessary  to  bear  in  mind,  however,  the  varia- 
tions which  exist  in  the  sexes  and  at  different  periods  of  life,  as  well  as  the 


INFLUENCE  OF  RESPIRATION  UPON  THE  HEART.  51 

possibility  of  individual  peculiarities,  when  the  action  of  the  heart  is  extra- 
ordinarily rapid  or  slow. 

Influence  of  Respiration  upon  the  Action  of  the  Heart. — The  relations  be- 
tween the  circulation  and  respiration  are  very  intimate  and  one  process  can 
not  go  on  without  the  other.  If  circulation  be  arrested,  the  muscles,  being 
no  longer  supplied  with  fresh  blood,  soon  lose  their  contractile  power,  and 
respiration  ceases.  Circulation,  also,  is  impossible  if  respiration  be  perma- 
nently arrested.  When  respiration  is  imperfectly  performed,  the  action  of 
the  heart  is  slow  and  labored.  The  effects  of  arrest  of  respiration  are  marked 
in  all  parts  of  the  circulatory  system,  arteries,  capillaries  and  veins ;  but  the 
disturbances  thus  produced  all  react  upon  the  heart. 

If  the  heart  be  exposed  in  a  living  animal  and  artificial  respiration  be 
kept  up,  although  the  pulsations  are  increased  in  frequency  and  diminished 
in  force,  after  a  time  they  become  perfectly  regular  and  continue  thus  so 
long  as  air  is  adequately  supplied  to  the  lungs.  Under  these  conditions,  res- 
piration is  entirely  under  control  and  the  effects  of  its  arrest  upon  the  heart 
can  easily  be  studied.  If  respiration  be  interrupted,  the  following  changes 
in  the  action  of  the  heart  are  observed :  For  a  few  seconds  pulsations  go 
on  as  usual,  but  in  about  a  minute  they  begin  to  diminish  in  frequency. 
At  the  same  time,  the  heart  becomes  engorged  with  blood  and  the  disten- 
tion  of  its  cavities  rapidly  increases.  For  a  time  its  contractions  are  com- 
petent to  discharge  the  entire  contents  of  the  left  ventricle  into  the  arterial 
system,  and  a  cardiometer  applied  to  an  artery  will  indicate  a  great 
increase  in  the  pressure  of  blood.  A  corresponding  increase  in  the  move- 
ments of  the  mercury  will  be  noted  at  each  contraction  of  the  heart,  indi- 
cating that  the  organ  is  acting  with  abnormal  vigor.  If  respiration  be  still 
interrupted,  the  engorgement  becomes  intense,  the  heart  at  each  diastole 
being  distended  to  its  utmost  capacity.  It  now  becomes  incapable  of  empty- 
ing itself,  the  contractions  become  very  unfrequent,  perhaps  three  or  four  in 
a  minute,  and  are  progressively  enfeebled.  The  organ  is  dark,  almost  black, 
owing  to  the  circulation  of  venous  blood  in  its  substance.  If  respiration  be 
not  resumed,  this  distention  continues,  the  contractions  become  less  frequent 
and  more  feeble,  and  in  a  few  minutes  they  cease. 

The  arrest  of  the  action  of  the  heart,  under  these  conditions,  is  chiefly 
mechanical.  The  unaerated  blood  passes  with  difficulty  through  the  capilla- 
ries of  the  system,  and  as  the  heart  is  constantly  at  work,  the  arteries  be- 
come largely  distended.  This  is  shown  by  the  great  increase  in  the  arterial 
pressure  while  these  vessels  are  full  of  black  blood.  If,  now,  the  heart  and 
great  vessels  be  closely  examined,  the  order  in  which  they  become  distended 
is  readily  observed.  These  phenomena  show  that  in  asphyxia  the  obstruction 
to  the  circulation  begins,  not  in  the  lungs,  as  is  commonly  supposed,  but  in 
the  capillaries  of  the  system,  and  is  propagated  backward  to  the  heart 
through  the  arteries  (Dalton).  The  distention  of  the  heart  in  asphyxia  is 
therefore  due  to  the  fact  that  unaerated  blood  can  not  circulate  freely  in  the 
systemic  capillaries.  When  thus  distended,  the  heart  becomes  paralyzed,  like 
any  muscle  after  a  severe  strain. 


52    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEAET. 

If  respiration  be  resumed  before  the  heart's  action  has  entirely  ceased, 
the  organ  in  a  few  moments  will  resume  its  contractions.  There  is  observed 
first  a  change  from  the  dusky  hue  it  had  assumed,  to  a  vivid  red,  which  is 
owing  to  the  circulation  of  arterial  blood  in  its  capillaries.  The  distention 
then  becomes  gradually  relieved,  and  for  a  few  moments,  the  pulsations 
are  abnormally  frequent.  The  arteries  will  then  be  found  to  contain  red 
blood.  An  instrument  applied  to  an  artery  will  show  a  diminution  in  ar- 
terial pressure  and  in  the  force  of  the  heart's  action,  if  the  arrest  of  respi- 
ration have  been  carried  only  far  enough  to  moderately  distend  the  heart ; 
or  there  is  an  increase  in  the  pressure  and  force  of  the  heart,  if  its  action 
have  been  nearly  arrested.  A  few  moments  of  regular  insufflation  will  cause 
the  pulsations  to  resume  their  normal  character  and  frequency. 

In  the  human  subject,  the  effects  of  temporary  or  permanent  arrest  of 
respiration  on  the  heart  are  undoubtedly  the  same  as  those  observed  in  ex- 
periments upon  the  warm-blooded  animals.  In  the  same  way,  also,  it  is  pos- 
sible to  restore  the  normal  action  of  the  organ,  if  respiration  be  not  too  long 
suspended,  by  the  regular  introduction  of  fresh  air  into  the  lungs.  Examples 
of  animation  restored  by  artificial  respiration,  in  drowning  etc.,  are  evidence 
of  this  fact.  In  cases  of  asphyxia,  those  measures  by  which  artificial  respira- 
tion is  most  effectually  maintained  have  been  found  most  efficient. 

CAUSE  OF  THE  EHYTHMICAL  CONTRACTIONS  OF  THE  HEART. 

The  question  of  the  actual  cause  of  the  rhythmical  contractions  of  the 
heart  is  one  of  great  importance  and  has  long  engaged  the  attention  of  physi- 
ologists. While  researches  have  resulted  in  much  positive  information  with 
regard  to  influences  which  regulate  or  modify  this  action,  there  seems  to  be 
little  known,  even  now,  concerning  the  main  question,  why  the  fibres  of  the 
heart,  unlike  the  ordinary  muscular  fibres,  seem  to  contract  spontaneously. 

The  heart  in  its  structure  resembles  the  voluntary  muscles  ;  but  it  has  a 
constant  office  to  perform  and  seems  to  act  without  any  palpable  excitation, 
while  the  latter  act  only  under  the  influence  of  a  natural  stimulus,  like  the 
nervous  impulse,  or  under  artificial  excitation.  The  movements  of  the  heart 
are  not  the  only  examples  of  what  seems  to  be  spontaneous  action.  The  cili- 
ated epithelium  is  in  motion  from  the  beginning  to  the  end  of  life,  and  will 
continue  for  a  certain  time,  even  after  the  cells  are  detached  from  the  organ- 
ism. This  motion  can  not  be  explained,  unless  it  be  called  an  explanation  to 
say  that  it  is  dependent  upon  vital  properties ;  but  if  the  actual  cause  of 
the  rhythmical  contraction  of  the  heart  be  unknown,  physiologists  are  ac- 
quainted with  certain  influences  which  render  its  action  regular,  powerful 
and  sufficient  for  the  purposes  of  the  economy. 

The  action  of  the  heart  is  involuntary.  Its  pulsations  can  be  neither 
arrested,  retarded  nor  accelerated  by  an  effort  of  the  will,  excepting,  of 
course,  examples  of  arrest  by  stoppage  of  respiration  or  acceleration  by 
violent  muscular  exercise  etc.  In  this  respect  the  heart  differs  from  cer- 
tain muscles,  like  the  muscles  of  respiration,  which  act  automatically,  but 
the  movements  of  which  may  be  temporarily  arrested  or  accelerated  by  a 


CAUSE  OF  THE  CONTRACTIONS  OF  THE  HEART.     53 

direct  voluntary  effort.  The  last-mentioned  fact  illustrates  the  difference  be- 
tween the  heart  and  all  other  striated  muscles.  All  of  them,  in  order  to  con- 
tract, must  receive  a  stimulus,  either  natural  or  artificial.  The  natural 
stimulus  comes  from  the  nerve-centres  and  is  conducted  by  the  nerves.  If 
the  nerves  going  to  any  of  the  respiratory  muscles,  for  example,  be  divided, 
the  muscle  is  paralyzed  and  will  not  contract  without  some  kind  of  stimula- 
tion. Connection  Avith  the  central  nervous  system  does  not  seem  necessary 
to  the  action  of  the  heart,  for  it  will  contract,  especially  in  the  cold-blooded 
animals,  some  time  after  its  removal  from  the  body.  If  the  supply  of  blood 
be  cut  off  from  the  substance  of  the  heart,  especially  in  the  warm-blooded 
animals,  the  organ  soon  loses  its  contractility. 

Erichsen,  after  exposing  the  heart  in  a  warm-blooded  animal  and  keeping 
up  artificial  respiration,  tied  the  coronary  arteries,  thus  cutting  off  the 
greatest  part  of  the  supply  of  blood  to  the  muscular  fibres.  He  found,  as 
the  mean  of  six  experiments,  that  the  heart  ceased  pulsating,  although 
artificial  respiration  was  continued,  in  twenty-three  and  a  half  minutes. 
After  the  pulsations  had  ceased,  they  could  be  restored  by  removing  the  liga- 
tures and  allowing  the  blood  to  circulate  again  in  the  substance  of  the  heart. 

The  regular  and  powerful  contractions  of  the  heart  are  promoted  by 
the  circulation  of  the  blood  through  its  cavities.  Although  the  heart, 
removed  from  the  body,  will  contract  for  a  time  without  a  stimulus,  it  can 
be  made  to  contract  during  the  intervals  of  repose  by  an  irritant,  such  as  the 
point  of  a  needle  or  a  feeble  electric  current.  For  a  certain  time  after  the 
heart  has  ceased  to  contract  spontaneously,  contractions  may  be  produced 
in  this  way.  This  can  easily  be  demonstrated  in  the  heart  of  any  animal, 
warm-blooded  or  cold-blooded.  This  excitability,  which  is  manifested,  under 
these  conditions,  in  the  same  way  as  in  ordinary  muscles,  is  different  in 
degree  in  different  parts  of  the  organ.  Haller  and  others  have  shown  that 
it  is  greater  in  the  cavities  than  on  the  surface  ;  for  long  after  stimulation 
applied  to  the  exterior  fails  to  excite  contraction,  the  organ  will  respond  to 
a  stimulus  applied  to  its  interior.  The  experiments  of  Haller  also  show  that 
fluids  in  the  cavities  of  the  heart  have  an  influence  in  exciting  and  keeping 
up  its  contractions.  This  observation  is  important,  as  showing  that  the 
presence  of  blood  is  necessary  to  the  natural  and  regular  action  of  the  heart. 
Schiff  succeeded  in  restoring  the  pulsations  in  the  heart  of  a  frog,  which 
had  ceased  after  it  had  been  emptied,  by  introducing  a  few  drops  of  blood 
into  the  auricle.  Experiments  upon  alligators  and  turtles  show  that 
when  the  heart  is  removed  from  the  body  and  emptied  of  blood,  the  pul- 
sations are  feeble,  rapid  and  irregular;  but  when  filled  with  blood,  the 
valves  being  destroyed  so  as  to  allow  free  passage  in  both  directions 
between  the  auricles  and  ventricle,  the  contractions  become  powerful 
and  regular.  In  these  experiments,  when  water  was  introduced  instead 
of  blood,  the  pulsations  were  more  frequent  and  not  so  powerful  as 
when  blood  was  used  (Flint,  1861).  These  experiments  show,  also, 
that  the  action  of  the  heart  may  be  affected  by  the  character,  particularly 
the  density,  of  the  fluid  which  passes  through  its  cavities,  which  may  ex- 


54:    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

plain  its  rapid  and  feeble  action  in  certain  cases  of  anaemia.  The  heart, 
therefore^  although  capable  of  independent  action,  is  excited  to  contraction 
by  the  blood  as  it  passes  through  its  cavities.  A  glance  at  the  succession  of 
its  movements,  particularly  in  cold-blooded  animals — in  which  they  are  so 
slow  that  the  phenomena  can  be  easily  observed — will  show  how  these  con- 
tractions are  produced.  There  is  first  a  distention  of  the  auricle,  and  this  is 
immediately  followed  by  a  contraction  filling  the  ventricle,  which  in  its 
turn  contracts.  Undoubtedly,  the  tension  of  the  fibres,  as  well  as  the  con- 
tact of  blood  in  its  interior,  acts  as  a  stimulus ;  and  as  all  the  fibres  of  each 
cavity  are  put  on  the  stretch  at  the  same  instant,  they  contract  simul- 
taneously. The  successive  and  regular  distention  of  each  cavity  thus  produces 
rhythmical  and  forcible  contractions ;  and  the  mere  fact  that  the  action  of 
the  heart  alternately  empties  and  dilates  its  cavities  insures  regular  pulsa- 
tions, so  long  as  blood  is  supplied  and  no  disturbing  influences  are  in 
operation. 

The  intermittent  contraction  and  successive  action  of  the  fibres  of  the 
heart,  when  the  organ  has  been  removed  from  the  body,  are  dependent,  to  a 
great  extent,  upon  sympathetic  ganglia  situated  near  its  base.  If  the 
ventricle  of  a  frog's  heart  be  divided  transversely  at  the  upper  third,  the 
lower  two-thirds  will  no  longer  contract  spontaneously,  while  the  auricles 
and  the  upper  third  of  the  ventricle  continue  to  pulsate.  If  a  stimulus  be 
then  applied  to  the  lower  two-thirds  of  the  ventricle,  this  is  usually  followed 
by  a  single  contraction,  and  not  by  a  series  of  more  or  less  regular  pulsations. 
It  has  been  observed,  also,  that  small,  detached  pieces  of  the  auricles  will 
pulsate  regularly  for  a  time. 

In  the  frog  there  are  three  ganglia  closely  connected  with  the  heart ;  one 
at  an  expansion  of  the  inferior  vena  cava  just  before  it  enters  the  auricle, 
called  the  venous  sinus  (Eemak),  another  between  the  left  auricle  and  the 
ventricle  (Bidder),  and  a  third  between  the  two  auricles  (Ludwig).  Accord- 
ing to  Robert  Meade  Smith,  the  first  two  ganglia  communicate  the  motor 
impulse  to  the  muscular  fibres  of  the  heart.  The  third  is  the  inhibitory 
ganglion,  and  this  regulates,  through  its  action  upon  the  motor  ganglia,  the 
transmission  of  motor  impulses.  "  As  regards  the  manner  in  which  these 
ganglia  produce  the  rhythmical  contraction  of  the  heart,  little  is  known ; 
but  that  they  are  the  prime  factors  in  producing  not  only  the  rhythm  of 
the  cardiac  revolutions,  with  its  various  modifications,  but  also  the  starting 
point  of  each  individual  contraction,  is  one  of  the  best  established  facts  in 
physiology." 

In  man  and  in  most  warm-blooded  animals,  collections  of  sympathetic 
ganglia  are  found  attached  to  the  nerves  at  the  line  of  junction  of  the 
auricles  with  the  ventricles. 

Nearly  all  of  the  experiments  just  referred  to  were  made  upon  the  hearts 
of  cold-blooded  animals,  particularly  the  frog;  but  in  all  animals,  under 
normal  conditions,  the  contractions  of  the  heart  seem  to  start  from  the 
auricles.  The  fact,  however,  that  the  ventricles  will  contract  regularly  in  a 
living  animal,  after  the  excitability  of  the  auricles  has  been  exhausted  by 


CAUSE  OF  THE  CONTRACTIONS  OF  THE  HEART. 


55 


MO 


repeated  stimulations  and  they  have  ceased  to  pulsate,  shows  that  the  so- 
called  pulsating  wave  coming  from  the  auricles  is  not  absolutely  essential  to 
the  contraction  of  the  ventricles. 

Finally,  in  view  especially  of  the  results  of  experiments  upon  the  cold- 
blooded animals,  it  may  be  stated  that  the  muscular  fibres  of  the  auricles 
and  of  the  upper  third  of  the  ventricles  have  the  property  of  intermittent 
and  regular  contraction,  which  is  dependent,  to  a  great  extent,  upon  the 
influence  of  the  so-called  motor  ganglia  of  the  heart ;  and  that  the  wave  of 
contraction  is  transmitted  to  the  lower  two-thirds  of  the  ventricles,  the  fibres 
of  which  do  not  seem  to  possess  the  property  of  independent  contraction. 
The  muscular  tissue  of  the  heart,  however,  may  be  thrown  into  contraction 
during  diastole  by  the  application  of  a  stimulus,  a  property  which  is  observed 
in  all  musular  fibres.  The  excitability  manifested  in  this  way  is  much  more 
marked  in  the  interior  than  on  the  exterior  of  the  organ.  Blood  in  contact 
with  the  lining  membrane  of  the  heart  acts  as  a  stimulus  in  a  remarkable 
degree  and  is  even  capable  of  restoring  excitability  after  it  has  become 
extinct.  The  passage  of  blood  through  the  heart  is  the  natural  stimulus  of 
the  organ  and  is  an  important  element  in  the 
production  of  regular  pulsations,  although  it  by 
no  means  endows  the  fibres  with  their  contractile 
properties. 

Accelerator  Nerves. — Experiments  on  the  in- 
fluence of  the  sympathetic  nerves  upon  the  heart 
have  not  been  entirely  satisfactory.  It  has  been 
observed  that  the  action  of  the  heart  is  immedi- 
ately arrested  by  destroying  the  cardiac  plexus; 
but  with  regard  to  this,  the  difficulty  of  making 
the  operation  and  the  disturbance  of  the  heart 
consequent  upon  the  necessary  manipulations 
must  be  taken  into  account.  It  has  been  shown, 
however,  that  stimulation  of  the  sympathetic  in 
the  neck  has  the  effect  of  accelerating  the  car- 
diac movements. 

According  to  Strieker,  there  exists  in  the  me- 
dulla oblongata  a  centre,  stimulation  of  which  in- 
creases the  rapidity  of  the  heart's  action;  and 
from  this  centre,  fibres  descend  in  the  substance  of 
the  spinal  cord,  pass  out  with  the  communicating 
branches  of  the  lower  cervical  and  upper  dorsal 
nerves  to  the  sympathetic,  and  go  to  the  cardiac 
plexus.  In  the  cat,  the  accelerator  fibres  pass 
through  the  first  thoracic  sympathetic  ganglion. 
Taking  all  precautions  to  eliminate  the  influence 
of  variations  in  the  blood  pressure,  it  has  been  shown  that  after  division  of 
the  pneumogastric,  stimulation  of  the  accelerator  fibres  increases  the  number 
of  beats  of  the  heart.  This  action  is  direct  and  not  reflex. 


TAG. 


FIG.  22. — Scheme  of  the  course  of 
the  accelerans  fibres  (Stirling). 

p,  pons ;  MO,  medulla  oblonga- 
ta ;  v,  inhibitory  centre  for 
the  heart ;  A,  accelerans  cen- 
tre ;  VAG.,  vagus :  SL,  supe- 
rior, IL,  inferior  laryngeal ; 
sc,  superior  cardiac  ;  H, 
heart ;  c,  cerebral  impulse  ; 
s.  cervical  sympathetic;  a,  a, 
accelerans  fibres. 


56    CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

Direct  Inhibition  of  the  Heart. — Division  of  the  pneumogastric  nerves 
in  the  neck  increases  the  frequency  and  diminishes  the  force  of  the  contrac- 
tions of  the  heart.  To  anticipate  a  little  of  the  history  of  the  pneumogastric 
nerves,  it  may  be  stated  that  while  they  are  exclusively  sensory  at  their  origin, 
they  receive,  after  having  emerged  from  the  cranial  cavity,  a  number  of  fila- 
ments from  various  motor  nerves.  That  they  influence  certain  muscles,  is 
shown  by  the  paralysis  of  these  muscles  after  division  of  the  nerves  in  the 
neck,  as,  for  example,  the  arrest  of  the  movements  of  the  glottis. 

A  moderate  Faradic  current  passed  through  both  pneumogastrics  arrests 
the  action  of  the  heart  in  diastole  (Ed.  Weber).  This  observation  has  been 
made  upon  living  animals,  both  with  and  without  exposure  of  the  heart ; 
and  this  kind  of  action  is  known  as  inhibitory,  or  restraining.  Its  nervous 
mechanism  is  direct  and  not  reflex ;  and  the  inhibitory  influence  is  conveyed 
to  the  heart  through  filaments  in  the  pneumogastric  which  are  derived  from 
the  spinal  accessory. 

It  is  said  that  direct  stimulation  of  the  medulla  oblongata  will  have  the 
same  effect  upon  the  heart  as  stimulation  of  the  pneumogastrics ;  but  it  must 
be  very  difficult  to  limit  the  stimulation  to  a  particular  point  in  the  medulla 
and  to  avoid  conditions  which  would  complicate  such  an  experiment.  A 
sufficiently  powerful  stimulus  applied  to  one  pneumogastric  will  arrest  the 
cardiac  pulsation^,  and  in  some  animals  the  inhibitory  action  is  confined  to 
the  nerve  of  the  right  side.  It  is  not  known  that  any  such  difference  between 
the  two  nerves  exists  in  the  human  subject,  and  certainly  there  is  no  marked 
difference  in  most  of  the  mammalia. 

If  both  pneumogastrics  be  Faradized  for  two  or  three  minutes,  the  con- 
tractions of  the  heart  return,  even  though  the  stimulation  be  continued,  pro- 
vided the  current  be  not  too  powerful  but  of  sufficient  strength  to  promptly 
arrest  the  pulsations.  It  is  probable  that  this  is  due  to  the  fact  that  the 
excitability  of  the  nerve  after  a  time  becomes  exhausted  by  the  prolonged 
excitation,  and  its  inhibitory  influence  is  for  the  time  destroyed. 

Stimulation  of  the  pneumogastrics  in  any  part  of  their  course  is  followed 
by  the  usual  inhibitory  phenomena,  and  the  same  results  sometimes  follow 
stimulation  of  the  thoracic  cardiac  branches.  It  has  also  been  observed  that 
when  the  heart's  action  has  been  arrested  and  the  organ  is  quiescent  in  dias- 
tole, direct  mechanical  stimulation  of  the  heart  is  followed  by  a  single  con- 
traction, showing  that  the  excitability  of  the  fibres  has  not  been  entirely 
suspended. 

After  section  of  both  pneumogastrics  in  the  neck,  digitalis  fails  to  diminish 
the  number  of  beats  of  the  heart  (Traube) ;  showing  that  separation  of  the 
heart  from  its  connections  with  the  cerebro-spinal  nerves  removes  the  organ 
from  the  characteristic  and  peculiar  effects  of  the  poison. 

Feeble  stimulation  of  one  or  both  pneumogastrics,  when  it  produces  any 
effect,  almost  always  slows  the  action  of  the  heart.  In  some  animals,  how- 
ever, the  pneumogastrics  contain  a  few  accelerator  fibres,  and  feeble  excita- 
tion sometimes  is  followed  by  a  slight  increase  in  the  rapidity  of  the  cardiac 
pulsations,  but  this  is  unusual. 


INHIBITION  OF  THE  HEART.  57 

Reflex  Inhibition  of  the  Heart. — Like  most  of  the  direct  operations  of 
nerves  that  can  be  imitated  by  electric  stimulation,  the  inhibitory  action  of 
the  pneumogastrics  can  be  produced  by  reflex  action.  The  action  of  the  heart 
may  be  arrested  in  the  frog  by  sharply  tapping  the  exposed  intestines  (Goltz). 
The  same  effect  has  been  produced  by  stimulation  of  the  splanchnic  nerves  or 
the  cervical  sympathetic.  In  some  animals,  if  one  pneumogastric  be  divided 
in  the  neck,  the  other  being  left  intact,  stimulation  of  the  central  end  of  the 
divided  nerve  will  produce  inhibition  of  the  heart,  by  an  action  induced  in 
the  undivided  nerve.  In  all  of  these  instances,  the  inhibition  is  reflex. 
The  stimulation  is  carried  by  the  afferent  fibres  of  the  nerves  stimulated,  to 
the  inhibitory  centre  in  the  medulla  oblongata,  and  is  reflected  to  the  heart 
through  the  efferent  fibres  of  the  pneumogastric. 

While  moderate  stimulation  of  ordinary  sensory  nerves  is  sometimes  fol- 
lowed by  inhibition  of  the  heart,  very  powerful  stimulation  arrests  the  cardio- 
inhibitory  action  of  the  pneumogastrics,  as  well  as  certain  other  reflexes. 

The  inhibitory  fibres  of  the  pneumogastrics  undoubtedly  have  an  impor- 
tant office  in  connection  with  the  regulation  of  the  rapidity  and  force  of  the 
cardiac  pulsations.  It  is  important,  of  course,  that  the  heart  should  act  at 
all  times  with  nearly  the  same  force  and  frequency.  It  has  been  seen  that 
the  inherent  properties  of  its  fibres  and  the  action,  probably,  of  the  cardiac 
ganglia  are  competent  to  make  it  contract,  and  the  necessary  intermittent 
dilatation  of  its  cavities  makes  these  contractions  assume  a  certain  regularity ; 
but  the  quantity  and  density  of  the  blood  are  subject  to  very  considerable 
variations  within  the  limits  of  health,  which,  without  some  regulating  influ- 
ence, would  undoubtedly  cause  variations  in  the  heart's  action,  so  considerable 
as  to  be  injurious.  This  is  shown  by  the  palpitating  and  irregular  action  of 
the  heart  when  the  pneumogastrics  have  been  divided.  These  nerves  convey 
to  the  heart  a  constant  influence,  which  may  be  compared  to  the  insensible 
tonicity  imparted  to  voluntary  muscles  by  the  general  motor  system.  When 
a  set  of  muscles  on  one  side  is  paralyzed,  as  in  facial  palsy,  their  tonicity  is 
lost,  they  become  flaccid,  and  the  muscles  on  the  other  side,  without  any  effort 
of  the  will,  distort  the  features.  An  exaggeration  of  this  force  may  be  imitated 
by  a  feeble  Faradic  current,  which  renders  the  pulsations  of  the  heart  less 
frequent  and  more  powerful,  or  it  may  be  still  farther  exaggerated  by  a 
more  powerful  current,  which  arrests  the  action  of  the  heart.  Phemonena 
are  not  wanting  in  the  human  subject  to  verify  these  views.  Causes  which 
operate  through  the  nervous  system  frequently  produce  palpitation  and 
irregular  action  of  the  heart.  Cases  are  not  uncommon  in  which  palpitation 
habitually  occurs  after  a  full  meal.  There  are  instances  on  record  of  death 
from  arrest  of  the  heart's  action  as  a  consequence  of  fright,  anger,  grief  or. 
other  severe  mental  emotions.  Syncope  from  these  causes  is  by  no  means 
uncommon.  In  the  latter  instance,  when  the  heart  resumes  its  contractions, 
the  nervous  shock  carried  along  the  pneumogastrics  is  only  sufficient  to  arrest 
its  action  temporarily.  When  death  takes  place,  the  shock  is  so  great  that 
the  heart  never  recovers  from  its  effects. 


58     CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 


SUMMARY  OF  CERTAIN  CAUSES  OF  ARREST  OF  THE  ACTIOX  OF  THE 

HEART. 

In  warm-blooded  animals,  the  heart's  action  speedily  ceases  after  the  organ 
is  deprived  of  its  natural  stimulus,  the  blood.  Proof  of  this  is  not  derived  alone 
from  experiments  on  the  inferior  animals.  It  is  well  known  that  in  profuse 
haemorrhage  in  the  human  subject,  the  contractions  of  the  heart  are  progress- 
ively enfeebled,  and  when  the  loss  of  blood  has  proceeded  to  a  certain  extent, 
are  permanently  arrested.  Cases  of  transfusion  after  haemorrhage  show  that 
when  blood  is  introduced  the  heart  may  be  made  to  resume  its  pulsations. 
The  same  result  takes  place  in  death  by  asthenia ;  and  cases  are  on  record 
in  which  life  has  been  prolonged,  as  in  haemorrhage,  by  transfusion  of  even 
a  small  quantity  of  healthy  blood.  These  facts  have  been  demonstrated  on 
the  inferior  animals  by  experiments  already  cited.  The  experiment  of 
Haller,  in  which  the  action  of  the  right  side  of  the  heart  of  a  cat  was 
arrested  by  emptying  it  of  blood,  while  the  left  side,  which  was  filled  with 
blood,  continued  to  pulsate,  showed  that  the  absence  of  blood  is  competent 
of  itself  to  arrest  contractions  of  the  heart.  The  experiments  of  Erichsen, 
who  paralyzed  the  heart  by  tying  the  coronary  arteries,  and  of  Schiff,  who 
produced  a  local  paralysis  by  tying  the  vessel  going  to  the  right  ventricle, 
show  that  the  action  of  the  heart  may  also  be  arrested  by  cutting  off  the 
circulation  of  blood  in  its  substance.  Both  of  these  causes  must  operate  in 
arrest  of  the  heart's  action  in  haemorrhage. 

The  mechanical  causes  of  arrest  of  the  heart's  action  are  of  considerable 
pathological  importance.  The  heart,  in  common  with  other  muscles,  may 
be  paralyzed  by  mechanical  injury.  A  violent  blow  upon  the  deltoid 
paralyzes  the  arm ;  a  severe  strain  will  paralyze  the  muscles  of  an  extremity ; 
and  in  the  same  way,  excessive  distention  of  the  cavities  of  the  heart  will 
arrest  its  pulsations.  This  is  shown  by  arrest  of  the  circulation  in  asphyxia ; 
which  is  due  to  the  fact  that  the  heart  is  incapable  of  forcing  the  unaerated 
blood  through  the  systemic  capillaries.  The  heart,  in  asphyxia,  finally  be- 
comes enormously  strained  and  distended  and  is  consequently  paralyzed. 
The  same  result  follows  the  application  of  a  ligature  to  the  aorta.  This 
effect  may  be  produced  also,  in  the  cold-blooded  animals,  in  which,  if  the 
heart  be  left  undisturbed,  the  pulsations  will  continue  for  a  long  time.  The 
following  experiment  illustrating  this  point  was  performed  upon  the  heart  of 
a  large  alligator  : 

The  animal  was  poisoned  with  curare,  and  twenty-eight  hours  after  death 
the  heart,  which  had  been  exposed  and  left  in  situ,  was  pulsating  regularly. 
It  was  then  removed  from  the  body,  and  after  some  experiments  on  the  com- 
parative force,  etc.,  of  the  pulsations  when  empty  and  when  filled  with  blood, 
was  filled  with  water,  the  valves  having  been  destroyed  so  as  to  allow  free 
passage  of  the  fluid  through  the  cavities,  and  the  vessels  were  tied.  The 
ventricles,  still  filled  with  water  confined  in  their  cavity,  were  then  firmly 
compressed  with  the  hand.  From  that  time,  the  heart  entirely  ceased  its 
contractions  and  became  hard  like  a  muscle  in  a  state  of  cadaveric  rigidity. 


ARREST  OF  THE  HEART'S  ACTION.  59 

This  experiment  shows  how  completely  and  promptly  the  heart,  even  of  a 
cold-blooded  animal,  may  be  arrested  in  its  action  by  mechanical  injury 
(Flint,  1861). 

Cases  of  death  from  engorgement  of  the  heart  are  not  unusual  in  prac- 
tice ;  and  the  form  of  organic  disease  which  most  frequently  leads  to  sudden 
death  is  that  in  which  the  heart  is  liable  to  great  distentlon.  In  other  lesions 
there  is  not  this  tendency ;  but  when  the  aortic  orifice  is  contracted  or  the 
valves  are  insufficient,  any  great  disturbance  of  the  circulation  will  cause  the 
heart  to  become  engorged,  Avhich  is  liable  to  produce  a  fatal  result. 

Most  persons  are  practically  familiar  with  the  distressing  sense  of  suffoca- 
tion which  frequently  follows  a  blow  upon  the  epigastrium ;  and  a  few  cases 
are  on  record  of  instantaneous  death  following  a  comparatively  slight  concus- 
sion in  this  region.  Although  these  cases  are  rare,  they  are  well  recognized, 
and  the  effects  are  generally  attributed  to  injury  of  the  solar  plexus.  The 
distress  is  precisely  what  would  occur  from  sudden  arrest  of  the  heart's  ac- 
tion. It  is  the  blood  charged  with  oxygen  which  supplies  the  wants  of  the 
tissues,  and  not  the  simple  entrance  of  air  into  the  lungs ;  and  arrest  of  the 
circulation  of  arterial  blood,  from  any  cause,  produces  suffocation  as  com- 
pletely as  though  the  trachea  were  tied.  It  is  a  question  whether  the  ar- 
rest of  the  heart,  if  this  be  the  pathological  condition,  be  due  to  concussion 
of  the  nervous  centre  or  to  the  direct  effects  of  the  blow  upon  the  organ  it- 
self. Present  data  do  not  afford  a  definite  answer  to  this  question,  but  they 
sustain,  to  a  certain  extent,  the  opinion  that  in  such  accidents,  the  symptoms 
are  due  to  direct  injury  of  the  heart.  An  additional  argument  in  favor  of 
this  view  is  founded  on  what  is  known  of  the  mode  of  operation  of  the  sym- 
pathetic system.  The  effects  of  stimulation  or  irritation  of  this  system  are 
not  instantaneously  manifested,  as  is  the  case  in  the  cerebro-spinal  system,  but 
are  developed  slowly  and  gradually. 

As  far  as  the  results  of  experiments  are  concerned,  the  nervous  influences 
which  arrest  the  action  of  the  heart  seem  to  operate  through  the  pneumogas- 
trics  and  are  derived  from  the  spinal  accessory  nerves.  This  action  can  be 
closely  imitated  by  electricity.  The  causes  of  arrest  in  this  way  are  many  and 
varied.  Among  them  may  be  mentioned,  sudden  and  severe  bodily  pain  and 
severe  mental  emotions.  With  the  exception  of  arrest  of  the  heart's  action 
from  loss  of  blood  and  from  distention,  from  whatever  cause  it  may  occur, 
stoppage  of  the  heart  takes  place  from  influences  operating  through  the 
nervous  system.  It  may  be  temporary,  as  in  syncope,  or  it  may  be  permanent ; 
and  examples  of  the  latter,  though  rare,  are  sufficiently  well  authenticated. 

In  an  animal  just  killed,  as  the  pulsations  of  the  heart  become  slower  and 
slower  until  they  are  finally  arrested,  it  is  constantly  observed  that  the  auric- 
ular appendage  on  the  right  side  continues  to  contract  for  some  time  after 
the  other  portions  of  the  heart  have  ceased  their  action. 


60  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

CHAPTER  III. 

CIRCULATION  OF  TEE  BLOOD  IN  THE  VESSELS. 

Physiological  anatomy  of  the  arteries— Course  of  blood  in  the  arteries— Locomotion  of  the  arteries  and 
production  of  the  pulse— Pressure  of  blood  in  the  arteries— Pressure  in  different  parts  of  the  arterial  sys- 
tem—Depressor nerve— Influence  of  respiration  on  the  arterial  pressure— Rapidity  of  the  current  of  blood 
in  the  arteries— Rapidity  in  different  parts  of  the  arterial  system— Circulation  of  the  blood  in  the  capil- 
laries—Physiological anatomy  of  the  capillaries— Pressure  of  blood  in  the  capillaries— Relations  of  the 
capillary  circulation  to  respiration— Causes  of  the  capillary  circulation — Influence  of  temperature  on  the 
capillary  circulation — Influence  of  direct  irritation  on  the  capillary  circulation — Circulation  of  the  blood 
in  the  veins — Physiological  anatomy  of  the  veins — Course  of  the  blood  in  the  veins — Pressure  of  blood  in 
the  veins — Rapidity  of  the  venous  circulation — Causes  of  the  venous  circulation — Air  in  the  veins — Uses 
of  the  valves— Conditions  which  impede  the  venous  circulation— Regurgitant  venous  pulse— Circulation 
in  the  cranial  cavity — Circulation  in  erectile  tissues — Derivative  circulation— Pulmonary  circulation — Cir- 
culation in  the  walls  of  the  heart — Passage  of  the  blood-corpuscles  through  the  walls  of  the  vessels  (dia- 
pedesis) — Rapidity  of  the  circulation— Phenomena  in  the  circulatory  system  after  death. 

IN"  man  and  in  all  animals  possessed  of  a  double  heart,  each  cardiac  con- 
traction forces  a  charge  of  blood  from  the  right  ventricle  into  the  pulmo- 
nary artery,  and  from  the  left  ventricle  into  the  aorta ;  and  the  valves  which 
guard  the  orifices  of  these  vessels  effectually  prevent  regurgitation  during  the 
intervals  of  contraction.  There  is,  therefore,  but  one  direction  in  which  the 
blood  can  flow  in  obedience  to  this  intermittent  force ;  and  the  fact  that  even 
in  the  smallest  arteries,  there  is  an  acceleration  in  the  current  coincident  with 
each  contraction  of  the  heart,  which  disappears  when  the  action  of  the  heart 
is  arrested,  shows  that  the  ventricular  systole  is  the  cause  of  the  arterial  cir- 
culation. The  arteries  have  the  important  office  of  supplying  nutritive  mat- 
ters to  all  the  tissues  and  furnishing  to  the  glands  materials  out  of  which  the 
secretions  are  formed,  and,  in  short,  are  the  vessels  of  supply  to  every  part  of 
the  organism.  The  supply  of  blood  regulates,  to  a  considerable  extent,  the 
processes  of  nutrition  and  has  an  important  bearing  on  the  general  and  spe- 
cial functions;  and  the  various  physiological  processes  necessarily  demand 
considerable  modifications  in  the  quantity  of  arterial  blood  which  is  furnished 
to  parts  at  different  times.  The  force  of  the  heart,  however,  varies  but  little 
within  the  limits  of  health ;  and  the  conditions  necessary  to  the  proper  distri- 
bution of  blood  in  the  economy  are  regulated  almost  exclusively  by  the  arte- 
rial system.  These  vessels  are  endowed  with  elasticity,  by  which  the  circula- 
tion is  considerably  facilitated,  and  with  contractility,  by  which  the  supply  to 
any  part  may  be  modified,  independently  of  the  action  of  the  heart.  Sudden 
flushes  or  pallor  of  the  countenance  are  examples  of  the  facility  with  which 
this  may  be  effected.  It  is  evident,  therefore,  that  the  properties  of  the  coats 
of  the  arteries  are  of  great  physiological  importance. 

PHYSIOLOGICAL  ANATOMY  OF  THE  ARTERIES. 

The  vessels  which  carry  the  venous  blood  to  the  lungs  are  branches  of  a 
great  trunk  which  takes  its  origin  from  the  right  ventricle.  They  do  not 
differ  in  structure  from  the  vessels  which  carry  the  blood  to  the  general  sys- 
tem, except  in  the  fact  that  their  coats  are  somewhat  thinner  and  more  dis- 
tensible. The  aorta,  branches  and  ramifications  of  which  supply  all  parts  of 


PHYSIOLOGICAL  ANATOMY  OF  THE  ARTERIES.  61 

the  body,  is  given  off  from  the  left  ventricle.  Just  at  its  origin,  behind  the 
semilunar  valves,  the  aorta  has  three  sacculated  pouches,  called  the  sinuses  of 
Valsalva.  Beyond  this  point  the  vessels  are  cylindrical.  The  arteries  then 
branch,  divide  and  subdivide,  until  they  are  reduced  to  microscopic  size. 
The  branches,  with  the  exception  of  the  intercostal  arteries,  which  make 
nearly  a  right  angle  with  the  thoracic  aorta,  are  given  off  at  an  acute  angle. 
As  a  rule,  the  arteries  are  nearly  straight,  taking  the  shortest  course  to  the 
parts  which  they  supply  with  blood ;  and  while  the  branches  progressively 
diminish  in  size,  but  few  are  given  off  between  the  great  trunk  and  small  ves- 
sels which  empty  into  the  capillary  system.  So  long  as  a  vessel  gives  off  no 
branches,  its  caliber  does  not  progressively  diminish ;  as  the  common  carotids, 
which  are  as  large  at  their  bifurcation  as  they  are  at  their  origin.  There  are 
one  or  two  instances  in  which  vessels,  although  giving  off  many  branches  in 
their  course,  do  not  diminish  in  size  for  some  distance ;  as  the  aorta,  which  is 
as  large  at  the  point  of  division  into  the  iliacs  as  it  is  in  the  chest,  and  the 
vertebral  arteries,  which  do  not  diminish  in  caliber  until  they  enter  the  fora- 
men magnum.  It  has  long  been  remarked  that  the  combined  caliber  of  the 
branches  of  an  arterial  trunk  is  greater  than  that  of  the  main  vessel ;  so  that 
the  arterial  system,  as  it  branches,  increases  in  capacity.  A  single  exception 
to  this  rule  is  in  the  instance  of  the  common  iliacs,  the  combined  caliber  of 
which  is  less  than  the  caliber  of  the  abdominal  aorta. 

The  arrangement  of  the  arteries  is  such  that  the  requisite  supply  of  blood 
is  sent  to  all  parts  of  the  economy  by  the  shortest  course  and  with  the  least 
possible  expenditure  of  force  by  the  heart.  Generally  the  vessels  are  so  situ- 
ated as  not  to  be  exposed  to  pressure  and  consequent  interruption  of  the 
current  of  blood ;  but  in  certain  situations,  as  about  some  of  the  joints,  there 
is  necessarily  some  liability  to  occasional  compression.  In  certain  situations, 
also,  as  in  the  vessels  going  to  the  brain,  particularly  in  some  of  the  inferior 
animals,  it  is  necessary  to  moderate  the  force  of  the  blood-current,  on  account 
of  the  delicate  structure  of  the  organs  in  which  they  are  distributed.  Here 
there  is  a  provision  in  the  shape  of  anastomoses,  by  which,  on  the  one  hand, 
compression  of  a  vessel  simply  diverts,  and  does  not  arrest  the  current  of 
blood,  and  on  the  other  hand,  the  current  is  rendered  more  equable  and  the 
force  of  the  heart  is  moderated. 

The  arteries  are  provided  with  fibrous  sheaths,  of  greater  or  less  strength, 
as  the  vessels  are  situated  in  parts  more  or  less  exposed  to  disturbing  influ- 
ences or  accidents. 

The  arteries  have  three  well  defined  coats.  As  these  vary  very  consider- 
ably in  arteries  of  different  sizes,  it  will  be  convenient,  in  their  description, 
to  divide  the  vessels  into  three  classes : 

1.  The  largest  arteries;  in  which  are  included  all  that  are  larger  than  the 
carotids  and  common  iliacs. 

2.  The  arteries  of  medium  size ;  that  is,  between  the  carotids  and  iliacs 
and  the  smallest. 

3.  The  smallest  arteries ;  or  those  less  than  -^  to  -^  of  an  inch  (1-7  to 
2-1  mm.)  in  diameter. 

6 


62  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

The  largest  arteries  are  very  strong  and  elastic.  Their  external  coat  is 
composed  of  ordinary  fibrous  tissue,  with  a  few  longitudinal  and  oblique 
fasciculi  of  non-striated  muscular  fibres.  This  coat  is  no  thicker  in  the 
largest  vessels  than  in  some  of  the  vessels  of  medium  size ;  and  in  some 
medium-sized  vessels  it  is  actually  thicker  than  in  the  aorta.  This  is  the 
only  coat  that  is  vascular. 

The  middle  coat,  on  which  the  thickness  of  the  walls  of  the  vessel  de- 
pends, is  composed  chiefly  of  yellow  elastic  tissue.  This  tissue  i3  disposed  in 
a  number  of  layers.  Externally  there  is  a  thin  layer  of  ramifying  elastic 
fibres,  and  then  a  number  of  layers  of  elastic  membrane,  with  oval,  longitudi- 
nal openings,  an  arrangement  which  has  given  it  the  name  of  the  "  f  enes- 
trated  membrane."  Between  the  different  layers  of  this  membrane  are  found 
a  few  non-striated  muscular  fibres.  These  muscular  fibres,  however,  are  not 
abundant  and  have  but  little  physiological  importance.  A  small  portion  of 
the  aorta  and  pulmonary  artery  near  the  heart  is  entirely  free  from  mus- 
cular fibres.  In  the  largest  arteries  the  fibres  are  arranged  in  fasciculi,  with 
amorphous  and  fibrous  connective  tissue  running  in  circular,  longitudinal 
and  oblique  directions.  The  longitudinal  and  oblique  fibres  exist  chiefly  in 
the  outer  coat. 

The  internal  coat  of  the  largest  arteries  does  not  differ  materially  from 
the  lining  membrane  of  the  rest  of  the  arterial  system.  It  is  nearly  identical 
in  structure  with  the  endocardium  and  is  continued  throughout  the  vascular 
system.  It  is  a  thin,  homogeneous,  elastic  membrane,  covered  with  a  layer 
of  elongated  cells  of  endothelium,  with  oval  nuclei,  the  long  diameter  of  the 
cells  and  nuclei  following  the  direction  of  the  vessel.  Between  the  endo- 
thelial  cells,  is  an  amorphous  cement-substance,  which  is  rendered  dark  by  a 
solution  of  silver  nitrate,  so  that  this  reagent  clearly  defines  their  borders. 

The  arteries  of  medium  size  possess  considerable  strength,  some  elasticity 
and  very  great  contractility.  In  the  outer  and  inner  coats  there  is  no  great 
difference  between  these  and  the  largest  arteries,  even  in  thickness.  The 
essential  difference  in  the  anatomy  of  these  vessels  is  found  in  the  middle 
coat.  Here  there  is  a  continuation  of  the  elastic  elements  found  in  the 
largest  vessels,  but  relatively  diminished  in  thickness  and  mingled  with  the 
fusiform,  non-striated  muscular  fibres  arranged  nearly  always  at  right  angles 
to  the  course  of  the  vessel.  These  fibres  are  found  chiefly  in  the  inner  layers 
of  the  middle  coat  and  only  in  arteries  smaller  than  the  carotids  and  primi- 
tive iliacs.  In  arteries  of  medium  size,  like  the  femoral,  prof unda  femoris, 
radial  or  ulnar,  the  muscular  fibres  exist  in  several  layers.  There  is  no  dis- 
tinct division,  as  regards  the  middle  coat,  between  the  largest  arteries  and 
those  of  medium  size.  As  the  arteries  branch,  muscular  fibres  make  their 
appearance  between  the  elastic  layers,  progressively  increasing  in  quantity, 
while  the  elastic  elements  are  diminished  in  their  relative  proportion. 

In  the  smallest  arteries,  the  external  coat  is  thin  and  disappears  just  be- 
fore the  vessels  empty  into  the  capillary  system ;  so  that  the  very  smallest 
arterioles  have  only  the  inner  coat  and  a  layer  of  muscular  fibres.  Although 
most  of  the  muscular  fibres  in  the  middle  coat  of  the  arteries  are  arranged 


PHYSIOLOGICAL  ANATOMY  OF  THE  ARTEEIES. 


63 


at  right  angles  to  the  course  of  the  vessels,  nearly  all  of  the  arteries  in  the 
human  subject  are  provided  with  longitudinal  and  oblique  muscular  fasciculi, 


FIG.  23.— Small  artery  from  the  mesentery  of  the  frog,  showing  endothelium  and  circular  muscular 
fibres ;  magnified  500  diameters  (from  a  photograph  taken  at  the  United  States  Army  Medical 
Museum). 

which  are  sometimes  external,  sometimes  internal  and  sometimes  on  both 
sides  of  the  circular  layers. 

The  middle  coat  is  composed  of  circular  muscular  fibres,  without  any  ad- 
mixture of  elastic  elements.  In  vessels  ^fa  of  an  inch  (254  p.)  in  diameter, 
there  are  two  or  three  layers  of  fibres ;  but  nearer  the  capillaries  and  as  the 
vessels  lose  the  external  fibrous  coat,  these  fibres  exist  in  a  single  layer. 

The  internal  coat  presents  no  essential  difference  from  the  coat  in  other 
vessels,  with  the  exception  that  the  endothelium  is  rather  less  distinctly 
marked. 

A  tolerably  rich  plexus  of  vessels  is  found  in  the  external  coat  of 
the  arteries.  These  are  called  vasa  vasorum  and  come  from  the  adjacent 
arterioles,  generally  having  no  direct  connection  with  the  vessel  on  which 
they  are  distributed.  A  few  vessels  penetrate  the  external  layers  of  the  mid- 
dle coat,  but  none  are  ever  found  in  the  internal  coat. 

Xervous  filaments  accompany  the  arteries,  in  all  probability,  to  their  re- 
motest ramifications.  These  are  not  distributed  in  the  walls  of  the  large 
vessels,  but  follow  them  in  their  course,  their  filaments  of  distribution  being 


64  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

found  in  those  vessels  in  which  the  muscular  element  of  the  middle  coat  pre- 
dominates. The  vaso-motor  nerves,  as  they  are  called,  play  an  important 
part  in  regulating  the  processes  of  nutrition. 

Course  of  the  Blood  in  the  Arteries. — With  every  pulsation  of  the  heart, 
all  the  blood  contained  in  the  ventricles,  excepting  perhaps  a  few  drops,  is 
forced  into  the  great  vessels.  The  valvular  arrangement  by  which  the  blood, 
once  forced  into  these  vessels,  is  prevented  from  returning  into  the  ventricles 
during  their  diastole,  has  already  been  described.  The  foregoing  sketch  of  the 
anatomy  of  the  arteries  indicates  a  complexity  of  phenomena  in  the  circula- 
tion in  these  vessels,  which  would  not  obtain  if  they  were  simple,  inelastic 
tubes.  In  this  case,  the  intermittent  force  of  the  heart  would  be  felt  equally 
in  all  the  vessels,  and  the  arterial  circulation  would  be  subject  to  no  modifi- 
cations which  did  not  come  from  the  action  of  the  central  organ.  As  it  is, 
the  blood  is  received  from  the  heart  into  vessels  endowed,  not  only  with  great 
elasticity,  but  with  contractility.  The  elasticity,  which  is  the  prominent 
property  of  the  largest  arteries,  moderates  the  intermittency  of  the  heart's 
.action,  providing  a  continuous  supply  to  the  parts ;  while  the  contractility  of 
the  smallest  arteries  is  capable  of  increasing  or  diminishing  the  supply  in  any 
part,  as  may  be  required  in  the  various  functions. 

Elasticity  of  the  Arteries. — This  property  is  particularly  marked  in  the 
largest  vessels.  If  the  aorta  be  forcibly  distended  with  water,  it  may  be  di- 
lated to  more  than  double  its  ordinary  capacity  and  will  resume  its  original 
.  size  and  form  as  soon  as  the  pressure  is  removed,  its  elasticity  being  absolutely 
perfect.  This  simple  experiment  shows  that  if  the  force  of  the  heart  be 
sufficient  to  distend  the  great  vessels,  their  elasticity  during  the  intervals  of 
its  action  must  be  continually  forcing  the  blood  toward  the  periphery.  The 
fact  that  the  arteries  are  distended  at  each  systole  has  been  shown  by  direct 
experiments ;  although  the  immense  capacity  of  the  arterial  system,  as  com- 
pared with  the  small  charge  of  blood  which  enters  at  each  pulsation,  renders 
the  actual  -distention  of  the  vessels  less  than  would  be  expected  from  the  force 
of  the  heart's  contraction. 

Division  of  an  artery  in  a  living  animal  illustrates  one  of  the  important 
phenomena  due  to  the  elastic  and  yielding  character  of  its  walls.  It  is  ob- 
served, even  dn  vessels  of  considerable  size,  as  the  carotid  or  femoral,  that  the 
flow  of  blood  is  not  intermittent  but  remittent.  With  each  ventricular  sys- 
tole there  is  a  sudden  and  marked  impulse ;  but  during  the  intervals  of  con- 
traction, the  blood  continues  to  flow  with  considerable  force.  In  the  smaller 
vessels,  the  impulse  becomes  less  and  less  marked ;  but  it  is  not  entirely  lost, 
even  in  the  smallest  vessels,  the  flow  becoming  constant  only  in  the  capillary 
system.  That  the  force  of  the  heart  is  absolutely  intermittent,  is  shown  by 
the  following  experiment :  If  the  heart  be  exposed  in  a  living  animal,  and  a 
canula  be  introduced  through  the  walls  into  one  of  the  ventricles,  there  is  a 
powerful  jet  at  each  systole,  but  no  blood  is  discharged  during  the  diastole. 
The  same  absolute  intermittency  of  the  current  is  observed  in  the  aorta  near 
the  heart.  The  conversion  of  the  intermittent  current  in  the  largest  vessels 
into  a  nearly  constant  flow  in  the  smallest  arterioles  is  effected  by  the  physical 


CIRCULATION  IN  THE  ARTERIES.  65 

property  of  elasticity ;  and  the  intermittent  impulse  may  be  said  to  be  pro- 
gressively absorbed  by  the  elastic  walls  of  the  vessels.  This  modification  of 
the  impulse  of  the  heart  has  great  physiological  importance ;  for  it  is  evi- 
dently essential  that  the  current  of  blood,  as  it  flows  into  the  delicate  capil- 
lary vessels,  should  not  be  alternately  intermitted  and  impelled  with  the  full 
power  of  the  ventricle. 

The  elasticity  of  the  arteries  favors  the  flow  of  blood  toward  the  capillaries 
by  a  mechanism  that  is  easily  understood.  The  blood  discharged  from  the 
heart  distends  the  elastic  vessel,  which  reacts,  after  the  distending  force 
ceases  to  operate,  and  compresses  its  fluid  contents.  This  reaction  would 
have  the  effect  of  forcing  the  blood  in  two  directions,  were  it  not  for  closure 
of  the  valves,  which  renders  regurgitation  into  the  heart  impossible.  The 
influence,  then,  can  be  exerted  only  in  the  direction  of  the  periphery.  It  is 
evident,  therefore,  that  in  vessels  removed  a  sufficient  distance  from  the  heart, 
the  force  exerted  on  the  blood  by  the  reaction  of  the  elastic  walls  is  compe- 
tent to  produce  a  very  considerable  current  during  the  intervals  of  the  heart's 
action. 

Contractility  of  the  Arteries. — The  medium-sized  and  smallest  arteries 
contain  non-striated  muscular  fibres ;  and  it  has  been  shown  that  as  a  con- 
sequence of  the  condition  of  these  fibres,  the  vessels  undergo  considerable 
variations  in  their  caliber.  These  changes  in  the  size  of  the  arteries  can  be 
produced  by  stimulation  or  section  of  the  vaso-motor  nerves.  If  the  sympa- 
thetic be  divided  in  the  neck  of  a  rabbit,  the  arteries  of  the  ear  on  that  side 
soon  become  dilated.  If  the  divided  extremity  of  the  nerve  be  stimulated, 
the  vessels  contract  and  may  become  smaller  than  on  the  opposite  side. 
These  experiments  demonstrate  the  contractile  properties  of  the  small  arteries 
and  give  an  idea  how  the  supply  of  blood  to  any  particular  part  may  be  regu- 
lated. The  contractility  of  the  arteries  has  great  physiological  importance. 
As  their  office  is  simply  to  supply  blood  to  the  various  tissues  and  organs,  it 
is  evident  that  when  the  vessels  going  to  any  particular  part  are  dilated,  the 
supply  of  blood  is  necessarily  increased.  This  is  particularly  well  marked  in 
the  glands,  which,  during  the  intervals  of  secretion,  receive  a  comparatively 
small  quantity  of  blood.  The  pallor  of  parts  exposed  to  cold  and  the  flush 
produced  by  heat  are  due,  on  the  one  hand,  to  contraction,  and  on  the  other, 
to  dilatation  of  the  small  arteries.  Pallor  and  blushing  from  mental  emo- 
tions are  examples  of  the  same  kind  of  action. 

The  idea,  which  at  one  time  obtained,  that  the  arteries  were  the  seat  of 
rhythmical  contractions  which  had  a  favorable  influence  on  the  current  of 
blood  is  erroneous ;  and  it  is  hardly  necessary  to  repeat  the  statement  that 
the  cause  of  the  arterial  circulation  is  the  force  of  the  left  ventricle.  It  has 
been  observed,  however,  that  the  arteries  in  the  ear  and  certain  other  parts 
in  the  rabbit  undergo  rhythmical  contractions  and  dilatations,  these  occur- 
ring ten  or  twelve  times  per  minute  (Schiff,  Loven,  Yulpian) ;  but  these 
movements  are  not  to  be  regarded  as  a  contributing  force  in  the  production 
of  the  circulation.  It  is  evident,  on  the  othei  hand,  that  the  elasticity  of  the 
arteries  must  actually  assist  the  circulation.  The  resiliency  of  the  vessels  is 


66  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

continually  pressing  their  contents  toward  the  periphery ;  the  dilatation  of 
the  vessels  with  each  systole  of  course  admits  an  increased  quantity  of  blood ; 
and  it  has  been  shown  that  the  same  intermittent  force  exerted  on  an  inelas- 
tic tube  will  discharge  a  less  quantity  of  liquid  from  openings  of  equal 
caliber. 

Superadded,  then,  to  the  direct  action  of  the  heart,  physiologists  now  rec- 
ognize, as  a  cause  influencing  the  flow  of  blood  in  the  arteries,  the  resiliency  of 
the  vessels,  especially  of  those  of  large  size,  this  force  being  derived  originally 
from  the  heart.  Thus  it  will  be  seen  that  the  arteries  are  constantly  kept 
distended  with  blood  by  the  heart ;  and  by  virtue  of  their  elasticity  and  the 
progressive  increase  in  the  capacity  of  this  system  as  they  branch,  the  power- 
ful contractions  of  the  central  organ  serve  only  to  keep  up  an  equable  current 
in  the  capillaries.  The  small  vessels,  by  the  action  of  their  contractile  walls, 
regulate  the  local  circulations. 

Locomotion  of  the  Arteries  and  Production  of  the  Pulse. — With  each 
contraction  of  the  heart,  the  arteries  are  increased  in  length  and  many  of 
them  undergo  a  considerable  locomotion.  This  may  be  readily  observed  in 
vessels  which  are  tortuous  in  their  course,  and  is  frequently  very  marked  in 
the  temporal  artery  in  old  persons.  The  elongation  may  also  be  observed  by 
watching  attentively  the  point  where  an  artery  bifurcates,  as  at  the  division 
of  the  common  carotid.  It  is  simply  the  mechanical  effect  of  sudden  disten- 
tion,  which,  while  it  increases  the  caliber  of  the  vessel,  causes  an  elongation 
even  more  marked. 

The  finger  placed  over  an  exposed  artery  or  one  which  lies  near  the  sur- 
face experiences  a  sensation  at  every  beat  of  the  heart  as  though  the  vessel 
were  striking  against  it.  This  has  long  been  observed  and  is  called  the  pulse. 
Ordinarily  it  is  appreciated  when  the  current  of  blood  is  subjected  to  a  cer- 
tain degree  of  obstruction,  as  in  the  radial,  which  can  readily  be  compressed 
against  the  bone.  In  an  artery  imbedded  in  soft  parts  which  yield  to  press- 
ure, the  actual  dilatation  of  the  vessel  being  very  slight,  pulsation  is  felt  with 
difficulty,  if  at  all.  When  obstruction  of  an  artery  is  complete,  as  after  tying 
a  vessel,  the  pulsation  above  the  point  of  ligature  is  very  marked  and  can  be 
readily  appreciated  by  the  eye.  The  explanation  of  this  exaggeration  of  the 
movement  is  the  following :  Normally,  the  blood  passes  freely  through  the 
arteries  and  produces,  in  the  smaller  vessels,  very  little  movement  or  dilata- 
tion ;  when,  however,  the  current  is  obstructed,  as  by  ligation  or  even  com- 
pression with  the  finger,  the  force  of  the  heart  is  not  sent  through  the  vessel 
to  the  periphery  but  is  arrested  and  therefore  becomes  more  marked  and 
easily  appreciated.  In  vessels  which  have  become  undilatable  and  incom- 
pressible from  calcareous  deposits,  the  pulse  can  not  be  felt.  The  character 
of  the  pulse  indicates,  to  a  certain  extent,  the  condition  of  the  heart  and 
vessels. 

Under  ordinary  conditions,  the  pulse  may  be  felt  in  all  arteries  that  are 
exposed  to  investigation ;  and  as  it  is  due  to  the  movement  of  the  blood  in 
the  vessels,  the  prime  cause  of  its  production  is  the  contraction  of  the  left 
ventricle.  The  impulse  given  to  the  blood  by  the  heart,  however,  is  not  felt 


PRODUCTION  OF  THE  PULSE.  67 

in  all  the  vessels  at  the  same  instant.  Marey  registered  simultaneously  the 
impulse  of  the  heart,  the  pulse  of  the  aorta  and  the  pulse  of  the  femoral 
artery,  and  ascertained  that  the  contraction  of  the  ventricle  is  anterior,  in 
point  of  time,  to  the  pulsation  of  the  aorta,  and  that  the  pulsation  of  the 
aorta  precedes  the  pulse  in  the  femoral.  This  only  confirmed  the  views  of 
other  physiologists,  particularly  Weber,  who  described  this  progressive  retar- 
dation of  the  pulse,  estimating  the  difference  between  the  ventricular  systole 
and  the  pulsation  of  the  artery  in  the  foot  at  one-seventh  of  a  second. 

It  is  evident  from  what  is  known  of  the  variations  which  occur  in  the 
force  of  the  heart's  action,  the  quantity  of  blood  in  the  vessels,  and  from  the 
changes  which  may  take  place  in  the  caliber  of  the  arteries,  that  the  charac- 
ters of  the  pulse  must  be  subject  to  great  variations.  Many  of  these  may  be 
appreciated  simply  by  the  sense  of  touch.  Writers  treat  of  the  soft  and  com- 
pressible pulse,  the  hard  pulse,  the  wiry  pulse,  the  thready  pulse  etc.,  as  indi- 
cating various  conditions  of  the  circulatory  system.  The  character  of  the 
pulse,  aside  from  its  frequency,  has  always  been  regarded  as  of  great  impor- 
tance in  disease. 

Form  of  the  Pulse. — It  is  evident  that  few  of  the  characters  of  a  pulsa- 
tion, occupying  as  it  does  but  one-seventieth  part  of  a  minute,  can  be 
ascertained  by  the  sense  of  touch  alone.  This  fact  has  been  appreciated  by 
physiologists,  and  within  the  last  few  years,  instruments  for  registering  the 
pulse  have  been  constructed,  with  the  view  of  analyzing  the  dilatation  and 
movements  of  the  vessels.  The  idea  of  such  an  instrument  was  probably 
suggested  by  the  following  simple  observation :  When  the  legs  are  crossed, 


FIG.  24. — Sphygmngraph  of  Marey. 

The  apparatus  is  securely  fixed  on  the  forearm,  so  that  the  spring  under  the  screw  V  is  directly  over 
the  radial  artery.  The  movements  of  the  pulse  are  transmitted  to  the  long  and  light  wooden  lever 
L  and  registered  upon  the  surface  P.  which  is  moved  at  a  known  rate  by  the  clock-work  H.  The 
apparatus  is  so  adjusted  that  the  movements  of  the  vessel  are  accurately  amplified  and  registered 
by  the  extreme  point  of  the  lever. 

with  one  knee  over  the  other,  the  beating  of  the  popliteal  artery  will 
produce  marked  movements  of  the  foot.  If  a  lever  provided  with  a  mark- 
ing-point in  contact  with  a  slip  of  paper  moving  at  a  definite  rate  could  be 
applied  to  an  artery,  the  point  of  the  lever  would  register  the  movements  of 


68 


CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 


the  vessel  and  its  changes  in  caliber.     The  first  physiologist  who  put  this  in 
practice   was  Vierordt,   who   constructed   quite   a  complex   instrument,  so 


FIG.  23. — Sphygmograph  of  Marey  applied  to  the  arm. 

arranged  that  the  impulse  from  an  accessible  artery,  like  the  radial,  was 
conveyed  to  a  lever,  which  marked  the  movement  upon  a  revolving  cylin- 
der of  paper.  This  instrument  was  called  a  sphygmograph.  The  traces 
made  by  it  were  perfectly  regular  and  simply  marked  the  extremes  of  dilata- 
tion —  exaggerated,  of 
course,  by  the  length  of 
the  lever — and  the  num- 
ber of  pulsations  in  a  giv- 
en time.  The  latter  can 
be  easily  estimated  by 
more  simple  means ;  and 
as  the  former  did  not  con- 
vey any  very  definite  physiological  idea,  the  apparatus  was  regarded  rather 
as  a  curiosity  than  an  instrument  for  accurate  research. 

The  principle  on  which  the  instrument  of  Vierordt  was  constructed  was 
correct;  and  it  remained  only  to  devise  one  which  would  be  easy  of  ap- 


FIG.  26.— Trace  of  Vierordt. 


FIG.  2~. — Trace  of  Marey. 
Portions  of  four  traces  taken  in  different  conditions  of  the  pulse. 

plication  and  produce  a  trace  representing  the  shades  of  dilatation  and 
contraction  of  the  vessels,  in  order  to  lead  to  important  practical  results. 
These  conditions  are  realized  in  the  sphygmographs  now  in  use,  which  differ 
from  each  other  mainly  in  the  convenience  with  which  they  are  applied, 
the  principle  of  all  being  substantially  that  of  the  sphygmograph  of  Marey, 
which  is  shown  in  Figs.  24  and  25.  The  modern  sphygmographs  simply 
amplify  the  changes  in  the  caliber  of  the  artery  incident  to  the  pulse ;  and 
although  their  application  is,  perhaps,  not  so  easy  as  to  make  these  instru- 
ments generally  useful  in  the  practice  of  medicine,  in  the  hands  of  Marey 
and  other  physiologists,  they  have  led  to  a  definite  knowledge  of  the 
physiological  characters  of  the  pulse  and  its  modifications  in  certain  diseases, 
information  which  could  hardly  be  arrived  at  by  other  means  of  investigation. 


PRODUCTION  OF  THE  PULSE.  69 

In  short,  their  mechanism  is  so  accurate,  that  when  skillfully  used,  they  give 
on  paper  the  actual  "form  of  the  pulse."  Tho  modern  instruments, 
applied  to  the  radial  artery,  give  traces  very  different  from  those  obtained 
by  Vierordt,  which  were  simply  series  of  regular  elevations  and  depressions. 
A  comparison  of  these  with  the  traces  obtained  by  Vierordt  gives  an  idea  of 
the  defects  which  have  been  remedied  by  Marey ;  for  it  is  evident  that  the 
dilatation  and  contraction  of  the  arteries  can  not  be  so  regular  and  simple 
as  \vould  be  inferred  merely  from  the  trace  made  by  the  instrument  of 
Vierordt. 

Analyzing  the  traces  taken  by  Marey,  it  is  seen  that  there  is  a  dilatation 
following  the  systole  of  the  heart,  marked  by  an  elevation  of  the  lever, 
more  or  less  sudden,  as  indicated  by  the  angle  of  the  trace,  and  of  greater 
or  less  amplitude.  The  dilatation  having  arrived  at  its  maximum,  u 
followed  by  reaction,  which  may  be  slow  and  regular,  or  may  be,  and 
generally  is,  interrupted  by  a  second  and  slighter  upward  movement  of  the 
lever.  This  second  impulse  varies  very  much  in  amplitude.  In  some  rare 
instances,  it  is  nearly  as  marked  as  the  first  and  may  be  appreciated  by  the 
finger,  giving  the  sensation  of  a  double  pulse  following  each  contraction  of 
the  heart.  This  is  called  the  dicrotic  pulse.  As  a  rule,  the  first  dilatation  of 
the  vessel  is  sudden  and  is  indicated  by  an  almost  vertical  line.  This  is 
followed  by  a  comparatively  slow  reaction,  indicated  by  a  gradual  descent  of 
the  trace,  which  is  not,  however,  absolutely  regular,  but  is  marked  by  a  slight 
elevation  indicating  a  second  impulse.  The  amplitude  of  the  trace,  or  the 
distance  between  the  highest  and  the  lowest  points  marked  by  the  lever, 
depends  upon  the  degree  of  constant*  tension  of  the  vessels.  Marey  has 
found  that  the  amplitude  is  in  an  inverse  ratio  to  the  tension ;  which  is  very 
easily  understood,  for  when  the  arteries  are  but  little  distended,  the  force  of 
the  heart  must  be  more  marked  in  its  effects  than  when  the  pressure  of 
blood  is  very  great.  Any  condition  which  facilitates  the  flow  of  blood 
from  the  arteries  into  the  capillaries  will,  of  course,  relieve  the  tension  of 
the  arterial  system,  lessen  the  obstacle  to  the  force  of  the  heart,  and  increasa 
the  amplitude  of  the  pulsation,  and  vice  versa.  In  support  of  this  view, 
Marey  has  found  that  cold  applied  to  the  surface  of  the  body,  contracting,  as 
it  does,  the  smallest  arteries,  increases  the  arterial  tension  and  diminishes  the 
amplitude  of  the  pulsation,  while  a  moderate  elevation  of  temperature  pro- 
duces an  opposite  effect. 

In  nearly  all  the  traces  given  by  Marey,  the  descent  of  the  lever  indicates 
more  or  less  oscillation  of  the  mass  of  blood.  The  physical  properties  of  the 
larger  arteries  render  this  inevitable.  As  they  yield  to  the  distending 
influence  of  the  heart,  reaction  occurs  after  this  force  is  taken  off,  and  if  the 
distention  be  very  great,  gives  a  second  impulse  to  the  blood.  This  is  quite 
marked,  unless  the  tension  of  the  arterial  system  be  so  great  as  to  offer  too 
much  resistance.  One  of  the  most  favorable  conditions  for  the  manifesta- 
tion of  dicrotism  is  diminished  tension,  which  is  always  found  co-existing 
with  a  very  marked  exhibition  of  this  phenomenon. 

Marey  accurately  determined  and  registered  these  various  phenomena,  by 


70  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

observations  on  the  arteries  of  the  human  subject  and  the  lower  animals ;  and 
by  means  of  a  " schema"  representing  the  arterial  system  by  elastic  tubes 
and  the  left  ventricle  by  an  elastic  bag  provided  with  valves  and  acting  as  a 
syringe,  he  established  the  conditions  of  tension  etc.,  necessary  to  their  pro- 
duction. In  this  schema,  the  registering  apparatus,  simpler  in  construction 
than  the  sphygmograph,  could  be  applied  to  the  tubes  with  more  accuracy 
and  ease.  He  demonstrated  by  experiments  with  this  system  of  tubes,  that 
the  amplitude  of  the  pulsations,  the  force  of  the  central  organ  being  the  same, 
is  greatest  when  the  tubes  are  moderately  distended,  or  when  the  tension  of 
fluid  is  low,  and  vice  versa.  He  demonstrated,  also,  that  a  low  tension 
favors  dicrotism.  In  this  latter  observation,  he  diminished  the  tension  by 
enlarging  the  orifices  by  which  the  fluid  was  discharged  from  the  tubes, 
imitating  the  dilatation  of  the  small  vessels,  by  which  the  tension  is  di- 
minished in  the  arterial  system.  He  also  demonstrated  that  an  important 
and  essential  element  in  the  production  of  dicrotism  is  the  tendency  to 
oscillation  of  the  fluid  in  the  vessels  during  the  intervals  between  the  con- 
tractions of  the  heart.  This  can  only  occur  in  a  fluid  which  has  a  cer- 
tain weight  and  acquires  a  velocity  from  the  impulse;  for  when  air  was 
introduced  into  the  apparatus,  dicrotism  could  not  be  produced  under  any 
conditions,  as  the  fluid  did  not  possess  weight  enough  to  oscillate  between 
the  impulses.  Water  produced  a  well  marked  dicrotic  impulse  under  favor- 
able conditions;  and  with  mercury,  the  oscillations  made  two,  three  or 
more  distinct  impulses.  By  these  experiments,  he  proved  that  the  blood 
oscillates  in  the  vessels,  if  this  movement  be  not  suppressed  by  too  great 
pressure  or  tension.  This  oscillation  gives  the  successive  rebounds  that  are 
marked  in  the  descending  line  of  the  pulse,  and  is  capable,  in  some  rare 
instances  when  the  arterial  tension  is  very  slight,  of  producing  a  second 
rebound  of  sufficient  force  to  be  appreciated  by  the  finger. 

Without  treating  of  the  variations  in  the  character  of  the  pulse  in 
disease,  due  to  the  action  of  the  muscular  coat  of  the  arteries,  it  will  be  use- 
ful to  consider  some  of  the  external  modifying  influences  which  come 
within  the  range  of  physiology.  The  smallest  vessels  and  those  of  medium 
size  possess  to  an  eminent  degree  what  is  called  tonicity,  or  the  property 
of  maintaining  a  certain  continued  degree  of  contraction.  This  contraction 
is  antagonistic  to  the  distending  force  of  the  blood,  as  is  shown  by  opening 
a  portion  of  an  artery  included  between  two  ligatures  in  a  living  animal, 
when  the  contents  will  be  forcibly  discharged  and  the  caliber  of  that 
portion  of  the  vessel  be  very  much  diminished.  Too  great  distention  of  the 
vessels  by  the  pressure  of  blood  seems  to  be  prevented  by  this  constant  action 
of  the  muscular  coat ;  and  thus  the  conditions  are  maintained  which  give 
to  the  pulse  the  characters  just  described. 

By  excessive  and  continued  heat,  the  muscular  tissue  of  the  arteries  may 
be  dilated  so  as  to  offer  less  resistance  to  the  distending  force  of  the  heart. 
Under  these  conditions,  the  pulse,  as  felt  by  the  finger,  will  be  found  to  be 
larger  and  softer  than  normal.  Cold,  either  general  or  local,  has  an  opposite 
effect ;  the  arteries  become  contracted,  and  the  pulse  assumes  a  harder  and 


PRESSURE  OF  BLOOD  IN  THE  ARTERIES.        71 

more  wiry  character.  As  a  rule,  prolonged  contraction  of  the  arteries  is  fol- 
lowed by  relaxation,  as  is  seen  in  the  full  pulse  and  glow  of  the  surface  which 
accompany  reaction  after  exposure  to  cold.  It  has  been  found,  also,  that 
there  is  a  considerable  difference  in  the  caliber  of  the  arteries  at  different 
periods  of  the  day.  The  diameter  of  the  radial  has  been  found  very  much 
greater  in  the  evening  than  in  the  morning,  producing,  naturally,  a  variation 
in  the  character  of  the  pulse. 

PEESSUEE  OF  BLOOD  IN  THE  AETEEIES. 

The  reaction  of  the  elastic  walls  of  the  arteries  during  the  intervals  of 
the  heart's  action  gives  rise  to  a  certain  degree  of  pressure,  by  which  the 
blood  is  continually  forced  toward  the  capillaries.  The  discharge  of  blood 
into  the  capillaries  has  a  constant  tendency  to  diminish  this  pressure ;  but 
the  contractions  of  the  left  ventricle,  by  forcing  repeated  charges  of  blood 
into  the  arteries,  have  a  compensating  action.  By  the  equilibrium  between 
these  two  agencies,  a  certain  tension  is  maintained  in  the  arteries,  which  is 
called  the  arterial  pressure. 

The  first  experiments  with  regard  to  the  extent  of  the  arterial  pressure 
were  made  by  Hales,  an  English  physiologist,  more  than  a  hundred  years 
ago.  This  observer,  adapting  a  long  glass  tube  to  the  artery  of  a  living  ani- 
mal, ascertained  the  height  of  the  column  of  blood  which  could  be  sustained 
by  the  arterial  pressure.  In  some  experiments  on  the  carotid  of  the  horse, 
the  blood  mounted  to  the  height  of  eight  to  ten  feet  (243  to  304  centi- 
metres). 

If  a  large  artery,  like  the  carotid,  be  exposed  in  a  living  animal,  and  a 
metallic  point,  connected  with  a  vertical  tube  of  smaller  caliber  and  seven  or 
eight  feet  (213  or  243  centimetres)  long  by  a  bit  of  elastic  tubing,  be  secured 
in  the  vessel,  the  blood  will  rise  to  the  height  of  about  six  feet  (183  centi- 
metres) and  remain  at  this  point  almost  stationary,  indicating,  by  a  slight 
pulsatile  movement,  the  action  of  the  heart.  On  carefully  watching  the  level 
in  the  tube,  in  addition  to  the  rapid  oscillation  coincident  with  the  pulse, 
another  oscillation  will  be  observed,  which  is  less  frequent  and  which  corre- 
sponds with  the  movements  of  respiration.  The  pressure,  as  indicated  by  an 
elevation  of  the  fluid,  is  slightly  increased  during  expiration  and  diminished 
during  inspiration.  In  such  experiments,  it  is  necessary  to  fill  part  of  the 
tube,  or  whatever  apparatus  be  used,  with  a  solution  of  sodium  carbonate,  in 
order  to  prevent  coagulation  of  the  blood  as  it  passes  out  of  the  vessels. 

The  experiment  with  the  long  tube  gives,  perhaps,  the  best  general  idea 
of  the  arterial  pressure,  which  will  be  found  to  vary  between  five  and  a  half 
and  six  feet  of  blood  (170  and  183  centimetres),  or  a  few  inches  more  of 
water.  The  oscillations  produced  by  the  contractions  of  the  heart  are  not 
very  marked,  on  account  of  the  great  friction  in  so  long  a  tube ;  but  this  is 
favorable  to  the  study  of  the  constant  pressure.  It  has  been  found  that  the 
estimates  above  given  do  not  vary  very  much  in  animals  of  different  sizes. 
Bernard  found  the  pressure  in  the  carotid  of  a  horse  but  little  more  than  in 
the  dog  or  rabbit.  In  the  larger  animals,  it  is  the  force  of  the  heart  which 


•72 


CIRCULATION   OF  THE  BLOOD  IN   THE  VESSELS. 


is  increased,  and  not,  to  any  considerable  extent,  the  constant  pressure  in  the 
vessels. 

The  experiments  of  Hales  were  made  with  a  view  of  calculating  the  force 
of  the  heart,  and  were  not  directed  particularly  to  the  modifications  and 
variations  of  the  arterial  pressure.  It  is  only  since  the  experiments 
performed  by  Poiseuille  with  the  hsemadynamorneter,  in  1828,  that 
physiologists  have  had  any  reliable  data  on  this  latter  point.  Poi- 
seuille's  instrument  for  measuring  the  force  of  the  blood  is  a  simple, 
graduated  TI-tube,  half  filled  with  mercury,  with  one  arm  bent  at  a 
right  angle,  so  that  it  can  easily  be  connected  with  the  artery.  The 
pressure  of  the  blood  is  indicated  by  a  depression  in  the  level  of  the 
mercury  on  one  side  and  a  corresponding  elevation  on  the  other. 
This  instrument  is  generally  considered  as  possessing  great  advan- 
tages over  the  long  glass  tube ;  but  for  estimating  simply  the  arterial 
pressure,  it  is  much  less  useful,  as  it  is  more  sensitive  to  the  impulse 
of  the  heart.  For  the  study  of  the  cardiac  pressure,  it  has  the  dis- 
advantage, in  the  first  place,  of  considerable  friction,  and  again,  the 
v/eight  of  the  column  of  mercury  produces  an  extent  of  oscillation 

by  its  mere  impetus,  greater  than  that 
which  would  actually  represent  the  alter- 
nation of  systole  and  diastole  of  the  heart. 
An  important  improvement  in  the 
hsemadynamometer  was  made  by  Magen- 
die.  This  apparatus,  the  cardiometer,  in 
which  Bernard  made  some  important  mod- 
ifications, is  the  one  now  generally  used. 
It  consists  of  a  small  but  thick  glass  bot- 
tle, with  a  fine,  graduated  glass  tube  about 
twelve  inches  (3O5  centimetres)  in  length, 
communicating  with  it,  either  through  the 
stopper  or  by  an  orifice  in  the  side.  The 
stopper  is  pierced  by  a  bent  tube  which  is 
to  be  connected  with  the  blood-vessel. 
The  bottle  is  filled  with  mercury  so  that  it 
will  rise  in  the  tube  to  a  point  which  is 
marked  zero.  It  is  evident  that  the  press- 
ure on  the  mercury  in  the  bottle  will  be  indicated  by  an  elevation  in  the 
graduated  tube ;  and,  moreover,  from  the  fineness  of  .  the  column  in  the 
tube,  some  of  the  inconveniences  which  are  due  to  the  weight  of  mercury 
in  the  hasmadynamometer  are  avoided,  and  there  is,  also,  less  friction. 
This  instrument  is  appropriately  called  the  cardiometer,  as  it  indicates  most 
accurately,  by  the  extreme  elevation  of  the  mercury,  the  force  of  the  heart ; 
but  it  is  not  as  perfect  in  its  indications  of  the  mean  arterial  pressure,  for  in 
the  abrupt  descent  of  the  mercury  during  the  diastole  of  the  heart,  the  im- 
petus causes  the  level  to  fall  below  the  real  standard  of  the  constant  pressure. 
Marey  has  corrected  this  difficulty  in  the  "  compensating  "  instrument,  which 


FIG.  28.— Section  of  the  cardiometer  of 
Magendie,  as  modified  by  Bernard. 

A  strong  glass  bottle  is  perforated  at  each 
side  and  fitted  with  an  iron  tube,  with 
an  opening,  T,  by  which  the  mercury 
enters.  One  end  of  the  iron  tube  is 
closed,  and  the  other  is  bent  upward 
and  connected  with  the  graudated  glass 
tube  T'.  which  has  a  caliber  of  TV  to 
A  of  an  inch (21  to  3'2  mm.).  The  bottle 
is  filled  with  mercury  HI,  until  it  rises 
to  n'  in  the  tube,  which  is  marked  zero. 
The  cork  is  perforated  by  the  tube  t, 
which  is  connected  by  a  rubber  tube  e 
with  the  point  C,  which  is  introduced 
into  the  vessel. 


PRESSURE  OF  BLOOD  IN  THE  ARTERIES. 


73 


is  constructed  on  the  following  principle :  Instead  of  a  simple  glass  tube 
which  communicates  with  the  mercury  in  the  bottle,  as  in  Magendie's 
cardiometer,  there  are  two  tubes, 
one  of  which  is  like  the  one 
already  described  and  represents 
oscillations  produced  by  the 
heart,  while  the  other  is  larger, 
and  has,  at  the  lower  part,  a 
constriction  of  its  caliber,  which 
is  here  reduced  to  capillary  fine- 
ness. The  latter  tube  is  de- 
signed to  give  the  mean  arterial 
pressure ;  the  constricted  portion 
offering  such  an  obstacle  to  the 
rise  of  the  mercury  that  the  in- 
termittent action  of  the  heart  is 
not  felt,  the  mercury  rising  slow- 
ly to  a  certain  level,  which  is 
constant  and  varies  only  with 
the  constant  pressure  in  the  ves- 
sels. 

Physiologists  have  only  an 
approximate  idea  of  the  arte- 
rial pressure  in  the  human  sub- 
ject, derived  from  experiments 
on  the  inferior  animals.  It  has 
already  been  stated  to  be  equal 
to  about  six  feet  (183  centime- 
tres) of  water  or  six  inches  (150 
mm.)  of  mercury. 

Pressure  in  Different  Arteries. — The  experiments  of  Hales,  Poiseuille, 
Bernard  and  others,  seem  to  show  that  the  constant  arterial  pressure  does 
not  vary  much  in  arteries  of  different  sizes.  These  physiologists  experi- 
mented particularly  on  the  carotid  and  crural,  and  found  the  pressure  in 
these  two  vessels  about  the  same.  From  their  experiments  they  concluded 
that  the  force  is  equal  in  all  parts  of  the  arterial  system.  T.he  experiments 
of  Volkmann,  however,  have  shown  that  this  conclusion  is  not  correct.  With 
the  registering  apparatus  of  Ludwig,  he  took  the  pressure  in  the  carotid 
and  the  metatarsal  arteries  and  always  found  a  considerable  difference  in 
favor  of  the  former.  In  an  experiment  on  a  dog,  he  found  the  pressure 
equal  to  about  seven  inches  (172  mm.)  in  the  carotid,  and  6-6  inches  (165 
mm.)  in  the  metatarsal.  In  an  experiment  on  a  calf,  the  pressure  was  4-64 
inches  (116  mm.)  in  the  carotid,  and  3'56  inches  (89  mm.)  in  the  meta- 
tarsal ;  and  in  a  rabbit,  3-64  inches  (91  mm.)  in  the  carotid,  and  3-44  inches 
(86  mm.)  in  the  crural.  These  experiments  show  that  the  pressure  is  not  ab- 
solutely the  same  in  all  parts  of  the  arterial  system,  that  it  is  greatest  in  the 


FIG.  29.— Compensating  instrument  of  Marey. 


74  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

arteries  nearest  the  heart,  and  that  it  gradually  diminishes  toward  the  capil- 
laries. The  difference  is  very  slight,  almost  inappreciable,  except  in  vessels 
of  very  small  size ;  but  here  the  pressure  is  directly  influenced  by  the  dis- 
charge of  blood  into  the  capillaries.  The  cause  of  this  diminution  of  press- 
ure in  the  smallest  vessels  is  the  proximity  of  the  great  outlet  of  the  arteries, 
the  capillary  system  ;  for,  as  will  be  seen  farther  on,  the  flow  into  the  capilla- 
ries has  a  constant  tendency  to  diminish  the  pressure  in  the  arteries. 

Influence  of  Respiration. — It  is  easy  to  see  in  studying  the  arterial  press- 
ure, that  there  is  a  marked  increase  with  expiration  and  a  diminution  with 
inspiration.  In  tranquil  respiration  the  influence  upon  the  flow  of  blood  is 
due  simply  to  the  mechanical  action  of  the  thorax.  With  every  inspiration 
the  air-cells  are  enlarged,  as  well  as  the  blood-vessels  of  the  lungs,  the  air 
rushes  in  through  the  trachea,  and  the  movement  of  the  blood  in  the  veins 
near  the  chest  is  accelerated.  At  the  same  time  the  blood  in  the  arteries  is 
somewhat  retarded  in  its  flow  from  the  thorax,  or  at  least  does  not  feel  the 
expulsive  influence  which  follows  with  the  act  of  expiration.  The  arterial 
pressure  at  that  time  is  at  its  minimum.  With  the  expiratory  act  the  air  is  ex- 
pelled by  compression  of  the  lungs,  the  flow  of  blood  into  the  thorax  by  the 
veins  is  retarded  to  a  certain  extent,  while  the  flow  of  blood  into  the  arteries 
is  favored.  This  is  strikingly  exhibited  in  the  augmented  force,  with  expi- 
ration, in  the  jet  from  a  divided  artery.  Under  these  conditions  the  ar- 
terial pressure  is  at  its  maximum.  In  perfectly  tranquil  respiration,  the 
changes  due  to  inspiration  and  expiration  are  slight,  presenting  a  difference 
of  not  more  than  half  an  inch  or  an  inch  (12-7  or  25-4  mm.)  in  the  cardi- 
ometer.  When  the  respiratory  movements  are  exaggerated,  the  oscillations 
are  very  much  more  marked. 

Interruption  of  respiration  is  followed  by  a  very  great  increase  in  the  ar- 
terial pressure.  This  is  due,  not  to  causes  within  the  chest,  but  to  obstruction 
to  the  circulation  in  the  capillaries.  With  an  interruption  of  the  respiratory 
movements,  the  non-aerated  blood  passes  into  the  arteries  but  can  not  flow 
readily  through  the  capillaries,  and  as  a  consequence,  the  arteries  are  abnor- 
mally distended  and  the  pressure  is  greatly  increased.  If  respiration  be  per- 
manently arrested,  the  arterial  pressure  becomes,  after  a  time,  diminished  be- 
low the  normal  standard,  and  is  finally  abolished  on  account  of  the  stoppage 
of  the  action  of  the  heart.  If  respiration  be  resumed  before  the  action  of 
the  heart  has  fbecome  arrested,  the  pressure  soon  returns  to  its  normal 
standard. 

Influence  of  Muscular  Action  etc. — Muscular  effort  considerably  increases 
the  arterial  pressure.  This  is  due  to  two  causes.  In  the  first  place,  the 
chest  is  generally  compressed,  and  this  favors  the  flow  of  blood  into  the  great 
vessels.  In  the  second  place,  muscular  exertion  produces  a  certain  degree  of 
obstruction  to  the  discharge  of  blood  from  the  arteries  into  the  capillaries. 
Experiments  upon  the  inferior  animals  show  a  great  increase  in  pressure  in 
the  struggles  which  occur  during  severe  operations.  It  has  been  shown  that 
stimulation  of  the  sympathetic  in  the  neck  and  of  certain  of  the  cerebro-spi- 
nal  nerves  increases  the  arterial  pressure,  probably  from  an  influence  on  the 


PEESSUEE  OF  BLOOD  IN  THE  AETEEIES  75 

muscular  ooats  of  some  of  the  arteries,  causing  them  to  contract  and  thereby 
diminishing  the  total  capacity  of  the  arterial  system. 

Effects  of  Hemorrhage  etc. — Diminution  in  the  quantity  of  blood  has  a 
remarkable  effect  upon  the  arterial  pressure.  If,  in  connecting  the  instru- 
ment with  the  arteries,  even  one  or  two  jets  of  blood  be  allowed  to  escape,  the 
pressure  will  be  found  diminished  perhaps  one-half  or  even  more.  It  is 
hardly  necessary  to  discuss  the  mechanism  of  the  effect  of  the  loss  of  blood 
on  the  tension  of  the  vessels,  but  it  is  remarkable  how  soon  the  pressure  in 
the  arteries  regains  its  normal  standard  after  it  has  been  lowered  by  haemor- 
rhage. As  the  pressure  depends  largely  upon  the  quantity  of  blood,  as  soon 
as  the  vessels  absorb  the  serosities  in  sufficient  quantity  to  repair  the  loss, 
the  pressure  is  increased.  This  takes  place  in  a  very  short  time,  if  the  loss 
of  blood  be  not  too  great. 

Experiments  on  the  arterial  pressure,  with  the  cardiometer,  have  verified 
the  fact  stated  in  treating  of  the  form  of  the  pulse ;  namely,  that  the  pressure 
in  the  vessels  bears  an  inverse  ratio  to  the  distention  produced  by  the  con- 
tractions of  the  heart.  In  the  cardiometer,  the  mean  height  of  the  mercury 
indicates  the  constant,  or  arterial  pressure ;  and  the  oscillations,  the  disten- 
tion produced  by  the  heart.  It  is  found  that  when  the  pressure  is  great,  the 
extent  of  oscillation  is  small,  and  vice  versd.  It  will  be  remembered  that 
the  researches  of  Marey  demonstrated  that  an  increase  of  the  arterial 
pressure  diminishes  the  amplitude  of  the  pulsations,  as  indicated  by  the 
sphygmograph,  and  that  the  amplitude  is  very  great  when  the  pressure  is 
slight.  It  is  also  true,  as  a  general  rule,  that  the  force  of  the  heart,  as  in- 
dicated by  the  cardiometer,  bears  an  inverse  ratio  to  the  frequency  of  its  pul- 
sations. 

Depressor  Nerve  tf  the  Circulation. — Cyon  and  Ludwig  have  described 
a  nerve  arising  in  the  rabbit,  by  two  roots,  one  from  the  main  trunk  of  the 
pneumogastric  and  the  other  from  the  superior  laryngeal  nerve,  which  joins 
the  sympathetic  filaments  in  the  chest  and  passes  to  the  heart.  In  man  the 
depressor  nerve  is  not  isolated,  but  its  fibres  are  contained  in  the  sheath  of 
the  pneumogastric.  This  nerve  has  a  reflex  action,  as  was  shown  by  the  ex- 
periments of  Cyon,  its  Faradization  reducing  the  arterial  pressure  by  one- 
third  or  one-half.  This  action  is  known  to  be  reflex,  for  when  the  nerve  is 
divided,  stimulation  of  the  central  end  affects  the  arterial  pressure,  while  no 
such  result  follows  stimulation  of  the  peripheral  extremity ;  and  the  effect  is 
manifested  when  the  pneumogastrics  have  been  divided  and  no  direct  ner- 
vous influence  is  exerted  over  the  heart.  It  is  thought  that  the  reduction  in 
the  arterial  pressure  following  stimulation  of  the  so-called  depressor  nerves 
is  due  mainly  to  the  action  of  the  splanchnic  nerves,  by  which  the  abdominal 
vessels  become  largely  dilated.  If  the  abdomen  be  opened  and  one  or  more 
of  the  splanchnic  nerves  be  divided,  the  arterial  pressure  is  immediately 
diminished,  and  the  pressure  is  restored  if  the  divided  ends  of  the  nerves 
be  stimulated.  If,  after  division  of  the  splanchnic  nerves  and  the  conse- 
quent diminution  of  the  arterial  pressure,  the  depressor  nerves  be  stimulated, 
the  pressure  still  undergoes  some  additional  diminution,  but  this  is  much  less 


CIRCULATION   OF  THE  BLOOD  IN  THE  VESSELS. 


than  the  diminution  which  follows  stimulation  of  the  depressor  nerves  with- 
without  section  of  the  splanchnics. 

Rapidity  of  the  Current  of  Blood  in  flic  Arteries. — The  question  of  the 
rapidity  of  the  arterial  circulation  has  long  engaged  the  attention  of  physiol- 
ogists ;  but  the  experiments  of  Volkmann,  with  his  hsemadrometer,  and  of 
Vierordt,  with  a  peculiar  instrument  which  he  devised  for  the  purpose,  did 
not  lead  to  results  that  were  entirely  reliable.  The  apparatus  devised  by 
Chauveau,  however,  is  much  more  satisfactory.  This  will  give,  by  calcula- 
tion, the  actual  rapidity  of  the  circulation,  and  it  also  indicates  the  variations 
in  velocity  which  occur  at  different  periods  of  the  heart's  action. 

The  instrument  to  be  applied  to  the  carotid  of  the  horse  consists  of  a  thin 

brass  tube,  about  an  inch  and  a  half 
(38'1  mm.)  in  length  and  of  the  di- 
ameter of  the  artery  (about  three- 
eighths  of  an  inch,  or  9*5  mm.), 
which  is  provided  with  an  oblong, 
longitudinal  opening,  or  window, 
near  the  middle,  about  two  lines 
(4'2  mm.)  long  and  one  line  (2'1 
mm.)  wide.  A  piece  of  thin,  vul- 
canized rubber  is  wound  around 
the  tube  and  firmly  tied  so  as  to 
cover  this  opening.  Through  a 
transverse  slit  in  the  rubber,  is  in- 
troduced a  very  light,  metallic  nee- 
dle, an  inch  and  a  half  (38-1  mm.) 
in  length  and  flattened  at  its  lower 

FIG.  30.—  Chauveau's   instrument  for  measuring  the    ^o-f        Thk  i«  marlp  to  rnvn'ppf  ihrmf 
rapidity  of  the  flow  of  blood  in  the  arteries.  Part>  1  0]  6Ct  a  D 

The  instrument  viewed  in  face— a,  the  tube  to  be  fixed  half-Way    into    the    Caliber    of    the 
in  the  vessel ;  6,  the  dial  which  marks  the  extent  .    . 

of  movement  of  the  needle  d ;  e,  a  lateral  tube  for  tube.       A  flat,  semicircular  piece   of 
the  attachment  of  a  cardiometer,  if  desired.       -  ,-,••-,-,•,  • 

metal,  divided  into  an  arbitrary 

scale,  is  attached  to  the  tube,  to  indicate  the  deviations  of  the  point  of  the 
needle. 

The  apparatus  is  introduced  into  the  carotid  of  a  horse,  by  making  a  slit  in 
the  vessel,  introducing  first  one  end  of  the  tube  directed  toward  the  heart, 
then  allowing  a  little  blood  to  enter  the  instrument,  so  as  to  expel  the  air, 
and,  when  full,  introducing  the  other  end,  securing  the  whole  by  ligatures 
above  and  below. 

When  the  circulation  is  arrested,  the  needle  should  be  vertical,  or  mark 
zero  on  the  scale.  When  the  flow  is  established,  a  deviation  of  the  needle 
occurs,  which  varies  in  extent  with  the  rapidity  of  the  current.  Having 
removed  all  pressure  from  the  vessel  so  as  to  allow  the  current  to  resume 
its  normal  character,  the  deviations  of  the  needle  are  carefully  noted,  as  they 
occur  with  the  systole  of  the  heart,  with  the  diastole  etc.  After  withdrawing 
the  instrument,  it  is  applied  to  a  tube  of  the  size  of  the  artery,  in  which  a 
current  ol  water  is  made  to  pass  with  a  rapidity  Avhich  will  produce  the  same 


RAPIDITY  OF  THE  FLOW  IN  THE  ARTERIES.  77 

deviations  as  occurred  when  the  instrument  was  connected  with  the  blood- 
vessel. The  rapidity  of  the  current  in  this  tube  may  be  easily  calculated  by 
receiving  the  fluid  in  a  graduated  vessel  and  noting  the  time  occupied  in 
discharging  a  given  quantity.  By  this  means  the  rapidity  of  the  current 
of  blood  is  ascertained.  This  instrument  is  made  on  the  same  principle  as 
the  one  constructed  by  Vierordt,  but  in  sensitiveness  and  accuracy  it  is 
much  superior. 

Rapidity  of  the  Current  in  the  Carotid. — It  has  been  found  that  three 
currents,  with  different  degrees  of  rapidity,  may  be  distinguished  in  the  ca- 
rotid : 

1.  At  each  ventricular  systole,  as  the  average  of  the  experiments  of  Chau- 
veau,  the  blood  moves  in  the  carotids  at  the  rate  of  about  20*4  inches  (510 
mm.)  per  second.     After  this,  the  rapidity  quickly  diminishes  and  the  needle 
returns  quite  or  nearly  to  zero,  which  would  indicate  complete  arrest. 

2.  Immediately  succeeding  the  ventricular  systole,  a  second  impulse  is 
given  to  the  blood,  which  is  synchronous  with  the  closure  of  the  semilunar 
valves,  the  blood  moving  at  the  rate  of  about  8-6  inches  (215  mm.)  per  sec- 
ond.    This  is  the  dicrotic  impulse. 

3.  After  the  dicrotic  impulse,  the  rapidity  of  the  current  gradually  dimin- 
ishes until  just  before  the  systole  of  the  heart,  when  the  needle  is  nearly  at 
zero.     The  average  rate,  after  the  dicrotic  impulse,  is  about  5*9  inches  (147'5 
mm.)  per  second. 

The  experiments  of  Chauveau  correspond  with  the  experiments  of  Marey 
on  the  form  of  the  pulse.  Marey  showed  that  there  is  a  marked  oscillation 
of  the  blood  in  the  vessels,  due  to  a  reaction  of  their  elastic  walls,  following 
the  first  violent  distention  by  the  heart ;  that  at  the  time  of  closure  of  the 
semilunar  valves,  the  arteries  present  a  second,  or  dicrotic  distention,  much 
less  than  the  first ;  and  following  this,  there  is  a  gradual  decline  in  the  disten- 
tion until  the  minimum  is  reached.  According  to  the  observations  of  Chau- 
veau, corresponding  to  the  first  dilatation  of  the  vessels,  the  blood  moves  with 
great  rapidity ;  following  this,  the  current  suddenly  becomes  nearly  arrested ; 
this  is  followed  by  a  second  acceleration  in  the  current,  less  than  the  first ; 
and  following  this,  there  is  a  gradual  decline  in  the  rapidity,  to  the  time  of 
the  next  pulsation. 

Rapidity  in  Different  Parts  of  the  Arterial  System. — From  the  fact  that 
the  arterial  system  progressively  increases  in  capacity,  there  should  be  found 
a  corresponding  diminution  in  the  rapidity  of  the  flow  of  blood.  There  are, 
however,  many  conditions,  aside  from  simple  increase  in  the  capacity  of 
the  vessels,  which  modify  the  blood-current  and  render  inexact  any  calcula- 
tions made  upon  purely  physical  principles.  There  are  the  tension  of  the 
blood,  the  conditions  of  contraction  or  relaxation  of  the  smallest  arteries,  etc. 
It  is  necessary,  therefore,  to  have  recourse  to  actual  experiments  to  arrive  at 
any  definite  results  on  this  point.  Volkmann  found  a  great  difference  in  the 
rapidity  of  the  current  in  the  carotid  and  metatarsal  arteries,  the  averages 
being  about  10  inches  (254  mm.)  per  second  in  the  carotid,  and  about  2'2 
inches  (5G  mm.)  in  the  metatarsal.  The  same  difference,  although  not  quite 
7 


78 


CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 


so  marked,  was  found  by  Chauveau,  between  the  carotid  and  the  facial.  The 
last-named  observer  also  noted  an  important  modification  in  the  character  of 
the  current  in  the  smaller  vessels.  As  the  vessels  are  farther  and  farther  re- 
moved from  the  heart,  the  systolic  impulse  becomes  rapidly  diminished,  being 
reduced  in  one  experiment  about  two-thirds  ;  the  dicrotic  impulse  becomes 
feeble  or  may  even  be  abolished  ;  but  the  constant  flow  is  much  increased  in 
rapidity.  This  fact  coincides  with  the  ideas  already  advanced  with  regard  to 
the  gradual  conversion,  by  reason  of  the  elasticity  of  the  vessels,  of  the  im- 
pulse of  the  heart  into  first,  a  remittent,  and  in  the  very  smallest  arteries,  a 
nearly  constant  current. 

The  rapidity  of  the  flow  in  any  artery  must  be  subject  to  constant  modifi- 
cations due  to  the  condition  of  the  arterioles  which  are  supplied  by  it.  When 
these  little  vessels  are  dilated,  the  artery  of  course  empties  itself  with  greater 
facility  and  the  rapidity  is  increased.  Thus  the  rapidity  bears  a  relation  to 
the  arterial  pressure  ;  as  variations  in  the  pressure  depend  chiefly  on  causes 
which  facilitate  or  retard  the  flow  of  blood  into  the  capillaries.  A'  good  ex- 
ample of  enlargement  o±  the  capillaries  of  a  particular  part  is  in  mastication," 
when  the  salivary  glands  are  brought  into  activity  and  the  quantity  of  blood 
•which  they  receive  is  greatly  increased.  Chauveau  found  a  great  increase  in 
the  rapidity  of  the  flow  in  the  carotid  of  a  horse  during  mastication.  It  must 
•be  remembered  that  in  all  parts  of  the  arterial  system,  the  rapidity  of  the  cur- 
rent of  blood  is  constantly  liable  to  increase  from  dilatation  of  the  small  ves- 
.sels  and  to  diminution  from  their  contraction. 

CIRCULATION  OF  THE  BLOOD  IN  THE  CAPILLARIES. 

Before  entering  upon  the  study  of  the  capillary  circulation,  it  should  be 
'distinctly  stated  what  is  meant  by  capillary  vessels  as  distinguished  from  the 
.smallest  arteries  and  veins.  From  a  strictly  physiological  point  of  view,  the 

capillaries  are  to  be  regarded  as 
beginning  at  the  situation  where 
the  blood  is  brought  near  enough 
to  the  tissues  to  enable  them  to 
separate  the  matters  necessary 
for  their  regeneration  and  to 
give  up  the  products  of  their 
physiological  wear  ;  but  at  pres- 
ent it  is  impossible  to  assign 
any  limit  where  the  vessels  cease 
to  be  simple  carriers  of  blood, 
and  it  is  not  known  to  what 
part  of  the  vascular  system  the 
processes  of  nutrition  are  exclu- 
sively confined.  The  divisions 
of  the  blood-vessels  must  be,  to 

FIG.  31.—  Capillary  blood-vessels  (Landois).  .  ,  .          '1/1 

The  boundaries  of  the  cells  (cement-substance  between  the    a   certain    extent,  arbitrarily  de- 


endothelium)  is  blackened  with  silver  nitrate.    The  nu-     r»     _j 
clei  of  the  endothelium  are  brought  out  by  staining.         mied. 


/%c,f    c.imWlr> 
mosi    Simple, 


PHYSIOLOGICAL  ANATOMY  OF  THE  CAPILLARIES.  79 

what  seems  to  be  the  most  physiological  view,  is  to  regard  as  capillaries  those 
vessels  which  have  but  a  single  coat ;  for  in  these,  the  blood  is  brought  in 
closest  proximity  to  the  tissues.  Vessels  which  are  provided,  in  addition, 
with  a  muscular  or  with  muscular  and  fibrous  coats  are  to  be  regarded 
either  as  small  arteries  or  as  venous  radicles.  This  view  is  favored  by  the 
character  of  the  currents  of  blood  as  seen  in  microscopical  observation  of 
the  circulation  in  transparent  parts.  Here  an  impulse  is  observed  with 
each  contraction  of  the  heart,  until  the  vessels  have  but  one  coat  and  are 
so  narrow  as  to  allow  the  passage  of  but  a  single  line  of  blood-corpuscles. 

Physiological  Anatomy  of  the  Capillaries. — If  the  arteries  be  followed 
out  to  their  minutest  ramifications,  they  will  be  found  progressively  dimin- 
ishing in  size  as  they  branch,  and  their  coats,  especially  the  muscular  coat, 
becoming  thinner  and  thinner,  until  at  last  they  present  an  internal,  struct- 
ureless coat  lined  by  endothelium  with  oval,  longitudinal  nuclei,  a  middle 
coat  formed  of  but  a  single  layer  of  circular  muscular  fibres,  and  an  external 
coat  composed  of  a  very  thin  layer  of  longitudinal  bundles  of  fibrous  tis- 
sue. These  vessels  are  ffa  to  ^^-  of  an  inch  (62*5  to  125  /A)  in  diameter. 
They  become  smaller  as  they  branch,  and  undoubtedly  possess  the  property 
of  contractility,  which  is  particularly  marked  in  the  arterial  system.  Follow- 
ing the  course  of  the  vessels,  when  they  are  reduced  in  size  to  about  -^J-g-  of 
an  inch  (31  /A),  the  external,  fibrous  coat  is  lost,  and  the  vessel  then  presents 
only  the  internal  coat  and  a  single  layer  of  muscular  fibres.  The  vessels 
become  smaller  as  they  branch,  finally  lose  the  muscular  fibres,  and  have  then 
but  a  single  coat.  These  last  will  be  regarded  as  the  true  capillary  vessels. 

It  was  formerly  thought  that  the  smallest  vessels,  which  are  described  as 
the  true  capillaries,  were  composed  of  a  single,  homogeneous  membrane, 
rsior  to  ^-gVo  of  an  inch  (1  to  10  //,)  thick,  with  nuclei  embedded  in  its 
substance,  but  not  provided  with  an  endothelial  lining;  but  it  has  been 
shown  that  the  membrane  is  homogeneous,  elastic,  perhaps  contractile,  and, 
in  some  parts  at  least,  provided  with  fusiform  or  polygonal  endothelium  of  ex- 
cessive tenuity.  The  borders  of  the  endothelial  cells  may  be  seen  after  stain- 
ing the  vessels  with  silver  nitrate.  In  the  smallest  capillaries  the  cells  are 
narrow  and  elongated  or  fusiform ;  and  in  the  larger  vessels  they  are  more 
polygonal,  with  very  irregular  borders.  The  nuclei  in  the  walls  of  the  vessels 
belong  to  this  layer  of  endothelium.  By  the  same  process  of  staining  with 
silver  nitrate,  irregular,  non-nucleated  areas  are  frequently  brought  into  view ; 
and  it  has  been  supposed  by  some  that  these  indicate  the  presence  of 
stomata,  or  orifices  in  the  walls  of  the  vessels. 

The  diameter  of  the  capillaries  is  generally  as  small  as  that  of  the  blood- 
corpuscles,  or  it  may  be  smaller ;  so  that  these  bodies  always  move  in  a  single 
line  and  must  become  deformed  in  passing  through  the  smallest  vessels, 
recovering  their  normal  shape,  however,  when  they  pass  into  vessels  of  larger 
size.  The  capillaries  are  smallest  in  the  nervous  and  muscular  tissue,  retina 
and  patches  of  Peyer,  where  they  have  a  diameter  of  g^  to  ^^  of  an 
inch  (4-25  to  6*25  //,).  In  the  papillary  layer  of  the  skin  and  in  the  mucous 
membranes,  they  are  ^^^  to  ^g-^  of  an  inch  (6*25  to  10  /*)  in  diameter. 


80 


CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 


They  are  largest  in  the  glands  and  bones,  where  they  are  ^oW  to 
of  an  inch  (8-3  to  12-5  //.)  in  diameter.  These  measurements  indicate  the 
size  of  the  vessels  and  not  their  caliber.  Taking  out  the  thickness  of  their 
walls,  it  is  only  the  very  largest  of  them  that  will  allow  the  passage  of  a 
blood-disk  without  a  change  in  its  form.  The  average  length  of  the  capil- 
lary vessels  is  about  -g^  of  an  inch  (0-5  mm.). 


FIG.  32. — Small  artery  and  capillaries  from  the  musct — 

magnified  400  diameters  (from  a  photograph  taken  at  the  Ui 
This  preparation  shows  the  endothelium  of  the  vessels.    It  is  injected  with  silver  nitrate,  stained  with 
carmine  and  mounted  in  Canada  balsam. 


•xi  ts  of  the  urinary  bladder  of  the  frog  ; 
United  States  Army  Medical  Museum). 


Unlike  the  arteries,  which  grow  smaller  as  they  branch,  and  the  veins, 
which  become  larger,  in  following  the  course  of  the  blood,  by  union  with 
each  other,  the  capillaries  form  a  true  plexus  of  vessels  of  nearly  uniform 
diameter,  branching  and  inosculating  in  every  direction  and  distributing 
blood  to  the  parts  as  their  physiological  necessities  demand.  This  mode  of 
inosculation  is  peculiar  to  these  vessels,  and  the  plexus  is  rich  in  the  tissues, 
as  a  general  rule,  in  proportion  to  the  activity  of  their  nutrition.  Although 
their  arrangement  presents  certain  differences  in  different  organs,  the  capil- 
lary vessels  have  everywhere  the  same  general  characteristics,  the  most  promi- 
nent of  which  are  the  nearly  uniform  diameter  and  an  absence  of  any  definite 
direction.  The  net-work  thus  formed  is  very  rich  in  the  substance  of  the 
glands  and  in  the  organs  of  absorption ;  but  the  vessels  are  distended  with 


PHYSIOLOGICAL  ANATOMY  OF  THE  CAPILLARIES. 


81 


blood  only  during  the  physiological  activity  of  these  parts.  In  the  lungs  the 
meshes  are  particularly  close.  In  other  parts  the  vessels  are  not  so  abun- 
dant, presenting  great  variations  in  different  tissues.  In  the  muscles  and 
nerves,  in  which  nutrition  is  very  active,  the  supply  is  much  more  abundant 
than  in  other  parts,  like  fibro-serous  membranes,  tendons  etc.  In  none  of 
the  tissues  do  the  capillaries  penetrate  the  anatomical  elements  of  the  part, 
as  the  ultimate  muscular  or  nervous  fibres.  Some  tissues  receive  no  blood,  or 
at  least  they  contain  no  vessels  which  are  capable  of  carrying  red  blood,  and 
are  nourished  by  imbibition  of  the  nutrient  plasma  of  the  circulating  fluid. 
Examples  of  these,  which  are  called  extra  vascular  tissues,  are  cartilage,  nails 
and  hair. 

The  capacity  of  the  capillary  system  is  very  great.  It  is  necessary  only  to 
consider  the  great  vascularity  of  the  skin,  mucous  membranes  or  muscles,  to 
appreciate  this  fact.  In  injections  of  these  parts,  it  seems,  on  microscopical 
examination,  as  though  they  contained  nothing  but  capillaries ;  but  in  prepa- 
rations of  this  kind,  the  elastic  and  yielding  coats  of  the  capillaries  are 
distended  to  their  utmost  limit.  Under  some  conditions,  in  health,  they 
are  largely  distended  with  blood,  as  in  the  mucous  lining  of  the  alimentary 
canal  during  digestion,  the  whole  surface  presenting  a  vivid-red  color,  indi- 
cating the  great  richness  of  the  capillary  plexus.  Estimates  of  the  capacity 
of  the  capillary  system,  as  compared  with  the  arterial  system,  have  been 
made,  but  they  are  simply  approximative.  The  various  estimates  given  are 
founded  upon  calculations  from  microscopical  examinations  of  the  rapidity 
of  the  capillary  circulation  as  compared  with  the  circulation  in  the  arteries. 
In  this  way,  it 
has  been  estima- 
ted that  the  ca- 
pacity of  the 
capillary  system 
is  between  five 
hundred  and 
eight  hundred 
times  that  of  the 
arterial  system. 
These  estimates, 
however,  must 
be  regarded  as 
mere  supposi- 
tions based  up- 
on no  very  ac- 
curate data. 

Phenomena  of  the  Capillary  Circulation. — The  most  convenient  situation 
for  observation  of  the  capillary  circulation  is  the  tongue  or  the  web  of  the 
frog.  Here  may  be  studied,  not  only  the  movement  of  the  blood  in  the  true 
capillaries,  but  the  circulation  in  the  smallest  arteries  and  veins,  the  variations 
in  caliber  of  these  vessels,  especially  the  arterioles,  by  the  action  of  their 


FIG.  33.— Web  of  the  frog's  hind-foot ;  magnified  (Wagner). 
a,  a,  veins  ;  6,  b,  b,  arteries. 


82 


CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 


muscular  coat,  and,  indeed,  the  action  of  vessels  of  considerable  size.  This 
has  been  a  valuable  means  of  studying  the  circulation  in  the  capillaries  as 
contrasted  with  the  flow  in  the  small  arteries  and  veins,  and  the  only  one, 
indeed,  which  could  give  any  definite  idea  of  the  action  of  these  vessels. 

In  studying  the  circulation  under  the  microscope,  the  anatomical  division 
of  the  blood  into  corpuscles  and  a  clear  plasma  is  observed.  This  is  peculiarly 
evident  in  cold-blooded  animals,  the  corpuscles  being  comparatively  large  and 
floating  in  a  plasma  which  forms  a  distinct  layer  next  the  walls  of  the  vessel. 

The  leucocytes,  which 
are  much  fewer  than 
the  red  corpuscles,  are 
generally  found  in  the 
layer  of  plasma. 

In  vessels  of  consid- 
erable size  as  well  as  in 
some  capillaries,  the  cor- 
puscles, occupying  the 
central  portion,  move 
with  much  greater  ra- 
pidity than  the  rest  of 
the  blood,  leaving  a  lay- 
er of  clear  plasma  at 
the  sides,  which  is  near- 
ly motionless.  This 
phenomenon  is  in  obe- 

dience      to      a 


Fra.  34.—  Circulation  in  the  web  of  the  frog's  foot  (Wagner). 
The  black  spots,  some  of  them  star-shaped,  are  collections  of  pigment. 

a,  a  venous  trunk,  composed  of  three  principal  branches  (6,  6,  b),    law  regulating  the  paS- 
and  covered  with  a  plexus  of  smaller  vessels  (c,  c).  „  ,  .       .  ,      .  , 

sage  of  liquids  through 

capillary  tubes  for  which  they  have  an  attraction,  such  as  exists,  for  exam- 
ple, between  the  blood  and  the  vessels.  In  tubes  reduced  to  a  diameter  ap- 
proximating that  of  the  capillaries,  the  attractive  force  exerted  by  their  walls 
upon  a  liquid,  causing  it  to  enter  the  tube  to  a  certain  distance,  becomes  an 
obstacle  to  the  passage  of  fluid  in  obedience  to  pressure.  Of  course,  as  the 
diameter  of  the  tube  is  reduced,  this  force  becomes  relatively  increased,  for 
a  larger  proportion  of  the  liquid  contents  is  brought  in  contact  with  it.  In 
the  smallest  arteries  and  veins,  and  still  more  in  the  capillaries,  the  capillary 
attraction  is  sufficient  to  produce  the  motionless  layer,  sometimes  called  the 
"  still  layer,"  and  the  liquid  moves  only  in  the  central  portion.  The  plasma 
occupies  the  position  next  the  walls  of  the  vessels,  for  it  is  this  portion  of  the 
blood  which  is  capable  of  "  wetting  "  the  tubes.  The  transparent  layer  was 
observed  by  Malpighi,  Haller  and  all  who  have  described  the  capillary  circu- 
lation. Poiseuille  recognized  its  true  relation  to  the  blood-current  and  ex- 
plained the  phenomenon  of  the  still  layer  by  physical  laAvs,  which  had  been 
previously  established  with  regard  to  the  flow  of  liquids  in  tubes  of  the  di- 
ameter of  one  twenty-fifth  to  one  one-eighth  of  an  inch  (1  to  3'2  mm.),  but 
which  he  had  succeeded  in  applying  to  tubes  of  the  size  of  the  capillaries. 


CIRCULATION  IN  THE  CAPILLARIES. 


83 


A  red  corpuscle  occasionally  becomes  involved  in  the  still  layer,  when  it 
moves  slowly,  turning  over  and  over,  or  even  remains  stationary  for  a  time, 


FIG.  35.—  Small  artery  and  capillaries  from  the  lung  of  a  frog ;  magnified  500  diameters  (from  a 
photograph  taken  at  the  United  States  Army  Medical  Museum). 

until  it  is  taken  up  again  and  carried  along  with  the  central  current.  A  few 
leucocytes  are  constantly  seen  in  this  layer.  They  move  along  slowly  and 
apparently  have  a  tendency  to  adhere  to  the  walls  of  the  vessel.  This  is  due 
to  the  adhesive  character  of  the  surface  of  the  white  corpuscles  as  compared 
with  the  red,  which  can  easily  be  observed  in  examining  a  drop  of  blood 
between  glass  surfaces,  the  red  corpuscles  moving  about  freely,  while  the 
white  corpuscles  have  a  tendency  to  adhere  to  the  glass. 

Great  differences  exist  in  the  character  of  the  flow  of  blood  in  the  three 
varieties  of  vessels  which  are  under  observation.  In  the  arterioles,  which 
may  be  distinguished  from  the  capillaries  by  their  size  and  the  presence  of 
the  muscular  and  fibrous  coats,  the  movement  is  distinctly  remittent,  even  in 
their  most  minute  ramifications.  The  blood  moves  in  them  with  much 
greater  rapidity  than  in  either  the  capillaries  or  veins.  They  become  smaller 
as  they  branch,  and  carry  the  blood  always  in  the  direction  of  the  capillaries. 
The  veins,  which  are  relatively  larger  than  the  arteries,  carry  the  blood 
more  slowly  and  in  a  continuous  stream  from  the  capillaries  toward  the 
heart.  In  b.oth  the  arteries  and  veins  the  current  is  frequently  so  rapid 


CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 


that  the  form  of  the  corpuscles  can  not  be  distinguished.  Only  a  few  of 
the  white  corpuscles  occupy  the  still  layer,  the  others  being  carried  on  in  the 
central  current. 

The  circulation  in  the  true  capillaries  is  sui  generis.  Here  the  blood  is 
distributed  in  every  direction,  in  vessels  of  nearly  uniform  diameter.  The 
vessels  are  generally  so  small  as  to  admit  but  a  single  row  of  corpuscles.  In 
a  single  vessel,  a  line  of  corpuscles  may  be  seen  moving  in  one  direction  at 
one  moment,  a  few  moments  after,  taking  a  directly  opposite  course.  When 
the  circulation  is  normal,  the  movement  in  the  capillaries  is  always  quite 
slow  as  compared  with  the  movement  in  the  arterioles,  and  is  continuous. 
Here,  at  last,  the  intermittent  impulse  of  the  heart  is  lost.  The  corpuscles 
do  not  necessarily  circulate  in  all  the  capillaries  that  are  in  the  field  of  view. 
Certain  vessels  may  not  receive  a  corpuscle  for  some  time,  but  afterward, 
one  or  two  corpuscles  become  engaged  in  them  and  a  current  is  estab- 
lished. A  corpuscle  is  sometimes  seen  caught  at  the  angle  where  a  vessel 
divides  into  two,  remaining  fixed  for  a  time,  distorted  and  bent  by  the  force 
of  the  current.  It  soon  becomes  released,  and  as  it  enters  the  vessel,  it 
regains  its  original  form.  In  some  of  the  vessels  of  smallest  size,  the  cor- 
puscles are  slightly  de- 
formed as  they  pass 
through.  The  scene  is 
changed  with  every  dif- 
ferent part  which  is  ex- 
amined. In  the  tongue, 
in  addition  to  the  arte- 
rioles and  venules  with 
the  rich  net- work  of  cap- 
illaries, dark  -  bordered 
nerve  -  fibres,  striated 
muscular  fibres,  and  epi- 
thelium can  be  distin- 
guished. In  the  lungs 
large,  polygonal  air-cells 
are  observed,  bounded 
by  capillary  vessels,  in 
which  the  corpuscles 
move  with  great  rapidi- 
ty. It  has  been  observed, 
also,  that  the  larger  ves- 
sels in  the  lungs  are 
crowded  to  their  utmost 
capacity  with  corpuscles,  leaving  no  still  layer  next  the  walls,  such  as  is  seen 
in  the  circulation  in  other  situations. 

Pressure  of  Blood  in  the  Capillaries. — There  is,  'apparently,  no  way  of 
directly  estimating  the  pressure  of  blood  in  the  capillaries.  If,  however,  a 
glass  plate  be  placed  upon  a  part  in  which  the  capillary  circulation  is  active 


FIG.  36.—  Portion  of  the  lung  of  a  live  triton,  drawn  under  the  mi- 
croscope and  magnified  150  diameters  (Wagner). 


CIRCULATION  IN  THE  CAPILLARIES.  85 

and  be  weighted  until  the  subjacent  capillaries  are  emptied,  an  approximate 
idea  of  the  blood-pressure  in  the  vessels  may  be  obtained.  Experiments 
made  in  this  way,  by  Von  Kries,  show  that  the  pressure  in  the  capillaries  of 
the  hand  raised  above  the  head  is  equal  to  a  little  less  than  one  inch  (24  mm.) 
of  mercury ;  in  the  hand  hanging  down,  a  little  more  than  two  inches  (54 
mm.) ;  and  in  the  ear,  about  0*8  of  an  inch  (20  mm). 

Rapidity  of  tlu1  Capillary  Circulation. — The  circulation  in  the  capillaries 
of  a  part  is  subject  to  such  great  variations  and  the  differences  in  different 
situations  are  so  considerable,  that  it  is  impossible  to  give  any  definite  rate 
which  will  represent  the  general  rapidity  of  the  capillary  circulation.  It  is 
for  this  reason  that  it  lias  been  found  impracticable  to  estimate  accurately 
the  capacity  of  the  capillary  as  compared  with  the  arterial  system.  In  view 
of  the  great  uncertainty  in  the  methods  employed  in  the  estimation  of  the 
rapidity  of  the  flow  of  blood  in  the  capillaries,  it  seems  unnecessary  to  discuss 
this  question  fully.  Volkmann  calculated  the  rapidity  in  the  mesentery  of 
the  dog  and  found  it  to  be  about  one-thirtieth  of  an  inch  (0-85  mm.)  per 
second.  Vierordt  made  a  number  of  curious  observations  upon  himself,  by 
which  he  professed  to  be  able  to  estimate  the  rapidity  of  the  circulation  in 
the  little  vessels  of  the  eye ;  and  by  certain  calculations,  he  formed  an  esti- 
mate of  its  rapidity,  putting  it  at  one-fortieth  to  one-twenty-eighth  of  an 
inch  (O63  and  O9  mm.)  per  second,  which  estimate  may  be  provisionally 
adopted  as  the  probable  rate  in  the  human  subject. 

Relations  of  the  Capillary  Circulation  to  Respiration. — In  treating  of  the 
influence  of  respiration  upon  the  action  of  the  heart,  the  arterial  pressure, 
pulse  etc.,  it  has  already  been  stated  that  non-aerated  blood  can  not  circulate 
freely  in  the  capillaries.  Various  ideas  with  regard  to  the  effects  of  asphyxia 
upon  the  circulation  have  been  advanced,  which  will  be  again  discussed  in 
connection  with  the  physiology  of  respiration.  It  is  well  known  that  arrest 
of  respiration  produces  arrest  of  circulation. 

The  immediate  effects  of  asphyxia  upon  the  circulation  are  referable  to 
the  general  capillary  system.  In  a  series  of  experiments  made  in  1857,  the 
medulla  oblongata  was  broken  up,  and  the  web  of  the  foot  was  submitted  to 
microscopical  examination.  This  operation  does  not  interfere  with  the  cir- 
culation, which  may  be  observed  for  hours  without  difficulty.  The  cuta- 
neous surface  was  then  coated  with  collodion,  care  only  being  taken  to  avoid 
the  web  under  observation.  The  effect  on  the  circulation  was  immediate. 
It  instantly  became  less  rapid,  until,  at  the  expiration  of  twenty  minutes,  it 
had  entirely  ceased.  The  entire  coating  of  collodion  was  then  instantly  peeled 
off.  Quite  a  rapid  circulation  immediately  began,  but  it  soon  began  to  de- 
cline and  in  twenty  minutes  had  almost  ceased.  In  another  observation,  the 
coating  of  collodion  was  applied  without  destroying  the  medulla.  The  cir- 
culation was  affected  in  the  same  manner  as  before  and  ceased  in  twenty- 
five  minutes  (Flint).  These  experiments,  taken  in  connection  with  observa- 
tions on  the  influence  of  asphyxia  upon  the  arterial  pressure,  show  that  non- 
aerated  blood  can  not  circulate  freely  in  the  systemic  capillaries.  Non- 
aerated  blood,  however,  can  be  forced  through  them  with  a  syringe,  and 


86  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

even  in  asphyxia,  it  passes  slowly  into  the  veins.  If  air  be  admitted  to  the 
lungs  before  the  heart  has  lost  its  contractility,  the  circulation  is  restored. 
No  differences  in  the  capillary  circulation  have  been  noticed  accompanying 
the  ordinary  acts  of  inspiration  and  expiration. 

Causes  of  the  Capillary  Circulation. — The  contractions  of  the  left  ventri- 
cle are  evidently  capable  of  giving  an  impulse  to  the  blood  in  the  smallest 
arterioles ;  for  a  marked  acceleration  of  the  current  accompanying  each  sys- 
tole can  be  distinguished  in  all  but  the  true  capillaries.  It  has  also  been 
shown  by  experiments  after  death,  that  blood  can  be  forced  through  the 
capillary  system  and  returned  by  the  veins  by  a  force  less  than  that  exerted 
by  the  left  ventricle.  This,  however,  can  not  rigidly  be  applied  to  the  nat- 
ural circulation,  as  the  smallest  arteries  during  life  are  endowed  with  con- 
tractility, which  is  capable  of  modifying  the  blood-current.  Sharpey  adapted 
a  syringe,  with  a  hEemadynamometer  attached,  to  the  aorta  of  a  dog  just 
killed,  and  found  that  fresh  defibrinated  blood  could  be  made  to  pass  through 
the  double  capillary  systems  of  the  intestines  and  liver,  by  a  pressure  of  three 
and  a  half  inches  (89  mm.)  of  mercury.  It  spurted  out  at  the  vein  in  a  full 
jet  under  a  pressure  of  five  inches  (127  mm.).  In  this  observation,  the  aorta 
was  tied  just  above  the  renal  arteries.  The  same  pressure,  the  ligature  being 
removed,  forced  the  blood  through  the  capillaries  of  the  inferior  extremities. 

It  is  thus  seen  that  the  pressure  in  the  arteries  which  forces  the  blood 
toward  the  capillaries  is  competent,  unless  opposed  by  contraction  of  the 
arterioles,  not  only  to  cause  the  blood  to  circulate  in  the  capillaries,  but  to 
return  it  to  the  heart  by  the  veins ;  and  the  only  questions  to  be  considered 
are  first,  whether  there  be  any  reason  why  the  force  of  the  heart  should  not 
operate  on  the  blood  in  the  capillaries,  and  second,  whether  there  be  any 
force  in  these  vessels  which  is  superadded  to  the  action  of  the  heart.  The 
first  of  these  questions  is  answered  by  microscopical  observations  on  the  cir- 
culation. A  distinct  impulse,  following  each  ventricular  systole,  is  observed 
in  the  smallest  arteries ;  the  blood  flows  from  them  directly  and  freely  into 
the  capillaries ;  and  there  is  no  ground  for  the  supposition  that  the  force  is 
not  propagated  to  this  system  of  vessels.  There  is,  therefore,  a  force,  the 
action  of  the  heart,  which  is  capable  of  producing  the  capillary  circulation ; 
and  there  is  nothing  in  the  phenomena  of  the  circulation  in  these  vessels 
which  is  inconsistent  with  its  full  operation.  When  the  heart  ceases  its 
action,  movements  in  the  capillaries  are  sometimes  due  to  the  contractions  of 
the  arteries,  an  action  which  has  already  been  fully  described.  Movements 
which  have  been  observed  in  membranes  detached  from  the  body  were  un- 
doubtedly due  to  the  mere  emptying  of  the  divided  vessels  or  to  simple  gravi- 
tation. 

There  is  a  circulation  of  the  blood  in  the  area  vasculosa,  the  first  blood- 
vessels that  are  developed  before  the  heart  is  formed ;  but  there  are  no  defi- 
nite and  reliable  observations  which  show  that  there  is  any  regular  movement 
of  the  blood,  which  can  be  likened  to  the  circulation  as  it  is  observed  after 
the  development  of  the  heart,  anterior  to  the  appearance  of  a  contractile  cen- 
tral organ.  Another  example  of  what  is  supposed  to  be  circulation  without 


PHYSIOLOGICAL  ANATOMY  OF  THE  VEINS.  87 

the  intervention  of  the  heart  is  in  cases  of  acardiac  foetuses.  Monsters  with- 
out a  heart,  which  have  undergone  considerable  development  and  which  pre- 
sent systems  of  arteries,  capillaries  and  veins,  have  been  described.  All  of 
these,  however,  are  accompanied  by  a  twin,  in  which  the  development  of  the 
circulatory  system  is  quite  or  nearly  perfect. 

Influence  of  Temperature  on  the  Capillary  Circulation. — Within  moder- 
ate limits,  a  low  temperature,  produced  by  local  applications,  has  been  found 
to  diminish  the  quantity  of  blood  sent  to  the  capillaries  and  retard  the  circu- 
lation, white  a  high  temperature  increases  the  supply  of  blood  and  accelerates 
its  current.  Poiseuille  found  that  when  a  piece  of  ice  was  applied  to  the  web 
of  a  frog's  foot,  the  mesentery  of  a  small  warm-blooded  animal  or  to  any  part 
in  which  the  capillary  circulation  can  be  observed,  the  number  of  corpuscles 
circulating  in  the  arterioles  became  very  much  diminished,  "  those  which  car- 
ried two  or  three  rows  of  corpuscles  giving  passage  to  but  a  single  row."  The 
circulation  in  the  capillaries  first  became  slower  and  then  entirely  ceased  in 
parts.  On  removing  the  ice,  in  a  very  few  minutes  the  circulation  regained 
its  former  characters.  When,  on  the  other  hand,  the  part  was  covered  with 
water  at  104°  Fahr.  (40°  C.),  the  rapidity  of  the  current  in  the  capillaries  was 
so  much  increased  that  the  form  of  the  corpuscles  could  with  difficulty  be 
distinguished. 

CIRCULATION  OF  THE  BLOOD  IN  THE  VEINS. 

The  blood,  distributed  to  the  capillaries  of  all  the  tissues  and  organs  by 
the  arteries,  is  colected  from  these  parts  in  the  veins  and  carried  back  to  the 
heart.  In  studying  the  anatomy  of  the  capillaries  or  in  observing  the  passage 
of  the  blood  from  the  capillaries  to  larger  vessels  in  parts  of  the  living  organ- 
ism which  can  be  submitted  to  microscopical  examination,  it  is  seen  that 
the  capillaries,  vessels  of  nearly  uniform  diameter  and  anastomosing  in  every 
direction,  empty  into  a  system  of  vessels,  which,  by  union  with  others,  become 
larger  and  larger,  and  carry  the  blood  away  in  a  uniform  current.  These  are 
called  the  venules,  or  venous  radicles.  They  are  the  peripheral  radicles  of 
the  vessels  which  carry  the  blood  to  the  heart. 

The  venous  system  may  be  considered,  in  general  terms,  as  divided  into 
two  sets  of  vessels  ;  one,  which  is  deep-seated  and  situated  in  proximity  to  the 
arteries,  and  the  other,  which  is  superficial  and  receives  the  greatest  part  of 
the  blood  from  the  cutaneous  surface.  The  entire  capacity  of  these  vessels, 
as  compared  with  that  of  the  arteries,  is  very  great.  As  a  general  rule,  each 
vein,  when  fully  distended,  is  larger  than  its  adjacent  artesy.  Many  arteries 
are  accompanied  by  two  veins,  as  the  arteries  of  the  extremities ;  while  cer- 
tain of  them,  like  the  brachial  or  spermatic,  have  more  than  two.  Added  to 
these,  are  the  superficial  veins  which  have  no  corresponding  arteries.  It  is 
true  that  some  arteries  have  no  corresponding  veins,  but  examples  of  this 
kind  are  not  sufficient  in  number  to  diminish,  in  any  marked  degree,  the 
great  preponderance  of  the  veins,  both  in  number  and  volume.  It  is  impos- 
sible to  give  an  accurate  estimate  of  the  extreme  capacity  of  the  veins  as 
compared  with  the  arteries,  but  it  must  be  much  greater.  Borelli  estimated 


88 


CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 


that  the  capacity  of  the  veins  was  to  the  capacity  of  the  arteries,  as  4  to  1 ; 
and  Haller,  as  2J  to  1.     The  proportion  is  very  variable  in  different  parts  of 


FIG.  37. — Venous  radicles  uniting  to  form  a  small  vein,  from  the  muscular  coat  of  the  urinary  bladder 
of  the  frog ;  magnified  400  diameters  (from  a  photograph  taken  at  the  United  States  Army  Medical 
Museum). 

This  preparation  shows  the  endothelium  of  the  vessels.    It  is  injected  with  silver  nitrate,  stained  with 
carmine  and  mounted  in  Canada  balsam. 

the  body.  In  some  situations  the  capacity  of  the  veins  and  arteries  is  about 
equal ;  while  in  others,  as  in  the  pia  mater,  the  veins  will  contain,  when  fully 
distended,  six  times  as  much  as  the  arteries. 

In  attempting  to  compare  the  quantity  of  blood  normally  circulating  in 
the  veins  with  that  contained  in  the  arteries,  such  variations  are  found  at 
different  times  and  in  different  parts,  both  in  the  quantity  of  blood,  rapidity 
of  circulation,  pressure  etc.,  that  a  definite  estimate  is  impossible.  It  would  be 
unprofitable  to  attempt  even  an  approximate  comparison,  as  the  variations  in 
the  venous  circulation  constitute  one  of  its  most  important  physiological 
peculiarities,  which  must  be  fully  appreciated  in  order  to  form  a  just  idea  of 
the  uses  of  the  veins.  The  arteries  are  always  full,  and  their  tension  is  sub- 
ject to  comparatively  slight  variations.  Following  the  blood  into  the  capil- 
laries, important  modifications  in  the  circulation  are  observed,  with  varying 
physiological  conditions  of  the  parts.  As  would  naturally  be  expected,  the 
condition  of  the  veins  varies  with  the  changes  in  the  capillaries  from  which 
the  blood  is  received.  In  addition  to  this,  there  are  independent  variations, 


PHYSIOLOGICAL  ANATOMY  OP  THE  VEINS.  89 

as  in  the  erectile  tissues,  in  the  veins  of  the  alimentary  canal  during  absorp- 
tion, in  veins  subject  to  pressure,  etc. 

Following  the  veins  in  their  course,  it  is  observed  that  anastomoses  with 
each  other  form  the  rule,  and  not  the  exception,  as  in  the  arteries.  There 
is  always  a  number  of  channels  by  which  the  blood  may  be  returned  from  a 
part ;  and  if  one  vessel  be  obstructed  from  any  cause,  the  current  is  simply 
diverted  into  another.  The  veins  do  not  present  a  true  anastomosing  plexus, 
such  as  exists  in  the  capillary  system,  but  simply  an  arrangement  by  which 
the  blood  can  readily  find  its  way  back  to  the  heart,  and  by  which  the  vessels 
may  accommodate  themselves  to  the  frequent  variations  in  the  quantity  of 
their  fluid  contents.  This,  with  the  peculiar  valvular  arrangement  which 
exists  in  all  but  the  veins  of  the  cavities,  provides  against  obstruction  to  the 
flow  of  blood  through  as  well  as  from  the  capillaries,  in  which  it  seems  essen- 
tial to  the  proper  nutrition  and  action  of  parts  that  the  quantity  and  course 
of  the  blood  should  be  regulated  exclusively  through  the  arterial  system. 

Collected  by  the  veins  from  all  parts  of  the  body,  the  blood  is  returned  to 
the  right  auricle,  from  the  head  and  upper  extremities  by  the  superior  vena 
cava,  from  the  trunk  and  lower  extremities,  by  the  inferior  vena  cava,  and 
from  the  substance  of  the  heart,  by  the  coronary  veins. 

Structure  and  Properties  of  the  Veins. — The  structure  of  the  veins  is 
more  complex  than  that  of  the  arteries.  Their  walls,  which  are  always  much 
thinner  than  the  walls  of  the  arteries,  may  be  divided  into  a  number  of  layers ; 
but  for  convenience  of  physiological  description,  they  may  be  regarded  as 
presenting  three  distinct  coats.  These  have  properties  which  are  somewhat 
distinctive  for  each,  although  not  as  much  so  as  those  of  the  three  coats  of 
the  arteries. 

The  internal  coat  of  the  veins  is  a  continuation  of  the  single  coat  of  the 
capillaries  and  of  the  internal  coat  of  the  arteries.  It  is  a  simple,  homogene- 
ous membrane,  somewhat  thinner  than  in  the  arteries,  lined  by  a  delicate 
layer  of  polygonal  endothelium,  the  cells  of  which  are  shorter  and  broader 
than  the  endothelial  cells  of  the  arteries. 

The  middle  coat  is  divided  by  some  anatomists  into  two  layers ;  an  in- 
ternal layer,  which  is  composed  chiefly  of  longitudinal  fibres,  and  an  external 
layer,  in  which  the  fibres  have  a  circular  direction.  These  two  layers  are 
intimately  adherent  and  are  quite  closely  attached  to  the  internal  coat.  The 
longitudinal  fibres  are  composed  of  connective-tissue  fibres  mingled  with  a 
large  number  of  the  smallest  variety  of  the  elastic  fibres.  This  layer  con- 
tains a  large  number  of  capillary  vessels  (vasa  vasorum).  The  circular  fibres 
are  composed  of  elastic  tissue,  some  of  the  fibres  of  the  same  variety  as  is 
found  in  the  longitudinal  layer,  some  of  medium  size,  and  some  in  the  form 
of  the  "  fenestrated  membrane."  In  addition,  there  are  inelastic  fibres  inter- 
lacing in  every  direction  and  mingled  with  capillary  blood-vessels,  and  non- 
striated  muscular  fibres.  In  the  human  subject,  in  the  veins  of  the  central 
portion  of  the  nervous  system,  the  dura  mater,  the  pia  mater,  the  bones,  the 
retina,  the  vena  cava  descendens,  the  thoracic  portion  of  the  vena  cava 
ascendens,  the  external  and  internal  jugulars  and  the  subclavian  veins,  there 


90  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

are  no  muscular  fibres  in  the  middle  coat.  In  the  larger  veins,  such  as  the 
abdominal  vena  cava,  the  iliac,  crural,  popliteal,  mesenteric  and  axillary  veins, 
there  are  both  longitudinal  and  circular  fibres.  In  the  smaller  veins,  the 
fibres  are  circular.  In  the  smallest  veins,  the  middle  coat  is  composed  of 
fine  fibres  of  connective  tissue  with  a  very  few  muscular  fibres. 

The  external  coat  of  the  veins  is  composed  of  ordinary  fibrous  tissue,  like 
that  of  the  corresponding  coat  of  the  arteries.  In  the  largest  veins,  particu- 
larly those  of  the  abdominal  cavity,  this  coat  contains  a  layer  of  longitudinal, 
non-striated  muscular  fibres.  In  the  veins  near  the  heart,  are  found  a  few 
striated  fibres,  which  are  continued  on  to  the  veins  from  the  auricles.  In  some 
of  the  inferior  animals,  as  the  turtle,  these  fibres  are  quite  thick,  and  pulsa- 
tion of  the  veins  in  the  immediate  vicinity  of  the  heart  is  very  marked.  In 
nearly  all  veins,  the  external  coat  is  several  times  thicker  than  the  internal 
coat.  This  is  most  marked  in  the  larger  veins,  in  which  the  middle  coat, 
particularly  the  layer  of  muscular  fibres,  is  very  slightly  developed. 

The  venous  sinuses  and  the  veins  which  pass  through  bony  tissue  have 
only  the  internal  coat,  to  which  are  superadded  a  few  longitudinal  fibres,  the 
whole  being  closely  attached  to  the  surrounding  parts.  As  examples,  may  be 
mentioned  the  sinuses  of  the  dura  mater  and  the  veins  of  the  large  bones  of 
the  skull.  In  the  first  instance,  there  is  little  more  than  the  internal  coat  of 
the  vein  firmly  attached  to  the  surrounding  layers  of  the  dura  mater.  In 
the  second  instance,  the  same  thin  membrane  is  adherent  to  canals  formed 
by  a  layer  of  compact  bony  tissue.  The  veins  are  much  more  closely  adher- 
ent to  the  surrounding  tissues  than  the  arteries,  particularly  when  they  pass 
between  layers  of  aponeurosis. 

The  peculiarities  in  the  anatomy  of  the  veins  indicate  considerable  dif- 
ferences in  their  properties  as  compared  with  the  arteries.  When  a  vein  is  cut 
across,  its  walls  fall  together,  if  not  supported  by  adhesions  to  surrounding 
tissues,  so  that  its  caliber  is  nearly  or  quite  obliterated.  The  elastic  tissue, 
which  gives  to  the  larger  arteries  their  great  thickness,  is  very  scanty  in  the 
veins,  and  the  thin  walls  collapse  when  not  sustained  by  liquid  in  the  interior 
of  the  vessels. 

Although  with  much  thinner  and  apparently  weaker  walls,  the  veins,  as  a 
rule,  will  resist  a  greater  pressure  than  the  arteries.  Wintringham  (1740) 
showed  that  the  inferior  vena  cava  of  a  sheep,  just  above  the  opening  of 
the  renal  veins,  was  ruptured  by  a  pressure  of  one  hundred  and  seventy-six 
pounds  (79-8  kilos.),  while  the  aorta,  at  a  corresponding  point,  yielded  to  a 
pressure  of  one  hundred  and  fifty-eight  pounds  (71'7  kilos).  The  strength  of 
the  portal  vein  was  even  greater,  supporting  a  pressure  of  nearly  five  atmos- 
pheres, bearing  a  relation  to  the  vena  cava  of  six  to  five ;  yet  these  vessels  had 
hardly  one-fifth  the  thickness  of  the  arteries.  In  the  lower  extremities  in  the 
human  subject,  the  veins  are  much  thicker  and  stronger  than  in  other 
situations,  a  provision  against  the  increased  pressure  to  which  they  are  habit- 
ually subjected  in  the  upright  posture.  Wintringham  noticed  a  singular 
exception  to  the  general  rule  just  given.  In  the  vessels  of  the  glands  and  of 
the  spleen,  the  strength  of  the  arteries  was  much  greater  than  that  of  the 


VALVES  OF  THE  VEINS.  91 

veins.  The  splenic  vein  gave  way  under  a  pressure  of  little  more  than  one 
atmosphere,  while  the  artery  supported  a  pressure  of  more  than  six  atmos- 
pheres. 

The  different  influences  to  which  the  venous  and  arterial  circulations  are 
subject  serve  to  indicate  the  physiological  importance  of  the  great  difference 
in  the  strength  of  the  two  varieties  of  vessels.  It  is  true  that  in  the  arteries 
the  constant  pressure  is  greater  than  in  the  veins ;  but  it  is  nearly  the  same 
throughout  the  arterial  system,  and  the  great  extent  of  the  outlet  at  the 
periphery  provides  against  any  very  great  increase  in  pressure,  so  long  as  the 
blood  is  in  a  condition  which  enables  it  to  pass  into  the  capillaries.  The  mus- 
cular fibres  of  the  left  ventricle  have  but  a  limited  power,  and  when  the  pressure 
in  the  arteries  is  sufficient,  as  it  sometimes  is  in  asphyxia,  to  close  the  aortic 
valves  so  firmly  that  the  force  of  the  ventricle  will  not  open  them,  it  can  not  be 
increased.  At  the  same  time,  the  pressure  is  being  gradually  relieved  by  the 
capillaries,  through  which  the  blood  slowly  filters  even  when  completely  un- 
aerated.  With  the  veins  it  is  different.  The  blood  has  a  comparatively 
restricted  outlet  at  the  heart  and  is  received  by  the  capillaries  from  all  parts 
of  the  system.  The  vessels  are  provided  with  valves,  which  render  a  general 
backward  action  impossible.  Thus,  restricted  portions  of  the  venous  system, 
from  pressure  in  the  vessels,  increase  of  fluid  from  absorption,  accumulation 
by  force  of  gravity  and  other  causes,  may  be  subjected  to  great  and  sudden 
variations  in  pressure.  The  great  strength  of  these  vessels  enables  them 
ordinarily  to  suffer  these  variations  without  injury ;  although  varicose  veins 
in  various  parts  present  examples  of  the  effects  of  repeated  and  continued 
distention. 

The  veins  possess  a  considerable  degree  of  elasticity,  although  this  prop- 
erty is  not  so  marked  as  it  is  in  the  arteries.  If  a  portion  of  a  vein  distended 
with  blood  be  included  between  two  ligatures  and  a  small  opening  be  made  in 
the  vessel,  the  blood  will  be  ejected  with  some  force,  and  the  vessel  becomes 
much  reduced  in  caliber. 

It  has  been  shown  by  direct  experiment  that  the  veins  are  endowed  with 
the  peculiar  contractility  characteristic  of  the  action  of  the  non-striated  muscu- 
lar fibres.  On  the  application  of  electric  or  mechanical  stimulation,  they  con- 
tract slowly  and  gradually,  the  contraction  being  followed  by  a  correspond- 
ingly gradual  relaxation.  There  is  never  any  rhythmical  or  peristaltic 
movement  in  the  veins,  sufficient  to  assist  the  circulation.  The  only  regular 
movements  which  occur  are  seen  in  the  vessels  in  immediate  proximity  to  the 
right  auricle,  which  are  provided  with  a  few  fibres  similar  to  those  which  ex- 
ist in  the  walls  of  the  heart. 

Nerves  from  the  vaso-motor  system  have  been  demonstrated  in  the  walls 
of  the  larger  veins  but  have  not  been  followed  out  to  the  smaller  ramifica- 
tions of  the  vessels. 

Valves  of  the  Veins. — In  all  parts  of  the  venous  system,  except,  in  general 
terms,  in  the  abdominal,  thoracic  and  cerebral  cavities,  there  exist  little  mem- 
branous, semilunar  folds,  resembling  the  aortic  and  pulmonic  valves  of  the 
heart.  When  the  valves  are  closed,  their  convexities  look  toward  the  periph- 


92  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

ery.  In  the  great  majority  of  instances,  the  valves  exist  in  pairs,  but  they 
are  occasionally,  although  very  rarely  in  the  human  subject,  found  in  groups 
of  three.  They  are  seldom  if  ever  found  in  veins  of  a  less  diameter  than  one 
line  (2-l  mm.).  The  valves  are  formed  in  part  of  the  lining  membrane  of 
the  veins,  with  fine  fibres  of  connective  tissue,  elastic  fibres  and  non-striated 
muscular  fibres.  There  exists,  also,  a  fibrous  ring  following  the  line  of 
attachment  of  the  valvular  curtains  to  the  vein,  which  renders  the  vessel 
much  stronger  and  less  dilatable  here  than  in  the  intervals  between  the 
valves.  The  valves  are  most  abundant  in  the  veins  of  the  lower  extremities. 
They  are  generally  situated  just  below  the  point  where  a  small  vein  empties 
into  one  of  larger  size,  so  that  the  blood  as  it  enters  finds  an  immediate 
obstacle  to  passage  in  the  wrong  direction.  The  situation  of  the  valves  may 
be  readily  observed  in  any  of  the  superficial  veins.  If  the  flow  of  blood  be 
obstructed,  little  knots  will  be  formed  in  the  congested  vessels,  which  indicate 
the  position  and  action  of  the  valves.  When  the  vein  is  thus  congested  and 
knotted,  if  the  finger  be  pressed  along  the  vessel  in  the  direction  of  the  blood- 
current,  a  portion  situated  between  two  valves  may  be  emptied  of  blood ;  but 
it  is  impossible  to  empty  any  portion  of  the  vessel  by  pressing  the  blood  in 
the  opposite  direction  (Harvey).  On  slitting  open  a  vein,  it  is  easy  to  ob- 
serve the  shape,  attachment  and  extreme  delicacy  of  structure  of  the  valves. 
When  the  vessel  is  empty  or  when  fluid  moves  toward  the  heart,  the  valves 
are  closely  applied  to  the  walls ;  but  if  liquid  or  air  be  forced  in  the  opposite 
direction,  they  project  into  its  caliber,  and  by  the  application  of  their  free 
edges  to  each  other,  effectually  prevent  any  backward  current.  When  closed 
the  application  of  their  free  edges  form  a  line  which  runs  across  the  vessel. 
It  is  found  that  in  successive  sets  of  valves,  these  lines  are  at  right  angles  to 
each  other,  so  that  if,  in  one  set,  this  line  have  a  direction  from  before  back- 
ward, in  the  sets  above  and  below,  the  lines  run  from  side  to  side  (Fabricius). 
There  are  certain  exceptions  to  the  general  proposition  that  the  veins  of 
the  great  cavities  are  not  provided  with  valves.  Valves  are  found  in  the 
portal  system  of  some  of  the  inferior  animals,  as  the  horse.  They  do  not 
exist,  however,  in  this  situation  in  the  human  subject.  Generally,  in  following 
out  the  branches  of  the  inferior  vena  cava,  no  valves  are  found  until  the  crural 
vein  is  reached ;  but  occasionally  there  is  a  double  valve  at  the  origin  of  the 
external  iliac.  In  some  of  the  inferior  animals,  there  exists  constantly  a 
single  valvular  fold  in  the  vena  cava  at  the  openings  of  the  hepatic,  and  one 
at  the  opening  of  the  renal  vein.  This  is  not  constant  in  the  human  subject. 
Valves  are  found  in  the  spermatic,  but  not  in  the  ovarian  veins.  A  single 
valvular  fold  has  been  described  at  the  opening  of  the  right  spermatic  into 
the  vena  cava.  There  are  two  valves  in  the  azygos  vein  near  its  opening  into 
the  superior  vena  cava.  There  is  a  single  valve  at  the  orifice  of  the  coronary 
vein.  There  are  no  valves  at  the  openings  of  the  brachip-cephalic  into  the 
superior  vena  cava ;  but  there  is  a  strong,  double  valve  at  the  point  where 
the  internal  jugular  opens  into  the  brachio-cephalic.  Between  this  point 
and  the  capillaries  of  the  brain,  the  vessels  have  no  valves,  except  in  very 
rare  instances,  when  one  or  two  are  found  in  the  course  of  the  jugular. 


CIRCULATION  IN  THE  VEINS.  93 

In  addition  to  the  double,  or  more  rarely  triple  valves  which  have  just 
been  described,  there  is  another  variety,  found  in  certain  parts,  at  the  point 
where  a  tributary  vein  opens  into  a  main  trunk.  This  consists  of  a  single 
fold,  which  is  attached  to  the  smaller  vessel  but  projects  into  the  larger.  Its 
action  is  to  prevent  regurgitation,  by  the  same  mechanism  as  that  by  which 
the  ileo-caseal  valve  prevents  the  passage  of  matters  from  the  large  into  the 
small  intestine. 

The  veins  are  adapted  to  the  return  of  blood  to  the  heart  in  a  compara- 
tively slow  and  unequal  current.  Distention  of  certain  portions  is  provided 
for ;  and  the  vessels  are  so  protected  with  valves,  that  whatever  influences  the 
current  must  favor  its  flow  in  the  direction  of  the  heart. 

Course  of  the  Blood  in  the  Veins. — The  experiments  of  Hales  and  Sharpey, 
showing  that  defibrinated  blood  can  be  made  to  pass  from  the  arteries  into 
the  capillaries  and  out  at  the  veins  by  a  pressure  less  than  that  which  exists 
in  the  arterial  system,  and  the  observations  of  Magendie  upon  the  circulation 
in  the  leg  of  a  living  dog,  showing  that  ligation  of  the  artery  arrests  the  flow 
in  the  vein,  have  established  the  fact  that  the  force  exerted  by  the  left  ven- 
tricle is  sufficient  to  account  for  the  venous  circulation.  The  heart  must  be 
regarded  as  the  prime  cause  of  the  movement  of  blood  in  the  veins.  Re- 
garding this  as  definitely  ascertained,  there  remain  to  consider,  in  the  study 
of  the  course  of  the  blood  in  the  veins,  the  character  of  the  current,  the  influ- 
ence of  the  vessels  themselves,  the  question  of  the  existence  of  forces  which 
may  assist  the  vis  a  tergo  from  the  heart,  and  conditions  which  may  interfere 
with  the  flow  of  blood. 

As  a  rule,  in  the  normal  circulation,  the  flow  of  blood  in  the  veins  is  con- 
tinuous and  uniform.  The  intermittent  impulse  of  the  heart,  which  pro- 
gressively diminishes  toward  the  periphery  but  is  still  felt  even  in  the  small- 
est arteries,  is  lost  in  the  capillaries.  Here,  for  the  first  time,  the  blood 
moves  in  a  constant  current ;  and  as  the  pressure  in  the  arteries  is  continu- 
ally supplying  fresh  blood,  that  which  has  circulated  in  the  capillaries  is 
forced  into  the  venous  radicles  in  a  steady  stream.  As  the  supply  to  the 
capillaries  of  different  parts  is  regulated  by  the  action  of  the  small  arteries, 
and  as  this  supply  is  subject  to  great  variations,  there  must  necessarily  be 
corresponding  variations  in  the  current  in  the  veins  and  in  the  quantity  of 
blood  which  these  vessels  receive.  Consequently,  the  venous  circulation  is 
subject  to  very  great  variations  due  to  irregularity  in  the  supply  of  blood, 
aside  from  any  action  of  the  vessels  themselves  or  any  external  disturbing 
influences. 

It  often  happens  that  a  vein  becomes  obstructed  from  some  cause  which  is 
entirely  physiological,  such  as  the  action  of  muscles.  The  great  number  of 
veins,  as  compared  with  the  arteries,  and  their  free  communications  with  each 
other,  provide  that  the  current,  under  these  conditions,  is  simply  diverted, 
passing  to  the  heart  by  another  channel.  When  any  part  of  the  venous  sys- 
tem is  distended,  the  vessels  react  on  the  blood  and  exert  a  certain  influence 
on  the  current,  always  pressing  it  toward  the  heart,  for  the  valves  oppose  a 
flow  in  the  opposite  direction. 


94:  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

The  intermittent  action  of  the  heart,  which  pervades  the  whole  arterial 
system,  is  generally  absorbed,  as  it  were,  in  the  passage  of  the  blood  through 
the  capillaries ;  but  when  the  arterioles  of  any  part  are  very  much  relaxed, 
the  cardiac  impulse  may  extend  to  the  veins.  When  the  glands  are  pouring 
out  their  secretions,  the  quantity  of  blood  which  they  receive  is  very  much 
increased.  It  is  then  furnished  to  supply  material  for  the  secretion,  and  not 
exclusively  for  nutrition.  If  the  vein  be  opened  at  such  a  time,  it  is  found 
that  the  blood*  has  not  lost  its  arterial  character,  that  the  quantity  which 
escapes  is  increased,  and  that  the  flow  is  in  an  intermittent  jet,  as  from  a  divided 
artery  (Bernard).  This  is  due  to  the  relaxed  condition  of  the  arterioles  of 
the  part,  and  the  phenomenon  thus  observed  constitutes  the  true  venous 
pulse.  What  thus  occurs  in  a  restricted  portion  of  the  circulatory  system 
may  take  place  in  all  the  veins,  though  in  a  less  marked  degree.  Physicians 
have  frequently  noticed,  after  the  blood  has  been  flowing  for  some  time  in 
the  operation  of  venesection,  that  the  color  changes  from  black  to  red  and 
the  stream  becomes  intermittent,  often  leading  the  operator  to  fear  that  he 
has  pricked  the  artery.  In  all  probability  this  is  due  to  the  relaxation  of 
the  arterioles  as  one  of  the  effects  of  abstraction  of  blood,  producing  the 
same  condition  that  has  been  rioted  in  some  of  the  glands  during  their 
activity. 

Pressure  of  Blood  in  the  Veins. — The  pressure  in  the  veins  is  always 
much  less  than  in  the  arteries.  It  is  very  variable  in  different  parts  of  the 
venous  system  and  in  the  same  part  at  different  times.  As  a  rule,  it  is  in 
an  inverse  ratio  to  the  arterial  pressure.  Whatever  favors  the  passage  of  blood 
from  the  arteries  into  the  capillaries  has  a  tendency  to  diminish  the  arterial 
pressure,  and  as  it  increases  the  quantity  of  blood  which  passes  into  the  veins, 
it  must  increase  the  venous  pressure.  The  great  capacity  of  the  venous  sys- 
tem-, its  frequent  anastomoses  and  the  presence  of  valves  which  may  shut  off  a 
portion  from  the  rest,  are  conditions  which  involve  considerable  variations 
in  pressure  in  different  vessels.  It  has  been  ascertained  that  as  a  rule,  the 
pressure  is  greatest  at  the  periphery  and  progressively  diminishes  in  the  direc- 
tion of  the  heart.  In  an  observation  on  the  calf,  Volkmann  found  that  with 
a  pressure  of  about  6'5  inches  (165'1  mm.)  of  mercury  in  the  carotid,  the 
pressure  in  the  metatarsal  vein  was  1-1  inch  (28  mm.),  and  but  0*36  (9'1  mm.) 
in  the  jugular.-  Analogous  results  were  obtained  in  the  more  recent  experi- 
ments by  Jacobson.  Muscular  effort  has  a  marked  influence  on  the  force  of 
the  circulation  in  certain  veins  and  produces  an  elevation  in  the  pressure. 
As  the  reduced  pressure  in  the  veins  is  due  in  a  measure  to  the  great  rela- 
tive capacity  of  the  venous  system  and  the  free  communications  between  the 
vessels,  it  would  seem  that  if  it  were  possible  to  reduce  the  capacity  of  the 
veins  in  a  part  and  force  all  the  blood  to  pass  to  the  heart  by  a  single  vessel 
corresponding  to  the  artery,  the  pressure  in  this  vessel  would  be  greatly 
increased.  Poiseuille  has  shown  this  to  be  the  fact  by  the  experiment  of 
tying  all  the  veins  coming  from  a  part,  except  one  which  had  the  vol- 
ume of  the  artery  by  which  the  blood  was  supplied,  forcing  all  the  blood 
to  return  by  this  single  channel.  This  being  done,  he  found  the  press- 


CAUSES  OF  THE   VENOUS  CIRCULATION.  95 

ure  in  the  vein  very  much  increased,  becoming  nearly  equal  to  that  in  the 
artery. 

Rapidity  of  the  Venous  Circulation. — It  is  impossible  to  fix  upon  any 
definite  rate  as  representing  the  rapidity  of  the  current  of  blood  in  the  veins. 
It  will  be  seen  that  various  conditions  are  capable  of  increasing  very  con- 
siderably the  rapidity  of  the  flow  in  certain  veins,  and  that  under  certain 
conditions,  the  current  in  some  parts  of  the  venous  system  is  very  much  re- 
tarded. Undoubtedly,  the  general  movement  of  blood  in  the  veins  is  very 
much  slower  than  in  the  arteries,  from  the  fact  that  the  quantity  of  blood  is 
greater.  If  it  be  assumed  that  the  quantity  of  blood  in  the  veins  is  double 
that  contained  in  the  arteries,  the  general  average  of  the  current  would  be 
diminished  one-half.  Near  the  heart,  however,  the  flow  becomes  more  uni- 
form and  progressively  increases  in  rapidity. 

As  the  effect  of  the  heart's  action  upon  the  venous  circulation  is  subject 
to  so  many  modifying  influences  through  the  small  arteries  and  capillaries, 
and  as  there  are  other  forces  influencing  the  current,  which  are  by  no  means 
uniform  in  their  action,  estimates  of  the  general  rapidity  of  the  venous  cir- 
culation or  of  the  variations  in  different  vessels  must  necessarily  be  very 
indefinite. 

CAUSES  OF  THE  VESTOUS  CIRCULATION. 

In  the  veins  the  blood  is  farthest  removed  from  the  influence  of  the  con- 
tractions of  the  left  ventricle ;  and  although  these  are  felt,  there  are  many 
other  causes  which  combine  to  carry  on  the  venous  circulation,  and  many 
influences  by  which  it  is  retarded  or  obstructed. 

The  great  and  uniform  force  which  operates  on  the  circulation  in  these 
vessels  is  the  vis  a  tergo.  Reference  has  been  made  to  the  entire  adequacy 
of  the  arterial  pressure,  propagated  through  the  capillaries,  to  account  for 
the  movement  of  blood  in  the  veins,  provided  there  be  no  great  obstacles 
to  the  current.  The  other  forces  which  concur  to  produce  movement  of 
blood  in  the  veins  are  the  following  : 

1.  Muscular  action,  by  which  many  of  the  veins  are  at  times  compressed, 
thus  forcing  the  blood  toward  the  heart,  regurgitation  being  prevented  by 
the  action  of  the  valves. 

2.  A  suction  force  exerted  by  the  action  of  the  thorax  in  respiration, 
operating,  however,  only  on  the  veins  in  the  immediate  neighborhood  of  the 

chest. 

*. 

3.  A  possible   influence  from   contraction   of  the  coats  of  the  vessels 
themselves.     This  is  marked  in  the  veins  near  the  heart,  in  some  of  the  in- 
ferior animals. 

4.  The  force  of  gravity,  which  operates  only  on  vessels  which  carry  blood 
from  above  downward  to  the  heart,  and  a  slight  suction  force  which  may  be 
exerted  upon  the  blood  in  a  small  vein  as  it  passes  into  a  larger  vessel  in 
which  the  current  is  more  rapid. 

The  obstacles  to  the  venous  circulation  are :  pressure  sufficient  to  oblit- 
erate the  caliber  of  a  vessel,  when,  from  the  free  communications  with  other 


96  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

vessels,  the  current  is  simply  diverted  into  another  channel ;  expiratory 
efforts ;  the  contractions  of  the  right  side  of  the  heart ;  and  the  force  of 
gravity,  which  operates,  in  the  erect  posture,  on  the  current  in  all  excepting 
the  veins  of  the  head,  neck  and  parts  of  the  trunk  above  the  heart. 

Influence  of  Muscular  Contraction. — That  the  action  of  muscles  has  con- 
siderable influence  on  the  current  of  blood  in  the  veins  situated  between 
them  and  in  their  substance,  has  long  been  recognized ;  and  this  action  is  so 
marked,  that  the  parts  of  the  venous  system  which  are  situated  in  the  sub- 
stance of  muscles  have  been  compared  by  Chassaignac  to  a  sponge  full  of 
liquid,  vigorously  pressed  by  the  hand.  It  must  always  be  remembered,  how- 
ever, that  although  the  muscles  are  capable  of  acting  on  the  blood  contained 
in  veins  in  their  substance  with  great  vigor,  the  heart  is  fully  competent  to 
carry  on  the  venous  circulation  without  their  aid ;  a  fact  which  is  exemplified 
in  the  venous  circulation  in  paralyzed  parts. 

It  has  been  shown  by  actual  observations  with  the  haemadynamometer,  that 
muscular  action  is  capable  of  increasing  the  pressure  in  certain  veins.  Ber- 
nard found  that  the  pressure  in  the  jugular  of  a  horse,  in  repose,  was  1-4 
inch  (31'8  mm.) ;  but  the  action  of  the  muscles  in  raising  the  head  increased 
it  to  a  little  more  than  five  inches  (127  mm.),  or  nearly  four  times.  Such  ob- 
servations show  at  once  the  great  variations  in  the  current  and  the  impor- 
tant influence  of  muscular  contraction  on  the  venous  circulation. 

In  order  that  contractions  of  muscles  shall  assist  the  venous  circulation, 
two  conditions  are  necessary  : 

1.  The  contraction  must  be  intermittent.     This  is  always  the  case  in  the 
voluntary  muscles.     It  is  a  view  entertained  by  many  physiologists  that  each 
muscular  fibre  relaxes  immediately  after  its  contraction,  which  is  instantane- 
ous, and  that  a  certain  period  of  repose  is  necessary  before  it  can  contract 
again.     However  this  may  be,  it  is  well  known  that  all  active  muscular  con- 
traction, as  distinguished  from  the  efforts  necessary  to  maintain  the  body  in 
certain  ordinary  positions,  is  intermittent  and  not  very  prolonged.     Thus 
the  veins,  which  are  partly  emptied  by  the  compression,  are  filled  again 
during  the  repose  of  the  muscle. 

2.  There  should  be  no  possibility  of  a  retrograde  movement  of  the  blood. 
This  condition  is  fulfilled  by  the  action  of  the  valves.    Anatomical  researches 
have  shown,  also,  that  these  valves  are  most  abundant  in  veins  situated  in  the 
substance  of  or  between  the  muscles,  and  they  do  not  exist  in  the  veins  of 
the  cavities,  which  are  not  subject  to  the  same  kind  of  compression. 

Force  of  Aspiration  from  the  Thorax. — -During  the  act  of  inspiration,  the 
enlargement  of  the  thorax,  by  depression  of  the  diaphragm  and  elevation  of 
the  ribs,  affects  the  movements  of  fluids  in  all  the  tubes  in  its  vicinity.  The 
air  enters  by  the  trachea  and  expands  the  lungs  so  that  they  follow  the  move- 
ments of  the  thoracic  walls.  The  flow  of  blood  into  the  great  arteries  is 
somewhat  retarded,  as  is  indicated  by  a  diminution  in  the  arterial  pressure ; 
.and  finally,  the  blood  in  the  great  veins  passes  to  the  heart  with  greater 
facility  and  in  increased  quantity.  This  last-mentioned  phenomenon  can  be 
readily  observed,  when  the  veins  are  prominent,  in  profound  or  violent  inspi- 


CAUSES  OF  THE  VENOUS  CIRCULATION.  97 

ration.  The  veins  at  the  lower  part  of  the  neck  are  then  seen  to  empty 
themselves  of  blood  during  inspiration,  and  they  become  distended  during 
expiration,  producing  a  sort  of  pulsation  which  is  synchronous  with  respira- 
tion. This  can  always  be  observed  after  exposure  of  the  jugular  in  the  lower 
part  of  the  neck  in  an  inferior  animal.  Direct  observations  on  the  jugulars 
show  conclusively  that  the  influence  of  inspiration  can  not  be  felt  much 
beyond  these  vessels.  They  are  seen  to  collapse  with  each  inspiratory  act,  a 
condition  which  limits  this  influence  to  the  veins  near  the  heart.  The  flac- 
cidity  of  the  walls  of  the  veins  will  not  permit  the  extended  action  of  any 
suction  force.  In  the  circulation  the  veins  are  moderately  distended  with 
blood  by  the  vis  a  tergo,  and,  to  a  certain  extent,  they  are  supported  by  con- 
nections with  surrounding  tissues,  so  that  the  force  of  aspiration  is  felt  far- 
ther than  in  experiments  on  vessels'  removed  from  the  body.  The  blood, 
as  it  approaches  the  thorax,  impelled  by  other  forces,  is  considerably  accel- 
erated in  its  flow ;  but  it  is  evident  that  beyond  a  certain  point,  and  that 
point  very  near  the  chest,  ordinary  aspiration  has  no  influence,  and  violent 
efforts  rather  retard  than  favor  the  venous  current. 

In  the  liver  the  influence  of  inspiration  becomes  a  very  important  ele- 
ment in  the  mechanism  of  the  circulation.  This  organ  presents  a  vascular 
arrangement  which  is  exceptional.  The  blood,  distributed  by  the  arteries  in 
a  capillary  plexus  in  the  mucous  membrane  of  the  alimentary  canal  and  in 
the  spleen,  instead  of  being  returned  directly  to  the  heart  by  the  veins,  is 
collected  into  the  portal  vein,  carried  to  the  liver,  and  is  there  distributed  in 
a  second  set  of  capillary  vessels.  It  is  then  collected  in  the  hepatic  veins  and 
carried  by  the  vena  cava  to  the  heart.  The  three  hepatic  veins  open  into  the 
inferior  vena  cava  near  the  point  where  it  passes  the  diaphragm,  where  the 
force  of  aspiration  from  the  thorax  would  materially  assist  the  current  of 
blood.  On  following  these  vessels  into  the  substance  of  the  liver,  it  is  found 
that  their  walls  are  so  firmly  adherent  to  the  tissue  of  the  organ,  that  when 
cut  across,  they  remain  patulous ;  and  it  is  evident  that  they  must  remain 
open  under  all  conditions.  The  thorax  can  therefore  exert  a  powerful  influ- 
ence upon  the  hepatic  circulation ;  for  it  is  only  the  flaccidity  of  the  walls  of 
the  vessels  which  prevents  this  influence  from  operating  throughout  the 
entire  venous  system.  Although  this  must  be  a  very  important  element  in 
the  production  of  the  circulation  in  the  liver,  the  fact  that  the  blood  circu- 
lates in  this  organ  in  the  foetus  before  any  movements  of  the  thorax  take 
place  shows  that  it  is  not  essential. 

A  farther  proof,  if  any  were  needed,  of  the  suction  force  of  inspiration  is 
found  in  an  accident  which  is  not  infrequent  in  surgical  operations  on  the 
lower  part  of  the  neck.  When  the  veins  in  this  situation  are  kept  open  by  a 
tumor  or  by  induration  of  the  surrounding  tissues,  an  inspiratory  effort  has 
occasionally  been  followed  by  the  entrance  of  air  into  the  vessels,  an  acci- 
dent which  is  likely  to  lead  to  the  gravest  results.  This  occurs  only  when  a 
divided  vein  is  kept  patulous ;  and  the  accident  proves  both  the  influence  of 
inspiration  on  liquids  in  the  veins  near  the  chest  and  its  restriction  to  the 
vessels  in  this  particular  situation  by  the  flaccidity  of  their  walls. 


98  CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

The  cause  of  death  from  air  in  the  veins  is  purely  mechanical.  The  air, 
finding  its  way  to  the  right  ventricle,  is  mixed  with  the  blood  in  the  form  of 
minute  bubbles  and  is  carried  into  the  pulmonary  artery.  Once  in  this  ves- 
sel, it  is  impossible  for  it  to  pass  through  the  capillaries  of  the  lungs,  and 
death  by  suffocation  is  the  result,  if  the  quantity  of  air  be  large.  It  is 
because  no  blood  can  pass  through  the  lungs,  that  the  left  cavities  of  the 
heart  are  usually  found  empty. 

Air  injected  into  the  arteries  produces  no  such  serious  effects  as  air  in  the 
veins.  It  is  arrested  in  the  capillaries  of  certain  parts  and  in  the  course  of 
a  short  time  is  absorbed. 

Aside  from  the  pressure  exerted  by  the  contraction  of  muscles  and  the 
force  of  aspiration  from  the  thorax,  the  influences  which  assist  the  venous 
circulation  are  very  slight.  There  is  a  slight  contraction  in  the  venae  cavaB 
in  the  immediate  proximity  of  the  heart,  which  is  much  more  extended  in 
many  of  the  lower  vertebrate  animals  and  may  be  mentioned  as  having  an 
influence — very  insignificant  it  is  true — on  the  flow  of  blood  from  the  great 
veins. 

In  the  veins  which  pass  from  above  downward,  the  force  of  gravity  favors 
the  flow  of  blood.  This  is  seen  by  the  turgescence  of  the  veins  of  the  neck 
and  face  when  the  head  is  kept  for  a  short  time  below  the  level  of  the  heart. 
If  the  arm  be  elevated  above  the  head,  the  veins  of  the  back  of  the  hand  will 
be  much  reduced  in  size,  from  the  greater  facility  with  which  the  blood 
passes  to  the  heart,  while  they  are  distended  when  the  hand  is  allowed  to 
hang  by  the  side  and  the  blood  has  to  rise  against  the  force  of  gravity. 

Some  physiologists  are  of  the  opinion  that  the  right  ventricle  exerts  an 
active  suction  force  during  its  diastole ;  but  experiments  on  animals  do  not 
fully  sustain  this  view,  and  if  such  a  force  be  exerted,  its  effect  upon  the  cir- 
culation, even  in  the  veins  near  the  heart,  must  be  very  slight.  In  the  great 
irregularity  in.  the  rapidity  of  the  circulation  in  different  veins,  it  must  fre- 
quently happen  that  a  vessel  empties  its  blood  into  another  of  larger  size, 
in  which  the  current  is  more  rapid.  In  such  an  instance,  as  a  physical  neces- 
sity, the  more  rapid  current  in  the  large  vein  exerts  a  certain  suction  force 
on  the  fluid  in  the  smaller  vessel. 

USES  OF  THE  VALVES  OF  THE  VEIXS. 

It  is  evident  that  the  principal  use  of  the  valves  of  the  veins  is  to  present 
an  obstacle  to  the  reflux  of  blood  toward  the  capillaries ;  and  it  remains  only 
to  study  the  conditions  under  which  they  are  brought  into  action. 

There  are  two  distinct  conditions  under  which  the  valves  of  the  veins  may 
be  closed.  One  of  them  is  the  arrest  of  circulation^ from  any  cause,  in  veins 
in  which  the  blood  has  to  rise  against  the  force  of  gravity;  and  the  other, 
compression  of  veins,  from  any  cause — generally  from  muscular  contraction — 
which  tends  to  force  the  blood  from  the  vessels  compressed,  into  others,  when 
the  valves  offer  an  obstruction  to  a  flow  toAvard  the  capillaries  and  necessitate 
a  current  in  the  direction  of  the  heart.  In  the  first  of  these  conditions,  the 
valves  are  antagonistic  to  the  force  of  gravity,  and  when  the  caliber  of  any 


USES  OF  THE  VALVES  OF  THE  VEINS.  99 

vessel  is  temporarily  obliterated,  they  aid  in  directing  the  current  into  anas- 
tomosing vessels.  It  is  but  rarely,  however,  that  they  act  thus  in  opposition 
to  the  force  of  gravity ;  and  it  is  only  when  many  of  the  veins  of  a  part  are 
simultaneously  compressed  that  they  aid  in  diverting  the  current.  When  a 
single  vein  is  obstructed,  it  is  not  probable  that  the  valves  are  necessary  to 
divert  the  current  into  other  vessels,  for  this  would  take  place  in  obedience  to 
the  vis  a  tergo  ;  but  when  many  veins  are  obstructed  in  a  dependent  part  and 
the  avenues  to  the  heart  become  insufficient,  the  valves  divide  the  columns  of 
blood,  so  that  the  pressure  is  equally  distributed  throughout  the  extent  of  the 
vessels.  This  is,  however,  but  an  occasional  action  of  the  valves ;  and  it  is 
evident  that  their  influence  is  only  to  prevent  the  weight  of  the  entire  col- 
umn of  blood,  in  vessels  thus  obstructed,  from  operating  on  the  smallest 
veins  and  the  capillaries.  It  can  not  make  the  work  of  the  heart,  when 
the  blood  is  again  put  in  motion,  any  less  than  if  the  column  were  undi- 
vided, as  this  organ  must  have  sufficient  power  to  open  successively  each  set 
of  valves. 

It  is  in  connection  with  the  intermittent  compression  of  the  veins  that  the 
valves  have  their  principal  and  almost  constant  use.  Their  situation  alone 
would  lead  to  this  supposition.  They  are  found  in  greatest  numbers  through- 
out the  muscular  system,  having  been  demonstrated  in  vessels  one  line  (2pl 
mm.)  in  diameter.  They  are  also  found  in  the  upper  parts  of  the  body, 
where  they  certainly  do  not  operate  against  the  force  of  gravity  ;  while  they 
do  not  exist  in  the  cavities,  where  the  venous  trunks  are  not  subject  to  com- 
pression. It  has  already  been  made  sufficiently  evident  that  the  action  of 
muscles  seconds  most^powerfully  the  contractions  of  the  heart.  The  vis  a 
tergo  from  the  heart  is,  doubtless,  generally  sufficient  to  turn  this  influence  of 
muscular  compression  from  the  capillary  system,  and  the  valves  of  the  veins 
are  open ;  but  they  stand  ready,  nevertheless,  to  oppose  regurgitation. 

In  the  action  of  muscles,  the  skin  is  frequently  stretched  over  the  part, 
and  the  cutaneous  veins  are  somewhat  compressed.  This  may  be  seen  in  the 
hand,  by  letting  it  hang  by  the  side  until  the  veins  become  somewhat  swollen, 
and  then  contracting  the  muscles,  when  the  skin  will  become  tense  and  the 
veins  are  very  much  less  prominent.  Here  the  valves  have  an  important  ac- 
tion. The  compression  of  the  veins  is  much  greater  in  the  substance  of  and 
between  the  muscles  than  in  the  skin ;  but  the  blood  is  forced  from  the  mus- 
cles into  the  skin,  and  the  valves  act  to  prevent  it  from  taking  a  retrograde 
course. 

A  full  consideration  of  the  venous  anastomoses  belongs  to  descriptive 
anatomy.  It  is  sufficient  to  state,  in  this  connection,  that  they  are  very 
abundant  and  provide  for  a  return  of  the  blood  to  the  heart  by  a  number  of 
channels.  The  azygos  vein,  the  veins  of  the  spinal  canal  and  veins  in  the 
walls  of  the  abdomen  and  thorax  connect  the  inferior  with  the  superior  vena 
cava.  Even  the  portal  vein  has  been  shown  to  have  its  communications  -with 
the  general  venous  system.  Thus,  in  all  parts  of  the  organism,  temporary 
compression  of  a  vein  merely  diverts  the  current  into  some  'other  vessel,  and* 
permanent  obliteration  of  a  vein  produces  enlargement -cf  communicating  ' 


100          CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

branches,  which  soon  become  sufficient  to  meet  all  the  requirements  of  the 
circulation. 

CONDITIONS  WHICH  IMPEDE  THE  VENOUS  CIRCULATION. 

Influence  of  Expiration. — The  influence  of  expiration  on  the  circulation 
in  the  veins  near  the  thorax  is  directly  opposed  to  that  of  inspiration.  As 
the  act  of  inspiration  has  a  tendency  to  draw  the  blood  from  these  vessels 
into  the  chest,  the  act  of  expiration  assists  in  forcing  the  blood  out  from  the 
vessels  of  the  thorax  and  opposes  a  flow  in  the  opposite  direction.  The  effect 
of  prolonged  and  violent  expiratory  efforts  is  quite  marked,  these  being  fol- 
lowed by  congestion  of  the  veins  of  the  face  and  neck  and  a  sense  of  fullness 
in  the  head,  which  may  become  very  distressing.  The  opposition  to  the 
venous  current  generally  extends  only  to  vessels  in  the  immediate  vicinity  of 
the  thorax,  or  it  may  be  stated  in  general  terms,  to  those  veins  in  which 
the  flow  of  blood  is  assisted  by  the  movements  of  inspiration ;  but  while  the 
inspiratory  influence  is  absolutely  confined  to  a  very  restricted  circuit  of  ves- 
sels, the  obstructive  influence  of  very  violent  and  prolonged  expiration  may 
be  extended  very  much  farther,  as  is  seen  when  the  vessels  of  the  neck,  face 
and  conjunctiva  become  congested  in  prolonged  vocal  efforts,  blowing  etc. 
The  mechanism  of  this  is  not  a  mere  reflux  from  the  large  trunks  of  the 
thoracic  cavity.  Were  this  the  case,  it  would  be  necessary  to  assume  an  insuf- 
ficiency of  certain  valves,  which  does  not  exist.  In  extreme  congestion,  reflux 
of  blood  may  take  place  to  a  certain  extent  in  the  external  jugular,  for  this 
vessel  has  but  two  valves,  which  are  not  competent  to  prevent  regurgitation. 
The  chief  cause  of  congestion,  however,  is  due,  not  to  regurgitation,  but  to 
accumulation  from  the  periphery  and  an  obstruction  to  the  flow  of  blood  into 
ithe  great  vessels. 

It  is  in  the  internal  jugular  that  the  influence  of  expiration  is  most 
important,  both  on  account  of  its  great  size  in  the  human  subject,  as  com- 
pared with  the  other  vessels,  and  the  importance  and  delicacy  of  the  parts 
from  which  it  collects  the  blood.  At  the  opening  of  this  vessel  into  the 
innominate  vein,  is  a  pair  of  strong  and  perfect  valves,  which  effectually  close 
the  orifice  when  there  is  a  tendency  to  regurgitation.  When  the  act  of  expi- 
ration arrests  the  onward  flow  in  the  veins  near  the  thorax,  these  valves  are 
closed  and  effectually  protect  the  brain  from  congestion  by  regurgitation. 
The  blood  accumulates  behind  the  valves,  but  the  free  communication  of  the 
internal  jugular  with  the  other  veins  of  the  neck  relieves  the  brain  from  con- 
gestion, unless  the  effort  be  extraordinarily  violent  and  prolonged. 

The  above  remarks  with  regard  to  the  influence  of  expiration  are  appli- 
cable to  vocal  efforts,  violent  coughing  or  sneezing,  or  any  unusual  muscular 
efforts,  such  as  straining,  in  which  the  glottis  is  closed. 

Regurgitant  Venous  Pulse. — In  the  inferior  animals,  such  as  the  dog,  if  the 
external  jugular  be  exposed,  a  distention  of  the  vessel  is  seen  to  accompany 
each  expiratory  act.  This  is  sometimes  observed  in  the  human  subject  when 
respiration  is  '-exaggerated,  and  has  been  called  improperly  the  venous  pulse. 
Tilers  is-  no  sufficient-obstacle  to  the  regurgitation  of  blood  from  the  thorax 


CIRCULATION  IN  THE  CRANIAL  CAVITY.  101 

into  the  external  jugular,  and  distinct  pulsations,  synchronous  with  the  move- 
ments of  respiration,  may  be  produced  in  this  way. 

It  is  evident  that  there  are  various  other  conditions  which  may  impede 
the  venous  circulation.  Accidental  compression  may  temporarily  arrest  the 
flow  in  any  particular  vein.  When  the  whole  volume  of  blood  is  materially 
increased,  as  after  a  full  meal  with  copious  ingestion  of  liquids,  the  additional 
quantity  of  blood  accumulates  chiefly  in  the  venous  system  and  proportion- 
ally diminishes  the  rapidity  of  the  venous  circulation. 

The  force  of  gravity  also  has  an  important  influence.  It  is  much  more 
difficult  for  the  blood  to  pass  from  below  upward  to  the  heart  than  to  flow 
downward  from  the  head  and  neck.  The  action  of  this  is  seen  if  comparison 
be  made  between  the  circulation  in  the  arm  elevated  above  the  head  and 
hanging  by  the  side.  In  the  one  case  the  veins  are  readily  emptied  and  con- 
tain but  little  blood,  and  in  the  other  the  circulation  is  more  difficult  and 
the  vessels  are  moderately  distended.  The  walls  of  the  veins  are  thickest 
and  the  valves  are  most  abundant  in  parts  of  the  body  which  are  habitually 
dependent.  The  influence  of  gravity  is  exemplified  in  the  production  of 
varicose  veins  in  the  lower  extremities.  This  disease  is  frequently  produced 
by  occupations  which  require  constant  standing ;  but  the  exercise  of  walking, 
aiding  the  venous  circulation,  as  it  does,  by  the  muscular  effort,  has  no  such 
tendency. 

Circulation  in  the  Cranial  Cavity. — In  the  encephalic  cavity  there  are 
certain  peculiarities  in  the  anatomy  of  some  of  the  vessels,  with  exceptional 
conditions  of  the  blood  as  regards  atmospheric  pressure,  which  have  been 
regarded  as  capable  of  essentially  modifying  the  circulation.  In  the  adult 
the  cranium  is  a  closed,  air-tight  box,  containing  the  incompressible  cerebral 
substance,  blood,  lymph  and  the  cephalo-rachidian  fluid ;  and  the  blood  is 
here  under  conditions  widely  different  from  those  presented  in  other  parts  of 
the  system.  The  venous  passages  in  the  brain,  which  correspond  to  the  great 
veins  of  other  parts,  are  in  the  form  of  sinuses  between  the  folds  of  the  dura 
mater  and  are  but  slightly  dilatable.  In  the  perfectly  consolidated  adult  head 
the  blood  is  not  subjected  to  atmospheric  pressure,  as  in  other  parts,  and  the 
semi-solids  and  liquids  which  make  up  the  encephalic  mass  can  not  increase 
in  size  in  congestion  and  diminish  in  anaemia.  Notwithstanding  these  con- 
ditions, the  fact  remains,  that  examinations  of  the  vessels  of  the  brain  after 
death  show  great  differences  in  the  quantity  of  blood  which  they  contain. 
The  question  then  arises  as  to  what  is  displaced  to  make  room  for  the  blood 
in  congestion,  and  what  supplies  the  place  of  the  blood  in  anaemia.  An  ana- 
tomical peculiarity  which  has  not  yet  been  considered  offers  an  explanation  of 
these  phenomena.  Between  the  pia  mater  and  the  arachnoid  of  the  brain  and 
spinal  cord  there  exists  a  liquid,  the  cephalo-rachidian  fluid,  which  is  capable 
of  passing  from  the  surface  of  the  brain  to  the  spinal  canal  and  communicates 
with  the  fluid  in  the  ventricles  (Magendie).  The  communication  between  the 
cranial  cavity  and  the  spinal  canal  is  very  free.  It  is  easy  to  see  one  of  the 


102          CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

physiological  uses  of  this  liquid.  When  the  pressure  of  blood  in  the  arteries 
going  to  the  brain  is  increased  or  when  there  is  an  obstacle  to  its  return  by 
the  veins,  more  or  less  congestion  takes  place,  and  the  blood  forces  the  liquid 
from  the  cranial  into  the  spinal  cavity.  The  reverse  takes  place  when  the 
supply  of  blood  to  the  brain  is  diminished.  The  physiological  action  of  all 
highly  organized  and  vascular  parts  seems  to  require  certain  variations  in  the 
supply  of  blood ;  and  there  is  no  good  reason  to  suppose  that  the  brain,  in  its 
varied  conditions  of  activity  and  repose,  is  an  exception  to  this  general  rule. 

Physiologists,  even  before  the  time  of  Haller,  had  noticed  alternate  move- 
ments of  expansion  and  contraction  in  the  brain,  connected  with  the  acts  of 
respiration.  This  is  observed  in  children  before  the  f ontanels  are  closed,  and 
in  the  adult  when  the  brain  is  exposed  by  an  injury  or  a  surgical  operation. 
The  movements  are  an  expansion  with  the  act  of  expiration,  which,  in  vio- 
lent efforts,  is  sometimes  so  considerable  as  to  produce  cerebral  hernia,  and 
contraction  with  inspiration.  With  the  act  of  expiration  the  flow  of  blood  in 
the  arteries  is  favored  and  the  current  in  the  veins  is  retarded.  If  the  effort 
be  violent,  the  valve  at  the  opening  of  the  internal  jugular  may  be  closed. 
This  act  would  produce  an  expansion  of  the  brain,  not  from  reflux  by  the 
veins,  but  from  the  fact  that  the  flow  into  the  chest  is  impeded,  and  the 
blood,  while  passing  in  more  freely  by  the  arteries,  is  momentarily  confined. 
With  inspiration  the  flow  into  the  thorax  is  materially  aided,  and  the  brain 
is  in  some  degree  relieved  of  this  expanding  force. 

Circulation  in  Erectile  Tissues. — In  the  organs  of  generation  of  both 
sexes,  there  exists  a  tissue  which  is  subject  to  increase  in  volume  and  rigidity 
when  in  a  condition  of  what  is  called  erection.  The  parts  in  which  the  erect- 
ile tissue  exists  are,  in  the  male,  the  corpora  cavernosa  of  the  penis,  the  cor- 
pus spongiosum  and  the  glans  penis ;  and  in  the  female,  the  corpora  caver- 
nosa of  the  clitoris,  the  gland  of  the  clitoris  and  the  bulb  of  the  vestibule. 

The  vascular  arrangement  in  erectile  organs,  of  which  the  penis  may  be 
taken  as  the  type,  is  peculiar  and  is  not  found  in  any  other  part  of  the  circu- 
latory system.  Taking  the  penis  as  an  example,  the  arteries,  which  have  an 
unusually  thick,  muscular  coat,  after  they  have  entered  the  organ,  do  not 
simply  branch  and  divide  dichotomously,  as  in  most  other  parts,  but  send  off 
large  numbers  of  arborescent  branches,  which  immediately  become  tortuous 
and  are  distributed  in  the  cavernous  and  spongy  bodies  in  anastomosing  ves- 
sels, with  but  a  single,  thin,  homogeneous  coat,  like  the  true  capillaries. 
These  vessels  are  larger,  even,  than  the  arterioles  which  supply  them  with 
blood,  some  having  a  diameter  of  ^  to  -fa  of  an  inch  (1  to  1*5  mm.). 
The  cavernous  bodies  have  an  external  investment  of  strong,  fibrous  tissue 
of  considerable  elasticity,  which  sends  bands,  or  trabecula?,  into  the  inte- 
rior, by  which  it  is  divided  up  into  cells.  The  trabeculae  are  composed  of 
fibrous  tissue  mixed  with  a  large  number  of  non-striated  muscular  fibres. 
These  cells  lodge  the  blood-vessels,  which  ramify  in  the  tortuous  manner 
already  indicated  and  finally  terminate  in  the  veins.  The  anatomy  of  the 
corpora  spongiosa  is  essentially  the  same,  the  only  difference  being  that  the 
fibrous  envelops  and  the  trabsculas  are  more  delicate  and  the  cells  are  smaller. 


PULMONARY  CIRCULATION.      -  103 

Without  going  fully  into  the  mechanism  of  erection,  it  may  be  stated  in 
general  terms  that  during  sexual  excitement,  or  when  erection  occurs  from 
any  cause,  the  thick,  muscular  walls  of  the  arteries  of  supply  relax  and  allow 
the  arterial  pressure  to  distend  the  capacious  vessels  lodged  in  the  cells  of  the 
cavernous  and  spongy  bodies.  This  produces  the  characteristic  change  in  the 
volume  and  position  of  the  organ.  It  is  evident  that  erection  depends  upon 
the  peculiar  arrangement  of  the  blood-vessels,  and  is  not  simply  a  congestion, 
such  as  could  occur  in  any  vascular  part.  During  erection  there  is  not  a 
stasis  of  blood  ;  but  if  it  continue  for  any  length  of  time,  the  quantity  which 
passes  out  of  the  part  by  the  veins  must  be  equal  to  that  which  passes  in  by 
the  arteries. 

Derivative  Circulation. — In  some  parts  of  the  circulatory  system,  there 
exists  a  direct  communication  between  the  arteries  and  the  veins,  so  that  all 
the  blood  does  not  necessarily  pass  through  the  minute  vessels  which  have 
been  described  as  true  capillaries.  This  peculiarity,  which  had  been  noted 
by  Todd  and  Bowman,  Paget  and  others,  has  been  studied  by  Sucquet.  By 
using  a  black,  solidifiable  injection,  he  found  that  there  were  certain  parts  of 
the  upper  and  lower  extremities  and  the  head  which  became  colored  by  the 
injection,  while  other  parts  were  not  penetrated.  Following  the  vessels  by 
dissection,  he  showed  that  in  the  upper  extremity,  the  skin  of  the  fingers  and 
part  of  the  palm  of  the  hand,  and  the  skin  over  the  olecranbn  are  provided 
with  vessels  of  considerable  size,  which  allowed  the  fluid  injected  by  the  axil- 
lary artery  to  pass  directly  into  some  of  the  veins,  while  in  other  parts  the 
veins  were  entirely  empty.  Extending  his  researches  to  the  lower  extremity, 
he  found  analogous  communications  between  the  vessels  in  the  knee,  toes 
and  parts  of  the  sole  of  the  foot.  He  also  found  communications  in  the 
nose,  cheeks,  lips,  forehead  and  ends  of  the  ears,  parts  which  are  particularly 
liable  to  changes  in  color  from  congestion  of  vessels.  These  observations 
have  been  in  the  main  confirmed  by  the  more  recent  researches  of  Hoyer.  It 
is  evident  that  under  certain  conditions  a  larger  quantity  of  blood  than 
usual  may  pass  through  these  parts,  without  necessarily  penetrating  the  true 
capillaries  and  thus  exerting  a  modifying  influence  upon  nutrition. 

Pulmonary  Circulation. — The  vascular  system  of  the  lungs  merits  the 
name,  which  is  frequently  applied  to  it,  of  the  lesser  circulation.  The  right 
side  of  the  heart  acts  simultaneously  with  the  left,  but  is  entirely  distinct 
from  it,  and  its  muscular  walls  are  very  much  less  powerful.  The  pulmonary 
artery  has  thinner  and  more  distensible  coats  than  the  aorta  and  distributes 
its  blood  to  a  single  system,  of  capillaries,  situated  very  near  the  heart.  In 
the  substance  of  the  lungs,  the  pulmonary  artery  is  broken  up  into  capilla- 
ries, most  of  them  just  large  enough  to  allow  the  passage  of  the  blood-cor- 
puscles in  a  single  row.  These  vessels  are  provided  with  a  single  coat  and 
form  a  very  close  net- work  surrounding  the  air-cells.  From  the  capillaries 
the  blood  is  collected  by  the  pulmonary  veins  and  conveyed  to  the  left  auri- 
cle. There  is  no  great  disparity  between  the  arteries  and  veins  of  the  pul- 
monary system  as  regards  capacity.  The  pulmonary  veins  in  the  human 
subject  are  not  provided  with  valves. 


104          CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

The  blood  in  its  passage  through  the  lungs  does  not  meet  with  the  resist- 
ance which  is  presented  in  the  systemic  circulation  ;  and  the  anatomy  of  the 
pulmonary  vessels  and  of  the  right  side  of  the  heart  shows  that  the  blood 
must  circulate  in  the  lungs  with  comparative  facility.  The  power  of  the 
right  ventricle  is  evidently  less  than  half  that  of  the  left,  and  the  pulmonary 
artery  will  sustain  a  much  less  pressure  than  the  aorta. 

The  two  sides  of  the  heart  act  simultaneously ;  and  at  the  same  time  that 
the  blood  is  sent  by  the  left  ventricle  to  the  system  it  is  sent  by  the  right 
ventricle  to  the  lungs.  The  pressure  of  blood  in  the  pulmonary  artery,  meas- 
ured by  connecting  a  cardiometer  with  a  trocar  introduced  into  the  pul- 
monary artery  of  a  living  horse  through  one  of  the  intercostal  spaces,  has 
been  found  to  be  about  one-third  as  great  as  the  pressure  in  the  aorta, 
which  corresponds  pretty  nearly  with  an  estimate  of  the  comparative  power 
of  the  two  ventricles,  judging  from  the  thickness  of  their  muscular  walls 
(Chauveau  and  Faivre). 

On  microscopical  examination  of  the  circulation  in  the  lower  animals,  as 
the  frog,  the  movement  of  blood  in  the  capillaries  of  the  lungs  does  not  pre- 
sent any  differences  from  the  capillary  circulation  in  other  parts,  except  that 
the  vessels  seem  more  crowded  with  corpuscles  and  there  is  no  "  still  layer  " 
next  their  walls. 

Circulation  in  the  Walls  of  the  Heart. — The  circulation  in  the  walls  of 
the  heart  does  not  present  any  important  peculiarities.  It  has  been  shown 
that  the  pressure  of  blood  in  the  coronary  arteries  in  the  dog,  during  the 
ventricular  systole,  is  sufficient  to  supply  the  arterioles  in  the  substance  of 
the  heart  with  blood  precisely  as  it  is  supplied  to  the  general  arterial  system. 
In  a  number  of  experiments,  in  which  simultaneous  traces  of  the  pulse-beats 
were  obtained,  it  has  been  found  that  the  coronary  and  carotid  pulses  were 
practically  synchronous  (Martin). 

Passage  of  the  Blood- Corpuscles  through  the  Walls  of  the  Vessels  (Diape- 
desis). — In  the  frog  it  has  been  observed  that  the  leucocytes  sometimes  pass 
through  the  walls  of  the  blood-vessels,  either  by  means  of  small  orifices 
(stromata)  or  by  a  kind  of  filtration  through  the  substance  which  unites  the 
borders  of  the  endothelial  cells.  This  phenomenon  was  described  by  Waller, 
in  1841,  but  has  attracted  much  attention  since  the  more  recent  researches 
of  Cohnheim.  In  this  process  it  is  observed  that  the  leucocytes,  which  first 
adhere  to  the  vascular  walls,  send  out  little  projections  which  penetrate  the 
membrane,  so  that  a  point  appears  on  the  outside  of  the  vessel.  This  point 
becomes  larger  and  larger,  until  the  entire  mass  of  the  corpuscle  has  passed 
through.  The  corpuscles  then  migrate  a  certain  distance  by  means  of  the 
movements  known  as  amoeboid,  which  have  already  been  described.  It  was 
supposed  by  Cohnheim  that  this  was  one  of  the  early  phenomena  of  inflam- 
mation, the  migrating  corpuscles  afterward  multiplying  by  division,  consti- 
tuting the  so-called  pus-corpuscles.  Following  stasis  of  blood  in  the  small 
vessels,  the  red  corpuscles,  it  is  supposed,  pass  out  in  the  same  way.  It  is 
not  certain  that  diapedesis,  even  of  leucocytes,  is  a  normal  process  or  that  it 
takes  place  in  the  human  subject.  According  to  Hering,  the  red  corpuscles 


RAPIDITY  OF  THE  CIRCULATION. 


105 


FIG.  38.— Small  blood-vessel  of  the  mesentery  of  the 
frog,  showing  diapedesis  of  leucocytes  (Landois). 

w,  w,  walls  of  the  vessel ;  A,  A,  still  layer  ;  B,  R,  red 
blood-corpuscles  ;  L,  L,  leucocytes  in  contact  with 
the  wall,  c,  c,  in  different  stages  of  diapedesis ; 
F,  F,  leucocytes  that  have  passed  out  of  the  vessel. 


pass  through  the  walls  of  the  vessels,  only  when  the  pressure  is  sufficient 
to   produce    transudation    of    the  w 

blood-plasma. 

RAPIDITY  OF  THE  CIRCULATION. 

Several  questions  of  considerable 
physiological  importance  arise  in 
connection  with  the  general  rapidity 
of  the  circulation : 

1.  What  length  of  time  is  occu- 
pied  in  the  passage  of  the  blood 
through  both  the   lesser   and   the 
greater  circulations  ? 

2.  What  is  the  time  required  for 
the  passage  of  the  entire  mass  of 
blood  through  the  heart  ? 

3.  What  influence  has  the  num- 
ber of  pulsations  of  the  heart  on  the  general  rapidity  of  the  circulation  ? 

The  first  of  these  questions  is  the  one  which  has  been  most  satisfactorily 
answered  by  experiments  on  living  animals.  In  1827,  Hering  made  the 
experiment  of  injecting  into  the  jugular  vein  of  a  living  animal  a  solution 
of  potassium  ferrocyanide,  noting  the  time  which  elapsed  before  it  could  be 
detected  in  the  blood  of  the  vein  of  the  opposite  side.  This  gave  the  first 
.correct  idea  of  the  rapidity  of  the  circulation.  He  drew  the  blood  at  inter- 
vals of  five  seconds  after  beginning  the  injection,  and  thus,  by  repeated  ob- 
servations, ascertained  pretty  nearly  the  rapidity  of  a  circuit  of  blood  in  the 
animals  upon  which  he  experimented.  Vierordt  (1858)  collected  the  blood 
as  it  flowed,  in  little  vessels  fixed  on  a  disk  revolving  at  a  known  rate,  which 
gave  more  exactness  to  the  observations.  The  results  obtained  by  these  two 
observers  were  nearly  identical. 

The  only  objection  which  could  be  made  to  these  experiments  is  that  a 
saline  solution,  introduced  into  the  circulation,  would  have  a  tendency  to 
diffuse  itself  throughout  the  whole  mass  of  blood,  it  might  be,  with  consider- 
able rapidity.  This  certainly  is  an  element  which  should  be  taken  into  ac- 
count ;  but  from  the  definite  data  which  have  been  obtained  concerning  the 
rapidity  of  the  arterial  circulation  and  the  inferences  which  are  unavoidable 
with  regard  to  the  rapidity  of  the  venous  circulation,  it  would  seem  that  the 
saline  solution  must  be  carried  on  by  the  mere  rapidity  of  the  arterial  flow  to 
the  capillaries,  which  are  very  short,  taken  up  from  them,  and  carried  on  by 
the  veins,  and  thus  through  the  entire  circuit,  before  it  has  had  time  to  diffuse 
itself  to  any  considerable  extent.  It  is  not  apparent  how  this  objection  can 
be  overcome,  for  a  substance  must  be  used  which  will  mix  with  the  blood ; 
otherwise  it  could  not  pass  through  the  capillaries. 

There  seems  no  reason  why,  with  the  above  restrictions,  the  results  obtained 
by  Hering  should  not  be  accepted  and  their  application  be  made  to  the  human 
subject. 


106          CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

Hering  found  that  the  rapidity  of  the  circulation  in  different  animals 
had  an  inverse  ratio  to  their  size  and  a  direct  ratio  to  the  rapidity  of  the 
action  of  the  heart. 

The  following  are  the  mean  results  in  certain  of  the  domestic  animals, 
taking  the  course  from  jugular  to  jugular,  when  the  blood  passes  through  the 
lungs  and  through  the  capillaries  of  the  face  and  head : 

In  the  Horse,  the  circulation  is  accomplished  in  27'3  seconds. 
"       Dog,  "  15-2      " 

Goat,  "  "  12-8      " 

"       Rabbit,  "  "  6-9      " 

Applying  these  results  to  the  human  subject  and  taking  into  account  the 
size  of  the  body  and  the  rapidity  of  the  heart's  action,  the  duration  of  the 
circuit  from  one  jugular  to  the  other  may  be  estimated  at  21'4  seconds,  and 
the  general  average  through  the  entire  system,  at  23  seconds.  This  estimate 
is  simply  approximate ;  but  the  results  in  the  inferior  animals  may  be  received 
as  very  nearly  accurate. 

Estimates  of  the  time  required  for  the  passage  of  the  whole  mass  of  blood 
through  the  heart  are  even  less  definite  than  the  estimate  of  the  general 
rapidity  of  the  circulation.  To  arrive  at  any  satisfactory  result,  it  is  neces- 
sary to  know  the  entire  quantity  of  blood  in  the  body  and  the  exact  quantity 
which  passes  through  the  heart  at  each  pulsation.  If  the  whole  mass  of  blood 
be  divided  by  the  quantity  discharged  from  the  heart  with  each  ventricular 
systole,  the  result  gives  the  number  of  pulsations  required  for  the  passage  of 
the  whole  mass  of  blood  through  the  heart ;  and  knowing  the  number  of  beats- 
per  minute,  the  length  of  time  thus  occupied  is  ascertained.  The  objection 
to  this  kind  of  estimate  is  the  inaccuracy  of  the  data  respecting  the  quantity 
of  blood  in  the  system  as  well  as  the  quantity  which  passes  through  the  heart 
with  each  pulsation.  Nevertheless,  an  estimate  can  be  made,  which,  if  it  be 
not  entirely  accurate,  can  not  be  very  far  from  the  truth. 

The  entire  quantity  of  blood,  according  to  estimates  which  seem  to  be 
based  on  the  most  reliable  data,  is  about  one-tenth  the  weight  of  the  body,  or 
fourteen  pounds  (6-35  kilos.),  in  a  man  weighing  one  hundred  and  forty 
pounds  (63*5  kilos.).  The  quantity  discharged  at  each  ventricular  systole  is 
estimated  by  Valentin  at  five  ounces  (141-7  grammes),  and  by  Volkmaim,  at 
six  ounces  (170-1  grammes).  Assuming  that  at  each  systole,  the  left  ventricle 
discharges  all  its  blood,  except  perhaps  a  few  drops,  and  that  this  quantity  in 
an  ordinary-sized  man  is  five  ounces  (141-7  grammes),  it  would  require  forty- 
five  pulsations  for  the  passage  through  the  heart  of  the  entire  mass  of  blood. 
Assuming  the  pulsations  to  be  seventy-two  per  minute,  this  would  occupy 
thirty-seven  and  a  half  seconds. 

The  relation  of  the  rapidity  of  the  circulation  to  the  frequency  of  the 
heart's  action  is  a  question  which  was  not  neglected  in  the  experiments  of 
Hering.  It  is  evident  that  if  the  charge  of  blood  sent  into  the  arteries  be  the 
same,  or  nearly  the  same,  under  all  conditions,  any  increase  in  the  number  of 
pulsations  of  the  heart  would  produce  a  corresponding  acceleration  of  the 
general  current  of  blood.  This  is  a  proposition,  however,  which  can  not  be 


RAPIDITY  OF  THE  CIRCULATION.  107 

taken  for  granted ;  and  there  are  many  facts  which  favor  a  contrary  opinion. 
It  may  be  stated  as  a  general  rule,  that  when  the  acts  of  the  heart  increase  in 
frequency  they  diminish  in  force ;  and  this  renders  it  probable  that  the  ven- 
tricle is  most  completely  distended  and  emptied  when  its  action  is  moderately 
slow.  When,  however,  the  pulse  is  very  much  accelerated,  the  increased 
number  of  pulsations  of  the  heart  might  be  sufficient  to  overbalance  the 
diminished  force  of  each  act  and  would  thus  actually  increase  the  rapidity  of 
the  circulation.  In  observations  made  on  horses,  by  increasing  the  frequency 
of  the  pulse,  on  the  one  hand,  physiologically,  by  exercise,  and  on  the  other 
hand,  pathologically,  by  producing  inflammatory  action,  it  is  shown  that  when 
the  pulse  is  accelerated  in  inflammation,  the  value  of  the  contractions  of  the 
heart,  as  represented  by  the  quantity  of  blood  discharged,  bears  an  inverse 
ratio  to  their  number  and  is  so  much  diminished  as  absolutely  to  produce  a 
current  of  less  rapidity  than  normal.  In  the  physiological  increase  in  the 
rate  of  the  pulse  by  exercise,  there  was  a  considerable  increase  in  the  actual 
rapidity  of  the  circulation  (Hering). 

With  regard  to  the  relations  between  the  rapidity  of  the  heart's  action 
and  the  general  rapidity  of  the  circulation,  the  following  conclusions  may  be 
given  as  the  results  of  experimental  inquiry : 

1.  In  physiological  increase  in  the  number  of  beats  of  the  heart,  as  the 
result  of  exercise,  for  example,  the  general  circulation  is  somewhat  increased 
in  rapidity,  though  not  in  proportion  to  the  increase  in  the  rapidity  of  the 
pulse. 

2.  In  pathological  increase  in  the  rapidity  of  the  heart's  action,  as  in 
febrile  movement,  the  rapidity  of  the  general  circulation  is  generally  dimin- 
ished, it  may  be,  to  a  very  great  extent. 

3.  Whenever  the  number  of  beats  of  the  heart  is  considerably  increased 
from  any  cause,  the  quantity  of  blood  discharged  at  each  ventricular  systole 
is  very  much  diminished,  either  from  lack  of  complete  distention  or  from 
imperfect  emptying  of  the  cavities. 

Phenomena  in  the  Circulatory  System  after  Death. — Nearly  every  autopsy 
shows  that  after  death,  the  blood  does  not  remain  equally  distributed  in  the 
arteries,  capillaries  and  veins.  Influenced  by  gravitation,  it  accumulates  in 
and  discolors  the  most  dependent  parts  of  the  body.  The  arteries  are  always 
found  empty,  and  all  the  blood  in  the  body  accumulates  in  the  venous  system 
and  capillaries ;  a  fact  which  was  observed  by  the  ancients  and  gave  rise  to 
the  belief  that  the  arteries  were  air-bearing  tubes.  This  is  readily  explained 
by  the  post-mortem  contraction  of  the  muscular  coat  of  the  arteries.  If  the 
artery  and  vein  of  a  limb  be  exposed  in  a  living  animal  and  all  the  other  ves- 
sels be  tied,  compression  of  the  artery  does  not  immediately  arrest  the  current 
in  the  vein,  but  the  blood  will  continue  to  flow  until  the  artery  is  entirely 
emptied  (Magendie).  The  artery,  when  relieved  from  the  distending  force 
of  the  heart,  reacts  on  its  contents  by  virtue  of  its  contractile  coat  and  com- 
pletely empties  itself  of  blood.  An  action  similar  to  this  takes  place  through- 
out the  arterial  system  after  death.  The  vessels  react  on  their  contents  and 
gradually  force  all  the  blood  into  and  through  the  capillaries,  which  are  very 


108  RESPIRATION— RESPIEATORY  MOVEMENTS. 

short,  to  the  veins,  which  are  capacious,  distensible  and  but  slightly  con- 
tractile. This  begins  immediately  alter  death  while  the  contractility  of  the 
muscular  coat  of  the  arteries  remains,  and  is  seconded  by  the  subsequent 
cadaveric  rigidity,  which  affects  all  the  involuntary  as  well  as  the  voluntary 
muscular  fibres.  Once  in  the  venous  system,  the  blood  can  not  return  on 
account  of  the  valves.  Thus,  after  death,  the  blood  is  found  in  the  veins  and 
capillaries  of  dependent  parts  of  the  body. 


CHAPTER   IV. 

RE8PIRA  TION—RESPIRA  TORY  MO  VEMENTS. 

General  considerations— Physiological  anatomy  of  the  respiratory  organs— Movements  of  respiration— Inspi- 
ration—Muscles  of  inspiration— Expiration— Muscles  of  expiration— Types  of  respiration— Frequency 
of  the  respiratory  movements— Relations  of  inspiration  and  expiration  to  each  other— Respiratory 
sounds— Capacity  of  the  lungs  and  the  quantity  of  air  changed  in  the  respiratory  acts— Residual  air 
— Reserve  air — Tidal,  or  breathing  air — Complemental  air — Extreme  breathing  capacity — Relations  in 
Volume  of  the  expired  to  the  inspired  air — Diffusion  of  air  in  the  lungs. 

THE  characters  of  the  blood  are  by  no  means  identical  in  the  three  great 
divisions  of  the  vascular  system ;  but  physiologists  have  thus  far  been  able  to 
investigate  only  the  differences  which  exist  between  arterial  and  venous  blood, 
for  the  capillaries  are  so  short,  communicating  directly  with  the  arteries  on 
the  one  side  and  the  veins  on  the  other,  that  it  is  impossible  to  obtain  a  speci- 
men of  true  capillary  blood.  In  the  capillaries,  however,  the  nutritive  fluid, 
which  is  identical  in  all  parts  of  the  arterial  system,  undergoes  changes  which 
render  it  unfit  for  nutrition.  Thus  modified  it  is  known  as  venous  blood ; 
and  the  only  office  of  the  veins  is  to  carry  it  back  to  the  right  side  of  the 
heart,  to  be  sent  to  the  lungs,  where  it  loses  the  vitiating  substances  it  has  col- 
lected in  the  tissues,  takes  in  a  fresh  supply  of  oxygen  and  goes  to  the  left, 
or  systemic  heart,  again  prepared  for  nutrition.  As  the  processes  of  nutrition 
vary  in  different  parts  of  the  organism,  there  are  of  necessity  corresponding 
variations  in  the  composition  of  the  blood  in  different  veins. 

The  important  substances  that  are  given  off  by  the  lungs  are  exhaled 
from  the  blood ;  and  the  gas  which  disappears  from  the  air  is  absorbed  by 
the  blood,  mainly  by  the  red  corpuscles. 

A  proper  supply  of  oxygen  is  indispensable  to  nutrition  and  even  to  the 
comparatively  mechanical  process  of  circulation ;  but  it  is  no  less  necessary 
to  the  nutritive  processes  that  carbon  dioxide,  which  the  blood  acquires  in 
the  tissues,  should  be  removed. 

Respiration  may  be  defined  strictly  as  the  process  by  which  the  various 
tissues  and  organs  receive  and  appropriate  oxygen. 

As  it  is  almost  exclusively  through  the  blood  that  the  tissues  and  organs 
are  supplied  with  oxygen,  and  as  the  blood  receives  and  exhales  most  of  the 
carbon  dioxide,  the  respiratory  process  in  the  lungs  may  be  said  to  consist 


GENERAL  CONSIDERATIONS.  109 

chiefly  in  the  change  of  venous  into  arterial  blood ;  but  experiments  have 
demonstrated  that  the  tissues  themselves,  detached  from  the  body  and  placed 
in  an  atmosphere  of  oxygen,  will  absorb  this  gas  and  exhale  carbon  diox- 
ide. Under  these  conditions  they  certainly  respire ;  and  it  is  evident,  there- 
fore, that  in  this  process,  the  intervention  of  the  blood  is  not  an  absolute 
necessity. 

The  tide  of  air  in  the  lungs  does  not  strictly  constitute  respiration. 
These  organs  merely  serve  to  facilitate  the  introduction  of  oxygen  into  the 
blood  and  the  exhalation  of  carbon  dioxide.  If  the  system  be  drained  of 
blood  or  if  the  blood  be  rendered  incapable  of  interchanging  its  gases  with 
the  air,  respiration  ceases,  and  all  the  phenomena  of  asphyxia  are  presented, 
although  air  be  introduced  into  the  lungs  with  perfect  regularity.  It  must 
be  remembered  that  the  essential  processes  of  respiration  take  place  in  all 
the  tissues  and  organs  of  the  system  and  not  in  the  lungs.  Eespiration  is  a 
process  similar  to  what  are  known  as  the  processes  of  nutrition ;  and  although 
it  is  much  more  active  and  uniform  than  are  the  ordinary  nutritive  changes, 
it  is  inseparably  connected  with  and  strictly  a  part  of  the  general  process. 
As  in  the  nutrition  of  the  tissues  the  nitrogenized  constituents  of  the  blood, 
united  with  inorganic  substances,  are  transformed  into  the  tissue  itself, 
finally  changed  into  excrementitious  products,  such  as  the  urinary  mat- 
ters, and  discharged  from  the  body,  so  the  oxygen  of  the  blood  is  appro- 
priated, and  carbon  dioxide,  which  is  an  excrementitious  substance,  is  pro- 
duced, whenever  tissues  are  worn  out.  and  regenerated.  There  is  a  necessary 
and  inseparable  connection  between  all  these  processes ;  and  they  must  be 
considered,  not  as  distinct  in  themselves,  but 'as  different  parts  of  the  general 
function  of  nutrition. 

As  physiologists  are  unable  to  follow  out  all  the  intermediate  changes 
which  take  place  between  the  appropriation  of  nutritive  materials  from  the 
blood  and  the  production  of  effete,  or  excrementitious  substances,  it  is  impos- 
sible to  say  precisely  how  oxygen  is  used  by  the  tissues  and  how  carbon  dioxide 
is  produced.  It  is  known  only  that  more  or  less  oxygen  is  necessary  to  the 
nutrition  of  all  tissues,  in  all  animals,  high  or  low  in  the  scale,  and  that  the 
tissues  produce  a  certain  quantity  of  carbon  dioxide.  The  fact  that  oxygen 
is  consumed  with  much  greater  rapidity  than  any  other  nutritive  substance 
and  that  the  production  of  carbon  dioxide  is  correspondingly  active,  as  com- 
pared with  other  effete  products,  points  to  a  connection  between  the  absorp- 
tion of  the  one  and  the  production  of  the  other. 

The  essential  conditions  for  respiration  in  animals  which  have  a  circulat- 
ing nutritive  fluid  are  air  and  blood  separated  by  a  membrane  which  will 
allow  the  passage  of  gases.  The  effete  products  of  respiration  contained  in 
the  blood,  the  most  important  of  which  is  carbon  dioxide,  pass  out  and  vitiate 
the  air.  The  air  is  deprived  of  a  certain  portion  of  its  oxygen,  which  passes 
into  the  blood,  to  be  conveyed  to  the  tissues.  Thus  the  air  must  be  changed 
to  supply  fresh  oxygen  and  get  rid  of  the  carbon  dioxide.  The  rapidity  of 
this  change  is  in  proportion  to  the  nutritive  activity  of  the  animal  and  the 
rapidity  of  the  circulation  of  the  blood. 
9 


110 


RESPIRATION— RESPIRATORY  MOVEMENTS. 


PHYSIOLOGICAL  ANATOMY  OF  THE  RESPIKATOKY  OKGAXS. 

Passing  backward  from  the  mouth  to  the  pharynx,  two  openings  are 
observed ;  a  posterior  opening,  which  leads  to  the  oesophagus,  and  an  ante- 
rior opening,  the  opening  of  the  larynx,  which  is  the  beginning  of  the  pas- 
sages concerned  exclusively  in  respiration. 

Beginning  with  the  larynx,  it  is  seen  that  the  cartilages  of  which  it  is 
composed  are  sufficiently  rigid  and  unyielding  to  resist  the  pressure  produced 
by  any  inspiratory  effort.  Across  its  superior  opening  are  the  vocal  chords, 
which  are  four  in  number  and  have  a  direction  from  before  backward.  The 
two  superior  are  called  the  false  vocal  chords,  because  they  are  not  concerned 
in  the  production  of  the  voice.  The  two  inferior  are  the  true  vocal  chords. 
They  are  ligamentous  bands  covered  by  folds  of  mucous  membrane,  which  is 


13 


Fio.  39. — Trachea  and  bronchial  tubes  (Sappey). 

1,  2,  larynx  ;  3,  3,  trachea  ;  4,  bifurcation  of  the  trachea  ;  5,  right  bronchus  :  6,  left  bronchus  ;  7,  bron- 
chial division  to  the  upper  lobe  of  the  right  lung  ;  8,  division  to  the  middle  lobe  ;  9,  division  to  the 
lower  lobe  ;  10,  division  to  the  upper  lobe  of  the  left  lung  :  11,  division  to  the  lower  lobe  ;  12,  12,  12, 
12,  ultimate  ramifications  of  the  bronchia;  13, 13, 13, 13,  lungs,  represented  in  contour;  14,  14,  summit 
of  the  luugs  ;  15,  15,  base  of  the  lungs. 

quite  thick  on  the  superior  chords  and  very  thin  and  delicate  on  the  true 
vocal  chords.     These  bands  are  attached  anteriorly  to  a  fixed  point  between 


ANATOMY  OF  THE  RESPIRATORY  ORGANS.  Ill 

the  thyroid  cartilages,  and  posteriorly,  to  the  movable  arytenoid  cartilages. 
Air  is  admitted  to  the  trachea  through  an  opening  between  the  chords,  which 
is  called  the  rima  glottidis.  Little  muscles,  arising  from  the  thyroid  and  cri- 
coid  and  attached  to  the  arytenoid  cartilages,  are  capable  of  separating  and 
approximating  the  points  to  Avhich  the  vocal  chords  are  attached  posteriorly, 
so  as  to  open  and  close  the  rima  glottidis. 

If  the  glottis  be  exposed  in  a  living  animal,  certain  regular  movements  are 
presented,  which  are  synchronous  with  the  acts  of  respiration.  The  larynx 
is  slightly  opened  at  each  inspiration,  by  the  action  of  the  muscles  referred  to 
above,  so  that  the  air  has  a  free  entrance  to  the  trachea.  At  the  termination 
of  the  inspiratory  act  these  muscles  are  relaxed,  the  vocal  chords  fall  together 
by  their  own  elasticity,  and  in  expiration,  the  chink  of  the  glottis  returns  to 
the  condition  of  a  narrow  slit.  The  expulsion  of  air  from  the  lungs  in  tran- 
quil respiration  is  a  passive  process  and  tends  in  itself  to  separate  the  vocal 
chords ;  but  inspiration,  which  is  active,  were  it  not  for  the  movements  of 
the  glottis,  would  have  a  tendency  to  draw  the  vocal  chords  together.  The 
muscles  which  are  concerned  in  producing  these  movements  are  animated  by 
the  inferior  laryngeal  branches  of  the  pneumogastric  nerves.  The  respiratory 
movements  of  the  larynx  are  entirely  distinct  from  those  concerned  in  the 
production  of  the  voice. 

Attached  to  the  anterior  portion  of  the  larynx,  is  the  epiglottis,  a  little, 
leaf-shaped  lamella  of  fibro-cartilage,  which,  during  ordinary  respiration,  pro- 
jects upward  and  lies  against  the  posterior  portion  of  the  tongue.  During 
the  act  of  deglutition,  respiration  is  momentarily  interrupted,  and  the  air- 
passages  are  protected  by  the  tongue,  which  presses  backward,  carrying  the 
epiglottis  before  it  and  completely  closing  the  opening  of  the  larynx.  Physi- 
ologists have  questioned  whether  the  epiglottis  be  necessary  to  the  complete 
protection  of  the  air-passages  ;  and  it  has  frequently  been  removed  from  the 
lower  animals  without  apparently  interfering  with  the  proper  deglutition  of 
solids  or  liquids  (Magendie).  It  is  a  question,  however,  whether  the  results 
of  this  experiment  can  be  absolutely  applied  to  the  human  subject.  In  a  case 
of  loss  of  the  entire  epiglottis,  which  was  observed  in  the  Bellevue  Hospital, 
the  patient  experienced  slight  difficulty  in  swallowing,  from  the  passage  of 
little  particles  into  the  larynx,  which  produced  cough.  This  case,  and  others 
of  a  similar  character  which  are  on  record,  show  that  the  presence  of  the 
epiglottis,  in  the  human  subject  at  least,  is  necessary  to  the  complete  protec- 
tion of  the  air-passages  in  deglutition. 

Passing  down  the  neck  from  the  larynx  toward  the  lungs,  is  the  trachea, 
which  is  four  to  four  and  a  half  inches  (10-16  to  11-43  centimetres)  in  length 
and  about  three-quarters  of  an  inch  (19-1  mm.)  in  diameter.  It  is  provided 
with  cartilaginous  rings,  sixteen  to  twenty  in  number,  which  partially  sur- 
round the  tube,  leaving  about  one-third  of  its  posterior  portion  occupied  by 
fibrous  tissue  mixed  with  a  certain  number  of  non-striated  muscular  fibres. 
Passing  into  the  chest,  the  trachea  divides  into  the  two  primitive  bronchia, 
the  right  being  shorter,  larger  and  more  horizontal  than  the  left.  These 
tubes,  provided,  like  the  trachea,  with  imperfect  cartilaginous  rings,  enter  the 


112 


RESPIRATION— RESPIRATORY  MOVEMENTS. 


lungs,  divide  and  subdivide,  until  the  minute  ramifications  of  the  bronchial 
tree  open  directly  into  the  air-cells.     After  penetrating  the  lungs,  the  carti- 


FIG.  40.—  Lungs,  anterior  view  (Sappey). 

1,  upper  lobe  of  the  left  lung ;  2,  lower  lobe ;  3.  fissure  ;  4,  notch  corresponding  to  the  apex  of  the  heart ; 
5,  pericardium  :  6,  upper  lobe  of  the  right  lung  ;  7,  middle  lobe  ;  8,  lower  lobe  ;  9,  fissure  ;  10,  fissure  ; 
11,  diaphragm  ;  12,  anterior  mediastinum  ;  13,  thyroid  gland  ;  14,  middle  cervical  aponeurosis  ;  15, 
process  of  attachment  of  the  mediastinum  to  the  pericardium  ;  16,  16,  seventh  ribs;  17. 17,  transver- 
sales  muscles  ;  18,  linea  alba. 

lages  become  irregular  and  are  in  the  form  of  oblong,  angular  plates,  which 
are  so  disposed  as  to  completely  encircle  the  tubes.  In  tubes  of  very  small 
size,  these  plates  are  fewer  than  in  the  larger  bronchia,  until,  in  tubes  of  a 
less  diameter  than  -^  of  an  inch  (0-5  mm.),  they  disappear. 

The  walls  of  the  trachea  and  bronchial  tubes  are  composed  of  two  distinct 
membranes ;  an  external  membrane,  between  the  layers  of  which  the  carti- 
lages are  situated,  and  a  lining,  mucous  membrane.  The  external  membrane 
is  composed  of  inelastic  and  elastic  fibrous  tissue.  Posteriorly,  in  the  space 
not  covered  by  cartilaginous  rings,  these  fibres  are  mixed  with  a  certain  num- 
ber of  non-striated  muscular  fibres,  which  exist  in  two  layers ;  a  thick,  internal 
layer,  in  which  the  fibres  are  transverse,  and  a  thinner,  longitudinal  layer, 


ANATOMY  OF  THE  RESPIRATORY  ORGANS. 


113 


.16 


which  is  external.  The  collection  of  muscular  fibres  in  the  posterior  part  of 
the  trachea  is  sometimes  called  the  trachealis  muscle.  Throughout  the 
bronchial  tubes, 
there  are  circular 
fasciculi  of  non- 
striated  muscular 
fibres  lying  just 
beneath  the  mu- 
cous membrane, 
with  a  number  of 
longitudinal  elas- 
tic fibres.  The 
character  of  the 
bronchia  abruptly 
changes  in  tubes 
less  than  -fa  of  an 
inch  (0-5  mm.)  in 
diameter.  They 
then  lose  the  car- 
tilaginous rings, 
and  the  external 
and  the  mucous 
membranes  be- 
come so  closely 
united  that  they 
can  no  longer  be 
separated  by  dis- 
section. The  cir- 
cular muscular  fibres  continue  as  far  as  the  air-cells.  The  mucous  mem- 
brane is  smooth,  covered  by  ciliated  epithelium,  the  movements  of  the  cilia 
being  always  from  within  outward,  and  it  is  provided  with  mucous  glands. 
These  glands  are  of  the  racemose  variety  and  in  the  larynx  they  are  of  con- 
siderable size.  In  the  trachea  and  bronchia,  racemose  glands  exist  in  the 
membrane  on  the  posterior  surface  of  the  tubes ;  but  anteriorly  are  small  fol- 
licles, terminating  in  a  single,  and  sometimes  a  double,  blind  extremity. 
These  follicles  are  lost  in  tubes  measuring  less  than  -fa  of  an  inch  (O5  mm.) 
in  diameter. 

When  moderately  inflated,  the  lungs  have  the  appearance  of  irregular 
cones,  with  rounded  apices,  and  concave  bases  resting  upon  the  diaphragm. 
They  fill  that  part  of  the  cavity  of  the  thorax  which  is  not  occupied  by  the 
heart  and  great  vessels,  and  are  completely  separated  from  each  other  by  the 
mediastinum.  The  lungs  are  in  contact  with  the  thoracic  walls,  each  lung 
being  covered  by  a  reflection  of  the  serous  membrane  which  lines  the  cavity 
of  the  corresponding  side.  Thus  they  necessarily  follow  the  movements  of 
expansion  and  contraction  of  the  thorax.  Deep  fissures  divide  the  right  lung 
into  three  lobes  and  the  left  lung  into  two.  The  surface  of  the  lungs  is  di- 


FIG.  41.  —  Bronchia  and  lungs,  posterior  view  (Sappey). 
5,  division  to  the  upper  lobe  of  the  lung  ;  6,  division  to  the  lower  lobe  ;  7, 


1,  1,  summit  of  the  lungs  ;  2.  2.  base  of  the  lungs  ;  3,  trachea  ;  4,  right  bronchus; 
5,  division  to  the  upper  lobe  of  the  lung  ;  6,  division  to  the  lower  lobe  ;  7, 
left  bronchus  ;  8,  division  to  the  upper  lobe  ;  9,  division  to  the  lou'er  lobe  ; 


, 

10,  left  branch  of  the  pulmonary  artery;  11  ,  right  branch  ;  12,  left  auricle 
of  the  heart  :  13,  left  superior  pulmonary  vein  ;  14,  left  inferior  pulmonary 
vein  ;  15,  right  superior  pulmonary  vein  ;  16.  right  inferior  pulmonary 
vein  ;  17,  inferior  vena  cava  ;  18,  left  ventricle  of  the  heart  ;  19,  right  ven- 
tricle. 


114 


RESPIRATION— RESPIRATORY  MOVEMENTS. 


vided  into  irregularly  polygonal  spaces,  £  of  an  inch  to  an  inch  (6*4  to  25-4 
mm.)  in  diameter,  which  mark  what  are  sometimes  called  the  pulmonary 
lobules ;  although  this  term  is  incorrect,  as  each  of  these  divisions  includes 
quite  a  number  of  the  true  lobules. 

Following  out  the  bronchial  tubes  from  the  diameter  of  -gL  Of  an  inch 
(0-5  mm.),  the  smallest,  which  are  y^  to  ^  of  an  inch  (0'21  to  0-33  mm.) 
in  diameter,  open  into  a  collection  of  oblong  vesicles,  which  are  the  air- 
cells.  Each  collection  of  vesicles  constitutes  one  of  the  true  pulmonary 
lobules  and  is  -g^  to  y^  of  an  inch  (0-5  to  2-1  mm.)  in  diameter.  After 
entering  the  lobule,  the  tube  forms  a  tortuous  central  canal,  sending  off 
branches  which  terminate  in  groups  of  eight  to  fifteen  pulmonary  cells. 
The  cells  are  a  little  deeper  than  they  are  wide  and  have  each  a  rounded, 

blind  extremity.  Some  are  smooth, 
but  many  are  marked  by  little  cir- 
cular constrictions,  or  rugae.  In 
the  healthy  lung  of  the  adult,  after 
death,  they  measure  -g-J-g-  to  y^  or 
-^  of  an  inch  (0-125  to  0'21  or 
0'36  mm.)  in  diameter,  but  are 
capable  of  very  great  distention. 
The  smallest  cells  are  in  the  deep 
portions  of  the  lungs,  and  the 
largest  are  situated  near  the  sur- 
face. There  are  considerable  vari- 
ations in  the  size  of  the  cells  at 
different  periods  of  life.  The 
smallest  cells  are  found  in  young 
children,  and  they  progressively 
increase  in  size  with  age.  The 
walls  of  the  air-cells  contain  very 
abundant  small,  elastic  fibres, 
which  do  not  form  distinct  bun- 
dles for  each  air-cell,  but  anasto- 
mose freely  with  each  other,  so 
that  the  same  fibres  belong  to  two 
or  more  cells.  This  structure  is 
peculiar  to  the  parenchyma  of  the  lungs  and  gives  to  these  organs  their  great 
distensibility  and  elasticity,  properties  which  play  an  important  part  in  ex- 
pelling the  air  from  the  chest,  as  a  consequence  simply  of  cessation  of  the 
action  of  the  inspiratory  muscles.  Interwoven  with  these  elastic  fibres,  is  the 
richest  plexus  of  capillary  blood-vessels  found  in  the  economy.  The  vessels 
are  larger  than  the  capillaries  in  other  situations,  and  the  plexus  is  so  close 
that  the  spaces  between  them  are  narrower  than  the  vessels  themselves. 
When  distended,  the  blood-vessels  form  the  greatest  part  of  the  walls  of  the 
cells. 
.  Lining  the  air-cells,  are  very  thin  cells  of  flattened  epithelium, 


FIG.  42. — Mould  of  a  terminal  bronchus  and  a  group  of 
air-cells  moderately  distended  by  injection,  from 
the  human  subject  (Robin). 


INSPIRATION.  115 

^OQ-  of  an  inch  (10  to  12-5  //,),  in  diameter,  which  are  applied  directly  to  the 
walls  of  the  blood-vessels.  The  epithelium  here  does  not  seem  to  be  regular- 
ly desquamated  as  in  other  situations.  Examination  of  injected  specimens 
shows  that  the  blood-vessels  are  so  situated  between  the  cells,  that  the  blood 
in  the  greater  part  of  their  circumference  is  exposed  to  the  action  of  the  air. 
The  entire  mass  of  venous  blood  is  distributed  in  the  lungs  by  the  pul- 
monary artery.  Arterial  blood  is  conveyed  to  these  organs  by  the  bronchial 
arteries,  which  ramify  and  subdivide  on  the  bronchial  tubes  and  follow  their 
course  into  the  lungs,  for  the  nourishment  of  these  parts.  It  is  possible  that 
the  tissue  of  the  lungs  may  receive  some  nourishment  from  the  blood  of 
the  pulmonary  artery ;  but  as  this  vessel  does  not  send  any  branches  to  the 


FIG.  43. — Section  of  the  parenchyma  of  the  human  htng,  injected  through  the  pulmonary 

artery  (Schulze). 
a,  a,  c,  c,  walls  of  the  air-cells  ;  6,  small  arterial  branch. 

bronchial  tubes,  the  bronchial  arteries  supply  the  matters  for  their  nutrition 
and  for  the  secretion  of  the  mucous  glands. 

The  foregoing  anatomical  sketch  shows  the  adaptation  of  the  trachea  and 
bronchial  tubes  to  the  passage  of  the  air  by  inspiration  to  the  deep  portions 
of  the  lungs,  and  the  favorable  conditions  which  it  there  meets  with  for  an 
interchange  of  gases.  It  is  also  evident,  from  the  great  number  of  air-cells, 
that  the  respiratory  surface  must  be  very  large,  although  it  is  impossible  to 
form  an  accurate  estimate  of  its  extent. 

MOVEMENTS  OF  RESPIRATION. 

In  man  and  in  the  warm-blooded  animals  generally,  inspiration  takes 
place  as  a  consequence  of  enlargement  of  the  thoracic  cavity  and  the  en- 
trance of  a  quantity  of  air  through  the  respiratory  passages,  corresponding 


116 


RESPIRATION— RESPIRATORY  MOVEMENTS. 


to  the  increased  capacity  of  the  lungs.     In  the  mammalia,  the  chest  is  en- 
larged by  the  action  of  muscles ;   and  in  .ordinary  respiration,  inspiration  is 

an  active  process,  while  ordinary  expira- 
tion is  passive. 

A  glance  at  the  physiological  anato- 
my of  the  thorax  in  the  human  subject 
makes  it  evident  that  the  action  of  cer- 
tain muscles  will  considerably  increase  its 
capacity.  In  the  first  place,  the  dia- 
phragm mounts  up  into  its  cavity  in  the 
form  of  a  vaulted  arch.  By  contraction 
of  its  fibres,  it  is  brought  nearer  a  plane, 
and  thus  the  vertical  diameter  of  the 
thorax  is  increased.  The  walls  of  the 
thorax  are  formed  by  the  dorsal  vertebrae 
and  ribs  posteriorly,  by  the  upper  ten 
ribs  laterally,  and  by  the  sternum  and 
costal  cartilages  anteriorly.  The  direc- 
FIG.  44.— Thorax,  anterior  view  (Sappey).  tion  of  the  ribs,  their  mode  of  connection 

1,  2,  3,  sternum  ;  4,  circumference  of  the  upper  wifh  flip  orprrmm  hv  fhp  nrvsfal  c 

portion  of  the  thorax  ;  5,  circumference  of  W11  ™  IJ 

the  base  of  the  thorax  ;  6,  first  rib  ;  7,  sec-  orirl    fhpiv    artirMila-t-irm  wifh    flip 

ond  rib  ;  8,  8,  last  five  sternal  ribs  ;  9,  up-  dn 

mgrfb^/f'cos^^  column,  are  such  that  by  their  move- 

ments, the  antero-posterior   and    trans- 
verse diameters  of  the  chest  may  be  considerably  modified. 

Inspiration. — The  ribs  are  somewhat  twisted  upon  themselves  and  have  a 
general  direction  forward  and  downward.  The  first  rib  is  nearly  horizontal, 
but  the  obliquity  of  the  ribs  progressively 
increases  from  the  upper  to  the  lower 
part  of  the  chest.  They  are  articulated 
with  the  bodies  of  the  vertebrae,  so  as  to 
allow  of  considerable  motion.  The  up- 
per seven  ribs  are  attached  by  the  costal 
cartilages  to  the  sternum,  these  cartilages 
running  upward  and  inward.  The  car- 
tilages of  the  eighth,  ninth  and  tenth 
ribs  are  joined  to  the  cartilage  of  the  sev- 
enth. The  eleventh  and  twelfth  are 
floating  ribs  and  are  attached  only  to  the 
vertebrae. 

It  may  be  stated  in  general  terms  that 
inspiration  is  effected  by  descent  of  the 
diaphragm  and  elevation  of  the  ribs ;  and 
expiration,  by  elevation  of  the  diaphragm 

and  descent  of  the  ribs.  FIG.  45.— Thorax,  posterior  view  (Sappey). 

A    •   •  11      «  IT       i  1, 1,  spinous  processes  of  the  dorsal  vertebrae ; 

Arising  Severally  from  the   lower   bor-  2.  2,  lamina?  of  the  vertebra  ;  3,  3,  trans 

der  of  each  rib  and  attached  to  the  up- 


MUSCLES  OF  INSPIRATION.  117 

per  border  of  the  rib  below,  are  the  eleven  external  intercostal  muscles,  the 
fibres  of  which  have  an  oblique  direction  from  above  downward  and  forward. 
Attached  to  the  inner  borders  of  the  ribs,  are  the  internal  intercostals,  which 
have  a  direction  from  above  downward  and  backward,  nearly  at  right  angles 
to  the  fibres  of  the  external  intercostals.  There  are  also  certain  muscles 
attached  to  the  thorax  and  spine,  thorax  and  head,  upper  part  of  humerus, 
etc.,  which  are  capable  of  elevating  either  the  entire  chest  or  the  ribs.  These 
must  act  as  muscles  of  inspiration  when  the  attachments  to  the  thorax  be- 
come the  movable  points.  Some  of  them  are  called  into  action  during  ordi- 
nary respiration ;  others  act  as  auxiliaries  when  respiration  is  a  little  exag- 
gerated, as  after  exercise,  and  are  called  ordinary  auxiliaries ;  while  others, 
which  ordinarily  have  different  uses,  act  only  when  respiration  is  difficult, 
and  are  called  extraordinary  auxiliaries. 

The  following  are  the  principal  muscles  concerned  in  inspiration  : 

MUSCLES   OF   INSPIRATION. 
Ordinary  Respiration. 

MUSCLE.  ATTACHMENTS. 

Diaphragm Circumference  of  lower  border  of  thorax. 

Scalenus  anticus Transverse  processes  of  third,  fourth,  fifth  and 

sixth  cervical  vertebras tubercle  of  first  rib. 

Scalenus  medius Transverse  processes  of  lower  six  cervical  vertebrae 

• upper  surface  of  first  rib. 

Scalenus  posticus Transverse  processes  of  lower  two  or  three  cer- 
vical vertebras outer  surface  of  second  rib. 

External  intercostals Outer  borders  of  the  ribs. 

Sternal  portion  of  internal  intercostals.  .Borders  of  the  costal  cartilages. 

Twelve  levatores  costarum Transverse  processes  of  dorsal  vertebras ribs, 

between  the  tubercles  and  angles. 

Ordinary  Auxiliaries. 

Serratus  posticus  superior Liganientum  nuchae,  spinous  processes  of  last  cer- 
vical and  upper  two  or  three  dorsal  vertebrae 

upper  borders  of  second,  third,  fourth  and  fifth 
ribs,  just  beyond  the  angles. 

Sterno-mastoideus Upper  part  of  sternum mastoid  process  of  tem- 
poral bone. 

Extraordinary  Auxiliaries. 

Levator  anguli  scapulae Transverse  processes  of  upper  three  or  four  cer- 
vical vertebrae posterior  border  of  superior 

angle  of  scapula. 

Trapezius  (superior  portion) Liganientum  nuchae  and  seventh  cervical  verte- 
bra;  upper  border  of  spine  of  scapula. 

Pectoralis  minor Coracoid  process  of  scapula anterior  surface 

and  upper  margins  of  third,  fourth  and  fifth 
ribs,  near  the  cartilages. 

Pectoralis  major  (inferior  portion) Bicipital  groove  of  humerus costal  cartilages 

and  lower  part  of  sternum. 

Serratus  magnus Inner  margin  of  posterior  border  of  scapula — 

external  surface  and  upper  border  of  upper 
eight  ribs. 


118 


RESPIRATION— RESPIRATORY  MOVEMENTS. 

13 


20 

FIG.  46.— Diaphragm  (Sappey). 

1,  2.  3,  central  tendon  ;  4,  right  pillar  ;  5,  left  pillar  ;  6,  7,  processes  between  the  pillars  ;  8,  8,  openings 
for  the  splanchnic  nerves  ;  9,  fibrous  arch  passing  over  the  psoas  magnus  ;  10,  fibrous  arch  passing 
over  the  quadratus  lumborum  :  11,  muscular  fibres  arising  from  these  two  arches  ;  12,  12,  muscular 
fibres  arising  from  the  lower  six  ribs  ;  13,  fibres  from  the  ensiform  cartilage  ;  14,  opening  for  the 
vena  cava  ;  15,  opening  for  the  oesophagus  ;  16,  opening  for  the  aorta  ;  17,  17,  part  of  the  transver- 
salis  muscle  ;  18,  18,  aponeurosis  ;  19,  19,  quadratus  lumborum  ;  20,  20,  psoas  magnus  ;  21,  fourth 
lumbar  vertebra. 

Action  of  the  Diaphragm. — The  descriptive  and  general  anatomy  of  the 
diaphragm  gives  a  pretty  correct  idea  of  its  uses  in  respiration.     It  arises 

from  the  border  of  the  lower  circumfer- 
ence of  the  thorax  and  mounts  into  the 
cavity  of  the  chest,  forming  a  vaulted 
arch,  or  dome,  with  its  concavity  toward 
the  abdomen  and  its  convexity  toward 
the  lungs.  In  the  central  portion,  there 
is  a  tendon  of  considerable  size  and  shaped 
something  like  the  club  on  a  playing- 
card,  with  middle,  right  and  left  leaflets. 
The  remainder  of  the  organ  is  composed 
of  radiating  fibres  of  striated  muscular 
tissue.  The  resophagus,  aorta  and  infe- 
rior vena  cava  pass  through  the  dia- 
phragm from  the  thoracic  to  the  abdom- 
inal cavity,  by  three  openings. 

The  opening  for  the  oesophagus  is  sur- 
rounded by  muscular  fibres,  by  which  it 
FIG.  47.— Action  of  the  diaphragm  in  inspira-  is  partially  closed  when  the  diaphragm 
tion  (Hermann).  contracts   in   inspiration,   as    the    fibres 

Vertical  section  through  the  second  rib  on  the 

right  side    The  broken  and  dotted  lines  simply  surround  the  tube  and  none  are 

show  the  descent  of  the  diaphragm.  "  * 

attached  to  its  walls. 


MUSCLES  OF  INSPIRATION.  119 

The  orifice  for  the  aorta  is  bounded  by  the  bone  and  aponeurosis  posteri- 
orly, and  in  front,  by  a  fibrous  band  to  which  the  muscular  fibres  are  attached, 
so  that  their  contraction  has  a  tendency  rather  to  increase  than  to  diminish 
the  caliber  of  the  vessel. 

The  orifice  for  the  vena  cava  is  surrounded  entirely  by  tendinous  struct- 
ure, and  contraction  of  the  diaphragm,  although  it  might  render  the  form  of 
the  orifice  more  nearly  circular,  can  have  no  effect  upon  its  size. 

In  ordinary  respiration,  the  descent  of  the  diaphragm  and  its  approxima- 
tion to  a  plane  are  the  chief  phenomena  observed ;  but  as  there  is  some  re- 
sistance to  the  depression  of  the  central  tendon,  it  is  probable  that  there  is 
also  a  slight  elevation  of  the  inferior  ribs. 

The  phenomena  referable  to  the  abdomen  which  coincide  with  the  de- 
scent of  the  diaphragm  can  easily  be  observed  in  the  human  subject.  As  the 
diaphragm  is  depressed,  it  necessarily  pushes  the  viscera  before  it,  and  inspi- 
ration is  therefore  accompanied  by  protrusion  of  the  abdomen.  This  may 
be  rendered  very  marked  by  a  forced  or  deep  inspiration. 

The  effects  of  the  action  of  the  diaphragm  upon  the  size  of  its  orifices 
are  limited  chiefly  to  the  oesophageal  opening.  The  anatomy  of  the  parts  is 
such  that  contraction  of  the  muscular  fibres  has  a  tendency  to  close  this 
orifice.  The  contraction  of  the  diaphragm  is  auxiliary  to  the  action  of  the 
muscular  walls  of  the  oesophagus  itself,  by  which  the  cardiac  opening  of  the 
stomach  is  regularly  closed  during  inspiration.  This  may  become  impor- 
tant when  the  stomach  is  much  distended ;  for  descent  of  the  diaphragm 
compresses  all  the  abdominal  organs  and  might  otherwise  cause  regurgitation 
of  food. 

The  contractions  of  the  diaphragm  are  animated  almost  exclusively,  if  not 
exclusively,  by  the  phrenic  nerve ;  a  nerve  which,  having  the  office  of  sup- 
plying the  most  important  respiratory  muscle,  derives  its  filaments  from  a 
number  of  sources.  It  arises  from  the  third  and  fourth  cervical  nerves,  re- 
ceiving a  branch  from  the  fifth  and  sometimes  from  the  sixth.  It  then  passes 
through  the  chest,  penetrates  the  diaphragm,  and  is  distributed  to  its  under 
surface.  Stimulation  of  this  nerve  produces  convulsive  contractions  of  the 
diaphragm,  and  its  section  paralyzes  the  muscle  almost  completely. 

From  the  great  increase  in  the  capacity  of  the  chest  produced  by  the  ac- 
tion of  the  diaphragm  and  its  constant  and  universal  action  in  respiration,  it 
must  be  regarded  as  by  far  the  most  important  and  efficient  of  the  muscles 
of  inspiration. 

Hiccough,  sobbing,  laughing  and  crying  are  due  mainly  to  the  action  of 
the  diaphragm,  particularly  hiccough  and  sobbing,  which  are  produced  by 
spasmodic  contractions  of  this  muscle,  generally  not  under  the  control  of  the 
will. 

Action  of  the  Muscles  which  elevate  the  Ribs. — Scalene  Muscles. — In  ordi- 
nary respiration,  the  ribs  and  the  entire  chest  are  elevated  by  the  combined 
action  of  a  number  of  muscles.  The  three  scalene  muscles  are  attached  to 
the  cervical  vertebrae  and  the  first  and  second  ribs.  These  muscles,  which 
act  particularly  upon  the  first  rib,  must  elevate  with  it,  in  inspiration,  the 


120  RESPIRATION— RESPIRATORY  MOVEMENTS. 

rest  of  the  thorax.  The  articulation  of  the  first  rib  with  the  vertebral  column 
is  very  movable,  but  it  is  joined  to  the  sternum  by  a  very  short  cartilage, 
which  allows  of  very  little  movement,  so  that  its  elevation  necessarily  carries 
with  it  the  sternum.  This  movement  increases  both  the  transverse  and  an- 
tero-posterior  diameters  of  the  thorax,  on  account  of  the  mode  of  articulation 
and  direction  of  the  ribs,  which  are  somewhat  rotated  as  well  as  rendered 
more  horizontal. 

Intercostal  Muscles. — Concerning  the  mechanism  of  the  action  of  these 
muscles  there  is  considerable  difference  of  opinion  among  physiologists ;  so 
much,  indeed,  that  the  question  is  still  left  in  some  uncertainty.  The  most 
extended  researches  on  this  point  are  those  of  Beau  and  Maissiat  (1843),  and 
Sibson  (1846).  The  latter  seem  to  settle  the  question  of  the  mode  of  action 
of  the  intercostals  and  explain  satisfactorily  certain  points  which  even  now 
are  not  generally  appreciated.  Onimus,  and  more  recently,  Laborde,  have 
shown,  by  experiments  upon  decapitated  criminals,  that  the  external  inter- 
costals raise  and  the  internal  intercostals  depress  the  ribs,  thus  confirming 
the  views  of  Sibson. 

In  the  dorsal  region,  the  spinal  column  forms  an  arch  with  its  concavity 
looking  toward  the  chest,  and  the  ribs  increase  in  length  progressively,  from 
above  downward,  to  the  deepest  portion  of  the  arch,  where  they  are  longest, 
and  then  become  progressively  shorter.  "During  inspiration  the  ribs  ap- 
proach to  or  recede  from  each  other  according  to  the  part  of  the  arch  with 
which  they  articulate ;  the  four  superior  ribs  approach  each  other  anteriorly 
and  recede  from  each  other  posteriorly ;  the  fourth  and  fifth  ribs,  and  the 
intermediate  set  (sixth,  seventh,  and  eighth),  move  further  apart  to  a  mod- 
erate, the  diaphragmatic  set  (four  inferior),  to  a  great  extent.  The  upper 
edge  of  each  of  these  ribs  glides  toward  the  vertebrae  in  relation  to  the  lower 

edge  of  the  rib  above,  with  the  exception  of  the 
lowest  rib  which  is  stationary"  (Sibson).  These 
movements  increase  the  antero-posterior  and  trans- 
verse diameters  of  the  thorax.  As  the  ribs  are  ele- 
vated and  become  more  nearly  horizontal,  they 
must  push  forward  the  lower  portion  of  the  ster- 
num. Their  configuration  and  mode  of  articula- 
tion with  the  vertebras  are  such  that  they  can  not 
be  elevated  without  undergoing  a  considerable  ro- 
tation, by  which  the  concavity  looking  directly  to- 
ward the  lungs  is  increased,  and  with  it  the  lateral 
diameter  of  the  chest.  All  the  intercostal  spaces 
FIG.  4S.-E^tion  «L  nbs  in  posteriorly  are  widened  in  inspiration. 

inspiration  (B6ciard).  The  ribs  are  elevated  by  the  action  of  the  ex- 

The  dark  lines  represent  the  ribs,  i  «    ,  ,in  ,  •  •  »i       »    i 

sternum  and  costal  cartilages  ternal  intercostals,  the  sternal  portion  oi  the  inter- 
nal intercostals  and  the  levatores  costarum.     The 

external  intercostals  are  situated  between  the  ribs  only,  and  are  wanting  in 
the  region  of  the  costal  cartilages.  As  the  vertebral  extremities  of  the  ribs 
are  the  pivots  on  which  these  levers  move,  and  as  the  sternal  extremities  are 


MUSCLES  OF  INSPIRATION.  121 

movable,  the  direction  of  the  fibres  of  the  intercostals  from  above  downward 
and  forward  renders  elevation  of  the  ribs  a  necessity  of  their  contraction,  if 
it  can  be  assumed  that  the  first  rib  is  fixed  or  at  least  does  not  move  down- 
ward. The  scalene  muscles  elevate  the  first  rib  in  ordinary  inspiration ;  and 
in  deep  inspiration,  this  takes  place  to  such  an  extent  as  to  palpably  carry 
with  it  the  sternum  and  the  lower  ribs.  Theoretically,  then,  the  external  in- 
tercostals can  do  nothing  but  render  the  ribs  more  nearly  horizontal. 

If  the  external  intercostals  be  exposed  in  the  dog — in  which  the  costal 
type  of  respiration  is  very  marked — close  observation  can  hardly  fail  to  show 
that  these  muscles  enter  into  action  in  inspiration.  If  attention  be  directed 
to  the  sternal  portion  of  the  internal  intercostals,  situated  between  the  costal 
cartilages,  their  fibres  having  a  direction  from  above  downward  and  back- 
ward, it  is  equally  evident  that  they  enter  into  action  with  inspiration.  By 
artificially  inflating  the  lungs  after  death,  it  is  seen  that  when  the  lungs  are 
filled  with  air,  the  fibres  of  these  muscles  are  shortened  (Sibson).  In  inspira- 
tion the  ribs  are  all  separated  posteriorly ;  but  laterally  and  anteriorly,  some 
are  separated  (all  below  the  fourth),  and  some  are  approximated  (all  above 
the  fourth).  Thus  all  the  interspaces,  except  the  anterior  portion  of  the  up- 
per three,  are  widened  in  inspiration.  Sibson  has  shown  by  inflation  of  the 
chest,  that  although  the  ribs  are  'separated  from  each  other,  the  attachments 
of  the  intercostals  are  approximated.  The  ribs,  from  an  oblique  position,  are 
rendered  nearly  horizontal ;  and  consequently  the  inferior  attachments  of  the 
intercostals  are  brought  nearer  the  spinal  column,  while  the  superior  attach- 
ments to  the  upper  borders  of  the  ribs  are  slightly  removed  from  it.  Thus 
these  muscles  are  shortened.  If,  by  separating  and  elevating  the  ribs,  the 
muscles  be  shortened,  it  follows  that  shortening  of  the  muscles  will  necessa- 
rily elevate  and  separate  the  ribs.  In  the  three  superior  interspaces,  the  con- 
stant direction  of  the  ribs  is  nearly  horizontal,  and  the  course  of  the  inter- 
costal fibres  is  not  so  oblique  as  in  those  situated  between  the  lower  ribs. 
These  spaces  are  narrowed  in  inspiration.  The  muscles  between  the  costal 
cartilages  have  a  direction  opposite  to  that  of  the  external  intercostals  and 
act  upon  the  ribs  from  the  sternum,  as  the  others  do  from  the  spinal  column. 
The  superior  interspace  is  narrowed,  and  the  others  are  widened  in  inspiration. 

Levatores  Costarum. — The  action  of  these  muscles  can  not  be  mistaken. 
They  have  immovable  points  of  origin,  the  transverse  processes  of  twelve 
vertebrae  from  the  last  cervical  to  the  eleventh  dorsal,  and  spreading  out  like 
a  fan,  are  attached  to  the  upper  edges  of  the  ribs  between  the  tubercles  and 
the  angles.  In  inspiration  they  contract  and  assist  in  the  elevation  of  the 
ribs. 

Auxiliary  Muscles  of  Inspiration. — The  muscles  which  have  just  been 
considered  are  competent  to  increase  the  capacity  of  the  thorax  sufficiently  in 
ordinary  respiration ;  but  there  are  certain  muscles  attached  to  the  chest  and 
the  upper  part  of  the  spinal  column  or  the  upper  extremities,  which  may  act 
in  inspiration,  although  ordinarily  the  chest  is  the  fixed  point  and  they  move 
the  head,  neck  or  arms.  These  muscles  are  brought  into  action  when  the 
movements  of  respiration  are  exaggerated.  When  this  exaggeration  is  but 


122  RESPIRATION— RESPIRATORY  MOVEMENTS. 

slight  and  is  physiological,  as  after  exercise,  certain  of  the  ordinary  auxilia- 
ries act  for  a  time,  until  the  tranquillity  of  the  movements  is  restored  ;  but 
when  there  is  obstruction  in  the  respiratory  passages  or  when  respiration  is 
difficult  from  any  cause,  threatening  suffocation,  all  the  muscles  which  can 
by  any  possibility  raise  the  chest  are  brought  into  action.  These  are  put  down 
in  the  table  under  the  head'  of  extraordinary  auxiliaries.  Most  of  these  mus- 
cles can  voluntarily  be  brought  into  play  to  raise  the  chest,  and  the  mechan- 
ism of  their  action  can  in  this  way  be  demonstrated. 

Serratus  Posticus  Superior. — This  muscle,  by  reversing  its  ordinary 
action,  is  capable  of  increasing  the  capacity  of  the  thorax. 

Sterno-mastoideus. — That  portion  of  the  muscle  which  is  attached  to  the 
mastoid  process  of  the  temporal  bone  and  the  sternum,  when  the  head  is  fixed, 
is  capable  of  acting  as  a  muscle  of  inspiration.  It  does  not  act  in  ordinary 
respiration,  but  its  contractions  can  be  readily  observed  whenever  respiration 
is  hurried  or  exaggerated. 

The  following  muscles  as  a  rule  act  as  muscles  of  inspiration  only  when 
respiration  is  very  difficult  or  labored  : 

Levator  Anguli  Scapulce  and  Superior  Portion  of  the  Trapezius. — Move- 
ments of  the  scapula  have  often  been  observed  in  labored  respiration.  Its 
elevation  during  inspiration  is  effected  chiefly  by  the  levator  anguli  scapulae 
and  the  upper  portion  of  the  trapezius. 

Pectoralis  Minor  and  Inferior  Portion  of  the  Pectoralis  Major. — These 
muscles  act  together  to  raise  the  ribs  in  difficult  respiration.  The  pectoralis 
minor  is  the  more  efficient.  With  the  coracoid  process  as  the  fixed  point, 
this  muscle  is  capable  of  powerfully  assisting  in  the  elevation  of  the  ribs. 
That  portion  of  the  pectoralis  major  which  is  attached  to  the  lower  part  of 
the  sternum  and  costal  cartilages  is  capable  of  acting  from  its  insertion  into 
the  bicipital  groove  of  the  humerus,  when  the  shoulders  are  fixed,  in  concert 
with  the  pectoralis  minor. 

Serratus  Magnus. — Acting  from  the  scapula  as  the  fixed  point,  this  mus- 
cle is  capable  of  assisting  the  pectorals  in  raising  the  ribs  and  becomes  a  pow- 
erful auxiliary  in  difficult  inspiration. 

The  uses  of  the  principal  inspiratory  muscles  have  been  considered  with- 
out taking  up  those  which  have  an  insignificant  or  undetermined  action.  In 
many  animals,  the  nares  are  considerably  distended  in  inspiration ;  and  in 
the  horse,  which  does  not  respire  by  the  mouth,  these  movements  are  as  es- 
sential to  life  as  are  the  respiratory  movements  of  the  larynx.  In  man,  as 
a  rule  the  nares  undergo  no  movements  unless  respiration  be  somewhat  ex- 
aggerated. In  very  difficult  respiration  the  mouth  is  opened  at  each  inspira- 
tory act. 

The  division  into  muscles  of  ordinary  inspiration,  ordinary  auxiliaries  and 
extraordinary  auxiliaries,  must  not  be  taken  as  absolute.  In  the  male,  in 
ordinary  respiration,  the  diaphragm,  intercostals  and  levatores  costarum  are 
the  principal  inspiratory  muscles,  and  the  action  of  the  scaleni,  with  the  con- 
sequent elevation  of  the  sternum,  is  commonly  very  slight  or  it  may  be  want- 
ing. In  the  female  the  movements  of  the  upper  parts  of  the  chest  are  more 


EXPIRATION.  123 

marked,  and  the  scaleni,  the  serratus  posticus  superior,  and  sometimes  the 
sterno-mastoid,  are  brought  into  action  in  ordinary  respiration.  In  the 
different  types  of  respiration,  the  action  of  the  muscles  engaged  in  ordinary 
respiration  necessarily  presents  considerable  variations. 

Expiration. — The  air  is  expelled  from  the  lungs,  in  ordinary  expiration, 
by  a  simple  and  comparatively  passive  process.  The  lungs  contain  a  large 
number  of  elastic  fibres  surrounding  the  air-cells  and  the  smallest  ramifica- 
tions of  the  bronchial  tubes,  which  give  them  great  elasticity.  The  thoracic 
walls  are  also  very  elastic,  particularly  in  young  persons.  After  the  muscles 
which  increase  the  capacity  of  the  thorax  cease  their  action,  the  elasticity  of 
the  costal  cartilages  and  the  tonicity  of  the  muscles  which  have  been  put  on 
the  stretch  restore  the  chest  to  what  may  be  called  its  passive  dimensions. 
This  elasticity  is  likewise  capable  of  acting  as  an  inspiratory  force  when  the 
chest  has  been  compressed  in  any  way.  There  are  also  certain  muscles,  the 
action  of  which  is  to  draw  the  ribs  downward  and  which,  in  tranquil  respira- 
tion, are  antagonistic  to  those  which  elevate  the  ribs.  Aside  from  this,  many 
operations,  such  as  speaking,  blowing,  singing  etc.,  require  powerful,  pro- 
longed or  complicated  acts  of  expiration,  in  which  many  muscles  are  brought 
into  play. 

Expiration  may  be  considered  as  depending  upon  two  causes : 

1.  The  passive  influence  of  the  elasticity  of  the  lungs  and  thoracic  walls. 

2.  The  action  of  certain  muscles,  which  either  diminish  the  transverse 
and  antero-posterior  diameters  of  the  chest  by  depressing  the  ribs  and  ster- 
num, or  the  vertical  diameter,  by  pressing  up  the  abdominal  viscera  against 
the  diaphragm. 

Influence  of  the  Elasticity  of  the  Pulmonary  Structure  and  Walls  of  the 
Chest. — It  is  easy  to  understand  the  influence  of  the  elasticity  of  the  pul- 
monary structure  in  expiration.  From  the  collapse  of  the  lungs  when  open- 
ings are  made  in  the  chest,  it  is  seen  that  even  after  the  most  complete  expi- 
ration, these  organs  have  a  tendency  to  expel  part  of  their  gaseous  contents, 
which  can  not  be  fully  satisfied  until  the  chest  is  opened.  They  remain  par- 
tially distended,  on  account  of  the  impossibility  of  collapse  of  the  thoracic 
walls  beyond  a  certain  point ;  and  by  virtue  of  their  elasticity,  they  exert  a 
suction  force  upon  the  diaphragm,  causing  it  to  form  a  vaulted  arch,  or  dome 
above  the  level  of  the  lower  circumference  of  the  chest.  When  the  lungs 
are  collapsed,  the  diaphragm  hangs  loosely  between  the  abdominal  and  tho- 
racic cavities.  In  inspiration  and  in  expiration,  then,  the  relations  between 
the  lungs  and  diaphragm  are  reversed.  In  inspiration,  the  descending  dia- 
phragm exerts  a  suction  force  on  the  lungs,  drawing  them  downward ;  in 
expiration,  the  elastic  lungs  exert  a  suction  force  upon  the  diaphragm,  draw- 
ing it  upward.  This  antagonism  is  one  of  the  causes  of  the  great  power  and 
importance  of  the  diaphragm  as  an  inspiratory  muscle. 

The  elasticity  of  the  lungs  operates  chiefly  upon  the  diaphragm  in  reduc- 
ing the  capacity  of  the  chest ;  for  the  walls  of  the  thorax,  by  reason  of  their 
own  elasticity,  have  a  reaction  which  succeeds  the  movements  produced  by 
the  inspiratory  muscles.  Although  this  is  the  main  action  of  the  lungs 


121  RESPIRATION— RESPIRATORY  MOVEMENTS. 

themselves  in  expiration,  their  relations  to  the  walls  of  the  thorax  are  impor- 
tant. By  virtue  of  their  elasticity,  they  assist  the  passive  collapse  of  the 
chest.  When  they  lose  this  property  to  any  considerable  extent,  as  in  vesic- 
ular emphysema,  they  offer  a  notable  resistance  to  the  contraction  of  the 
thorax ;  so  much  indeed,  that  in  old  cases  of  this  disease  the  thoracic  move- 
ments are  restricted,  and  the  chest  presents  a  characteristic  rounded  and  dis- 
tended appearance. 

Little  more  need  be  said  concerning  the  passive  movements  of  the  tho- 
racic walls.  When  the  action  of  the  inspiratory  muscle  ceases,  the  ribs  regain 
their  oblique  direction,  the  intercostal  spaces  are  narrowed,  and  the  sternum, 
if  it  have  been  elevated  and  drawn  forward,  falls  back  to  its  place,  simply  by 
virtue  of  the  elasticity  of  the  parts. 

Action  of  Muscles  in  Expiration. — The  following  are  the  principal  mus- 
cles concerned  in  expiration : 

MUSCLES   OF   EXPIRATION. 
Ordinary  Respiration. 

MUSCLE.  ATTACHMENTS. 

Osseous  portion  of  internal  intercostals .  .Inner  borders  of  the  ribs. 

Inf racostales Inner  surfaces  of  the  ribs. 

Triangularis  sterni Ensiform  cartilage,  lower  borders  of  sternum, 

lower  three  or  four  costal  cartilages carti- 
lages of  the  second,  third,  fourth  and  fifth  ribs. 

Auxiliaries. 

Obliquus  externus External  surface  and  inferior  borders  of  eight 

inferior  ribs anterior  half  of  the  crest  of 

the  ileum,  Poupart's  ligament,  linea  alba. 

Obliquus  internus Outer  half  of  Poupart's  ligament,  anterior  two- 
thirds  of  the  crest  of  the  ileum,  lumbar  fascia 

cartilages  of  four  inferior  ribs,  linea  alba, 

crest  of  the  pubis,  pectineal  line. 

Transversalis Outer  third  of  Poupart's  ligament,  anterior  two- 
thirds  of  the  crest  of  the  ileum,  lumbar  verte- 
brae, inner  surface  of  cartilages  of  six  inferior 

ribs crest  of  the  pubis,  pectineal  line,  linea 

alba. 

Sacro-lumbalis Sacrum angles  of  six  inferior  ribs. 

Internal  Intercostals. — The  internal  intercostals  have  different  uses  in 
different  parts  of  the  thorax.  They  are  attached  to  the  inner  borders  of  the 
ribs  and  costal  cartilages.  Between  the  ribs  they  are  covered  by  the  external 
intercostals,  but  between  the  costal  cartilages  they  are  covered  simply  by 
aponeurosis.  Their  direction  is  from  above  downward  and  backward,  nearly 
at  right  angles  to  the  external  intercostals.  The  action  of  that  portion  of 
the  internal  intercostals  situated  between  the  costal  cartilages  has  already 
been  noted.  They  assist  the  external  intercostals  in  elevating  the  ribs  in 
inspiration.  Between  the  ribs  these  muscles  are  directly  antagonistic  to  the 
external  intercostals.  They  are  more  nearly  at  right  angles  to  the  ribs,  par- 
ticularly in  that  portion  of  the  thorax  where  the  obliquity  of  the  ribs  is 


MUSCLES  OF  EXPIRATION.  125 

greatest.  They  are  elongated  when  the  chest  is  distended,  and  are  shortened 
when  the  chest  is  collapsed  (Sibson).  This  fact,  taken  in  connection  with 
experiments  on  living  animals,  shows  that  they  are  muscles  of  expiration. 
Their  contraction  tends  to  depress  the  ribs  and  consequently  to  diminish  the 
capacity  of  the  chest. 

Infracostalcs. — These  muscles,  situated  at  the  posterior  part  of  the  tho- 
rax, are  variable  in  size  and  number.  They  are  most  common  at  the  lower 
part  of  the  chest.  Their  fibres  arise  from  the  inner  surface  of  one  rib  to  be 
inserted  into  the  inner  surface  of  the  first,  second  or  third  rib  below.  The 
fibres  follow  the  direction  of  the  internal  intercostals,  and  acting  from  their 
lower  attachments,  their  contractions  assist  these  muscles  in  drawing  the  ribs 
downward. 

Trianyultiris  Sterni. — There  has  never  been  any  doubt  concerning  the 
expiratory  action  of  the  triangularis  sterni.  From  its  origin,  the  ensiform 
cartilage,  lower  borders  of  the  sternum,  and  lower  three  or  four  costal  carti- 
lages, it  acts  upon  the  cartilages  of  the  second,  third,  fourth  and  fifth  ribs, 
to  which  it  is  attached,  drawing  them  downward  and  thus  diminishing  the 
capacity  of  the  chest. 

The  above-mentioned  muscles  are  called  into  action  in  ordinary,  tranquil 
respiration,  and  their  sole  office  is  to  diminish  the  capacity  of  the  chest.  In 
labored  or  difficult  expiration,  and  in  the  acts  of  blowing,  phonation  etc., 
other  muscles,  which  are  called  auxiliaries,  play  a  more  or  less  important  part. 
These  muscles  all  enter  into  the  formation  of  the  walls  of  the  abdomen,  and 
their  general  action  in  expiration  is  to  press  the  abdominal  viscera  and  dia- 
phragm into  the  thorax  and  diminish  its  vertical  diameter.  Their  action  is 
voluntary ;  and  by  an  effort  of  the  will,  it  may  be  opposed  more  or  less  by  the 
diaphragm,  by  which  means  the  duration  or  extent  of  the  expiratory  act  is 
regulated.  They  are  also  attached  to  the  ribs  or  costal  cartilages,  and  while 
they  press  the  diaphragm  upward,  they  depress  the  ribs  and  thus  dimin- 
ish the  antero-posterior  and  transverse  diameters  of  the  chest.  In  this 
action,  they  may  ba  opposed  by  the  voluntary  contraction  of  the  muscles 
which  raise  the  ribs,  also  for  the  purpose  of  regulating  the  force  of  the  ex- 
piratory act. 

In  labored  respiration  in  disease  and  in  the  hurried  respiration  which  fol- 
lows violent  exercise,  the  auxiliary  muscles  of  expiration,  as  well  as  of  inspi- 
ration, are  called  into  action  to  a  considerable  extent. 

Obliquus  Externus. — This  muscle,  in  connection  with  the  obliquus  in- 
ternus  and  tnmsversalis,  is  efficient  in  forced  or  labored  expiration,  by  press- 
ing the  abdominal  viscera  against  the  diaphragm.  Acting  from  its  attach- 
ments to  the  linea  alba,  the  crest  of  the  ileum  and  Poupart's  ligament,  by  its 
attachment  to  the  eight  inferior  ribs,  it  draws  the  ribs  downward. 

Obliquus  Interims. — This  muscle  also  acts  in  forced  expiration,  by  com- 
pressing the  abdominal  viscera.  The  direction  of  its  fibres  is  from  below 
upward  and  forward.  Acting  from  its  attachments  to  the  crest  of  the  ileum, 
Poupart's  ligament  and  the  lumbar  fascia,  by  its  attachments  to  ihe  carti- 
lages of  the  four  inferior  ribs,  it  draws  them  downward.  The  direction  of  the 
10 


126  RESPIRATION— RESPIRATORY  MOVEMENTS. 

fibres  of  this  muscle  is  the  same  as  that  of  the  internal  intercostals.  By  its 
action  the  ribs  are  drawn  inward  as  well  as  downward. 

Transversalis. — The  expiratory  action  of  this  muscle  is  mainly  in  com- 
pressing the  abdominal  viscera. 

Sacro-lumbalis. — This  muscle  is  situated  at  the  posterior  portion  of  the 
abdomen  and  thorax.  Its  fibres  pass  from  its  origin  at  the  sacrum,  upward 
and  a  little  outward,  to  be  inserted  into  the  six  inferior  ribs  at  their  angles. 
In  expiration  it  draws  the  ribs  downward,  acting  as  an  antagonist  to  the 
lower  levatores  costarum. 

There  are  some  other  muscles  which  may  be  used  in  forced  expiration, 
assisting  in  the  depression  of  the  ribs,  such  as  the  serratus  posticus  inferior, 
the  superior  fibres  of  the  serratus  magnus  and  the  inferior  portion  of  the 
trapezius,  but  their  action  in  respiration  is  unimportant. 

Types  of  Respiration. — In  the  movements  of  expansion  of  the  chest,  al- 
though all  the  muscles  which  have  been  classed  as  ordinary  inspiratory  mus- 
cles are  brought  into  action  to  a  greater  or  less  extent,  the  fact  that  certain 
sets  may  act  in  a  more  marked  manner  than  others  has  led  physiologists  to 
recognize  different  types  of  respiration.  Three  types  are  generally  given  in 
works  on  physiology : 

1.  The  Abdominal  Type. — In  this,  the  action  of  the  diaphragm  and  the 
consequent  movements  of  the  abdomen  are  most  prominent. 

2.  The  Inferior  Costal  Type. — In  this,  the  action  of  the  muscles  which 
expand  the  lower  part  of  the  thorax,  from  the  seventh  rib  inclusive,  is  most 
prominent. 

3.  The  Superior  Costal  Type. — In  this,  the  action  of  the  muscles  which 
dilate  the  thorax  above  the  seventh  rib  and  which  elevate  the  entire  chest  is 
most  prominent. 

The  abdominal  type  is  most  marked  in  children  less  than  three  years  of 
age,  irrespective  of  sex,  respiration  being  carried  on  almost  exclusively  by  the 
diaphragm. 

At  a  variable  period  after  birth,  a  difference  in  the  types  of  respiration  in 
the  sexes  is  observed.  In  the  male  the  abdominal  conjoined  with  the  inferior 
costal  type  is  predominant,  and  this  continues  through  life.  In  the  female 
the  inferior  costal  type  is  insignificant  and  the  superior  costal  type  predom- 
inates. Without  discussing  the  question  as  to  the  exact  age  when  this  differ- 
ence in  the  sexes  first  makes  its  appearance,  it  may  be  stated  in  general 
terms,  that  a  short  time  before  the  age  of  puberty  in  the  female,  the  superior 
costal  type  becomes  more  marked  and  soon  predominates.  In  the  male, 
respiration  continues  to  be  carried  on  mainly  by  the  diaphragm  and  the 
lower  part  of  the  chest. 

The  cause  of  the  pronounced  movements  of.  the  upper  part  of  the  chest  in 
the  female  has  been  the  subject  of  considerable  discussion.  It  is  probably  due, 
in  a  great  measure,  to  the  mode  of  dress  now  so  general  in  civilized  countries, 
which  confines  the  lower  part  of  the  chest  and  renders  movements  of  expan- 
sion somewhat  difficult.  In  a  series  of  observations  by  Thomas  J.  Mays 
^(1887),  upon  eighty-two  chests  of  Indian  girls  at  the  Lincoln  Institution  in 


FREQUENCY  OF  THE  RESPIRATORY  MOVEMENTS.          12T 

Philadelphia,  between  ten  and  twenty  years  of  age,  who  had  never  worn  tight 
clothing,  the  abdominal  type  of  respiration  was  found  to  predominate,  the 
respiratory  tracings  hardly  differing  from  the  tracings  in  the  male.  These 
observations  seem  to  show,  in  opposition  to  the  views  of  Hutchinson  and 
others,  that  the  predominance  of  the  superior  costal  type  in  the  female  is 
confined  to  civilized  races ;  but  it  is  certain  that  females  accommodate  them- 
selves more  readily  than  the  male  to  the  superior  costal  type ;  and  this  is 
probably  a  provision  against  the  physiological  enlargement  of  the  uterus  in 
pregnancy,  which  nearly  arrests  all  respiratory  movements  except  those  of  the 
upper  part  of  the  chest.  In  pathology  it  is  observed  that  females  are  able  to 
carry,  without  great  inconvenience,  a  large  quantity  of  water  in  the  abdominal 
cavity ;  while  a  much  smaller  quantity,  in  the  male,  produces  great  distress 
from  difficulty  of  breathing. 

Frequency  of  the  Respiratory  Movements. — In  counting  the  respiratory 
acts,  it  is  desirable  that  the  subject  be  unconscious  of  the  observation,  other- 
wise their  normal  rhythm  is  likely  to  be  disturbed.  Of  all  who  have  written 
on  this  subject,  Hutchinson  has  presented  the  largest  and  most  reliable  col- 
lection of  facts.  This  observer  ascertained  the  number  of  respiratory  acts 
per  minute,  in  the  sitting  posture,  in  1,897  males.  The  results  of  his  ob- 
servations, with  reference  to  frequency,  are  given  in  the  following  table  : 

RESPIRATIONS  PER  MINUTE.  NUMBER  OF  CASES. 

9  to  1 6 79 

16 239 

17 105 

18 195 

19 74 

20 561 

21 129 

22 143 

23 42 

24 243 

24  to  40 ; 87 

Although  this  table  shows  considerable  variation  in  different  individuals, 
the  great  majority  (1,731)  breathed  sixteen  to  twenty-four  times  per  minute. 
Nearly  a  third  breathed  twenty  times  per  minute,  a  number  which  may  be 
taken  as  the  average. 

The  relations  of  the  respiratory  acts  to  the  pulse  are  quite  constant  in 
health.  It  has  been  shown  by  Hutchinson  that  the  proportion  in  the  great 
majority  of  instances  is  one  respiratory  act  to  four  pulsations  of  the  heart. 
The  same  proportion  generally  obtains  when  the  pulse  is  accelerated  in  dis- 
ease, except  when  the  pulmonary  organs  are  involved. 

Age  has  an  influence  on  the  frequency  of  the  respiratory  acts,  correspond- 
ing with  what  has  already  been  noted  with  regard  to  the  pulsations  of  the 
heart. 

The  following  are  the  results  of  observations  on  300  males  (Quetelet) : 

44  respirations  per  minute,  soon  after  birth ; 


128  EESPIRATION— EESPIRATORY  MOVEMENTS. 

26,  at  the  age  of  five  years ; 

20,  between  fifteen  and  twenty  years ; 

19,  between  twenty  and  twenty-five  years ; 

16,  about  the  thirtieth  year ; 

18,  between  thirty  and  fifty  years. 

The  influence  of  sex  is  not  marked  in  very  young  children.  There  is  no 
difference  between  males  and  females  at  birth ;  but  in  young  women,  the 
respirations  are  a  little  less  frequent  than  in  young  men  of  the  same  age. 

The  various  physiological  conditions  which  have  been  noted  as  affecting 
the  pulse  have  a  corresponding  influence  on  respiration.  In  sleep  the  num- 
ber of  respiratory  acts  is  diminished  by  about  twenty  per  cent.  (Quetelet). 
Muscular  effort  accelerates  the  respiratory  movements  pari  passu  with  the 
movements  of  the  heart. 

Relations  of  Inspiration  and  Expiration  to  each  other — Respiratory 
Sounds. — In  ordinary  respiration,  inspiration  is  produced  by  the  action  of 
muscles,  and  expiration,  by  the  passive  reaction  of  the  lungs  and  of  the  elas- 
tic walls  of  the  thorax.  The  inspiratory  and  expiratory  acts  do  not  immedi- 
ately follow  each  other.  Beginning  with  inspiration,  it  is  found  that  this 
act  maintains  about  the  same  intensity  throughout.  There  is  then  a  very 
brief  interval,  when  expiration  follows,  which  has  its  maximum  of  intensity 
at  the  beginning  of  the  act  and  gradually  dies  away.  Between  the  acts  of 
expiration  and  inspiration  is  an  interval,  which  is  somewhat  longer  than  the 
interval  between  inspiration  and  expiration. 

The  duration  of  expiration  is  generally  somewhat  longer  than  that  of 
inspiration,  although  the  two  acts  may  be  nearly,  or  in  some  instances,  quite 
equal.  After  five  to  eight  ordinary  respiratory  acts,  an  effort  generally  occurs 
which  is  rather  more  profound  than  usual,  by  which  the  air  in  the  lungs  is 
more  thoroughly  changed.  The  temporary  arrest  of  the  acts  of  respiration 
in  violent  muscular  efforts,  in  straining,  in  parturition  etc.,  is  sufficiently 
familiar. 

Ordinarily  respiration  is  not  accompanied  by  any  sound  which  can  be 
heard  without  applying  the  ear  directly,  or  by  the  intervention  of  a  stetho- 
scope, to  the  chest,  except  when  the  mouth  is  closed  and  breathing  is  carried 
on  exclusively  through  the  nasal  passages,  when  a  soft,  breezy  sound  accom- 
panies both  acts.  If  the  mouth  be  opened  sufficiently  to  admit  the  free  pas- 
sage of  air,  no  sound  is  to  be  heard  in  health.  In  sleep  the  respirations  are 
more  profound;  and  if  the  mouth  be  closed  the  sound  is  rather  more 
intense. 

Snoring,  which  sometimes  accompanies  the  respiratory  acts  during  sleep, 
occurs  when  the  air  passes  through  both  the  mouth  and  the  nose.  It  is  more 
marked  in  inspiration,  sometimes  accompanying  both  acts,  and  sometimes  it 
is  not  heard  in  expiration.  It  is  not  necessary  to  describe  the  characters 
of  a  sound  so  familiar.  Snoring  is  an  idiosyncrasy  in  many  individuals, 
although  those  who  do  not  snore  habitually  may  do  so  when  the  system  is 
unusually  exhausted  and  relaxed.  It  occurs  only  when  the  mouth  is  open, 
and  the  sound  is  produced  by  vibration  and  a  sort  of  flapping  of  the  velum 


RESPIRATORY  SOUNDS.  129 

pendulum  palati,  between  the  two  currents  of  air  from  the  mouth  and  nose, 
together  with  a  vibration  in  the  column  of  air  itself. 

Applying  the  stethoscope  over  the  larynx  or  trachea,  a  sound  is  heard,  of 
a  distinctly  and  purely  tubular  character,  accompanying  both  acts  of  respira- 
tion. In  inspiration,  according  to  the  late  Dr.  Austin  Flint,  "  it  attains  its 
maximum  of  intensity  quickly  after  the  development  of  the  sound  and  main- 
tains the  same  intensity  to  the  close  of  the  act,  when  the  sound  abruptly  ends, 
as  if  suddenly  cut  off."  After  a  brief  interval,  the  sound  of  expiration  fol- 
lows. This  is  also  tubular  in  quality.  It  soon  attains  its  maximum  of  inten- 
sity, but  unlike  the  sound  of  inspiration,  it  gradually  dies  away  and  is  lost  im- 
perceptibly. It  is  seen  that  these  phenomena  correspond  with  the  nature  of 
the  two  acts  of  respiration. 

Sounds  approximating  in  character  to  the  foregoing  are  heard  over  the 
bronchial  tubes  before  they  penetrate  the  lungs. 

Over  the  substance  of  the  lungs,  a  sound  may  be  heard  entirely  different 
in  its  character  from  that  heard  over  the  larynx,  trachea  or  bronchial  tubes. 
In  inspiration  the  sound  is  much  less  intense  than  over  the  trachea  and  has 
a  breezy,  expansive,  or  what  is  called  in  auscultation,  a  vesicular  character. 
It  is  much  lower  in  pitch  than  the  tracheal  sound.  It  is  continuous  and 
rather  increases  in  intensity  from  its  beginning  to  its  termination,  ending 
abruptly,  like  the  tracheal  inspiratory  sound.  The  sound  is  produced  in  part 
by  the  movement  of  air  in  the  small  bronchial  tubes,  but  chiefly  by  the  expan- 
sion of  the  air-cells  of  the  lungs.  It  is  followed,  without  an  interval,  by  the 
sound  of  expiration,  which  is  shorter — one-fifth  or  one-fourth  as  long — lower 
in  pitch  and  much  less  intense.  A  sound  is  not  always  heard  in  expiration. 

The  variations  in  the  intensity  of  the  respiratory  sounds  in  different  indi- 
viduals are  very  considerable.  As  a  rule  they  are  more  intense  in  young  per- 
sons ;  which  has  given  rise  to  the  term  puerile  respiration,  when  the  sounds 
are  exaggerated  in  parts  of  the  lung,  in  certain  cases  of  disease.  The  sounds 
are  generally  more  intense  in  females  than  in  males,  particularly  in  the  upper 
regions  of  the  thorax. 

It  is  difficult  by  any  description  or  comparison  to  convey  an  accurate  idea 
of  the  character  of  the  sounds  heard  over  the  lungs  and  air-passages,  and  it 
is  unnecessary  to  make  the  attempt,  when  they  can  be  so  easily  studied  in  the 
living  subject. 

Coughing,  Sneezing,  Sighing,  Yawning,  Laughing,  Sobbing  and  Hic- 
cough.— These  peculiar  acts  demand  a  few  words  of  explanation.  Coughing 
and  sneezing  are  generally  involuntary  acts,  produced  by  irritation  in  the  air- 
tubes  or  nasal  passages,  although  coughing  is  often  voluntary.  In  both  of 
these  acts,  there  is  first  a  deep  inspiration  followed  by  a  convulsive  action  of 
the  expiratory  muscles,  by  which  the  air  is  violently  expelled  with  a  charac- 
teristic sound,  in  the  one  case  by  the  mouth,  and  in  the  other  by  the  mouth 
and  nares.  Foreign  bodies  lodged  in  the  air-passages  are  frequently  expelled 
in  violent  fits  of  coughing.  In  hypersecretion  of  the  bronchial  mucous  mem- 
brane, the  accumulated  mucus  is  carried  by  the  act  of  coughing  either  to  the 
mouth  or  well  into  the  larynx,  when  it  may  be  expelled  by  the  act  of  exspui- 


130  RESPIRATION— RESPIRATORY  MOVEMENTS. 

tion.  "When  either  of  these  acts  is  the  result  of  irritation  from  a  foreign 
substance  or  from  secretions,  it  may  be  modified  or  partly  smothered  by  the 
will,  but  is  not  completely  under  control.  The  sensibility  of  the  mucous 
membrane  at  the  summit  of  the  air-passages  usually  protects  them  from  the 
entrance  of  foreign  matters,  both  liquid  and  solid;  for  the  slightest  im- 
pression received  by  the  membrane  gives  rise  to  a  violent  and  involuntary 
cough,  by  which  the  offending  substance  is  removed.  The  glottis,  also,  is 
spasmodically  contracted. 

In  sighing,  a  prolonged  and  deep  inspiration  is  followed  by  a  rapid  and 
generally  an  audible  expiration.  This  occurs,  as  a  general  rule,  once  in  five 
to  eight  respiratory  acts,  for  the  purpose  of  changing  the  air  in  the  lungs 
more  completely,  and  it  is  due  to  an  exaggeration  of  the  cause  which  gives 
rise  to  the  ordinary  acts  of  respiration.  When  due  to  depressing  emotions, 
it  has  the  same  cause ;  for  at  such  times  respiration  is  less  efficiently  per- 
formed. Yawning  is  an  analogous  process,  but  it  differs  from  sighing  in  the 
fact  that  it  is  involuntary  and  can  not  be  produced  by  an  effort  of  the  will. 
It  is  characterized  by  a  wide  opening  of  the  mouth  and  a  very  profound 
inspiration.  Yawning  is  generally  assumed  to  be  an  evidence  of  fatigue,  but 
it  often  occurs  from  a  sort  of  contagion.  When  not  the  result  of  imitation, 
it  has  the  same  exciting  cause  as  sighing — deficient  oxygenation  of  the  blood 
— and  it  is  followed  by  a  sense  of  satisfaction,  which  shows  that  it  meets 
some  decided  want  on  the  part  of  the  system. 

Laughing  and  sobbing,  although  expressing  opposite  conditions,  are 
produced  by  very  nearly  the  same  action.  The  characteristic  sounds  accom- 
panying these  acts  are  the  result  of  short,  rapid  and  convulsive  movements 
of  the  diaphragm,  attended  with  contractions  of  the  muscles  of  the  face, 
which  produce  the  expressions  characteristic  of  hilarity  or  grief.  Although 
to  a  certain  extent  under  the  control  of  the  will,  these  acts  are  mainly  invol- 
untary. Violent  and  convulsive  laughter  may  be  excited  in  many  individuals 
by  titillation  of  certain  portions  of  the  surface  of  the  body.  Laughter  and 
sometimes  sobbing,  like  yawning,  may  be  the  result  of  involuntary  imitation. 

Hiccough  is  a  peculiar  modification  of  the  act  of  inspiration,  to  which  it 
is  exclusively  confined.  It  is  produced  by  a  sudden,  convulsive  and  entirely 
involuntary  contraction  of  the  diaphragm,  accompanied  by  a  spasmodic  con- 
striction of  the  glottis.  The  contraction  of  the  diaphragm  is  more  extensive 
than  in  laughing  and  sobbing  and  occurs  only  once  every  four  or  five  respir- 
atory acts. 

CAPACITY  OF  THE  LUNGS,  AND  THE  QUANTITY  OF  AIR  CHANGED  IN 
THE  EESPIKATOBY  ACTS. 

The  volume  of  air  ordinarily  contained  in  the  lungs  is  about  two  hun- 
dred cubic  inches  (3,277  c.c.) ;  but  it  is  evident,  from  the  simple  experiment  of 
opening  the  chest,  when  the  elastic  lungs  collapse  and  expel  a  certain  quan- 
tity of  air  which  can  not  be  removed  while  the  lungs  are  in  situ,  that  a  part 
of  the  gaseous  contents  of  these  organs  necessarily  remains  after  the  most 
complete  and  forcible  expiration.  After  an  ordinary  act  there  is  a  certain 


CAPACITY  OF  THE  LUNGS.  131 

quantity  of  air  in  the  lungs  which  can  be  expelled  by  a  forced  expiration.  In 
ordinary  respiration  a  comparatively  small  volume  of  air  is  introduced  with 
inspiration,  and  a  nearly  equal  quantity  is  expelled  by  the  succeeding  expira- 
tion. By  the  extreme  action  of  all  the  inspiratory  muscles  in  a  forced  inspi- 
ration, a  supplemental  quantity  of  air  may  be  introduced  into  the  lungs,  which 
then  contain  much  more  than  they  ever  do  in  ordinary  respiration.  For 
convenience  of  description,  physiologists  have  adopted  the  following  names, 
which  are  applied  to  these  various  volumes  of  air : 

1.  Residual  Air  ;  that  which  is  not  and  can  not  be  expelled  by  a  forced 
expiration. 

2.  Reserve  Air  ;  that  which  remains  after  an  ordinary  expiration,  deduct- 
ing the  residual  air. 

3.  Tidal,  or   Ordinary  Breathing  Air ;  that  which  is  changed  by  the 
ordinary  acts  of  inspiration  and  expiration. 

4.  Complemental  Air  ;  the  excess  over  the  ordinary  breathing  air,  which 
may  be  introduced  by  a  forcible  inspiration. 

In  measuring  the  air  changed  in  ordinary  breathing,  it  has  been  found 
that  the  acts  of  respiration  are  so  easily  influenced  and  it  is  so  difficult  to 
experiment  on  any  individual  without  his  knowledge,  that  the  results  of 
many  good  observers  are  not  to  be  relied  upon.  This  is  one  of  the  most 
important  of  the  questions  under  consideration.  The  difficulties  in  the  way 
of  estimating  with  accuracy  the  residual,  reserve  or  complemental  volumes, 
will  readily  suggest  themselves.  The  observations  on  these  points  which 
may  be  taken  as  the  most  definite  and  exact  are  those  of  Herbst  and  of 
Hutchinson.  Those  of  the  last-named  observer  are  very  elaborate  and 
were  made  on  a  large  number  of  subjects  of  both  sexes  and  of  all  ages  and 
occupations.  They  are  generally  accepted  by  physiologists,  as  the  most  ex- 
tended and  accurate. 

Residual  Air. — Perhaps  there  is  not  one  of  the  questions  under  consider- 
ation more  difficult  to  answer  definitely  than  that  of  the  quantity  of  air 
which  remains  in  the  lungs  after  a  forced  expiration ;  but  it  fortunately  is 
not  one  of  any  great  practical  importance.  The  residual  air  remains  in  the 
lungs  as  a  physical  necessity.  The  lungs  in  health  are  always  in  contact 
with  the  walls  of  the  thorax ;  and  when  this  cavity  is  reduced  to  its  smallest 
dimensions,  it  is  impossible  that  any  more  air  should  be  expelled.  The  vol- 
ume which  thus  remains  has  been  variously  estimated.  The  residual  volume 
has  been  estimated  at  about  one  hundred  cubic  inches  (1,639  c.c.),  but  the 
quantity  varies  very  considerably  in  different  individuals  (Hutchinson). 
Taking  everything  into  consideration,  it  may  be  assumed  that  this  estimate 
is  as  nearly  correct  as  any. 

Reserve  Air. — This  name  is  given  to  the  volume  of  air  which  may  be  ex- 
pelled and  changed  by  a  voluntary  effort,  but  which  remains  in  the  lungs, 
added  to  the  residual  air,  after  an  ordinary  act  of  expiration.  It  may  be 
estimated,  without  any  reference  to  the  residual  air,  by  forcibly  expelling  air 
from  the  lungs,  after  an  ordinary  expiration.  The  average  volume,  accord- 
ing to  Hutchinson,  is  one  hundred  cubic  inches  (1,639  c.c.). 


132  RESPIRATION— RESPIRATORY  MOVEMENTS. 

More  or  less  of  the  reserve  air  is  changed  whenever  there  is  a  necessity  for 
a  more  complete  renovation  of  the  contents  of  the  lungs  than  ordinary.  It  is 
encroached  upon  in  the  unusually  profound  inspiration  and  expiration  which 
occur  once  in  every  five  to  eight  acts.  It  is  used  in  certain  prolonged  vocal 
efforts,  in  blowing  etc.  Added  to  the  residual  air,  it  constitutes  the  mini- 
mum capacity  of  the  lungs  in  ordinary  respiration.  As  it  is  continually  re- 
ceiving watery  vapor  and  carbon  dioxide,  it  is  always  more  or  less  vitiated, 
and  when  reenforced  by  the  breathing  air,  which  enters  with  inspiration,  is 
continually  in  circulation,  in  obedience  to  the  law  of  the  diffusion  of  gases. 
Those  who  are  in  the  habit  of  arresting  respiration  for  a  time,  learn  to 
change  the  reserve  air  as  completely  as  possible  by  several  forcible  acts  and 
then  fill  the  lungs  with  fresh  air.  In  this  way  they  are  enabled  to  sus- 
pend the  respiratory  acts  for  two  or  three  minutes  without  inconvenience. 
The  introduction  of  fresh  air  with  each  inspiration,  and  the  constant 
diffusion  which  is  going  on  and  by  which  the  proper  quantity  of  oxygen  finds 
its  way  to  the  air-cells,  give,  in  ordinary  breathing,  a  composition  to  the  air 
in  the  deepest  portions  of  the  lungs  which  insures  a  constant  aeration  of  the 
blood. 

Tidal,  or  Ordinary  Breathing  Air. — The  volume  of  air  which  is  changed 
in  the  ordinary  acts  of  respiration  is  subject  to  certain  physiological  varia- 
tions ;  and  the  respiratory  movements,  as  regards  their  extent,  are  so  easily 
influenced,  that  great  care  is  necessary  to  avoid  error  in  estimating  the  vol- 
ume of  ordinary  breathing  air.  As  a  mean  of  the  results  obtained  by 
Herbst  and  by  Hutchinson,  the  average  volume  of  breathing  air,  in  a  man  of 
ordinary  stature,  is  twenty  cubic  inches  (327'7  c.c.).  According  to  Hutchin- 
son, in  perfect  repose,  when  the  respiratory  movements  are  hardly  perceptible, 
not  more  than  seven  to  twelve  cubic  inches  (114-7  to  196*6  c.c.)  are  changed ; 
while,  under  excitement,  the  volume  may  be  increased  to  seventy-seven  cubic 
inches  (1,261-8  c.c.).  The  breathing  volume  progressively  increases  in  pro- 
portion to  the  stature  of  the  individual,  and  bears  no  definite  relation  to  the 
apparent  capacity  of  the  chest  (Herbst). 

Complemental  Air. — The  thorax  may  be  so  enlarged  by  an  extreme  vol- 
untary inspiratory  effort  as  to  contain  a  quantity  of  air  much  larger  than 
after  an  ordinary  inspiration.  The  additional  volume  of  air  thus  taken  in 
may  be  estimated  by  measuring  all  the  air  which  can  be  expelled  from  the 
lungs  after  the  most  profound  inspiration,  and  deducting  the  sum  of  the 
reserve  air  and  breathing  air.  This  quantity  has  been  found  by  Hutchinson 
to  vary  in  different  individuals,  bearing  a  close  relation  to  stature.  The 
mean  complemental  volume  is  one  hundred  and  ten  cubic  inches  (1,802-9  c.  c.). 

The  complemental  air  is  drawn  upon  whenever  an  effort  is  made  which 
requires  a  temporary  arrest  of  respiration.  Brief  and  violent  muscular  exer- 
tion is  generally  preceded  by  a  profound  inspiration.  In  sleep,  as  the  vol- 
ume of  breathing  air  is  somewhat  increased,  the  complemental  air  is  en- 
croached upon.  A  part  or  the  whole  of  the  complemental  air  is  also  used  in 
certain  vocal  efforts,  in  blowing,  in  yawning,  in  the  deep  inspiration  which 
precedes  sneezing,  in  straining  etc. 


CAPACITY  OF  THE  LUNGS.  133 

Extreme  Breathing  Capacity. — By  the  extreme  breathing  capacity  is 
meant  the  volume  of  air  which  can  be  expelled  from  the  lungs  by  the  most 
forcible  expiration  after  the  most  profound  inspiration.  This  has  been 
called  by  Hutchinson,  the  vital  capacity,  as  signifying  "  the  volume  of  air 
which  can  be  displaced  by  living  movements."  Its  volume  is  equal  to  the 
sum  of  the  reserve  air,  the  breathing  air  and  the  complemental  air,  and  it 
represents  the  extreme  capacity  of  the  chest,  less  the  residual  air.  Its 
physiological  importance  is  due  to  the  fact  that  it  can  readily  be  determined 
by  an  appropriate  apparatus,  the  spirometer,  and  comparisons  can  thus  be 
made  between  different  individuals,  both  healthy  and  diseased.  The  number 
of  observations  on  this  point  made  by  Hutchinson  amounts  in  all  to  a  little 
less  than  five  thousand. 

The  extreme  breathing  capacity  in  health  is  subject  to  variations  which 
have  been  shown  to  bear  a  very  close  relation  to  the  stature  of  the  individual. 
Hutchinson  begins  with  the  proposition  that  in  a  man  of  medium  height 
(five  feet  eight  inches,  or  170*2  centimetres),  it  is  equal  to  two  hundred  and 
thirty  cubic  inches  (3,768*6  c.  c.). 

The  most  striking  result  of  the  experiments  of  Hutchinson,  with  regard 
to  the  modifications  of  the  vital  capacity,  is  that  it  bears  a  definite  relation  to 
stature,  without  being  affected  in  a  very  marked  degree  by  weight  or  by  the 
circumference  of  the  chest.  This  is  especially  remarkable,  as  it  is  well  known 
that  height  does  not  depend  so  much  upon  the  length  of  the  body  as  upon 
the  length  of  the  lower  extremities.  He  ascertained  that  for  every  inch 
(£  centimetre)  in  height,  between  five  and  six  feet  (152*4  and  182*9  centi- 
metres), the  extreme  breathing  capacity  is  increased  by  eight  cubic  inches 
(131*1  c.  c.). 

Age  has  an  influence,  though  less  marked  than  stature,  upon  the  extreme 
breathing  capacity.  As  the  result  of  4,800  observations  on  males,  it  was  ascer- 
tained that  the  volume  increases  with  age  up  to  the  thirtieth  year,  and  pro- 
gressively decreases,  with  tolerable  regularity,  from  the  thirtieth  to  the  six- 
tieth year.  These  figures,  though  necessarily  subject  to  certain  individual 
variations,  may  be  taken  as  a  basis  for  examinations  of  the  extreme  breath- 
ing capacity  in  disease. 

Relations  in  Volume  of  the  Expired  to  the  Inspired  Air. — A  certain  pro- 
portion of  the  inspired  air  is  lost  in  respiration,  so  that  the  air  expired  is 
always  a  little  less  in  volume  than  that  which  is  taken  into  the  lungs.  The 
loss  was  put  by  Davy  at  fa,  and  by  Cuvier  at  -§L  of  the  volume  of  air  intro- 
duced. Observations  on  this  point,  to  be  exact,  must  include  a  considerable 
number  of  respiratory  acts ;  and  from  the  difficulty  of  continuing  respiration 
in  a  perfectly  regular  and  normal  manner  when  the  attention  is  directed  to 
the  respiratory  movements,  the  most  accurate  results  may  probably  be  obtained 
from  experiments  on  the  lower  animals.  Despretz  caused  six  young  rabbits 
to  respire  for  two  hours  in  a  confined  space  containing  2,090  cubic  inches 
(49,000  c.  c.)  of  air,  and  ascertained  that  the  volume  had  diminished  by 
sixty-one  cubic  inches  (1,000  c.  c.),  or  a  little  more  than  one-fiftieth.  Adopt- 
ing the  approximations  of  Davy  and  Cuvier,  applied  to  the  human  subject,  as 


134  RESPIRATION— RESPIRATORY  MOVEMENTS. 

nearly  correct,  it  may  be  assumed  that  in  the  lungs,  ^  to  -fa  of  the  inspired 
air  is  lost. 

Diffusion  of  Air  in  the  Lungs. — When  it  is  remembered  that  .with  each 
inspiration,  but  about  twenty  cubic  inches  (327'7  c.  c.)  of  fresh  air  are  intro- 
duced, sufficient  only  to  fill  the  trachea  and  larger  bronchial  tubes,  it  is  evi- 
dent that  some  forces  must  act  by  which  this  fresh  air  finds  its  way  into  the 
air-cells,  and  the  vitiated  air  is  brought  into  the  larger  tubes,  to  be  expelled 
with  the  succeeding  expiration. 

The  interchange  between  the  fresh  air  in  the  upper  portions  of  the  respira- 
tory apparatus  and  the  air  in  the  deeper  parts  of  the  lungs  is  constantly  going 
on  by  simple  diffusion  aided  by  the  active  currents  or  impulses  produced  by 
the  alternate  movements  of  the  chest.  In  the  respiratory  apparatus,  at  the 
end  of  an  inspiration,  the  atmospheric  air,  composed  of  a  mixture  of  oxygen 
and  nitrogen,  is  introduced  into  the  tubes  with  a  considerable  impetus  and  is 
brought  into  contact  with  the  gas  in  the  lungs,  which  is  heavier,  as  it  con- 
tains a  certain  quantity  of  carbon  dioxide.  Diffusion  then  takes  place,  aided 
by  the  elastic  lungs,  which  are  gradually  forcing  the  gaseous  contents  out  of 
the  cells,  until  a  certain  portion  of  the  air  loaded  with  carbon  dioxide  finds 
its  way  to  the  larger  tubes,  to  be  thrown  off  in  expiration,  its  place  being 
supplied  by  the  fresh  air. 

In  obedience  to  the  law  established  by  Graham,  that  the  diffusibility  of 
gases  is  inversely  proportionate  to  the  square  root  of  their  densities,  the 
penetration  of  atmospheric  air,  which  is  the  lighter  gas,  to  the  deep  portions 
of  the  lungs  would  take  place  with  greater  rapidity  than  the  ascent  of  the 
air  charged  with  carbon  dioxide ;  so  that  eighty-one  parts  of  carbon  dioxide 
should  be  replaced  by  ninety-five  parts  of  oxygen.  It  is  found,  indeed,  that 
the  volume  of  carbon  dioxide  exhaled  is  always  less  than  the  volume  of 
oxygen  absorbed.  This  diffusion  is  constantly  going  on,  so  that  the  air  in 
the  pulmonary  vesicles,  where  the  interchange  of  gases  with  the  blood  takes 
place,  maintains  a  nearly  uniform  composition.  The  process  of  aeration  of 
the  blood,  therefore,  has  little  of  that  intermittent  character  which  attends 
the  muscular  movements  of  respiration,  which  would  occur  if  the  entire 
gaseous  contents  of  the  lungs  were  changed  with  each  respiratory  act. 


COMPOSITION  OF  THE  AIR.  135 

CHAPTER  V. 

CHANGES    WHICH  THE  AIR  AND   THE  BLOOD   UNDERGO  IN  RESPIRATION. 

Composition  of  the  air— Consumption  of  oxygen— Exhalation  of  carbon  dioxide— Kelations  between  the 
quantity  of  oxygen  consumed  and  the  quantity  of  carbon  dioxide  exhaled— Sources  of  carbon  dioxide 
in  the  expired  air— Exhalation  of  watery  vapor— Exhalation  of  ammonia— Exhalation  of  organic  matter 
—Exhalation  of  nitrogen— Changes  of  the  blood  in  respiration  (haematosis)— Difference  in  color  between 
arterial  and  venous  blood— Comparison  of  the  gases  in  venous  and  arterial  blood— Analysis  of  the  blood 
for  gases— Nitrogen  of  the  blood— Condition  of  the  gases  in  the  blood— Relations  of  respiration  to  nutri- 
tion etc.— The  respiratory  sense — Sense  of  suffocation— Respiratory  efforts  before  birth — Cutaneous 
respiration— Breathing  in  a  confined  space— Asphyxia. 

FROM  the  allusions  already  made  to  the  general  process  of  respiration,  it 
is  apparent  that  before  the  discovery  of  the  nature  of  the  gases  which  com- 
pose the  air  and  those  which  are  exhaled  from  the  lungs,  it  was  impossible 
for  physiologists  to  have  any  correct  ideas  of  the  nature  of  this  important 
function.  It  is  also  evident  that  no  definite  knowledge  of  the  processes  of 
respiration  could  exist  prior  to  the  discovery  of  the  circulation  of  the  blood. 

The  discovery  of  the  properties  of  oxygen  and  carbon  dioxide  were  simply 
isolated  facts  and  failed  to  develop  any  definite  idea  of  the  changes  of  the  air 
and  blood  in  respiration.  The  application  of  these  facts  was  made  by  La- 
voisier, whose  observations  mark  the  beginning  of  an  accurate  knowledge  of 
the  physiology  of  respiration.  Wi^i  the  balance,  Lavoisier  showed  the  nature 
of  the  oxides  of  the  metals ;  he  discovered  that  carbon  dioxide  is  formed  by  a 
union  of  carbon  and  oxygen ;  and  noting  the  consumption  of  oxygen  and  the 
production  of  carbon  dioxide  in  respiration,  he  advanced,  for  the  first  time, 
the  view  that  the  one  was  concerned  in  the  production  of  the  other.  Although, 
as  would  naturally  be  expected,  the  doctrines  of  Lavoisier  have  been  modified 
with  the  advances  in  science,  he  developed  facts  which  have  served  as  the 
starting-point  of  definite  knowledge  on  this  subject. 

Composition  of  the  Air. — Pure  atmospheric  air  is  a  mechanical  mixture 
of  79-19  parts  of  nitrogen  with  20-81  parts  of  oxygen  (Dumas  arid  Boussin- 
gault).  It  contains,  in  addition,  a  very  small  quantity  of  carbon  dioxide, 
about  one  part  in  two  thousand.  The  air  is  never  free  from  moisture,  which 
is  very  variable  in  quantity,  being  generally  more  abundant  at  a  high  than  at 
a  low  temperature.  Floating  in  the  atmosphere,  are  large  numbers  of  minute 
organic  bodies ;  and  various  odorous  and  other  gaseous  matters  sometimes  are 
present  as  accidental  constituents. 

In  considering  the  processes  of  respiration,  it  is  not  necessary  to  take 
account  of  any  of  the  constituents  of  the  atmosphere  except  oxygen  and 
nitrogen,  the  others  being  either  inconstant  or  existing  in  excessively  minute 
quantity.  It  is  necessary  to  the  regular  performance  of  respiration,  that  the 
air  should  contain  about  four  parts  of  nitrogen  to  one  of  oxygen,  and  have 
about  the  density  which  exists  on  the  general  surface  of  the  globe.  When 
the  density  is  very  much  increased,  as  in  mines,  respiration  is  more  or  less 
disturbed.  By  exposure  to  a  rarefied  atmosphere,  as  in  the  ascent  of  high 
mountains  or  in  aerial  voyages,  respiration  may  be  very  seriously  interfered 
with,  from  the  fact  that  less  oxygen  than  usual  is  presented  to  the  respiratory 


136          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

surface  and  the  reduced  atmospheric  pressure  diminishes  the  capacity  of  the 
blood  for  retaining  gases. 

Magendie  and  Bernard,  in  experimenting  on  the  minimum  proportion  of 
oxygen  in  the  air  which  is  capable  of  sustaining  life,  found  that  a  rabbit, 
confined  under  a  bell-glass,  with  an  arrangement  for  removing  the  carbon 
dioxide  and  water  exhaled,  as  fast  as  they  were  produced,  died  of  asphyxia 
when  the  quantity  of  oxygen  became  reduced  to  between  three  and  five  per 
cent. 

A  few  experiments  are  on  record  in  which  the  human  subject  and  the 
lower  animals  have  been  made  to  respire  for  a  time  pure  oxygen.  Allen  and 
Pepys  confined  animals  for  twenty-four  hours  in  an  atmosphere  of  pure  oxy- 
gen without  any  notable  results ;  but  these  experiments  do  not  show  that  it 
would  be  possible  to  respire  unmixed  oxygen  indefinitely  without  incon- 
venience. As  it  exists  in  the  air,  oxygen  is  undoubtedly  in  the  best  condi- 
tion for  the  permanent  maintenance  of  the  respiratory  function.  The  blood 
seems  to  have  a  certain  capacity  for  the  absorption  of  oxygen,  which  is  not 
materially  increased  when  the  pure  gas  is  respired. 

The  only  other  gas  which  has  the  power  of  maintaining  respiration,  even 
for  a  time,  is  nitrogen  monoxide.  This  is  appropriated  by  the  blood-cor- 
puscles with  great  avidity,  and  for  a  time  it  produces  an  exaggeration  of  the 
vital  processes,  with  delirium  etc.,  whicl^  has  given  it  the  common  name  of 
the  laughing  gas ;  but  this  condition  is  followed  by  angesthesia,  and  finally 
by  asphyxia,  probably  because  the  gas  has  so  strong  an  affinity  for  the  blood- 
corpuscles  as  to  remain  to  a  certain  extent  fixed,  interfering  with  the  inter- 
change of  gases  which  is  essential  to  life.  Notwithstanding  this,  experiment- 
ers have  confined  with  impunity  rabbits  and  other  animals  in  an  atmosphere 
of  nitrogen  monoxide  for  a  number  of  hours.  In  all  cases  they  became 
asphyxiated,  but  in  some  instances  they  were  restored  on  being  brought  again 
into  the  ordinary  atmosphere. 

Other  gases  which  may  be  introduced  into  the  lungs  either  produce  as- 
phyxia, negatively,  from  the  fact  that  they  are  incapable  of  carrying  on  respi- 
ration, like  hydrogen  or  nitrogen,  or  positively,  by  a  poisonous  effect  011  the 
system.  The  most  important  of  the  gases  which  act  as  poisons  are  carbon 
monoxide,  hydrogen  monosulphide  and  arsenious  hydride.  Carbon  mo- 
noxide unites  with  the  coloring  matter  of  the  red  corpuscles,  forming  carbon- 
monoxide-haemaglobine.  This  union  is  so  stable  that  it  paralyzes  the  cor- 
puscles as  oxygen-carriers  and  produces  death  by  asphyxia.  It  is  probable 
that  carbon  dioxide  is  not  in  itself  poisonous.  Regnault  and  Reiset  exposed 
animals  (dogs  and  rabbits)  for  many  hours,  to  an  atmosphere  containing 
twenty-three  per  cent,  of  carbon  dioxide  artificially  introduced,  with  between 
thirty  and  forty  per  cent,  of  oxygen,  without  any  ill  effects. 

Consumption  of  Oxygen. — The  determination  of  the  quantity  of  oxygen 
which  is  removed  from  the  air  by  the  process  of  respiration  is  important ;  and 
on  this  point,  there  is  an  accumulated  mass  of  observations  which  are  com- 
paratively unimportant  from  the  fact  that  they  were  made  before  the  means 
of  analysis  of  the  gases  were  as  accurate  as  they  now  are.  In  the  observations 


CONSUMPTION  OF  OXYGEN.  137 

of  Eegnault  and  Reiset,  animals  were  placed  in  a  receiver  filled  with  air,  a 
measured  quantity  of  oxygen  was  introduced  as  fast  as  it  was  consumed  by 
respiration,  and  the  carbon  dioxide  was  constantly  removed  and  carefully  esti- 
mated. In  most  of  the  experiments,  the  confinement  did  not  appear  to  inter- 
fere with  the  functions  of  the  animal,  which  ate  and  drank  in  the  apparatus 
and  was  in  as  good  condition  at  the  termination  as  at  the  beginning  of  the 
observation.  This  method  is  much  more  accurate  than  that  of  simply  causing 
an  animal  to  breathe  in  a  confined  space,  when  the  consumption  of  oxygen 
and  accumulation  of  carbon  dioxide  and  other  matters  must  interfere  more  or 
less  with  the  proper  performance  of  the  respiratory  function.  As  employed 
by  Eegnault  and  Reiset,  it  is  adapted  only  to  experiments  on  animals  of  small 
size.  These  give  but  an  approximate  idea,  however,  of  the  processes  as  they 
take  place  in  the  human  subject.  Pettenkofer  constructed  a  chamber  large 
enough  to  admit  a  man  and  allow  perfect  freedom  of  motion,  eating,  sleep- 
ing etc.,  into  which  air  could  be  constantly  introduced  in  definite  quantity, 
and  from  which  the  products  of  respiration  were  constantly  removed  and 
estimated.  This  method  had  been  adapted  to  the  human  subject  on  a  small 
scale  in  1843,  by  Scharling,  but  there  was  no  arrangement  for  estimating  the 
quantity  of  oxygen  consumed. 

Estimates  of  the  absolute  quantities  of  oxygen  consumed  or  of  carbon 
dioxide  exhaled,  based  on  analyses  of  the  inspired  and  expired  air,  calcula- 
tions from  the  average  quantity  of  air  changed  with  each  respiratory  act,  and 
the  average  number  of  respirations  per  minute,  are  by  no  means  so  reliable  as 
analyses  showing  the  actual  changes  in  the  air,  like  those  of  Regnault  and 
Reiset,  provided  the  physiological  conditions  be  fulfilled,  Where  there  is  so 
much  multiplication  and  calculation,  a  very  slight  inaccuracy  in  the  estimates 
of  the  quantities  consumed  or  produced  in  a  single  respiration  will  make  a 
large  error  in  the  estimate  for  a  day  or  even  for  an  hour.  Bearing  in  mind 
all  these  sources  of  error,  from  the  experiments  of  Valentin  and  Brunner,  Du- 
mas, Regnault  and  Reiset  and  others,  a  sufficiently  accurate  approximate  esti- 
mate of  the  proportion  of  oxygen  consumed  by  the  human  subject  may  be 
made.  The  air,  which  contains,  when  inspired,  2O81  parts  of  oxygen  per 
100,  is  found  on  expiration  to  contain  but  about  16  parts  per  100.  In  other 
words,  the  volume  of  oxygen  absorbed  in  the  lungs  is  five  per  cent,  or  ^  of 
the  volume  of  air  inspired.  It  is  useful  to  extend  this  estimate  as  far  as  pos- 
sible to  the  quantity  of  oxygen  absorbed  in  a  definite  time ;  for  the  regulation 
of  the  supply  of  oxygen  where  many  persons  are  assembled,  as  in  public  build- 
ings, hospitals  etc.,  is  a  question  of  great  practical  importance.  Assuming 
that  the  average  respirations  per  minute  are  eighteen,  and  that  with  each  act, 
twenty  cubic  inches  (327'7  c.  c.)  of  air  are  changed,  fifteen  cubic  feet  (424'8 
litres)  of  oxygen  are  consumed  in  the  twenty-four  hours,  which  represent 
three  hundred  cubic  feet  (8'5  cubic  metres)  of  pure  air.  This  is  the  mini- 
mum quantity  of  air  which  is  actually  used,  making  no  allowance  for  any  in- 
crease in  the  activity  of  the  respiratory  processes,  which  is  liable  to  occur 
from  various  causes.  To  meet  all  the  respiratory  exigencies  of  the  system,  in 
hospitals,  prisons  etc.,  it  has  been  found  necessary  to  allow  at  least  eight 


138          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

hundred  cubic  feet  (22-65  cubic  metres)  of  air  for  each  person,  unless  the  con- 
ditions be  such  that  the  air  is  changed  with  unusual  frequency ;  for  in  ad- 
dition to  the  actual  loss  of  oxygen  in  the  respired  air,  emanations  from  both 
the  pulmonary  and  cutaneous  surfaces  are  constantly  taking  place,  which 
should  be  removed.  In  some  institutions  as  much  as  twenty-five  hundred 
cubic  feet  (70*79  cubic  metres)  of  air  are  allowed  for  each  person. 

The  quantity  of  oxygen  consumed  is  subject  to  great  variations,  depend- 
ing upon  temperature,  the  condition  of  the  digestive  system,  muscular  activ- 
ity etc.  The  following  conclusions,  the  results  of  the  observations  of  La- 
voisier and  Seguin,  give  at  a  glance  the  variations  from  the  above-mentioned 
causes : 

"  1.  A  man,  in  repose  and  fasting,  with  an  external  temperature  of  about 
90°  Fahr.  (32-5°  C.),  consumes  1,465  cubic  inches  (24  litres)  of  oxygen  per 
hour. 

"  2.  The  same  man,  in  repose  and  fasting,  with  an  external  temperature 
of  59°  Fahr.  (15°  C.),  consumes  1,627  cubic  inches  (26-66  litres)  of  oxygen 
per  hour. 

"  3.  The  same  man,  during  digestion,  consumes  2,300  cubic  inches  (37*69 
litres)  of  oxygen  per  hour. 

"  4.  The  same  man,  fasting,  accomplishing  the  labor  necessary  to  raise,  in 
fifteen  minutes,  a  weight  of  about  16  Ib.  3  oz.  (7*343  kilos.)  to  the  height  of 
656  feet  (200  metres)  consumes  3,874  cubic  inches  (63*48  litres)  of  oxygen  per 
hour. 

"  5.  The  same  man,  during  digestion,  accomplishing  the  labor  necessary 
to  raise,  in  fifteen  minutes,  a  weight  of  about  16  Ib.  3  oz.  (7*343  kilos.)  to  the 
height  of  692  feet  (211-146  metres),  consumes  5,568  cubic  inches  (91-24  litres) 
of  oxygen  per  hour." 

All  who  have  experimented  on  the  influence  of  temperature  upon  the  con- 
sumption of  oxygen,  in  the  warm-blooded  animals  and  in  the  human  subject, 
have  noted  a  marked  increase  at  low  temperatures.  Immediately  after  birth 
the  consumption  of  oxygen  in  the  warm-blooded  animals  is  relatively  very 
slight.  Buffon  and  Legallois  have  shown  that  just  after  birth,  dogs  and 
other  animals  will  live  for  half  an  hour  or  longer  under  water ;  and  cases  are 
on  record  in  which  life  has  been  restored  in  newborn  children  after  seven, 
and  it  has  been  stated,  after  twenty-three  hours  of  asphyxia  (Milne-Edwards). 
During  the  first  periods  of  existence  the  condition  of  the  newly  born  is  near- 
ly that  of  a  cold-blooded  animal.  The  lungs  are  relatively  very  small,  and  it 
is  some  time  before  they  fully  assume  their  office.  The  muscular  movements 
are  hardly  more  than  are  necessary  to  take  the  small  quantity  of  nourishment 
consumed  at  that  period,  and  nearly  all  of  the  time  is  passed  in  sleep.  There 
is  also  very  little  power  of  resistance  to  a  low  temperature.  Although  accu- 
rate researches  regarding  the  comparative  quantities  of  oxygen  in  the  venous 
and  arterial  blood  of  the  foetus  are  wanting,  it  has  been  frequently  observed 
that  the  difference  in  color  is  not  so  marked  as  it  is  after  pulmonary  respira- 
tion has  become  established.  The  direct  researches  of  "W.  F.  Edwards  have 
shown  that  the  absolute  consumption  of  oxygen  by  very  young  animals  is 


CONSUMPTION  OF  OXYGEN.  139 

quite  small ;  and  the  observations  of  Legallois,  on  rabbits,  made  every  five 
days  during  the  first  month  of  life,  show  a  rapidly  increasing  demand  for 
oxygen. 

The  consumption  of  oxygen  is  greater  in  lean  than  in  very  fat  animals, 
provided  they  be  in  perfect  health.  The  consumption  is  greater,  also,  in  car- 
nivorous than  in  herbivorous  animals ;  and  in  animals  of  different  sizes,  it  is 
relatively  much  greater  in  those  which  are  very  small.  In  small  birds,  such 
as  the  sparrow,  the  relative  quantity  of  oxygen  absorbed  was  ten  times  greater 
than  in  the  fowl  (Eegnault  and  Keiset). 

During  sleep  the  quantity  of  oxygen  consumed  is  considerably  dimin- 
ished ;  and  in  hibernation  it  is  so  small,  that  Spallanzani  could  not  detect 
any  difference  in  the  composition  of  the  air  in  which  a  marmot,  in  a  state  of 
torpor,  had  remained  for  three  hours.  In  experiments  on  a  marmot  in  hiber- 
nation, Regnault  and  Reiset  observed  a  reduction  in  the  oxygen  consumed  to 
about  ^  of  the  ordinary  quantity. 

It  has  been  shown  by  experiments,  that  the  consumption  of  oxygen  bears 
a  nearly  constant  ratio  to  the  production  of  carbon  dioxide ;  and  as  the 
observations  upon  the  influence  of  sex,  the  number  of  respiratory  acts  etc.,  on 
the  activity  of  the  respiratory  processes  have  been  made  chiefly  with  reference 
to  the  carbon  dioxide  exhaled,  these  influences  will  be  considered  in  connec- 
tion with  the  products  of  respiration. 

Experiments  on  the  effect  of  increasing  the  proportion  of  oxygen  in  the 
air  have  led  to  varied  results  in  the  hands  of  different  observers.  Regnault 
and  Reiset,  whose  observations  on  this  point  are  generally  accepted,  did  not 
discover  any  increase  in  the  consumption  of  oxygen  when  this  gas  was  largely 
in  excess  in  the  atmosphere. 

The  results  of  confining  an  animal  in  an  atmosphere  composed  of  twenty- 
one  parts  of  oxygen  and  seventy-nine  parts  of  hydrogen  are  very  remarkable. 
When  hydrogen  is  thus  substituted  for  the  nitrogen  of  the  air,  the  consump- 
tion of  oxygen  is  largely  increased.  Regnault  and  Reiset  attributed  this  to 
the  superior  refrigerating  power  of  the  hydrogen  ;  but  a  more  rational  expla- 
nation would  seem  to  be  in  its  greater  diffusibility.  Hydrogen  is  the  most 
diffusible  of  all  gases ;  and  when  introduced  into  the  lungs  in  place  of  the 
nitrogen  of  the  air,  the  vitiated  air,  charged  with  carbon  dioxide,  is  undoubt- 
edly more  readily  removed  from  the  deep  portions  of  the  lungs,  giving  place 
to  the  mixture  of  hydrogen  and  oxygen.  It  is  probably  for  this  reason  that 
the  quantity  of  oxygen  consumed  is  increased.  It  is  probable  that  the  nitro- 
gen of  the  air  plays  an  important  part  in  the  phenomena  of  respiration,  by 
virtue  of  its  degree  of  diffusibility. 

In  view  of  the  great  variations  in  the  consumption  of  oxygen,  dependent 
on  different  physiological  conditions,  such  as  digestion,  exercise,  temperature 
etc.,  it  is  impossible  to  fix  upon  any  number  which  will  represent,  even  ap- 
proximately, the  average  quantity  consumed  per  hour.  The  estimate  arrived 
at  by  Longet,  from  a  comparison  of  the  results  obtained  by  different  reliable 
observers,  is  perhaps  as  near  the  truth  as  possible.  This  estimate  puts  the 
hourly  consumption  at  1,220  to  1,525  cubic  inches  (20  to  25  litres),  "  in  an 


140          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

adult  male,  during  repose  and  in  normal  conditions  of  health  and  tem- 
perature." 

In  passing  through  the  lungs,  the  air,  in  addition  to  losing  a  certain  pro- 
portion of  its  oxygen,  undergoes  the  following  changes  : 

1.  Elevation  in  temperature. 

2.  Gain  of  carbon  dioxide. 

3.  Gain  of  watery  vapor. 

4.  Gain  of  ammonia. 

5.  Gain  of  a  small  quantity  of  organic  matter. 

6.  Gain,  and  occasionally  loss,  of  nitrogen. 

The  elevation  in  temperature  of  the  air  which  has  passed  through  the 
lungs  has  been  studied  by  Grehant.  He  found  that  with  an  external  tem- 
perature of  72°  Fahr.  (22-22°  C.),  respiring  seventeen  times  per  minute,  the 
air  taken  in  by  the  nares,  and  expired  by  the  mouth  through  an  apparatus 
containing  a  thermometer  carefully  protected  from  external  influences,  marked 
a  temperature  of  95-4°  Fahr.  (35-22°  C.).  Taking  in  the  air  by  the  mouth, 
the  temperature  of  the  expired  air  was  93°  Fahr.  (33-89°  C.).  At  the  begin- 
ning of  the  expiration,  Grehant  noted  a  temperature  of  94°  Fahr.  (34-44°  C.). 
After  a  prolonged  expiration,  the  temperature  was  96°  Fahr.  (35-55°  C.).  In 
these  observations  the  temperature  taken  beneath  the  tongue  was  98°  Fahr. 
(36-67°  C.) 

Exhalation  of  Carbon  Dioxide. — On  account  of  the  variations  in  the  quan- 
tities of  carbon  dioxide  exhaled  at  different  times  of  the  day,  and  particularly 
the  great  influence  of  the  rapidity  of  the  respiratory  movements,  it  is  difficult 
to  fix  upon  any  number  that  will  represent  the  average  proportion  of  this  gas 
contained  in  the  expired  air.  The  same  influences  were  found  affecting  the 
consumption  of  oxygen,  and  the  same  difficulties  were  experienced  in  form- 
ing an  estimate  of  the  proportion  of  this  gas  consumed.  As  it  was  assumed, 
after  a  comparison  of  the  results  obtained  by  different  observers,  that  the 
volume  of  oxygen  consumed  is  about  five  per  cent,  of  the  entire  volume  of 
air,  it  may  be  stated,  as  an  approximation,  that  in  the  intervals  of  digestion, 
in  repose  and  under  normal  conditions  as  regards  the  frequency  of  the  pulse 
and  respiration,  the  volume  of  carbon  dioxide  exhaled  is  about  four  per  cent, 
of  the  volume  of  the  expired  air.  As  the  volume  of  oxygen  which  enters 
into  the  composition  of  a  definite  quantity  of  carbon  dioxide  is  equal  to  the 
volume  of  the  carbon  dioxide,  it  is  seen  that  a  certain  quantity  of  oxygen 
disappears  in  respiration  and  is  not  represented  in  the  carbon  dioxide  ex- 
haled. 

There  are  great  differences  in  the  proportion  of  carbon  dioxide  in  the 
expired  air,  depending  upon  the  time  during  which  the  air  has  remained  in 
the  lungs.  This  point  was  studied  by  Vierordt,  in  a  series  of  ninety-four 
experiments  made  upon  his  own  person,  with  the  following  results  : 

"When  the  respirations  are  frequent,  the  quantity  of  carbon  dioxide 
expelled  at  each  expiration  is  much  less  than  in  a  slow  expiration ;  but  the 
quantity  of  carbon  dioxide  produced  during  a  given  time  by  frequent  respira- 
tions is  greater  than  that  which  is  thrown  off  by  slow  expirations." 


EXHALATION  OF  CAEBON  DIOXIDE.  141 

The  air  which  escapes  during  the  first  part  of  an  expiration  is  less  rich 
in  carbon  dioxide  than  that  which  is  last  expelled  and  comes  directly  from 
the  deeper  portions  of  the  lungs.  Dividing,  as  nearly  as  possible,  the  expira- 
tion into  two  equal  parts,  Vierordt  found,  as  the  mean  of  twenty-one  experi- 
ments, a  percentage  of  3'72  in  the  first  part  of  the  expiration  and  5'44  in  the 
second  part. 

Temporary  arrest  of  the  respiratory  movements  has  a  marked  influence 
in  increasing  the  proportion  of  carbon  dioxide  in  the  expired  air,  although 
the  absolute  quantity  exhaled  in  a  given  time  is  diminished.  In  a  number 
of  experiments  on  his  own  person,  Vierordt  ascertained  that  the  percentage 
of  carbon  dioxide  becomes  uniform  in  all  parts  of  the  respiratory  organs, 
after  holding  the  breath  for  forty  seconds.  Holding  the  breath  after  an 
ordinary  inspiration,  for  twenty  seconds,  the  percentage  of  carbon  dioxide  in 
the  expired  air  was  increased  T73  above  the  normal  standard ;  but  the  abso- 
lute quantity  exhaled  was  diminished  by  2'642  cubic  inches  (43-3  c.  c.)  After 
taking  the  deepest  possible  inspiration  and  holding  the  breath  for  one  hun- 
dred seconds,  the  percentage  was  increased  3-08  above  the  normal  standard ; 
but  the  absolute  quantity  was  diminished  more  than  fourteen  cubic  inches 
(229'4  c.  c.).  Allen  and  Pepys  noted  that  air  which  had  passed  nine  or  ten 
times  through  the  lungs  contained  9'5  per  cent,  of  carbon  dioxide. 

Vierordt  has  given  the  following  formula  as  representing  the  influence  of 
the  frequency  of  the  respirations  on  the  production  of  carbon  dioxide : 
Taking  2-5  parts  per  hundred  as  representing  the  constant  value  of  the  gas 
exhaled  by  the  blood,  the  increase  over  this  proportion  in  the  expired  air  is 
in  exact  ratio  to  the  duration  of  the  contact  of  the  air  and  blood. 

The  absolute  quantity  of  carbon  dioxide  exhaled  in  a  given  time  is  a  more 
important  subject  of  inquiry  than  the  proportion  contained  in  the  expired 
air ;  for  the  latter  varies  with  every  modification  in  the  number  and  extent 
of  the  respiratory  acts,  and  the  volume  of  breathing  air  is  subject  to  great 
fluctuations  and  is  very  difficult  of  determination. 

Among  the  most  reliable  observations  on  the  quantity  of  carbon  dioxide 
exhaled  by  the  human  subject  in  a  definite  time  and  the  variations  to  which 
it  is  subject,  are  those  of  Andral  and  Gavarret  and  of  Edward  Smith.  The 
observations  of  Lavoisier  and  Seguin,  Prout,  Davy,  Dumas,  Allen  and  Pepys, 
Scharling  and  others,  do  not  seem  to  have  fulfilled  the  necessary  experimental 
conditions  so  completely.  The  observations  of  Andral  and  Gavarret  were 
made  on  sixty-two  persons  of  both  sexes  and  different  ages,  and  under  identi- 
cal conditions  as  regards  digestion,  time  of  the  day,  barometric  pressure  and 
temperature ;  and  the  observations  on  males  between  the  ages  of  sixteen  and 
thirty,  between  1  and  2  P.  M.,  under  identical  conditions  of  the  digestive  and 
muscular  systems,  each  experiment  lasting  eight  to  thirteen  minutes,  showed 
an  exhalation  of  about  1,220  cubic  inches  (20  litres)  of  carbon  dioxide  per 
hour. 

Edward  Smith  employed  the  following  method  for  the  estimation  of 
the  carbon  dioxide  exhaled :  He  used  a  mask,  fitting  closely  to  the  face,  which 
covered  only  the  air-passages.  The  air  was  admitted  after  having  been  meas- 
11 


142          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

ured  by  an  ordinary,  dry  gas-meter.  The  expired  air  was  passed  through  a 
drying  apparatus,  and  the  carbon  dioxide  was  absorbed  by  a  solution  of 
potassium  hydrate,  arranged  in  a  number  of  layers  so  as  to  present  a  surface 
of  about  seven  hundred  square  inches  (45  square  decimetres),  and  was  care- 
fully weighed.  This  apparatus  was  capable  of  collecting  all  the  carbon  dioxide 
exhaled  in  an  hour.  The  estimates  were  made  for  eighteen  waking  hours 
and  six  hours  of  sleep.  The  observations  occupied  ten  minutes  each  and 
were  made  every  hour  and  half -hour  for  eighteen  hours.  The  average  for 
the  eighteen  hours  gave  20,082  cubic  inches  (329  litres)  of  carbon  dioxide  for 
the  whole  period.  Observations  during  the  six  hours  of  sleep  showed  a  total 
exhalation  of  4,126  cubic  inches  (7'145  litres).  This,  added  to  the  quantity 
exhaled  during  the  day,  gives  as  the  total  exhalation  in  the  twenty-four  hours, 
during  complete  repose,  24,208  cubic  inches  (about  14-24  cubic  feet,  or 
336-145  litres),  containing  7'144  oz.  (202-47  grammes)  of  carbon.  In  view 
of  the  great  variations  in  the  exhalation  of  carbon  dioxide,  this  estimate  can 
be  nothing  more  than  an  approximation. 

One  of  the  important  modifying  influences  is  muscular  exertion,  by  which 
the  production  of  carbon  dioxide  is  largely  increased.  This  would  indicate 
a  larger  quantity  during  ordinary  conditions  of  exercise,  and  a  much  larger 
quantity  in  the  laboring  classes.  Dr.  Smith  has  given  the  following  approxi- 
mate estimates  of  these  differences : 

In  quietude 7-144  oz.  (202-47  grammes)  of  carbon. 

Non- laborious  class 8-68     "   (246-04  grammes)          " 

Laborious  class 11-7       "   (331-61  grammes)          " 

In  studying  the  variations  in  the  exhalation  of  carbon  dioxide,  important 
imformation  has  been  derived  from  experiments  by  many  observers  on  the 
inferior  animals,  as  well  as  from  the  observations  of  Dumas,  Prout,  Scharling, 
Pettenkofer  and  others,  on  the  human  subject.  The  principal  conditions 
which  influence  the  exhalation  of  this  principle  are  the  following :  Age  and 
sex ;  activity  or  repose  of  the  digestive  system ;  kind  of  diet ;  sleep ;  muscu- 
lar activity ;  fatigue ;  moisture  and  surrounding  temperature ;  season  of  the 
year. 

Influence  of  Age. — In  treating  of  the  consumption  of  oxygen,  it  was  stated 
that  during  the  first  few  days  of  extraiiterine  existence,  the  demand  for  oxy- 
gen on  the  part  of  the  system  is  very  small.  At  this  period  there  is  a  corre- 
spondingly feeble  exhalation  of  carbon  dioxide.  It  is  well  known  that  during 
the  first  hours  and  days  after  birth,  the  new  being  has  little  power  of  generat- 
ing heat,  needs  constant  protection  from  changes  in  temperature,  and  the 
voluntary  movements  are  very  imperfect.  During  the  first  few  days,  indeed, 
the  infant  does  little  more  than  sleep  and  take  the  small  quantity  of  colostrum 
which  is  furnished  by  the  mammary  glands  of  the  mother.  While  the  ani- 
mal functions  are  so  imperfectly  developed  and  until  the  alimentation  be- 
comes more  abundant  and  the  child  begins  to  increase  rapidly  in  weight,  the 
quantity  of  carbon  dioxide  exhaled  is  very  small. 

After  the  respiratory  function  has  become  fully  established,  it  is  probable, 


EXHALATION  OF  CARBON  DIOXIDE.  143 

from  the  greater  number  of  respiratory  movements  in  early  life,  that  the  pro- 
duction of  carbon  dioxide,  in  proportion  to  the  weight  of  the  body,  is  greater 
in  infancy  than  in  adult  life.  Direct  observations,  however,  are  wanting  on 
this  point. 

The  observations  of  Andral  and  Gavarret  show  the  comparative  exhala- 
tion of  carbon  dioxide  in  the  male,  between  the  ages  of  twelve  and  eighty- 
two,  and  give  the  results  of  a  single  observation  at  the  age  of  one  hundred 
and  two  years.  They  show  an  increase  in  the  absolute  quantity  exhaled,  from 
the  age  of  twelve  to  thirty-two ;  a  slight  diminution,  from  thirty-two  to  sixty ; 
and  a  considerable  diminution,  from  sixty  to  eighty-two.  Taking  into  con- 
sideration the  increase  in  the  weight  of  the  body  with  age,  it  is  evident  that 
the  respiratory  activity  is  much  greater  in  youth  than  in  adult  life,  and  there 
can  be  no  doubt  that  there  is  a  rapid  diminution  in  the  relative  quantity  of 
carbon  dioxide  produced  in  old  age.  Scharling,  in  a  series  of  observations 
on  a  boy  nine  years  of  age,  an  adult  of  twenty-eight,  and  one  of  thirty-five 
years,  showed  that  the  respiratory  activity  in  the  child  was  nearly  twice  as 
great,  in  proportion  to  his  weight,  as  the  average  in  the  adults. 

Influence  of  Sex. — All  observers  have  found  a  marked  difference  between 
the  sexes,  in  favor  of  the  male,  in  the  proportion  of  carbon  dioxide  exhaled. 
Andral  and  Gavarret  noted  an  absolute  difference  of  about  forty-five  cubic 
inches  (737-4  c.  c.)  per  hour,  but  did  not  take  into  consideration  the  differ- 
ences in  the  weight  of  the  body.  Scharling,  taking  the  proportion  exhaled 
to  the  weight  of  the  body,  noted  a  marked  difference  in  favor  of  the  male. 
The  difference  in  muscular  activity  in  the  sexes  is  sufficient  to  account  for 
the  greater  elimination  of  carbon  dioxide  in  the  male,  for  this  substance 
is  exhaled  in  proportion  to  the  muscular  development  of  the  individual ; 
but  there  is  an  important  difference  connected  with  the  variations  with 
age,  which  depends  upon  the  condition  of  the  generative  system  of  the 
female.  The  absolute  increase  in  the  exhalation  of  carbon  dioxide  with  age, 
in  the  female,  is  arrested  at  the  time  of  puberty  and  remains  stationary  until 
the  cessation  of  the  menses,  provided  the  menstrual  flow  occur  with  regular- 
ity (Andral  and  Gavarret).  During  this  time  the  average  exhalation  per 
hour  is  714  cubic  inches  (11-69  litres).  After  the  cessation  of  the  menses 
the  quantity  gradually  increases,  until,  at  the  age  of  sixty,  it  amounts  to  915 
cubic  inches  (15  litres)  per  hour.  From  the  age  of  sixty  to  eighty-two  the 
quantity  diminishes  to  793  (13  litres),  and  finally  to  670  cubic  inches  (about 
11  litres).  When  the  menses  are  suppressed,  there  is  an  increase  in  the 
exhalation  of  carbon  dioxide,  which  continues  until  the  flow  becomes  reestab- 
lished. In  a  case  of  pregnancy  observed  by  Scharling  the  exhalation  was 
increased  to  about  885  cubic  inches  (14-5  litres). 

Influence  of  Digestion. — Almost  all  observers  agree  that  the  exhalation  of 
carbon  dioxide  is  largely  increased  during  digestion.  Lavoisier  and  Seguin 
found  that  in  repose  and  fasting,  the  quantity  exhaled  per  hour  was  1,210 
cubic  inches  (19-82  litres),  which  was  raised  to  1,800  and  1,900  (29-5  and 
31-14  litres)  during  digestion.  A  series  of  observations  on  this  point  was 
made  by  Tierordt  upon  his  own  person.  Taking  his  dinner  between  12-30 


144          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

and  1  P.  M.,  having  noted  the  frequency  of  the  pulse  and  respirations  and  the 
exhalation  of  carbon  dioxide  at  12  M.,  he  found  at  2  P.  M.,  the  pulse  and  res- 
pirations increased  in  frequency,  the  volume  of  expired  air  augmented,  and 
the  carbon  dioxide  exhaled  increased  from  15-77  to  18-22  cubic  inches 
(258-43  to  298-6  c.  c.)  per  minute.  In  order  to  ascertain  that  this  variation 
did  not  depend  upon  the  time  of  day,  independently  of  the  digestive  process, 
he  made  a  comparison  at  12  M.,  at  1  and  at  2  P.  M.  without  taking  food,  which 
showed  no  notable  variation,  either  in  the  pulse,  number  of  respirations,  volume 
of  expired  air  or  quantity  of  carbon  dioxide  exhaled. 

The  effect  of  inanition  is  to  gradually  diminish  the  exhalation  of  carbon 
dioxide.  Bidder  and  Schmidt  noted  the  daily  production  in  a  cat  which 
was  subjected  to  eighteen  days  of  inanition,  at  the  end  of  which  time  it  died. 
The  quantity  diminished  gradually  from  day  to  day,  until  just  before  death 
it  was  reduced  a  little  more  than  one-half.  Edward  Smith  noted  in  his  own 
person  the  influence  of  a  fast  of  twenty-seven  hours.  There  was  a  marked 
dimunition  in  the  quantity  of  air  respired,  in  the  quantity  of  vapor  exhaled, 
in  the  number  of  respirations  and  in  the  rapidity  of  the  pulse.  The  exhala- 
tion of  carbon  dioxide  was  diminished  one-fourth.  An  important  point  in 
this  observation  was  that  the  quantity  was  as  small  four  and  a  half  hours 
after  eating  as  at  the  end  of  the  twenty-seven  hours. 

Influence  of  Diet. — The  most  extended  series  of  investigations  on  the  in- 
fluence of  diet  upon  the  absolute  quantity  of  carbon  dioxide  exhaled  are  those 
of  Edward  Smith.  This  observer  made  a  large  number  of  experiments  on 
the  influence  of  various  kinds  of  food,  and  extended  his  inquiries  into  the 
influence  of  certain  beverages,  such  as  tea,  coffee,  cocoa,  malt  liquors  and  fer- 
mented liquors.  He  divided  food  into  two  classes :  one  which  increases  the 
exhalation  of  carbon  dioxide,  which  he  called  respiratory  excitants,  and  the 
other,  which  diminishes  the  exhalation,  he  called  non-exciters.  The  follow- 
ing are  the  results  of  a  large  number  of  observations  upon  four  persons  : 

"  The  excito-respiratory  are  nitrogeneous  food,  milk  and  its  components, 
sugars,  rum,  beer,  stout,  the  cereals,  and  potato. 

"  The  non-exciters  are  starch,  fat,  certain  alcoholic  compounds,  the  vola- 
tile elements  of  wines  and  spirits,  and  coffee-leaves. 

''  Respiratory  excitants  have  a  temporary  action ;  but  the  action  of  most 
of  them  commences  very  quickly,  and  attains  its  maximum  within  one  hour. 

"  The  most  powerful  respiratory  excitants  are  tea  and  sugar ;  then  coffee, 
rum,  milk,  cocoa,  ales,  and  chiccory;  then  casein  and  gluten,  and  lastly, 
gelatin  and  albumen.  The  amount  of  action  was  not  in  uniform  propor- 
tion to  their  quantity.  Compound  aliments,  as  the  cereals,  containing  sev- 
eral of  these  substances,  have  an  action  greater  than  that  of  any  of  their  ele- 
ments. 

"  Most  respiratory  excitants,  as  tea,  coffee,  gluten,  and  casein,  cause  an 
increase  in  the  evolution  of  carbon  greater  than  the  quantity  which  they 
supply,  while  others,  as  sugar,  supply  more  than  they  evolve  in  this  excess, 
that  is,  above  the  basis.  No  substance  containing  a  large  amount  of  carbon 
evolves  more  than  a  small  portion  of  that  carbon  in  the  temporary  action 


EXHALATION   OF  CARBON  DIOXIDE.  145 

occurring  above  the  basis-line,  and  hence  a  large  portion  remains  unaccounted 
for  by  these  experiments." 

The  comparative  observations  upon  the  four  persons  who  were  the  sub- 
jects of  experiment  demonstrated  one  very  important  fact ;  namely,  that  the 
action  of  different  kinds  of  food  upon  respiration  is  modified  by  idiosyncra- 
sies and  the  tastes  of  different  individuals. 

The  following  are  the  results  of  observations  upon  the  effects  of  different 
alcoholic  beverages  taken  during  the  intervals  of  digestion  : 

"  Brandy,  whiskey,  and  gin,  and  particularly  the  latter,  almost  always  less- 
ened the  respiratory  changes  recorded,  while  rum  as  commonly  increased 
them.  Eum-and-milk  had  a  very  pronounced  and  persistent  action,  and 
there  was  no  effect  on  the  sensorium.  Ale  and  porter  always  increased  them, 
while  sherry  wine  lessened  the  quantity  of  air  inspired,  but  slightly  increased 
the  carbonic  acid  evolved. 

"  The  volatile  elements  of  alcohol,  gin,  rum,  sherry,  and  port-wine,  when 
inhaled,  lessened  the  quantity  of  carbonic  acid  exhaled,  and  usually  lessened 
the  quantity  of  air  inhaled.  The  effect  of  fine  old  port- wine  was  very  de- 
cided and  uniform ;  and  it  is  known  that  wines  and  spirits  improve  in  aroma 
and  become  weaker  in  alcohol  by  age.  The  excito-respiratory  action  of  rum 
is  probably  not  due  to  its  volatile  elements." 

From  these  facts  it  would  seem  that  the  most  constant  effect  of  alcohol 
and  of  alcoholic  liquors,  such  as  wines  and  spirits,  is  to  diminish  the  exhala- 
tion of  carbon  dioxide.  This  effect  is  almost  instantaneous,  when  the  articles 
are  taken  into  the  stomach  fasting ;  and  when  taken  with  the  meals,  the 
increase  in  carbon  dioxide,  which  habitually  accompanies  the  process  of 
digestion,  is  materially  lessened.  Bum,  which  was  found  to  be  a  respiratory 
excitant,  is  an  exception  to  this  rule.  Malt  liquors  seem  to  increase  the  ex- 
halation of  carbon  dioxide.  "  The  action  of  pure  alcohol  was  much  more  to 
increase  than  to  lessen  the  respiratory  changes,  and  sometimes  the  former 
effect  was  well  pronounced." 

Influence  of  Sleep. — All  who  have  directed  attention  to  the  influence  of 
sleep  upon  the  respiratory  products  have  noted  a  marked  diminution  in  the 
exhalation  of  carbon  dioxide.  According  to  Edward  Smith,  the  quantity 
during  the  night  is  to  the  quantity  during  the  day,  in  complete  repose,  as  ten 
to  eighteen. 

It  has  already  been  stated  that  there  is  great  diminution  in  the  quantity 
of  oxygen  consumed  in  hibernating  animals  while  in  a  torpid  condition. 
Regnault  and  Reiset  found  that  a  marmot  in  hibernation  consumed  only  ^ 
of  the  oxygen  ordinarily  appropriated  in  the  active  condition.  In  the  same 
animal  they  noted  an  exhalation  of  carbon  dioxide  equal  to  but  little  more 
than  half  the  weight  of  oxygen  absorbed. 

Influence  of  Muscular  Activity. — Vierordt,  in  a  number  of  observations 
on  the  human  subject,  ascertained  that  moderate  exercise  increased  the  average 
quantity  of  air  respired  per  minute  by  nearly  nineteen  cubic  inches  (311-4 
c.  c.),  and  that  there  was  an  increase  of  1-197  cubic  inch  (19-63  c.  c.)  per 
minute  in  the  absolute  quantity  of  carbon  dioxide  exhaled. 


146          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

The  results  of  the  experiments  of  Dr.  Edward  Smith  on  the  influence  of 
exercise  are  as  follows  : 

In  walking  at  the  rate  of  two  miles  (3-22  kilometres)  per  hour,  the  exhala- 
tion of  carbon  dioxide  during  one  hour  was  equal  to  the  quantity  produced 
during  1£  hour  of  repose  with  food  or  2£  hours  of  repose  without  food. 

Walking  at  the  rate  of  three  miles  (4-828  kilometres)  per  hour,  one  hour 
was  equal  to  2f  hours  with  food  or  3£  hours  without  food. 

One  hour's  labor  at  the  tread- wheel,  while  actually  working  the  wheel, 
was  equal  to  4£  hours  of  rest  with  food  or  6  hours  without  food. 

It  has  been  observed,  however,  that  when  muscular  exertion  is  carried  so 
far  as  to  produce  great  fatigue  and  exhaustion,  the  exhalation  of  carbon 
dioxide  is  notably  diminished. 

Influence  of  Moisture  and  Temperature. — It  has  been  shown  that  the  ex- 
halation of  carbon  dioxide  is  greater  in  a  moist  than  in  a  dry  atmosphere 
(Lehmann).  It  has  also  been  ascertained  that  the  exhalation  is  much  greater 
at  low  than  at  high  temperatures,  within  the  limits  of  heat  and  cold  that  are 
easily  endured,  amounting,  according  to  the  experiments  of  Vierordt  on 
the  human  subject,  to  an  increase  of  about  one-sixth,  under  the  influence  of 
a  moderate  diminution  in  temperature.  It  was  found,  also,  that  the  quantity 
of  air  taken  into  the  lungs  was  slightly  increased  at  low  temperatures. 

Influence  of  the  Season  of  the  Year,  etc. — It  has  been  shown  by  the  re- 
searches of  Edward  Smith,  that  spring  is  the  season  of  the  greatest,  and  fall 
the  season  of  the  least  activity  of  the  respiratory  function. 

The  months  of  maximum  are  January,  February,  March  and  April. 

The  months  of  minimum  are  July,  August  and  a  part  of  September. 

The  months  of  decrease  are  June  and  July. 

The  months  of  increase  are  October,  November  and  December. 

Observations  on  the  influence  of  barometric  pressure  have  not  been  suf- 
ficiently definite  in  their  results  to  warrant  any  exact  conclusions. 

Some  physiologists  have  attempted  to  fix  certain  hours  of  the  day  when 
the  exhalation  of  carbon  dioxide  is  at  its  maximum  and  at  its  minimum ;  but 
the  respiratory  activity  is  influenced  by  such  a  variety  of  conditions  that  it  is 
impossible  to  do  this  with  any  degree  of  accuracy. 

RELATIONS  BETWEEN  THE  QUANTITY  OF  OXYGEN  CONSUMED  AND  THE 
QUANTITY  OF  CARBON  DIOXIDE  EXHALED. 

Oxygen  unites  with  carbon  in  a  certain  proportion  to  form  carbon  dioxide, 
the  volume  of  which  is  equal  to  the  volume  of  the  oxygen  which  enters  into 
its  composition.  It  is  possible,  therefore,  to  .study  the  relations  of  the  vol- 
umes of  these  gases  in  respiration,  by  simply  comparing  the  volumes  of  the 
inspired  and  expired  air.  It  is  now  generally  recognized  that  the  volume  of 
air  expired  is  less,  at  an  equal  temperature,  than  the  volume  of  air  inspired. 
Assuming,  then,  that  the  changes  in  the  expired  air,  as  regards  nitrogen  and 
all  gases  except  oxygen  and  carbon  dioxide,  are  insignificant,  it  must  be  ad- 
mitted that  a  certain  quantity  of  the  oxygen  consumed  by  the  economy  is 
unaccounted  for  by  the  oxygen  which  enters  into  the  composition  of  the 


EXHALATION  OF  CARBON  DIOXIDE.  147 

carbon  dioxide  exhaled.  It  has  already  been  stated  that  -^  to  -fa  (1-4  to  2  per 
cent.)  of  the  inspired  air  is  lost  in  the  lungs ;  or  it  may  be  said  in  general 
terms,  that  the  oxygen  absorbed  is  equal  to  about  five  per  cent,  of  the  volume 
of  air  inspired,  and  the  carbon  dioxide  exhaled,  only  about  four  per  cent.  A 
part  of  the  deficiency  in  volume  of  the  expired  air  is  to  be  accounted  for, 
then,  by  a  deficiency  in  the  exhalation  of  carbon  dioxide. 

The  experiments  of  Eegnault  and  Eeiset  have  an  important  bearing  on 
the  question  under  consideration.  As  these  observers  were  able  to  accurately 
measure  the  entire  quantities  of  oxygen  consumed  and  carbon  dioxide  pro- 
duced in  a  given  time,  the  relation  between  the  two  gases  was  kept  constantly 
in  view.  They  found  great  variations  in  this  relation,  mainly  dependent  upon 
the  regimen  of  the  animal.  The  total  loss  of  oxygen  was  found  to  be  much 
greater  in  carnivorous  than  in  herbivorous  animals;  and  in  animals  that 
could  be  subjected  to  a  mixed  diet,  by  regulating  the  food  this  was  made  to 
vary  between  the  two  extremes.  The  mean  of  seven  experiments  on  dogs 
showed  that  for  every  1,000  parts  of  oxygen  consumed,  745  parts  were  exhaled 
in  the  form  of  carbon  dioxide.  In  six  experiments  on  rabbits,  the  mean  was 
919  for  every  1,000  parts  of  oxygen. 

In  animals  fed  on  grains,  the  proportion  of  carbon  dioxide  exhaled  was 
greatest,  sometimes  passing  a  little  beyond  the  volume  of  oxygen  consumed. 

"  The  relation  is  nearly  constant  for  animals  of  the  same  species  which  are 
subjected  to  a  perfectly  uniform  alimentation,  as  is  easy  to  realize  as  regards 
dogs ;  but  it  varies  notably  in  animals  of  the  same  species,  and  in  the  same 
animal,  submitted  to  the  same  regimen,  but  in  which  we  can  not  regulate  the 
alimentation,  as  in  fowls." 

When  herbivorous  animals  were  entirely  deprived  of  food,  the  relation 
between  the  gases  was  the  same  as  in  carnivorous  animals. 

The  final  result  of  the  experiments  of  Eegnault  and  Eeiset  was  that  the 
"  relation  between  the  oxygen  contained  in  the  carbon  dioxide  and  the  total 
oxygen  consumed,  varies,  in  the  same  animal,  between  0-62  and  1-04,  accord- 
ing to  the  regimen  to  which  it  is  subjected."  These  observations  on  animals 
have  been  confirmed  in  the  human  subject  by  Doyere,  who  found  a  great 
variation  in  the  relations  of  the  two  gases  in  respiration;  the  volume  of 
carbon  dioxide  exhaled  varying  between  0-862  and  1-087  for  1  part  of  oxygen 
consumed. 

As  regards  the  destination  of  the  oxygen  which  is  not  represented  in  the 
carbon  dioxide  exhaled,  it  is  certain  that  a  part  of  it,  at  least,  unites  with 
hydrogen  to  form  water,  this  contributing  to  the  production  of  animal  heat, 
a  question  that  will  be  fully  discussed  in  another  connection. 

The  variations  in  the  relative  volumes  of  oxygen  consumed  and  carbon 
dioxide  produced  in  respiration  are  not  favorable  to  the  hypothesis  that  the 
carbon  dioxide  is  always  a  result  of  the  direct  action  of  oxygen  upon  the  car- 
bohydrates and  fats.  Such  a  definite  relation  between  these  two  gases  can 
not  be  assumed  to  exist,  in  view  of  the  fact  that  carbon  dioxide  may  be  given 
off  by  the  tissues  in  the  absence  of  oxygen. 

Many  of  the  points  that  have  been  considered  with  relation  to  the  varia- 


148          CHANGES  OF  AIE  AND  BLOOD  IN  RESPIRATION. 

tions  in  the  exhalation  of  carbon  dioxide  have  been  investigated  in  Petten- 
kofer's  chamber,  and  the  results  very  nearly  correspond  with  the  observations 
quoted  from  Scharling,  Edward  Smith  and  others. 

Sources  of  Carbon  Dioxide  in  the  Expired  Air. — All  the  carbon  dioxide 
in  the  expired  air  comes  from  the  venous  blood,  where  it  exists  in  two  forms ; 
in  a  free  state  in  simple  solution,  or  at  least  in  a  state  of  very  feeble  combina- 
tion, and  in  union  with  bases,  forming  the  carbonates  and  bicarbonates.  The 
fact  that  carbon  dioxide,  as  regards  the  quantity  absorbed  by  the  blood,  does 
not  obey,  in  all  regards,  the  laws  which  regulate  the  absorption  of  gases  by 
liquids  under  different  conditions  of  pressure,  has  led  some  physiologists  to 
regard  all  of  this  gas  as  existing  in  the  blood  in  a  condition  of  chemical  com- 
bination ;  the  greater  part  being  very  loosely  united  with  certain  other  sub- 
stances, and  a  small  quantity  of  that  which  is  thrown  off  in  the  expired 
air  being  in  a  condition  of  union  much  more  stable.  The  greater  part  of  the 
carbon  dioxide  exhaled  comes  from  the  plasma,  where  it  is  in  feeble  combina- 
tion, if  it  be  not  simply  in  solution.  Another  and  a  smaller  part  is  probably 
set  free  by  the  action  of  the  oxyhaemaglobine,  which  is  distinctly  acid.  It 
has  been  shown  that  more  carbon  dioxide  can  be  extracted  by  means  of  a 
vacuum  from  the  entire  blood  than  from  the  serum ;  and  this  gas  is  more 
readily  extracted  from  arterial  than  from  venous  blood.  The  mechanism  by 
which  the  carbon  dioxide  is  discharged  from  the  venous  blood  is  probably  the 
following : 

Carbon  dioxide  is  carried  from  the  tissues  to  the  lungs,  in  the  venous 
blood.  Here  it  exists  mainly  in  the  plasma,  a  small  quantity,  only,  existing 
in  the  corpuscles.  As  the  venous  blood  passes  through  the  lungs,  the  greater 
part  of  the  carbon  dioxide  of  the  plasma  either  simply  diffuses  from  the  blood 
into  the  air-cells  or  passes  out  by  a  process  known  to  chemists  as  dissociation 
(Deville).  It  is  certain  that  the  oxyhaemaglobine,  which  is  constantly  form- 
ing in  the  lungs,  assists  materially  in  this  process. 

There  can  be  no  doubt  with  regard  to  the  existence  of  an  acid  of  some 
kind  in  the  lungs,  which  possibly  deeomposes  a  portion  of  the  bicarbonates 
of  the  blood,  in  ordinary  respiration.  When  sodium  bicarbonate  is  injected 
into  the  jugular  of  a  living  animal,  a  rabbit,  for  example,  it  is  decomposed  as 
fast  as  it  gets  to  the  lungs,  and  carbon  dioxide  is  evolved.  This  experiment 
produces  no  inconvenience  to  the  animal  when  the  bicarbonate  is  introduced 
slowly ;  but  when  it  is  injected  in  large  quantity,  the  evolution  of  gas  in  the 
lungs  is  so  great  as  to  fill  the  pulmonary  structure  and  even  the  heart  and 
great  vessels,  and  death  is  the  result  (Bernard). 

Exhalation  of  Watery  Vapor. — From  a  large  number  of  observations  on  his 
own  person  and  upon  eight  others,  collecting  the  water  by  sulphuric  acid, 
Valentin  made  the  following  estimates  of  the  quantities  of  water  exhaled 
from  the  lungs  in  twenty-four  hours : 

In  his  own  person  the  exhalation  in  twenty-four  hours  was  5,934  grains 
(384-48  grammes). 

In  a  young  man  of  small  size  the  quantity  was  5,401  grains  (350 
grammes). 


EXHALATION  OF  WATEEY  VAPOR  ETC.  149 

In  a  student  rather  above  the  ordinary  height  the  quantity  was  11,929 
grains  (773  grammes). 

The  mean  of  his  observations  gave  a  daily  exhalation  of  8,333  grains  (540 
grammes),  or  about  a  pound  and  a  half. 

The  extent  of  respiratory  surface  has  a  marked  influence  on  the  quantity 
of  watery  vapor  exhaled.  This  fact  is  very  well  shown  by  a  comparison  of 
the  exhalation  in  the  adult  and  in  old  age,  as  in  advanced  life  the  extent  of 
respiratory  surface  is  much  diminished.  Barral  found  the  exhalation  in  an 
old  man  less  than  half  that  of  the  adult.  It  is  evident  that  the  absolute 
quantity  of  vapor  exhaled  is  increased  when  respiration  is  accelerated.  The 
quantity  of  water  in  the  blood  also  exerts  an  important  influence.  Valentin 
found  that  the  pulmonary  transpiration  was  more  than  doubled  in  a  man 
immediately  after  drinking  a  large  quantity  of  water. 

The  vapor  in  the  expired  air  is  derived  from  the  entire  surface  over  which 
the  air  passes  in  respiration,  and  not  exclusively  from  the  air-cells.  The  air 
which  passes  into  the  lungs  derives  a  certain  quantity  of  moisture  from 
the  mouth,  nares  and  trachea.  The  great  vascularity  of  the  mucous  mem- 
branes in  these  situations,  as  well  as  of  the  air-cells,  and  the  great  number 
of  mucous  glands  which  they  contain,  serve  to  keep  the  respiratory  surfaces 
constantly  moist.  This  is  important,  for  only  moist  membranes  allow  the 
free  passage  of  gases,  which  is  of  course  essential  to  the  process  of  respira- 
tion. 

Exhalation  of  Ammonia,  Organic  Matter  etc. — A  small  quantity  of  am- 
monia is  exhaled  by  the  lungs  in  health,  and  this  is  increased  in  certain  dis- 
eases, particularly  in  uraemia.  Its  characters  in  the  expired  air  are  frequently 
so  marked,  that  patients  who  are  entirely  unacquainted  with  the  pathology 
of  uraemia  sometimes  recognize  an  ammoniacal  odor  in  their  own  breath. 

The  pulmonary  surface  exhales  a  small  quantity  of  organic  matter.  This 
has  never  been  collected  in  sufficient  quantity  for  analysis,  but  its  presence 
may  be  demonstrated  by  the  fact  that  a  sponge  completely  saturated  with  the 
exhalations  from  the  lungs,  or  the  vapor  from  the  lungs  condensed  in  a  glass 
vessel,  will  undergo  putrefaction,  which  is  a  property  distinctive  of  organic 
substances. 

It  is  well  known  that  certain  substances  which  are  but  occasionally  found 
in  the  blood  may  be  eliminated  by  the  lungs.  Certain  odorous  matters  in 
the  breath  are  constant  in  those  who  take  liquors  habitually  in  considerable 
quantity.  The  odor  of  garlics,  onions,  turpentine  and  of  many  other  articles 
taken  into  the  stomach,  may  be  recognized  in  the  expired  air. 

The  lungs  eliminate  certain  gases  which  are  poisonous  in  very  small 
quantities  when  they  are  absorbed  in  the  lungs  and  carried  to  the  general 
system  in  the  arterial  blood.  Hydrogen  monosulphide,  which  produces  death 
in  a  bird  when  it  exists  in  the  atmosphere  in  the  proportion  of  one  to  eight 
hundred,  may  be  taken  in  solution  into  the  stomach  with  impunity  and  even 
be  injected  into  the  venous  system ;  in  both  instances  being  eliminated  by 
the  lungs  with  great  promptness  and  rapidity  (Bernard).  The  lungs,  while 
they  present  an  immense  and  rapidly  absorbing  surface  for  volatile  poisonous 


150          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

substances,  are  capable  of  relieving  the  system  of  some  of  these  by  exhalation 
when  they  find  their  way  into  the  veins. 

Exhalation  of  Nitrogen. — The  most  accurate  direct  experiments,  particu- 
larly those  of  Kegnault  and  Beiset,  show  that  the  exhalation  of  a  small  quan- 
tity of  nitrogen  is  a  nearly  constant  respiratory  phenomenon.  As  the  result 
of  a  large  number  of  experiments,  these  observers  came  to  the  conclusion  that 
when  animals  are  subjected  to  their  habitual  regimen,  they  exhale  a  quantity 
of  nitrogen  equal  in  Aveight  to  y^j-  or  -g^  of  the  weight  of  oxygen  consumed. 
In  birds,  during  inanition,  they  sometimes  observed  an  absorption  of  nitrogen, 
but  this  was  rarely  seen  in  mammals.  Boussingault,  estimating  the  nitrogen 
taken  into  the  body  and  comparing  it  with  the  entire  quantity  discharged, 
arrived  at  the  same  results  in  experiments  upon  a  cow.  Barral,  by  the  same 
method,  confirmed  these  observations  by  experiments  on  the  human  subject. 
Notwithstanding  the  conflicting  testimony  of  physiologists,  there  can  be  little 
doubt  that  under  ordinary  physiological  conditions,  there  is  an  exhalation  of 
a  small  quantity  of  nitrogen  by  the  lungs. 

CHANGES  OF  THE  BLOOD  IN  BESPIRATION  (H^MATOSIS). 

It  is  to  be  expected  that  the  blood,  receiving,  on  the  one  hand,  all  the 
products  of  digestion,  and  on  the  other,  the  products  of  disassimilation,  or 
wear  of  the  tissues,  connected  with  the  lymphatic  system,  and  exposed  to  the 
action  of  the  air  in  the  lungs,  should  present  important  differences  in  compo- 
sition in  different  parts  of  the  vascular  system. 

In  the  first  place,  there  is  a  marked  difference  in  color,  composition  and 
properties,  between  the  blood  in  the  arteries  and  in  the  veins ;  the  change 
from  venous  to  arterial  blood  being  effected  almost  instantaneously  in  its  pas- 
sage through  the  lungs.  The  blood  which  goes  to  the  lungs  is  collected  from 
all  parts  of  the  body  and  presents  great  differences  in  its  composition  in  dif- 
ferent veins.  In  some  veins  it  is  almost  black,  and  in  some  it  is  nearly  as  red 
as  in  the  arteries.  In  the  hepatic  vein  it  contains  sugar,  and  its  nitrogenized 
constituents  and  the  corpuscles  are  diminished ;  in  the  portal  vein,  during  di- 
gestion, it  contains  matters  absorbed  from  the  alimentary  canal ;  and  finally, 
there  is  every  reason  to  suppose  that  parts  which  require  different  substances 
for  their  nutrition  and  produce  different  excrementitious  matters  exert  differ- 
ent influences  on  the  constitution  of  the  blood  which  passes  through  them. 
After  this  mixture  of  different  kinds  of  blood  has  been  collected  in  the  right 
side  of  the  heart  and  passed  through  the  lungs,  it  is  returned  to  the  left  side 
and  sent  to  the  system,  thoroughly  changed  and  renovated,  and  as  arterial 
blood,  it  has  a  nearly  uniform  composition.  The  change,  therefore,  which 
the  blood  undergoes  in  its  passage  through  the  lungs,  is  the  transformation 
of  the  mixture  of  venous  blood  from  all  parts  of  the  organism  into  a  fluid  of 
uniform  character  which  is  capable  of  nourishing  every  tissue  and  organ  of 
the  body. 

The  capital  phenomena  of  respiration,  as  regards  the  air  in  the  lungs,  are 
loss  of  oxygen  and  gain  of  carbon  dioxide,  the  other  phenomena  being  com- 
paratively unimportant.  As  the  blood  is  capable  of  absorbing  gases,  the 


CHANGES  OF  THE  BLOOD  IN  RESPIRATION.  151 

essential  changes  which  this  fluid  undergoes  in  respiration  are  to  be  looked 
for  in  connection  with  the  proportions  of  oxygen  and  carbon  dioxide  before 
and  after  it  has  passed  through  the  lungs. 

The  change  of  color  in  the  blood  from  dark-blue  to  red,  in  its  passage 
through  the  lungs,  was  recognized  by  Lower,  Goodwyn  and  others,  as  due 
to  the  action  of  the  air,  long  before  the  discovery  of  oxygen.  Since  the 
discovery  of  oxygen,  it  has  been  ascertained  that  this  is  the  only  constituent 
of  the  air  which  is  capable  of  arterializiiig  the  blood.  Priestley  showed 
that  venous  blood  is  not  changed  in  color  by  nitrogen,  hydrogen  or  car- 
bon dioxide ;  while  all  these  gases,  by  displacing  oxygen,  will  change  the 
arterial  blood  from  red  to  black.  Carbon  monoxide,  although  it  is  not  a 
respirable  gas  and  does  not  properly  arterialize  the  blood,  changes  it  from 
black  to  red. 

The  elements  of  the  blood  which  absorb  the  greater  part  of  the  oxygen 
are  the  red  corpuscles.  While  the  plasma  will  absorb,  perhaps,  twice  as  much 
gas  as  pure  water,  it  has  been  shown  that  the  volume  of  oxygen  fixed  by  the 
corpuscles  is  about  twenty-five  times  that  which  is  dissolved  in  the  plasma 
(Fernet,  Lothar  Meyer). 

Comparison  of  the  Gases  in  Venous  and  Arterial  Blood. — The  demon- 
stration of  the  fact  that  oxygen  and  carbon  dioxide  exist  in  the  blood,  with  a 
knowledge  of  the  relative  proportion  of  these  gases  in  the  blood  before  and 
after  its  passage  through  the  lungs,  are  points  hardly  second  in  importance  to 
the  relative  composition  of  the  air  before  and  after  respiration.  The  idea  enun- 
ciated by  Mayow,  about  two  hundred  years  ago,  that  "  there  is  something  in 
the  air,  absolutely  necessary  to  life,  which  is  conveyed  into  the  blood,"  except 
that  the  vivifying  principle  was  not  named  or  its  other  properties  described, 
expresses  what  is  now  regarded  as  one  of  the  great  objects  of  respiration. 
This  is  even  more  strictly  in  accordance  with  facts  than  the  idea  of  Lavoisier, 
who  supposed  that  all  the  chemical  processes  of  respiration  took  place  in  the 
lungs.  Mayow  also  described  the  evolution  of  gas  from  blood  placed  in  a 
vacuum.  Many  observers  have  since  succeeded  in  extracting  gases  from 
the  blood  by  various  processes ;  but  notwithstanding  this,  before  the  experi- 
ments of  Magnus,  in  1837,  many  denied  the  existence  of  free  gases  in  the 
blood. 

Analysis  of  the  Blood  for  Gases. — There  were  certain  grave  sources  of 
error  in  the  method  employed  by  Magnus,  which  render  his  observations  of 
little  value,  except  as  demonstrating  that  oxygen,  carbon  dioxide  and  nitro- 
gen may  be  extracted  by  the  air-pump  from  both  arterial  and  venous  blood. 
The  only  source  of  error  in  the  results  which  he  fully  recognized  lay  in  the 
difficulty  in  extracting  the  entire  quantity  of  gas;  but  a  careful  study  of  his 
essay  shows  another  element  of  inaccuracy  which  is  even  more  important. 
The  relative  quantities  of  oxygen  and  carbon  dioxide  in  any  single  specimen 
of  blood  present  great  variations,  dependent  upon  the  length  of  time  that  the 
blood  has  been  allowed  to  stand  before  the  estimate  of  the  gases  is  made.  As 
it  is  difficult  to  make  this  estimate  immediately  after  the  blood  is  drawn,  on 
account  of  the  froth  produced  by  agitation  with  a  gas  when  the  method  by 


152          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

displacement  is  employed,  and  the  bubbling  of  the  gas  when  extracted  by  the 
air-pump,  the  objection  is  very  serious.  It  is  necessary  to  wait  until  the  froth 
has  subsided  before  attempting  to  make  an  accurate  estimate  of  the  volume 
of  gas  given  off.  This  fact  is  illustrated  by  one  of  the  published  observations 
of  Magnus  upon  three  different  specimens  of  human  blood.  In  this  observa- 
tion the  specimens  of  blood  were  thoroughly  mixed  with  hydrogen.  The 
excess  of  carbon  dioxide  found  twenty-four  hours  after,  over  the  quantity 
found  six  hours  after,  in  two  specimens,  was  a  little  more  than  fifty  per  cent., 
while  in  one  specimen  it  is  very  nearly  one  hundred  per  cent.  In  these  analyses 
the  proportion  of  oxygen  was  not  given.  The  question  naturally  arises  as  to 
the  source  of  the  carbon  dioxide  which  was  evolved  during  the  last  eighteen 
hours  of  the  observation.  The  question  is  readily  solved  by  certain  experi- 
ments, which  are  by  no  means  of  recent  date,  although  the  results  of  these 
observations  have  been  'confirmed  by  modern  investigations.  A  number  of 
years  ago,  Spallanzani  demonstrated  that  in  common  with  other  parts  of  the 
body,  fresh  blood  has,  of  itself,  the  property  of  consuming  oxygen ;  and  W.  F. 
Edwards  has  shown  that  the  blood  will  exhale  carbon  dioxide.  In  1856,  Har- 
ley  found  that  blood,  kept  in  contact  with  air  in  a  closed  vessel  for  twenty- 
four  hours,  consumed  oxygen  and  gave  off  carbon  dioxide.  More  recently, 
Bernard  has  shown  that  for  a  certain  time  after  the  blood  is  drawn  from  the 
vessels,  it  will  continue  to  consume  oxygen  and  exhale  carbon  dioxide.  If 
all  the  carbon  dioxide  be  removed  from  a  specimen  of  blood  by  treating  it 
with  hydrogen,  and  if  it  be  allowed  to  stand  for  twenty-four  hours,  another 
portion  of  gas  can  be  removed  by  again  treating  the  blood  with  hydrogen, 
and  still  another  quantity,  by  treating  it  with  hydrogen  a  third  time.  From 
these  facts  it  is  clear  that  in  the  experiment  of  Magnus,  the  excess  of  carbon 
dioxide  involved  a  post-mortem  consumption  of  oxygen;  and  no  analyses 
made  in  the  ordinary  way,  by  displacement  with  hydrogen  or  by  the  air- 
pump,  in  which  the  blood  is  allowed  to  remain  in  contact  with  oxygen  for 
a  number  of  hours,  can  be  accurate.  The  only  process  which  can  give  a 
rigorous  estimate  of  the  relative  quantities  of  oxygen  and  carbon  dioxide 
in  the  blood  is  one  in  which  the  gases  can  be  estimated  without  allowing 
the  blood  to  stand,  or  in  which  the  formation  of  carbon  dioxide,  at  the  ex- 
pense of  the  oxygen  in  the  specimen,  is  prevented.  All  others  will  give  a 
less  quantity  of  oxygen  and  a  greater  quantity  of  carbon  dioxide  than  exists 
in  the  blood  circulating  in  the  vessels  or  immediately  after  it  is  drawn  from 
the  body. 

Carbon  monoxide,  one  of  the  most  active  of  the  poisonous  gases,  has  a  re- 
markable affinity  for  the  blood-corpuscles.  When  taken  into  the  lungs,  it  is 
absorbed  by  and  becomes  fixed  in  the  corpuscles,  preventing  the  consumption 
of  oxygen  and  the  production  of  carbon  dioxide,  which  normally  take  pla^o 
in  the  capillary  system  and  which  are  indispensable  conditions  of  nutrition. 
The  mechanism  of  poisoning  by  the  inhalation  of  this  gas  is  by  its  fixation 
in  the  blood-corpuscles,  their  consequent  paralysis,  and  the  arrest  of  their 
action  as  oxygen-carriers.  As  it  is  the  continuance  of  this  transformation 
of  oxygen  into  carbon  dioxide,  after  the  blood  is  drawn  from  the  vessels, 


CHANGES  OF  THE  BLOOD  IN  RESPIRATION.  153 

which  interferes  with  the  ordinary  analysis  of  the  blood  for  gases,  it  would 
seem  possible  to  extract  all  the  oxygen  by  immediately  saturating  the  blood 
with  carbon  monoxide.  The  experiments  of  Bernard  on  this  point  are  con- 
clusive. He  ascertained  that  by  mixing  carbon  monoxide  in  sufficient  quan- 
tity with  a  specimen  of  fresh  arterial  blood,  in  about  two  hours,  all  the  oxy- 
gen which  it  contained  was  displaced.  Introducing  a  second  quantity  of 
carbon  monoxide  after  two  hours  and  leaving  it  in  contact  with  the  blood  for 
an  hour,  a  quantity  of  oxygen  was  removed  so  small  that  it  might  be  disre- 
garded. A  third  experiment  on  the  same  blood  failed  to  disengage  any  oxy- 
gen or  carbon  dioxide. 

The  view  entertained  by  Bernard  of  the  action  of  carbon  monoxide  in 
displacing  the  oxygen  of  the  blood  is  that  the  former  gas  has  a  remark- 
able affinity  for  the  blood-corpuscles,  in  which  nearly  all  the  oxygen  is 
contained,  and  when  brought  in  contact  with  them  unites  with  the  hsema- 
globine,  setting  free  the  oxygen,  in  the  same  way  that  an  acid  entering  into 
the  composition  of  a  salt  is  set  free  by  any  other  acid  Avhich  has  a  stronger 
affinity  for  the  base.  There  is  every  reason  to  suppose  that  this  view  is  cor- 
rect, as  carbon  monoxide  is  much  less  soluble  than  oxygen  and  as  it  has 
the  property  of  disengaging  this  gas  only  from  the  blood,  leaving  the  other 
gases  still  in  solution.  In  drawing  the  blood  for  analysis,  Bernard  took 
the  fluid  directly  from  the  vessels  by  a  syringe  and  passed  it  under  mer- 
cury into  a  tube,  in  such  a  way  that  it  did  not  come  in  contact  with  the 
air.  In  this  tube,  which  was  graduated,  the  blood  was  brought  in  contact 
with  carbon  monoxide,  which  displaced  the  oxygen  from  the  corpuscles 
and  prevented  the  formation  of  carbon  dioxide  at  the  expense  of  a  portion 
of  the  oxygen. 

As  carbon  monoxide  displaces  the  oxygen  alone,  it  is  necessary  to  resort 
to  some  other  process  to  disengage  the  other  gases  contained  in  the  blood. 
Modern  experimenters,  Ludwig,  Lothar  Meyer  and  others,  have  made  use  of 
the  mercurial  gas-pumps,  either  of  Ludwig  or  of  Pfliiger,  in  which  all  the 
gases  of  the  blood  are  disengaged  by  removing  the  atmospheric  pressure. 
By  means  of  a  "  froth-chamber,"  the  gases  can  be  collected  and  analyzed, 
with  but  little  loss  of  time ;  but  it  is  probable  that  there  is  always  a  slight 
error  in  estimates,  made  in  this  way,  of  the  relative  proportions  of  oxygen 
and  carbon  dioxide,  the  proportion  of  oxygen  being  too  small,  and  of  carbon 
dioxide,  too  large.  Nevertheless,  the  results  obtained  by  this  method  corre- 
spond pretty  closely  with  what  is  known  of  the  nature  of  the  respiratory 
process ;  and  analyses  of  the  blood  taken  at  different  periods  show  variations 
in  the  quantities  of  oxygen  in  the  arterial  blood  and  of  carbon  dioxide  in  the 
venous  blood,  corresponding  with  some  of  the  variations  which  have  been 
noted  in  the  loss  of  oxygen  and  gain  of  carbon  dioxide  in  the  air  in  respira- 
tion. Nearly  all  the  gases  contained  in  the  blood  may  be  disengaged  by 
means  of  the  gas-pump,  but  according  to  most  observers,  a  small  quantity  of 
carbon  dioxide  remains  in  the  blood  in  combination.  This  may  be  removed 
by  the  introduction  into  the  apparatus  of  a  small  quantity  of  tartaric  acid. 
It  was  justly  remarked  by  Bert,  that  as  the  apparatus  for  the  exhaustion  of 


154          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

air  has  been  made  more  and  more  nearly  perfect,  the  quantity  of  carbon 
dioxide  in  combination  has  seemed  less  and  less.  By  far  the  greatest 
quantity  of  the  excrementitious  carbon  dioxide  in  the  blood  is  extracted 
by  the  removal  of  atmospheric  pressure  in  the  most  carefully  perfected 
apparatus. 

According  to  Bernard,  arterial  blood,  while  an  animal  is  fasting,  contains 
nine  to  eleven  parts  per  hundred  in  volume  of  oxygen.  In  full  digestion,  the 
proportion  is  raised  to  seventeen,  eighteen  or  even  twenty  parts  per  hundred. 
The  proportion  varies  in  different  animals,  being  much  greater,  for  example, 
in  birds  than  in  mammals.  The  quantity  of  carbon  dioxide  is  even  more 
variable  than  the  quantity  of  oxygen.  During  digestion  there  are  five  to  six 
parts  per  hundred  of  carbon  dioxide  in  the  arterial  blood.  During  the  inter- 
vals of  digestion  this  quantity  is  reduced  to  almost  nothing ;  and  after  fasting 
for  twenty-four  hours,  frequently  not  a  trace  is  to  be  discovered. 

The  quantity  of  carbon  dioxide  varies  considerably  in  different  parts  of 
the  venous  system.  It  is  well  known  that  the  venous  blood  coming  from 
some  glands  is  dark,  during  the  intervals  of  secretion,  and  nearly  as  red  as 
arterial  blood,  during  secretion.  In  the  venous  blood  from  the  submaxillary 
gland  of  a  dog,  Bernard  found  18-07  per  cent,  of  carbon  dioxide  during  repose 
and  10-14  per  cent,  during  secretion.  The  blood  coming  from  the  muscles 
is  the  darkest  in  the  body  and  contains  the  greatest  quantity  of  carbon  dioxide. 
The  quantity  of  carbon  dioxide  is  increased  in  the  venous  blood  during  diges- 
tion ;  and  it  is  owing  to  this  that  the  gas  then  exists  in  quantity  in  the  arte- 
rial blood.  Bearing  in  mind  the  fact  that  the  proportion  of  gases  in  the 
arterial  and  venous  blood  varies  considerably  under  different  conditions  of 
the  system  and  that  it  is  variable  in  the  blood  of  different  veins,  the  following 
general  statement,  taken  from  Bert  (1870),  may  be  accepted  as  representing  the 
average  results  obtained  up  to  that  time.  The  most  recent  results,  particularly 
those  obtained  by  German  observers,  present  no  important  variations  from 
this  average : 

Carbon  dioxide    Carbon  dioxide  Total  gas 

disengaged  in  combi-       Carbon  dioxide,  in  volume 

Oxygen,     by  a  vacuum.  nation.  total.  Nitrogen.  per  100. 

"Arterial  blood.  15-03  27-99  1-15  29-14  1-60  45-77 

Venous  blood..     8-17  31-27  2-38  33-65  1-37  43-19 

"  If  the  blood  coming  from  different  parts  of  the  body  be  now  examined, 
it  is  found  that  the  blood  of  the  hepatic  veins  is  poorer  in  oxygen  and 
richer  in  carbon  dioxide  than  the  general  venous  blood ;  that  the  blood  of 
the  portal  vein  presents  the  same  characters  to  a  higher  degree;  that  the 
blood  of  the  muscles  in  contraction  presents  the  same  relations  as  compared 
with  the  blood  of  muscles  in  repose  or  paralyzed ;  that,  on  the  other  hand, 
the  blood  of  the  glands  has  more  oxygen  during  their  activity  than  during 
their  repose. 

"  In  comparing  the  venous  blood  of  the  right  side  of  the  heart  with  the 
arterial  blood  of  the  left  side,  it  is  found  that  the  latter  is  richer  in  oxygen 
and  poorer  in  carbon  dioxide.  In  examining  this  more  closely,  it  is  seen  that 


CHANGES  OF  THE  BLOOD  IN  RESPIRATION.  155 

the  difference  in  the  oxygen  is  greater  than  in  the  carbon  dioxide ;  this  being 
in  accordance  with  the  well  known  fact  that  animals  absorb  more  oxygen 
than  is  eouivalent  to  the  carbon  dioxide  exhaled." 

These  facts  coincide  with  the  views  which  are  now  held  regarding  the 
essential  processes  of  respiration.  The  blood  going  to  the  lungs  contains 
carbon  dioxide  and  but  a  small  proportion  of  oxygen.  In  the  lungs  carbon 
dioxide  is  given  off,  appearing  in  the  expired  air,  and  the  oxygen  which  dis- 
appears from  the  air  is  carried  away  by  the  arterial  blood. 

Nitrogen  of  the  Blood. — As  far  as  is  known,  nitrogen  has  no  important 
office  connected  with  respiration.  There  is  sometimes  a  slight  exhalation  of 
this  gas  by  the  lungs,  and  analyses  have  demonstrated  its  existence  in  solution 
in  the  blood.  Magnus  found  generally  a  larger  proportion  in  the  arterial 
than  in  venous  blood,  although  in  one  instance  there  was  a  large  proportion 
in  the  venous  blood.  It  is  not  absolutely  certain  whether  the  nitrogen 
•which  exists  in  the  blood  be  derived  from  the  air  or  from  the  tissues.  Its 
almost  constant  exhalation  in  the  expired  air  would  lead  to  the  supposition 
that  it  is  produced  in  small  quantity  in  the  system  or  is  supplied  by  the  food. 
There  is  no  evidence  that  nitrogen  enters  into  combination  with  the  blood- 
corpuscles.  It  exists  simply  in  solution  in  the  blood,  which  is  capable  of  ab- 
sorbing about  ten  times  as  much  as  can  be  absorbed  by  pure  water.  Nothing 
is  known  with  regard  to  the  relations  of  the  free  nitrogen  of  the  blood  to  the 
processes  of  nutrition. 

Condition  of  the  Gases  in  the  Blood. — It  is  now  generally  admitted  that 
the  oxygen  of  the  blood  exists,  not  in  simple  solution,  but  in  a  condition  of 
combination  with  the  haemaglobine  of  the  blood-corpuscles.  In  studying  the 
composition  of  the  corpuscles,  it  has  been  seen  that  when  air  is  admitted  to 
venous  blood,  oxygen  unites  with  the  hasmaglobine,  forming  oxyhsemaglobine. 
Carbon  monoxide,  which  has  a  great  affinity  for  the  corpuscles,  displaces" 
almost  immediately  all  the  oxygen  which  the  blood  contains.  When  the  cor- 
puscles are  destroyed,  as  they  may  be  readily  by  receiving  fresh  blood  into  a 
quantity  of  pure  water,  the  red  color  is  instantly  changed  to  black. 

The  condition  under  which  carbon  dioxide  exists  in  the  blood  has  already 
been  considered  in  connection  with  the  mechanism  of  its  passage  from  the 
venous  blood  into  the  air-cells.  This  gas  is  contained  chiefly  in  the  plasma ; 
a  small  quantity,  however,  probably  exists  in  the  red  blood-corpuscles.  The 
greatest  part  of  the  carbon  dioxide  of  the  plasma  is  either  in  simple  solution 
or  in  a  condition  of  very  feeble  combination,  the  exact  nature  of  which  is  not 
understood.  It  has  been  ascertained  that  the  blood-serum  will  absorb  much 
more  carbon  dioxide  than  is  absorbed  under  similar  conditions  by  pure  water. 
It  has  been  shown,  also,  that  neutral  sodium  phosphate  increases  to  a  remark- 
able degree  the  quantity  of  carbon  dioxide  that  can  be  absorbed  by  any  liquid. 
It  is  probable  that  a  small  part  of  the  carbon  dioxide  of  the  plasma,  which 
passes  into  the  expired  air,  is  in  combination  with  sodium  in  the  form  of 
sodium  bicarbonate. 

General  Differences  in  the  Composition  of  Arterial  and  Venous  Blood. — 
All  observers  agree  that  there  are  certain  marked  differences  in  the  composi- 


156          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

tion  of  arterial  and  venous  blood,  aside  from  the  proportion  of  gases.  The 
arterial  blood  contains  less  water  and  is  richer  in  organic  and  in  most  inor- 
ganic constituents  than  the  venous  blood.  It  also  contains  a  larger  propor- 
tion of  corpuscles.  It  is  more  coagulable  and  offers  a  larger  and  firmer  clot 
than  the  clot  of  venous  blood.  The  only  constituents  which  are  constantly 
more  abundant  in  venous  blood  are  water  and  the  alkaline  carbonates.  Ac- 
cording to  Longet,  10,000  parts  of  venous  blood  contained  12-3  parts  of  car- 
bon dioxide  combined,  and  the  same  quantity  of  arterial  blood  contained  but 
8-3  parts.  The  deficiency  of  water  in  the  blood  which  comes  from  the  lungs 
is  readily  explained  by  the  escape  of  watery  vapor  in  the  expired  air. 

An  important  distinction  between  arterial  and  venous  blood  is  that  the 
former  has  a  uniform  composition  in  all  parts  of  the  arterial  system,  while 
the  composition  of  the  latter  varies  very  much  in  the  blood  coming  from  dif- 
ferent organs.  Arterial  blood  is  capable  of  carrying  on  the  processes  of 
nutrition,  while  venous  blood  is  not,  and  it  can  not  even  circulate  freely  in 
the  systemic  capillaries. 

Relations  of  Respiration  to  Nutrition,  etc. — It  has  been  demonstrated 
that  all  tissues,  so  long  as  they  retain  their  absolute  integrity  of  composition, 
have  the  property  of  appropriating  oxygen  and  exhaling  carbon  dioxide,  in- 
dependently of  the  presence  of  blood;  and  that  the  arterial  blood  carries 
oxygen  from  the  lungs  to  the  tissues,  there  gives  it  up,  and  receives  carbon 
dioxide,  which  is  carried  by  the  venous  blood  to  the  lungs,  to  be  exhaled. 
This  fact  alone  shows  that  respiration  is  inseparably  connected  with  the 
general  act  of  nutrition.  Its  processes  must  be  studied,  therefore,  as  they 
take  place  in  the  tissues  and  organs  of  the  body. 

Oxygen  taken  from  the  air  is  immediately  absorbed  by  the  blood  and  en- 
ters into  the  composition  of  the  red  corpuscles.  Part  of  the  oxygen  disap- 
'pears  in  the  red  corpuscles  themselves,  and  carbon  dioxide  is  given  off.  To 
how  great  an  extent  this  takes  place,  it  is  impossible  to  say ;  but  it  is  evident, 
even  from  a  study  of  the  methods  of  analysis  of  the  blood  for  gases,  that  the 
property  of  absorbing  oxygen  and  giving  off  carbon  dioxide,  which  belongs 
to  the  tissues,  is  possessed  as  well  by  the  red  corpuscles.  During  life  it  is 
not  possible  to  determine  how  far  this  takes  place  in  the  blood  and  how  far 
it  occurs  in  the  tissues.  The  theory  has  been  proposed  that  the  respiratory 
change  takes  place  in  the  blood  as  it  circulates ;  but  the  avidity  of  the  tissues 
for  oxygen  and  the  readiness  with  which  they  exhale  carbon  dioxide  leave  no 
room  for  doubt  that  much  of  this  change  is  effected  in  their  substance. 

Oxygen,  carried  by  the  blood  to  the  tissues,  is  appropriated  and  consumed 
in  their  substance,  together  with  the  nutritive  materials  contained  in  the  cir- 
culating fluid.  Physiologists  are  acquainted  with  some  of  the  laws  which 
regulate  its  consumption,  but  have  not  been  able  to  ascertain  the  exact  nature 
of  the  changes  which  take  place.  All  that  can  be  said  definitely  on  this  point 
is  that  oxygen  unites  with  the  organic  constituents  of  the  body,  satisfying 
the  "  respiratory  sense  "  and  supplying  an  imperative  want  which  is  felt  by 
all  animals  and  which  extends  to  all  parts  of  the  organism.  After  its  absorp- 
tion, oxygen  is  lost  in  the  processes  of  nutrition.  There  is  no  evidence  in 


THE  RESPIRATORY  SENSE.  157 

favor  of  the  view  that  oxygen  unites  directly  with  carbonaceous  matters  in 
the  blood  which  it  meets  in  the  lungs,  and  by  direct  union  with  carbon, 
forms  carbon  dioxide. 

That  carbon  dioxide  makes  its  appearance  in  the  blood  itself,  produced 
in  the  red  corpuscles,  has  been  abundantly  proved  by  observations  already 
cited,  although  it  is  impossible  to  determine  to  what  extent  this  takes  place 
during  life.  It  is  likewise  a  product  of  the  physiological  wear  of  the  tissues, 
is  absorbed  by  the  blood  circulating  in  the  capillaries  and  is  conveyed  by  the 
veins  to  the  right  side  of  the  heart.  It  has  been  shown  that  its  production  is 
not  immediately  dependent  upon  the  absorption  of  oxygen,  for  its  formation 
continues  in  an  atmosphere  of  hydrogen  or  of  nitrogen.  It  is  most  reason- 
able to  consider  the  carbon  dioxide  thus  formed  as  a  product  of  excretion. 
The  fact  that  it  may  easily  be  produced  artificially,  out  of  the  body,  does  not 
demonstrate  that  its  formation  in  the  body  is  as  simple  as  when  it  is  formed 
by  the  process  of  combustion.  It  may  be  possible  at  some  future  time  to 
produce  artificially  all  the  excremetitious  principles,  as  has  already  been  done 
in  the  case  of  urea ;  but  it  can  not  be  assumed  that  the  mode  of  formation 
of  carbon  dioxide,  as  one  of  the  phenomena  of  nutrition,  is  precisely  the  same 
as  when  it  is  made  by  chemical  manipulations. 

THE  RESPIRATORY  SENSE. 

It  is  generally  admitted  that  there  exists  in  the  system  what  may  be  re- 
garded as  a  respiratory  sense,  which  operates  upon  the  respiratory  nerve- 
centre  and  gives  rise  to  the  involuntary  movements  of  respiration ;  and  that 
this  sense  is  exaggerated  by  anything  which  interferes  with  respiration,  and 
is  then  conveyed  to  the  brain,  where  it  is  appreciated  as  dyspnoea  and  finally 
as  the  sense  of  suffocation.  An  exaggeration  of  the  respiratory  sense  consti- 
tutes a  sense  of  oppression,  which  is  referred  to  the  lungs ;  but  it  can  not  be 
assumed,  from  sensations  only,  that  the  sense  of  want  of  air  is  really  situated 
in  the  lungs. 

At  the  present  day  it  is  hardly  necessary  to  discuss  the  views  of  those 
who  attributed  the  sense  of  want  of  air,  at  least  in  its  exaggerated  form, 
to  an  accumulation  of  carbon  dioxide  in  the  lungs  (Marshall  Hall),  distention 
of  the  right  cavities  of  the  heart  (Berard),  or  to  impressions  conveyed  to  the 
medulla  oblongata,  exclusively  by  the  pneumogastric  nerves.  These  theories 
have  long  since  been  disproved  and  are  now  merely  of  historical  interest. 
Volkmann,  in  1841,  advanced  the  view  that  this  sense  is  dependent  upon  a 
deficiency  of  oxygen  in  the  tissues,  producing  an  impression  which  is  con- 
veyed to  the  medulla  oblongata  by  the  nerves  of  general  sensibility.  By  a 
series  of  experiments,  this  observer  disproved  the  view  that  the  respiratory 
sense  always  originates  in  the  lungs  and  is  transmitted  by  the  pneumogastric 
nerves ;  and  by  exclusion,  he  located  it  in  the  general  system.  In  a  series  of 
experiments  (Flint,  1861)  the  following  facts,  some  of  which  had  been  previ- 
ously noted,  were  observed  : 

The  chest  was  opened  in  a  living  animal,  artificial  respiration  was  care- 
fully performed,  inflating  the  lungs  sufficiently  but  cautiously  and  taking 
12 


158          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

care  to  change  the  air  in  the  bellows  every  few  moments.  So  long  as  this 
was  continued,  the  animal  made  no  respiratory  effort ;  showing  that  for  the 
time  the  respiratory  sense  was  abolished.  This  was  little  more  than  a 
repetition  of  the  classical  experiment  of  Robert  Hook,  an  account  of  which 
was  published  in  1C  64. 

When  the  artificial  respiration  was  interrupted,  the  respiratory  muscles 
were  thrown  into  contraction,  and  the  animal  made  regular,  and  at  last  vio- 
lent efforts.  An  artery  was  then  opened  and  the  color  of  the  blood  was 
noted.  It  was  observed  that  the  respiratory  efforts  began  only  when  the  blood 
in  the  vessel  became  dark.  When  artificial  respiration  was  resumed,  the  re- 
spiratory efforts  ceased  onjy  when  the  blood  became  red  in  the  arteries. 

While  artificial  respiration  was  being  regularly  performed,  a  large  artery 
was  opened  and  the  system  was  drained  of  blood.  When  the  haemorrhage 
had  proceeded  to  a  certain  extent,  the  animal  made  respiratory  efforts,  which 
became  more  and  more  violent,  until  they  terminated,  just  before  death,  in 
general  convulsions. 

These  facts,  which  may  be  successively  observed  in  a  single  experiment, 
remained  precisely  the  same  when  both  pneumogastric  nerves  had  been 
divided  in  the  neck. 

The  conclusion  which  may  legitimately  be  drawn  from  the  above-men- 
tioned facts  is  that  the  respiratory  sense  does  not  always  and  necessarily 
originate  in  the  lungs,  for  it  operates  when  the  lungs  are  regularly  filled  with 
pure  air,  if  the  system  be  drained  of  the  oxygen-carrying  fluid. 

A  similar  conclusion  was  arrived  at  by  Rosenthal  (1862)  and  by  Pfliiger 
(1868).  Pfliiger  produced  asphyxia  in  dogs  by  causing  them  to  respire  pure 
nitrogen.  In  his  experiments,  he  analyzed  the  blood  after  thirty  seconds 
and  after  one  minute  of  inhalation  of  nitrogen.  He  found  a  great  diminu- 
tion in  oxygen  with  very  slight  increase  in  carbon  dioxide  at  the  end  of 
thirty  seconds.  After  one  minute  the  oxygen  was  reduced  from  14-35  per 
cent,  in  volume  to  0*2  per  cent.,  and  the  carbon  dioxide  from  36-9  to  29-9. 
As  a  conclusion  he  stated  that  "  no  one,  therefore,  can  be  of  the  opinion  that 
dyspnoea  and  asphyxia  in  breathing  indifferent  gases  are  connected  with  the 
accumulation  of  carbon  dioxide." 

In  1877  the  experiments  made  in  1861  were  repeated  and  extended  (Flint). 
The  later  experiments  were  made  upon  dogs,  in  the  following  way :  The  ani- 
mals were  brought  under  the  influence  of  ether,  the  chest  was  opened  and 
artificial  respiration  was  carried  on  by  means  of  a  bellows  fixed  in  the  trachea. 
The  great  vessels  given  off  from  the  arch  of  the  aorta  were  isolated  so  that 
they  could  be  separately  constricted  at  will.  In  a  number  of  experiments 
upon  different  animals,  the  innominate  artery  and  the  left  subclavian  were 
constricted,  and  the  animal  began  to  make  respiratory  efforts  about  two  min- 
utes after,  although  artificial  respiration  was  kept  up  constantly  and  effi- 
ciently. The  animals  made  no  respiratory  efforts  when  the  vessels  given  off 
from  the  arch  of  the  aorta  were  left  free  and  when  the  aorta  was  tied  in  the 
chest,  which  cut  off  the  supply  of  blood  from  the  trunk  and  the  lower  ex- 
tremities. In  the  experiments  in  which  the  vessels  going  to  the  head  and 


THE  RESPIRATORY  SENSE.  159 

upper  extremities  were  constricted,  the  respiratory  efforts  always  ceased  when 
the  vessels  were  freed. 

The  object  of  these  experiments  was  to  study  the  effects  of  cutting  off  the 
supply  of  oxygenated  blood  from  different  parts.  It  may  be  assumed  that 
the  respiratory  nervous  centre  is  in  the  medulla  oblongata,  and  an  attempt 
was  made  to  devise  some  means  of  cutting  off  the  arterial  supply  from 
this  part.  Animals  respire  when  all  of  the  encephalic  centres  have  been  de- 
stroyed except  the  medulla  oblongata,  so  that  it  is  improbable  that  cutting 
off  the  supply  of  blood  from  the  brain  would  affect  the  muscles  of  respiration, 
provided  that  artificial  respiration  were  efficiently  maintained.  Blood  may 
be  supplied  to  the  medulla  oblongata  by  the  internal  carotids,  which  are  con- 
nected with  the  circle  of  Willis,  by  the  vertebral  arteries,  which  unite  to  form 
the  basilar  artery,  and  perhaps  by  other  vessels ;  but  it  is  certain  that  if  all 
the  arteries  given  off  from  the  arch  of  the  aorta  be  tied,  the  medulla  must  be 
deprived  of  oxygenated  blood. 

In  one  experiment,  the  innominate  artery  and  the  left  subclavian  artery 
were  constricted,  and  the  animal  made  respiratory  efforts  in  two  minutes  and 
eight  seconds,  notwithstanding  that  artificial  respiration  was  kept  up. 

In  another  experiment,  the  same  vessels  were  constricted,  and  the  animal 
made  respiratory  efforts  in  two  minutes  and  five  seconds. 

In  a  third  experiment,  both  subclavian  arteries  and  both  carotids  were 
constricted,  and  the  animal  made  respiratory  efforts  in  two  minutes  and  seven 
seconds.  Both  vertebral  arteries  and  both  carotids  were  constricted,  and  the 
animal  made  no  respiratory  efforts  for  five  minutes ;  but  respiratory  efforts 
were  made  in  one  minute  and  thirty-five  seconds  after  both  subclavians  had 
been  constricted  in  addition  to  the  vertebrals  and  carotids. 

It  seems  from  these  experiments,  that  in  order  to  induce  respiratory 
efforts  in  an  animal  under  the  influence  of  ether  and  with  the  lungs  supplied 
with  air  by  artificial  respiration,  either  the  innominate  artery  and  the  left 
subclavian  artery,  or  both  subclavians,  both  carotids  and  both  vertebral  arte- 
ries, must  be  tied.  In  other  words,  according  to  the  view  taken  of  the  cause 
of  these  respiratory  efforts,  the  supply  of  blood  to  the  medulla  oblongata  can 
not  be  cut  off  completely  except  by  tying  all  the  vessels  given  off  from  the 
arch  of  the  aorta. 

These  observations,  taken  in  connection  with  the  experiments  of  1861, 
lead  to  the  conclusion  that  the  sense  of  want  of  air,  under  certain  conditions, 
is  due  to  a  want  of  circulation  of  oxygenated  blood  in  the  medulla  oblongata. 
This  view  has  been  advanced  by  some  writers,  but  it  has  lacked  the  positive 
experimental  proof  afforded  by  the  experiments  of  1877. 

If  the  sense  of  want  of  air  be  regarded  as  due,  under  certain  conditions, 
to  a  deficiency  of  oxygen  in  the  medulla  oblongata — which  can  hardly  be 
doubted — it  becomes  an  important  question  to  determine  whether  the  normal 
respiratory  movements  be  actually  reflex  in  their  character  or  whether  they 
be  due  to  direct  excitation  of  the  nerve-cells  in  the  respiratory  centre. 

It  is  difficult  to  account  for  the  phenomena  observed  in  experiments  in 
which  the  pneumogastrics  are  divided  or  stimulated,  without  assuming  that 


160         CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

these  nerves  sometimes — and  possibly  always,  in  tranquil  respiration — convey 
an  impression  to  the  respiratory  nervous  centre,  which  gives  rise  to  the  ordi- 
nary automatic  and  periodical  action  of  the  muscles  of  inspiration.  If  such 
an  impression  be  conveyed  from  the  lungs  by  the  afferent  fibres  of  the  pneu- 
mogastrics,  it  could  not  operate  when  both  pneumogastrics  are  divided  in  the 
neck.  This  operation,  as  is  well  known,  profoundly  affects  the  respiratory 
movements.  After  division  of  both  nerves,  the  respirations  become  slow  and 
unusually  deep,  without,  as  a  rule,  any  evidence  of  respiratory  distress.  In 
dogs,  the  number  of  respirations  often  falls  to  four  or  five  per  minute,  and 
their  nervous  mechanism  seems  to  be  modified.  Any  respiratory  distress  that 
occurs  is  due  to  the  arrest  of  the  respiratory  movements  of  the  larynx,  and 
not  to  an  exaggeration  of  the  sense  of  want  of  air.  When  a  feeble  Faradic 
current  is  passed  through  the  nerves,  the  respiratory  movements  are  increased 
in  frequency,  but  the  movements  are  arrested  by  a  relatively  powerful  current. 
This  action  is  reflex. 

In  view  of  all  the  experimental  facts  bearing  upon  the  question,  it  is  proba- 
ble that  the  respiratory  movements  are  sometimes  reflex  and  sometimes  due 
to  direct  excitation  of  the  cells  of  the  respiratory  centre  by  the  absence  of 
oxygen. 

In  perfectly  normal  and  tranquil  respiration,  an  impression  is  probably 
conveyed  from  the  lungs  to  the  respiratory  centre  by  the  pneumogastrics, 
which  stimulates  this  centre  to  excite  movements  of  inspiration.  This  is 
probably  due  to  a  gradual  and  progressive  change  in  the  character  of  the  con- 
tents of  the  air-cells,  although  experiments  are  wanting  to  show  the  exact 
mechanism  of  this  process. 

When  this  reflex  action  is  abolished,  as  by  section  of  both  pneumogastrics 
in  the  neck,  the  respiratory  centre  is  stimulated  only  when  the  deficiency  in 
the  supply  of  oxygen  becomes  considerable.  This  excitation  of  the  respira- 
tory centre  is  direct.  It  requires  a  certain  time  for  its  operation,  and  this 
accounts  for  the  slow  respirations  in  animals  after  the  pneumogastrics  have 
been  divided.  Under  certain  physiological  conditions,  this  direct  stimulation 
may  be  added  to  the  impression  conveyed  by  the  pneumogastrics,  and  it  is 
probable  that  this  always  occurs  in  dyspnoea. 

Sense  of  Suffocation. — The  respiratory  sense  must  not  be  confounded 
with  the  sense  of  distress  from  want  of  air,  and  its  extreme  degree,  the  sense 
of  suffocation.  The  first  is  not  a  sensation,  but  an  impression  made  upon  the 
medulla  oblongata,  giving  rise  to  involuntary  respiratory  movements.  The 
necessities  for  oxygen  on  the  part  of  the  system  regulate  the  supply  of  air  to 
the  lungs.  Once  in  every  seven  or  eight  respirations,  or  when  the  respiratory 
movements  are  restricted  under  the  influence  of  depressing  emotions,  an 
involuntary,  deep  or  sighing  inspiration  is  made,  for  the  purpose  of  changing 
the  air  in  the  lungs  more  completely.  The  increased  consumption  of  oxygen 
and  a  certain  degree  of  interference  with  the  mechanical  process  of  respira- 
tion during  violent  muscular  exercise  put  one  "  out  of  breath,"  and  for  a  time 
the  respiratory  movements  are  exaggerated.  This  is  perhaps  the  first  physio- 
logical way  in  which  the  want  of  air  is  appreciated  by  the  senses.  A  defi- 


EESPIEATORY  EFFORTS  BEFORE  BIRTH.  161 

ciency  in  hsematosis,  either  from  a  vitiated  atmosphere,  mechanical  obstruc- 
tion in  the  air-passages  or  grave  trouble  in  the  general  circulation,  produces 
all  grades  of  sensations,  from  the  slight  oppression  which  is  felt  in  a  crowded 
room,  to  the  intense  distress  of  suffocation.  When  hsematosis  is  but  slightly 
interfered  with,  only  an  indefinite  sense  of  oppression  is  experienced,  and  the 
respiratory  movements  are  a  little  increased,  the  most  marked  effect  being 
an  increase  in  the  number  and  extent  of  sighing  inspirations. 

RESPIRATORY  EFFORTS  BEFORE  BIRTH. 

It  is  generally  admitted  that  one  of  the  most  important  uses  of  the  pla- 
centa, and  the  one  which  is  most  immediately  connected  with  the  life  of  the 
foetus,  is  a  respiratory  interchange  of  gases,  analogous  to  that  which  takes 
place  in  the  gills  of  aquatic  animals.  The  placental  villi  are  bathed  in  the 
blood  of  the  uterine  sinuses,  and  this  is  the  only  way  in  which  the  fatal  blood 
can  receive  oxygen.  Legallois  observed  a  bright-red  color  in  the  blood  of  the 
umbilical  vein ;  and  on  alternately  compressing  and  releasing  the  vessel,  he 
saw  the  blood  change  in  color  successively  from  red  to  dark  and  from  dark 
to  red.  Zweifel  has  demonstrated  the  presence  of  oxyhaemaglobine  in  the 
blood  of  the  umbilical  vessels  by  means  of  the  spectroscope,  thus  showing 
that  it  contains  oxygen.  As  oxygen  is  thus  adequately  supplied  to  the  sys- 
tem, the  fcetus  is  in  a  condition  similar  to  that  of  the  animals  in  which  arti- 
ficial respiration  was  effectually  performed.  The  want  of  oxygen  is  fully 
met,  and  therefore  no  respiratory  efforts  take  place.  Respiratory  movements 
will  take  place,  however,  even  in  very  young  animals,  when  there  is  a  defi- 
ciency of  oxygen  in  the  system.  It  has  been  observed  that  the  liquor  amnii 
occasionally  finds  its  way  into  the  respiratory  passages  of  the  fcetus,  where  it 
could  enter  only  during  efforts  at  respiration.  Winslow,  in  the  latter  part 
of  the  last  century,  first  noticed  respiratory  efforts  in  the  foetuses  of  cats  and 
dogs  in  the  uterus  of  the  mother  during  life ;  and  many  others  have  observed 
that  when  foetuses  are  removed  from  vascular  connection  with  the  mother,  they 
make  vigorous  efforts  at  respiration.  After  the  death  of  the  mother,  the 
foetus  always  makes  a  certain  number  of  distinct  and  unmistakable  respiratory 
efforts,  which  follow  each  other  at  regular  intervals. 

From  what  has  been  experimentally  demonstrated  with  regard  to  the  seat 
and  cause  of  the  respiratory  sense  after  birth,  it  is  evident  that  want  of  oxy- 
gen is  the  cause  of  respiratory  movements  in  the  fcetus.  When  the  circulation 
in  the  maternal  portion  of  the  placenta  is  interrupted  from  any  cause  or 
when  the  blood  of  the  fcetus  is  obstructed  in  its  course  to  and  from  the  pla- 
centa, the  impression  due  to  want  of  oxygen  is  made  upon  the  medulla  oblon- 
gata,  and  efforts  at  respiration  are  the  result. 

CUTANEOUS  RESPIRATION". 

Respiration  by  the  skin,  although  very  important  in  many  of  the  lower 
forms  of  animals,  is  inconsiderable  in  the  human  subject  and  is;  even  more 
insignificant  in  animals  covered  with  hair  or  feathers;  still,  ant  appreciable 


162          CHANGES  OF  AIR  AND  BLOOD  IN  RESPIRATION. 

quantity  of  oxygen  is  absorbed  by  the  skin  of  the  human  subject,  and  a  quan- 
tity of  carbon  dioxide,  which  is  relatively  larger,  is  exhaled.  Exhalation  of 
carbon  dioxide,  which  is  connected  with  the  uses  of  the  skin  as  a  general 
eliminating  organ  and  is  by  no  means  an  essential  part  of  the  respiratory 
process,  will  be  more  fully  considered  in  connection  with  the  physiology  of 
excretion.  Carbon  dioxide  is  given  off  with  the  general  emanations  from  the 
surface,  being  found,  also,  in  solution  in  the  urine  and  in  most  of  the  secre- 
tions. It  is  well  known  that  death  follows  the  application  of  an  imperme- 
able coating  to  the  entire  cutaneous  surface ;  but  this  is  by  no  means  due  to  a 
suppression  of  its  respiratory  office  alone.  The  skin  has  other  uses,  particu- 
larly in  connection  with  regulation  of  the  animal  temperature,  which  arc 
much  more  important. 

An  estimate  of  the  extent  of  the  cutaneous,  as  compared  with  pulmonary 
respiration,  has  been  made  by  Scharling,  by  comparing  the  relative  quantities 
of  carbon  dioxide  exhaled  in  the  twenty-four  hours.  According  to  this  ob- 
server, the  skin  performs  ^  to  ^  of  the  respiratory  office.  It  is  difficult  to 
collect  all  the  carbon  dioxide  given  off  by  the  skin  under  perfectly  normal 
conditions.  In  the  observations  by  Aubert,  the  estimate  is  very  much  lower 
than  that  given  by  Scharliug. 

ASPHYXIA. 

The  effects  of  cutting  off  the  supply  of  oxygen  from  the  lungs  are  mainly 
referable  to  the  circulatory  system  and  have  already  been  considered  in  treat- 
ing of  the  influence  of  respiration  upon  the  circulation.  It  will  be  remem- 
bered that  in  asphyxia  the  unaerated  blood  passes  with  so  much  difficulty 
through  the  systemic  capillaries  as  finally  to  arrest. the  action  of  the  heart. 
It  is  the  experience  of  experimenters  on  living  animals,  that  the  movements 
of  the  heart,  once  arrested  in  this  way,  can  not  be  restored ;  but  that  while 
the  slightest  regular  movements  continue,  the  heart's  action  will  gradually 
return  if  air  be  re-admitted  to  the  lungs. 

A  remarkable  power  of  resisting  asphyxia  exists  in  newborn  animals 
that  have  never  breathed.  This  was  noticed  by  Haller  and  others  and  has 
been  the  subject  of  many  experiments.  Legallois  found  that  young  rabbits 
would  live  for  fifteen  minutes  deprived  of  air  by  submersion,  but  that  this 
power  of  resistance  diminished  rapidly  with  age.  W.  F.  Edwards  has  shown 
that  there  exists  a  great  difference  in  this  regard  in  different  species.  Dogs 
and  cats,  which  are  born  with  the  eyes  shut  and  in  which  there  is  at  first  a 
very  slight  development  of  animal  heat,  will  show  signs  of  life  after  submer- 
sion for  more  than  half  an  hour ;  while  Guinea-pigs,  which  are  born  with 
the  eyes  open,  are  much  more  active  and  produce  a  greater  amount  of  heat, 
will  not  live  for  more  than  seven  minutes.  The  explanation  of  this  is  that 
in  most  warm-blooded  animals,  during  the  very  first  periods  of  extraiiterine 
life,  the  demands  on  the  part  of  the  system  for  oxygen  are  comparatively 
slight.  At  this  time,  there  is  very  little  activity  in  the  general  processes  of 
nutrition  and  in  the  consumption  of  oxygen  and  the  exhalation  of  carbon 
dioxide.  The  actual  difference  between  the  consumption  of  oxygen  imme- 


ASPHYXIA.  163 

diately  after  birth  and  at  the  age  of  a  few  days  is  sufficient  to  explain  the 
remarkable  power  of  resisting  asphyxia  just  after  birth. 

Breathing  in  a  Confined  Space. — An  important  question  connected  with 
the  physiology  of  asphyxia,  is  the  effect  on  the  system,  of  air  vitiated  by  breath- 
ing in  a  confined  space.  There  are  here  several  points  which  present  them- 
selves for  consideration.  The  effect  of  respiration  on  the  air  is  to  take  away  a 
certain  proportion  of  oxygen  and  to  add  certain  matters  which  are  regarded 
as  deleterious.  The  emanation  which  has  been  generally  regarded  as  hav- 
ing the  most  decided  influence  upon  the  system  is  carbon  dioxide ;  but  this 
influence  has  been  much  over-estimated.  In  death  from  charcoal-fumes, 
it  is  generally  carbon  monoxide  which  is  the  poisonous  agent.  Kegnault  and 
Reiset  exposed  dogs  and  rabbits  for  many  hours  to  an  atmosphere  contain- 
ing twenty-three  parts  per  hundred  of  carbon  dioxide  artificially  introduced, 
and  between  thirty  and  forty  parts  of  oxygen,  without  any  ill  effects.  They 
took  care,  however,  to  keep  up  a  free  supply  of  oxygen. 

These  experiments  are  at  variance  with  the  result  obtained  by  others,  but 
Regnault  and  Reiset  explained  this  difference  by  the  supposition  that  the 
gases  in  other  observations  were  probably  impure,  containing  a  little  chlorine 
or  carbon  monoxide.  This  view  is  sustained  by  the  experiments  of  Bernard 
with  carbon  monoxide.  In  animals  killed  by  this  gas,  the  blood,  both  venous 
and  arterial,  is  of  a  bright-red  color,  which  is  due  to  the  fixation  of  the  gas 
by  the  blood-corpuscles.  In  this  way,  the  red  corpuscles,  which  act  normally 
as  respiratory  agents,  carrying  oxygen  to  the  tissues,  are  paralyzed,  and  the 
animal  dies  from  asphyxia. 

In  breathing  in  a  confined  space,  the  distress  and  the  fatal  results  are 
produced,  in  all  probability,  more  by  animal  emanations  and  a  deficiency  of 
oxygen  than  by  the  presence  of  carbon  dioxide.  When  the  latter  gas  is  re- 
moved as  fast  as  it  is  produced,  the  effects  of  diminution  in  the  proportion  of 
oxygen  are  soon  very  marked,  and  they  progressively  increase  until  death  oc- 
curs. The  influence  of  emanations  from  the  lungs  and  general  surface  is 
undoubtedly  very  considerable ;  and  this  fact,  which  almost  all  have  experi- 
enced more  or  less,  has  been  fully  illustrated  in  several  instances  of  large 
numbers  of  persons  confined  without  proper  change  of  air.  Overcrowding 
is  one  of  the  most  prolific  sources  of  disease  among  the  poprer  classes  of 
society ;  and  there  are  many  forms  of  disease  prevalent  in  large  cities,  that 
are  almost  unknown  in  the  rural  districts  and  that  can  be  alleviated  only  by 
proper  sanitary  regulations,  which,  unfortunately,  it  is  often  difficult  'to  en- 
force. 

In  crowded  assemblages,  the  slight  diminution  of  oxygen,  the  elevation 
of  temperature,  increase  in  moisture,  and  particularly  the  presence  of  organic 
emanations,  combine  to  produce  unpleasant  sensations.  The  effects  of  this 
carried  to  an  extreme  degree  were  exemplified  in  the  confinement  of  the  one 
hundred  and  forty-six  English  prisoners,  for  eight  hours  only,  in  the  "  Black 
Hole  "  of  Calcutta,  a  chamber  eighteen  feet  (  5*486  metres )  square,  with  only 
two  small  windows,  and  those  obstructed  by  a  veranda.  Out  of  this  number, 
ninety-six  died  in  six  hours,  and  one  hundred  and  twenty-three,  at  the  end 


164  ALIMENTATION. 

of  the  eight  hours.  Many  of  those  who  immediately  survived  died  afterward 
of  putrid  fever  ("Annual  Eegister,"  1758).  The  incident  of  the  "Black 
Hole  of  Calcutta  "  has  frequently  been  repeated  on  emigrant  and  slave  ships, 
by  confining  great  numbers  in  the  hold  of  the  vessel,  where  they  were 
entirely  shut  out  from  the  fresh  air. 

The  condition  of  the  system  has  a  marked  and  important  influence  on 
the  rapidity  with  which  the  effects  of  vitiated  atmosphere  are  manifested. 
As  a  rule,  the  immediate  effects  of  confined  air  are  not  developed  so  soon  in 
weak  and  debilitated  persons  as  in  those  who  are  active  and  powerful.  It 
has  sometimes  been  observed,  in  cases  where  a  male  and  female  have  attempted 
suicide  together  by  the  fumes  of  charcoal,  that  the  female  has  been  restored 
some  time  after  life  had  become  extinct  in  the  male.  This  is  probably  owing 
to  the  greater  demand  for  oxygen  on  the  part  of  the  male. 

When  poisoning  by  confined  air  is  gradual,  the  system  becomes  accus- 
tomed to  the  toxic  influence,  the  temperature  of  the  body  is  lowered,  and  an 
animal  will  live  in  an  atmosphere  which  will  produce  instantaneous  death  in 
one  that  is  fresh  and  vigorous.  Bernard  has  made  a  number  of  experiments 
on  this  point.  In  one  of  them,  a  sparrow  was  confined  under  a  bell-glass  for 
an  hour  and  a  half,  at  the  end  of  which  time  another  was  introduced,  the 
first  being  still  quite  vigorous.  The  second  became  instantly  much  distressed 
and  died  in  five  minutes ;  but  ten  minutes  after,  the  sparrow  which  had 
been  confined  for  more  than  an  hour  and  a  half  was  released  and  flew  away. 


CHAPTER  VI. 

ALIMENTATION. 

General  considerations — Hunger— Seat  of  the  sense  of  hunger— Thirst— Seat  of  the  sense  of  thirst— Dura- 
tion of  life  in  inanition— Classification  of  alimentary  substances — Nitrogenized  alimentary  substances— 
Non-nitrogenized  alimentary  substances— Inorganic  alimentary  substances— Alcohol— Coffee— Tea — 
Chocolate— Condiments  and  flavoring  articles— Quantity  and  variety  of  food  necessary  to  nutrition — 
Necessity  of  a  varied  diet. 

IN  the  organism  of  animals,  every  part  is  continually  undergoing  what 
may  be  called  physiological  wear  ;  the  nitrogenized  constituents  of  the  body 
are  being  constantly  transformed  into  effete  matter ;  and  as  these  constitu- 
ents never  exist  without  inorganic  matters,  with  which  they  are  closely  and 
inseparably  united,  it  is  found  that  the  products  of  their  disassimilation 
are  always  discharged  from  the  body  in  combination  with  inorganic  sub- 
stances. This  process  of  molecular  change  is  a  necessary  condition  of  life. 
Its  activity  may  be  increased  or  retarded  by  various  means,  but  it  can  not  be 
arrested.  The  excrementitious  matters  which  are  thus  formed  are  produced 
constantly  by  the  tissues  and  must  be  continually  removed  from  the  or- 
ganism. 


HUNGER  AND  THIRST.  165 

It  is  evident,  from  the  amount  of  matter  that  h  daily  discharged  from 
the  body,  that  the  process  of  disassimilation  must  bo  very  active.  Its  constant 
operation  necessitates  a  constant  appropriation  of  new  matter  by  the  parts, 
in  order  that  they  may  maintain  their  integrity  of  composition  and  be  al- 
ways ready  to  perform  their  offices  in  the  economy.  The  blood  contains 
all  the  materials  necessary  for  the  regeneration  of  the  organism.  Its  inor- 
ganic constituents  are  found  generally  in  the  form  in  which  they  exist  in 
the  substance  of  the  tissues ;  but  the  organic  constituents  of  the  parts  are 
formed  in  the  substance  of  the  tissues  themselves,  by  a  transformation  of 
matters  furnished  by  the  blood.  The  physiological  wear  of  the  organism  is, 
therefore,  being  constantly  repaired  by  the  blood ;  but  in  order  to  keep  the 
great  nutritive  fluid  from  becoming  impoverished,  the  matters  which  it  is 
constantly  losing  must  be  supplied  from  some  source  out  of  the  body,  and 
this  necessitates  the  ingestion  of  articles  which  are  known  as  food.  Food  is 
taken  into  the  body  in  obedience  to  a  want  on  the  part  of  the  system,  which 
is  expressed  by  the  sensation  of  hunger,  when  it  relates  to  solid  or  semi-solid 
matters,  and  of  thirst,  when  it  relates  to  water. 

HUNGER  AND  THIRST. 

The  term  hunger  may  be  applied  to  all  degrees  of  that  peculiar  want  felt 
by  the  system,  which  leads  to  the  ingestion  of  nutritive  substances.  Its 
first  manifestations  are,  perhaps,  best  expressed  by  the  term  appetite ;  a  sen- 
sation by  no  means  disagreeable,  and  one  which  may  be  excited  by  the  sight, 
smell,  or  even  the  recollection  of  savory  articles,  at  times  when  it  does  not 
absolutely  depend  on  a  want  in  the  system.  In  the  ordinary  and  moderate 
development  of  the  appetite,  it  is  impossible  to  say  that  the  sensation  is  refer- 
able to  any  distinct  part  or  organ.  It  is  influenced  in  some  degree  by  habit ; 
in  many  persons,  the  feeling  being  experienced  at  or  near  the  hours  when  food 
is  ordinarily  taken.  If  not  soon  gratified,  the  appetite  is  rapidly  intensified 
until  it  becomes  actual  hunger.  Except  when  the  quantity  of  food  taken  is 
unnecessarily  large,  the  appetite  simply  disappears  on  the  introduction  of 
food  into  the  stomach  and  gives  place  to  the  sense  of  satisfaction  which 
accompanies  the  undisturbed  and  normal  action  of  the  digestive  organs ;  or 
in  those  who  are  in  the  habit  of  engaging  in  absorbing  occupations  at  that 
time,  the  only  change  experienced  is  the  absence  of  desire  for  food. 

It  has  been  observed  that  children  and  old  persons  do  not  endure  depri- 
vation of  food  so  well  as  adults.  This  was  noted  in  the  case  of  the  wreck 
of  the  frigate  Medusa.  After  the  wreck,  one  hundred  and  fifty  persons,  of 
all  ages,  were  exposed  on  a  raft  for  thirteen  days,  with  hardly  any  food.  Out 
of  this  number  only  fifteen  survived ;  and  the  children,  the  young  persons 
and  the  aged,  were  the  first  to  succumb. 

Important  modifications  in  the  appetite  are  due  to  temperature.  In  cold 
climates  and  during  the  winter  season  in  all  climates,  the  desire  for  food  is 
notably  increased,  and  the  tastes  are  somewhat  modified.  Animal  food,  and 
particularly  fats,  are  more  agreeable  at  that  time,  and  the  quantity  of  nutri- 
ment which  is  demanded  by  the  system  is  then  considerably  increased.  In 


1GG  ALIMENTATION. 

many  persons  the  difference  in  the  appetite  in  warm  and  cold  seasons  is  very 
marked. 

Exercise  and  occupation,  both  mental  and  physical,  when  riot  pushed  to 
the  point  of  exhaustion,  increase  the  desire  for  food  and  undoubtedly  facili- 
tate digestion.  Certain  articles,  especially  the  vegetable  bitters,  taken  into 
the  stomach  immediately  before  the  time  when  food  is  habitually  taken,  fre- 
quently have  the  same  effect ;  while  other  articles  which  do  not  satisfy  the 
requirements  of  the  system  have  a  tendency  to  diminish  the  desire  for  food. 
Many  articles  of  the  materia  medica,  especially  preparations  of  opium, 
have,  in  some  persons,  a  marked  influence  in  diminishing  the  appetite.  The 
abuse  of  alcoholic  stimulants  will  sometimes  take  away  all  desire  for  food. 
When  hunger  is  pressing,  it  has  been  observed  that  tobacco,  in  those  who 
are  accustomed  to  its  use,  will  frequently  allay  the  sensation  for  a  time. 

If  food  be  not  taken  in  obedience  to  the  demands  of  the  system  as  ex- 
pressed by  the  appetite,  the  sensation  of  hunger  becomes  most  distressing. 
It  is  then  manifested  by  a  peculiar  and  indescribable  sensation  in  the  stom- 
ach, which  soon  becomes  developed  into  actual  pain.  This  is  generally  accom- 
panied with  intense  pain  in  the  head  and  a  feeling  of  general  distress,  which 
soon  render  the  satisfaction  of  this  imperative  demand  on  the  part  of  the 
system  the  absorbing  idea  of  existence.  Furious  delirium  frequently  super- 
venes after  a  few  days  of  complete  abstinence ;  and  this  is  generally  the 
immediate  precursor  of  death.  It  is  unnecessary  to  cite  the  many  instances 
in  which  murder  and  cannibalism  have  been  resorted  to  when  starvation  is 
imminent ;  suffice  it  to  say,  that  the  extremity  of  hunger  or  of  thirst,  like 
the  sense  of  impending  suffocation,  is  a  demand  on  the  part  of  the  system  so 
imperative,  that  it  must  be  satisfied  if  within  the  range  of  possibility. 

The  question  of  the  seat  of  the  sense  of  hunger  is  one  of  considerable 
physiological  interest.  Saying  that  it  is  instinctively  referred  to  the  stomach, 
'is  simply  expressing  the  fact  that  the  sensation  is  of  a  nature  to  demand 
the  introduction  of  food  in  the  usual  way.  When  the  system  is  suffering 
from  defective  nutrition,  as  after  prolonged  abstinence  or  during  recovery 
from  diseases  which  have  been  accompanied  by  a  lack  of  assimilation,  the 
mere  filling  of  the  stomach  produces  a  sensation  of  repletion  of  this  organ, 
but  the  sense  of  hunger  is  not  relieved ;  but  if,  on  the  other  hand,  the  nutri- 
tion be  active  and  sufficient,  the  stomach  is  frequently  entirely  empty  for  a 
considerable  time  without  the  development  of  the  sense  of  hunger.  The 
appetite  is  preserved  and  hunger  is  felt  by  persons  who  suffer  from  extensive 
organic  disease  of  the  stomach,  and  the  sensation  has  been  occasionally 
relieved  by  nutritious  enemata  or  by  injections  into  the  veins.  It  is  certain 
that  the  appetite  and  the  sense  of  hunger  are  expressions  of  a  want  on  the 
part  of  the  organism,  referred  by  the  sensations  to  the  stomach,  but  really 
existing  in  the  general  system.  This  can  be  completely  satisfied  only  by  the 
absorption  of  digested  alimentary  matters  by  the  blood  and  their  assimilation 
by  the  tissues. 

The  sense  of  hunger  is  undoubtedly  appreciated  by  the  cerebrum,  and  it 
has  been  a  question  whether  there  be  any  special  nerves  which  convey  this 


HUNGER  AND  THIRST.  .167 

impression  to  the  encephalon.  The  nerve  which  would  naturally  be  sup- 
posed to  have  this  office  is  the  pneumogastric ;  but  notwithstanding  certain 
observations  to  the  contrary,  it  has  been  shown  that  section  of  both  of  these 
nerves  by  no  means  abolishes  the  desire  for  food.  Longet  has  observed  that 
dogs  eat,  apparently  with  satisfaction,  after  section  of  the  glosso-pharyngeal 
and  lingual  nerves.  This  observer  is  of  the  opinion  that  the  sensation  of 
hunger  is  conveyed  to  the  brain  through  the  sympathetic  system.  Although 
there  are  various  considerations  which  render  this  somewhat  probable,  it  is 
not  apparent  how  it  could  be  demonstrated  experimentally.  It  is  undoubt- 
edly the  sympathetic  system  of  nerves  which  presides  specially  over  nutrition ; 
and  hunger,  which  depends  upon  deficiency  of  nutrition,  is  certainly  not  con- 
veyed to  the  brain  by  any  of  the  cerebro-spinal  nerves. 

Thirst  is  the  peculiar  sensation  which  leads  to  the  ingestion  of  water. 
In  its  moderate  development,  this  is  usually  an  indefinite  feeling,  accom- 
panied by  more  or  less  sense  of  dryness  and  heat  of  the  throat  and  fauces, 
and  sometimes,  after  the  ingestion  of  a  quantity  of  very  dry  food,  by  a 
sensation  referred  to  the  stomach.  When  the  sensation  of  thirst  has  become 
intense,  the  immediate  satisfaction  which  follows  the  ingestion  of  a  liquid, 
particularly  water,  is  very  great.  Thirst  is  very  much  under  the  influence  of 
habit ;  some  persons  experiencing  a  desire  to  take  liquids  only  two  or  three 
times  daily,  while  others  do  so  much  more  frequently.  The  sensation  is  also 
sensibly  influenced  by  the  condition  of  the  atmosphere  as  regards  moisture, 
by  exercise  and  by  other  conditions  which  influence  the  discharge  of 
water  from  the  body,  particularly  by  the  skin.  A  copious  loss  of  blood  is 
always  followed  by  great  thirst.  This  is  frequently  noticed  in  the  inferior 
animals.  After  an  operation  involving  haemorrhage,  they  nearly  always  drink 
with  avidity  as  soon  as  released.  In  diseases  which  are  characterized  by 
increased  discharge  of  liquids,  thirst  is  generally  excessive. 

The  demand  on  the  part  of  the  system  for  water  is  much  more  imperative 
than  for  solids ;  in  this  respect  being  second  only  to  the  demand  for  oxygen. 
Animals  will  live  much  longer  when  deprived  of  solid  food  but  allowed  to 
drink  freely  than  if  deprived  of  both  food  and  drink.  A  man,  supplied  with 
dry  food  but  deprived  of  water,  will  not  survive  more  than  a  few  days.  Water 
is  necessary  to  the  processes  of  nutrition,  and  acts,  moreover,  as  a  solvent  in 
removing  from  the  system  the  products  of  disassimilation. 

After  deprivation  of  water  for  a  considerable  time,  the  intense  thirst  be- 
comes most  distressing.  The  dryness  and  heat  of  the  throat  and  fauces  are 
increased  and  accompanied  with  a  sense  of  constriction.  A  general  febrile 
condition  supervenes,  the  blood  is  diminished  in  quantity  and  becomes  thick- 
ened, the  urine  is  scanty  and  scalding,  and  there  seems  to  be  a  condition  of 
the  principal  viscera  approaching  inflammation.  Death  takes  place  in  a  few 
days,  generally  preceded  by  delirium. 

The  sensation  of  thirst  is  instinctively  referred  to  the  mouth,  throat  and 
fauces ;  but  it  is  not  necessarily  appeased  by  the  passage  of  water  over  these 
parts,  and  it  may  be  effectually  relieved  by  the  introduction  of  water  into  the 
system  by  other  channels,  as  by  injecting  it  into  the  veins.  Bernard  has 


168  ALIMENTATION. 

demonstrated,  by  the  following  experiment,  that  water  must  be  absorbed 
before  the  demands  of  the  system  can  be  satisfied :  He  made  an  opening  into 
the  oesophagus  of  a  horse,  tied  the  lower  portion,  and  allowed  the  animal  to 
drink  after  he  had  been  deprived  of  water  for  a  number  of  hours.  The  ani- 
mal drank  an  immense  quantity,  but  the  water  did  not  pass  into  the  stomach 
and  the  thirst  was  not  relieved.  He  modified  this  experiment  by  causing 
dogs  to  drink,  with  a  fistulous  opening  into  the  stomach  by  which  the  water 
was  immediately  discharged.  They  continued  to  drink  without  being  satis- 
fied, until  the  fistula  was  closed  and  the  water  could  be  absorbed. 

In  a  case  reported  by  Gairdner  (1820),  in  the  human  subject,  all  the 
liquids  swallowed  passed  out  at  a  wound  in  the  neck,  by  which  the  oesophagus 
had  been  cut  across.  The  thirst  in  this  case  was  insatiable,  although 
buckets  of  water  were  taken  in  the  day ;  but  on  injecting  water,  mixed  with 
a  little  spirit,  into  the  stomach,  the  sensation  was  soon  relieved. 

Although  the  sensation  of  thirst  is  referred  to  special  parts,  it  is  an  ex- 
pression of  the  want  of  liquids  in  the  system  and  is  to  be  effectually  relieved 
only  by  their  absorption  by  the  blood.  There  are  no  nerves  belonging  to  the 
cerebro-spinal  system  which  have  the  office  of  conveying  this  sensation  to  the 
brain,  division  of  which  will  abolish  the  desire  for  liquids.  Experiments 
show  that  no  effectual  relief  of  the  sensation  is  afforded  by  simply  moistening 
the  parts  to  which  the  heat  and  dryness  are  referred.  As  a  demand  on  the 
part  of  the  system,  it  is  entirely  analogous  to  the  sense  of  want  of  air  and  of 
hunger,  differing  only  in  the  way  in  which  it  is  manifested. 

The  length  of  time  that  life  continues  after  complete  deprivation  of  food 
and  drink  is  very  variable.  The  influences  of  age  and  obesity  have  already 
been  referred  to.  Without  citing  the  individual  instances  of  starvation  in 
the  human  subject  which  have  been  reported,  it  may  be  stated,  in  general 
terms,  that  death  occurs  within  five  to  eight  days  after  total  deprivation 
of  food.  In  the  instance  of  the  one  hundred  and  fifty  persons,  wrecked  on 
the  frigate  Medusa,  in  1816,  who  were  exposed  on  a  raft  in  the  open  sea  for 
thirteen  days,  only  fifteen  were  found  alive.  Savigny,  one  of  the  survivors, 
gave,  in  an  inaugural  thesis,  a  very  instructive  and  accurate  account  of  this 
occurrence,  which  has  been  very  generally  quoted  in  works  of  physiology. 
Authentic  instances  are  on  record  in  which  life  has  been  prolonged  much 
beyond  the  period  above  mentioned ;  but  they  generally  occurred  in  persons 
who  were  so  situated  as  not  to  suffer  from  cold,  which  the  system,  under  this 
condition,  has  very  little  power  to  resist.  In  these  cases,  also,  there  was  no 
muscular  exertion,  and  water  was  generally  taken  in  abundance. 

Berard  quoted  the  example  of  a  convict  who  died  of  starvation  after  sixty- 
three  days,  but  in  this  case  water  was  taken.  An  instance  of  eight  miners 
who  survived  after  five  days  and  sixteen  hours  of  almost  complete  deprivation 
of  food  is  referred  to  in  works  upon  physiology.  Berard  has  also  quoted,  from 
various  authors,  instances  of  deprivation  of  food  for  periods  varying  between 
four  months  and  sixteen  years ;  but  these  accounts  are  not  properly  authen- 
ticated and  are  discredited  by  physiologists.  They  generally  occurred  in 
hysterical  females,  and  their  consideration  belongs  to  psychology  rather  than 


HUNGER  AND  THIRST.  169 

to  physiology.  According  to  Chossat,  death  from  starvation  occurs  after  a 
loss  of  four-tenths  of  the  weight  of  the  body,  the  time  of  death  being  variable 
in  different  classes  of  animals. 

Thirty  to  thirty-five  days  may  be  taken  as  the  average  duration  of  life  in. 
dogs  deprived  entirely  of  food  and  drink.  It  is  important  to  bear  in  mind 
this  fact  in  connection  with  observations  on  the  nutritive  value  of  different 
articles  of  food. 

ALIMENTATION". 

Under  the  name  of  aliment,  in  its  widest  signification,  it  is  proposed  to 
include  all  articles  composed  of  or  containing  substances  in  a  form  which  en- 
ables them  to  be  used  for  the  nourishment  of  the  body,  either  by  being  them- 
selves appropriated  by  the  organism,  by  influencing  favorably  the  process  of 
nutrition,  or  by  retarding  disassimilation.  Those  substances  which  are  them- 
selves appropriated  may  be  called  direct  aliments ;  and  those  which  simply 
assist  nutrition  without  contributing  reparative  material,  together  with  those 
which  retard  disassimilation,  may  be  termed  accessory  aliments.  In  this 
definition  of  aliment,  nothing  is  excluded  which  contributes  to  nutrition. 
The  air  must  be  considered  in  this  light,  as  well  as  water  and  all  articles 
which  are  commonly  called  drinks. 

In  the  various  articles  used  as  food,  nutritious  substances  are  frequently 
combined  with  each  other  and  with  indigestible  and  innutritious  matters. 
The  constituents  of  the  food  which  are  directly  used  in  nutrition  are  the  true 
alimentary  substances,  embracing,  thus,  only  those  which  are  capable  of 
absorption  and  assimilation.  The  ordinary  food  of  the  warm-blooded  ani- 
mals contains  alimentary  matters  united  with  innutritious  substances  from 
which  they  are  separated  in  digestion.  This  necessitates  a  complicated 
digestive  apparatus.  In  some  of  the  inferior  animals,  the  quantity  of  nu- 
tritious matter  forms  so  small  a  part  of  the  ingesta  that  the  digestive 
apparatus  is  even  more  complicated  than  in  the  human  subject.  This  is 
specially  marked  in  the  herbivora,  the  flesh  of  which  forms  an  important  part 
of  the  diet  of  man.  In  addition  to  what  are  distinctly  recognized  as  ali- 
mentary substances,  food  has  many  constituents  which  exert  an  important 
influence  on  nutrition,  which  have  never  been  isolated  and  analyzed,  but 
which  render  it  agreeable.  Many  of  these  are  developed  in  the  process  of 
cooking. 

Alimentary  substances  belong  to  the  inorganic,  vegetable,  and  animal 
kingdoms.  They  are  generally  divided  into  the  following  classes  : 

1.  Organic  uitrogeni^ed   substances  (albumin,   fibrin,  caseine,  myosine 
etc.),  belonging  to  the  animal  kingdom,  and  vegetable  nitrogenized  substances, 
such  as  gluten  and  legumine. 

2.  Organic  non-nitrogenized  substances  (sugars,  starch  and  fats). 

3.  Inorganic  substances. 

Nitrogenized  Alimentary  Substances. — In  the  nutrition  of  certain  classes 
of  animals,  these  substances  are  derived  exclusively  from  the  animal  king- 
dom, and  in  others,  exclusively  from  the  vegetable  kingdom ;  but  in  man, 


170  ALIMENTATION. 

both  animals  and  vegetables  contribute  nitrogenized  matters.  In  both  ani- 
mal and  vegetable  food,  nitrogenized  substances  are  always  found  combined 
with  inorganic  matters  (water,  sodium  chloride,  the  phosphates,  sulphates  etc.), 
and  frequently  with  non-nitrogenized  matters,  especially  the  carbohydrates. 

The  most  important  nitrogenized  alimentary  constituents  of  food  are  con- 
tained in  the  muscular  substance,  eggs,  milk,  the  juices  of  vegetables,  cereal 
grains  etc.  Many  of  these  substances  have  been  isolated  and  studied  by 
chemists.  Among  the  most  important  are  myosine,  the  chief  organic  con- 
stituent of  muscle,  the  various  albumins  found  in  eggs  and  in  animal  fluids, 
analogous  substances  existing  in  vegetables,  caseine  in  milk,  a  substance 
sometimes  called  vegetable  caseine,  vitelline  in  yelk  of  egg,  fibrin,  gelatine, 
and  gluten,  an  important  alimentary  substance  found  in  the  cereal  grains, 
etc.  A  distinctive  character  of  these  substances  is  that  they  all  contain  nitro- 
gen, being  composed  of  carbon,  oxygen,  hydrogen  and  nitrogen,  with  prob- 
ably a  small  quantity  of  sulphur.  They  are  all  either  liquid  or  semi-solid  in 
consistence,  not  crystallizable,  and  are  coagulable  by  various  reagents.  The 
type  of  substances  of  this  class  is  albumin,  which  has  the  provisional  formula, 
C72Hn3022N18S  (Lieberkiihn) ;  and  they  are  sometimes  called  albuminoids. 
They  are  also  called  proteids,  after  a  hypothetical  substance  described  by 
Mulder,  under  the  name  of  proteine. 

The  nitrogenized  substances  are  found  in  animal  bodies,  as  has  already 
been  stated.  They  originate  in  vegetables  by  a  union  of  nitrogen,  derived 
from  saline  matters,  with  the  carbohydrates,  the  carbohydrates  in  vegetables 
being  produced  from  carbonic  acid  and  water.  No  part  of  the  nitrogen  used 
by  vegetables  in  the  formation  of  the  albuminoids  is  derived  from  the  atmos- 
phere (Hoppe-Seyler). 

A  distinctive  character  of  substances  of  this  class  is  that  under  favorable 
conditions  of  heat  and  moisture  they  undergo  a  peculiar  form  of  decomposi- 
tion, called  putrefaction.  In  the  process  of  digestion,  these  substances  are 
changed  into  peptones,  and  afterward,  it  is  thought,  into  leucine,  tyrosine 
and  some  other  substances  not  well  defined.  An  analogous  decomposition  is 
said  to  take  place  under  the  influence  of  dilute  hydrochloric  acid,  at  a  tem- 
perature of  104°  Fahr.  (40°  C.),  and  of  dilute  sulphuric  acid,  at  a  tempera- 
ture of  212°  Fahr.  (100°  C.).  The  chemical  history  of  these  substances 
would  require  for  its  comprehension  an  elaborate  description  such  as  proper- 
ly belongs  only  to  special  works  on  physiological  chemistry. 

Non- Nitrogenized  Alimentary  Substances. — The  important  non-nitro- 
genized alimentary  substances  are  sugars,  starch  and  fats.  They  are  all  com- 
posed of  carbon,  hydrogen  and  oxygen.  In  sugars  and  starch,  the  hydrogen 
and  oxygen  exist  in  the  proportion  to  form  water,  and  these  matters  are  there- 
fore called  carbohydrates.  The  non-nitrogenized  constituents  of  food  are  of 
organic  origin,  definite  chemical  composition  and  crystallizable. 

Sugars. — Many  varieties  of  sugar  occur  in  food,  and  this  substance 
may  be  derived  from  both  the  animal  and  the  vegetable  kingdoms.  The 
most  common  varieties  derived  from  animals  are  sugar  of  milk,  and  honey, 
beside  a  small  quantity  of  liver-sugar,  which  is  taken  whenever  the  liver  is 


NON-NITROGENIZED  ALIMENTARY  SUBSTANCES.  171 

used  as  food.  The  sugars  derived  from  the  vegetable  kingdom  are  cane- 
sugar,  under  which  head  may  be  classed  all  varieties  of  sugar  except  that  ob- 
tained from  fruits,  and  grape-sugar,  which  comprises  all  the  varieties  existing 
in  fruits.  The  following  are  the  formula?  for  the  different  varieties  of  sugar 
in  a  crystalline  form  : 

Cane-Sugar  (Saccharose),  C2SH.12On 

Milk-Sugar  (Lactose),  C^H^Ojg 

Grape-Sugar  (Glucose,  Dextrose),  C6H1206 

All  varieties  of  sugar  have  a  peculiar,  sweet  taste ;  they  are  all  soluble  in 
water,  glucose  being  more  soluble  than  cane-sugar  or  lactose;  glucose  is 
sparingly  soluble  in  alcohol,  which  dissolves  small  quantities,  only,  of  cane- 
sugar  or  lactose ;  glucose  ferments  readily  and  is  changed  into  alcohol  and 
carbon  dioxide ;  cane-sugar  and  lactose  are  said  to  be  incapable  of  fermenta- 
tion, but  cane-sugar  may  easily  be  converted  into  fermentable  glucose,  and 
lactose,  into  a  fermentable  sugar  called  galactose,  by  boiling  with  dilute 
mineral  acids ;  they  are  capable  of  being  converted  into  lactic  acid  in  the 
presence  of  decomposing  nitrogenized  matters ;  they  are  inflammable,  leav- 
ing an  abundant  carbonaceous  residue  and  giving  off  a  peculiar  odor  of  cara- 
mel ;  they  undergo  other  modifications  when  treated  with  the  mineral  acids 
or  with  alkalies,  which  are  interesting  more  in  a  chemical  than  a  physiolog- 
ical point  of  view.  Of  all  the  varieties  of  sugar,  that  made  from  the  sugar- 
cane is  the  most  soluble,  the  sweetest  and  the  most  agreeable.  Beet-root 
sugar  is  identical  with  cane-sugar. 

Much  of  the  sugar  used  in  the  nutrition  of  the  organism  is  formed  in  the 
body  by  the  digestion  of  starch.  This  transformation  of  starch  may  be 
effected  artificially.  The  sugar  thus  formed,  called  glucose,  is  identical  in 
composition  with  grape-sugar.  Except  in  the  milk  during  lactation,  this 
is  the  only  form  in  which  sugar  exists  in  the  organism,  all  the  sugar  of  the 
food  being  converted  into  glucose  before  it  is  taken  into  the  blood. 

Starch. — A  non-nitrogenized  substance,  closely  resembling  sugar  in  its 
ultimate  composition  (CGH1005),  is  contained  in  abundance  in  a  great  num- 
ber of  vegetables.  It  is  found  particularly  in  the  cereals  (wheat,  rye,  corn, 
barley,  rice  and  oats),  in  the  potato,  chestnuts,  and  in  the  grains  of  legumi- 
nous plants  (beans,  peas,  lentils  and  kidney-beans),  in  the  tuberous  roots  of 
the  yam,  tapioca  and  sweet-potato,  in  the  roots  of  the  maranta  arundinacea 
(arrowroot),  in  the  sago-plant  and  in  the  bulbs  of  orchis.  In  the  cereals, 
after  desiccation,  the  proportion  of  starch  is  usually  between  sixty  and  sev- 
enty per  cent.  It  is  most  abundant  in  rice,  which  contains,  after  desiccation, 
88*65  per  cent. 

When  extracted  in  a  pure  state,  starch  is  in  the  form  of  granules,  varying 
in  size  between  y^^o  and  -f^  of  an  inch  (2*5  and  62-5  //,),  and  presenting,  in 
most  varieties,  certain  peculiarities  of  form.  The  granule  frequently  is 
marked  by  a  little  conical  excavation  called  the  hilum,  and  the  starch- 
substance  is  arranged  in  the  form  of  concentric  lamin<B,  the  outlines  of 
which  are  often  quite  distinct.  When  starch  is  rubbed  between  the 
fingers,  these  little,  hard  bodies  give  it  rather  a  gritty  feel  and  produce  a 


172 


ALIMENTATION. 


FIG.  49.  —  Arrowroot  starch-granules  ;  magnified 
370  diameters  (from  a  photograph  taken  at  the 
United  States  Army  Medical  Museum). 


crackling  sound.     The  different  varieties  of  starch  may  be  recognized  micro- 
scopically by  the  peculiar  appearance  of  the  granules. 

Starch  is  insoluble  in  cold  water ;  but  when  boiled  with  several  times  its 
volume  of  water,  the  granules  swell  up,  become  transparent,  and  finally  fuse 

together,  mingling  with  the  water 
and  giving  it  a  mucilaginous  con- 
sistence. The  mixture  on  cooling 
forms  a  jelly-like  mass  of  greater  or 
less  consistence.  This  change  in 
starch  is  called  hydration  and  is  im- 
portant as  one  of  the  transforma- 
tions which  take  place  in  the  process 
of  digestion,  when  starch  is  taken 
uncooked.  This  change  is  generally 
effected  more  or  less  completely, 
however,  in  the  process  of  cooking. 
The  most  important  properties 
of  starch  are  connected  with  its 
transformation,  first  into  dextrine, 
and  finally  into  glucose.  This  al- 
ways takes  place  in  digestion,  before 
starch  can  be  absorbed.  In  the  digestive  apparatus,  the  change  into  sugar  is 
almost  instantaneous,  and  the  intermediate  substance,  dextrine,  is  not  easily 
recognized.  By  boiling  starch  for  a  number  of  hours  with  dilute  sulphuric 
acid,  it  is  transformed,  without  any  change  in  chemical  composition,  into 
dextrine,  which  is  soluble.  If  the  action  be  continued,  it  appropriates  one 
atom  of  water  and  is  converted  into  glucose.  The  change  of  starch  into 
dextrine  may  be  effected  by  a  dry  heat  of  about  400°  Fahr.  (204°  C.),  a  pro- 
cess which  is  commonly  employed  in  commerce. 

Vegetable  Substances  resembling  Starch. — In  certain  vegetables,  substances 
isomeric  with  starch,  but  presenting  slight  differences  as  regards  general 
properties  and  reactions,  have  been  described,  but  they  possess  no  great  im- 
portance as  alimentary  matters  and  demand  only  a  passing  mention.  These 
are  inuline,  lichenine,  cellulose,  pectose,  mannite,  mucilages  and  gums.  Inu- 
line  is  found  in  certain  roots.  It  is  convertible  into  sugar  but  does  not  pass 
through  the  intermediate  stage  of  dextrine.  It  differs  from  starch  in  being 
very  soluble  in  hot  water.  Lichenine  is  found  in  many  kinds  of  edible  mosses 
and  lichens.  It  differs  from  starch  only  in  its  solubility.  Mannite  is  a 
sweetish  substance  found  in  manna,  mushrooms,  celery,  onions  and  asparagus. 
It  is  perhaps  more  analogous  to  sugar  than  to  starch,  but  it  is  not  fermentable 
and  has  no  influence  on  polarized  light. 

Gums  and  mucilages  may  enter  to  a  certain  extent  into  the  composition 
of  food,  but  they  can  hardly  be  considered  as  alimentary  matters.  Gums  are 
found  exuding  from  certain  trees,  first  in  a  fluid  state,  but  becoming  hard  on 
exposure  to  the  air.  A  viscid,  stringy  mucilage  is  found  surrounding  many 
grains,  such  as  the  flax-seed  and  quince-seeds,  and  exists  in  various  roots 


NON-NITEOGENIZED  ALIMENTAEY  SUBSTANCES. 


173 


and  leaves.  Both  gums  and  mucilages  mix  readily  with  water,  giving  it  a 
consistence  called  mucilaginous.  The  composition  of  gum  is  C20H10010. 
Experiments  have  shown  that  gum  passes  unchanged  through  the  alimentary 
canal  and  has  no  nutritive  properties.  Gum  is  mentioned  in  this  con- 
nection from  the  fact  that  it  is  frequently  used  in  the  treatment  of  disease 
and  is  thought  by  many  to  be  nutritious. 

The  carbohydrates,  although  important  articles  of  food  and  especially  use- 
ful in  the  processes  involved  in  the  production  of  animal  heat,  are  not  in 
themselves  capable  of  sustaining  life. 

Fats. — Fatty  matters,  derived  from  both  the  animal  and  the  vegetable 
kingdoms,  are  important  articles  of  food.  As  a  constituent  of  the  organism, 
fat  is  found  in  all  parts  of  the  body, 
with  the  exception  of  the  bones,  teeth 
and  fibrous  tissues.  It  necessarily  con- 
stitutes an  important  part  of  all  animal 
food  and  is  taken  in  the  form  of  adipose 
tissue,  infiltrated  in  the  various  tissues 
in  the  form  of  globules  and  granules  of 
oil,  and  in  suspension  in  the  caseine  and 
water  in  milk.  Animal  fat  is  a  mixture 
of  oleine,  palmitine  and  stearins,  in  va- 
rious proportions,  and  possesses  a  con- 
sistence which  depends  upon  the  relative 
quantities  of  these  substances. 

The  different  varieties  of  animal  fats 
do  not  demand  special  consideration  as 
articles  of  diet.  Butter,  an  important 
article  of  food,  is  somewhat  different  from  the  fat  extracted  from  adipose 
tissue,  but  most  varieties  of  fat  lose  their  individual  peculiarities  in  the  pro- 
cess of  digestion  and  are  apparently 
identical  when  they  find  their  way  into 
the  lacteal  vessels. 

In  the  vegetable  kingdom,  fat  is 
particularly  abundant  in  seeds  and 
grains,  but  it  exists  in  quantity  in  some 
fruits,  as  in  the  olive.  Here  it  is  gen- 
erally called  oil.  It  exists  in  consider- 
able proportion  in  nuts  and  in  certain 
quantity  in  the  cereals,  particularly  In- 
dian corn. 

Fat,   both    animal    and    vegetable, 
may  be  either  liquid  or  solid.     It  has  a 
peculiar  oily  feel,  a  neutral  reaction, 
and  is  insoluble  in  water  and  soluble  in 
alcohol — particularly  hot  alcohol — chlo- 
roform, ether,  benzine  and  solutions  of  soaps.     The  solid  varieties  are  exceed- 
13 


FIG.  50. — Crystals  of  palmitine  and  palmitic 
acid  (Funke).  a,  a,  a,  palmitine  ;  6,  pal- 
mitic acid. 


Fio.  51.— Crystals  of  stearine  and  stearic  acid 
(Funke).    a,  a,  a,  stearine  ;  6,  stearic  acid. 


174  ALIMENTATION. 

ingly  soluble  in  the  oils.  Treated  with  alkalies  at  a  high  temperature  and  in 
the  presence  of  water,  the  fats  are  decomposed  into  fatty  acids  and  glycerine, 
the  acids  uniting  with  the  bases  to  form  soaps.  Alkaline,  mucilaginous,  and 
some  animal  fluids — particularly  the  pancreatic  juice — are  capable  of  holding 
fat  in  a  state  of  minute  and  permanent  subdivision  and  suspension,  forming 
what  are  known  as  emulsions. 

The  three  varieties  of  fats  usually  recognized  are  stearine  and  palmitine, 
which  are  solid  at  the  temperature  of  the  body,  and  oleine,  which  is  liquid. 
The  formulae  for  these  varieties  are  the  following : 

Stearine  (Tristearine),  C57H11006 

Palmitine  (Tripalmitine),  C51H9806 

Oleine  (Trioleine),  C57H10406 

It  is  noticeable  that  in  the  composition  of  fats,  the  hydrogen  and  oxygen 
do  not  exist  in  the  proportions  to  form  water,  as  they  do  in  the  carbohy- 
drates, and  that  they  are  relatively  poor  in  oxygen.  One  variety  of  fat  can 
not  be  converted  into  another  by  chemical  manipulation. 

As  alimentary  substances,  fats  are  undoubtedly  of  great  importance. 
They  are  supposed  by  many  to  be  particularly  concerned  in  the  production 
of  animal  heat.  It  has  been  proved  by  repeated  experiments  that  fat,  as  a 
single  article  of  diet,  is  insufficient  for  the  purposes  of  nutrition. 

Inorganic  Alimentary  Substances. — It  has  been  shown  that  all  the  or- 
gans, tissues  and  fluids  of  the  body  contain  inorganic  matter  in  greater  or 
less  abundance.  The  same  is  true  of  vegetable  products.  All  the  organic 
nitrogenized  matters  contain  mineral  substances  which  can  not  be  separated 
without  incineration.  When  new  organic  matter  is  appropriated  by  the  tis- 
sues to  supply  the  place  of  that  which  has  become  effete,  the  mineral  sub- 
stances are  deposited  with  them ;  and  the  organic  matters,  as  they  are  trans- 
formed into  excrementitious  substances  and  discharged  from  the  body,  are 
always  thrown  off  in  connection  with  the  mineral  substances  which  enter  into 
their  composition.  This  constant  discharge  of  inorganic  matters,  forming, 
as  they  do,  an  essential  part  of  the  organism,  necessitates  their  introduction 
with  the  food,  in  order  to  maintain  the  normal  constitution  of  the  parts. 
As  these  matters  are  necessary  to  the  proper  constitution  of  the  body,  they 
must  be  regarded  as  alimentary  substances. 

Water. — This  is  one  of  the  most  important  of  the  constituents  of  the 
organism,  is  found  in  every  tissue  and  part  without  exception,  is  introduced 
with  all  kinds  of  food  and  is  the  basis  of  almost  all  drinks.  As  a  rule  it  is 
taken  in  greater  or  less  quantity  in  a  nearly  pure  state.  Although,  as  a 
drink,  water  should  be  colorless,  odorless  and  tasteless,  it  always  contains  more 
or  less  saline  and  other  matters  in  solution,  with  a  certain  quantity  of  air. 
The  air  and  gases  may  be  driven  off  by  boiling  or  by  removing  the  atmos- 
pheric pressure.  The  demand  on  the  part  of  the  system  for  water  is  regu- 
lated, to  a  certain  extent,  by  the  quantity  discharged  from  the  organism,  and 
this  is  subject  to  great  variations.  The  quantity  taken  as  drink  also  depends 
very  much  on  the  constitution  of  the  food  as  regards  the  water  which  enters 
into  its  composition. 


INORGANIC  ALIMENTARY  SUBSTANCES.  175 

Sodium  Chloride. — Of  all  saline  substances,  sodium  chloride  is  the  one 
most  widely  distributed  in  the  animal  and  the  vegetable  kingdoms.  It  exists 
in  all  varieties  of  food ;  but  the  quantity  which  is  taken  in  combination  with 
other  matters  is  usually  insufficient  for  the  purposes  of  the  economy,  and 
common  salt  is  generally  added  to  certain  articles  of  food,  as  a  condiment, 
when  it  improves  their  flavor,  promotes  the  secretion  of  certain  of  the  digest- 
ive fluids  and  meets  a  nutritive  demand  on  the  part  of  the  system.  Experi- 
ments and  observations  have  shown  that  a  deficiency  of  sodium  chloride  in  the 
food  has  an  unfavorable  influence  on  the  general  processes  of  nutrition. 

Calcium  Phosphate. — This  is  almost  as  common  a  constituent  of  vegetable 
and  animal  food  as  sodium  chloride.  It  is  seldom  taken  except  in  combina- 
tion, particularly  with  nitrogenized  alimentary  matters.  Its  importance  in 
alimentation  has  been  experimentally  demonstrated,  it  having  been  shown 
that  in  animals  deprived  as  completely  as  possible  of  this  salt,  the  nutrition 
of  the  body,  particularly  in  parts  which  contain  it  in  considerable  quantity, 
as  the  bones,  is  seriously  affected. 

Iron. — Haemaglobine,  the  coloring  matter  of  the  blood,  contains,  inti- 
mately united  with  organic  matter,  a  certain  proportion  of  iron.  Examples 
of  simple  anaemia,  which  are  frequently  met  with  in  practice  and  are  almost 
always  relieved  in  a  short  time  by  the  administration  of  iron,  are  proof  of 
the  importance  of  this  substance  in  alimentation.  The  quantity  of  iron 
which  is  discharged  from  the  body  is  very  slight,  only  a  trace  being  discov- 
erable in  the  urine.  A  small  quantity  of  iron  is  frequently  introduced  in 
solution  in  the  water  taken  as  drink,  and  it  is  a  constant  constituent  of  milk 
and  eggs.  When  its  supply  in  the  food  is  insufficient,  it  is  necessary,  in 
order  to  restore  the  normal  processes  of  nutrition,  to  administer  it  in  some 
form,  until  its  proportion  in  the  organism  shall  have  reached  the  proper 
standard. 

It  is  hardly  necessary  even  to  enumerate  the  other  inorganic  alimentary 
substances,  as  nearly  all  are  in  a  state  of  such  intimate  combination  with 
nitrogenized  matters  that  they  may  be  regarded  as  part  of  their  substance. 
Suffice  it  to  say,  that  all  the  inorganic  matters  which  exist  as  constituents  of 
the  organism  are  found  in  the  food.  That  these  are  essential  to  nutrition, 
can  not  be  doubted  ;  but  it  is  evident  that  by  themselves  they  are  incapable 
of  supporting  life,  as  they  can  not  be  converted  into  either  nitrogenized  or 
non-nitrogenized  organic  matters. 

Alcohol — All  distilled  and  fermented  liquors  and  wines  contain  a  greater 
or  less  proportion  of  alcohol.  As  these  are  so  generally  used  as  beverages, 
and  as  the  effects  of  their  excessive  use  are  so  serious,  the  influence  of  alco- 
hol upon  the  organism  has  become  one  of  the  most  important  questions  con- 
nected with  alimentation.  Some  alcoholic  beverages  influence  the  functions 
solely  through  the  alcohol  which  they  contain ;  while  others,  as  beer  and  por- 
ter,, with  a  comparatively  small  proportion  of  alcohol,  contain  a  considerable 
quantity  of  solid  matter. 

Alcohol  (C^HjO),  from  its  composition,  is  to  be  classed  with  the  non-nitro- 
genized substances.  It  has  already  been  stated  that  sugar  and  fat  are  essen- 


176  ALIMENTATION. 

tial  to  proper  nutrition  and  that  they  undergo  important  changes  in  the  or- 
ganism. Alcohol  is  absorbed  and  taken  into  the  blood ;  and  it  becomes  a 
question  of  importance  to  determine  whether  it  be  consumed  in  the  economy 
or  whether  it  be  discharged  unchanged  by  the  various  emunctories. 

Alcohol  has  long  since  been  recognized  in  the  expired  air  after  it  has  been 
taken  into  the  stomach  ;  and  late  researches  have  confirmed  the  earlier  ob- 
servations with  regard  to  its  elimination  in  its  original  form,  and  have  shown 
that  after  it  has  been  taken  in  quantity,  it  exists  in  the  blood  and  all  the  tis- 
sues and  organs,  particularly  the  liver  and  nervous  system.  Lallemand,  Per- 
rin  and  Duroy  have  stated,  also,  that  there  is  a  considerable  elimination  of  al- 
cohol by  the  lungs,  skin  and  kidneys ;  but  the  accuracy  of  the  experiments 
by  which  these  results  were  arrived  at  has  been  questioned.  The  observa- 
tions of  Anstie  and  of  Dupre  have,  indeed,  thrown  great  doubt  upon  the 
chromic-acid  test  for  alcohol,  which  was  employed  by  the  French  observers 
above  mentioned.  Nevertheless,  when  alcohol  has  been  taken  in  narcotic 
doses,  there  is  some  alcoholic  elimination  in  the  urine,  as  was  shown  long  ago 
by  Percy. 

As  the  result  of  the  final  experiments  of  Anstie,  it  is  certain  that  most 
of  the  alcohol  which  is  taken  in  quantities  not  sufficient  to  produce  alcoholic 
intoxication  is  consumed  in  the  organism,  and  but  a  trivial  quantity  is 
thrown  off,  either  in  the  urine,  the  fasces,  the  breath  or  the  cutaneous  tran- 
spiration. This  question  is  of  importance  with  regard  to  the  moderate  use 
of  alcohol  under  normal  conditions,  and  especially  in  its  bearing  upon  the 
therapeutical  action  of  the  various  alcoholic  drinks  administered  in  cases  of 
disease. 

Taken  in  moderate  quantity,  alcohol  generally  produces  a  certain  degree  of 
nervous  exaltation  which  gradually  passes  off.  In  some  individuals  the  men- 
tal faculties  are  sharpened  by  alcohol,  while  in  others  they  are  blunted. 
There  is  nothing,  indeed,  more  variable  than  the  immediate  effects  of  alcohol 
on  different  persons.  In  large  doses  the  effects  are  the  well  known  phenom- 
ena of  intoxication,  delirum,  more  or  less  anaesthesia,  coma,  and  sometimes, 
if  the  quantity  be  excessive,  death.  As  a  rule,  the  mental  exaltation  pro- 
duced by  alcohol  is  followed  by  reaction  and  depression,  except  in  debilitated 
or  exhausted  conditions  of  the  system,  when  the  alcohol  seems  to  supply  a  de- 
cided want. 

The  views  of  physiologists  concerning  the  influence  of  a  moderate  quanti- 
ty of  alcohol  on  the  nervous  system  are  somewhat  conflicting.  That  it  may 
temporarily  give  tone  and  vigor  to  the  system  when  the  energies  are  unusually 
taxed,  can  not  be  doubted ;  but  this  effect  is  not  produced  in  all  individuals. 
The  constant  use  of  alcohol  may  create  an  apparent  necessity  for  it,  produc- 
ing a  condition  of  the  system  which  must  be  regarded  as  pathological. 

The  immediate  effects  of  the  ingestion  of  a  moderate  quantity  of  alcohol, 
continued  for  a  few  days,  are  decided.  It  notably  diminishes  the  exhalation 
of  carbon  dioxide  and  the  discharge  of  other  excrementitious  matters,  par- 
ticularly urea.  These  facts  have  long  since  been  experimentally  demonstrat- 
ed. Proper  mental  and  physical  exercise,  tranquillity  of  the  nervous  system, 


ALCOHOL.  177 

and  all  conditions  which  favor  the  vigorous  nutrition  and  development  of 
the  organism  physiologically  increase,  rather  than  diminish,  the  quantity  of 
the  excretions,  correspondingly  increase  the  demand  for  food,  and  if  contin- 
ued, are  of  permanent  benefit.  Alcohol,  on  the  other  hand,  diminishes  the 
activity  of  nutrition.  If  its  use  be  long  continued,  the  assimilative  powers 
of  the  system  become  so  weakened  that  the  proper  quantity  of  food  can  not 
be  appropriated,  and  alcohol  is  craved  to  supply  a  self-engendered  want. 
The  organism  may,  in  many  instances,  be  restored  to  its  physiological  condi- 
tion by  discontinuing  the  use  of  alcohol ;  but  it  is  generally  some  time  before 
the  nutritive  powers  become  active,  and  alcohol,  meanwhile,  seems  absolutely 
necessary  to  existence. 

Under  ordinary  conditions,  when  the  organism  can  be  adequately  supplied 
with  food,  alcohol  is  undoubtedly  injurious.  When  the  quantity  of  food  is 
insufficient,  alcohol  may  supply  the  want  for  a  time  and  temporarily  restore 
the  powers  of  the  body ;  but  the  effects  of  its  continued  use,  conjoined  with 
insufficient  nourishment,  show  that  it  can  not  take  the  place  of  other  assimi- 
lable matters.  These  effects  are  too  well  known  to  the  physician,  particularly 
in  hospital-practice,  to  need  farther  comment.  Notwithstanding  these  un- 
doubted physiological  facts,  alcohol,  in  some  form,  is  used  by  almost  every 
people  on  the  face  of  the  earth,  civilized  or  savage.  Whether  this  be  in  order 
to  meet  some  want  occasionally  felt  by  and  peculiar  to  the  human  organism, 
is  a  question  upon  which  physiologists  have  found  it  impossible  to  agree. 
That  alcohol,  at  certain  times,  taken  in  moderation,  soothes  and  tranquillizes 
the  nervous  system  and  relieves  exhaustion  dependent  upon  unusually  severe 
mental  or  physical  exertion,  can  not  be  doubted.  It  is  by  far  too  material  a 
view  to  take  of  existence,  to  suppose  that  the  highest  condition  of  man  is 
that  in  which  the  functions,  possessed  in  common  with  the  lower  animals,  are 
most  perfectly  performed.  Inasmuch  as  temporary  insufficiency  of  food,  great 
exhaustion  of  the  nervous  system,  and  various  conditions  in  which  alcohol 
seems  to  be  useful,  must  of  necessity  often  occur,  it  is  hardly  proper  that  this 
agent  should  be  absolutely  condemned ;  but  it  is  the  article,  par  excellence, 
which  is  liable  to  abuse,  and  the  effects  of  which  on  the  mind  and  body,  when 
taken  constantly  in  excess,  are  most  serious. 

Although  alcohol  imparts  a  certain  warmth  when  the  system  is  suffering 
from  excessive  cold,  it  is  not  proved  that  it  enables  men  to  endure  a  very  low 
temperature  for  a  great  length  of  time.  This  end  can  be  effectually  attained 
only  by  an  increased  quantity  of  food.  The  testimony  of  Dr.  Hayes,  the  Arc- 
tic explorer,  is  very  strong  upon  this  point.  He  says :  "  While  fresh  animal 
food,  and  especially  fat,  is  absolutely  essential  to  the  inhabitants  and  travellers 
in  Arctic  countries,  alcohol  is,  in  almost  any  shape,  not  only  completely  use- 
less but  positively  injurious  ....  Circumstances  may  occur  under  which  its 
administration  seems  necessary ;  such,  for  instance,  as  great  prostration  from 
long-continued  exposure  and  exertion,  or  from  getting  wet;  but  then  it 
should  be  avoided,  if  possible,  for  the  succeeding  reaction  is  always  to  be 
dreaded ;  and,  if  a  place  of  safety  is  not  near  at  hand,  the  immediate  danger 
is  only  temporarily  guarded  against,  and  becomes,  finally,  greatly  augmented 


178  ALIMENTATION. 

by  reason  of  decreased  vitality.  If  given  at  all,  it  should  be  in  very  small 
quantities  frequently  repeated,  and  continued  until  a  place  of  safety  is  reached. 
I  have  known  the  most  unpleasant  consequences  to  result  from  the  injudi- 
cious use  of  whiskey  for  the  purpose  of  temporary  stimulation,  and  have  also 
known  strong  able-bodied  men  to  have  become  utterly  incapable  of  resisting 
cold  in  consequence  of  the  long-continued  use  of  alcoholic  drinks."  In  a  recent 
paper  by  General  Greely  (1887),  is  the  following,  which  confirms  the  results 
of  the  experience  of  Hayes  :  "  It  seems  to  me  to  follow  from  these  Arctic  ex- 
periences that  the  regular  use  of  spirits,  even  in  moderation,  under  conditions 
of  great  physical  hardship,  continued  and  exhausting  labor,  or  exposure  to 
severe  cold  can  not  be  too  strongly  deprecated,  and  that  when  used  as  a  men- 
tal stimulus  or  as  a  physical  luxury  they  should  be  taken  in  moderation. 
When  habit  or  inclination  induces  the  use  of  alcohol  in  the  field,  under  con- 
ditions noted  above,  it  should  be  taken  only  after  the  day's  work  is  done,  as 
a  momentary  stimulus  while  waiting  for  the  preferable  hot  tea  and  food;  or 
better,  after  the  food,  when  going  to  bed,  for  then  it  may  quickly  induce 
sleep  and  its  reaction  pass  unfelt." 

It  is  not  demonstrated  that  alcohol  increases  the  capacity  to  endure  severe 
and  protracted  bodily  exertion.  Its  influence  as  a  therapeutic  agent,  in  pro- 
moting assimilation  in  certain  conditions  of  defective  nutrition,  in  relieving 
.shock  and  nervous  exhaustion,  in  sustaining  the  powers  of  life  in  acute  dis- 
eases characterized  by  rapid  emaciation  and  abnormally  active  disassimilation, 
etc.,  can  hardly  be  doubted;  but  the  consideration  of  these  questions  does 
not  belong  to  physiology. 

Coffee. — Coffee  is  an  article  consumed  daily  by  many  millions  of  human 
beings  in  all  quarters  of  the  globe.  In  armies  it  has  been  found  almost  in- 
dispensable, enabling  men  on  moderate  rations  to  perform  an  amount  of  labor 
which  would  otherwise  be  impossible.  After  exhausting  efforts  of  any  kind, 
there  is  no  article  which  relieves  the  overpowering  sense  of  fatigue  so  com- 
pletely as  coffee.  Army-surgeons  say  that  at  night,  after  a  severe  march,  the 
first  desire  of  the  soldier  is  for  coffee,  hot  or  cold,  with  or  without  sugar,  the 
only  essential  being  a  sufficient  quantity  of  the  pure  article.  Almost  every 
one  can  bear  testimony  from  personal  experience  to  the  effects  of  coffee  in 
relieving  the  sense  of  fatigue  after  mental  or  bodily  exertion  and  in  increasing 
the  capacity  for  labor,  especially  mental  work,  by  producing  wakefulness  and 
clearness  of  intellect.  From  these  facts,  the  importance  of  coffee,  either  as 
an  alimentary  substance  or  as  taking  the  place,  to  a  certain  extent,  of  ali- 
ment, is  apparent. 

Except  in  persons  who,  from  idiosyncrasy,  are  unpleasantly  affected  by  it, 
coffee,  taken  in  moderate  quantity  and  at  proper  times,  produces  an  agreeable 
sense  of  tranquillity  and  comfort,  with,  however,  no  disinclination  to  exertion, 
either  mental  or  physical.  Its  immediate  influence  upon  the  system,  which 
is  undoubtedly  stimulant,  is  peculiar  and  is  not  followed  by  reaction  or 
unpleasant  after-effects.  Habitual  use  renders  coffee  almost  a  necessity,  even 
in  those  who  are  otherwise  well  nourished  and  subjected  to  no  extraordinary 
mental  or  bodily  strain.  Taken  in  excessive  quantity,  or  in  those  unaccus- 


COFFEE,  TEA  ETC.  179 

tomed  to  its  use,  particularly  when  taken  at  night,  it  produces  persistent  wake- 
fulness.  These  effects  are  so  well  known  that  it  is  often  taken  for  the  pur- 
pose of  preventing  sleep. 

Experimental  researches  have  shown  that  the  use  of  coffee  permits  a 
reduction  in  the  quantity  of  food,  in  workingmen  especially,  much  below  the 
standard  which  would  otherwise  be  necessary  to  maintain  the  organism  in 
proper  condition.  In  the  observations  of  De  Gasparin  upon  the  regimen  of 
the  Belgian  miners,  it  was  found  that  the  addition  of  a  quantity  of  coffee  to 
the  daily  ration  enabled  them  to  perform  their  arduous  labors  on  a  diet  which 
was  even  below  that  found  necessary  in  prisons  where  this  article  was  not 
used.  Experiments  have  shown,  also,  that  coffee  diminishes  the  absolute  quan- 
tity of  urea  discharged  by  the  kidneys.  In  this  respect,  as  far  as  has  been 
ascertained,  the  action  of  coffee  is  like  that  of  alcohol,  and  it  may  reasonably 
be  supposed  to  retard  disassimilation,  with  the  important  difference  that  it  is 
followed  by  no  unfavorable  after-effects  and  can  be  used  in  moderation  for 
an  indefinite  time  with  advantage. 

A  study  of  the  composition  of  coffee  shows  a  considerable  proportion  of 
what  must  be  considered  as  alimentary  matter.  The  following  is  the  result 
of  analyses  by  Payen  : 

Cellulose .'. 34-000 

Water  (hygroscopic) 12-000 

Fatty  substances 10  to  13-000 

Glucose,  dextrine,  indeterminate  vegetable  acid 15-500 

Legumine,  caseine  etc 10-000 

Potassium  chlorolignate  and  caffeine    3-5  to  5-000 

Nitrogenized  organic  matter 3-000 

Free  caffeine 0-800 

Concrete,  insoluble  essential  oil 0-001 

Aromatic  essence,  of  agreeable  odor,  soluble  in  water 0-002 

Mineral  substances ;  potash,  magnesia,  lime,  phosphoric,  silicic,  and  sul- 
phuric acid  and  chlorine 6-697 


100-000 

The  above  is  the  composition  of  raw  coffee,  but  the  berry  is  seldom  used 
in  that  form,  being  usually  subjected  to  roasting  before  an  infusion  is  made. 
During  this  process,  the  grains  are  considerably  swollen,  but  they  lose  sixteen 
or  seventeen  per  cent,  in  weight.  A  peculiar  aromatic  substance  is  also 
developed  by  roasting.  If  the  torrefaction  be  pushed  too  far,  much  of  the 
agreeable  flavor  of  coffee  is  lost,  and  an  acrid,  empyreumatic  substance  is 
produced. 

Tea. — An  infusion  of  the  dried  and  prepared  leaves  of  the  tea-plant  is 
perhaps  as  common  a  beverage  as  coffee,  and  taking  into  consideration  its 
large  consumption  in  China  and  Japan,  it  is  actually  used  by  a  greater 
number  of  persons.  Its  effects  upon  the  system  are  similar  to  those  of  coffee, 
but  they  are  generally  not  so  marked.  Ordinary  tea,  taken  in  moderate 
quantity,  like  coffee,  relieves  fatigue  and  increases  mental  activity,  but  does 
not  usually  produce  such  persistent  wakefulness. 


180 


ALIMENTATION. 


It  is  unnecessary  to  describe  all  the  varieties  of  tea  in  common  use. 
There  are,  however,  certain  varieties,  called  green  teas,  which  present  impor- 
tant differences,  as  regards  composition  and  physiological  effects,  from  the 
black  teas,  which  latter  are  more  commonly  used.  The  following  is  a  com- 
parative analysis  of  these  two  varieties  by  Mulder : 


CONSTITUENTS. 

CHINESE   TEA. 

JAVANESE    TEA. 

Green. 

Black. 

Green. 

Black. 

Volatile  oil        

0-79 

2-22 
0-28 
2-22 
8-56 
17-80 
0-43 
22-80 

0-60 

1-84 

'3-64 

7-28 
12-88 
0-46 
19-88 
1-48 
19-12 
2-80 
28-32 

0-98 
3-24 
0-32 
1-64 
12-20 
17-56 
0-60 
21-68 

20-36 
3-64 
18-20 

0-65 
1-28 

2'-44 
11-08 
14-80 
0-65 
18-64 
1-64 
18-24 
1-28 
27-00 

Chlorophyl  

Wax   

Resin    

Gum         .      

Tannin  

Theine  

Extractive  

Extract  obtained  by  hydrochloric  acid  .... 
Albumin          

23-60 
3-00 

17-08 

Fibrous  matter            '. 

Salts  included  in  the  above  

98-78 
5-56 

98-30 
5-24 

100-42 
4-76 

97-70 
5-36 

Both  tea  and  coffee  contain  peculiar  organic  substances.  The  active  prin- 
ciple of  tea  is  called  theine,  and  the  active  principle  of  coffee,  caffeine.  As 
they  are  supposed  to  be  particularly  efficient  in  producing  the  peculiar  effects 
upon  the  nervous  system  which  are  characteristic  of  both  tea  and  coffee,  there 
is  good  reason  to  suppose  that  they  are  nearly  identical  in  their  physiological 
effects.  Analyses  more  recent  than  the  one  quoted  from  Mulder  (Stenhouse, 
Peligot)  have  shown  that  theine,  or  caffeine  (C8H10N402  +  H20),  exists  in 
greater  proportion  in  tea  than  in  coffee ;  but  as  a  rule,  a  greater  quantity  of 
soluble  matter  is  extracted  in  the  preparation  of  coffee,  which  may  account 
for  its  more  marked  effects  upon  the  system.  Some  analyses  have  given  as 
much  as  six  per  cent,  as  the  proportion  of  theine  in  tea  (Landois). 

Chocolate. — Chocolate  is  made  from  the  seeds  of  the  cocoa-tree,  roasted, 
deprived  of  their  husks,  and  ground  with  warm  rollers  into  a  pasty  mass  with 
sugar,  flavoring  substances  being  sometimes  added.  It  is  then  made  into 
cakes,  cut  into  small  pieces  or  scraped  to  a  powder,  and  boiled  with  milk  or 
milk  and  water,  when  it  forms  a  thick,  gruel-like  drink,  which  is  highly 
nutritive  and  has  some  of  the  exhilarating  properties  of  coffee  or  tea.  Beside 
containing  a  large  proportion  of  nitrogenized  matter  resembling  albumen, 
the  cocoa-seed  is  particularly  rich  in  fatty  matter,  and  contains  a  peculiar 
substance,  theobromine  (C7H8N402),  analogous  to  caffeine  and  theine,  which 
is  supposed  to  possess  similar  physiological  properties. 

The  following  is  an  analysis  by  Payen  of  the  cocoa-seeds  freed  from  the 
husks  but  not  roasted.  Torrefaction  has  the  effect  of  developing  the  pecul- 
iar aromatic  principle,  and  of  moderating  the  bitterness,  which  is  always  more 
or  less  marked  : 


NECESSARY  QUANTITY  AND  VARIETY  OF  FOOD.  181 

Fatty  matter  (cocoa-butter) 48  to  50 

Albumin,  fibrin  and  other  nitrogenized  matter 21  "  20 

Theobromine 4  "     2 

Starch  (with  traces  of  saccharine  matter) 11  "  10 

Cellulose  8  "     2 

Coloring  matter,  aromatic  essence Traces. 

Mineral  substances 3  to    4 

Hygroscopic  water 10  "  12 

100      100 

It  is  evident,  from  the  above  table,  that  cocoa  with  milk  and  sugar,  the 
ordinary  form  in  which  chocolate  is  taken,  must  form  a  very  nutritious  mixt- 
ure. Its  influence  as  a  stimulant,  supplying  the  place  of  matter  which  is 
directly  assimilated,  and  retarding  disassirnilation,  is  dependent,  if  it  exist  at 
all,  upon  the  theobromine ;  but  its  stimulating  properties  are  slight  as  com- 
pared with  those  of  coffee  and  tea. 

Condiments  and  Flavoring  Articles. — The  refinements  of  cookery  involve 
the  use  of  many  articles  which  can  not  be  classed  as  alimentary  substances. 
Pepper,  capsicum,  vinegar,  mustard,  spices  and  other  articles  of  this  class, 
which  are  so  commonly  used  in  various  sauces,  have  no  decided  influence 
on  nutrition,  except  in  so  far  as  they  promote  the  secretion  of  the  digestive 
fluids.  Common  salt,  however,  is  very  important,  and  this  has  been  consid- 
ered in.  connection  with  inorganic  alimentary  substances.  The  various  flavor- 
ing seeds  and  leaves,  truffles,  mushrooms  etc.  have  no  physiological  impor- 
tance except  as  they  render  articles  of  food  more  palatable. 

Quantity  and  Variety  of  Food  necessary  to  Nutrition. — The  inferior 
animals,  especially  those  not  subjected  to  the  influence  of  man,  regulate  by 
instinct  the  quantity  and  kind  of  food  which  they  consume.  The  same  is 
true  of  man  during  the  earliest  periods  of  his  existence ;  but  later  in  life, 
the  diet  is  variously  modified  by  taste,  habit,  climate,  and  what  may  be 
termed  artificial  wants.  It  is  usually  a  safe  rule  to  follow  the  appetite  with 
regard  to  quantity,  and  the  tastes,  when  they  are  not  manifestly  vitiated  or 
morbid,  with  regard  to  variety.  The  cravings  of  nature  indicate  when  to 
change  the  form  in  which  nutriment  is  taken ;  and  that  a  sufficient  quantity 
has  been  taken  is  manifested  by  a  sense,  not  exactly  of  satiety,  but  of  evi- 
dent satisfaction  of  the  demands  of  the  system.  During  the  first  periods 
of  life,  the  supply  must  be  a  little  in  excess  of  the  actual  loss,  in  order 
to  furnish  materials  for  growth ;  during  the  later  periods,  the  quantity  of 
nitrogenized  matter  assimilated  is  somewhat  less  than  the  loss ;  but  in  adult 
age,  the  system  is  maintained  at  a  tolerably  definite  standard  by  the  assimi- 
lation of  matter  about  equal  in  quantity  to  that  which  is  discharged  in  the 
form  of  excretions. 

Although  the  loss  of  substance  by  disassimilation  creates  and  regulates 
the  demand  for  food,  it  is  an  important  fact,  never  to  be  lost  sight  of,  that 
the  supply  of  food  has  a  very  great  influence  upon  the  quantity  of  the  excre- 
tions. An  illustration  of  this  is  the  influence  of  food  upon  the  exhalation 
of  carbon  dioxide ;  and  this  is  but  an  example  of  what  takes  place  with  re- 


182  ALIMENTATION. 

gard  to  other  excretions.  The  quantity  of  the  excretions  is  even  more  strik- 
ingly modified  by  exercise,  which,  within  physiological  limits,  increases  the 
vigor  of  the  system,  provided  the  increased  quantity  of  food  required  be 
supplied. 

While  a  certain  amount  of  waste  of  the  system  is  inevitable,  it  is  a  con- 
servative provision,  that  when  the  supply  of  new  material  is  diminished,  life 
is  preserved — not,  indeed,  in  all  its  vigor — by  a  corresponding  reduction 
in  the  quantity  of  excretions  ;  and  in  the  same  way,  the  forces  are  retained 
after  complete  deprivation  of  food  much  longer  than  if  disassimilation  pro- 
ceeded always  with  the  same  activity. 

As  regards  the  quantity  of  food  necessary  to  maintain  the  system  in 
proper  condition,  it  is  evident  that  this  must  be  greatly  modified  by  habit, 
climate,  the  condition  of  the  muscular  system,  age,  sex  etc.,  as  well  as  by 
idiosyncrasies. 

The  daily  loss  of  substance  which  must  be  supplied  by  matters  introduced 
from  without  is  very  great.  A  large  portion  of  this  discharge  takes  place  by 
the  lungs,  and  a  consideration  of  the  mode  of  introduction  of  gases  to  supply 
part  of  this  waste  belongs  to  the  subject  of  respiration.  The  most  abundant 
discharge  which  is  compensated  by  absorption  from  the  alimentary  canal  is 
that  of  water,  both  in  a  liquid  and  vaporous  condition.  The  entire  quantity 
of  water  daily  removed  from  the  system  has  been  estimated  at  about  four  and 
a  half  pounds  (2,041  grammes),  and  it  is  probable  that  about  the  same  quan- 
tity is  introduced  in  the  form  of  drink  and  as  a  constituent  of  the  so-called 
solid  articles  of  food.  The  quantity  which  is  taken  in  the  form  of  drink 
varies  with  the  character  of  the  food.  When  the  solid  articles  contain  a 
large  proportion  of  water,  the  quantity  of  drink  may  be  diminished ;  and  it  is 
possible,  by  taking  a  large  quantity  of  the  watery  vegetables,  to  exist  entirely 
without  drink.  There  is  no  article  more  frequently  taken  than  water,  merely 
as  a  matter  of  habit,  any  excess  being  readily  removed  by  the  kidneys,  skin 
and  lungs.  Dalton  estimates  the  daily  quantity  necessary  for  a  full-grown, 
healthy  male,  at  fifty-four  fluid  ounces  (1,530  grammes),  or  3-38  pounds. 

The  quantity  of  solid  food  necessary  to  the  proper  nourishment  of  the 
body  is  shown  by  estimating  the  solid  matter  in  the  excretions ;  and  the 
facts  thus  ascertained  correspond  very  closely  with  the  quantity  of  material 
which  the  system  has  been  found  to  actually  demand.  The  estimates  of 
Payen,  the  quantity  of  carbon  and  of  nitrogenized  matter  in  a  dry  state 
being  given,  are  generally  quoted  and  adopted  in  works  on  physiology.  Ac- 
cording to  this  observer,  the  following  are  the  daily  losses  of  the  organism : 

Carbon  (or  its  (  Respiration,  8-825  oz.  (250  grammes)  )  _  <10.941  oz  (310  grammes). 

equivalent).  (  Excretions,    2'116  oz.  (  60  grammes)  ) 
Nitrogenized  substances  (containing  308*64  grains, 

or  20  grammes  of  nitrogen) 4-586  oz.  (130  grammes). 

15-527  oz.  (440  grammes). 

From  this  he  estimates  that  the  normal  ration,  supposing  the  food  to 
consist  of  lean  meat  and  bread,  is  as  follows : 


NECESSARY  QUANTITY  AND    VARIETY  OF  FOOD.          183 

Bread 35-300  oz.  (1,000  grammes). 

Meat  (without  bones) 10-088  oz.     (286  grammes). 

45-388  oz.  (1,286  grammes). 

Nitrogenized  substances.  Carbon. 

Bread  contains 2-469  oz.    (70-00  grammes)  and  10-582  oz.  (300-00  grammes). 

Meat  contains  . .    . .  2-125  oz.    (60-26  grammes)  and    1-109  oz.    (31-46  grammes). 

4-594  oz.  (130-26  grammes)  and  11-691  oz.  (331-46  grammes). 

This  daily  ration,  which  is  purely  theoretical,  is  shown  by  actual  observa- 
tion to  be  nearly  correct.  Dalton  says  :  "  According  to  our  own  observa- 
tions, a  man  in  full  health,  taking  active  exercise  in  the  open  air,  and  re- 
stricted to  a  diet  of  bread,  fresh  meat,  and  butter,  with  water  and  coffee  for 
drink,  consumes  the  following  quantities  per  day : 

Meat 453  grammes,  or  about  16  oz. 

Bread 540          "              "        19  oz. 

Butter  or  fat 100          "              "       3-5  oz. 

Water 1,530          "              "        54  oz. 

Bearing  in  mind  the  great  variations  in  the  nutritive  demands  of  the  sys- 
tem in  different  persons,  it  may  be  stated,  in  general  terms,  that  in  an  adult 
male,  ten  to  twelve  ounces  (282  to  340  grammes)  of  carbon  and  four  to  five 
ounces  (113  to  142  grammes)  of  nitrogenized  matter,  estimated  dry,  are  dis- 
charged from  the  organism  and  must  be  replaced  by  the  ingesta ;  and  this 
demands  a  daily  consumption  of  between  two  and  three  pounds  (907  and 
1,361  grammes)  of  solid  food,  the  quantity  of  food  depending,  of  course, 
greatly  on  its  proportion  of  solid,  nutritive  constituents. 

It  is  undoubtedly  true  that  the  daily  ration  has  frequently  been  dimin- 
ished considerably  below  the  physiological  standard,  in  charitable  institutions, 
prisons  etc. ;  but  when  there  is  complete  inactivity  of  body  and  mind,  this 
produces  no  other  effect  than  that  of  slightly  diminishing  the  weight  and 
strength.  The  system  then  becomes  reduced  without  any  actual  disease,  and 
there  is  simply  a  diminished  capacity  for  labor ;  but  in  the  alimentation  of 
large  bodies  of  men  subjected  to  exposure  and  frequently  called  upon  to  per- 
form severe  labor,  the  question  of  food  is  of  great  importance,  and  the  men 
collectively  are  like  a  powerful  machine  in  which  a  certain  quantity  of  ma- 
terial must  be  furnished  in  order  to  produce  the  required  amount  of  force. 
This  important  physiological  fact  is  strikingly  exemplified  in  armies ;  and 
the  history  of  the  world  presents  few  examples  of  warlike  operations  in  which 
the  efficiency  of  the  men  has  not  been  impaired  by  insufficient  food. 

The  influence  of  diet  upon  the  capacity  for  labor  was  well  illustrated  by  a 
comparison  of  the  amount  of  work  accomplished  by  English  and  French 
laborers,  in  1841,  on  a  railway  from  Paris  to  Rouen.  The  French  laborers 
engaged  on  this  work  were  able  at  first  to  perform  only  about  two-thirds  of 
the  labor  accomplished  by  the  English.  It  was  suspected  that  this  was  due 
to  the  more  substantial  diet  of  the  English,  which  proved  to  be  the  fact ; 
for  when  the  French  laborers  were  subjected  to  a  similar  regimen,  they 
were  able  to  accomplish  an  equal  amount  of  work.  In  all  observations  of 


184  ALIMENTATION. 

this  kind,  it  has  been  shown  than  an  animal  diet  is  much  more  favorable  to 
the  development  of  the  physical  forces  than  one  consisting  mainly  of  vege- 
tables. 

Climate  has  an  important  influence  on  the  quantity  of  food  demanded  by 
the  system.  It  is  generally  acknowledged  that  the  consumption  of  all  kinds 
of  food  is  greater  in  cold  than  in  warm  climates,  and  almost  every  one  has 
experienced  in  his  own  person  a  considerable  difference  in  the  appetite  at 
different  seasons  of  the  year.  Travelers'  accounts  of  the  quantity  of  food 
taken  by  the  inhabitants  of  the  frigid  zone  are  almost  incredible.  They  speak 
of  men  consuming  more  than  a  hundred  pounds  (45-36  kilos.)  of  meat  in  a 
day ;  and  a  Russian  admiral,  Saritcheff,  gave  an  instance  of  a  man  who,  in 
his  presence,  ate  at  a  single  meal  a  mess  of  boiled  rice  and  butter  weighing 
twenty-eight  pounds  (12'7  kilos.).  Although  it  is  difficult  to  regard  these 
statements  with  entire  confidence,  the  general  opinion  that  the  appetite  is 
greater  in  cold  than  in  warm  climates  is  undoubtedly  well  founded. 
Hayes  stated,  from  his  personal  observation,  that  the  daily  ration  of  the  Es- 
quimaux is  twelve  to  fifteen  pounds  (5-443  to  6*804  kilos.),  of  meat,  about 
one-third  of  which  is  fat.  On  one  occasion  he  saw  an  Esquimau  consume 
ten  pounds  (4-536  kilos.)  of  walrus-flesh  and  blubber  at  a  single  meal,  which 
lasted,  however,  several  hours.  The  continued  low  temperature  he  found 
had  a  remarkable  effect  on  the  tastes  of  his  own  party.  With  the  thermom- 
eter ranging  from-60°  to— 70°  Fahr.  (—51°  to-57°  C.),  there  was  a  persist- 
ent craving  for  a  strong  animal  diet,  particularly  fatty  substances.  Some 
members  of  the  party  were  in  the  habit  of  drinking  the  contents  of  the  oil- 
kettle  with  evident  relish. 

Necessity  of  a  Varied  Diet. — In  considering  the  nutritive  value  of  the 
various  alimentary  substances,  the  fact  that  no  single  one  of  them  is  capable 
of  supplying  all  the  material  for  the  regeneration  of  the  organism  has  fre- 
quently been  mentioned.  The  normal  appetite,  which  is  the  best  guide  as 
regards  the  quantity  and  the  selection  of  food,  indicates  that  a  varied  diet  is 
necessary  to  proper  nutrition.  This  fact  is  exemplified  in  a  marked  degree 
in  long  voyages  and  in  the  alimentation  of  armies,  when,  from  necessity  or 
otherwise,  the  necessary  variety  of  aliment  is  not  presented.  Analytical  chem- 
istry fails  to  show  why  this  change  in  alimentation  is  necessary  or  in  what 
the  deficiency  in  a  single  kind  of  diet  consists ;  but  it  is  nevertheless  true 
that  after  the  organic  constituents  of  the  organism  have  appropriated  the 
nutritious  elements  of  particular  kinds  of  food  for  a  certain  time,  they  lose 
the  power  of  effecting  the  changes  necessary  to  proper  nutrition.  This  fact 
is  particularly  well  marked  when  the  diet  consists  in  great  part  of  salted 
meats,  although  it  sometimes  occurs  when  a  single  kind  of  fresh  meat  is  con- 
stantly used.  After  long  confinement  to  a  diet  restricted  as  regards  variety, 
a  supply  of  other  matters,  such  as  fresh  vegetables,  the  organic  acids,  and 
articles  which  are  called  generally  antiscorbutics,  becomes  indispensable; 
otherwise,  the  modifications  in  nutrition  and  in  the  constitution  of  the  blood 
incident  to  the  scorbutic  condition  are  almost  always  developed. 

It  is  thus  apparent  that  adequate  quantity  and  proper  quality  of  food  are 


MEATS,  BREAD  ETC.  185 

not  all  that  is  required  in  alimentation ;  and  those  who  have  the  responsi- 
bility of  regulating  the  diet  of  a  large  number  of  persons  must  bear  in  mind 
the  fact  that  the  organism  demands  considerable  variety.  Fresh  vegetables, 
fruits  etc.,  should  be  taken  at  the  proper  seasons.  It  is  almost  always  found, 
when  there  is  of  necessity  some  sameness  of  diet,  that  there  is  a  craving  for 
particular  articles,  and  these,  if  possible,  should  be  supplied.  This  was  fre- 
quently exemplified  in  the  civil  war.  At  times  when  the  diet  was  necessarily 
somewhat  monotonous,  there  was  an  almost  universal  craving  for  onions  and 
raw  potatoes,  which  were  found  by  army  surgeons  to  be  excellent  antiscor- 
butics. 

With  those  who  supply  their  own  food,  the  question  of  variety  of  diet 
generally  regulates  itself ;  and  in  institutions,  it  is  a  good  rule  to  follow  as 
far  as  possible  the  reasonable  tastes  of  the  inmates.  In  individuals,  particu- 
larly females,  it  is  not  uncommon  to  observe  marked  disorders  in  nutrition 
attributable  to  want  of  variety  in  the  diet  as  well  as  to  an  insufficient  quan- 
tity of  food  as  a  matter  of  education  or  habit. 

A  full  consideration  of  the  varieties  of  food  and  of  the  different  methods 
employed  in  its  preparation  belongs  properly  to  special  works  on  dietetics. 
Among  the  ordinary  articles  of  diet,  the  most  important  are  meats,  bread, 
potatoes,  milk,  butter  and  eggs ;  and  it  is  necessary  only  to  treat  of  these 
very  briefly. 

Meats. — Among  the  various  kinds  of  muscular  tissue,  beef  has  been  found 
to  possess  the  greatest  nutritive  value.  Other  varieties  of  flesh,  even  that  of 
birds,  fishes  and  animals  in  a  wild  state,  do  not  present  an  appreciable  differ- 
ence, as  far  as  can  be  ascertained  by  chemical  analysis ;  but  when  taken  daily 
for  a  long  time,  they  become  distasteful,  the  appetite  fails,  and  the  system 
seems  to  demand  a  change  of  diet.  The  flesh  of  carnivorous  animals  is  rarely 
used  as  food ;  and  animals  that  eat  animal  as  well  as  vegetable  food,  such  as 
pigs  or  ducks,  acquire  a  disagreeable  flavor  when  they  are  not  fed  on  vege- 
tables. Soups,  broths,  and  most  of  the  liquid  extracts  of  meat  really  pos- 
sess but  little  nutritive  value  and  they  can  not  replace  the  ordinary  cooked 
meats.  The  following  is  the  composition  of  roasted  meat,  no  dripping  be- 
ing lost,  according  to  the  analysis  of  Ranke,  quoted  by  Pavy : 

Nitrogenous  matters 27-60 

Fat 15-45 

Saline  matters 2-95 

Water  .  54-00 


100-00 

Bread. — Bread  presents  a  considerable  variety  of  alimentary  constituents 
and  is  a  very  important  article  of  diet.  The  constituents  of  flour  undergo 
peculiar  changes  in  panification,  which  give  to  good  bread  its  character- 
istic flavor.  Bread,  especially  coarse,  brown  bread,  as  a  single  article  of 
food,  is  capable  of  sustaining  life  for  a  long  time.  It  contains  a  large  pro- 
portion of  starch,  but  its  important  nitrogenized  constituent  is  gluten,  which 
is  not  a  simple  substance  but  contains  vegetable  fibrin,  vegetable  albumm,  a 


186  ALIMENTATION. 

peculiar  substance  soluble  in  alcohol,  called  glutine,  with  fatty  and  inorganic 
matters.     The  following  is  the  composition  of  bread,  according  to  Letheby : 

Nitrogenized  matters 8*1 

Carbohydrates  (chiefly  starch) 51-0 

Fatty  matters 1-6 

Saline  matters 2-3 

Water  . .  37-0 


100-0 

Potatoes. — Potatoes  are  very  useful  as  an  article  of  diet,  especially  on 
account  of  the  agreeable  form  in  which  starchy  matter  is  presented ;  for  they 
contain  but  a  small  proportion  of  nitrogenized  matter  and  do  not  possess  as 
much  nutritive  value  as  exists  in  bread.  They  are  selected  for  description 
from  the  vegetable  foods  for  the  reason  that  they  are  almost  universally  used 
in  civilized  countries  throughout  the  year.  They  are  usually  cooked  thor- 
oughly, but  the  raw  potato  is  a  valuable  antiscorbutic.  The  following  is  the 
composition  of  potato,  according  to  Letheby  : 

Nitrogenized  matter 2'1 

Starchy  matters 18'8 

Sugar 3-2 

Fat 0-2 

Saline  matters 0*7 

Water  . .  75-0 


1000 

Milk. — Milk,  and  articles  prepared  from  milk,  such  as  butter,  cheese  etc., 
are  important  articles  of  food.  In  the  treatment  of  disease,  milk  is  frequently 
used  as  a  single  article  of  diet.  On  account  of  the  great  variety  of  aliment- 
ary matters  which  it  contains,  including  a  great  number  of  inorganic  salts 
and  even  a  small  quantity  of  iron,  milk  will  meet  all  the  nutritive  demands 
of  the  system,  probably  for  an  indefinite  time.  It  is  largely  used  in  the  prep- 
aration of  other  articles  of  food  by  cooking.  Pure  butter,  which  represents 
the  fatty  constituents  of  milk,  contains,  in  100  parts,  30  parts  of  oleine,  68 
parts  of  palmitine,  and  2  parts  of  other  fats  peculiar  to  milk  (Bromeis). 
The  following  is  the  composition  of  cow's  milk,  according  to  Letheby : 

Nitrogenized  matters 4-1 

Fatty  matters 3-9 

Sugar 5-2 

Inorganic  matters 0-8 

Water  . .                                                                 86-0 


100-0 


In  connection  with  the  composition  of  human  milk,  to  be  given  farther 
on,  the  great  variety  of  its  constituents  will  be  more  fully  considered,  -jji^  ? 

Eggs. — As  regards  nutrition,  the  analogy  between  eggs  and  butter  is  evi- 
dent when  it  is  remembered  that  the  constituents  of  eggs  furnish  materials 
for  the  growth  of  the  chick,  to  which  must  be  added  certain  saline  matters 


MEATS,  BREAD  ETC.  187 

absorbed  from  the  shell  during  the  process  of  incubation.  Among  the  inor- 
ganic constituents  of  eggs,  there  is  always  a  small  quantity  of  iron.  The 
following  is  the  composition  of  the  entire  contents  of  the  egg,  quoted  from 
Pavy : 

Nitrogenized  matters 14-0 

Fatty  matters 10-5 

Inorganic  matters 1'5 

Water  . .  74'0 


100-0 

A  number  of  different  nitrogenized  and  fatty  matters,  a  small  quantity  of 
saccharine  matter,  as  well  as  a  great  variety  of  inorganic  salts,  exist  in  eggs. 

The  physiological  effects  of  a  diet  restricted  to  a  single  constituent  of  food 
or  to  a  few  articles  have  been  closely  studied  both  in  the  human  subject  and 
in  the  inferior  animals.  Animals  subjected  to  a  diet  composed  exclusively 
of  non-nitrogenized  matters  die  in  a  short  time  with  all  the  symptoms  of 
inanition.  The  same  result  follows  when  dogs  are  confined  to  white  bread 
and  water ;  but  these  animals  live  very  well  on  the  military  brown  bread,  as 
this  contains  a  greater  variety  of  alimentary  matters  (Magendie).  Facts  of 
this  nature  were  multiplied  by  the  "  gelatine  commission,"  and  the  experi- 
ments were  extended  to  nitrogenized  substances  and  articles  containing  a 
considerable  variety  of  alimentary  matters.  In  these  experiments,  it  was 
shown  that  dogs  could  not  live  on  a  diet  of  pure  myosine,  the  appetite  en- 
tirely failing  at  the  forty-third  to  the  fifty-fifth  day.  They  were  nourished 
perfectly  well  by  gluten,  which  is  composed  of  a  number  of  different  ali- 
mentary substances.  Among  the  conclusions  arrived  at  by  this  commission, 
which  bear  particularly  011  the  questions  under  consideration,  were  the  fol- 
lowing : 

"  Gelatine,  albumin,  fibrin,  taken  separately,  do  not  nourish  animals  ex- 
cept for  a  very  limited  period  and  in  a  very  incomplete  manner.  In  general, 
these  substances  soon  excite  an  insurmountable  disgust,  to  the  point  that  ani- 
mals prefer  to  die  of  hunger  rather  than  touch  them. 

"  The  same  substances  artificially  combined  and  rendered  agreeably  sapid 
by  seasoning  are  accepted  more  readily  and  longer  than  if  they  were  isolated, 
but  ultimately  they  have  no  better  influence  on  nutrition,  for  animals  that 
take  them,  even  in  considerable  quantity,  finally  die  with  all  the  signs  of 
complete  inanition. 

"  Muscular  flesh,  in  which  gelatine,  albumin  and  fibrin  are  united  accord- 
ing to  the  laws  of  organic  nature,  and  when  they  are  associated  with  other 
matters,  such  as  fat,  salts  etc.,  suffices,  even  in  very  small  quantity,  for  com- 
plete and  prolonged  nutrition." 

In  Burdach's  treatise  on  physiology,  is  an  account  of  some  interesting 
experiments  by  Ernest  Burdach  on  rabbits,  showing  the  influence  of  a  re- 
stricted diet  upon  nutrition.  Three  young  rabbits  from  the  same  litter  were 
experimented  upon.  One  was  fed  with  potato  alone  and  died  on  the  thir- 


188  ALIMENTATION. 

teenth  day,  with  all  the  appearances  of  inanition.  Another  fed  on  barley 
alone  died  in  the  same  way  during  the  fourth  week.  The  third  was  fed 
alternately  day  by  day  with  potato  and  barley,  for  three  weeks,  and  afterward 
with  potato  and  barley  given  together.  This  animal  increased  in  size  and 
was  perfectly  well  nourished. 

In  1769,  long  before  any  of  the  above-mentioned  experiments  were  per- 
formed, Dr.  Stark,  a  young  English  physiologist,  fell  a  victim  at  an  early  age 
to  experiments  on  his  own  person  on  the  physiological  effects  of  different 
kinds  of  food.  He  lived  for  forty-four  days  on  bread  and  water,  for  twenty- 
nine  days  on  bread,  sugar  and  water,  and  for  twenty-four  days  on  bread, 
water  and  olive-oil ;  until  finally  his  constitution  became  broken,  and  he  died 
from  the  effects  of  his  experiments. 


CHAPTER   VII. 

DIGESTION— MASTICATION,  INSALIVATION  AND  DEGLUTITION. 

Prehension  of  food— Mastication— Physiological  anatomy  of  the  teeth— Anatomy  of  the  maxillary  bones — 
Temporo-maxillary  articulation— Muscles  of  mastication— Action  of  the  tongue,  lips  and  cheeks  in 
mastication— Parotid  saliva — Submaxillary  saliva — Sublingual  saliva— Fluids  from  the  smaller  glands  of 
the  mouth,  tongue  and  fauces — Mixed  saliva — Quantity  of  saliva — General  properties  and  composition 
of  the  saliva — Action  of  the  saliva  on  starch — Uses  of  the  saliva — Physiological  anatomy  of  the  parts 
concerned  in  deglutition— Mechanism  of  deglutition— First  period  of  deglutition— Second  period  of  deg- 
lutition—Protection of  the  posterior  nares  during  the  second  period  of  deglutition— Protection  of  the 
opening  of  the  larynx  and  uses  of  the  epiglottis  in  deglutition— Third  period  of  deglutition — Deglutition 
of  air. 

INORGANIC  alimentary  substances  are,  with  few  exceptions,  introduced 
in  the  form  in  which  they  exist  in  the  blood  and  require  no  preparation  or 
change  before  they  are  absorbed ;  but  organic  nitrogenized  substances  are 
always  united  with  more  or  less  matter  possessing  no  nutritive  properties, 
from  which  they  must  be  separated,  and  even  when  pure,  they  always  undergo 
certain  changes  before  they  are  taken  up  by  the  blood.  The  non-nitrogenized 
matters  also  undergo  changes  in  constitution  or  in  form  preparatory  to  ab- 
sorption. 

Prehension  of  Food. — Prehension  of  food  in  the  adult  is  a  process  so 
simple  and  well  known  that  it  demands  little  more  than  a  passing  mention. 
The  mechanism  of  sucking  in  the  infant  and  of  drinking  is  a  little  more 
complicated.  In  sucking,  the  lips  are  closed  around  the  nipple,  the  velum 
pendulum  palati  is  applied  to  the  back  of  the  tongue  so  as  to  close  the  buccal 
cavity  posteriorly,  and  the  tongue,  acting  as  a  piston,  produces  a  virtual 
vacuum  in  the  mouth,  by  which  the  liquids  are  drawn  in  with  considerable 
force.  This  may  be  done  independently  of  the  act  of  respiration,  which  is 
necessarily  arrested  only  during  deglutition ;  for  the  mere  act  of  suction  has 
never  anything  to  do  with  the  condition  of  the  thoracic  walls.  The  mechan- 
ism of  drinking'  from  a  vessel  is  essentially  the  same.  The  vessel  is  inclined 


MASTICATION.  189 

so  that  the  lips  are  kept  covered  with  the  liquid  and  are  closed  around  the 
edge.  By  a  gentle,  sucking  action  the  liquid  is  then  introduced.  This  is 
the  ordinary  mechanism  of  drinking ;  but  sometimes  the  head  is  thrown  back 
and  the  liquid  is  poured  into  the  mouth,  as  in  "  tossing  off  "  the  contents  of 
a  small  vessel. 

MASTICATIOX. 

In  order  that  digestion  may  take  place  in  a  perfectly  natural  manner,  it 
is  necessary  that  the  food,  as  it  is  received  into  the  stomach,  should  be  so  far 
comminuted  and  incorporated  with  the  fluids  of  the  mouth  as  to  be  readily 
acted  upon  by  the  gastric  juice ;  otherwise,  gastric  digestion  is  prolonged  and 
difficult.  Non-observance  of  this  physiological  law  is  a  frequent  cause  of 
what  is  generally  called  dyspepsia. 

Physiological  Anatomy  of  the  Organs  of  Mastication. — In  the  adult,  each 
jaw  is  provided  with  sixteen  teeth,  all  of  which  are  about  equally  developed. 
The  canines,  so  largely  developed  in  the  carnivora  but  which  are  rudimentary 
in  the  herbivora,  and  the  incisors  and  molars,  so  fully  developed  in  the  her- 
bivora,  are,  in  man,  of  nearly  the  same  length.  Each  tooth  presents  for  ana- 
tomical description  a  crown,  a  neck  and  a  root,  or  fang.  The  crown  is  that 
portion  which  is  entirely  uncovered  by  the  gums ;  the  root  is  that  portion 
embedded  in  the  alveolar  cavities  of  the  maxillary  bones ;  and  the  neck  is 
the  portion,  sometimes  slightly  constricted,  situated  between  the  crown  and 
the  root  and  covered  by  the  edge  of  the  gum.  Each  tooth  presents,  on  sec- 
tion, several  distinct  structures. 

Enamel  of  the  Teeth. — The  crown  is  covered  by  the  enamel,  which  is  by 
far  the  hardest  structure  in  the  economy.  This  is  white  and  glistening  and 
is  thickest  on  the  lower  portion  of  the  tooth,  especially  over  the  surfaces 
which,  from  being  opposed  to  each  other  on  either  jaw,  are  most  exposed  to 
wear.  It  here  exists  in  several  concentric  layers.  The  incrustation  of  enamel 
becomes  gradually  thinner  toward  the  neck,  where  it  ceases.  The  enamel  is 
made  up  of  pentagonal  or  hexagonal  rods,  one  end  resting  upon  the  subjacent 
structure,  and  the  other,  when  there  exists  but  a  single  layer  of  enamel,  ter- 
minating just  beneath  the  cuticle  of  the  teeth. 

The  exposed  surfaces  of  the  teeth  are  still  farther  protected  by  a 
membrane,  -OUTFIT  to  TTJrnr  of  an  inch  (0*8  to  1-7  /*)  in  thickness,  closely 
adherent  to  the  enamel,  called  the  cuticle  of  the  enamel  (Nasmyth's  mem- 
brane). The  cuticle  presents  a  strong  resistance  to  reagents  and  is  useful  in 
protecting  the  teeth  from  the  action  of  acids  which  may  find  their  way  into 
the  mouth. 

Dentine. — The  largest  portion  of  the  teeth  is  composed  of  dentine,  or 
ivory.  In  many  respects,  particularly  in  its  composition,  this  resembles  bone ; 
but  it  is  much  harder  and  does  not  possess  the  lacunas  and  canaliculi  which 
are  characteristic  of  the  true  osseous  structure.  The  dentine  bounds  and 
encloses  the  central  cavity  of  the  tooth,  extending  in  the  crown  to  the  enamel, 
and  in  the  root,  to  the  cement.  It  is  formed  of  a  homogeneous,  fundamental 
substance,  which  is  penetrated  by  a  large  number  of  canals  radiating  from 
14 


190    DIGESTION— MASTICATION,   INSALIVATION,  DEGLUTITION. 


the  pulp-cavity  toward  the  exterior.  These  are  called  the  dentinal  tubules  or 
canals.  They  are  2g^00  to  T2^00  of  an  inch  (1  to  3  /*)  in  diameter,  with 
walls  of  a  thickness  a  little  less  than  their  caliber.  Their  course  .is  slightly 
wavy  or  spiral.  Beginning  at  the  pulp-cavity,  into  which  these  canals  open, 
they  are  found  to  branch  and  occasionally  anastomose,  their  communications 
and  branches  becoming  more  frequent  as  they  approach  the  external  surface 
of  the  tooth.  The  canals  of  largest  diameter  are  found  next  the  pulp-cavity, 
and  they  become  smaller  as  they  branch.  The  structure  which  forms  the 
walls  of  these  tubules  is  somewhat  denser  than  the  intermediate  portion, 
which  is  sometimes  called  the  intertubular  substance  of  the  dentine ;  but  in 

some  portions  of  the  tooth,  the  tu- 
bules are  so  abundant  that  their 
walls  touch  each  other,  and  there 
is,  therefore,  no  intertubular  sub- 
stance. Near  the  origin  and  near 
the  peripheral  terminations  of  the 
dentinal  tubules,  are  sometimes 
found  solid,  globular  masses  of 
dentine,  called  dentine  -  globules, 
which  irregularly  bound  triangular 
or  stellate  cavities  of  very  variable 
size.  Sometimes  these  cavities  form 
regular  zones  near  the  peripheral 
termination  of  the  tubules.  The 
dentine  is  sometimes  marked  by 
concentric  lines,  indicating  a  lam- 
ellated  arrangement.  In  the  nat- 
ural condition,  the  dentinal  tubules 
are  filled  with  a  clear  liquid,  which 
penetrates  from  the  vascular  struct- 
ures in  the  pulp-cavity. 

Cement. — Covering  the  dentine 
of  the  root,  is  a  thin  layer  of  true 
bony  structure,  called  the  cement, 
or  crusta  petrosa.  This  is  thickest 
at  the  summit  and  at  the  deeper 
portions  of  the  root,  where  it  is 
sometimes  lamellated,  and  it  be- 
comes thinner  near  the  neck.  It 

finallJ    becomes     Continuous     with 

1,  enamel ;  2,  dentine  ;  3,  cement :  4,  periosteum  of  the  the   enamel    of   the    Crown,  SO   that 
alveolar  cavity  ;  5,  lower  jaw  ;  6,  pulp-cavity. 

the  dentine  is  everywhere  com- 
pletely covered.  The  cement  is  closely  adherent  to  the  dentine  and  to  the 
periosteum  lining  the  alveolar  cavities. 

Pulp-Cavity. — In  the  interior  of  each  tooth,  extending  from  the  apex  of 
the  root  or  roots  into  the  crown,  is  the  pulp-cavity,  which  contains  minute 


MASTICATION.  191 

blood-vessels  and  nervous  filaments,  held  together  by  longitudinal  fibres  of 
connective  tissue.  This  is  the  only  portion  of  the  tooth  endowed  with  sensi- 
bility. The  blood-vessels  and  nerves  penetrate  by  a  little  orifice  at  the  ex- 
tremity of  each  root. 

The  dentine  and  enamel  of  the  teeth  must  be  regarded  as  perfected  struct- 
ures ;  for  when  the  second,  or  permanent  teeth  are  lost,  they  are  never  re- 
produced, and  when  these  parts  are  invaded  by  wear  or  by  decay,  they  are 
not  restored. 

The  thirty-two  permanent  teeth  are  classified  as  follows : 

1.  Eight  incisors,  four  in  each  jaw,  called  the  central  and  lateral  incisors. 

2.  Four  canines,  or  cuspidati,  two  in  each  jaw,  just  back  of  the  incisors. 
The  upper  canines  are  sometimes  called  the  eye-teeth,  and  the  lower  canines, 
the  stomach-teeth. 

3.  Eight  bicuspid — the  small,  or  false  molars — just  back  of  the  canines ; 
four  in  each  jaw. 

4.  Twelve  molars,  or  multicuspid,  situated  just  back  of  the  bicuspid ;  six 
in  each  jaw. 

The  incisors  are  wedge-shaped,  flattened  antero-posteriorly,  and  bevelled 
at  the  expense  of  the  posterior  face,  giving  them  a  sharp,  cutting  edge,  which 
is  sometimes  perfectly  straight  but  is  generally  more  or  less  rounded.  Each 
incisor  has  a  single  root.  The  special  use  of  the  incisor  teeth  is  to  divide  the 
food  as  it  is  taken  into  the  mouth.  The  permanent  incisors  make  their  ap- 
pearance between  the  seventh  and  the  eighth  years. 

The  canines  are  more  conical  and  pointed  than  the  incisors,  and  have 
longer  and  larger  roots,  especially  those  in  the  upper  jaw.  Their  roots  are 
single.  They  are  used,  with  the  incisors,  in  dividing  the  food.  The  perma- 
nent canines  make  their  appearance  between  the  eleventh  and  the  twelfth 
years. 

The  bicuspid  teeth  are  shorter  and  thicker  than  the  canines.  Their  op- 
posed surfaces  are  rather  broad  and  are  marked  by  two  eminences.  The 
upper  bicuspids  are  larger  than  the  lower.  The  roots  are  single,  but  in  the 
upper  jaw  they  are  slightly  bifurcated  at  their  extremities.  They  are  used, 
with  the  true  molars,  in  triturating  the  food.  The  permanent  bicuspids 
make  their  appearance  between  the  ninth  and  the  tenth  years. 

The  molar  teeth,  called  respectively — counting  from  before  backward — 
the  first,  second  and  third  molars,  are  the  largest  of  all  and  are,  par  excel- 
lence, the  teeth  used  in  mastication.  Their  form  is  that  of  a  cube,  rounded 
laterally  and  provided  with  four  or  five  eminences  on  their  opposed  surfaces. 
The  first  molars  are  the  largest.  They  have  generally  three  roots  in  the 
upper  jaw  and  two  in  the  lower,  although  they  sometimes  have  four  or  even 
five  roots.  The  second  molars  are  but  little  smaller  than  the  first  and  resem- 
ble them  in  nearly  every  particular.  The  third  molars,  called  frequently  the 
wisdom-teeth,  are  much  smaller  than  the  others  and  are  by  no  means  so  use- 
ful in  mastication.  The  first  molars  are  the  first  of  the  permanent  teeth, 
making  their  appearance  between  the  sixth  and  the  seventh  years.  The  sec- 
ond molars  appear  between  the  twelfth  and  the  thirteenth  years;  and  the 


192    DIGESTION— MASTICATION,  INSALIVATION,  DEGLUTITION. 

third  molars,  between  the  seventeenth  and  the  twenty-first  years,  and  some- 
times even  much  later.  In  some  instances  the  third  molars  are  never  de- 
veloped. 

The  upper  jaw  has  ordinarily  a  somewhat  longer  and  broader  arch  than 
the  lower;  so  that  when  the  mouth  is  closed  the  teeth  are  not  brought 
into  exact  apposition,  but  the  upper  teeth  overlap  the  lower  teeth  both,  in 
front  and  laterally.  The  lower  teeth  are  all  somewhat  smaller  than  the  cor- 
responding teeth  in  the  upper  jaw  and  generally  make  their  appearance  a 
little  earlier. 

The  physiological  anatomy  of  the  maxillary  bones  and  of  the  temporo- 
maxillary  articulation  necessarily  precedes  the  study  of  the  muscles  of  masti- 
cation and  the  mechanism  of  their  action. 

The  superior  maxillary  bones  are  immovably  articulated  with  the  other 
bones  of  the  head,  and  do  not  usually  take  any  active  part  in  mastication. 
Their  inferior  borders,  with  the  upper  teeth  embedded  in  the  alveolar  cavi- 
ties, present  fixed  surfaces  against  which  the  food  is  pressed  by  the  action  of 
the  muscles  which  move  the  lower  jaw. 

The  inferior  maxilla  is  a  single  bone.  Its  body  is  horizontal,  of  a  horse- 
shoe shape,  and  in  the  alveolar  cavities  in  its  superior  border,  are  the  lower 
teeth.  Below  the  teeth,  both  externally  and  internally,  are  surfaces  for  the 

attachments  of  the  muscles  concerned  in 
the  various  movements  of  the  jaw  and  for 
one  of  the  muscles  of  the  tongue. 

Temporo- Maxillary  A  rticulation. — In 
man  the  articulation  of  the  lower  jaw  with 
the  temporal  bone  is  such  as  to  allow  an 
autero-posterior  sliding  movement  and  a 
lateral  movement,  in  addition  to  the  move- 
ments of  elevation  and  depression.  The 
condyloid  process  is  convex,  with  an  ovoid 
surface,  the  general  direction  of  its  long 
FIG.  ^.-inferior  maxilla  (Sappey)  diameter  being  transverse,  and  slightly  ob- 

1,  body  ;  2,  ramus  ;  3,  symphysis  ;  4,  incisive  J 

fossa  ;  5,  mental  foramen  ;  6  attachment    lique  from  without  inward  and  from  before 
of  the  digastric  muscle  ;  7,  depression  at 

the  site  of  the  facial  artery :  8,  an^ie ;  9,   backward.     This  process  is  received  into  a 

attachment  of  the  superior  constrictor  A  . 

of  the  pharynx :  10,  coronoid  process ;   cavity  of  corresponding  shape  in  the  tem- 

11,  condyle  ;  12,  sisrmoid  notch  ;  13,  open- 

ing;  of  the   inferior   dental    canal  ;    14,    poral     bone,    the    glenOld    lOSSa,    WHICH    IS 

groove  for  the  mylo-hyoid  muscle  ;  15, 

alveolae  border ;  i,  incisor  teeth ;  c,  ca-   bounded  anteriorly  by  a  rounded  eminence, 

nine  teeth  ;  b.  bicuspid  teeth  ;  m,  molars.         n-,,i  •          ,  •          ,  •      i      • 

called  the  emmentia  articulans. 

Between  the  condyle  of  the  lower  jaw  and  the  glenoid  fossa,  is  an  oblong, 
interarticular  disk  of  fibro-cartilage.  This  disk  is  thicker  at  the  edges  than 
in  the  centre.  It  is  pliable  and  is  so  situated  that  when  the  lower  jaw  is  pro- 
jected forward,  making  the  lower  teeth  project  beyond  the  upper,  it  is  ap- 
plied to  the  convex  surface  of  the  eminentia  articularis  and  presents  a  con- 
cave surface  for  articulation  with  the  condyle.  One  of  the  uses  of  this 
cartilage  is  to  constantly  present  a  proper  articulating  surface  upon  the 
articular  eminence  and  thus  permit  the  antero-posterior  sliding  movement 


MASTICATION.  193 

of  the  lower  jaw.  It  is  also  important  in  the  lateral  movements  of  the  jaw, 
in  which  one  of  the  condylea  remains  in  the  glenoid  cavity  and  the  other  is 
projected,  so  that  the  bone  undergoes  a  slight  rotation. 

Muscles  of  Mastication. — To  the  lower  jaw  are  attached  certain  muscles 
by  which  it  is  depressed,  and  others  by  which  it  is  elevated,  projected  for- 
ward, drawn  backward  and  moved  from  side  to  side.  The  following  are  the 
principal  muscles  concerned  in  the  production  of  these  varied  movements : 

MUSCLES    OF    MASTICATION". 
Muscles  which  depress  the  lower  jaw. 

MUSCLE.  ATTACHMENTS. 

Digastric Mastoid  process  of  the  temporal  bone — Lower 

border  of  the  inferior  maxilla  near  the  symphy- 
sis,  with  its  central  tendon  held  to  the  side  of 
the  body  of  the  hyoid  bone. 

Mylo-hyoid Body  of  the  hyoid  bone — Mylo-hyoid  ridge  on  the 

internal  surface  of  the  inferior  maxilla. 

Genio-hyoid Body  of  the  hyoid  bone — Inferior  genial  tubercle 

on  the  inner  surface  of  the  inferior  maxilla,  near 
the  symphysis. 

Platysma  myoides Clavicle,  acromion  and  fascia — Anterior  half  of 

the  body  of  the  inferior  maxilla,  near  the  infe- 
rior border. 

Muscles  which  elevate  the  lower  jaw  and  move  it  laterally  and  antero-posteriorly. 

Temporal Temporal  fossa — Coronoid  process  of  the  inferior 

maxilla. 

Masseter Malar  process  of  the  superior  maxilla,  lower  border 

and  internal  surface  of  the  zygomatic  arch — 
Surface  of  the  ramus  of  the  inferior  maxilla. 

Internal  pterygoid  Pterygoid  fossa — Inner  side  of  the  ramus,  and 

angle  of  the  inferior  maxilla. 

External  pterygoid Pterygoid  ridge  of  the  sphenoid,  the  surface  be- 
tween it  and  the  pterygoid  process,  external 
pterygoid  plate,  tuberosity  of  the  palate  and  the 
superior  maxillary  bone — Inner  surface  of  the 
neck  of  the  condyle  of  the  inferior  maxilla  and 
the  interarticular  flbro-cartilage. 

Action  of  the  Muscles  which  depress  the  Lower  Jaw. — The  most  impor- 
tant of  these  muscles  have  for  their  fixed  point  of  action,  the  hyoid  bone, 
which  is  fixed  by  the  muscles  extending  from  it  to  the  upper  part  of  the 
chest.  The  central  tendon  of  the  digastric,  as  it  perforates  the  stylo-hyoid, 
is  connected  with  the  hyoid  bone  by  a  loop  of  fibrous  tissue ;  and  acting 
from  this  bone  as  the  fixed  point,  the  anterior  belly  must  of  necessity  tend 
to  depress  the  jaw.  The  attachments  of  the  mylo-hyoid  and  the  genio- 
hyoid  render  their  action  in  depressing  the  jaw  sufficiently  evident,  which 
is  also  the  case  with  the  platysma  myoides,  acting  from  its  attachments  to  the 
upper  part  of  the  thorax.  In  ordinary  mastication  the  upper  jaw  undergoes  a 
slight  movement  of  elevation,  and  this  becomes  somewhat  exaggerated  when 
the  mouth  is  opened  to  the  fullest  possible  extent. 


194    DIGESTION— MASTICATION,   INSALIVATION,  DEGLUTITION. 

Action  of  the  Muscles  which  elevate  the  Lower  Jaw  and  move  it  laterally 
and  antero-posteriorly. — The  temporal,  masseter  and  internal  pterygoid 
muscles  are  chiefly  concerned  in  the  simple  act  of  closing  the  jaws.  Their 
anatomy  alone  gives  a  sufficiently  clear  idea  of  their  mode  of  action ;  and 
their  great  power  is  explained  by  the  number  of  their  fibres,  by  the  attach- 
ments of  many  of  these  fibres  to  the  strong  aponeuroses  by  which  they  are 
covered,  and  by  the  fact  that  the  distance  from  their  origin  to  their  insertion 
is  very  short. 

The  attachments  of  the  internal  and  external  pterygoids  are  such  that  by 
their  alternate  action  on  either  side,  the  jaw  may  be  moved  laterally,  as  their 
points  of  origin  are  situated  in  front  of  and  internal  to  the  temporo-maxil- 
lary  articulation.  The  articulation  of  the  lower  jaw  is  of  such  a  kind  that 
in  its  lateral  movements  the  condyles  themselves  can  not  be  sufficiently  dis- 
placed from  side  to  side ;  but  with  the  condyle  on  one  side  fixed  or  moved 
slightly  backward,  the  other  may  be  brought  forward  against  the  articular 
eminence,  producing  a  movement  of  rotation. 

The  above  explanation  of  the  lateral  movements  of  the  jaw  presupposes 
the  possibility  of  movements  in  an  antero-posterior  direction.  Movements  in 
a  forward  direction,  so  as  to  make  the  lower  teeth  project  beyond  the  upper, 
are  effected  by  the  pterygoids,  the  oblique  fibres  of  the  masseter  and  the  an- 
terior fibres  of  the  temporal.  By  the  combined  action  of  the  posterior  fibres 
of  the  temporal,  the  digastric,  mylo-hyoid  and  genio-hyoid,  the  jaw  is  brought 
back  to  its  position.  By  the  same  action  it  may  also  be  drawn  back  slightly 
from  its  normal  position  while  at  rest. 

Action  of  the  Tongue,  Lips  and  Cheeks,  in  Mastication. — Experiments  on 
living  animals  and  phenomena  observed  in  cases  of  lesions  of  the  nervous 
system  in  the  human  subject  have  shown  the  importance  of  the  tongue  and 
cheeks  in  mastication.  Section  of  the  facial  nerves  is  a  common  physiologi- 
cal experiment.  Operations  of  this  kind,  and  cases  of  facial  palsy,  which  are 
not  uncommon  in  the  human  subject,  show  that  when  the  cheek  is  paralyzed 
the  food  accumulates  between  it  and  the  teeth,  producing  great  incon- 
venience. 

The  varied  and  complex  movements  of  the  tongue  during  mastication 
are  not  easily  described.  After  solid  food  is  taken  into  the  mouth,  the 
tongue  prevents  its  escape  from  between  the  teeth,  and  by  its  constant 
movements,  rolls  the  alimentary  bolus  over  and  over  and  passes  it  at 
times  from  one  side  to  the  other,  so  that  the  food  may  undergo  thorough 
trituration.  Aside  from  the  uses  of  the  tongue  as  an  organ  of  taste,  its  sur- 
face is  endowed  with  peculiar  sensibility  as  regards  the  consistence,  size  and 
form  of  different  articles ;  and  this  is  undoubtedly  important  in  determining 
when  mastication  is  completed,  although  the  thoroughness  with  which  mas- 
tication is  accomplished  is  much  influenced  by  habit. 

Tonic  contraction  of  the  orbicularis  oris  is  necessary  to  keep  the  fluids 
within  the  mouth  during  repose  ;  and  this  muscle  is  sometimes  brought  into 
action  when  the  mouth  is  very  full,  to  assist  in  keeping  the  food  between 
the  teeth.  This  latter  office,  however,  is  performed  mainly  by  the  buccina- 


SALIVA. 


195 


tor  ;  the  action  of  which  is  to  press  the  food  between  the  teeth  and  keep  it  in 
place  during  mastication,  assisting,  from  time  to  time,  in  turning  the  ali- 
mentary bolus  so  as  to  subject  new  portions  to  trituration. 

The  process  of  mastication  is  regulated  to  a  very  great  extent  by  the 
sensibility  of  the  teeth  to  the  impressions  of  hard  and  soft  substances.  It  is 
only  necessary  to  call  attention  to  the  ease  and  certainty  with  which  the 
presence  and  the  consistence  of  the  smallest  substance  between  the  teeth  are 
recognized,  to  show  the  importance  of  this  tactile  sense  in  mastication. 

SALIVA. 

The  fluid  which  is  mixed  with  the  food  in  mastication,  which  moistens 
the  mucous  membrane  of  the  mouth  and  which  may  be  collected  at  any  time 
in  small  quantity  by  the  simple  act  of  sputation,  is  composed  of  the  secretions 
of  a  considerable  number  and  variety  of  glands.  The  most  important  of  these 
are  the  parotid,  submaxillary  and  sublingual,  which  are  usually  called  the 
salivary  glands.  The  labial  and  buc- 
cal  glands,  the  glands  of  the  tongue 
and  general  mucous  surface  and  cer- 
tain glandular  structures  in  the  mu- 
cous membrane  of  the  pharynx  also 
contribute  to  the  production  of  the 
saliva.  The  liquid  which  becomes 
more  or  less  incorporated  with  the 
food  before  it  descends  to  the  stom- 
ach, and  which  must  be  regarded  as 
the  digestive  fluid  of  the  mouth,  is 
known  as  the  mixed  saliva ;  but  the 
study  of  the  composition  and  prop- 
erties of  this  fluid  as  a  whole  should 
be  prefaced  by  a  consideration  of 
the  different  secretions  of  which  it 
is  composed.  The  salivary  glands 
belong  to  the  variety  of  glands 
called  racemose.  They  resemble  the  other  glands  belonging  to  this  class, 
and  their  structure  will  be  more  fully  considered  in  connection  with  the 
physiology  of  secretion. 

Parotid  Saliva. — The  .parotid  is  the  largest  of  the  three  salivary  glands. 
It  is  situated  below  and  in  front  of  the  ear  and  opens  by  the  duct  of  Steno 
into  the  mouth,  at  about  the  middle  of  the  cheek.  The  papilla  which  marks 
the  orifice  of  the  duct  is  situated  opposite  the  second  large  molar  tooth  of  the 
upper  jaw. 

The  organic  matter  of  the  parotid  saliva  is  coagulable  by  heat  (212°  Fahr., 
or  100°  C.),  alcohol  or  the  strong  mineral  acids.  A  compound  of  sulpho- 
cyanogen  is  now  generally  acknowledged  to  be  a  constant  constituent  of  the 
parotid  saliva.  This  can  not  be  recognized  by  the  ordinary  tests  in  the  fresh 
saliva  taken  from  the  duct  of  Steno,  but  in  the  clear,  filtered  fluid  which 


FIG.  54.— Salivary  glands  (Tracy). 


196    DIGESTION— MASTICATION,  INSALIVATION,  DEGLUTITION. 

passes  after  the  precipitation  of  the  organic  matter,  there  is  always  a  distinct, 
red  color  on  the  addition  of  ferric  sulphate.  As  this  reaction  is  more  marked 
in  the  mixed  saliva,  the  methods  by  which  the  presence  of  a  sulphocyanide 
is  to  be  recognized  will  be  considered  in  connection  with  that  fluid.  In  the 
human  subject,  the  parotid  secretion  is  more  abundant  than  that  of  any  other 
of  the  salivary  glands ;  but  the  entire  quantity  in  the  twenty-four  hours  has 
not  been  directly  estimated. 

In  the  horse,  ass  and  ox,  it  has  been  found  that  when  mastication  is  per- 
formed on  one  side  of  the  mouth,  the  flow  from  the  gland  on  that  side  is 
greatly  increased,  exceeding  by  several  times  the  quantity  produced  upon  the 
opposite  side  (Colin).  This  fact  has  been  confirmed  by  Dalton  in  the  human 
subject. 

The  flow  of  saliva  from  the  parotid  takes  place  with  greatly  increased 
activity  during  the  process  of  mastication.  The  orifice  of  the  parotid  duct  is 
so  situated  that  the  fluid  is  poured  directly  upon  the  mass  of  food  as  it  is  un- 
dergoing trituration  by  the  teeth ;  and  as  the  secretion  is  more  abundant  on 
the  side  on  which  mastication  is  going  on,  and  the  consistence  of  the  fluid  is 
such  as  to  enable  it  to  mix  readily  with  the  food,  the  office  of  this  gland 
is  supposed  to  be  particularly  connected  with  mastication.  This  is  undoubt- 
edly the  fact ;  although  its  flow  is  not  absolutely  confined  to  the  period  of 
mastication,  but  continues  in  small  quantity  during  the  intervals.  Its  quan- 
tity is  regulated  somewhat  by  the  character  of  the  food,  being  much  greater 
when  the  articles  taken  into  the  mouth  are  dry  than  when  they  contain  con- 
siderable moisture.  In  the  human  subject,  the  stimulus  produced  by  sapid 
substances  will  sometimes  cause  a  great  increase  in  the  flow  of  the  parotid 
saliva.  Mitscherlich  and  Eberle  observed  this  in  persons  suffering  from  sali- 
vary fistula  and  noted,  farthermore,  that  the  mere  sight  or  odor  of  food  pro- 
duced the  same  effect.  The  supposition  that  the  flow  from  the  parotid  is 
dependent  upon  the  mechanical  pressure  of  the  muscles  or  of  the  condyle  of 
the  lower  jaw  during  mastication  has  no  foundation  in  fact.  In  the  horse 
and  in  the  dog,  it  has  been  observed  that  the  secretion  of  the  parotids  is  com- 
pletely arrested  during  the  deglutition  of  liquids,  while  the  flow  from  the 
other  salivary  glands  is  not  affected  (Bernard). 

The  parotid  saliva — aside  from  any  chemical  action  which  it  may  have 
upon  the  food,  which  will  be  fully  considered  in  connection  with  the  mixed 
saliva — evidently  has  an  important  mechanical  office.  It  is  discharged  in 
large  quantity  during  the  act  of  mastication  and  .is  poured  into  the  mouth 
in  such  a  manner  as  to  become  of  necessity  thoroughly  incorporated  with  the 
food.  Its  use  is  chiefly,  although  not  exclusively,  connected  with  mastication 
and  indirectly,  with  deglutition ;  for  it  is  only  by  becoming  incorporated 
with  this  saliva,  that  dry,  pulverulent  substances  can  be  swallowed. 

Submaxiliary  Saliva. — In  the  human  subject,  the  submaxiliary  is  the  sec- 
ond of  the  salivary  glands  in  point  of  size.  Its  minute  structure  is  nearly 
the  same  as  that  of  the  parotid.  As  its  name  implies,  it  is  situated  below  the 
inferior  maxillary  bone.  It  is  in  the  anterior  part  of  what  is  known  as  the 
submaxiliary  triangle  of  the  neck.  Its  excretory  duct,  the  duct  of  Wharton, 


SALIVA.  197 

is  about  two  inches  (5  centimetres)  in  length  and  passes  from  the  gland,  be- 
neath the  tongue,  to  open  by  a  small  papilla  by  the  side  of  the  frenum. 

The  pure  submaxillary  saliva  presents  many  important  points  of  difference 
from  the  secretion  of  the  parotid.  It  may  be  obtained  by  exposing  the  duct 
and  introducing  a  fine  silver  tube,  when,  on  the  introduction  of  any  sapid 
substance  into  the  mouth,  the  secretion  will  flow  in  large,  pearly  drops.  This 
variety  of  saliva  is  much  more  viscid  than  the  parotid  secretion.  It  is  per- 
fectly clear,  and  on  cooling,  it  frequently  becomes  of  a  gelatinous  consist- 
ence. Its  organic  matter  is  not  coagulable  by  heat.  It  contains  a  sulpho- 
cyanide,  but  in  very  small  quantity. 

The  submaxillary  gland  pours  out  its  secretion  in  greatest  abundance  when 
sapid  substances  are  introduced  into  the  mouth  ;  but  unlike  the  parotid  saliva, 
the  secretion  does  not  alternate  on  the  two  sides  with  alternation  in  mas- 
tication. Although  sapid  articles  excite  an  abundant  secretion  from  the 
submaxillary  glands,  they  also  increase  the  secretions  from  the  parotids  and 
sublinguals;  and  on  the  other  hand,  movements  of  mastication  increase 
somewhat  the  flow  from  the  submaxillaries,  and  these  glands  secrete  a  certain 
quantity  of  fluid  during  the  intervals  of  digestion.  The  viscid  consistence 
of  the  submaxillary  saliva  renders  it  less  capable  than  the  parotid  secretion 
of  penetrating  the  alimentary  mass  during  mastication. 

Sublingual  Saliva. — The  sublinguals,  the  smallest  of  the  salivary  glands, 
are  situated  beneath  the  tongue,  on  either  side  of  the  frenum.  In  minute 
structure  they  resemble  the  parotid  and  the  submaxillary  glands.  Each  gland 
has  a  number  of  excretory  ducts,  eight  to  twenty,  which  open  into  the  mouth 
by  the  side  of  the  frenum ;  and  one  of  the  ducts,  larger  than  the  others, 
joins  the  duct  of  the  submaxillary  gland  near  its  opening  in  the  mouth. 

The  secretion  of  the  sublingual  glands  is  more  viscid,  even,  than  the  sub- 
maxillary saliva,  but  it  differs  in  the  fact  that  it  does  not  gelantinize  on  cooling. 
It  is  so  glutinous  that  it  adheres  strongly  to  any  vessel  and  flows  with  diffi- 
culty from  a  tube  introduced  into  the  duct.  Like  the  secretion  from  the 
other  salivary  glands,  its  reaction  is  distinctly  alkaline.  Its  organic  matter  is 
not  coagulable  by  heat,  acids  or  the  metallic  salts. 

It  has  been  shown  that  the  sublingual  glands  may  be  excited  to  secretion 
by  impressions  made  by  sapid  substances  upon  the  nerves  of  taste,  although 
the  flow  is  always  less  than  from  the  submaxillary  glands.  The  great  viscid- 
ity of  the  sublingual  saliva  renders  it  less  easily  mixed  with  the  alimentary 
bolus  than  the  secretions  from  the  parotid  or  the  submaxillary  glands. 

Fluids  from  the  Smaller  Glands  of  the  Mouth,  Tongue  and  Pharynx. — 
Beneath  the  mucous  membrane  of  the  inner  surface  of  the  lips,  are  small, 
rounded,  glandular  bodies,  opening  into  the  buccal  cavity,  called  the  labial 
glands ;  and  in  the  submucous  tissue  of  the  cheeks,  are  similar  bodies,  called 
the  buccal  glands.  The  latter  are  somewhat  smaller  than  the  labial  glands. 
Two  or  three  of  the  buccal  glands  are  of  considerable  size  and  have  ducts 
opening  opposite  the  last  molar  tooth.  These  are  sometimes  distinguished  as 
the  molar  glands.  There  are  also  a  few  small  glands  in  the  mucous  mem- 
brane of  the  posterior  half  of  the  hard  palate ;  but  the  glands  on  the  under 


198    DIGESTION— MASTICATION,   INSALIVATION,  DEGLUTITION. 

surface  of  the  soft  palate  are  larger  and  here  form  a  continuous  layer.  The 
glands  of  the  tongue  are  situated  beneath  the  mucous  membrane,  mainly  on 
the  posterior  third  of  the  dorsum ;  but  a  few  are  found  at  the  edges  and  the 
tip,  and  there  is  a  gland  of  considerable  size  on  either  side  of  the  frenum, 
near  the  tip.  All  of  these  are  small,  racemose  glands,  similar  in  structure  to 
those  which  have  been  called  the  true  salivary  glands.  In  addition  to  these 
structures,  the  mucous  membrane  of  the  tongue  is  provided  with  simple  and 
compound  follicular  glands,  which  extend  over  its  entire  surface,  but  are 
most  abundant  at  the  posterior  portion,  behind  the  circumvallate  papillae. 
The  most  important  of  the  glands  of  the  tongue  will  be  described  in  connec- 
tion with  the  physiology  of  gustation. 

In  the  pharynx  and  the  posterior  portion  of  the  buccal  cavity,  are  the 
pharyngeal  glands  and  the  tonsils.  In  the  pharynx,  particularly  the  upper 
portion,  racemose  glands,  like  those  found  in  the  mouth,  exist  in  large  num- 
bers. The  mucous  membrane  is  provided,  also,  with  simple  and  compound 
mucous  follicles.  The  tonsils,  situated  on  either  side  of  the  fauces  between 
the  pillars  of  the  soft  palate,  consist  of  an  aggregation  of  compound  follicular 
glands.  The  number  of  glands  entering  into  the  composition  of  each  tonsil 
is  ten  to  twenty. 

The  secretion  from  the  glands  and  follicles  above  enumerated  can  not  be 
obtained,  in  the  human  subject,  unmixed  with  the  fluids  from  the  true  sali- 
vary glands.  It  has  been  collected  in  small  quantity,  however,  from  the  in- 
ferior animals,  after  ligature  of  all  the  salivary  ducts.  This  secretion  is  simply 
a  grayish,  viscid  mucus,  containing  a  number  of  leucocytes  and  desquamated 
epithelial  scales.  It  is  this  which  gives  the  turbid  and  opaline  character  to 
the  mixed  saliva,  as  the  secretions  of  the  salivary  glands  are  all  perfectly 
transparent.  The  fluid  from  these  glands  in  the  mouth  is  mixed  with  the 
salivary  secretions ;  and  that  from  the  posterior  part  of  the  tongue,  the  ton- 
sils, and  the  pharyngeal  glands  passes  down  to  the  stomach  with  the  aliment- 
ary bolus.  This  secretion,  consequently,  forms  a  constant  and  essential  part 
of  the  mixed  saliva. 

Mixed  Saliva. — Although  the  study  of  the  distinct  secretions  discharged 
into  the  mouth  possesses  considerable  physiological  importance,  it  is  only  the 
fluid  resulting  from  a  union  of  them  all,  which  can  properly  be  considered  in 
connection  with  the  general  process  of  insalivation.  In  man  it  is  necessary 
that  the  cavity  of  the  mouth  should  be  continually  moistened,  if  for  nothing 
else;  to  keep  the  parts  in  a  proper  condition  for  phonation.  A  little  reflec- 
tion will  make  it  apparent  that  the  flow,  from  some  of  the  glands  at  least,  is 
constant,  and  that  from  time  to  time  a  certain  quantity  of  saliva  is  swallowed. 
The  discharge  of  the  fluid  into  the  mouth,  though  diminished,  is  not  arrested 
during  sleep.  In  the  review  of  the  different  kinds  of  saliva,  it  has  been  seen 
that  the  flow  from  none  of  the  glands  is  absolutely  intermittent ;  unless  it  be  so 
occasionally  from  the  parotid,  the  secreting  action  of  which  is  most  powerfully 
influenced  by  the  act  of  mastication  and  the  impression  of  sapid  substances. 

Upon  the  introduction  of  food  the  quantity  of  saliva  is  greatly  increased ; 
and  the  influence  of  the  sight,  odor,  and  occasionally  even  the  thought  of 


SALIVA.  199 

agreeable  articles  has  already  been  mentioned.  The  experiments  of  Frerichs 
on  dogs  with  gastric  fistulas,  and  the  observations  of  Gardner  on  a  patient 
with  a  wound  in  the  oesophagus,  have  demonstrated  that  the  flow  of  saliva 
may  be  excited  by  the  stimulus  of  food  introduced  directly  into  the  stomach 
without  passing  through  the  mouth. 

Quantity  of  Saliva. — It  is  not  easy  to  estimate  in  the  human  subject 
the  entire  quantity  of  saliva  secreted  in  the  twenty-four  hours ;  and  great 
variations  in  this  regard  undoubtedly  exist  in  different  persons  and  even  in  the 
same  individual  at  different  times.  An  approximate  estimate  may  be  arrived 
at  by  noting  as  nearly  as  possible  the  average  quantity  secreted  during  the 
intervals  of  digestion  and  adding  to  it  the  quantity  absorbed  by  the  various 
articles  of  food.  Estimates  of  this  kind  can  be  approximate  only,  and  those 
made  by  Dalton  are  apparently  the  most  satisfactory.  The  following  repre- 
sents, according  to  Dalton,  the  quantities  of  saliva  secreted  during  mastica- 
tion and  during  the  intervals  of  meals : 

Saliva  required  for  mastication 17'32  oz.     (491  grammes). 

Saliva  secreted  in  intervals  of  meals 27'93  oz.     (792  grammes). 

Total  quantity  per  day 45*25  oz.  (1,283  grammes). 

The  total  daily  quantity  of  saliva,  therefore,  is  a  little  more  than  two  and 
three-fourths  pounds. 

Eemembering  that  the  quantity  of  saliva  must  necessarily  be  subject  to 
great  variations,  this  estimate  may  be  taken  as  giving  a  sufficiently  close  ap- 
proximation of  the  quantity  of  saliva  ordinarily  secreted.  It  must  be  borne 
in  mind,  however,  with  reference  to  this  and  the  other  digestive  secretions, 
that  this  large  quantity  of  fluid  is  at  no  one  time  removed  from  the  blood  but 
is  reabsorbed  nearly  as  fast  as  secreted,  and  that  normally,  none  of  it  is  dis- 
charged from  the  organism. 

General  Properties  and  Composition  of  the  Saliva. — The  mixed  fluid  taken 
from  the  mouth  is  colorless,  somewhat  opaline,  frothy  and  slightly  viscid.  It 
generally  has  a  faint  and  somewhat  disagreeable  odor  very  soon  after  it  is 
discharged.  If  it  be  allowed  to  stand,  it  deposits  a  whitish  sediment,  com- 
posed mainly  of  desquamated  epithelial  scales  with  a  few  leucocytes,  leaving 
the  supernatant  fluid  tolerably  clear.  Its  specific  gravity  is  variable,  ranging 
between  1004  or  1006  and  1008.  Its  reaction  is  almost  constantly  alkaline ; 
although,  under  certain  abnormal  conditions  of  the  system,  it  has  occasion- 
ally been  observed  to  be  neutral,  and  sometimes,  though  rarely,  acid.  The 
saliva  becomes  slightly  opalescent  by  boiling  or  on  the  addition  of  strong 
acids.  The  addition  of  absolute  alcohol  produces  an  abundant,  whitish,  floc- 
culent  precipitate.  Almost  invariably  the  mixed  saliva  presents  a  more  or 
less  intense  blood -red  tint  on  the  addition  of  a  per-salt  of  iron,  which  is  due 
to  the  presence  of  a  sulphocyanide  either  of  potassium  or  of  sodium. 

A  number  of  analyses  of  the  human  mixed  saliva  have  been  made  by  dif- 
ferent chemists,  presenting,  however,  few  differences,  except  in  the  relative 
proportions  of  water  and  solid  ingredients,  which  are  probably  quite  variable. 
The  following  is  an  analysis  by  Bidder  and  Schmidt : 


200    DIGESTION— MASTICATION,  INSALIVATION,  DEGLUTITION. 


COMPOSITION    OF    HUMAN    SALIVA. 

Water 995-16 

Epithelium 1-62 

Soluble  organic  matter 1-34 

Potassium  sulphocyanide O06 

Sodium,  calcium  and  magnesium  phosphates 0-98 

Potassium  chloride  [  »  „ . 
Sodium  chloride      ) 


1,000-00 

The  organic  matter  of  the  mixed  saliva,  called  by  Berzelius,  ptyaline,  on 
the  addition  of  an  excess  of  absolute  alcohol,  is  coagulated  in  the  form  of 
whitish  flakes  which  may  be  readily  separated  by  filtration.  This  substance 
has  been  studied  by  Mialhe  and  is  described  by  him  under  the  name  of 
animal  diastase.  This  author  regards  it  as  the  active  principle  of  the  saliva. 
It  has  no  direct  influence  upon  the  nitrogenized  alimentary  matters,  but 
when  brought  in  contact  with  hydrated  starch,  readily  transforms  it,  first  into 
dextrine  and  afterward  into  glucose.  According  to  Mialhe,  the  energy  of 
this  action  is  such  that  one  part  is  sufficient  to  effect  the  transformation  of 
more  than  two  thousand  parts  of  starch. 

The  presence  of  a  certain  quantity  of  potassium  sulphocyanide  in  the 
mixed  saliva  can  be  demonstrated  by  the  addition  of  a  per-salt  of  iron.  That 
this  is  a  constant  and  normal  ingredient  of  the  human  saliva,  can  not  be 
doubted. 

Very  little  need  be  said  concerning  the  other  inorganic  constituents  of 
saliva,  except  that  they  are  of  such  a  nature  as  almost  invariably  to  render 
the  fluid  distinctly  alkaline.  They  exist  in  small  proportion  and  do  not 
appear  to  be  connected  in  any  way  with  the  action  of  the  saliva  as  a  digest- 
ive fluid. 

USES  OF  THE  SALIVA. 

In  1831,  Leuchs  discovered  that  hydrated  starch,  mixed  with  fresh  saliva 
and  warmed,  became  liquid  and  was  converted  into  sugar.  This  fact  has 
since  been  repeatedly  confirmed ;  and  it  is  now  a  matter  of  common  observa- 
tion that  hydrated  starch  or  unleavened  bread,  taken  into  the  mouth,  almost 
instantly  loses  the  property  of  striking  a  blue  color  with  iodine  and  responds 
to  the  ordinary  tests  for  sugar.  Of  the  rapidity  of  this  action  any  one  can 
easily  convince  himself  by  the  simple  experiment  of  taking  a  little  cooked 
starch  into  the  mouth,  mixing  it  well  with  the  saliva,  and  testing  in  the  ordi- 
nary way  for  sugar.  This  can  hardly  be  done  so  rapidly  that  the  reaction 
is  not  manifested,  and  the  presence  of  sugar  is  also  indicated  by  the  taste. 
Although  the  human  mixed  saliva  will  finally  exert  the  same  action  on  un- 
cooked starch,  the  transformation  takes  place  much  more  slowly. 

It  has  been  shown  that  all  the  varieties  of  human  saliva  have  the  same 
effect  on  starch  as  the  mixed  fluids  of  the  mouth.  Dalton  found  no  differ- 
ence between  the  pure  parotid  saliva  and  the  mixed  saliva  of  the  human 
subject,  as  regards  the  power  of  transforming  starch  into  sugar.  Bernard 


SALIVA.  201 

obtained  the  pure  secretions  from  the  parotid  and  from  the  submaxillary 
glands  in  the  human  subject,  by  drawing  the  fluids  out  of  the  ducts  as  they 
open  into  the  mouth,  by  means  of  a  small  syringe  with  the  nozzle  arranged  so 
as  to  fit  over  the  papillae,  and  demonstrated  their  action  on  starch.  Longet 
showed  that  a  mixture  of  the  secretions  of  the  submaxillary  and  the  sub- 
lingual  glands  has  the  same  property. 

Several  carbohydrates  are  formed  as  intermediate  products  between  the 
hydrated  starch  and  glucose,  which  latter  is  the  final  result  of  the  action  of 
the  salivary  ferment.  After  passing  through  one  or  two  conditions  slightly 
different  from  that  of  pure  dextrine,  the  starch  is  converted  into  dextrine, 
which  is  changed  into  maltose  (C13H22On),  and  the  maltose  is  finally  con- 
verted into  glucose  (C6H1206).  This  action  is  due  entirely  to  the  presence  of 
ptyaline,  although  its  intensity  is  increased  in  moderately  alkaline  solutions 
or  by  the  addition  of  certain  salts,  especially  sodium  chloride.  Feeble  acids 
diminish  the  activity  of  this  change,  and  it  is  arrested  by  strong  mineral 
acids ;  although  direct  experiments  have  shown  that  the  action  of  the  saliva 
is  slowly  and  feebly  continued  in  the  stomach.  The  temperature  at  which  the 
action  of  the  salivary  ferment  is  most  vigorous  is  about  100°  Fahr.  (38°  C.) ; 
and  any  considerable  variation  from  this  temperature  arrests  the  process. 

In  early  infancy  the  action  of  the  saliva  upon  starch  is  not  so  vigorous  as 
in  the  adult,  and  it  is  said  that  immediately  after  birth  the  parotid  secretion 
is  the  only  one  of  the  salivary  fluids  which  contains  ptyaline.  In  a  few 
months,  however,  ptyaline  appears  in  the  submaxillary  and  sublingual  secre- 
tions. 

It  is  evident  that  the  saliva,  in  addition  to  its  mechanical  action,  trans- 
forms a  considerable  portion  of  the  cooked  starch,  which  is  the  common 
form  in  which  starch  is  taken  by  the  human  subject,  into  sugar ;  but  it 
is  by  no  means  the  only  fluid  engaged  in  its  digestion,  similar  properties 
belonging  to  the  pancreatic  and  the  intestinal  juices.  The  last-named  fluids 
are  probably  more  active,  even,  than  the  saliva.  The  saliva  acts  slowly  and 
imperfectly  on  raw  starch,  which  becomes  hydrated  in  the  stomach  and  is 
digested  mainly  by  the  fluids  of  the  small  intestine.  In  all  probability  the 
saliva  does  not  digest  all  the  hydrated  starch  taken  as  food,  the  greater  part 
passing  unchanged  from  the  stomach  into  the  intestine.  Those  who  attribute 
merely  a  mechanical  action  to  the  saliva  draw  their  conclusions  entirely 
from  experiments  on  the  lower  animals,  particularly  the  carnivora ;  and  such 
observations  can  not  properly  be  applied  to  the  human  subject. 

In  treating  of  the  various  fluids  which  are  combined  to  form  the  mixed 
saliva,  their  mechanical  uses  have  necessarily  been  touched  upon.  To  sum 
up  this  part  of  the  subject,  however,  it  may  be  stated  that  the  fluids  of  the 
mouth  and  pharynx  have  quite  as  important  an  office  in  preparing  the  food 
for  deglutition  and  for  the  action  of  the  juices  in  the  stomach  as  in  the  diges- 
tion of  starch.  It  is  a  matter  of  common  experience  that  the  rapid  deglu- 
tition of  very  dry  articles  is  impossible.  In  the  human  subject,  although 
mastication  and  insalivation  are  by  no  means  so  complete  as  in  some  of  the 
lower  animals,  the  quantity  of  saliva  absorbed  by  the  various  articles  of  food 


202    DIGESTION— MASTICATION,  INSALIVATION,   DEGLUTITION. 

is  very  large.  It  seems  impossible  that  the  fluid  thus  incorporated  with  the 
food  should  not  have  an  important  influence  on  the  changes  which  take 
place  in  the  stomach,  although  it  must  be  confessed  that  information  on  this 
point  is  very  meagre,  except  as  regards  the  digestion  of  starch. 

It  is  undoubtedly  the  abundant  secretion  of  the  parotid  glands  which 
becomes  most  completely  incorporated  with  the  food  during  mastication  and 
which  serves  to  unite  the  dry  particles  into  a  coherent  mass.  The  secre- 
tions from  the  submaxillary  and  sublingual  glands  and  from  the  small 
glands  and  follicles  of  the  mouth,  being  more  viscid  and  less  in  quantity  than 
the  parotid  secretion,  penetrate  the  alimerrtary  bolus  less  easily  and  form  a 
glairy  coating  on  its  exterior,  agglutinating  the  particles  near  the  surface 
with  peculiar  tenacity. 

When  the  processes  of  mastication  and  insalivation  have  been  completed, 
and  the  food  has  passed  into  the  pharynx,  it  meets  with  the  secretion  of  the 
pharyngeal  glands,  which  still  farther  coats  the  surface  with  the  viscid  fluid 
which  covers  the  mucous  membrane  in  this  situation,  thus  facilitating  the 
first  processes  of  deglutition. 

It  has  been  observed  that  the  saliva  engages  bubbles  of  air  in  the  ali- 
mentary mass.  In  mastication,  a  considerable  quantity  of  air  is  mixed  with 
the  food,  and  this  facilitates  the  penetration  of  the  gastric  juice.  It  is  well 
known  that  moist,  heavy  bread,  and  articles  that  can  not  become  impregnated 
in  this  way  with  air,  are  not  easily  acted  upon  in  the  stomach. 

DEGLUTITION. 

Deglutition  is  the  act  by  which  solid  and  liquid  articles  are  passed  from 
the  mouth  into  the  stomach.  The  process  involves  first,  the  passage,  by  an 
automatic  movement,  of  the  alimentary  mass  through  the  isthmus  of  the 
fauces  into  the  pharynx ;  then  a  rapid  contraction  of  the  constrictors  of  the 
pharynx,  by  which  it  is  forced  into  the  oesophagus ;  and  finally,  a  peristaltic 
action  of  the  muscular  walls  of  the  oesophagus,  extending  from  its  opening  at 
the  pharynx  to  the  stomach. 

Physiological  Anatomy  of  the  Parts  concerned  in  Deglutition. — The  parts 
concerned  in  this  process  are  the  tongue,  the  muscular  walls  of  the  pharynx 
and  the  oesophagus.  In  the  passage  of  food  and  drink  through  the  pharynx, 
it  is  necessary  to  completely  protect  from  the  entrance  of  foreign  matters  a 
number  of  openings  which  are  exclusively  for  the  passage  of  air.  These  are 
the  posterior  nares  and  the  Eustachian  tubes  above,  and  the  opening  of  the 
larynx  below. 

The  tongue — a  muscular  organ  capable  of  a  great  variety  of  movements 
— is  the  chief  agent  in  the  first  processes  of  deglutition.  A  study  of  the 
muscles  which  are  brought  into  action  in  deglutition  would  involve  an  ana- 
tomical description  so  elaborate  as  to  be  out  of  place  in  this  work.  The 
movements  of  the  tongue,  however,  will  be  described  in  connection  with  the 
mechanism  of  deglutition. 

The  pharynx,  in  which  the  most  complex  of  the  movements  of  deglutition 
take  place,  is  an  irregular,  funnel-shaped  cavity,  its  longest  diameter  being 


DEGLUTITION. 


transverse  and  opposite  the  cornua  of  the  hyoid  bone,  with  its  smallest  por- 
tion at  the  opening  into  the  oesophagus.     Its  length  is  about  four  and  a  half 
inches  (11-43  cen- 
timetres), 
connected 


is 


It 

superi- 
orly and  posterior- 
ly with  the  basilar 
process  of  the  oc- 
cipital bone  and 
with  the  upper  cer- 
vical vertebrae.  It 
is  incompletelysep- 
arated  from  the 
cavity  of  the  mouth 
by  the  velum  pen- 
dulum palati,  a 
movable,  musculo- 
membranous  fold 
continuous  with 
the  roof  of  the 
mouth  and  marked 
by  a  line  in  the 
centre,  which  in- 
dicates its  original 
development  by 
two  lateral  halves. 
This,  which  is 
called  the  soft 
palate,  when  re- 
laxed, presents  a 
concave  surface 
looking  toward 
the  mouth,  a  free, 

arched  border,  and  a  conical  process  hanging  from  the  centre,  called 
the  uvula.  On  either  side  of  the  soft  palate,  are  two  curved  pillars,  or 
arches. 

The  anterior  pillars  of  the  fauces  are  formed  by  the  palato-glossus  muscle 
on  either  side  and  run  obliquely  downward  and  forward,  the  mucous  mem- 
brane which  covers  them  becoming  continuous  with  the  membrane  over  the 
base  of  the  tongue.  The  posterior  pillars  are  more  closely  approximated  to 
each  other  than  the  anterior.  They  run  obliquely  downward  and  backward, 
their  mucous  membrane  becoming  continuous  with  the  membrane  covering 
the  sides  of  the  pharynx.  Between  the  lower  portion  of  the  anterior  and 
posterior  pillars,  are  the  tonsils ;  and  in  the  substance  of  and  beneath  the 
mucous  membrane  of  the  palate  and  pharynx,  are  small  glands,  which  have 
already  been  described. 


Fio.  55.— Cavities  of  the  mouth  and  pharynx,  etc.  (Sappey). 
Section,  in  the  median  line,  of  the  face  and  the  superior  portion  of  the  neck, 
designed  to  show  the  mouth  in  its  relations  to  the  nasal  fossae,  the  phar- 
ynx and  the  larynx  :  1.  sphenoidal  sinuses  ;  2,  internal  orifice  of  the  Eu- 
stachian  tube  ;  3,  palatine  arch  ;  4,  velum  pendulum  palati ;  5,  anterior 
pillar  of  the  soft  palate  ;  6,  posterior  pillar  of  the  soft  palate  :  7,  tonsil ; 
8,  lingual  portion  of  the  cavity  of  the  pharynx  ;  9,  epiglottis  ;  10.  section 
of  the  hyoid  bone;  11.  laryrigeal  portion  of  the  cavity  of  the  pharynx ; 
12,  cavity  of  the  larynx. 


204    DIGESTION— MASTICATION,   INSALIVATION,   DEGLUTITION. 


In  Fig.  55,  are  shown  the  cavities  of  the  mouth  and  pharynx  with  their 
relations  to  the  nares  and  the  larynx. 

The  isthmus  of  the  fauces,  or  the  strait  through  which  the  food  passes 
from  the  mouth  to  the  pharynx,  is  bounded  above,  by  the  soft  palate  and  the 
uvula  ;  laterally,  by  the  pillars  of  the  palate  and  the  tonsils ;  and  below,  by 

the   base    of    the 
tongue. 

The  openings 
into  the  pharynx 
above  are  the  pos- 
terior nares  and 
'20  the  orifices  of  the 
Eustachian  tubes. 
Below,  are  the 
openings  of  the 
oesophagus  and  of 
the  larynx. 

The  muscles  of 
the  pharynx  are 
the  superior  con- 
strictor, the  stylo- 
pharyngeus,  the 
middle  constrictor 
and  the  .  inferior 
constrictor  ;  and 
it  is  easy  to  see, 
from  the  situation 
of  these  muscles, 
which  is  shown  in 
Fig.  56,  how,  by 
their  successive 
action  from  above 

FIG.  W.-Muscles  of  the  pharynx,  etc.  (Sappey).  downward,          the 

1,  2,  3,  4,  4,  superior  constrictor  ;  5,  6,  7,  8,  middle  constrictor  ;  9,  10,  II,  12,  in-  fnnr]  ia  i-vaceorl  intr> 

ferior  constrictor  ;  13,  13,  stylo-pharyngeus  ;   14,  stylo-hyoid  muscle  ;  15,  l 

stylo-glossus  ;    16,  hyo-glossus  ;   17,  mylo-hyoid  muscle;   18,  buccinator  4-]-,p  rr>«rmliarms 
mliscle  ;  19,  tensor  palati ;  20,  levator  palati.  SOpnagUS. 

The     muscles 

which  form  the  fleshy  portions  of  the  soft  palate  are  likewise  important  in 
deglutition.  These  are  the  levator  palati,  the  tensor  palati,  the  palato-glossus 
and  the  palato-pharyngeus.  The  azygos  uvulas,  which  forms  the  fleshy  por- 
tion of  the  uvula,  has  no  marked  or  important  action  in  deglutition. 

The  mucous  membrane  of  the  pharynx,  aside  from  the  various  glands  sit- 
uated beneath  it  and  in  its  substance,  which  have  already  been  described,  pre- 
sents some  peculiarities,  which  are  interesting  more  from  an  anatomical  than 
a  physiological  point  of  view.  In  the  superior  portion,  which  forms  a  cuboid- 
al  cavity  just  behind  the  posterior  nares,  the  membrane  is  darker  and  much 
richer  in  blood-vessels  than  in  other  parts.  Its  surface  is  smooth  and  pro- 


DEGLUTITION.  205 

vided  with  ciliated,  columnar  epithelium,  like  that  which  covers  the  mem- 
brane of  the  posterior  nares.  Laterally,  below  the  level  of  the  opening  of  the 
Eustachian  tubes,  and  posteriorly,  at  the  point  where  it  becomes  vertical,  the 
mucous  membrane  abruptly  changes  its  character.  The  epithelial  covering 
is  here  composed  of  flattened  cells,  similar  to  those  which  cover  the  mucous 
membrane  of  the  resophagus.  The  membrane  is  also  paler  and  less  vascular. 
It  is  provided  with  papillas,  some  of  which  are  simple,  conical  elevations,  while 
others  present  two  to  six  conical  processes  with  a  single  base.  These  papillae 
are  rather  thinly  distributed  over  all  of  that  portion  of  the  mucous  surface 
which  is  covered  with  flattened  epithelium. 

The  contractions  of  the  muscular  walls  of  the  pharynx  force  the  aliment- 
ary bolus  into  the  oesophagus,  a  tube  possessed  of  thick,  muscular  walls,  ex- 
tending to  the  stomach.  The  ossophagus  is  about  nine  inches  (23  centi- 
metres) in  length.  It  is  cylindrical  and  is  slightly  constricted  at  its  superior 
and  inferior  extremities.  Its  upper  extremity  is  in  the  median  line,  behind 
the  lower  border  of  the  cricoid  cartilage  and  opposite  the  fifth  cervical  verte- 
bra. At  first,  as  it  descends,  it  passes  a  little  to  the  left  of  the  cervical 
vertebrae.  It  then  passes  from  left  to  right  from  the  fourth  or  fifth  to  the 
ninth  dorsal  vertebra,  to  give  place  to  the  aorta.  It  finally  passes  a  little  to 
the  left  again,  and  from  behind  forward,  to  its  opening  into  the  stomach. 
In  its  passage  through  the  diaphragm,  it  is  surrounded  by  muscular  fibres,  so 
that  when  this  muscle  is  contracted  in  inspiration,  its  action  has  a  tendency 
to  close  the  opening. 

The  coats  of  the  oesophagus  are  two  in  number,  unless  there  be  included, 
as  a  third  coat,  the  fibrous  tissue  which  attaches  the  mucous  membrane  to 
the  subjacent  muscular  tissue. 

The  external  coat  is  composed  of  an  external  longitudinal,  and  an  inter- 
nal circular  or  transverse  layer  of  muscular  fibres.  In  the  superior  portion, 
the  longitudinal  fibres  are  arranged  in  three  distinct  fasciculi ;  one  in  front, 
which  passes  downward  from  the  posterior  surface  of  the  cricoid  cartilage, 
and  one  on  either  side,  extending  from  the  inferior  constrictors  of  the  pharynx. 
As  the  fibres  descend,  the  fasciculi  become  less  distinct  and  are  finally  blended 
into  a  uniform  layer.  The  circular  layer  is  somewhat  thinner  than  the  ex- 
ternal layer.  Its  fibres  are  transverse  near  the  superior  and  inferior  extrem- 
ities of  the  tube  and  are  somewhat  oblique  in  the  intermediate  portion.  The 
muscular  coat  is  -fo  to  ^  of  an  inch  (0-5  to  2-1  mm.)  in  thickness. 

In  the  upper  third  of  the  oesophagus,  the  muscular  fibres  are  exclusively 
of  the  red  or  striated  variety,  with  some  anastomosing  bundles ;  but  lower 
down,  there  is  a  mixture  of  non-striated  fibres,  which  appear  first  in  the  cir- 
cular layer.  These  latter  fibres  become  gradually  more  abundant,  until,  in 
the  lower  fourth,  they  largely  predominate.  A  few  striated  fibres,  however, 
are  found  as  low  down  as  the  diaphragm. 

The  mucous  membrane  of  the  oesophagus  is  attached  to  the  muscular 
tissue  by  a  dense,  fibrous  layer.  It  is  quite  vascular  and  reddish  above,  but 
gradually  becomes  paler  in  the  inferior  portion.  The  mucous  membrane  is 
ordinarily  thrown  into  longitudinal  folds,  which  are  obliterated  when  the 

15 


206    DIGESTION— MASTICATION,  INSALIVATION,  DEGLUTITION. 

tube  is  distended.  Its  epithelium  is  thick,  of  the  squamous  variety,  and  is 
continuous  with  and  similar  to  the  covering  of  the  lower  portion  of  the 
pharynx.  It  is  provided  with  papillae  of  the  same  structure  as  those  found 
in  the  pharynx,  the  conical  variety  predominating.  Small,  racemose  glands 
are  found  throughout  the  tube,  forming,  by  their  aggregation  at  the  lower 
extremity  just  before  it  opens  into  the  stomach,  a  glandular  ring. 

Mechanism  of  Deglutition. — For  convenience  of  description,  physiologists 
have  generally  divided  the  process  of  deglutition  into  three  periods.  The  first 
period  is  occupied  by  the  passage  of  the  alimentary  bolus  backward  to  the 
isthmus  of  the  fauces.  This  may  appropriately  be  considered  as  a  distinct 
period,  because  the  movements  are  effected  by  the  action  of  muscles  under 
the  control  of  the  will.  The  second  period  is  occupied  by  the  passage  of  the 
food  from  the  isthmus  of  the  fauces,  through  the  pharynx,  into  the  upper 
part  of  the  oesophagus.  The  third  period  is  occupied  by  the  passage  of  the 
food  through  the  oesophagus  into  the  stomach. 

In  the  first  period  the  tongue  is  the  important  agent.  At  the  beginning 
of  this  period,  the  mouth  is  closed  and  the  tongue  becomes  slightly  increased 
in  width,  and  with  the  alimentary  bolus  behind  it,  is  pressed  from  before 
backward  against  the  roof  of  the  mouth.  The  act  of  swallowing  is  always 
performed  with  difficulty  when  the  mouth  is  not  completely  closed ;  for  the 
tongue,  from  its  attachments,  must  follow,  to  a  certain  extent,  the  movements 
of  the  lower  jaw.  The  first  part  of  the  first  period  of  deglutition,  therefore, 
is  simple ;  but  when  the  food  has  passed  beyond  the  hard  palate,  it  comes  in 
contact  with  the  hanging  velum,  and  the  muscles  are  brought  into  action 
which  render  this  membrane  tense  and  oppose  it  in  a  certain  degree  to  the 
backward  movement  of  the  base  of  the  tongue.  This  is  effected  by  the  action 
of  the  tensor-palati  and  the  palato-glossus.  The  moderate  tension  of  the  soft 
palate  admits  of  its  being  applied  to  the  smaller  morsels,  while  the  opening 
is  dilated  somewhat  forcibly  by  masses  of  greater  size. 

It  is  easy  to  see,  in  analyzing  the  first  period  of  deglutition,  that  liquids 
and  the  softer  articles  of  food  are  assisted  in  their  passage  to  the  isthmus  of 
the  fauces  by  a  slight  suction  force.  This  is  effected  by  the  action  of  the 
muscles  of  the  tongue,  elevating  the  sides  and  depressing  the  centre  of  the 
dorsum,  while  the  soft  palate  is  applied  to  the  base. 

The  importance  of  the  movements  of  the  tongue  during  the  first  period 
of  deglutition  is  shown  by  experiments  on  the  inferior  animals  and  by  cases 
of  loss  of  this  organ  in  the  human  subject.  In  the  case  of  a  young  girl, 
reported  by  De  Jussieu  (1718),  in  which  there  was  congenital  absence  of  the 
tongue,  deglutition  was  impossible  until  the  food  had  been  pushed  with  the 
finger  far  back  into  the  mouth.  In  cases  of  amputation  of  the  tongue,  a  por- 
tion of  its  base  generally  remains,  which  is  sufficient  to  press  against  the 
palate  and  thus  act  in  the  first  period  of  deglutition. 

The  movements  in  the  first  period  of  deglutition  are  under  the  control  of 
the  will  but  are  generally  automatic.  When  the  food  has  been  thoroughly 
masticated,  it  requires  an  effort  to  prevent  the  act  of  swallowing.  In  this 
respect,  the  movements  are  like  the  acts  of  respiration,  except  that  the  imper- 


DEGLUTITION.  207 

ative  necessity  of  air  in  the  system  must,  in  a  short  time,  overcome  any  vol- 
untary effort  by  which  respiration  has  been  arrested. 

The  second  period  of  deglutition  involves  more  complex  and  important 
muscular  action  than  the  first.  By  a  rapid  succession  of  movements,  the  food 
is  made  to  pass  through  the  pharynx  into  the  oesophagus.  The  movements 
are  then  entirely  beyond  the  control  of  the  will  and  belong  to  the  kind  called 
reflex.  After  the  alimentary  mass  has  passed  beyond  the  isthmus  of  the 
fauces,  it  is  easy  to  observe  a  sudden  and  peculiar  movement  of  elevation  of 
the  larynx,  by  the  action  of  muscles  which  usually  depress  the  lower  jaw,  but 
which  are  now  acting  from  this  bone  as  the  fixed  point.  The  muscles  which 
produce  this  movement  act  chiefly  upon  the  hyoid  bone.  They  are  the  di- 
gastric (particularly  the  anterior  belly),  the  mylo-hyoid,  the  genio-hyoid,  the 
stylo-hyoid  and  some  of  the  fibres  of  the  genio-glossus.  It  is  probable,  also, 
that  the  thyro-hyoid  acts  at  this  time  to  draw  the  larynx  toward  the  hyoid  bone. 
With  this  elevation  of  the  larynx,  there  is  necessarily  an  elevation  of  the  ante- 
rior and  inferior  portions  of  the  pharynx,  which  are,  as  it  were,  slipped  under 
the  alimentary  bolus  as  it  is  held  by  the  constrictors  of  the  isthmus  of  the  fauces. 

Contraction  of  the  constrictor  muscles  of  the  pharynx  takes  place  almost 
simultaneously  with  the  movement  of  elevation ;  and  the  superior  constrictor 
is  so  situated  as  to  grasp  the  morsel  of  food,  and  with  it  the  soft  palate.  The 
muscles,  the  constrictors  acting  from  the  median  raphe,  draw  up  the  anterior 
and  inferior  walls  of  the  pharynx  and  pass  the  food  rapidly  into  the  upper 
part  of  the  oesophagus.'  All  these  complex  movements  are  accomplished 
with  great  rapidity,  and  the  larynx  and  pharynx  are  then  returned  to  their 
original  position. 

Protection  of  the  Posterior  Nares  during  the  Second  Period  of  Degluti- 
tion.— When  the  act  of  deglutition  is  performed  with  regularity,  no  portion 
of  the  liquids  and  solids  swallowed  ever  finds  its  way  into  the  air-passages. 
The  entrance  of  foreign  substances  into  the  posterior  nares  is  prevented  in 
part  by  the  action  of  the  superior  constrictors  of  the  pharynx,  which  embrace, 
during  their  contraction,  not  only  the  alimentary  mass,  but  the  velum  pend- 
ulum palati  itself,  and  in  part,  also,  by  contraction  of  the  muscles  which  form 
the  posterior  pillars  of  the  soft  palate. 

During  the  first  part  of  the  second  period  of  deglutition,  the  soft  palate  is 
slightly  raised,  being  pressed  upward  by  the  morsel  of  food.  This  fact  has 
been  observed  in  cases  in  which  the  parts  have  been  exposed  by  surgical  oper- 
ations, and  its  mechanism  has  also  been  observed  in  the  human  subject,  by 
Bidder  and  by  Kobelt. 

While  the  food  is  passing  through  the  pharynx,  the  palato-pharyngeal 
muscles,  which  form  the  posterior  pillars  of  the  soft  palate,  are  in  a  con- 
dition of  contraction  by  which  the  edges  of  the  pillars  are  nearly  approxi- 
mated, forming,  with  the  uvula  between  them,  almost  a  complete  diaphragm 
between  the  postero-superior  and  the  antero-inferior  parts  of  the  pharynx. 
This,  with  the  application  of  the  posterior  wall  of  the  pharynx  to  the  superior 
face  of  the  soft  palate,  completes  the  protection  of  the  posterior  openings  of 
the  nasal  fossa?. 


208    DIGESTION— MASTICATION,  INSALIVATION,  DEGLUTITION. 

Protection  of  the  Opening  of  the  Larynx  and  Uses  of  the  Epiglottis  in 
Deglutition. — The  entrance  of  the  smallest  quantity  of  solid  or  liquid  foreign 
matter  into  the  larynx  produces  a  violent  cough.  This  accident  is  of  not 
infrequent  occurrence,  especially  when  an  act  of  inspiration  is  inadvert- 
ently performed  while  solids  or  liquids  are  in  the  pharynx.  During  inspi- 
ration, the  glottis  is  opened,  and  at  that  time  only  can  a  substance  of  any 
considerable  size  find  its  way  into  the  respiratory  passages.  Respiration  is  in- 
terrupted, however,  during  each  and  every  act  of  deglutition ;  and  there  can, 
therefore,  be  hardly  any  tendency  at  that  time  to  the  entrance  of  foreign  sub- 
stances into  the  larynx.  During  a  regular  act  of  swallowing,  nothing  can  find 
its  way  into  the  respiratory  passages,  so  complete  is  the  protection  of  the  larynx 
during  the  period  when  the  food  passes  through  the  pharynx  into  the  oasophagus. 

It  is  evident,  from  the  anatomy  of  the  parts  and  the  necessary  results  of 
the  contractions  of  the  muscles  of  deglutition,  that  while  the  food  is  passing 
through  the  pharynx,  the  larynx,  by  its  elevation,  passes  under  the  tongue  as 
it  moves  backward,  and  the  soft  base  of  this  organ  is,  as  it  were,  moulded 
over  the  glottis.  With  the  parts  removed  from  the  human  subject  or  from 
one  of  the  inferior  animals,  the  natural  movements  of  the  tongue  and  larynx 
can  be  imitated,  and  it  is  seen  that  they  must  be  sufficient  to  protect  the 
larynx  from  the  entrance  of  solid  or  semi-solid  particles  of  food,  particu- 
larly when  it  is  remembered  how  the  alimentary  particles  are  agglutinated 
by  the  saliva  and  how  easy  their  passage  becomes  over  the  membrane  coated 
with  mucus.  It  is  impossible,  also,  for  the  muscles  of  the  pharynx  to  con- 
tract without  drawing  together  the  sides  of  the  larynx,  to  which  they  are 
attached,  and  assisting  to  close  the  glottis.  At  the  same  time,  as  the  move- 
ments of  respiration  are  arrested  during  deglutition,  the  lips  of  the  glottis 
fall  together,  as  they  always  do  except  in  inspiration.  In  addition  to  this 
passive  and  incomplete  approximation  of  the  vocal  chords,  it  has  repeatedly 
been  observed  that  the  lips  of  the  glottis  are  accurately  and  firmly  closed 
during  each  act  of  deglutition. 

Longet  justly  attached  great  importance  to  the  acute  sensibility  of  the 
top  of  the  larynx  in  preventing  the  entrance  of  foreign  substances.  His 
experiments  of  dividing  all  the  nervous  filaments  distributed  to  the  intrinsic 
muscles  show  that  their  action  is  not  essential ;  but  after  division  of  the 
superior  laryngeal — the  nerve  which  gives  sensibility  to  the  parts — he  found 
that  liquids  occasionally  passed  in  small  quantity  into  the  trachea. 

With  reference  to  the  action  of  the  epiglottis  in  contributing  to  the  pro- 
tection of  the  larynx  during  the  second  period  of  deglutition,  observations  on 
the  human  subject  only  are  to  be  relied  upon.  Such  observations,  in  cases  of 
loss  of  the  epiglottis  especially,  show  that  this  part  is  necessary  to  the  com- 
plete protection  of  the  larynx.  While  loss  of  the  epiglottis  may  not  inter- 
fere always  with  the  perfect  deglutition  of  solids,  and  even  of  liquids,  parti- 
cles of  food  and  liquids  frequently  find  their  way  into  the  larynx,  and 
deglutition  is  often  effected  with  difficulty,  showing  that  complete  protection 
of  the  larynx  at  all  times,  does  not  exist  unless  the  epiglottis  be  intact. 

To  appreciate  the  mechanism  by  which  the  opening  of  the  larynx  is  pro- 


DEGLUTITION.  209 

tected  during  the  deglutition  of  solids  and  liquids,  one  has  only  to  carefully 
follow  the  articles  as  they  pass  over  the  inclined  plane  formed  by  the  back 
of  the  tongue  and  the  anterior  and  inferior  part  of  the  pharynx.  As  the 
food  is  making  this  passage  in  obedience  to  the  contraction  of  the  muscles 
which  carry  the  tongue  backward,  draw  up  the  larynx  and  constrict  the 
pharynx,  the  soft  base  of  the  tongue  and  the  upper  part  of  the  larynx  are 
applied  to  each  other,  with  the  epiglottis,  which  is  now  inclined  backward, 
between  them ;  at  the  same  time  the  glottis  is  closed,  in  part  by  the  action 
of  the  constrictor  muscles  attached  to  the  sides  of  the  thyroid  cartilages,  and 
in  part  by  the  action  of  the  intrinsic  muscles.  If  the  food  be  tolerably  con- 
sistent and  in  the  form  of  a  single  bolus,  it  slips  easily  from  the  back  of  the 
tongue  along  the  membrane  covering  the  anterior  and  inferior  part  of  the 
pharynx ;  but  if  it  be  liquid  or  of  soft  consistence,  a  portion  takes  this 
course,  while  another  portion  passes  over  the  epiglottis,  being  directed  by  it 
into  the  two  grooves  by  the  side  of  the  larynx.  It  is  by  these  means, 
together  with  those  by  which  the  posterior  nares  are  protected,  that  all  solids 
and  liquids  are  passed  into  the  cesophagus,  and  the  second  period  of  degluti- 
tion is  safely  accomplished. 

The  third  period  of  deglutition  is  the  most  simple  of  all.  It  merely 
involves  contractions  of  the  muscular  walls  of  the  oesophagus,  by  which  the 
food  is  passed  into  the  stomach.  The  longitudinal  fibres  shorten  the  tube 
and  slip  the  mucous  membrane,  lubricated  by  its  glairy  secretion,  above  the 
bolus ;  while  the  circular  fibres,  by  a  progressive  peristaltic  contraction  from 
above  downward,  propel  the  food  into  the  stomach.  In  experiments  on  the 
lower  animals,  it  has  been  observed  that  while  the  peristaltic  contractions  of 
the  upper  two-thirds  of  the  tube  is  immediately  followed  by  a  relaxation, 
which  continues  till  the  next  act  of  deglutition,  the  lower  third  remains  con- 
tracted generally  for  about  thirty  seconds  after  the  passage  of  the  food  into 
the  stomach.  During  its  contraction,  this  part  of  the  oesophagus  is  hard, 
like  a  cord  firmly  stretched.  This  is  followed  by  relaxation;  and  alter- 
nate contraction  and  relaxation  continue,  even  when  the  stomach  is  empty, 
although,  during  digestion,  the  contractions  are  frequent  in  proportion  to  the 
quantity  of  food  in  the  stomach.  The  contraction  is  always  increased  by 
pressing  the  stomach  and  attempting  to  pass  some  of  its  contents  into  the 
oesophagus  (Magendie).  This  provision  is  important  in  preventing  regurgi- 
tation  of  the  contents  of  the  stomach,  especially  when  the  organ  is  exposed 
to  pressure,  as  in  urination  or  defecation. 

An  approximate  estimate  of  the  duration  of  the  acts  of  deglutition  is 
given  in  the  following  quotation  from  Landois : 

"  According  to  Meltzer  and  Kronecker,  the  duration  of  deglutition  in  the 
mouth  is  0-3  sec. ;  then  the  constrictors  of  the  pharynx  contract  0-9  sec. ; 
afterward,  the  upper  part  of  the  oesophagus ;  then  after  1-8  sec.  the  middle ; 
and  after  another  3  sec.  the  lower  constrictor.  The  closure  of  the  cardia, 
after  the  entrance  of  the  bolus  into  the  stomach,  is  the  final  act  in  the  total 
series  of  movements." 


210    DIGESTION— MASTICATION,  INSALIVATION,   DEGLUTITION. 

The  entire  process  of  deglutition,  therefore,  occupies  about  six  seconds. 

The  muscular  movements  which  take  place  during  all  the  periods  of  deg- 
lutition are  peculiar.  The  first  act  is  generally  automatic,  but  it  is  under 
the  control  of  the  will.  The  second  act  is  involuntary  when  once  begun, 
but  it  may  be  excited  by  the  voluntary  passage  of  solids  or  liquids  beyond 
the  velum  pendulum  palati.  It  is  impossible  to  perform  the  second  act 
of  deglutition  unless  there  be  some  article,  either  solid  or  liquid,  in  the 
pharynx.  It  is  easy  to  make  three  or  four  successful  efforts  consecutively,  in 
which  there  is  elevation  of  the  larynx,  with  all  the  other  characteristic  move- 
ments ;  but  a  little  attention  will  show  that  with  each  act  a  small  quantity  of 
saliva  is  swallowed.  When  the  efforts  have  been  frequently  repeated,  the 
movements  become  impossible,  until  time  enough  has  elapsed  between  them 
for  the  saliva  to  collect. 

All  the  movements  of  deglutition,  except  those  of  the  first  period,  must 
be  regarded  as  reflex,  depending  upon  an  impression  made  upon  the  afferent 
nerves  distributed  to  the  mucous  membrane  of  the  pharynx  and  oesophagus. 

The  position  of  the  body  has  little  to  do  with  the  facility  with  which  deg- 
lutition is  effected.  Liquids  or  solids  may  be  swallowed  indifferently  in  all 
postures.  Berard  saw  a  juggler  pass  an  entire  bottle  of  wine  from  the  mouth 
to  the  stomach,  while  standing  on  his  head.  The  same  feat  was  accom- 
plished with  apparent  ease,  by  a  juggler  who  drank  three  glasses  of  beer 
while  standing  on  his  hands  in  the  inverted  posture  (Flint). 

Deglutition  of  Air. — In  his  essay  on  the  mechanism  of  vomiting,  Ma- 
gendie  stated  that  as  soon  as  nausea  occurred  the  stomach  began  to  fill 
with  air,  so  that  before  vomiting  occurred,  the  organ  became  tripled  in  size. 
Magendie  showed,  fathermore,  that  the  air  entered  the  stomach  by  the  oesoph- 
agus, for  the  distention  occurred  when  the  pylorus  was  ligated.  In  a  sub- 
sequent memoir,  the  question  of  the  deglutition  of  air,  aside  from  the  small 
quantity  which  is  incorporated  with  the  food  during  mastication  and  insali- 
vation,  was  farther  investigated.  It  was  found  that  some  persons  had  the 
faculty  of  swallowing  air,  and  by  practice,  Magendie  himself  was  able  to  ac- 
quire it,  although  it  occasioned  such  distress  that  it  wa£  discontinued.  Out 
of  a  hundred  students  of  medicine,  eight  or  ten  were  found  able  to  swallow 
air. 

It  is  not  very  uncommon  to  find  persons  who  have  gradually  acquired  the 
habit  of  swallowing  air,  in  order  to  relieve  uncomfortable  sensations  in  the 
stomach ;  and  when  confirmed,  it  occasions  persistent  disorder  in  digestion. 
Quite  a  number  of  cases  of  this  kind  were  reported  by  Magendie,  and  in  sev- 
eral it  was  carried  to  such  an  extent  as  to  produce  great  distention  of  the 
abdomen.  A  curious  case  of  habitual  air-swallowing  was  observed  by  the  late 
Dr.  Austin  Flint  and  is  reported  in  his  work  on  the  Practice  of  Medicine. 


PHYSIOLOGICAL  ANATOMY  OF  THE  STOMACH.  211 

CHAPTER  VIII. 

GASTRIC  DIGESTION. 

Physiological  anatomy  of  the  stomach — Glands  of  the  stomach — Closed  follicles— Gastric  jnice— Gastric 
fistula  in  the  human  subject  in  the  case  of  St.  Martin— Secretion  of  the  gastric  juice — Properties  and 
composition  of  gastric  juice— Action  of  the  gastric  jnice  in  digestion — Peptones — Action  of  the  gastric 
jnice  upon  fats,  sugars  and  amylaceous  substances — Duration  of  gastric  digestion— Conditions  which  in- 
fluence gastric  digestion— Movements  of  the  stomach. 

PHYSIOLOGICAL  ANATOMY  OF  THE  STOMACH. 

THE  stomach  serves  the  double  purpose  of  a  receptacle  for  the  food  and 
an  organ  in  which  certain  important  digestive  processes  take  place.  It  is 
situated  in  the  upper  part  of  the  abdominal  cavity  and  is  held  in  place  by 
folds  of  the  peritoneum  and  by  the  oesophagus.  Its  form  is  not  easily  de- 
scribed. It  has  been  compared  to  a  bagpipe,  which  it  resembles  somewhat, 
when  moderately  distended.  When  empty,  it  is  flattened,  and  in  many  parts 
its  opposite  walls  are  in  contact.  When  moderately  distended,  its  length  is 
thirteen  to  fifteen  inches  (33  to  38  centimetres),  its  greatest  diameter,  about 
five  inches  (12-7  centimetres),  and  its  capacity,  one  hundred  and  seventy-five 
cubic  inches  (2,868  c.  c.),  or  about  five  pints.  The  parts  usually  noted  in 
anatomical  descriptions  are  the  following :  a  greater  and  a  lesser  curvature ; 
a  greater  and  a  lesser  pouch;  a  cardiac,  or  oasophageal  opening;  a  pyloric 
opening,  which  leads  to  the  intestinal  canal.  The  great  pouch  is  sometimes 
called  the  fundus. 

The  coats  of  the  stomach  are  three  in  number ;  the  peritoneal,  muscular 
and  mucous.  By  some  anatomists  the  fibrous  tissue  which  unites  the  mucous 
to  the  muscular  coat  is  regarded  as  a  distinct  covering  and  is  called  the 
fibrous  coat. 

Peritoneal  Coat. — This  is  simply  a  layer  of  peritoneum,  similar  in  struct- 
ure to  the  membrane  which  covers  the  other  abdominal  viscera.  It  is  a  re- 
flection of  the  membrane  which  lines  the  general  abdominal  cavity,  which, 
on  the  viscera,  is  somewhat  thinner  than  it  is  on  the  walls  of  the  cavity. 
Over  the  stomach  the  peritoneum  is  -^  to  -^  of  an  inch  (83  to  125  /*) 
in  thickness.  It  is  a  serous  membrane  and  consists  of  ordinary  fibrous 
tissue  with  a  considerable  number  of  elastic  fibres.  It  is  closely  adherent 
to  the  subjacent  muscular  coat  and  is  not  very  abundantly  supplied  with 
blood-vessels  and  nerves.  Lymphatics  have  been  demonstrated  only  in  the 
subserous  structure.  The  surface  of  the  peritoneum  is  everywhere  covered 
with  regularly  polygonal  cells  of  pavement  endothelium,  closely  adherent  to 
each  other  and  presenting  a  perfectly  smooth  surface  which  is  moistened 
with  a  small  quantity  of  liquid.  An  important  office  of  this  membrane  is  to 
present  a  smooth  surface  covering  the  abdominal  parietes  and  viscera,  so  as 
to  allow  free  movements  of  the  organs  over  each  other  and  against  the  walls 
of  the  abdomen. 

Muscular  Coat. — Throughout  the  alimentary  canal,  from  the  cardiac 
opening  of  the  stomach  to  the  anus,  the  muscular  fibres  forming  the  middle 
coat  are  of  the  non-striated  variety.  These  fibres,  called  sometimes  muscu- 


212  GASTRIC  DIGESTION. 

lar  fibre-cells,  are  very  pale,  with  faint  outlines,  fusiform  or  spindle-shaped, 
and  contain  each  an  oval,  longitudinal  nucleus.  They  are  closely  adher- 
ent by  their  sides,  and  are  so  arranged  as  to  dovetail  into  each  other, 
forming  sheets  of  greater  or  less  thickness,  depending  upon  the  number 
of  their  layers.  The  muscular  coat  of  the  stomach  varies  in  thickness  in 
different  animals.  In  the  human  subject,  it  is  thickest  in  the  region  of  the 
pylorus  and  is  thinnest  at  the  fundus.  Its  average  thickness  is  about  -fa  of 
an  inch  (1  mm.).  In  the  pylorus  its  thickness  is  -fa  to  -j^  of  an  inch  (1*6  to 
2'1  mm.),  and  in  the  fundus,  -fa  to  -fa  of  an  inch  (O5  to  0-7  mm.). 

The  muscular  fibres  exist  in  the  stomach  in  two  principal  layers ;  an  ex- 
ternal longitudinal  layer  and  an  internal  circular  layer,  with  a  third  layer  of 
oblique  fibres  extending  over  the  great  pouch  only,  which  is  internal  to  the 
circular  layer.  The  longitudinal  fibres  are  continued  from  the  oesophagus 
and  are  most  marked  over  the  lesser  curvature.  They  are  not  continued 
very  distinctly  over  the  rest  of  the  stomach.  The  circular  and  oblique 
fibres  are  best  seen  with  the  organ  everted  and  the  mucous  membrane  care- 
fully removed.  The  circular  layer  is  not  very  distinct  to  the  left  of  the  car- 
diac opening,  over  the  great  pouch.  Toward  the  pylorus,  the  layers  of  fibres 
are  thicker,  and  at  the  opening  into  the  duodenum,  they  form  a  powerful 
muscular  ring,  which  is  sometimes  called  the  sphincter  of  the  pylorus,  or  the 
pyloric  muscle.  At  this  point  they  project  considerably  into  the  interior  of 
the  organ  and  cease  abruptly  at  the  opening  into  the  duodenum,  so  as  to  form 
a  sort  of  valve,  presenting,  when  contracted,  a  flat  surface  looking  toward  the 


10 


FIG.  57.—  Longitudinal  fibres  of  the  stomach  (Sappey). 

1  lesser  curvature  ;  2,  2,  greater  curvature  ;  3,  greater  pouch  ;  4,  lesser  pouch  ;  5,  6,  6,  lower  end  of  the 
oesophagus  ;  7  7,  pylorus  ;  8.  8,  longitudinal  fibres  at  the  lesser  curvature  ;  9,  fibres  extending  over 
the  greater  curvature  ;  10. 10,  a  very  thin  layer  of  longitudinal  fibres  over  the  anterior  surface  of  the 
stomach  ;  11,  circular  fibres  seen  through  the  thin  layer  of  longitudinal  fibres. 

intestine.     The  oblique  layer  takes  the  place,  in  great  part,  of  the  circular 
fibres,  over  the  great  pouch.     It  extends  obliquely  over  the  fundus  from  left 


PHYSIOLOGICAL  ANATOMY  OF  THE  STOMACH. 


213 


to  right  and  ceases  at  a  distinct  line  extending  from  the  left  margin  of  the 
03sophagus  to  about  the  junction  of  the  middle  with  the  last  third  of  the 
great  curvature.  At  about  the  line  where  the  oblique  layer  of  fibres  ceases 
the  stomach  becomes  constricted  during  the  movements  which  are  incident 
to  digestion,  dividing  the  organ  into  tolerably  distinct  compartments. 

The  blood-vessels  of  the  muscular  coat  are  quite  abundant  and  are  arranged 
in  a  peculiar,  rectangular  net-work,  which  they  always  present  in  the  non- 


FIG.  58. — Fibres  seen  with  the  stomach  everted  (Sappey). 

1,1,  oesophagus  ;  2,  circular  fibres  at  the  cesophageal  opening  ;  3,  3,  circular  fibres  at  the  lesser  curva- 
ture ;  4,  4,  circular  fibres  at  the  pylorus  ;  5,  5,  6,  7,  8,  oblique  fibres  ;  9,  10,  fibres  of  this  layer  cover- 
ing the  greater  pouch  ;  11,  portion  of  the  stomach  from  which  these  fibres  have  been  removed  to 
show  the  subjacent  circular  fibres. 

striated  muscular  tissue.     The  nerves  come  from  the  pneumogastrics  and  the 
sympathetic  system  and  are  demonstrated  with  difficulty. 

Mucous  Coat. — The  mucous  mem- 
brane of  the  stomach  is  soft  and  vel- 
vety in  appearance  and  of  a  reddish- 
gray  color.  It  is  loosely  attached  to 
the  submucous  muscular  tissue  and  is 
thrown  into  large,  longitudinal  folds, 
which  become  effaced  as  the  organ  is 
distended.  If  the  mucous  membrane 
be  stretched  or  if  the  stomach  be 
everted  and  distended  and  the  mucus 
be  gently  removed  under  a  stream  of 
water,  the  membrane  will  be  found 
marked  with  polygonal  pits  or  de- 
pressions, enclosed  by  ridges,  which,  FIG-  59.-P«s  in  the  mucous  membrane  of  the 
J  '  stomach,  and  orifices  of  the  glands  ;  magnified 

in  some  parts  of  the  organ,  are  quite       20  diameters  (Sappe.n 
regular.     These  are  best   seen 


i     1, 1,  1,  2,  2,  2,  3,  pits  of  different  sizes  ;  4,  5,  orifices 
Wltll  of  the  gastric  glands. 


214  GASTRIC  DIGESTION. 

the  aid  of  a  simple  lens,  as  many  of  them  are  quite  small.  The  diameter  of 
the  pits  is  very  variable,  but  the  average  is  about  -gfa  of  an  inch  (0-125  mm.). 
This  appearance  is  not  distinct  toward  the  pylorus ;  the  membrane  here  pre- 
senting irregular,  conical  projections  and  well  marked  villi  resembling  those 
found  in  the  small  intestine.  The  surface  of  the  mucous  membrane  is  cov- 
ered with  columnar  or  prismoidal  epithelium,  the  cells  being  tolerably  regular 
in  shape,  each  with  a  clear  nucleus  and  a  distinct  nucleolus.  According  to 
Landois,  these  cells,  which  he  calls  "  mucus-secreting  gob- 
let-cells," have  a  clear  portion  occupying  their  outer  half, 
which  is  open  and  discharges  a  viscid  secretion. 

The  thickness  of  the  mucous  membrane  of  the  stom- 
ach varies  in  different  parts.     Usually  it  is  thinnest  near 
the  resophagus  and  thickest  near  the  pylorus.     Its  thin- 
nest portion  measures  ^  to  -fa  of  an  inch  (0-34  to  0-5 
no.  w.-Gob"t.  cells     mm-) '  its  thickest  portion,  ^  to  jg  of  an  inch  (1-6  to 
&do§f   *tomat*     2-1  mm.),  and  the  intermediate  portion,  about  fa  of  an 

inch  (1  mm.). 

Glands  of  fhe  Stomach. — Extending  from  the  bottoms  of  the  pits  in  the 
mucous  membrane  of  the  stomach  to  the  submucous  connective  tissue,  are 
large  numbers  of  glands.  These  generally  are  arranged  in  tolerably  dis- 
tinct groups,  surrounded  by  fibrous  tissue,  each  group  belonging  to  one  of 
the  polygonal  depressions.  The  tissue  which  connects  the  tubes  is  dense  but 
not  abundant.  There  are  marked  differences  in  the  anatomy  of  the  glands 
in  different  parts  of  the  stomach,  which  are  supposed  to  correspond  with 
differences  in  the  uses  of  various  parts  of  the  mucous  membrane.  There  are, 
indeed,  two  distinct  varieties  of  glands;  the  peptic  glands,  which  secrete 
pepsine,  or  an  organic  substance  that  is  readily  changed  into  pepsine,  and  the 
acid-glands,  which  are  supposed  to  secrete  free  hydrochloric  acid.  The  pep- 
tic glands  are  most  abundant  in  the  pyloric  portion  of  the  stomach  and 
around  the  cardiac  opening.  The  so-called  acid-glands  are  found  through- 
out the  mucous  membrane,  especially  in  the  greater  pouch.  The  secretion 
in  the  pyloric  portion  of  the  stomach  is  not  acid  at  any  time,  while  the  se- 
cretion in  the  greater  pouch,  during  digestion,  is  always  strongly  acid.  The 
difference  in  the  action  of  these  two  kinds  of  glands  is  supposed  to  depend 
upon  differences  in  the  secreting  cells. 

The  pyloric  glands  are  lined  by  cells  which  may  be  called  peptic  cells  (the 
chief-cells  of  German  writers),  conoidal  or  cuboidal  in  form,  and  relatively 
clear,  especially  during  the  intervals  of  digestion.  Similar  cells  are  found,  in 
connection  with  the  so-called  acid-cells  (parietal  cells)  in  the  secreting  por- 
tion of  the  glands  of  the  greater  pouch. 

The  acid-glands  are  found  throughout  the  stomach,  except  near  the  pylo- 
rus. The  secreting  portion  of  these  glands  contains  peptic  cells,  but  near 
the  tubular  membrane  are  rounded  cells,  larger  than  the  peptic  cells,  darker 
and  more  granular,  which  are  the  acid,  or  parietal  cells.  These  are  strongly 
stained  when  treated  with  osmic  acid  (Nussbaum).  It  is  probable  that  the 
so-called  acid-glands  secrete  pepsine  as  well  as  an  acid,  while  the  pyloric 


PHYSIOLOGICAL  ANATOMY  OF  THE   STOMACH. 


215 


glands  secrete  pepsine  but  no  acid.  According  to  the  views  just  stated,  in 
the  glands  of  the  greater  pouch,  the  acid  is  secreted  by  the  rounded  acid-cells 
while  the  pepsine  is  secreted  by  cells  (peptic  cells)  similar  to  those  which  line 
the  secreting  portion  of  the  pyloric  glands.  During  the  intervals  of  diges- 
tion, pepsine  is  in  process  of  formation  by  the  peptic  cells,  and  no  acid  is 
produced ;  but  acid  begins  to  be  secreted  soon  after  food  is  received  into  the 
stomach.  It  is  now  thought  that  the  peptic  cells  do  not  produce  pepsine 
directly,  but  a  substance  sometimes  called  zymogen,  but  more  properly  pro- 
pepsine  or  pepsinogen,  which  is  changed  into  true  pepsiue  by  the  action  of 
hydrochloric  acid. 

There  is  some  confusion  among  writers  with  regard  to  the  names  of  the 
different  kinds  of  secreting  cells  of  the  stomach,  the  acid -cells  being  fre- 
quently described  as  "  peptic  cells."  It  seems  proper,  however,  to  call  the 


FIG.  61.— Glands  of  the  greater  pouch  of 
the  stomach  (Heidenhain). 


' 

"9o*es 

FIG.  62.—  Pyloric  glands  (Ebstein). 


cells  which  produce  pepsine,  peptic  cells,  and  the  cells  that  are  supposed  to 
produce  acid,  acid-cells. 

The  glands  of  the  stomach  have  an  excretory  portion  and  a  secreting 
portion,  the  latter  presenting  several  branches.  The  excretory  portion  is 
lined  by  cells  like  those  found  on  the  surface  of  the  mucous  membrane, 


216 


GASTEIC  DIGESTION. 


The  secreting  portion  is  lined  by  the  peptic  and  the  acid-cells  already 
described.  In  Fig.  Gl  the  darker  cells  are  the  acid-cells,  and  the  lighter 
cells,  the  peptic  cells.  In  Fig.  62  the  secreting  portion  contains  peptic  cells 
only. 

Closed  Follicles. — In  the  substance  of  the  mucous  membrane,  between  the 
tubes  and  near  their  caecal  extremities,  are  occasionally  found  closed  follicles, 
like  the  solitary  glands  and  patches  of  Peyer  of  the  intestines.  These  are 
not  always  present  in  the  adult  but  are  generally  found  in  children.  They 
are  usually  most  abundant  over  the  greater  curvature,  though  they  may  be 
found  in  other  situations.  In  their  anatomy  they  are  identical  with  the  closed 
follicles  of  the  intestines,  and  they  do  not  demand  special  consideration  in 
this  connection. 

Gastric  Juice. — The  observations  of  Beaumont  upon  Alexis  St.  Martin, 
the  Canadian  who  had  a  large  fistulous  opening  into  the  stomach,  gave  the 
first  definite  knowledge  of  the  most  important  of  the  physiological  properties 
of  the  gastric  juice.  St.  Martin,  the  subject  of  these  observations,  received  a 
gunshot  wound  in  the  left  side,  at  the  age  of  eighteen  years,  being  at  the  time 
of  good  constitution  and  in  perfect  health.  He  slowly  recovered  from  the 
injury,  and  after  three  years,  having  regained  his  health,  was  made  the  sub- 
ject of  a  great  number  and  variety  of  experiments.  Although  the  general 
health  had  been  restored,  there  remained  a  perforation  into  the  stomach, 
irregularly  circular  in  form  and  nearly  an  inch  (2'5  centimetres)  in  diameter. 

This  opening  was  closed 
by  a  protrusion  of  the 
mucous  membrane  in  the 
form  of  a  valve,  which 
could  readily  be  de- 
pressed by  the  finger  so 
as  to  expose  the  interior 
of  the  stomach. 

From  May,  1825,  un- 
til August  of  the  same 
year,  St.  Martin  was  un- 
der the  observation  of 
Beaumont.  At  the  end 
of  that  time  he  was  lost 
sight  of  for  four  years. 
He  then  came  again  un- 
der the  observation  of 

FIG.  63. — Ga.tric  fistula  in  the  case  of  St.  Martin  (Beaumont).  Beaumont  and  Continued 

A,  A,  A,  B,  borders  of  the  opening  into  the  stomach  :  c,  left  nipple  ;  .       .  .  .          ... 

D,  chest ;  E,  cicatrices  from  the  wound  made  for  the  removal  of  111    hlS    SCl'VlCe,  doing  tlie 
a  piece  of  cartilage  ;  F,  F,  F,  cicatrices  of  the  original  wound.  , ., 

work  ot  a  servant,  until 

March,  1831.  After  this  he  was  under  observation  from  time  to  time  until 
1836,  always  enjoying  perfect  health,  with  good  digestion.  The  last  pub- 
lished observations  made  upon  this  case  were  in  1856. 

The  following  was  the  method  employed  by  Beaumont  in  extracting  the 


GASTRIC  JUICE. 


217 


gastric  juice  :  The  subject  was  placed  on  the  right  side  in  the  recumbent 
posture,  the  valve  was  depressed  within  the  aperture,  and  a  gum-elastic  tube, 
of  the  size  of  a  large  quill,  was  passed  into  the  stomach  to  the  extent  of  five 
to  six  inches  (13  to  15  centimetres).  On  turning  him  upon  the  left  side 
until  the  opening  became  dependent,  the  stimulation  of  the  tube  caused  the 
secretion  to  flow,  sometimes  in  drops  and  sometimes  in  a  small  stream. 

Since  the  publication  of  Beaumont's  experiments,  many  observations 
have  been  made  upon  animals  in  which  a  permanent  gastric  fistula  had  been 
established.  In  these  experiments  the  dog  is  most  frequently  used,  as  in  this 
animal  the  operation  usually  is  successful.  The  animals  operated  upon  by 
Bassow,  who  was  the  first  to  establish  a  gastric  fistula  (1842),  were  merely 
objects  of  curiosity ;  but  Blondlot  (1843)  and  others  fixed  a  tube  in  the 
stomach,  collected  the  juice  and  made  important  observations  with  regard  to 
its  action  in  digestion.  Most  experimenters  follow  the  method  employed  by 
Blondlot  and  Bernard,  making  the  opening  in  the  abdomen  in  the  median 
line,  a  little  below  the  ensiform  cartilage. 

Having  established  a  permanent  fistula  into  the  stomach,  after  the  wound 
has  cicatrized  around  the  canula,  the  animal  suffers  no  inconvenience  and 
may  serve  indefinitely  for  experiments  on  the 
gastric  juice.  In  some  experiments,  the  flow  of 
gastric  juice  has  been  excited  by  the  introduc- 
tion into  the  stomach,  of  pieces  of  tendon  or 
hard,  indigestible  articles,  on  the-  ground  that 
the  fluid  taken  from  the  fistula,  under  these  con- 
ditions, is  unmixed  with  the  products  of  gastric 
digestion  ;  but  it  has  been  shown  that  the 
quantity  and  character  of  the  secretion  are  in- 
fluenced by  the  nature  of  the  stimulus,  and  it  is 
proper,  therefore,  to  excite  the  action  of  the 
stomach  by  articles  which  are  relished  by  the 
animal.  For  this  purpose,  lean  meat  may  be 
given,  cut  into  pieces  so  small  that  they  will  be 
swallowed  entire,  and  first  thrown  into  boiling 
water  so  that  their  exterior  may  become  some- 
what hardened.  The  cork  is  then  removed  from 
the  tube,  which  is  freed  from  mucus  etc.,  when 
the  gastric  juice  will  begin  to  flow,  sometimes 
immediately  and  sometimes  in  four  or  five  min- 
utes after  the  food  has  been  taken.  It  flows  in 
clear  drops  or  in  a  small  stream  for  about  fifteen 
minutes,  nearly  free  from  the  products  of  diges- 
tion. At  the  end  of  this  'time  it  is  generally  accompanied  with  grumous 
matter,  and  the  experiment  should  be  concluded  if  it  be  desired  simply  to 
obtain  the  pure  secretion.  In  fifteen  minutes,  two  to  three  ounces  (60  to 
90  c.c.)  of  fluid  may  be  obtained  from  a  good-sized  dog,  which,  when  filtered, 
is  perfectly  clear ;  and  this  operation  may  be  repeated  three  or  four  times  a 


FIG.  64.— Dog  with  a  gastric  fistula 
(.B<§clard). 


218  GASTRIC  DIGESTION. 

week  without  interfering  with  the  character  of  the  secretion  or  injuring  the 
health  of  the  animal. 

Although  instances  of  gastric  fistula  in  the  human  subject  had  been  re- 
ported before  the  case  of  St.  Martin  and  have  been  observed  since  that  time, 
the  remarkably  healthy  condition  of  the  subject  and  the  extended  experi- 
ments of  Beaumont  have  rendered  this  case  memorable  in  the  history  of 
physiology.  This  is  the  only  instance  on  record,  in  which  pure,  normal  gas- 
tric juice  has  been  obtained  from  the  human  subject ;  and  it  has  served  as 
the  standard  for  comparison  for  subsequent  experiments  on  the  inferior 
animals. 

Artificial  gastric  juice,  prepared  by  extracting  the  active  principle  from 
the  mucous  membrane  of  the  stomach  of  different  animals  and  adding  hydro- 
chloric acid,  is  useful  in  observations  with  regard  to  the  chemistry  of  the 
peculiar  ferment,  but  fluids  prepared  in  this  way  are  not  absolutely  identical 
with  the  natural  secretion.  Extracts  of  the  mucous  membrane  were  made 
by  Eberle  (1834),  Von  Wittich,  Briicke  and  many  others. 

Secretion  of  the  Gastric  Juice. — According  to  Beaumont,  during  the  in- 
tervals of  digestion,  the  mucous  membrane  is  comparatively  pale,  "  and  is 
constantly  covered  with  a  very  thin,  transparent,  viscid  mucus,  lining  the 
whole  interior  of  the  organ."  On  the  application  of  any  irritation,  or  better, 
on  the  introduction  of  food,  the  membrane  changes  its  appearance.  It 
becomes  red  and  turgid  with  blood ;  small  pellucid  points  begin  to  appear 
in  various  parts,  which  are  drops  of  gastric  juice ;  and  these  gradually  in- 
crease in  size  until  the  fluid  trickles  down  the  sides  in  small  streams.  The 
membrane  is  now  invariably  of  a  strongly  acid  reaction,  while  at  other  times 
it  is  either  neutral  or  faintly  alkaline.  The  thin,  watery  fluid  thua  produced 
is  the  true  gastric  juice.  Although  the  stomach  may  contain  a  clear  fluid  at 
other  times,  this  secretion  generally  is  abnormal.  It  is  but  slightly  acid  and 
does  not  possess  the  characteristic  properties  of  the  natural  secretion.  It  has 
been  shown  by  Beaumont,  and  his  observations  have  been  repeatedly  confirmed 
by  experiments  on  the  inferior  animals,  that  the  gastric  juice  is  secreted  in 
greatest  quantity  and  possesses  the  most  powerful  solvent  properties,  when 
food  has  been  introduced  into  the  stomach  by  the  natural  process  of  degluti- 
tion. The  stimulation  of  the  mucous  membrane  is  then  general,  and  secre- 
tion takes  place  from  the  entire  surface  capable  of  producing  the  fluid. 
When  any  foreign  substance,  as  the  gum-elastic  tube  used  in  collecting  the 
juice,  is  introduced,  the  stimulation  is  local,  and  the  flow  of  fluid  is  compara- 
tively slight.  It  has  been  also  observed  that  the  quantity  immediately 
secreted  on  the  introduction  of  food,  after  a  long  fast,  is  always  much  greater 
than  when  food  has  been  taken  after  the  ordinary  interval. 

While  natural  food  is  undoubtedly  the  proper  stimulus  for  the  stomach, 
and  while,  in  normal  digestion,  the  quantity  of  gastric  juice  is  perfectly 
adapted  to  the  work  it  has  to  perform,  it  has  been  noted  that  savory  and 
highly  seasoned  articles  generally  produce  a  more  abundant  secretion  than 
those  which  are  comparatively  insipid.  An  abundant  secretion  is  likewise 
excited  by  some  of  the  vegetable  bitters. 


GASTEIC  JUICE.  219 

Impressions  made  on  the  nerves  of  gustation  have  a  marked  influence  in 
exciting  the  action  of  the  mucous  membrane  of  the  stomach.  Blondlot 
found  that  sugar,  introduced  into  the  stomach  of  a  dog  by  a  fistula,  pro- 
duced a  flow  of  juice  much  less  abundant  than  when  the  same  quantity  was 
taken  by  the  mouth.  To  convince  himself  that  this  did  not  depend  upon 
the  want  of  admixture  with  the  alkaline  saliva,  he  mixed  the  sugar  with 
the  saliva  and  passed  it  in  by  the  fistula,  when  the  same  difference  was 
observed.  In  some  animals,  particularly  when  they  are  very  hungry,  the 
sight  and  odor  of  food  will  excite  secretion  of  gastric  juice. 

A  febrile  condition  of  the  system,  the  depression  resulting  from  an  excess 
in  eating  and  drinking,  or  even  purely  mental  conditions,  such  as  anger  or 
fear,  vitiate,  diminish  and  sometimes  entirely  suppress  secretion  by  the  stom- 
ach. At  some  times,  under  these  conditions,  the  mucous  membrane  becomes 
red  and  dry,  and  at  others  it  is  pale  and  moist.  In  the  morbid  conditions, 
drinks  are  immediately  absorbed,  but  food  remains  undigested  in  the  stomach 
for  twenty-four  to  forty-eight  hours  (Beaumont). 

After  the  food  has  been  in  part  liquefied  and  absorbed  and  in  part  reduced 
to  a  pultaceous  consistence,  the  secretion  of  gastric  juice  ceases ;  the  move- 
ments of  the  stomach  having  gradually  forced  that  portion  of  the  food  which 
is  but  partially  acted  upon  in  this  organ  or  is  digested  only  in  the  small  in- 
testines out  at  the  pylorus.  The  stomach  is  thus  entirely  emptied,  the  mucous 
membrane  becomes  pale,  and  its  reaction  loses  its  marked,  acid  character, 
becoming  neutral  or  faintly  alkaline. 

Quantity  of  Gastric  Juice. — The  data  for  determining  the  quantity  of 
gastric  juice  secreted  in  the  twenty-four  hours  are  so  uncertain  that  it  seems 
impossible  to  fix  upon  any  estimate  that  can  be  accepted  even  as  an  approxi- 
mation. Still,  the  quantity  must  be  considerable,  in  view  of  the  large  quan- 
tity of  alimentary  matter  which  is  acted  upon  in  gastric  digestion.  It  is 
probably  not  less  than  six  pounds  (2-72  kilos.)  or  more  than  fourteen  pounds 
(6-35  kilos.).  After  this  fluid  has  performed  its  office  in  digestion,  it  is  im- 
mediately reabsorbed,  and  but  a  small  quantity  of  the  secretion  exists  in  the 
stomach  at  any  one  time. 

Properties  and  Composition  of  Gastric  Juice. — The  gastric  juice  is  mixed 
in  the  stomach  with  more  or  less  mucus  secreted  by  the  lining  membrane. 
When  drawn  by  a  fistula,  it  generally  contains  particles  of  food,  which  have 
become  triturated  and  partially  disintegrated  in  the  mouth,  and  is  always 
mixed  with  a  certain  quantity  of  saliva,  which  is  swallowed  during  the  inter- 
vals of  digestion  as  well  as  when  the  stomach  is  active.  By  adopting  certain 
precautions,  however,  the  fluid  may  be  obtained  nearly  free  from  impurities, 
except  the  admixture  of  saliva.  The  juice  taken  from  the  stomach  during 
the  first  moments  of  its  secretion,  and  separated  from  mucus  and  foreign 
matters  by  filtration,  is  a  clear  fluid,  of  a  faint  yellowish  or  amber  tint  and 
possessing  little  or  no  viscidity.  Its  reaction  is  always  strongly  acid ;  and  it  is 
now  a  well  established  fact  that  any  fluid,  secreted  by  the  .mucous  membrane 
of  the  stomach,  which  is  either  alkaline  or  neutral,  is  not  normal  gastric  juice. 

The  specific  gravity  of  the  gastric  juice  in  the  case  of  St.  Martin,  accord- 


220  GASTRIC  DIGESTION. 

ing  to  the  observations  of  Beaumont  and  Silliman,  was  1005  ;  but  later,  F.  G. 
Smith  found  it  in  one  instance,  1008,  and  in  another,  1009.  There  is  every 
reason  to  suppose  that  the  fluid,  in  the  case  of  St.  Martin,  was  perfectly  nor- 
mal, and  1005  to  1009  may  be  taken  as  the  range  of  the  specific  gravity  of  the 
gastric  juice  in  the  human  subject. 

The  gastric  juice  is  described  by  Beaumont  as  inodorous,  when  taken 
directly  from  the  stomach ;  but  it  has  rather  an  aromatic  and  a  not  disagree- 
able odor  when  it  has  been  kept  for  some  time.  It  is  a  little  saltish,  and  its 
taste  is  similar  to  that  of  "  thin,  mucilaginous  water  slightly  acidulated  with 
muriatic  acid." 

It  has  been  found  by  Beaumont,  in  the  human  subject,  and  by  those  who 
have  experimented  on  the  gastric  juice  of  the  lower  animals,  that  this  fluid, 
if  kept  in  a  well  stoppered  bottle,  will  retain  its  chemical  and  physiological 
properties  for  an  indefinite  period.  The  only  change  which  it  undergoes  is 
the  formation  of  a  pellicle,  consisting  of  a  vegetable,  confervoid  growth,  upon 
the  surface,  some  of  which  breaks  up  and  falls  to  the  bottom  of  the  vessel, 
forming  a  whitish,  flocculent  sediment.  In  addition  to  this  remarkable  fac- 
ulty of  resisting  putrefaction,  putrefactive  changes  are  arrested  in  decompos- 
ing animal  substances,  both  when  taken  into  the  stomach  and  when  exposed 
to  the  action  of  the  gastric  juice  out  of  the  body. 

There  are  on  record  no  minute  quantitative  analyses  of  the  human  gastric 
juice,  except  those  by  Schmidt,  of  the  fluid  from  the  stomach  of  a  woman 
with  gastric  fistula ;  and  in  this  case  there  is  reason  to  suppose  that  the  se- 
cretion was  not  normal.  The  analysis  of  the  gastric  juice  of  St.  Martin  by 
Berzelius  was  not  minute.  The  analyses  of  Schmidt  give  less  than  six  parts 
per  thousand  of  solid  matter,  while  Berzelius  found  more  than  twelve  parts  per 
thousand.  In  all  the  comparatively  recent  analyses,  there  have  been  found 
a  free  acid  or  acids,  a  peculiar  organic  matter,  generally  called  pepsine,  and 
various  inorganic  salts. 

The  following  analysis  by  Bidder  and  Schmidt  gives  the  mean  of  nine 
observations  upon  dogs : 

COMPOSITION  OF  THE  GASTRIC  JUICE  OF  THE  DOG  (BIDDER  AND  SCHMIDT). 

Water 973-062 

Ferment  (pepsine) 17-127 

Free  hydrochloric  acid 3'050 

Potassium  chloride 1-125 

Sodium  chloride 2-507 

Calcium  chloride 0-624 

Ammonium  chloride 0-468 

Calcium  phosphate 1-729 

Magnesium  phosphate 0-226 

Ferric  phosphate 0-082 

1,000-000 

In  another  series  of  three  observations,  in  which  the  saliva  was  allowed  to 
pass  into  the  stomach,  the  proportion  of  free  acid  was  2-337,  and  the  propor- 
tion of  organic  matter  was  somewhat  increased. 


GASTRIC  JUICE.  221 

Organic  Constituent  of  the  Gastric  Juice. — Pepsine  is  an  organic  nitro- 
genized  substance,  which  is  peculiar  to  the  gastric  juice  and  essential  to  its 
digestive  properties.  When  the  gastric  fluid  was  first  obtained,  even  by  the 
imperfect  methods  employed  anterior  to  the  observations  of  Beaumont  and 
of  Blondlot,  an  organic  matter  was  spoken  of  as  one  of  its  constituents. 

Experiments  on  artificial  digestive  fluids,  by  Eberle,  Schwann  and  Miil- 
ler,  Wasmann  and  others,  have  demonstrated  that  acidulated  extracts  of  the 
mucous  membrane  of  the  stomach  contain  an  organic  matter,  first  isolated  by 
Wasmann,  on  which  the  solvent  powers  of  these  acid  fluids  seem  to  depend. 
Mialhe,  who  has  obtained  this  substance  in  great  purity  by  the  process  recom- 
mended by  Vogel,  described  the  following  properties  as  characteristic  of  the 
organic  matter  in  artificial  gastric  juice :  Dried  in  thin  slices  on  a  plate  of 
glass,  it  is  in  the  form  of  small,  grayish,  translucent  scales,  with  a  faint  and 
peculiar  odor  and  a  feebly  bitter  and  nauseous  taste.  It  is  soluble  in  water 
and  in  a  weak  alcoholic  mixture,  but  is  insoluble  in  absolute  alcohol.  A 
solution  of  it  is  rendered  somewhat  turbid  by  a  temperature  of  212°  Fahr. 
(100°  C.),  but  it  is  not  coagulated,  although  it  loses  its  digestive  properties. 
It  is  not  affected  by  acids  but  is  precipitated  by  tannin,  creosote  and  a  great 
number  of  metallic  salts.  This  substance  dissolved  in  water  slightly  acidu- 
lated possesses,  in  a  very  marked  degree,  the  solvent  properties  of  the  gastric 
^uice ;  but  it  has  been  found  by  Payen  and  Mialhe  not  to  be  so  active  as  the 
substance  extracted  from  the  gastric  juice  itself,  which  is  described  by  Payen, 
under  the  name  of  gasterase.  In  the  abattoirs  of  Paris,  Mialhe  collected 
from  the  secreting  stomachs  of  calves  as  they  were  killed,  between  six  and 
ten  pints  (2'8  and  4'7  litres)  of  gastric  juice ;  and  from  this  he  extracted  the 
pure  pepsine  by  the  process  recommended  by  Payen,  which  consists  merely  in 
one  or  two  precipitations  by  alcohol.  This  substance  he  found  to  be  identical 
with  the  substance  obtained  by  Payen  from  the  gastric  juice  of  the  dog.  Its 
action  upon  albuminoid  matters  was  precisely  the  same  as  that  of  pepsine 
extracted  from  artificial  gastric  juice,  except  that  it  was  more  powerful. 

Free  Acid  of  the  Gastric  Juice.. — The  character  of  the  free  acid  of  the 
gastric  juice  has  long  been  a  question  of  uncertainty  and  dispute.  In  former 
editions  of  this  work,  the  different  views  of  chemists  with  regard  to  the  nature 
of  this  acid  were  fully  discussed.  It  may  now  be  stated  that  almost  all  physi- 
ologists adopt  the  view  that  the  gastric  juice  contains  free  hydrochloric  acid, 
with  possibly  a  very  small  quantity  of  lactic  acid.  It  is  admitted,  however, 
that  the  degree  of  acidity  of  the  gastric  juice  is  variable,  and  that  the  normal 
acid  may  be  replaced,  without  loss  of  the  digestive  properties  of  the  fluid,  by 
lactic,  oxalic,  acetic,  formic,  succinic,  tartaric,  citric,  phosphoric,  nitric  or 
sulphuric  acid. 

Saline  Constituents  of  the  Gastric  Juice.  —  It  has  been  shown  that 
artificial  fluids  containing  the  organic  matter  of  the  gastric  juice  and  the 
proper  proportion  of  free  acid  are  endowed  with  all  the  digestive  properties 
of  the  normal  secretion  from  the  stomach,  and  that  these  properties  are 
rather  impaired  when  an  excess  of  its  normal  saline  constituents  is  added  or 
when  the  relation  of  the  salts  to  the  water  is  disturbed  by  concentration. 
16 


222  GASTRIC  DIGESTION. 

Boudault  and  Corvisart  evaporated  6*76  oz.  (200  c.  c.)  of  the  gastric  juice  of 
the  dog  to  dryness  and  added  to  the  residue,  1'69  oz.  (50  c.  c.)  of  water.  They 
found  that  the  fluid  thus  prepared,  containing  four  times  the  normal  propor- 
tion of  saline  constituents,  did  not  possess  by  any  means  the  energy  of  action 
on  alimentary  substances  of  the  normal  secretion.  These  facts  have  led 
physiologists  to  attach  little  importance  to  the  saline  constituents  of  the  gas- 
tric juice,  except  sodium  chloride,  which  is  thought  to  be  concerned  in  the 
production  of  hydrochloric  acid. 

Action  of  the  Gastric  Juice  in  Digestion. — Certain  of  the  substances  most 
readily  attacked  by  the  gastric  juice  are  acted  upon  by  weak,  acid  solutions 
containing  no  organic  matter ;  but  it  is  now  well  established  that  the  presence 
of  a  peculiar  organic  matter  is  a  condition  indispensable  to  actual  diges- 
tion. It  has  also  been  shown  that  fluids  containing  the  organic  constituent 
of  the  gastric  juice  have  no  digestive  properties  unless  they  also  possess  the 
proper  degree  of  acidity ;  and  it  is  as  well  settled  that  fluids  containing  acids 
alone  have  no  action  on  albuminoids  similar  to  that  which  takes  place  in 
digestion,  and  that  when  these  substances  are  dissolved  by  them  it  is  simply 
accidental. 

The  presence  of  any  one  particular  acid  does  not  seem  essential  to  the 
digestive  properties  of  the  gastric  juice,  so  long  as  the  proper  degree  of  acidity 
is  preserved,  and  it  is  undoubtedly  important  that  the  normal  acid  can  be  re- 
placed by  other  acids ;  for  in  case  any  salt  were  introduced  into  the  stomach 
which  would  be  decomposed  by  the  acid  of  the  gastric  juice,  digestion  would 
be  interfered  with,  unless  the  liberated  acid  could  take  its  place.  It  can 
readily  be  appreciated  that  transient  disturbances  might  occur  from  this 
cause,  were  the  existence  of  any  one  acid  indispensable  to  the  digestive  prop- 
erties of  the  gastric  juice ;  while  if  only  a  certain  degree  of  acidity  were  re- 
quired, this  condition  might  be  produced  by  any  acid,  either  derived  from  the 
food  or  secreted  by  the  stomach. 

In  studying  the  physiological  action  of  the  gastric  juice,  it  must  always  be 
borne  in  mind  that  the  general  process  of  digestion  is  accomplished  by  the 
combined  as  well  as  the  successive  action  of  the  different  digestive  fluids. 
The  act  should  be  viewed  in  its  ensemble,  rather  than  as  a  process  consisting 
of  several  successive  and  distinct  operations,  in  which  different  classes  of  ali- 
mentary matters  are  dissolved  by  distinct  fluids.  The  food  meets  with  the 
gastric  juice,  after  having  become  impregnated  with  a  large  quantity  of 
saliva ;  and  it  passes  from  the  stomach  to  be  acted  upon  by  the  intestinal 
fluids,  having  imbibed  both  saliva  and  gastric  juice. 

When  the  acts  which  take  place  in  the  mouth  are  properly  performed,  the 
following  alimentary  substances,  comminuted  by  the  action  of  the  teeth  and 
thoroughly  insalivated,  are  taken  into  the  stomach  :  muscular  tissue,  contain- 
ing the  muscular  substance  enveloped  in  its  sarcolemma,  blood-vessels,  nerves, 
ordinary  fibrous  tissue  holding  the  muscular  fibres  together,  interstitial  fat, 
and  a  small  quantity  of  albuminoids  and  corpuscles  from  the  blood,  all  com- 
bined with  a  considerable  quantity  of  inorganic  salts ;  albumin,  sometimes 
unchanged,  but  generally  in  a  more  or  less  perfectly  coagulated  condition ; 


ACTION  OF  THE  GASTRIC  JUICE.  223 

fatty  matter,  sometimes  in  the  form  of  oil  and  sometimes  enclosed  in  vesicles, 
constituting  adipose  tissue ;  gelatine  and  animal  matters  in  a  liquid  form 
extracted  from  meats,  as  in  soups ;  caseine,  in  its  liquid  form  united  with 
butter  and  salts  in  milk,  and  coagulated  in  connection  with  various  other 
matters,  in  cheese ;  vegetable  nitrogenized  matters,  of  which  gluten  may  be 
taken  as  the  type  ;  vegetable  fats  and  oils ;  sugars,  both  from  the  animal  and 
vegetable  kingdoms,  but  chiefly  from  vegetables ;  the  different  varieties  of 
amylaceous  substances ;  and  finally,  organic  acids  and  salts,  derived  chiefly 
from  vegetables.  These  matters,  particularly  those  from  the  vegetable  king- 
dom, are  united  with  more  or  less  innutritions  matter,  such  as  cellulose. 
They  are  also  seasoned  with  aromatic  substances,  condiments  etc.,  which  are 
not  directly  used  in  nutrition. 

The  various  articles  described  as  drinks  are  taken  without  any  consid- 
erable admixture  with  the  saliva.  They  embrace  water  and  the  various 
nutritious  or  stimulant  infusions  (including  alcoholic  beverages)  with  a  small 
proportion  of  inorganic  salts  in  solution. 

Action  of  the  Gastric  Juice  upon  Meats. — There  are  three  ways  in  which 
the  action  of  the  gastric  juice  upon  the  various  articles  of  food  may  be  studied. 
One  is  to  subject  them  to  the  action  of  the  pure  fluid  taken  from  the  stomach, 
as  was  done  by  Beaumont,  in  the  human  subject,  and  by  Blondlot  and  others, 
in  experiments  upon  the  inferior  animals ;  another  is  to  make  use  of  prop- 
erly prepared  acidulated  extracts  of  the  mucous  membrane  of  the  stomach, 
which  have  been  shown  to  have  many  of  the  properties  of  the  gastric  juice, 
differing  mainly  in  activity ;  and  another  is  to  examine  from  time  to  time  the 
contents  of  the  stomach  after  food  has  been  taken.  By  all  of  these  methods 
of  study  it  has  been  shown  that  the  digestion  of  meat  in  the  stomach  is  far 
from  complete.  The  parts  of  the  muscular  structure  most  easily  attacked 
are  the  fibrous  tissue  which  holds  the  muscular  fibres  together,  and  the  sar- 
colemma,  or  sheath  of  the  fibres  themselves.  If  the  gastric  juice  of  the  dog 
be  placed  in  a  vessel  with  finely  chopped  lean  meat  and  be  kept  in  contact 
with  it  for  a  number  of  hours  at  about  100°  Fahr.  (37'78°  C.),  agitating  the 
vessel  occasionally  so  as  to  subject,  as  far  as  possible,  every  particle  of  the 
meat  to  its  action,  the  filtered  fluid  will  be  found  increased  in  density,  its 
acidity  diminished,  and  presenting  all  the  evidences  of  having  dissolved  a 
considerable  portion  of  the  tissue.  There  always,  however,  will  remain  a  cer- 
tain portion  which  'has  not  been  dissolved.  Its  constitution  is  nevertheless 
materially  changed ;  for  it  no  longer  possesses  the  ordinary  character  of 
muscular  tissue,  but  easily  breaks  down  between  the  fingers  into  a  pultaceous 
mass.  On  subjecting  this  residue  to  microscopical  examination,  it  is  found 
not  to  contain  any  ordinary  fibrous  tissue  ;  and  the  fibres  of  muscular  tissue, 
although  presenting  the  well  marked  and  characteristic  striae,  are  broken  into 
short  pieces  and  possess  very  little  tenacity.  It  is  evidently  only  the  muscu- 
lar substance  which  remains ;  the  connective  tissue  and  the  sarcolemma  hav- 
ing been  dissolved.  These  facts  have  been  repeatedly  noted,  and  even  on 
adding  fresh  juice  to  the  undigested  matter,  it  is  not  dissolved  to  any  con- 
siderable extent,  the  residue  not  being  sensibly  diminished  in  quantity,  and 


224 


GASTRIC  DIGESTION. 


the  muscular  substance  always  presenting  its  characteristic  stride,  on  micro- 
scopical examination.  Bernard,  in  experiments  with  the  gastric  juice  of 
different  animals,  found  the  fluid  from  the  stomach  of  the  rabbit  or  the  horse 

much  inferior,  as  re- 
gards the  activity  of  its 
action  upon  meat,  to 
the  gastric  juice  of  the 
dog. 

Whether  the  gas- 
tric juice  be  entirely 
incapable  of  acting 
upon  the  muscular 
substance  or  not,  the 
above-mentioned  facts 
clearly  show  that  mus- 
cular tissue  usually  is 
not  completely  digest- 
ed in  the  stomach. 
The  action  in  this  or- 
gan is  to  dissolve  the 
intermuscular  fibrous 
tissue  and  the  sarco- 
lemma,  or  sheath  of 
the  muscular  fibres, 
setting  the  true  muscular  substance  free  and  breaking  it  up  into  small  par- 
ticles. The  mass  of  tissue  is  thus  reduced  to  the  condition  of  a  thin,  pulta- 
ceous  fluid,  which  passes  into  the  small  intestine,  where  the  process  of  diges- 
tion is  completed. 

The  constituents  of  the  blood,  albuminoids,  corpuscles  etc.,  which  may 
be  introduced  in  small  quantity  in  connection  with  muscular  tissue,  probably 
are  completely  dissolved  in  the  stomach. 

Action  upon  Albumin,  Fibrin,  Caseine  and  Gelatine. — The  action  of  the 
gastric  juice  upon  uncooked  white  of  egg  is  to  disintegrate  its  structure, 
separating  and  finally  dissolving  the  membranous  sacs  in  which  the  albumin 
is  contained.  It  also  acts  upon  the  albumin  itself,  forming  a  new  fluid  sub- 
stance, called  albumin-peptone,  which,  unlike  albumin,  is  not  coagulated 
by  heat  or  acids,  but  is  precipitated  by  alcohol,  tannin  and  many  of  the 
metallic  salts.  The  digestion  of  raw  or  imperfectly  coagulated  albumin 
takes  place  with  considerable  rapidity  in  the  stomach  ;  and  the  digestion  of 
albumin  in  this  form  is  more  rapid  than  when  it  has  been  completely  coagu- 
lated by  heat.  It  is  a  matter  of  common  as  well  as  of  scientific  observation, 
that  eggs  when  hard-boiled  are  less  easily  digested  than  when  they  are  soft- 
boiled  or  uncooked.  The  products  of  the  digestion  of  raw  or  of  coagulated 
albumin,  albumin-peptone,  are  essentially  the  same.  It  is  probable  that  the 
entire  process  of  digestion  and  absorption  of  albumin  takes  place  in  the 
stomach  ;  and  if  any  albumin  pass  out  of  the  pylorus,  the  quantity  is  very  small. 


FIG.  65.— Matters  taken  from  the  pyloric  portion  of  the  stomach  of  a 
dog  during  digestion  of  mixed  food  (Bernard). 

o,  disintegrated  muscular  fibres,  the  striae  having  disappeared ;  6,  c, 
muscular  fibres  in  which  the  striae  have  partly  disappeared  ;  d,  d,  d, 
globules  of  fat ;  e,  e,  e,  starch  ;  g,  molecular  granules. 


ACTION  OF  THE  GASTRIC  JUICE.  225 

Fibrin,  as  distinguished  from  the  so-called  fibrin  of  the  muscular  tissue, 
or  myosine,  is  not  a  very  important  article  of  food.  The  action  of  the  gas- 
tric juice  upon  it  is  more  rapid  and  complete  than  upon  albumin.  The  well 
known  action  upon  fibrin,  of  water  slightly  acidulated  with  hydrochloric 
acid,  has  led  some  physiologists  to  assume  that  the  acid  is  the  only  con- 
stituent in  the  gastric  juice  necessary  to  the  digestion  of  this  substance; 
but  observations  on  the  comparative  action  of  acidulated  water  and  of 
artificial  or  natural  gastric  juice  show  that  the  presence  of  the  organic 
matter  is  necessary  to  the  digestion  of  this  as  well  as  of  other  nitrogen- 
ized  alimentary  substances.  The  action  of  water  containing  a  small  propor- 
tion of  acid  is  to  render  fibrin  soft  and  transparent,  frequently  giving  to 
the  entire  mass  a  jelly-like  consistence.  The  result  of  the  digestion  of 
fibrin  in  the  gastric  juice  or  in  an  acidulated  fluid  to  which  pepsine  has  been 
added,  is  its  complete  solution  and  transformation  into  a  substance  which  is 
not  affected  by  heat,  acids  or  by  rennet.  The  substance  resulting  from  the 
action  of  gastric  juice  upon  fibrin,  called  fibrin-peptone,  resembles  albumin- 
peptone,  but  nevertheless  has  certain  distinctive  characters. 

Liquid  caseine  is  immediately  coagulated  by  the  gastric  juice,  by  the 
action  both  of  the  free  acid  and  the  organic  matter.  Once  coagulated,  caseine 
is  acted  upon  in  the  same  way  as  coagulated  albumen.  The  caseine  which  is 
taken  as  an  ingredient  of  cheese  is  digested  in  the  same  way.  According  to 
Lehmaun,  coagulated  caseine  requires  a  longer  time  for  its  solution  in  the 
stomach  than  most  other  nitrogenized  substances.  The  caseine  of  human 
milk,  which  coagulates  only  into  a  sort  of  jelly,  is  more  easily  digested  than 
caseine  from  cow's  milk  (Elasser).  The  product  of  the  digestion  of  caseine 
is  a  soluble  substance,  not  coagulable  by  heat  or  the  acids,  called  caseine- 
peptone. 

Gelatine  is  rapidly  dissolved  in  the  gastric  juice,  when  it  loses  the  char- 
acters by  which  it  is  ordinarily  recognized,  and  no  lo'nger  forms  a  jelly  on 
cooling.  This  substance  is  much  more  rapidly  disposed  of  than  the  tissues 
from  which  it  is  formed,  and  the  products  of  its  digestion  in  the  gastric 
juice  resemble  the  substances  resulting  from  the  digestion  of  the  albumi- 
noids generally. 

Action  on  Vegetable  Nitrogenized  Substances. — These  substances,  of  which 
gluten  may  be  taken  as  the  type,  undoubtedly  are  digested  chiefly  in  the 
stomach.  Raw  gluten  is  acted  upon  very  much  in  the  same  way  as  fibrin, 
and  cooked  gluten  behaves  like  coagulated  albumin.  '  Vegetable  articles  of 
food  generally  contain  gluten  in  greater  or  less  quantity,  or  substances  resem- 
bling it,  as  well  as  various  non-nitrogenized  matters,  and  cellulose.  The  fact 
that  these  articles  are  not  easily  attacked  in  any  portion  of  the  alimentary 
canal,  unless  they  have  been  well  comminuted  in  the  mouth,  is  shown  by 
the  passage  of  grains  of  corn,  beans  etc.,  in  the  faeces.  When  properly  pre- 
pared by  mastication  and  insalivation,  the  action  of  the  gastric  juice  is  to 
disintegrate  them,  dissolving  out  the  nitrogenized  matters,  freeing  the  starch 
and  other-  matters  so  that  they  may  be  more  easily  acted  upon  in  the  intes- 
tines, and  leaving  the  hard,  indigestible  matters,  such  as  cellulose,  to  pass 


226  .       GASTRIC  DIGESTION. 

away  in  the  faeces.  The  nitrogenized  constituents  of  bread  are  probably  acted 
upon  in  the  stomach  in  the  same  way  and  to  the  same  extent  as  albumen, 
fibrin  and  caseine. 

Peptones. — It  has  been  shown  that  gastric  digestion  is  not  merely  a  solu- 
tion of  certain  alimentary  matters,  but  that  these  substances  undergo  very 
marked  changes  and  lose  the  properties  by  which  they  are  generally  recog- 
nized. That  the  different  products  of  this  transformation  resemble  each 
other  very  closely  is  also  undoubted ;  but  there  are  certain  differences  in  the 
chemical  composition  of  the  products  of  digestion  of  the  different  constitu- 
ents of  food,  as  well  as  differences,  which  have  lately  been  noted,  as  regards 
their  behavior  with  reagents. 

The  peptones  in  solution  form  colorless  liquids,  having  a  feeble  odor  re- 
sembling that  of  meat.  They  are  not  coagulable  by  heat  or  by  most  acids,  a 
property  which  distinguishes  them  from  almost  all  of  the  nitrogenized  con- 
stituents of  food.  They  are  coagulated,  however,  by  many  of  the  metallic 
salts,  by  chlorine,  and  by  tannin,  in  slightly  acidulated  solutions.  On  evapo- 
rating peptones  to  dryness,  the  residue  consists  of  a  yellowish- white  substance, 
resembling  desiccated  white  of  egg.  This  is  soluble  in  water,  when  it  regains 
its  characteristic  properties,  but  is  entirely  insoluble  in  alcohol. 

It  is  evident  that  the  gastric  juice,  aside  from  its  action  in  preparing  cer- 
tain articles  for  digestion  by  the  intestinal  fluids,  does  not  simply  liquefy 
certain  of  the  alimentary  matters,  but  changes  them  in  such  a  way  as  to  ren- 
der them  osmotic  and  provides  against  the  coagulation  which  is  so  readily 
induced  in  ordinary  nitrogenized  bodies.  Peptones  pass  through  membranes 
with  great  facility. 

Another,  the  most  important  and  the  essential  change  which  is  exerted 
by  the  gastric  juice  upon  the  albuminoids,  is  that 'by  which  they  are  rendered 
capable  of  assimilation  by  the  system  after  their  absorption.  Pure  albumin 
and  gelatine,  when  injected  into  the  blood,  are  not  assimilable  and  are 
rejected  by  the  kidneys ;  but  albumin  and  gelatine  which  have  been  digested 
in  gastric  juice  are  assimilated  in  the  same  way  as  though  they  had  pene- 
trated by  the  natural  process  of  absorption  from  the  alimentary  canal  (Ber- 
nard and  Barreswil).  The  same  is  true  of  caseine  and  fibrin.  These  facts, 
showing  that  something  more  is  necessary  in  gastric  digestion  than  mere 
solution,  point  to  pepsine  as  the  important  agent  in  producing  the  peculiar 
modifications  so  necessary  to  proper  assimilation  of  nitrogenized  alimentary 
substances.  The  action  of  pepsine  is  essential  to  the  changes  which  occur  in 
the  albuminoid  alimentary  matters,  resulting  in  the  formation  of  what  are 
known  as  peptones ;  and  the  change  into  peptones  takes  place  in  all  nitro- 
genized substances  that  are  dissolved  in  the  stomach.  This  may  occur  even 
when  the  albuminoid  matters  are  somewhat  advanced  in  putrefaction ;  and 
the  gastric  juice  possesses  antiseptic  properties,  which  fact  accounts  for  the 
frequent  innocuousness  of  animal  substances  in  various  stages  of  decomposi- 
tion when  taken  into  the  stomach. 

The  change  of  the  albuminoids  into  peptones  in  the  stomach  is  not  direct. 
The  intermediate  processes  probably  are  the  following  :  The  albuminoids  are 


ACTION  OF  THE  GASTKIC  JUICE.  227 

first  changed  by  the  gastric  juice  into  an  acid-albumin  or  albuminate ;  this  is 
farther  changed  into  propeptone,  or  as  it  is  called  by  Kiihne,  hemialbumose ; 
and  the  final  action  is  a  change  into  the  true  peptones.  These  intermediate 
processes  have  been  studied  in  artificial  digestion,  and  the  acid-albumin  and 
propeptone  differ,  in  some  of  their  chemical  properties  which  it  is  not  neces- 
sary to  describe  in  detail,  from  both  albumin  and  peptone.  A  temperature 
near  that  of  the  body  is  necessary  to  the  various  changes  just  mentioned. 

Action  of  the  Gastric  Juice  on  Fats,  Sugars  and  Amylaceous  Substances. 
— Most  of  the  fatty  constituents  of  the  food  are  liquefied  at  the  temperature 
of  the  body ;  and  when  taken  in  the  form  of  adipose  tissue,  the  vesicles  in 
which  the  fatty  matters  are  contained  are  dissolved,  the  fat  is  set  free,  is 
melted  and  floats  in  the  form  of  drops  of  oil  on  the  alimentary  mass.  The 
action  of  the  stomach,  then,  seems  to  be  to  prepare  the  fats,  chiefly  by  dis- 
solving the  adipose  vesicles,  for  the  complete  digestion  which  takes  place  in 
the  small  intestine. 

The  varieties  of  sugar  of  which  glucose  is  the  type  undergo  little  if  any 
change  in  digestion  and  are  probably  in  greatest  part  directly  absorbed  by 
the  mucous  membrane  of  the  stomach.  This  is  not  the  case,  however,  with 
the  varieties  of  sugar  classed  with  cane-sugar.  It  has  been  shown  that  cane- 
sugar  injected  into  the  veins  of  a  living  animal  is  not  assimilated  by  the  sys- 
tem but  is  immediately  rejected  by  the  kidneys.  When,  however,  it  has  been 
changed  into  glucose  by  the  action  of  a  dilute  acid  or  by  digestion  in  the  gas- 
tric juice,  it  no  longer  behaves  as  a  foreign  substance  and  does  not  appear  in 
the  urine.  Experiments  have  shown  that  cane-sugar,  after  being  digested 
for  several  hours  in  the  gastric  juice,  is  slowly  converted  into  glucose.  This 
action  does  not  depend  upon  any  constituent  of  the  gastric  juice  except  the 
free  acid ;  and  a  dilute  mixture  of  hydrochloric  acid  had  an  equally  marked 
effect.  Experiments  in  artificial  digestion  have  shown  that  cane-sugar  is 
transformed  into  glucose  by  the  gastric  juice  very  slowly,  the  action  of  this 
fluid  in  no  way  differing  from  that  of  very  dilute  acids.  In  the  natural  pro- 
cess of  digestion,  this  action  may  take  place  to  a  certain  extent ;  but  it  is  not 
shown  to  be  constant  or  important. 

The  action  of  gastric  juice,  unmixed  with  saliva,  upon  starch  is  entirely 
negative,  as  far  as  any  transformation  into  sugar  is  concerned.  When  the 
starch  is  enclosed  in  vegetable  cells,  it  is  set  free  by  the  action  of  the  gastric 
juice  upon  the  nitrogenized  parts.  Eaw  starch  in  the  form  of  granules 
becomes  hydrated  in  the  stomach,  on  account  of  the  elevated  temperature 
and  the  acidity  of  the  contents  of  the  organ.  This  is  not  the  form,  however, 
in  which  starch  is  generally  taken  by  the  human  subject ;  but  when  it  is  so 
taken,  the  stomach  evidently  assists  in  preparing  it  for  the  more  complete 
processes  of  digestion  which  are  to  take  place  in  the  small  intestine. 

Cooked  or  hydrated  starch,  the  form  in  which  it  exists  in  bread,  fari- 
naceous preparations  generally  and  ordinary  vegetables,  is  not  affected  by 
the  pure  gastric  juice  and  passes  out  at  the  pylorus  unchanged.  It  must  be 
remembered,  however,  that  the  gastric  juice  does  not  entirely  prevent  a  con- 
tinuance of  the  action  of  the  saliva  ;  and  experiments  have  shown  that  gastric 


228  GASTRIC  DIGESTION. 

juice  taken  from  the  stomach,  when  it  contains  a  notable  quantity  of  saliva, 
has,  to  a  certain  extent,  the  power  of  transforming  starch  into  sugar. 

The  changes  which  vegetable  acids  and  salts,  the  various  inorganic  con- 
stituents of  food  and  the  liquids  which  are  classed  as  drinks  undergo  in  the 
stomach  are  very  slight.  Most  of  these  substances  can  hardly  be  said  to  be 
digested ;  for  they  are  either  liquid  or  in  solution  in  water  and  are  capable 
of  direct  absorption  and  assimilation.  With  regard  to  most  of  the  inorganic 
salts,  they  either  exist  in  small  quantity  in  the  ordinary  water  taken  as  drink 
or  are  united  with  organic  nitrogenized  substances.  In  the  latter  case,  they 
become  intimately  combined  with  the  organic  matters  resulting  from  gastric 
digestion.  It  has  been  noted  that  the  various  peptones  contain  the  same 
inorganic  salts  which  existed  in  the  nitrogenized  substances  from  which  they 
were  formed. 

Some  discussion  has  arisen  with  regard  to  the  action  of  the  fluids  of  the 
stomach  upon  calcium  phosphate  and  calcium  carbonate,  salts  which  are  con- 
sidered nearly  if  not  entirely  insoluble.  Observations  on  both  natural  and 
artificial  digestion  have  shown  that  the  calcareous  constituents  of  bone  are 
to  a  certain  extent  dissolved  in  the  gastric  juice.  Bones  are  digested  to  a 
considerable  extent  in  the  stomach,  although  the  greater  part  passes  through 
the  alimentary  canal  and  is  discharged  unchanged  in  the  fasces.  In  the  nat- 
ural process  of  digestion,  the  solution  of  the  calcareous  constituents  of  bone 
is  more  rapid  than  in  artificial  digestion,  from  the  fact  that  the  juice  is  being 
continually  absorbed  and  secreted  anew  by  the  mucous  membrane  of  the 
stomach. 

Duration  of  Gastric  Digestion. — Inasmuch  as  comparatively  few  articles, 
and  these  belonging  exclusively  to  the  class  of  organic  nitrogenized  sub- 
stances, are  completely  dissolved  in  the  stomach,  it  is  evident  that  the  length 
of  time  during  which  food  remains  in  this  organ,  or  the  time  occupied  in 
the  solution  of  food  by  gastric  juice  out  of  the  body,  does  not  represent  the 
absolute  digestibility  of  different  articles.  It  is,  nevertheless,  an  impor- 
tant question  to  ascertain,  as  nearly  as  possible,  the  duration  of  gastric  diges- 
tion. 

There  has  certainly  never  been  presented  so  favorable  an  opportunity  for 
determining  the  duration  of  gastric  digestion  as  in  the  case  of  St.  Martin. 
From  a  great  number  of  observations  made  on  digestion  in  the  stomach  itself, 
Beaumont  came  to  the  conclusion  that  "  the  time  ordinarily  required  for  the 
disposal  of  a  moderate  meal  of  the  fibrous  parts  of  meat,  with  bread,  etc.,  is 
three  to  three  and  a  half  hours."  The  observations  of  F.  G.  Smith,  made  .» 
upon  St.  Martin  many  years  later,  gave  two  hours  as  the  longest  time  that 
aliments  remained  in  the  stomach.  In  a  case  of  intestinal  fistula  reported 
by  Busch,  it  was  noted  that  food  began  to  pass  out  of  the  stomach  into  the 
intestines  fifteen  minutes  after  its  ingestion  and  continued  to  pass  for  three 
or  four  hours,  until  the  stomach  was  emptied. 

Undoubtedly,  the  duration  of  gastric  digestion  varies  in  different  individ- 
uals and  is  greatly  dependent  upon  the  kind  and  quantity  of  food  taken,  con- 
ditions of  the  nervous  system,  exercise  etc.  As  a  mere  approximation,  the 


ACTION  OF  THE  GASTRIC  JUICE.  229 

average  time  that  food  remains  in  the  stomach  after  an  ordinary  meal  may 
be  stated  to  be  between  two  and  four  hours. 

Milk  is  one  of  the  articles  digested  in  the  stomach  with  greatest  ease. 
Its  highly  nutritive  properties  and  the  variety  of  its  nutritious  constituents 
render  it  very  valuable  as  an  article  of  diet,  particularly  when  the  digest- 
ive powers  are  impaired  and  when  it  is  important  to  supply  the  system 
with  considerable  nutriment.  Eggs  are  likewise  highly  nutritious  and  are 
easily  digested.  Raw  and  soft-boiled  eggs  are  more  easily  digested  than 
hard-boiled  eggs.  "  Whipped  "  eggs  are  apparently  disposed  of  with  great 
facility.  As  a  rule  the  flesh  of  fish  is  more  easily  digested  than  that  of  the 
warm-blooded  animals.  Oysters,  especially  when  raw,  are  quite  easy  of 
digestion.  The  flesh  of  mammals  seems  to  be  more  easily  digested  than  the 
flesh  of  birds.  Of  the  different  kinds  of  meat,  venison,  lamb,  beef  and  mut- 
ton are  easily  digested,  while  veal  and  fat  roast-pork  are  digested  with  diffi- 
culty. Soups  are  generally  very  easily  digested.  The  animal  substances 
which  are  digested  most  rapidly,  however,  are  tripe,  pigs'  feet  and  brains. 
Vegetable  articles  are  digested  in  about  the  same  time  as  ordinary  animal 
food ;  but  a  great  part  of  the  digestion  of  these  substances  takes  place  in  the 
small  intestine.  Bread  is  digested  in  about  the  time  required  for  the  diges- 
tion of  the  ordinary  meats  (Beaumont). 

Conditions  which  influence  Gastric  Digestion. — The  various  conditions 
which  influence  gastric  digestion,  except  those  which  relate  exclusively  to 
the  character  or  the  quantity  of  food,  operate  mainly  by  influencing  the 
quantity  and  quality  of  the  gastric  juice.  It  is  seldom  that  temperature  has 
any  influence,  for  the  temperature  of  the  stomach  in  health  does  not  present 
variations  sufficient  to  have  any  marked  effect  upon  digestion. 

As  a  rule,  gentle  exercise,  with  repose  or  agreeable  and  tranquil  occupa- 
tion of  the  mind,  is  more  favorable  to  digestion  than  absolute  rest.  Violent 
exercise  or  severe  mental  or  physical  exertion  is  always  undesirable  immedi- 
ately after  the  ingestion  of  a  large  quantity  of  food,  and  as  a  matter  of  com- 
mon experience,  has  been  found  to  retard  digestion. 

The  effects  of  sudden  and  considerable  loss  of  blood  upon  gastric  di- 
gestion are  very  marked.  After  a  full  meal,  the  whole  alimentary  tract 
is  deeply  congested,  and  this  condition  is  undoubtedly  necessary  to  the 
secretion,  in  proper  quantity,  of  the  various  digestive  fluids.  When  the 
entire  quantity  of  blood  in  the  economy  is  greatly  diminished  from  any 
cause,  there  is  difficulty  in  supplying  the  amount  of  gastric  juice  neces- 
sary for  a  full  meal,  and  disorders  of  digestion  are  likely  to  occur,  es- 
pecially if  a  large  quantity  of  food  have  been  taken.  This  is  also  true  in 
inanition,  when  the  quantity  •  of  blood  is  greatly  diminished.  In  this  con- 
dition, although  the  system  constantly  craves  nourishment  and  the  ap- 
petite frequently  is  enormous,  food  should  be  taken  in  small  quantities  at  a 
time. 

As  a  rule  children  and  young  persons  digest  food  which  is  adapted  to 
them  more  easily  and  in  larger  relative  quantity  than  those  in  adult  life  or  in 
old  age ;  but  ordinarily  in  old  age  digestion  is  carried  on  with  more  vigor 


230  GASTRIC  DIGESTION. 

and  regularity  than  the  other  vegetative  processes,  such  as  general  assimila- 
tion, circulation  and  respiration. 

Influence  of  the  Nervous  System  on  the  Stomach. — It  is  well  known  that 
mental  emotions  frequently  have  a  marked  influence  on  digestion,  and  this, 
of  course,  can  take  place  only  through  the  nervous  system.  Of  the  two 
nerves  which  are  distributed  to  the  stomach,  the  pneumogastric  has  been  the 
more  carefully  studied,  experiments  upon  the  sympathetic  being  more  diffi- 
cult. Although  the  complete  history  of  the  influence  of  the  pneumogastrics 
upon  digestion  belongs  to  the  physiology  of  the  nervous  system,  it  will  be 
useful  in  this  connection  to  consider  briefly  some  of  the  facts  which  have 
been  ascertained  with  regard  to  the  influence  which  these  nerves  exert  upon 
the  stomach. 

The  experiments  of  Bernard  and  others  have  shown  that  the  vascular 
mechanism  of  the  mucous  membrane  is  to  a  great  extent  under  the  influence 
of  the  pneumogastrics.  If  these  nerves  be  divided  while  gastric  digestion  is  at 
its  height,  the  mucous  membrane  immediately  becomes  pale,  and  the  secre- 
tion of  gastric  juice  is  nearly  if  not  quite  arrested.  It  has  been  found,  how- 
ever, that  gastric  juice  may  be  secreted  in  small  quantity  under  the  stimulus 
of  food,  even  when  both  pneumogastrics  and  the  sympathetic  nerves  going 
to  the  stomach  have  been  divided  (Heidenhain). 

Section  of  both  pneumogastrics,  while  it  does  not  entirely  paralyze  the 
muscular  coat  of  the  stomach,  renders  its  contractions  irregular  and  feeble. 
It  is  stated  that  section  of  these  nerves  is  followed  by  "  a  short  temporary 
contraction  of  the  cardiac  aperture  "  (Stirling). 

Movements  of  the  Stomach. — As  the  articles  of  food  are  passed  into  the 
stomach  by  the  acts  of  deglutition,  the  organ  gradually  changes  its  form, 
size  and  position.  When  the  stomach  is  empty,  the  opposite  surfaces  of  its 
lining  membrane  are  in  contact  in  many  parts  and  are  thrown  into  longitu- 
dinal folds.  As  the  organ  is  distended,  these  folds  are  effaced,  the  stomach 
itself  becoming  more  rounded,  and  as  the  two  ends,  with  the  lesser  curva- 
ture are  comparatively  immovable,  the  whole  organ  undergoes  a  movement 
of  rotation,  by  which  the  anterior  face  becomes  superior  and  is  applied  to 
the  diaphragm.  At  this  time  the  great  pouch  has  nearly  filled  the  left  hypo- 
chondriac region  ;  the  greater  curvature  presents  anteriorly  and  comes  in  con- 
tact with  the  abdominal  walls.  Aside  from  these  changes,  which  are  merely 
due  to  the  distention,  the  stomach  undergoes  important  movements,  which 
continue  until  its  contents  have  been  dissolved  and  absorbed  or  have  passed 
out  at  the  pylorus;  but  while  these  movements  are  taking  place,  the  two 
orifices  are  guarded,  so  that  the  food  shall  remain  for  the  proper  time  exposed 
to  the  action  of  the  gastric  juice.  By  the  rhythmical  contractions  of  the 
lower  extremity  of  the  oesophagus,  regurgitation  of  food  is  prevented ;  and 
the  circular  fibres,  which  form  a  thick  ring  at  the  pylorus,  are  constantly 
contracted,  so  that — at  least  during  the  first  periods  of  digestion — only 
liquids  and  that  portion  of  food  which  has  been  reduced  to  a  pultaceous 
consistence  can  pass  into  the  small  intestine.  It  is  well  known  that  this 
resistance  at  the  pylorus  does  not  endure  indefinitely,  for  indigestible  articles 


MOVEMENTS  OF  THE  STOMACH.  231 

of  considerable  size,  such  as  stones,  have  been  passed  by  the  anus  after  having 
been  introduced  into  the  stomach ;  but  observations  have  shown  that  masses 
of  digestible  matter  are  passed  by  the  movements  of  the  stomach  to  the 
pylorus,  over  and  over  again,  and  that  they  do  not  find  their  way  into  the 
intestine  until  they  have  become  softened  and  more  or  less  disintegrated. 

The  contractions  of  the  walls  of  the  stomach  are  of  the  kind  character- 
istic of  the  non-striated  muscular  fibres.  If  the  finger  be  introduced  into 
the  stomach  of  a  living  animal  during  digestion,  it  is  gently  but  rather  firmly 
grasped  by  a  contraction,  which  is  slow  and  gradual,  enduring  for  a  few 
seconds  and  as  slowly  and  gradually  relaxing  and  extending  to  another  part 
of  the  organ.  The  movements  during  digestion  present  certain  differences 
in  different  animals;  but  there  can  be  no  doubt  that  the  phenomenon  is 
universal.  In  dogs,  when  the  abdomen  is  opened  soon  after  the  ingestion  of 
food,  the  stomach  appears  pretty  firmly  contracted  on  its  contents.  In  a  case 
reported  by  Todd  and  Bowman,  in  the  human  subject,  in  which  the  stomach 
was  very  much  hypertrophied  and  the  walls  of  the  abdomen  were  very  thin, 
the  vermicular  movements  could  be  distinctly  seen.  These  movements  were 
active,  resembling  the  peristaltic  movements  of  the  intestines,  for  which,  in- 
deed, they  were  mistaken,  as  the  nature  of  the  case  was  not  recognized  during 
life.  No  argument,  therefore,  seems  necessary  to  show  that  during  digestion, 
the  stomach  is  the  seat  of  tolerably  active  movements. 

A  peculiarity  in  the  movements  of  the  stomach,  which  has  been  repeatedly 
observed  in  the  lower  animals,  particularly  dogs  and  cats,  and  in  certain  cases 
has  been  confirmed  in  the  human  subject,  is  that  at  about  the  junction  of 
the  cardiac  two-thirds  with  the  pyloric  third,  there  is  frequently  a  transverse 
band  of  fibres  so  firmly  contracted  as  to  divide  the  cavity  into  two  almost 
distinct  compartments.  It  has  also  been  noted  that  the  contractions  in  the 
cardiac  division  are  much  less  vigorous  than  near  the  pylorus ;  the  stomach 
seeming  simply  to  adapt  itself  to  the  food  by  a  gentle  pressure  as  it  remains 
in  the  great  pouch,  while  in  the  pyloric  portion,  divided  off  as  it  is  by  the 
hour-glass  contraction  above  mentioned,  the  movements  are  more  frequent, 
vigorous  and  expulsive. 

As  the  result  chiefly  of  the  observations  of  Beaumont,  the  following  may 
be  stated  as  a  summary  of  the  physiological  movements  of  the  stomach  in 
digestion : 

The  stomach  normally  undergoes  no  movements  until  food  is  passed  into 
its  cavity.  When  food  is  received,  at  the  same  time  that  the  mucous  mem- 
brane becomes  congested  and  the  secretion  of  gastric  juice  begins,  contrac- 
tions of  the  muscular  coat  occur,  which  are  at  first  slow  and  irregular,  but 
become  more  vigorous  and  regular  as  the  process  of  digestion  advances.  After 
digestion  has  become  fully  established,  the  stomach  is  generally  divided,  by 
the  firm  and  almost  constant  contraction  of  an  oblique  band  of  fibres,  into  a 
cardiac  and  a  pyloric  portion ;  the  former  occupying  about  two-thirds,  and 
the  latter,  one-third  of  the  length  of  the  organ.  The  contractions  of  the 
cardiac  division  of  the  stomach  are  uniform  and  rather  gentle ;  while  in  the 
pyloric  division,  they  are  intermittent  and  more  expulsive.  The  effect  of  the 


232  GASTRIC  DIGESTION. 

contractions  of  the  stomach  upon  the  food  contained  in  its  cavity  is  to  sub- 
ject it  to  a  tolerably  uniform  pressure  in  the  cardiac  portion,  the  general 
tendency  of  the  movement  being  toward  the  pylorus,  along  the  greater  curva- 
ture, and  back  from  the  pylorus  toward  the  great  pouch,  along  the  lesser 
curvature.  At  the  constricted  part  which  separates  the  cardiac  from  the 
pyloric  portion,  there  is  an  obstruction  to  the  passage  of  the  food  until  it  has 
been  sufficiently  acted  upon  by  the  secretions  in  the  cardiac  division  to  have 
become  reduced  to  a  pultaceous  consistence.  The  alimentary  mass  then 
passes  into  the  pyloric  division,  and  by  a  more  powerful  contraction  than 
occurs  in  other  parts  of  the  stomach,  it  is  passed  into  the  small  intestine. 

The  revolutions  of  the  alimentary  mass,  thus  accomplished,  take  place 
slowly,  by  gentle  and  persistent  contractions  of  the  muscular  coat ;  the  food 
occupying  two  or  three  minutes  in  its  passage  entirely  around  the  stomach. 
Every  time  that  a  revolution  is  accomplished,  the  contents  of  the  stomach 
are  somewhat  diminished  in  quantity ;  probably,  in  a  slight  degree,  from  ab- 
sorption of  digested  matter  by  the  stomach  itself,  but  chiefly  by  the  gradual 
passage  of  the  softened  and  disintegrated  mass  into  the  small  intestine.  This 
process  continues  until  the  stomach  is  emptied,  lasting  between  two  and  four 
hours ;  after  which,  the  movements  of  the  stomach  cease  until  food  is  again 
introduced. 

Kegurgitation  of  food  by  contractions  of  the  muscular  coats  of  the  stom- 
ach, eructation,  or  the  expulsion  of  gas,  and  vomiting  are  not  physiological 
acts.  It  has  been  shown  that  vomiting  is  produced  by  contractions  of  the 
abdominal  muscles  and  the  diaphragm,  compressing  the  stomach,  which  is 
passive,  except  that  the  pyloric  opening  is  firmly  closed,  the  cardiac  opening 
being  relaxed.  Eructation,  although  usually  involuntary,  is  sometimes  under 
the  control  of  the  will.  When  it  occurs,  while  it  is  difficult  or  impossible  to 
prevent  the  discharge  of  the  gas,  the  accompanying  sound  may  be  readily 
suppressed.  Eructation  frequently  becomes  a  habit,  which  in  many  persons 
is  so  developed  by  practice  that  the  act  may  be  performed  voluntarily  at  any 
time.  The  gaseous  contents  of  the  stomach  during  digestion  are  composed 
of  oxygen,  carbon  dioxide,  hydrogen  and  nitrogen,  in  proportions  that  are 
very  variable. 


PHYSIOLOGICAL  ANATOMY  OF  THE  SMALL  INTESTINE.    233 

CHAPTER   IX. 

INTESTINAL  DIGESTION. 

Physiological  anatomy  of  the  small  intestine — Glands  of  Brunner — Intestinal  tubules,  or  follicles  of  Lieber- 
kuhn—  Intestinal  villi — Solitary  glands,  or  follicles,  and  patches  of  Peyer — Intestinal  juice — Action  of 
the  intestinal  juice  in  digestion — Pancreatic  juice — Action  of  the  pancreatic  juice  upon  starches  and 
sugars — Action  upon  nitrogenized  substances — Action  upon  fats — Action  of  the  bile  in  digestion — Bil- 
iary fistula — Variations  in  the  flow  of  bile — Movements  of  the  small  intestine — Peristaltic  and  antiperi- 
ctaltic  movements — Uses  of  the  gases  in  the  small  intestine — Physiological  anatomy  of  the  large  intes- 
tine— Processes  of  fermentation  in  the  intestinal  canal — Contents  of  the  large  intestine — Composition  of 
the  faeces — Excretine  and  excretoleic  acid — Stercorinc — Indol,  skatol,  phenol  etc. — Movements  of  the 
large  intestine— Defalcation— Gases  found  in  the  alimentary  canal. 

PHYSIOLOGICAL  ANATOMY  OF  THE  SMALL  INTESTINE. 

THE  small  intestine,  extending  from  the  pyloric  extremity  of  the  stomach 
to  the  ileo-csecal  valve,  is  loosely  held  to  the  spinal  column  by  a  double  fold  of 
serous  membrane,  called  the  mesentery.  As  the  peritoneum  which  lines  the 
cavity  of  the  abdomen  passes  from  either  side  to  the  spinal  column,  it  comes 
together  in  a  double  fold  just  in  front  of  the  great  vessels  along  the  spine,  and 
passing  forward,  it  divides  again  into  two  layers,  which  become  continuous 
with  each  other  and  enclose  the  intestine,  forming  its  external  coat.  The 
width  of  the  mesentery  is  usually  three  to  four  inches  (7*62  to  10-16  centi- 
metres) ;  but  at  the  beginning  and  at  the  termination  of  the  small  intestine, 
it  suddenly  becomes  shorter,  binding  the  duodenum  and  that  portion  of  the 
intestine  which  opens  into  the  caput  coli  closely  to  the  subjacent  parts.  The 
mesentery  thus  keeps  the  intestine  in  place,  but  it  allows  a  certain  degree  of 
motion,  so  that  the  tube  may  become  convoluted,  accommodating  itself  to 
the  size  and  form  of  the  abdominal  cavity.  The  form  of  these  convolutions 
is  irregular  and  is  continually  changing.  The  length  of  the  small  intestine, 
according  to  Gray,  is  about  twenty  feet  (6-1  metres) ;  but  the  canal  is  very 
distensible,  and  its  dimensions  are  subject  to  frequent  variations.  Its  average 
diameter  is  about  an  inch  and  a  quarter  (3-18  centimetres). 

The  small  intestine  has  been  divided  into  three  portions,  which  present 
anatomical  and  physiological  peculiarities,  more  or  less  marked.  These  are 
the  duodenum,  the  jejunum  and  the  ileum. 

The  duodenum  has  received  its  name  from  the  fact  that  it  is  about  the 
length  of  the  breadth  of  twelve  fingers,  or  eight  to  ten  inches  (20-32  to  25-4 
centimetres).  This  portion  of  the  intestine  is  considerably  wider  than  the 
constricted  pyloric  end  of  the  stomach,  with  which  it  is  continuous,  and  is 
also  much  wider  than  the  jejunum. 

The  coats  of  the  duodenum,  like  those  of  the  other  divisions  of  the 
intestinal  tube,  are  three  in  number.  The  external  is  the  serous,  or  peri- 
toneal coat,  which  has  already  been  described.  The  middle,  or  muscular 
coat  is  composed  of  non-striated  muscular  fibres,  such  as  exist  in  the  stomach, 
arranged  in  two  layers.  The  external,  longitudinal  layer  is  not  very  thick,  and 
the  direction  of  its  fibres  can  be  made  out  easily  only  at  the  outer  portions 
of  the  tube,  opposite  the  attachment  of  the  mesentery.  Near  the  mesenteric 
border  the  outlines  of  the  fibres  are  very  faint.  This  is  true  throughout  the 


234 


INTESTINAL  DIGESTION. 


whole  of  the  small  intestine ;  although  the  fibres  are  most  abundant  in  the 
duodenum.     The  internal  layer  of  fibres  is  considerably  thicker  than  the 

longitudinal  layer.  These 
fibres  encircle  the  tube, 
running  generally  at  right 
angles  to  the  external  layer, 
but  some  of  them  having 
rather  an  oblique  direction. 
The  circular  layer  is  thick- 
est in  the  duodenum,  di- 
minishing gradually  in 
thickness  to  the  middle  of 
the  jejunum,  but  afterward 
maintaining  a  nearly  uni- 
form thickness  throughout 
the  canal,  to  the  ileo-caecal 
valve. 

The  jejunum,  the  sec- 
ond division  of  the  small 
intestine,  is  continuous 
with  the  duodenum.  It 
presents  no  well  marked 
line  of  separation  from  the 
third  division,  but  is  gen- 
erally considered  as  in- 
cluding the  upper  two- 
fifths  of  the  small  intes- 
tine, the  lower  three-fifths 
being  called  the  ileum.  It 

FIG.  C6.—  Stomach,  liver,  small  intestine  etc.  (Sappey).  jiag  revived    the   name  16- 

1,  inferior  surface  of  the  liver ;  2,  round  ligament  of  the  liver  ;  3,  .  ** 

gall-bladder  ;  4,  superior  surface  of  the  right  lobe  of  the  liver ;  lUllUm    fl'Om   the  fact  that 

5,  diaphragm  ;  6,  lower  portion  of  the  oasophapus  ;  7,  stomach  ;  . 

ti,  gastro-hepaticomentum  ;  9,  spleen  ;  10,  c/axtro-splenic  omen-  it    IS    almost    always  lOlind 
turn ;  11,  duodenum  ;  12,  12,  small  intestine  ;  13,  caecum  ;  14,  , 

appendix  vermiformis ;  15,  15,  transverse  colon  ;  16,  sigmoid  empty  alter  death. 
flexure  of  the  colon  ;  17,  urinary  bladder. 

Ihe  ileum  is  some- 
what narrower  and  thinner  than  the  jejunum,  otherwise  possessing  no 
marked  peculiarities  except  in  its  mucous  membrane.  This  division  of  the 
intestine  opens  into  the  colon. 

Mucous  Membrane  of  the  Small  Intestine. — The  mucous  coat  of  the  small 
intestine  is  somewhat  thinner  than  the  lining  membrane  of  the  stomach. 
It  is  thickest  in  the  duodenum  and  gradually  becomes  thinner  toward  the 
ileum.  It  is  highly  vascular,  presenting,  like  the  mucous  membrane  of  the 
stomach,  a  great  increase  in  the  quantity  of  blood  during  digestion.  It  has  a 
peculiar  soft  and  velvety  appearance,  and  during  digestion  it  is  of  a  vivid- 
red  color,  being  pale  pink  during  the  intervals.  It  presents  for  anatomical 
description  the  following  parts :  1,  folds  of  the  membrane,  called  valvulae 
conniventes ;  2,  duodenal  racemose  glands,  or  glands  of  Brunner ;  3,  intestinal 


PHYSIOLOGICAL   ANATOMY  OF  THE  SMALL  INTESTINE.   235 


tubules,  or  follicles  of  Lieberkulm ;  4,  intestinal  villi ;  5,  solitary  glands,  or 
follicles ;  6,  agmiiiated  glands,  or  patches  of  Peyer. 

The  valvulaj  conniventes,  simple  transverse  duplicatures  of  the  mucous 
membrane  of  the  intestine,  are  particularly  well  marked  in  man,  although 
they  are  found  in  some  of  the  inferior  animals  belonging  to  the  class  of  mam- 
mals, as  the  elephant  and  the  camel.  They  render  the  extent  of  the  mucous 
membrane  much  greater  than  that  of  the  other  coats  of  the  intestine.  Be- 
ginning at  about  the  middle  of  the  duodenum,  they  extend,  with  no  diminu- 
tion in  number,  throughout  the  jejunum.  In  the  ileum  they  progressively 
diminish  in  number,  until  they  are  lost  at  about  its  lower  third.  There  are 
about  six  hundred  of  these  folds  in  the  first  half  of  the  small  intestine  and 
two  hundred  to  two  hundred  and  fifty  in  the  lower  half  (Sappey).  In  those 
portions  of  intestine  where  they  are  most  abundant,  they  increase  the  length 
of  the  mucous  membrane  to  about  double  that  of  the  tube  itself ;  but  in  the 
ileum  they  do  not  increase  the  length  more  than  one-sixth.  The  folds  are 
always  transverse  and  occupy  usually  one-third  to  one-half  of  the  circumfer- 
ence of  the  tube,  although  a  few  may  extend  entirely  around  it.  The  great- 
est width  of  each  fold  is  at  its  centre,  where  it  measures  a  quarter  to  half  an 
inch  (6-4  to  12'7  mm.).  From  this  point  the  width  gradually  diminishes 
until  the  folds  are  lost  in  the  membrane  as  it  is  attached  to  the  muscular 
coat.  Between  the  folds  are  found  fibres  of  connective  tissue  similar  to  those 
which  attach  the  membrane  throughout  the  whole  of  the  alimentary  tract. 
This,  though  loose,  is  constant,  and  it  prevents  the  folds  from  being  effaced, 
even  when  the  intestine  is  distended  to  its  utmost.  Between  the  folds  are 
also  found  blood-vessels,  nerves  and  lymphatics. 

The  position  and  arrangement  of  the  valvulse  conniventes  are  such  that 
they  move  freely  in  both  directions  and  may  be  applied  to  the  inner  surface 
of  the  intestine  either  above  or 
below  their  lines  of  attachment. 
It  is  evident  that  the  food,  as  it 
passes  along  in  obedience  to  the 
peristaltic  movements,  must,  by 
insinuating  itself  beneath  the 
folds  and  passing  over  them,  be 
exposed  to  a  greater  extent  of 
mucous  membrane  than  if  these 
valves  did  not  exist.  This  is 
about  the  only  definite  use  that 
can  be  assigned  to  them. 

Thickly  set  beneath  the  mu- 
cous membrane  in  the  first  half 
of  the  duodenum,  and  scattered 
here  and  there  throughout  the 
rest  of  its  extent,  are  the  duodenal  racemose  glands,  or  the  glands  of  Brun- 
ner.  These  are  not  found  in  other  parts  of  the  intestinal  canal.  In  their 
structure  they  closely  resemble  the  racemose  glands  of  the  (Esophagus.  On 


FIG.  67.— Gland  of  Brunner,  from  the  human  subject 
(Frey). 


236 


INTESTINAL  DIGESTION. 


dissecting  the  muscular  coat  from  the  mucous  membrane,  they  may  be  seen 
with  the  naked  eye,  in  the  areolar  tissue,  in  the  form  of  little,  rounded  bod- 
ies, about  one-tenth  of  an  inch  (2'5  mm.)  in  diameter.  Examined  micro- 
scopically, these  bodies  are  found  to  consist  of  a  large  number  of  rounded 
follicles  held  together  by  a  few  fibres  of  connective  tissue.  They  have  blood- 
vessels ramifying  on  their  exterior  and  are  lined  with  glandular  epithelium. 
They  communicate  with  an  excretory  duct  which  penetrates  the  mucous  mem- 
brane and  opens  into  the  intestinal  cavity.  When  these  structures  are  ex- 
amined in  a  perfectly  fresh  preparation,  the  excretory  duct  is  frequently 
found  to  contain  a  clear,  viscid  mucus,  of  an  alkaline  reaction.  This  secre- 
tion has  never  been  obtained  in  quantity  sufficient  to  admit  of  the  determi- 
nation of  its  chemical  or  physiological  properties.  Its  quantity  must  be  very 
small,  compared  with  the  secretion  produced  by  the  follicles  of  Lieberkiihn. 

The  intestinal  tubules,  or  follicles  of  Lieberkiihn,  the  most  important 
glandular  structures  in  the  intestinal  mucous  membrane,  are  found  through- 


FIG.  68. — Intestinal  tubules  ,•  magnified  100  diameters  (Sappey). 

A.  From  the  dog.    1,  excretory  canal ;  2.  2,  primary  branches ;  8,  3,  secondary  branches  ;  4,  4,  terminal 

culs-de-sac. 

B.  From  the  ox.    1,  excretory  canal ;  2,  principal  branch  dividing  into  two  ;  3,  branch  undivided  ;  4,  4, 

terminal  culs-de-sac. 

C.  From  the  sheep.    1,  trunk  ;  2,  2,  branches. 

D.  Single  tube,  from  the  pig. 

E.  From  the  rabbit  and  hare.    1,  simple  gland ;  2,  3,  4,  bind  glands  ;  5,  compound  gland  from  the 

duodenum. 


out  the  whole  of  the  small  and  large  intestines.     In  examining  a  thin  section 
of  the  mucous  membrane,  these  little  tubes  are  seen  closely  packed  together, 


PHYSIOLOGICAL  ANATOMY  OF  THE  SMALL  INTESTINE.    237 

occupying  nearly  the  whole  of  its  structure.  Between  the  tubules,  are  blood- 
vessels, embedded  in  a  dense  stroma  of  fibrous  tissue  with  non-striated  mus- 
cular fibres.  In  vertical  sections  of  the  mucous  membrane,  the  only  situa- 
tions where  the  tubules  are  not  seen  are  in  that  portion  of  the  duodenum 
occupied  by  the  ducts  of  the  glands  of  Brunner  and  immediately  over  the 
centre  of  the  larger  solitary  glands  and  some  of  the  closed  follicles  which 
are  collected  to  form  the  patches  of  Peyer.  The  tubes  are  not  entirely  absent 
in  the  patches  of  Peyer,  but  are  here  collected  in  rings,  twenty  or  thirty  tubes 
deep,  which  surround  each  of  the  closed  follicles.  Microscopical  examination 
of  the  surface  of  the  mucous  membrane  by  reflected  light  shows  that  the 
openings  of  the  tubules  are  between  the  villi. 

The  tubules  usually  are  simple,  though  sometimes  bifurcated,  are  com- 
posed externally  of  a  structureless  basement-membrane,  and  are  lined  with  a 
layer  of  cylindrical  epithelium  like  the  cells  which  cover  the  villi,  the  only 
'difference  being  that  in  the  tubes  the  cells  are  shorter.  These  cells  never 
contain  fatty  granules,  even  during  the  digestion  of  fat.  The  central  cavity 
which  the  cells  enclose,  which  is  about  one-fourth  of  the  diameter  of  the 
tube,  is  filled  with  a  clear,  viscid  fluid,  which  is  the  most  important  constitu- 
ent of  the  intestinal  juice.  The  length  of  the  tubules  is  equal  to  the  thick- 
ness of  the  mucous  membrane  and  is  about  -fa  of  an  inch  (0-33  mm.).  Their 
diameter  is  about  ^¥  of  an  inch  (0-07  mm.).  In  man  they  are  cylindrical, 
terminating  in  a  single,  rounded,  blind  extremity,  which  frequently  is  a  little 
larger  than  the  rest  of  the  tube.  These  tubules  are  the  chief  agents  concerned 
in  the  production  of  the  fluid  known  as  the  intestinal  juice. 

The  intestinal  villi,  though  chiefly  concerned  in  absorption,  are  most  con- 
veniently considered  in  this  connection.  These  exist  throughout  the  whole 
of  the  small  intestine,  but  are  not  found  beyond  the  ileo-caecal  valve,  although 
they  cover  that  portion  of  the  valve  which  looks  toward  the  ileum.  Their 
number  is  very  great,  and  they  give  to  the  membrane  its  peculiar  and  char- 
acteristic velvety  appearance.  They  are  found  on  the  valvtilaB  conniventes  as 
well  as  on  the  general  surface  of  the  mucous  membrane.  They  are  most 
abundant  in  the  duodenum  and  jejunum.  Sappey  estimated,  as  an  average, 
about  6,450  to  the  square  inch  (1,000  in  a  square  centimetre)  and  more  than 
ten  millions  (10,125,000)  throughout  the  whole  of  the  small  intestine.  In 
the  human  subject  the  villi  are  flattened  cylinders  or  cones.  In  the  duode- 
num, where  they  resemble  somewhat  the  elevations  found  in  the  pyloric  por- 
tion of  the  stomach,  they  are  shorter  and  broader  than  in  other  situations 
and  are  more  like  flattened,  conical  folds.  In  the  jejunum  and  ileum  they 
are  in  the  form  of  long,  flattened  cones  and  cylinders.  As  a  rule  the  cylin- 
drical form  predominates  in  the  lower  portion  of  the  intestine.  In  the  jeju- 
num they  attain  their  greatest  length,  measuring  here  ^  to  ^  of  an  inch 
(0-83  to  1-25  mm.)  in  length  by  ^  to  ^  of  an  inch  (0-36  to  0'21  mm.) 
in  breadth  at  their  base. 

The  structure  of  the  villi  shows  them  to  be  simple  elevations  of  the 
mucous  membrane,  provided  with  blood-vessels  and  with  lacteals,  or  intestinal 
lymphatics.  Externally  is  found  a  single  layer  of  long,  cylindrical  epithelial 
17 


238 


INTESTINAL  DIGESTION. 


FIG.  69.—  Intestinal  villus  (Ley- 
dig).  • 

a,  a,  a,  epithelial  covering  ;  6,  b, 
capillary  net- work  ;  c,  c,  longi- 
tudinal muscular  fibres  ;  d, 
lacteal. 


cells,  resting  on  a  structureless  basement-membrane.     These  cells,  though 
closely  adherent  to  the  subjacent  parts  during  life,  are  easily  detached  after 

death  and  are  almost  always 
destroyed  and  removed  in 
injected  preparations.  They 
adhere  firmly  to  each  other 
and  are  isolated  with  diffi- 
culty in  microscopical  prep- 
arations. The  borders  of 
the  free  surfaces  of  these 
cells  are  thickened  and  fine- 
ly striated,  forming,  as  it 
were,  a  special  membrane 
covering  the  villus  and  ex- 
ternal to  the  cells.  Between 
the  cylindrical  cells  are  a 
few  of  the  so-called  goblet- 
cells  similar  to  those  found 
on  the  mucous  membrane  of 
the  stomach  (see  Fig.  60, 
page  214). 

The  substance  of  the 
villus  is  composed  of  amor- 
phous matter,  in  which  are 
embedded  nuclei  and  a  few  fibres,  fibro-plastic  cells  and  non-striated  mus- 
cular fibres.  The  blood-vessels  are  very  abundant ;  four  or  five,  and  some- 
times as  many  as  twelve  or  fifteen  arterioles  entering  at  the  base,  rami- 
fying through  the  substance  of  the  vil- 
lus, but  not  branching  or  anastomosing 
or  even  diminishing  in  caliber  until,  by 
a  slightly  wavy  turn  or  loop,  they  com- 
municate with  the  venous  radicles,  each 
of  which  is  somewhat  larger  than  the 
arterioles.  The  veins  all  converge  to 
two  or  three  branches,  finally  emptying 
into  a  large  trunk  situated  nearly  in 
the  long  axis  of  the  villus. 

The  muscular  fibres  of  the  villi  are 
longitudinal,  forming  a  thin  layer  sur- 
rounding the  villus,  about  half-way  be- 
tween the  periphery  and  the  centre, 
and  continuous  with  the  muscular  coat 
of  the  intestine. 

In  the  central  portion  of  each  villus,  is  a  small  lacteal,  one  of  the  vessels  of 
origin  of  the  lacteal  system,  with  an  extremely  delicate  wall  composed  of 
endothelial  cells  with  frequent  stomata,  or  small  openings,  between  their 


FIG.  70.— Capillary  net-work 
of  an  intestinal  villus 
(Frey). 

a,  /venous  trunk  ;  b,  arterial 
trunk. 


FIG.  71.— Epithelium  of  the  small  intestine  of 
the  rabbit  (Funke). 


PHYSIOLOGICAL  ANATOMY  OF  THE  SMALL  INTESTINE.   239 

borders.  This  vessel  is  probably  in  the  form  of  a  single  tube,  either  simple 
or  presenting  a  few  short,  rounded  diverticula. 

The  stomata  of  the  lacteal  vessel  are  thought  to  communicate  with 
lymph-spaces  or  canals  in  the  substance  of  the  villus.  Owing  to  the  ex- 
cessive tenuity  of  the  walls  of  the  lacteals  in  the  villi,  it  has  been  found 
impossible  to  fill  these  vessels  with  an  artificial  injection,  although  the 
lymphatics  subjacent  to  them  may  be  easily  distended  and  studied  in  this 
way. 

No  satisfactory  account  has  ever  been  given  of  nerves  in  the  intestinal 
villi.  If  any  exist  in  these  structures,  they  probably  are  derived  from  the 
sympathetic  system. 

The  solitary  glands,  or  follicles,  and  the  patches  of  Peyer,  or  agminated 
glands,  have  one  and  the  same  structure,  the  only  difference  being  that  those 
called  solitary  are  scattered  singly  in  very  variable  numbers  throughout  the 
small  and  large  intestine,  while  the  agminated  glands  consist  of  these  folli- 
cles collected  into  patches  of  different  sizes.  These  patches  are  generally 
found  in  the  ileum.  The  number  of  the  solitary  glands  is  very  variable,  and 
they  are  sometimes  absent.  The  patches  of  Peyer  are  always  situated  in 
that  portion  of  the  intestine  opposite  the  attachment  of  the  mesentery. 
They  are  likewise  variable  in  number  and  are  irregular  in  size.  They  usu- 
ally are  irregularly  oval  in  form,  and  measure  half  an  inch  to  an  inch  and 
a  half  (12-7  to  38'1  mm.),  in  length  by  three-fourths  of  an  inch  (19-1  mm.) 
in  breadth.  Sometimes  they  are  three  to  four  inches  (7'6  to  10-1  centi- 
metres) long,  but  the  largest  are  always  found  in  the  lower  part  of  the 
ileum.  Their  number  is  about  twenty,  and  they  are  generally  confined  to 
the  ileum  ;  but  when  they  are  very  abundant — for  they  sometimes  exist  to 
the  number  of  sixty  or  eighty — they  may  be  found  in  the  jejunum  or  even 
in  the  duodenum. 

Two  varieties  of  the  patches  of  Peyer  have  been  described  by  anatomists. 
In  one  of  these  varieties,  the  patch  is  quite  prominent,  its  surface  being 
slightly  raised  above  the  general  mucous  surface ;  in  the  other,  the  surface  is 
smooth,  and  the  patch  is  distinguished  at  first  with  some  difficulty.  The 
more  prominent  patches  are  covered  with  mucous  membrane  arranged  in 
folds  something  like  the  convolutions  on  the  surface  of  the  brain.  The 
valvulae  conniventes  cease  at  or  very  near  their  borders.  These  are  the  only 
patches  which  are  generally  described  as 'the  glands  of  Peyer,  the  others, 
which  may  be  called  the  smooth  patches,  being  frequently  overlooked.  The 
latter  are  covered  with  a  smooth,  thin,  and  closely  adherent  mucous  mem- 
brane. Their  follicles  are  small  and  abundant.  The  borders  of  these  patches 
are  much  less  strongly  marked  than  in  those  of  the  first  variety.  As  they  are 
evident  only  upon  close  examination  and  as  they  are  the  only  patches  present 
in  certain  individuals,  it  is  said  that  sometimes  the  patches  of  Peyer  are 
wanting.  They  are  usually  in  less  number  than  the  first  variety. 

The  villi  are  very  large  and  prominent  on  the  mucous  membrane  cover- 
ing the  first  variety  of  Peyer's  patches,  especially  at  the  summit  of  the  folds. 
In  the  second  variety  the  villi  are  the  same  as  over  other  parts  of  the  mu- 


240 


INTESTINAL   DIGESTION. 


FIG.  : 

1,  1,  1 


cous  membrane,  except  that  they  are  placed  more  irregularly  and  are  not  so 

abundant. 

The  follicles  which  form  the  patches  of  Peyer  are  completely.  closed  and 

are  somewhat  pear-shaped,  with  their  pointed  projections  directed  toward 

the  cavity  of  the  intestine.  Just  above  the  fol- 
licle, there  generally  is  a  small  opening  in  the 
mucous  membrane,  surrounded  by  a  ring  of  in- 
testinal tubules,  and  leading  to  a  cavity,  the  base 
of  which  is  convex  and  is  formed  by  the  coni- 
cal projection  of  the  follicle.  The  diameter  of 
the  follicles  is  -fa  to  -fa  or  -fa  of  an  inch  (0-34  to 
1  or  2  mm.)  The  small  follicles  generally  are 
covered  by  mucous  membrane  and  have  no  open- 
ing leading  to  them.  Each  follicle  consists  of 
a  rather  strong  capsule  composed  of  an  almost 
homogeneous  or  slightly  fibrous  membrane,  en- 
closing a  semi-fluid,  grayish  substance,  cells, 
blood  -  vessels  and  possibly  lymphatics.  The 
semi-fluid  matter  is  of  an  albuminoid  character 

patch  of  Peyer;  2,  2,  folds  The  cells  are  Vei7  small>  rounded,  and  mingled 
with  small»  free  nuclei-     The  blood-vessels  have 
between  some  of  the  folds  ;  5,  5,  rather  a  peculiar  arrangement.     In  the  first  place 

5,  5,  5,  5,  5,  5,  valvulae  conmven- 

tes  ;  e,  6,  e,  6  solitary  glands  ;  7,  they  are  distributed  between  the  follicles,  so  as 

7,  7,  7,  smaller  solitary  glands  ; 

8,  8,  solitary  glands  upon  the  vai-  to  f  orm  a  rich  net-work  surrounding  each  one. 

vulae  conniventes. 

Capillary  branches  are  sent  from  these  vessels 

into  the  interior  of  the  follicle,  returning  in  the  form  of  loops.  Lymphatic 
vessels  have  not  been  distinctly  shown  within  the  investing  membrane. 
'They  have  been  demonstrated  surrounding  the  follicles,  but  it  is  still  doubt- 
ful whether  they  exist  in  their  interior.  All  .  ___ 
that  is  known  is  that  during  digestion,  the 
number  of  lacteals  coming  from  the  Peyerian 
patches  is  greater  than  in  other  parts  of  the 
mucous  membrane  ;  but  vessels  containing  a 
milky  fluid  are  never  seen  within  the  follicles. 
The  description  of  the  follicles  which  com- 
pose the  patches  of  Peyer  answers,  in  general 
terms,  for  the  solitary  glands,  except  that  the 
latter  are  found  in  both  the  small  and  large 
intestines. 

INTESTINAL  JUICE. 

Of  the  three  fluids  with  which  the  food  is 
brought  in   contact  in   the  intestinal   canal,  Fl»-  73.—  Patch  of  Peyer.  seen  from  its 

0  ....  ,     .  ,  attached  surface  (Sappey). 

namely,  the  bile,  the  pancreatic  juice  arid  the 
intestinal  juice,  the  last,  the  secretion  of  the 
mucous  membrane  of  the  small  intestine,  pre-  ^StaJii  conmvente5s.5'  5'  5'  5A 


i,  i,  serous  coat  of  the  intestine  ;  2,  2  2, 


INTESTINAL  JUICE. 

sents  the  greatest  difficulties  in  the  investigation  of  its  properties  and  uses. 
If  it  be  admissible  to  reason  from  the  known  mechanism  of  secretion  in  other 
parts,  it  is  fair  to  suppose  that  the  normal  secretion  of  the  glands  in  the 
mucous  memBraue  of  the  small  intestine  can  take  place  only  under  the 
stimulus  of  food.  The  same  cause  excites  the  secretion  of  the  pancreatic 
juice  and  increases  the  flow  of  bile ;  and  the  food,  as  it  passes  from  the 
stomach  into  the  duodenum,  is  to  a  great  extent  disintegrated  and  is  min- 
gled with  the  secretions  from  both  the  mouth  and  the  stomach.  Under  these 
circumstances,  it  is  evidently  impossible  to  collect  the  intestinal  juice  under 
perfectly  physiological  conditions,  in  a  state  of  purity  sufficient  to  admit  of 
extended  experiments  regarding  its  composition,  properties,  and  action  in 
digestion. 

The  experiments  of  Bidder  and  Schmidt,  Thiry,  Colin,  Meade  Smith  and 
others  have  given  but  little  positive  information  with  regard  to  the  general  prop- 
erties, even,  of  the  intestinal  juice,  to  say  nothing  of  its  digestive  action.  It  may 
be  stated  in  general  terms,  that  the  physiologists  just  mentioned  have  attempted 
to  obtain  the  pure  secretion  of  the  follicles  of  Lieberkiihn  by  isolating  portions 
of  the  intestine  and  either  taking  the  secretion  as  it  formed  spontaneously  or 
exciting  the  action  of  the  glands  by  various  means.  When  it  is  remembered 
how  different  the  secretion  of  the  stomach,  under  the  natural  stimulus  of  food, 
is  from  the  fluid  produced  during  the  intervals  of  digestion,  it  is  evident  that 
little  reliance  is  to  be  placed  upon  the  experiments  that  have  thus  far  been 
made  upon  the  lower  animals.  Nearly  all  observers  agree,  however,  that  the 
intestinal  juice  which  they  have  been  able  to  collect  is  yellow,  thin  and 
strongly  alkaline.  Some  have  found  it  thin  and  opalescent,  while  others 
state  that  it  is  viscid  and  clear.  According  to  Colin  the  closed  follicles  of  the 
intestine  produce  a  viscid  fluid,  which  probably  exudes  through  their  walls. 
Colin  came  to  this  conclusion  from  observations  upon  a  large,  ribbon-shaped 
agminate  gland,  about  six  feet  (183  centimetres)  in  length,  which  exists  in 
the  small  intestine  of  the  pig.  In  a  case  of  fistula  into  the  upper  third  of 
the  intestine  in  the  human  subject,  produced  by  a  penetrating  wound  of  the 
abdomen — which  will  be  referred  to  again — Busch  found  a  fluid  that  was 
white  or  of  a  pale  rose-color,  rather  viscid  and  always  strongly  alkaline.  The 
maximum  proportion  of  solid  matter  which  it  contained  was  7'4  and  the 
minimum,  3.87  per  cent.  The  secretion  apparently  could  not  be  obtained  in 
sufficient  quantity  for  ultimate  analysis.  No  better  opportunity  than  this 
has  been  presented  for  studying  the  intestinal  juice  in  its  pure  state.  The 
nature  of  the  case  made  it  impossible  that  there  should  be  any  admixture  of 
food,  pancreatic  juice,  bile  or  the  secretion  of  the  duodenal  glands;  and 
during  the  process  of  digestion,  the  lower  part  of  the  intestine  undoubtedly 
produced  a  perfectly  normal  fluid. 

From  what  has  been  ascertained  by  experiments  upon  the  lower  animals 
and  observations  on  the  human  subject,  the  intestinal  juice  has  been  shown 
to  possess  the  following  characters  : 

Its  quantity  in  any  portion  of  the  mucous  membrane  which  can  be  ex- 
amined is  small ;  but  when  the  extent  of  the  canal  is  considered,  it  is  evident 


242  INTESTINAL  DIGESTION. 

that  the  entire  quantity  of  intestinal  juice  must  be  great,  although  beyond 
this,  no  reliable  estimate  can  be  made. 

The  intestinal  juice  is  viscid  and  has  a  tendency  to  adhere  to  the  mucous 
membrane.  It  generally  is  either  colorless  or  of  a  faint  rose-tint,  and  its  re- 
action is  invariably  alkaline. 

With  regard  to  the  composition  of  the  intestinal  juice,  little  of  a  definite 
character  has  been  learned.  All  that  can  be  said  is  that  its  solid  constituents 
exist  in  the  proportion  of  about  five  and  a  half  parts  per  hundred.  In  most 
analyses  of  fluids  from  the  intestine,  there  is  reason  to  believe  that  the  normal 
intestinal  juice  was  not  obtained. 

The  structures  which  secrete  the  fluid  known  as  the  intestinal  juice  are 
the  follicles  of  Lieberkiihn,  the  glands  of  Brunner  and  possibly  the  solitary 
follicles  and  patches  of  Peyer.  The  secretion,  however,  is  produced  chiefly 
by  the  follicles  of  Lieberkuhn.  Although  the  other  structures  mentioned  do 
not  contribute  much  to  the  secretion,  they  produce  a  certain  quanity  of 
fluid ;  and  the  intestinal  juice  must  be  regarded  as  a  compound  fluid,  like 
the  saliva,  and  not  as  the  product  of  a  single  glandular  organ,  like  the  pan- 
creatic juice. 

Action  of  the  Intestinal  Juice  in  Digestion. — The  physiological  action  of 
the  intestinal  juice  has  been  studied  in  the  inferior  animals  by  Frerichs,  Bid- 
der and  Schmidt  and  many  others ;  but  their  experiments  have  been  some- 
what contradictory.  All  are  agreed,  however,  that  this  fluid  is  more  or  less 
active  in  transforming  starch  into  sugar.  The  observations  of  Busch,  on 
the  case  of  intestinal  fistula  in  the  human  subject,  have  given  the  most 
satisfactory  and  definite  information  on  this  point.  In  many  regards  these 
observations  simply  confirm  those  which  have  been  made  upon  the  infe- 
rior animals,  but  they  are  of  great  value,  as  they  establish  many  important 
facts  relating  to  the  physiological  action  of  the  intestinal  juice  in  the  human 
subject. 

The  case  reported  by  Busch  was  that  of  a  woman,  thirty-one  years  of  age, 
who,  in  the  sixth  month  of  her  fourth  pregnancy,  was  injured  in  the  abdo- 
men by  being  tossed  by  a  bull.  The  wound  was  between  the  umbilicus  and 
the  pubes,  presenting  two  contiguous  openings  connected  with  the  intestinal 
canal.  It  was  supposed  that  the  openings  were  into  the  upper  third  of  the 
small  intestine.  At  the  time  the  patient  first  came  under  observation,  every 
thing  that  was  taken  into  the  stomach  was  discharged  by  the  upper  opening, 
and  all  attempts  to  establish  a  communication  between  the  two  by  a  surgical 
operation  had  failed.  At  this  time  the  patient  was  extremely  emaciated,  had 
a  voracious  appetite,  and  was  evidently  suffering  from  defective  nutrition 
resulting  from  the  constant  discharge  of  alimentary  matters  from  the  fistula. 
Having  been  treated,  however,  by  the  introduction  of  cooked  food  into  the 
opening  connected  with  the  lower  end  of  the  intestine,  she  soon  improved  in 
her  nutrition  and  was  then  made  the  subject  of  extended  observations  upon 
intestinal  digestion. 

In  this  case,  starch,  both  raw  and  hydrated,  when  introduced  into  the 
lower  opening,  where  it  came  in  contact  only  with  the  intestinal  juice,  was 


PANCREATIC  JUICE. 


243 


invariably  changed  into  glucose.  Cane-sugar  was  not  transformed  into  glu- 
cose but  appeared  in  the  faeces  as  cane-sugar;  and  this  is  important  with 
reference  both  to  the  want  of  action  of  the  intestinal  juice  upon  cane-sugar 
and  the  fact  that  cane-sugar,  as  such,  is  not  absorbed  in  quantity  by  the  in- 
testinal mucous  membrane. 

Coagulated  albumin  and  cooked  meats  were  always  more  or  less  digested 
by  the  intestinal  juice.  This  fact  coincides  with  the  observations  of  Bidder 
and  Schmidt  in  their  experiments  upon  dogs  and  cats. 

The  observations  which  were  made  on  fats,  melted  butter  and  cod-liver 
oil  showed  that  the  pure  intestinal  juice  had  little  or  no  action  upon  them. 
These  substances  always  appeared  in  the  faeces  unchanged.  When,  however, 
fatter  matters  were  taken  into  the  stomach,  they  were  discharged  from  the 
upper  opening  in  the  intestine,  in  the  form  of  a  very  fine  emulsion,  and  could 
not  be  recognized  as  fat. 

It  is  evident  from  these  facts,  that  the  intestinal  juice  is  important  in 
digestion,  more  as  a  fluid  which  aids  the  general  process  as  it  takes  place  in 
the  small  intestine  than  as  one  having  a  peculiar  action  upon  any  distinct 
class  or  classes  of  alimentary  substances.  It  undoubtedly  assists  in  complet- 
ing the  digestion  of  the  albuminoids  and  in  transforming  starch  into  sugar. 
Although,  in  the  latter  process,  its  action  is  very  marked,  the  same  property 
belongs  to  the  saliva  and  the  pancreatic  juice.  Intimately  mingled — as  it 
always  is  during  digestion — with  the  bile  and  the  pancreatic  juice  as  well  as 
with  various  aliment- 
ary substances,  the  in- 
testinal juice  should 
be  studied  as  it  acts 
upon  the  food  in  con- 
nection with  the  other 
fluids  found  in  the 
small  intestine. 

PANCREATIC  JUICE. 


The  pancreas  is  sit- 
uated transversely  in 
the  upper  part  of  the 
abdominal  cavity  and 
is  closely  applied  to 
its  posterior  wall.  Its 
form  is  elongated,  pre- 
senting an  enlarged, 
thick  portion,  called 
the  head,  which  is  at- 
tached to  the  duodenum,  a  body,  and  a  pointed  extremity,  which  latter  is  in 
close  relation  to  the  hilum  of  the  spleen.  Its  average  weight  is  four  to  five 
ounces  (114-4  to  141-7  grammes);  its  length  is  about  seven  inches  (17'78 
centimetres) ;  its  greatest  breadth,  about  an  inch  and  a  half  (3-81  centime- 


FIG.  74. — Gall-bladder,  ductus  choledochus  and  pancreas  (Le  Bon), 
a,  gall-bladder  ;  fe,  hepatic  duct ;  c.  opening  of  the  second  duct  of  the 
pancreas  ;  rf,  opening  of  the  main  pancreatic  duct  and  the  bile-duct ; 
e,  e,  duodenum  ;  /,  ductus  choledochus ;  p,  pancreas. 


24:4 


INTESTINAL  DIGESTION. 


tres) ;  and  its  thickness,  three-quarters  of  an  inch  (1-91  centimetre).  It  lies 
behind  the  peritoneum,  which  covers  only  its  anterior  surface. 

*  There  are  nearly  always,  in  the  human  subject,  two  pancreatic  ducts 
opening  into  the  duodenum ;  one  which  opens  in  common  with  the  ductus 
communis  choledochus,  and  one  which  opens  about  an  inch  (25-4  mm.)  above 
the  main  duct.  The  main  duct  is  about  an  eighth  of  an  inch  (3-2  mm.)  in 
diameter  and  extends  along  the  body  of  the  gland,  becoming  larger  as  it 
approaches  the  opening.  The  second  duct  is  smaller  and  becomes  dimin- 
ished in  caliber  as  it  passes  to  the  duodenum.  In  general  appearance  and  in 
minute  structure,  the  pancreas  resembles  the  parotid  and  submaxillary  glands. 
The  normal  pancreatic  juice  may  be  obtained  by  establishing  a  temporary 
fistula  in  the  main  pancreatic  duct  of  a  living  animal  (Bernard).  This  may 
be  done  in  the  dog,  the  pancreas  being  exposed  by  an  incision  in  the  right 
hypochondrium,  and  a  canula  of  proper  size  being  introduced  through  a  slit 
made  in  the  duct,  and  secured  by  a  ligature.  The  external  wound  is  then 

closed  and  the 
end  of  the  tube 
is  allowed  to  pro- 
ject from  the  ab- 
domen. The  fluid 
as  it  is  dis- 
charged from  the 
tube  may  be  col- 
lected in  a  test- 
tube,  or  a  thin 
gum-elastic  bag, 
may  be  attached. 
Like  the  other 
digestive  fluids, 
the  pancreatic 
juice  is  secreted 
in  abundance  on- 
ly during  diges- 
tion. It  is  there- 
fore necessary  to 
feed  the  animal 

moderately  about  an  hour  before  the  operation,  so  that  the  pancreas  may  be 
in  full  activity.  When  the  gland  is  exposed  at  that  time,  it  is  filled  with 
blood  and  has  a  rosy  tint,  contrasting  strongly  with  its  pale  appearance  during 
the  intervals  of  digestion. 

The  secretion  of  normal  pancreatic  juice  is  entirely  suspended  during  the 
intervals  of  digestion.  This  fact  can  be  observed  by  opening  animals  in 
digestion  and  while  fasting.  During  digestion  the  pancreatic  duct  is  always 
found  full  of  normal  secretion;  and  during  the  intervals  it  generally  is 
empty.  The  secretion  begins  to  flow  into  the  duodenum  during  the  first 
periods  of  gastric  digestion,  before  alimentary  matters  have  begun  to  pass  in 


FIG.  75.— Canula  fixed  in  the  pancreatic  duct  (Bernard). 

A,  principal  pancreatic  duct  of  the  dog  ;  B,  smaller  pancreatic  duct ;  c,  ligature 
securing  a  canula  in  the  principal  duct ;  D,  D,  ligature  attaching  the  canula 
to  the  intestine,  for  security  :  E,  canula  ;  F,  bladder,  provided  with  a  stop- 
cock Q,  to  collect  the  pancreatic  juice  ;  p,  p,  pancreas  ;  i,  i,  intestine. 


PANCREATIC  JUICE. 


245 


quantity  into  the  intestine  (Bernard).  The  secretion  is  readily  modified  by 
irritation  and  inflammation  following  the  operation  of  making  the  fistula. 
The  normal  pancreatic  juice  is  strongly  alkaline,  viscid  and  coagulable  by 


FIG.  76.—  Pancreatic  fistula  (Bernard). 

Full- grown  shepherd-dog  (female),  in  which  a  pancreatic  fistula  has  been  established.  A,  silver  tube  to 
which  a  bladder  has  been  attached  ;  B,  bladder  ;  c,  stop-cock  for  the  purpose  of  collecting  the  juice 
which  accumulates  in  the  bladder. 

heat.  It  is  almost  always  the  case  that  a  few  hours  after  the  canula  is  fixed 
in  the  duct,  the  juice  loses  some  of  these  characters  and  flows  in  abnormal 
quantity.  With  respect  to  susceptibility  to  irritation,  the  pancreas  is  pecul- 
iar ;  and  its  secretion  is  sometimes  abnormal  from  the  first  moments  of  the 
experiment,  especially  if  the  operative  procedure  have  been  prolonged  and 
difficult.  That  the  properties  above  described  are  characteristic  of  the  nor- 
mal pancreatic  secretion,  there  can  be  no  doubt ;  as  in  all  instances,  fluid 
taken  from  the  pancreatic  duct  of  an  animal  suddenly  killed  while  in  full 
digestion  is  strongly  alkaline,  viscid  and  coagulable  by  heat.  This  excessive 
sensitiveness  of  the  pancreas  rendered  fruitless  all  the  attempts  to  establish  a 
permanent  pancreatic  fistula  from  which  the  normal  juice  could  be  collected 
(Bernard).  The  fluid  collected  from  a  permanent  fistula  does  not  represent 
the  normal  secretion. 

General  Properties  and  Composition  of  the  Pancreatic  Juice. — In  all  the 
inferior  animals  from  which  the  pancreatic  secretion  has  been  obtained  in  a 
normal  condition,  the  fluid  has  been  found  to  present  certain  uniform  char- 
acters. It  is  viscid,  slightly  opaline  and  has  a  distinctly  alkaline  reaction. 
Bernard  found  the  specific  gravity  of  the  fluid  from  the"  dog  to  be  1040.  The 
normal  fluid  from  a  temporary  fistula  in  a  dog  has  been  observed  with  a  spe- 


24:6  INTESTINAL  DIGESTION. 

cific  gravity  of  1019  (Flint).  The  quantity  of  organic  matters  in  the  normal 
secretion  is  very  great,  so  that  the  fluid  is  completely  solidified  by  heat.  This 
coagulability  is  one  of  the  properties  by  which  the  normal  fluid  may  be  dis- 
tinguished from  that  which  has  undergone  alteration. 

COMPOSITION    OF   THE    PANCREATIC    JUICE    OF   THE    DOG    (BERNARD). 

Water 900  to    920 

Organic  matters,  precipitable  by  alcohol  and  containing  always  a 

little  lime  (amylopsine,  trypsine,  steapsine  etc.) 90  to     73-60 

Sodium  carbonate "1 

Sodium  chloride 

Potassium  chloride. ..     f 10  to       6>4° 

Calcium  phosphate. ...  I 

1,000      1,000 

The  properties  of  the  organic  constituents  of  the  pancreatic  juice  are  dis- 
tinctive. Although,  like  albumen,  these  substances  are  coagulable  by  heat, 
the  strong  mineral  acids  and  absolute  alcohol,  they  differ  from  albumen  in  the 
fact  that  their  dried  alcoholic  precipitate  can  be  redissolved  in  water,  giving 
to  the  solution  the  physiological  properties  of  the  normal  pancreatic  secre- 
tion. Bernard  has  also  found  that  they  are  coagulable  by  an  excess  of  mag- 
nesium sulphate,  which  will  coagulate  caseine  but  has  no  effect  upon  albu- 
men. It  is  important  to  recognize  this  distinction  between  the  organic 
constituents  of  the  pancreatic  juice  and  other  nitrogenized  substances,  espe- 
cially albumen,  from  the  fact  that  the  last-named  substance  has  the  property 
of  forming  an  imcomplete  emulsion  with  fats.  The  name  pancreatine,  given 
to  the  organic  matter  of  the  pancreatic  juice,  is  inappropriate,  as  this  sub- 
stance is  now  known  to  be  composed  of  several  distinct  constituents. 

A  ferment,  almost  if  not  quite  identical  with  ptyaline,  may  be  extracted 
from  the  normal  juice  by  nearly  the  same  processes  as  those  employed  in  the 
isolation  of  the  active  principle  of  the  saliva.  On  account  of  its  vigorous 
action  upon  starch,  this  substance  has  been  called  amylopsine. 

Trypsine  is  a  ferment  capable  of  acting  upon  the  albuminoids,  changing 
them  into  peptones.  According  to  Heidenhain,  there  exists  in  the  secreting 
cells  of  the  gland  a  substance  called  zymogen  or  more  properly,  trypsinogen, 
which,  before  the  secretion  is  discharged,  becomes  oxygenated  and  is  changed 
into  trypsine.  The  action  of  trypsine  on  the  albuminoids  is  increased  by  the 
addition  of  small  quantities  of  sodium  chloride,  sodium  glycocholate  or  sodi- 
um carbonate  and  is  diminished  by  acids. 

A  substance  called  steapsine,  capable  of  decomposing  fats  into  fatty 
acids  and  glycerine,  has  been  described  as  one  of  the  organic  constituents  of 
the  pancreatic  juice.  This  action  upon  fats,  which  was  described  by 
Bernard,  though  slight,  probably  assists  in  their  emulsification. 

The  inorganic  constituents  of  the  pancreatic  juice,  beyond  giving  the 
fluid  an  alkaline  reaction,  do  not  possess  any  great  physiological  interest, 
inasmuch  as  they  do  not  seem  to  be  essential  to  its  peculiar  digestive  proper- 
ties. It  has  been  shown  that  the  organic  constituents  alone,  extracted  from 


PANCREATIC  JUICE.  247 

the  pancreatic  juice  and  dissolved  in  water,  are  capable  of  imparting  to  the 
fluid  the  characters  of  the  normal  secretion  (Bernard). 

The  entire  quantity  of  pancreatic  juice  secreted  in  the  twenty-four  hours 
has  been  variously  estimated  by  different  observers.  After  what  has  been 
said  concerning  the  variations  to  which  the  secretion  is  subject,  it  is  not  sur- 
prising that  these  estimates  should  present  great  differences.  Bernard  was 
able  to  collect  from  a  dog  of  medium  size  eighty  to  one  hundred  grains  (5'2 
to  6'5  grammes)  in  an  hour ;  but  it  must  be  remembered  that  only  one  of 
the  ducts  was  operated  upon,  and  that  the  gland  is  very  susceptible  to  irri- 
tation. There  is  no  accurate  basis  for  an  estimate  of  the  quantity  of  pan- 
creatic fluid  secreted  in  the  twenty-four  hours  in  the  human  subject  or  of  the 
quantity  necessary  for  the  digestion  of  a  definite  quantity  of  food. 

Unlike  the  gastric  juice,  the  pancreatic  juice,  under  ordinary  conditions 
of  heat  and  moisture,  rapidly  undergoes  decomposition.  In  warm  and 
stormy  weather,  the  alteration  is  marked  in  a  few  hours ;  but  at  a  tempera- 
ture of  50°  to  70°  Fahr.  (10°  to  21°  C.),  the  fluid  decomposes  gradually  in 
two  or  three  days.  As  it  thus  undergoes  decomposition,  the  fluid  acquires  a 
very  offensive,  putrefactive  odor,  and  its  coagubility  diminishes,  until  finally 
it  is  not  affected  by  heat.  The  alkalinity,  however,  increases  in  intensity, 
and  when  neutralized  with  an  acid,  there  is  a  considerable  evolution  of  car- 
bon dioxide. 

Action  of  the  Pancreatic  Juice  upon  Starches  and  Sugars. — The  action  of 
the  pancreatic  juice  in  transforming  starch  into  sugar  was  first  observed,  in 
1844,  by  Valentin,  who  experimented  with  an  artificial  fluid  made  by  infus- 
ing pioces  of  the  pancreas  in  water.  Bouchardat  and  Sandras  first  noted  this 
property  in  the  normal  pancreatic  secretion.  Amylopsine  is  undoubtedly  the 
substance  concerned  in  the  action  of  this  fluid  upon  starch. 

The  property  of  converting  starch  into  sugar  is  possessed  by  several  of 
the  digestive  fluids.  The  starchy  constituents  of  food  are  acted  upon  by  the 
saliva,  and  this  action  is  not  necessarily  arrested  as  the  food,  mixed  with  the 
saliva,  passes  into  the  stomach.  The  intestinal  juice  is  also  capable  of  effect- 
ing the  transformation  of  starch  into  sugar  to  a  considerable  extent.  It 
therefore  becomes  an  important  question  to  determine  precisely  how  far  the 
pancreas  is  actually  concerned  in  the  digestion  of  this  class  of  substances. 

Bernard  placed  the  pancreatic  juice  at  the  head  of  the  list  of  the  digestive 
fluids  which  act  upon  starch.  This  view  is  correct,  although  he  was  in 
error  in  claiming  that  starch  is  digested  almost  exclusively  by  the  pancreas. 
Bernard's  experiments,  however,  were  made  chiefly  on  dogs,  and  these  ani- 
mals do  not  naturally  take  starch  as  food.  In  man,  some  of  the  starchy 
constituents  of  the  food  are  acted  upon  by  the  saliva,  but  most  of  the  starch 
taken  as  food  is  digested  in  the  small  intestine.  Although  the  intestinal 
juice  is  capable  of  effecting  the  transformation  of  starch  into  sugar,  the  ex- 
perimental evidence  is  conclusive  that  in  this  it  is  subordinate  to  the  pancre- 
atic juice,  which  latter  effects  this  transformation,  at  the  temperature  of  the 
body,  with  great  activity.  It  is  possible  that  the  bile  assists  in  this  process 
to  a  slight  extent.  In  the  transformation  of  starch  into  sugar  in  the  small 


218  INTESTINAL  DIGESTION. 

intestine,  the  same  intermediate  processes  are  observed  as  occur  in  the  action 
of  the  saliva ;  but  the  change  in  the  intestine  into  glucose  is  very  rapid.  It 
is  stated  that  amylopsine  is  not  present  in  the  pancreas  of  the  new-born 
infant  (Korowin)  and  that  in  early  infancy — before  the  second  or  third 
month — the  pancreatic  extract  will  not  digest  starch. 

As  cane-sugar  passes  from  the  stomach  into  the  duodenum,  it  is  almost 
instantly  transformed  into  glucose.  This  fact,  which  has  been  observed  in 
the  lower  animals,  has  received  confirmation  in  the  case  of  intestinal  fistula 
in  the  human  subject,  observed  by  Busch.  In  this  case,  when  cane-sugar 
was  introduced  in  quantity  into  the  stomach,  fasting,  the  fluid  which  escaped 
from  the  upper  end  of  the  intestine  contained  a  small  quantity  of  glucose, 
but  never  any  cane-sugar. 

It  now  becomes  a  question  whether  the  transformation  of  cane-sugar  into 
glucose  be  effected  by  the  bile,  the  intestinal  juice  or  the  pancreatic  juice. 
The  pancreatic  juice  and  the  intestinal  juice  are  the  two  fluids  which  might 
be  supposed  to  have  this  effect ;  for  it  has  been  repeatedly  demonstrated  that 
the  bile  has  of  itself  but  little  direct  action  upon  any  of  the  alimentary  mat- 
ters. This  point  was  settled  by  the  experiments  of  Busch  upon  the  lower 
end  of  the  intestine,  in  his  case  of  fistula.  Matters  introduced  into  this 
lower  opening  came  in  contact  with  the  intestinal  juice  only.  He  found 
that  cane-sugar  exposed  thus  to  the  action  of  the  intestinal  juice  was  not 
converted  into  glucose,  but  a  large  portion  of  it  passed  unchanged  in  the 
faeces. 

Out  of  the  body,  the  pancreatic  juice  is  capable,  if  kept  but  for  a  short 
time  in  contact  with  any  of  the  saccharine  principles,  of  transforming  them 
into  lactic  acid.  The  contents  of  the  small  intestine  are  sometimes  alkaline 
or  neutral  and  are  sometimes  acid.  When  a  very  large  quantity  of  sugar  has 
been  taken,  a  part  of  it  may  be  converted  in  the  intestine  into  lactic  acid, 
and  this  may  happen  with  the  sugar  which  results  from  the  digestion  of 
starch ;  but  under  ordinary  conditions,  starch  and  cane-sugar  are  readily 
changed  into  glucose  and  are  absorbed  without  undergoing  farther  trans- 
formation. 

Action  of  the  Pancreatic  Juice  upon  Nitrogenized  Substances. — Reference 
has  already  been  made  to  the  great  relative  importance  of  intestinal  diges- 
tion ;  and  it  has  been  apparent  that  the  process  of  disintegration  of  food  in 
the  stomach  is  not  final,  even  as  regards  many  of  the  nitrogenized  substances, 
but  is  rather  preparatory  to  the  complete  liquefaction  of  these  matters, 
which  takes  place  in  the  small  intestine.  In  experiments  in  which  the  pan- 
creas has  been  partially  destroyed  in  dogs,  there  was  rapid  emaciation,  with 
great  voracity,  and  the  passage,  not  only  of  unchanged  fats  and  starch,  but 
of  undigested  nitrogenized  matter  in  the  dejections  (Bernard).  The  vora- 
cious appetite,  progressive  emaciation  and  the  passage  of  all  classes  of  ali- 
mentary substances  in  the  faeces,  after  this  operation,  indicate  the  great  im- 
portance of  the  pancreatic  juice  in  digestion ;  but  the  precise  mode  of  action 
of  this  fluid  upon  the  albuminoids  is  a  question  of  some  obscurity.  If  the 
bile  be  shut  off  from  the  intestine  and  discharged  externally  by  a  fistulous 


PANCEEATIC  JUICE.  249 

opening,  the  same  voracity  and  emaciation  are  observed ;  and  yet  there  is  no 
single  alimentary  substance  upon  which  the  bile,  of  itself,  can  be  shown  to 
exert  a  very  decided  digestive  action.  Farthermore,  the  pancreatic  juice  is 
evidently  adapted  to  act  upon  alimentary  matters  after  they  have  been  sub- 
jected to  the  action  of  the  stomach,  a  preparation  which  is  essential  to  proper 
intestinal  digestion ;  and  once  passed  into  the  intestine,  the  food  comes  in 
contact  with  a  mixture  of  pancreatic  juice,  intestinal  juice  and  bile.  It 
remains  to  study,  therefore,  the  special  action  of  the  pancreatic  secretion 
upon  the  albuminoids,  as  far  as  this  influence  can  be  isolated,  and  its  action 
in  conjunction  with  the  other  intestinal  fluids  and  in  the  presence  of  other 
alimentary  matters  in  process  of  digestion.  Nitrogenized  alimentary  sub- 
stances, when  exposed  to  the  action  of  the  pancreatic  juice  out  of  the  body, 
become  rapidly  softened  and  dissolved  in  some  of  their  parts,  but  soon  un- 
dergo putrefaction  (Bernard).  Analogous  changes  take  place  in  starchy  and 
fatty  matters  when  they  are  exposed  to  the  action  of  the  pancreatic  juice  out 
of  the  body,  and  they  pass  through  the  various  stages  of  transformation  re- 
spectively into  lactic  acid  and  the  fatty  acids.  Putrefactive  action,  however, 
does  not  readily  take  place  in  albuminoids  which  have  been  precipitated  after 
having  been  cooked  or  in  raw  gluten  or  caseine.  The  presence  of  fat  also 
interferes  with  putrefaction ;  so  that  Bernard  concluded  that  the  fats  have 
an  important  influence  in  the  intestinal  digestion  of  nitrogenized  substances. 
Experiments  made  since  the  observations  of  Bernard  have  shown  that  the 
ferment  of  the  pancreatic  juice  concerned  in  the  digestion  of  albuminoids  is 
trypsine. 

Trypsine,  in  an  alkaline  medium,  changes  the  albuminoids  into  their 
respective  peptones,  in  much  the  same  way  and  involving  nearly  the  same 
intermediate  conditions  as  in  the  digestion  of  these  substances  by  the  gastric 
juice ;  but  if  the  action  be  prolonged,  out  of  the  body,  the  changes  continue, 
and  substances  are  formed  which  yield  leucine,  tyrosine  and  other  analogous 
products.  The  final  putrefactive  changes,  which  result  in  indol,  skatol, 
phenol  etc.,  some  of  which  have  a  distinctly  faecal  odor,  are  probably  due  to 
the  influence  of  micro-organisms. 

Taking  into  consideration  what  has  been  ascertained  concerning  the 
action  of  the  pancreatic  juice  upon  the  albuminoids,  there  can  be  no  doubt 
with  regard  to  the  importance  of  its  office  in  the  digestion  of  these  sub- 
stances after  they  have  been  exposed  to  the  action  of  the  gastric  juice.  Ex- 
periments upon  the  digestion  of  the  albuminoids,  after  they  have  passed  out 
of  the  stomach,  show  that  they  undergo  important  and  essential  changes  as 
they  pass  down  the  intestinal  canal.  While  the  bile  and  the  intestinal  juice 
are  by  no  means  inert,  they  seem  to  be  only  auxiliary  in  their  action  to  the 
pancreatic  juice. 

The  preparation  which  the  albuminoids  undergo  in  the  stomach  is  un- 
doubtedly necessary  to  the  easy  digestion,  in  the  small  intestine,  of  that  por- 
tion which  is  not  dissolved  by  the  gastric  juice.  This  fact  has  been  shown 
by  experiments  on  intestinal  digestion  in  the  inferior  animals  and  by  the 
observations  of  Busch  in  the  case  of  intestinal  fistula  in  the  human  subject. 


250  INTESTINAL  DIGESTION. 

Action  of  the  Pancreatic  Juice  upon  Fats. — The  pancreatic  juice  is  the 
only  one  of  the  digestive  fluids  which  is  capable  of  forming  a  complete  and 
permanent  emulsion  with  fats.  The  fact  that  the  other  digestive  fluids  will 
not  accomplish  this  is  easily  demonstrated  as  regards  the  saliva,  gastric  juice 
arid  bile.  The  intestinal  juice  is  then  the  only  one  which  might  be  supposed 
to  have  this  property.  The  observations  of  Busch  on  this  point,  in  his  case 
of  intestinal  fistula,  are  conclusive.  He  found  that  fatty  matters  taken  into 
the  stomach  were  discharged  from  the  upper  opening  in  the  intestine  in  the 
form  of  a  fine  emulsion  and  were  never  recognizable  as  oil ;  but  that  fat 
introduced  into  the  lower  intestinal  opening  was  not  acted  upon  and  was 
discharged  unchanged  in  the  faeces.  The  emulsion  resulting  from  the  action 
of  pancreatic  juice  upon  fats  persists  when  diluted  with  water  and  will  pass 
through  a  moistened  filter,  like  milk.  This  does  not  take  place  in  the  imper- 
fect emulsion  formed  by  a  mixture  of  oil  with  any  other  of  the  digestive  fluids. 
Although  the  normal  pancreatic  juice  is  constantly  alkaline,  this  is  not  an 
indispensable  condition  as  regards  its  peculiar  action  upon  fats;  for  the 
emulsion  is  none  the  less  complete  when  the  fluid  has  been  previously  neu- 
tralized with  gastric  juice.  These  facts  with  regard  to  the  action  of  the 
pancreatic  juice  upon  fats  were  first  ascertained  by  Bernard,  in  1848. 

A  substance  called  steapsine,  extracted  from  the  fresh  pancreas,  has  the 
property  of  decomposing  fats  into  the  fatty  acids  and  glycerine,  but  the 
fatty  acids  do  not  appear  in  the  chyle.  The  emulsification  of  the  fats  by  the 
pancreatic  juice  is  to  a  great  extent  a  mechanical  process  dependent  upon 
the  general  physical  characters  of  the  fluid ;  but  although  the  fat  which  is 
contained  in  the  lacteal  vessels  is  always  neutral,  it  is  thought  that  steapsine 
assists  in  rendering  the  emulsion  fine  and  permanent. 

The  cases  of  fatty  diarrhoea  connected  with  disorganization  of  the  pan- 
creas, which  were  reported  by  Richard  Bright,  in  1832,  apparently  did  not 
direct  the  attention  of  physiologists  to  the  uses  of  this  organ.  These  cases, 
with  others  of  a  similar  character  which  have  been  reported  from  time  to 
time,  are  now  brought  forward  as  evidence  of  the  action  of  the  pancreas  in 
the  digestion  of  fats.  Many  of  them  presented  a  train  of  symptoms  anal- 
ogous to  those  observed  in  animals  after  partial  destruction  of  the  gland. 
The  presence  of  fat  in  the  alvine  dejections  was  marked  ;  and  as  is  now  well 
known,  this  could  be  nothing  but  the  undigested  fatty  constituents  of  the  food. 
In  the  three  cases  observed  by  Bright,  the  pancreas  was  found  so  disorga- 
nized that  its  secreting  action  must  have  been  almost  if  not  entirely  abol- 
ished. In  the  case  reported  by  Lloyd,  the  condition  was  the  same ;  and  in 
the  case  reported  by  Elliotson,  "  the  pancreatic  duct  and  the  larger  lateral 
branches  were  filled  with  white  calculi."  Another  case  of  disease  of  the 
pancreas  was  described  in  the  catalogue  of  the  Anatomical  Museum  of  the 
Boston  Society  for  Medical  Improvement,  in  1847.  In  this  case  it  was  ob- 
served by  the  patient  that  fatty  discharges  from  the  bowels  did  not  take  place 
unless  fatty  articles  of  food  had  been  taken.  After  death  a  large  tumor  was 
found  in  the  situation  of  the  pancreas,  but  all  trace  of  the  normal  structure 
of  the  organ  had  been  destroyed.  Many  cases  of  this  character  have  been 


ACTION  OF  THE  BILE  IN   DIGESTION. 


251 


quoted  by  Bernard  and  others,  and  they  confirm  the  observations  and  experi- 
ments made  upon  the  lower  animals.  They  all  seem  to  show  that  the  action 
of  the  pancreas  in  digestion  is  essential  to  life,  but  that  one  of  the  chief 
disorders  incident  to  the  destruction  of  this  gland  relates  to  the  digestion  of 
fats. 

Taking  into  consideration  all  the  facts  bearing  upon  this  subject,  it  is 
evident  that  the  chief  agent  in  the  digestion  of  fats  is  the  pancreatic  juice ; 
and  that  this  fluid  acts  by  forming  with  the  fat  a  very  fine  emulsion,  thus 
reducing  it  to  a  condition  in  which  it  can  be  absorbed.  How  far  the  bile  may 
assist  in  this  process,  is  a  question  which  will  come  up  for  consideration  farther 
on ;  but  the  facts  with  regard  to  the  pancreatic  juice  are  conclusive. 

ACTION  OF  THE  BILE  IN  DIGESTION. 

The  physiological  anatomy  of  the  liver  and  the  general  properties  and 
composition  of  the  bile  will  be  fully  considered  in  connection  with  the 


FIG.  It. —Dog  with  a  biliary  fistula. 

From  a  rou°-h  sketch  made  the  fourteenth  day  after  the  operation.  A  small  glass  vessel  is  tied  around 
the  body  to  collect  the  bile,  and  a  wire  muzzle,  the  lower  part  of  which  is  covered  with  oil-silk,  is 
placed  over  the  mouth  to  prevent  the  animal  from  licking  the  bile.  The  dog  is  considerably 
emaciated. 

physiology  of  secretion  and  excretion ;  and  here  it  will  be  necessary  only  to 
study  the  action  of  the  bile  in  digestion. 

The  question  whether  the  bile  be  a  purely  excrementitious  fluid  or  one 
concerned  in  digestion  was  formerly  the  subject  of  much  discussion ;  but  it 
is  now  admitted  by  all  physiologists  that  the  action  of  the  bile  in  digestion 
and  absorption,  whatever  the  office  of  the  bile  may  be  as  an  excretion,  is 
essential  to  life.  The  experiments  of  Swann,  Nasse,  Bidder  and  Schmidt, 
Bernard  and  others,  who  have  discharged  all  the  bile  by  a  fistula  into  the 
gall-bladder,  communication  between  the  bile-duct  and  the  duodenum  having 
been  cut  off,  show  that  dogs  operated  on  in  this  way  have  a  voracious  appetite 


252 


INTESTINAL  DIGESTION. 


but  die  of  inanition  after  having  lost  four-tenths  of  the  body-weight.  The 
following  is  an  example  of  experiments  of  this  kind  (Flint,  1861) :  A  fistula 
was  made  into  the  gall-bladder  of  a  dog,  after  excising  nearly  the  whole  of 
the  common  bile-duct.  The  animal  suffered  no  immediate  effects  from  the 
operation,  but  died  at  the  end  of  thirty-eight  days,  having  lost  37£  per 
cent,  in  weight.  He  had  a  voracious  appetite,  was  fed  as  much  as  he  would 
eat,  was  protected  from  cold  and  was  carefully  prevented  from  licking  the 
bile.  During  the  progress  of  the  experiment,  various  observations  were 
made  on  the  flow  of  bile.  During  the  last  five  or  six  days,  the  animal  was 
ravenous  but  was  not  allowed  to  eat  all  that  he  would  at  one  time.  At  that 
time  he  was  fed  twice  a  day,  but  he  would  not  eat  fat,  even  when  very  hun- 
gry. During  the  last  day,  when  too  weak  to  stand,  he  attempted  to  eat  while 
lying  down. 

Human  bile  is  a  moderately  viscid  fluid,  of  a  dark,  golden-brown  color,  an 
alkaline  reaction  and  a  specific  gravity  of  about  1018.  Among  other  con- 
stituents, which  will  be  described  in  connection  with  the  physiology  of  secre- 
tion, it  contains  sodium  united  with  two  acids  peculiar  to  the  bile,  called 
glycocholic  and  taurocholic  acids.  Sodium  taurocholate  is  much  more  abun- 
dant than  the  glycocholate.  The  viscidity  of  the  bile  is  due  to  mucus  de- 
rived in  part  from  the  lining  membrane  of  the  gall-bladder  and  in  part, 
probably,  from  little,  racemose  glands  attached  to  the  larger  bile-ducts  in  the 
substance  of  the  liver.  The  so-called  biliary  salts,  sodium  taurocholate  and 
sodium  glycocholate,  are  probably  the  constituents  of  the  bile  which  are  con- 
cerned in  digestion. 

Although  the  bile  is  constantly  discharged  in  certain  quantity  into  the 
duodenum,  its  flow  presents  marked  variations  corresponding  with  certain 
stages  of  the  digestive  process.  In  fasting  animals,  the  gall-bladder  is  dis- 
tended with  bile ;  but  in  animals  opened  soon  after  feeding,  it  is  nearly  always 
found  empty.  The  actual  secretion  of  bile  by  the  liver  is  also  influenced  by 
digestion.  The  following  table  gives  the  variations  observed  in  the  dog  with 
a  biliary  fistula  : 

TABLE    OF   VARIATIONS    IN   THE    FLOW   OF   BILE   WITH    DIGESTION. 

(At  each  observation  the  bile  was  drawn  for  thirty  minutes.) 


Time  after  feeding. 

Fresh  bile. 

Dried  bile. 

Percentage  of 
dry  residue. 

Immediately  .  .       

Grains.     Grammes. 
8-103        0-525 

Grains.    Grammes. 
0-370       0-024 

4-566 

One  hour  

20-527       1-330 

0-586        0-038 

2-854 

Two  hours  ...         

35-760       2-317 

1-080       0-070 

3-023 

Four  hours    

38-939       2-523 

1-404       0-091 

3-605 

Six  hours    ....             ... 

22-209       1-439 

0-987       0-051 

4-450 

Eight  hours  .... 

36-577       2-370 

1-327       0-086 

3-628 

Ten  hours  

24-447       1-584 

0-833       0-054 

3-407 

Twelve  hours  

5-710       0-370 

0-247       0-016 

4-325 

Fourteen  hours  

5-000       0-324 

0-170       0-011 

3-400 

Sixteen  hours  

8-643       0-560 

0-309       0-020 

3-575 

Eighteen  hours  

9-970       0-646 

0-277       0-018 

2-778 

Twenty  hours 

4-769       0-309 

0-170       0-011 

3-565 

Twenty-two  hours  

7-578       0-491 

0-293       0-019 

3-866 

ACTION  OF  THE  BILE  IN  DIGESTION.  253 

Disregarding  slight  variations  in  this  table,  which  may  be  accidental,  it 
may  be  stated,  in  general  terms,  that  the  bile  begins  to  increase  in  quantity 
immediately  after  eating ;  that  its  flow  is  at  its  maximum  from  the  second  to 
the  eighth  hour,  during  which  time  the  quantity  does  not  vary  to  any  great 
extent ;  after  the  eighth  hour  it  begins  to  diminish,  and  from  the  twelfth 
hour  to  the  time  of  feeding  it  is  at  its  minimum. 

One  of  the  uses  which  has  been  ascribed  to  the  bile  is  that  of  regulating 
the  peristaltic  movements  of  the  small  intestine  and  of  preventing  putrefac- 
tive changes  in  the  intestinal  contents  and  the  abnormal  development  of  gas ; 
but  observations  on  this  point  have  been  somewhat  conflicting.  During  the 
first  few  days  of  the  experiment  just  described,  the  dejections  were  very  rare ; 
but  they  afterward  became  regular,  and  at  one  time  there  was  even  a  tend- 
ency to  diarrhoea.  There  can  be  little  doubt,  however,  that  the  bile  retards 
the  putrefaction  of  the  contents  of  the  intestinal  canal,  particularly  when 
animal  food  has  been  taken.  The  fasces  in  the  dog  with  biliary  fistula  were 
always  extremely  offensive.  Bidder  and  Schmidt  found  this  to  be  the  case 
in  dogs  fed  entirely  on  meat ;  but  the  faeces  were  nearly  odorless  when  the 
animals  were  fed  on  bread  alone.  In  the  case  of  intestinal  fistula  in  the 
human  subject  (Busch),  the  evacuations  which  took  place  after  the  intro- 
duction of  alimentary  substances  into  the  lower  portion  of  the  intestine  had 
an  unnaturally  offensive  and  putrid  odor.  In  this  case,  as  it  was  impossible 
for  matters  to  pass  from  the  portions  of  the  intestine  above  the  fistula  to 
those  below,  the  food  introduced  into  the  lower  opening  was  completely 
removed  from  the  action  of  the  bile. 

It  has  been  shown  that  the  bile  of  itself  has  little  action  upon  any  of  the 
different  classes  of  alimentary  substances.  In  the  fa?ces  of  animals  with 
biliary  fistula,  the  only  peculiarity  which  has  been  observed,  aside  from  the 
putrefactive  odor  and  the  absence  of  the  coloring  matter  of  the  bile,  has  been 
the  presence  of  an  abnormal  proportion  of  fat.  This  was  observed  in  the 
faeces  of  a  patient  suffering  under  jaundice  apparently  due  to  temporary  ob- 
struction of  the  bile-duct  (Flint).  The  fact  was  also  noted  in  the  dogs 
experimented  upon  by  Bidder  and  Schmidt. 

The  various  experiments  which  have  been  performed  upon  animals  render 
it  almost  certain  that  the  bile  has  an  important  influence,  either  upon  the 
digestion  or  upon  the  absorption  of  fats.  Bidder  and  Schmidt  noted,  in  ani- 
mals with  biliary  fistula,  that  the  chyle  contained  very  much  less  fat  than  in 
health.  In  an  animal  with  a  fistula  and  the  bile-duct  obliterated,  the  pro- 
portion of  fat  was  1-90  parts  to  1,000  parts  of  chyle ;  while  in  an  animal 
with  the  biliary  passages  intact,  the  proportion  was  32-79  parts  per  1,000. 
In  animals  operated  upon  in  this  way  there  is  frequently  a  great  distaste  for 
fatty  articles  of  food.  In  the  observation  made  in  1861  the  dog  refused  fat 
meat,  even  when  very  hungry  and  when  lean  meat  was  taken  with  avidity. 

Experiments  on  animals,  with  regard  to  the  influence  of  the  bile  upon 

the  absorption   of  fats,  have  resulted   in  hardly  anything  definite.     It  is 

known,  however,  that  when  the  bile  is  diverted  from  the  intestine,  the 

quantity  of  fat  in  the  chyle  is  greatly  reduced  and  a  large  proportion  of 

18 


254  INTESTINAL  DIGESTION. 

the  fat  taken  with  the  food  passes  through  the  intestine  and  is  found  in  the 
faeces. 

The  action  of  the  bile  in  exciting  muscular  contraction,  particularly  in  the 
non-striated  muscular  fibres,  is  well  established.  It  has  been  shown  by  Schiff 
that  this  fluid  acts  upon  the  muscular  fibres  situated  in  the  substance  of  the 
intestinal  villi,  causing  them  to  contract,  and  according  to  his  view,  assisting 
in  the  absorption  of  chyle  by  emptying  the  lacteals  of  the  villi.  The  ques- 
tion, however,  of  the  absorption  of  fats  is  difficult  of  investigation.  Not- 
withstanding the  obscurity  in  which  this  subject  is  involved,  it  is  certain  that 
the  progressive  emaciation,  loss  of  strength,  and  final  death  of  animals  de- 
prived of  the  action  of  the  bile  in  the  intestine,  are  due  to  defective  digestion 
and  assimilation.  Notwithstanding  the  great  quantities  of  food  taken  by 
these  animals,  the  phenomena  which  precede  the  fatal  result  are  simply  those 
of  starvation.  It  may  be  that  the  biliary  salts  are  absorbed  by  the  blood  and 
are  necessary  to  proper  assimilation ;  but  there  is  no  experimental  basis  for 
this  supposition,  and  it  is  impossible  to  discover  these  salts  in  the  blood  of 
the  portal  system  by  the  ordinary  tests.  It  is  more  probable  that  the  biliary 
: salts  influence  in  some  way  the  digestive  process  and  are  absorbed  in  a  modi- 
fied form  with  the  food. 

The  observations  of  Bidder  and  Schmidt  show  that  the  characteristic  con- 
stituents of  the  bile  are  absorbed  in  their  passage  down  the  alimentary  canal. 
Having  arrived  at  an  estimate  of  the  quantity  of  bile  daily  produced  in  dogs, 
they  collected  and  analyzed  all  the  faecal  matter  passed  by  a  dog  in  five  days. 
Of  the  dry  residue  of  the  faeces,  the  proportion  which  could  by  any  possibil- 
ity represent  the  biliary  matters  did  not  amount  to  one-fourth  of  the  dry 
residue  of  the  bile  which  must  have  been  secreted  during  that  time.  They 
also  estimated  the  sulphur  contained  in  the  faeces  and  found  that  the  entire 
•quantity  was  hardly  one-eighth  of  that  which  was  discharged  into  the  intes- 
tine in  the  bile ;  and  inasmuch  as  nearly  one-half  of  that  found  in  the  faeces 
came  from  hairs  which  had  been  swallowed  by  the  animal,  the  experiment 
showed  that  nearly  all  the  sulphur  contained  in  the  sodium  taurocholate  had 
been  taken  up  again  by  the  blood.  These  observations  show  that  the  greater 
part  of  the  bile,  with  the  biliary  salts,  is  absorbed  by  the  intestinal  mucous 
membrane.  Dalton  attempted  to  follow  the  constituents  of  the  bile  into  the 
blood  of  the  portal  system,  but  was  unable  to  detect  the  biliary  salts.  Like 
the  peculiar  constituents  of  other  secretions  which  are  reabsorbed  in  the  ali- 
mentary canal,  these  substances  become  changed  and  are  not  to  be  recognized 
by  the  ordinary  tests,  after  they  are  taken  into  the  blood. 

While  it  is  the  digestion  and  absorption  of  fatty  substances  which  seem 
to  be  most  seriously  interfered  with  in  cases  of  biliary  fistula  in  the  inferior 
animals,  the  rapid  loss  of  weight  and  strength  show  great  disturbance  in 
the  digestion  and  absorption  of  other  constituents  of  food.  A  fact  which 
indicates  a  connection  between  the  bile  and  the  process  of  digestion,  is  that 
the  flow  of  this  secretion,  although  constant,  is  greatly  increased  when  food 
passes  into  the  intestinal  canal. 

Although  it  has  been  demonstrated  that  the  presence  of  the  bile  in  the 


MOVEMENTS  OF  THE  SMALL  INTESTINE.  355 

small  intestine  is  necessary  to  proper  digestion  and  even  essential  to  life,  and 
although  the  variations  in  the  flow  of  bile  with  digestion  are  now  well  estab- 
lished, physiologists  have  but  little  definite  information  concerning  the  exact 
mode  of  action  of  the  bile  in  intestinal  digestion  and  absorption.  Nearly  all 
that  can  be  said  on  this  subject  is  that  the  action  of  the  bile  seems  to  be 
auxiliary  to  that  of  the  other  digestive  fluids. 

MOVEMENTS  OF  THE  SMALL  INTESTINE. 

By  the  contractions  of  the  muscular  coat  of  the  small  intestine,  the  ali- 
mentary mass  is  made  to  pass  along  the  canal,  sometimes  in  one  direction  and 
sometimes  in  another,  the  general  tendency,  however,  being  toward  the  cae- 
cum ;  and  the  partially  digested  matters  which  pass  out  at  the  pylorus  are  pre- 
vented from  returning  to  the  stomach  by  the  peculiar  arrangement  of  the 
fibres  which  constitute  the  pyloric  muscle.  Once  in  the  intestine,  the  food  is 
propelled  along  the  canal  by  peculiar  movements  which  have  been  called  peri- 
staltic, when  the  direction  is  toward  the  large  intestine,  and  antiperistaltic, 
when  the  direction  is  reversed.  These  movements  are  of  the  character  pecul- 
iar to  the  non-striated  muscular  fibres ;  viz.,  slow  and  gradual,  the  contraction 
enduring  for  a  certain  time  and  being  followed  by  a  correspondingly  slow  and 
gradual  relaxation.  Both  the  circular  and  the  longitudinal  muscular  layers 
participate  in  these  movements. 

Although  the  mechanism  of  the  peristaltic  movements  of  the  intestine 
may  be  studied  in  living  animals  after  opening  the  abdomen  or  in  animals 
just  killed,  the  movements  thus  observed  do  not  entirely  correspond  with 
those  which  take  place  under  natural  conditions.  In  vivisections  no  move- 
ments are  observed  at  first,  but  soon  after  exposure  of  the  parts  nearly  the 
whole  intestine  moves  like  a  mass  of  worms.  In  the  normal  process  of  diges- 
tion the  movements  are  never  so  general  or  so  active.  They  take  place  more 
regularly  and  consecutively  in  those  portions  in  which  the  contents  are  most 
abundant,  and  the  movements  are  generally  intermittent,  being  interrupted 
by  long  intervals  of  repose.  In  Busch's  case  of  intestinal  fistula,  there  existed 
a  large  ventral  hernia,  the  coverings  of  which  were  so  thin  that  the  peristal- 
tic movements  could  be  readily  observed.  In  this  case  the  general  character 
of  the  movements  corresponded  with  what  has  been  observed  in  the  inferior 
animals.  It  was  noted  that  the  movements  were  not  continuous,  and  that 
there  were  often  intervals  of  rest  for  more  than  a  quarter  of  an  hour.  It  was 
also  observed  that  the  movements,  as  indicated  by  flow  of  matters  from  the 
upper  end  of  the  intestine,  were  intermitted  with  considerable  regularity  dur- 
ing part  of  the  night.  Antiperistaltic  movements,  producing  discharge  of 
matters  which  had  been  introduced  into  the  lower  portion  of  the  intestine, 
were  frequently  observed. 

As  far  as  has  been  ascertained  by  observations  upon  the  human  subject 
and  warm-blooded  animals,  the  regular  intestinal  movements  are  excited  by 
the  passage  of  alimentary  matters  from  the  stomach  through  the  tube  during 
the  natural  process  of  digestion.  By  a  very  slow  and  gradual  action  of  the 
muscular  coat  of  the  intestine,  its  contents  are  passed  along,  occasionally  the 


256  INTESTINAL  DIGESTION. 

action  being  reversed  for  a  time,  until  the  indigestible  residue,  mixed  with  a 
certain  quantity  of  intestinal  secretion,  more  or  less  modified,  is  discharged 
into  the  caput  coli.  These  movements  are  apparently  not  continuous,  and 
they  depend  in  some  degree  upon  the  quantity  of  matter  contained  in  different 
parts  of  the  intestinal  tract.  Judging  from  the  movements  in  the  inferior 
animals  after  the  abdomen  has  been  opened,  the  intestines  are  always  chang- 
ing their  position,  mainly  by  the  action  of  their  longitudinal  muscular  fibres, 
so  that  the  force  of  gravity  does  not  oppose  the  onward  passage  of  their  con- 
tents as  much  as  if  the  relative  position  of  the  parts  were  constant.  There 
are  no  definite  observations  concerning  the  relative  activity  of  the  peristaltic 
movements  in  different  portions  of  the  intestine ;  but  from  the  fact  that  the 
jejunum  is  constantly  found  empty,  while  the  ileum  contains  a  considerable 
quantity  of  pultaceous  matter,  it  would  seem  that  the  movements  must  be 
more  vigorous  and  efficient  in  the  upper  portions  of  the  canal. 

The  gases  which  are  found  in  the  intestine  have  an  important  mechanical 
office.  They  are  useful,  in  the  first  place,  in  keeping  the  canal  constantly 
distended  to  the  proper  degree,  thus  avoiding  the  liability  to  disturbances  in 
the  circulation  and  facilitating  the  passage  of  the  alimentary  mass  in  obedience 
to  the  peristaltic  contractions.  They  also  support  the  walls  of  the  intestine 
and  protect  these  parts  against  concussions,  in  walking,  leaping  etc.  The 
gases  are  useful,  likewise,  in  offering  an  elastic  but  resisting  mass  upon  which 
the  compressing  action  of  the  abdominal  muscles  may  be  exerted  in  straining 
and  in  expiration. 

There  can  be  hardly  any  question  that  the  normal  movements  of  the  in- 
testine are  due  principally  to  the  impression  made  upon  the  mucous  mem- 
brane by  the  alimentary  matters,  to  which  is  added,  perhaps,  the  stimulating 
action  of  the  bile.  It  is  difficult  to  determine  with  accuracy  what  part  the 
bile  plays  in  the  production  of  these  movements,  from  the  fact  that  the  nor- 
mal action  of  the  intestine  is  not  easily  observed.  In  the  case  of  intestinal 
fistula  so  often  referred  to,  when  food  was  introduced  into  the  lower  portion  of 
the  canal,  there  was  at  first  an  abundant  evacuation  every  twenty-four  hours ; 
but  subsequently  it  became  necessary  to  use  enemata.  As  there  was  no  com- 
munication between  the  lower  and  the  upper  portions  of  the  intestine,  this 
fact  is  an  evidence  that  the  peristaltic  movements  can  take  place  without  the 
action  of  the  bile. 

The  vigorous  peristaltic  movements  which  occur  soon  after  death  have 
been  explained  in  various  ways.  It  has  been  shown  that  these  movements 
are  not  due  to  a  lowering  of  the  temperature  or  to  exposure  of  the  intestines 
to  the  air.  The  latter  fact  may  be  easily  verified  by  killing  a  rabbit,  when 
vigorous  movements  may  be  seen  through  the  thin,  abdominal  walls,  even 
while  the  cavity  is  unopened.  According  to  Schiff,  the  cause  of  these  exag- 
gerated movements  is  diminution  or  arrest  of  the  circulation.  By  compress- 
ing the  abdominal  aorta  in-  a  living  animal,  he  was  able  to  excite  peristaltic 
movements  in  the  intestine  as  vigorous  as  those  which  take  place  after  death ; 
and  on  ceasing  the  compression,  the  movements  were  arrested. 

The  nerves  distributed  to  the  small  intestine  are  derived  from  the  sym- 


PHYSIOLOGICAL  ANATOMY  OF  THE  LARGE  INTESTINE.     257 

pathetic  and  from  branches  of  the  pneumogastric,  which  latter  come  from 
the  nerve  of  the  right  side  and  are  distributed  to  the  whole  of  the  intestinal 
tract,  from  the  pylorus  to  the  ileo-caecal  valve.  The  intestine  receives  no 
filaments  from  the  left  pneumogastric.  Throughout  the  intestinal  tract,  is  a 
plexus  of  non-medullated  nerve-fibres  with  groups  of  nerve-cells,  lying  be- 
tween the  longitudinal  and  circular  layers  of  the  muscular  coat.  This  is 
known  as  Auerbach's  plexus.  From  this  plexus,  very  fine,  non-medullated 
filaments  are  given  off,  which  form  a  wider  plexus,  also  with  ganglionic  cells, 
situated  just  beneath  the  mucous  membrane.  This  is  called  the  plexus  of 
Meissner. 

The  experiments  of  Brachet,  by  which  he  attempted  to  prove  that  the 
movements  of  the  intestines  were  under  the  control  of  the  pneumogastrics 
and  nerves  given  off  from  the  spinal  cord,  have  not  been  verified  by  other 
observers.  The  experiments  of  Miiller,  however,  render  it  certain  that  the 
peristaltic  movements  are  to  some  extent  under  the  influence  of  the  sympa- 
thetic system.  In  these  experiments,  movements  of  the  intestine  were  pro- 
duced by  stimulation  of  filaments  of  the  sympathetic  distributed  to  its  mus- 
cular coat,  after  the  ordinary  post-mortem  movements  had  ceased.  The 
same  results  followed  the  application  of  potassium  hydrate  to  the  semilunar 
ganglia,  the  movements  reappearing'  when  the  agent  was  applied,  "  with  ex- 
traordinary vivacity  "  in  the  rabbit,  after  the  abdomen  had  been  opened  and  the 
movements  had  entirely  ceased.  These  experiments  have  been  confirmed  by 
Longet,  who  found,  however,  that  the  movements  did  not  take  place  unless 
alimentary  matters  were  contained  in  the  intestine. 

The  fact  that  movements  occur  in  portions  of  intestine  cut  out  of  the 
body  and  separated,  of  course,  from  the  nervous  system,  has  led  to  the  view 
that  the  peristaltic  action  is  automatic,  like  the  action  of  the  excised  heart, 
and  these  automatic  movements  have  been  attributed  to  the  influence  of  the 
ganglia  found  in  the  intestinal  walls.  An  analogy  between  such  intestinal 
movements  and  the  movements  of  the  excised  heart  seems  probable ;  and  a 
reasonable  explanation  of  this  action  is  afforded  by  the  existence  of  ganglia 
in  the  plexuses  of  Auerbach  and  of  Meissner. 

PHYSIOLOGICAL  ANATOMY  OF  THE  LARGE  INTESTINE. 

The  entire  length  of  the  large  intestine  is  about  five  feet  (1*5  metre.)  Its 
diameter  is  greatest  at  the  caecum,  where  it  measures,  when  moderately  dis- 
tended, two  and  a  half  to  three  and  a  half  inches  (6 '35  to  8*89  cen- 
timetres). According  to  the  observations  of  Brinton,  the  average  diameter 
of  the  tube  beyond  the  caecum  is  one  and  two-thirds  to  two  and  two-thirds 
inches  (4'23  to  6'77  centimetres).  Passing  from  the  caecum,  the  canal 
diminishes  in  caliber,  gradually  and  very  slightly,  to  where  the  sigmoid  flex- 
ure opens  into  the  rectum.  This  is  the  narrowest  portion  of  the  canal. 
Beyond  this,  the  rectum  gradually  increases  in  diameter,  forming  a  kind  of 
pouch,  which  abruptly  diminishes  in  size  near  the  external  opening,  to  form 
the  anus. 

The  general  direction  of  the  large  intestine  is  from  the  caecum,  in  the 


258 


INTESTINAL  DIGESTION. 


right  iliac  fossa,  to  the  left  iliac  fossa,  thus  encircling  the  convoluted  mass 
formed  by  the  small  intestine,  in  the  form  of  a  horseshoe.     From  the  csecum 

to  the  rectum,  the  canal  is 
known  as  the  colon.  The 
first  division  of  the  colon, 
called  the  ascending  colon, 
passes  almost  directly  up- 
ward to  the  under  surface 
of  the  liver  ;  the  canal  here 
turns  at  nearly  a  right  an- 
gle, passes  across  the  upper 
part  of  the  abdomen  and 
is  called  the  transverse  co- 
lon ;  it  then  passes  down- 
ward at  nearly  a  right  an- 
gle, forming  the  descend- 
ing colon.  The  last  divis- 
ion of  the  colon,  called  the 
sigmoid  flexure,  is  situated 
in  the  left  iliac  fossa  and 
is  in  the  form  of  the  italic 
letter  S.  This  terminates 
in  the  rectum,  which  is  not 
_  straight,  as  its  name  would 
imply,  but  presents  at  least 
three  distinct  curvatures, 
as  follows  :  it  passes  first 
in  an  oblique  direction 
from  the  left  sacro-iliac 
svmphysis  to  the  median 

FIG.  78. — Stomach,  pancreas,  larcie  intestine  etc.  (Sappey).  ,.  .  .  .    _. 

1,  anterior  surface  of  the  liver  ;  2.  pall-bladder  ;  3,  3.  section  of  "°&      Opposite     the     third 

the  diaphragm  :  4,  posterior  surface  of  the  stomach  ;  5,  iobus  -.-.ion^    ^.f    4-no    oanvnm  •     if 

Spigelii  of  the  liver  ;  6,  creliac  axis  ;  7,  coronary  artery  of  the  Plfc 

stomach  ;  8.  splenic  artery  ;  9,  spleen  :  10,  pancreas  ;  11.  supe-  fnoT1    T-.OCOOO    rlnwnwnrrl    in 

rior  mesenteric  vessels  :  12,  duodenum  :  13.  upper  extremity  T 

of  the  small  intestine  :  14,  lower  end  of  the  ileum  :  15,  15,  mes-  f}lp  rnprlinn  lino    fnllnwino- 

entery  ;  16,  caicum  ;  17,  appendix  vermiformis ;  18,  ascending  l  Qe>  I( 

colon  ;  19,  19,  transverse  colon  ;  20,  descending  colon  ;  21.  sig-  f  V.p  nnnpfl  vitv  nf  flip  «flfm  m 
moid  flexure  of  the  colon  ;  22,  rectum  ;  23,  urinary  bladder.  *  1V  ° 

and  coccyx ;  and  the  lower 

portion,  which  is  about  an  inch  (2-54  centimetres)  in  length,  turns  backward 
to  terminate  in  the  anus. 

The  ca3cum,  or  caput  coli,  presents  a  rounded,  dilated  cavity  continuous 
with  the  colon  above  and  communicating  by  a  transverse  slit  with  the  ileum. 
At  its  lower  portion  is  a  small,  cylindrical  tube,  opening  below  and  a  little 
posterior  to  the  opening  of  the  ileum,  called  the  vermiform  appendix.  This 
is  covered  with  peritoneum  and  has  a  muscular  and  a  mucous  coat.  It  is 
sometimes  entirely  free  and  is  sometimes  provided  with  a  short  fold  of  mes- 
entery for  a  part  of  its  length.  The  coats  of  the  appendix  are  very  thick. 
The  muscular  coat  consists  of  longitudinal  fibres  only.  The  mucous  mem- 


PHYSIOLOGICAL  ANATOMY  OF  THE  LARGE  INTESTINE.     259 


brane  is  provided  with  tubules  and  closed  follicles,  the  latter  frequently 
being  very  abundant.  This  little  tube  generally  contains  a  quantity  of  clear, 
viscid  mucus.  The  uses  of  the  vermiform  appendix  are  unknown. 

Ileo-ccBcal  Valve.  —  The  opening  by  which  the  small  intestine  commu- 
nicates with  the  caecum  is  provided  with  a  valve,  known  as  the  ileo-csecal 
valve,  situated  at  the  inner  and  posterior  portion  of  the  caecum.  The  small 
intestine,  at  its  termination,  presents  a  shallow  concavity,  which  is  provided 
with  a  horizontal,  button-hole  slit  opening  into  the  caecum.  The  surface  of  the 
valve  which  looks  toward  the  small  intestine  is  covered  with  a  mucous  mem- 
brane provided  with  villi  and  in  all  respects  resembling  the  general  mucous 
lining  of  the  small  intestine.  Viewed  from  the  caecum,  a  convexity  is 
observed  corresponding  to  the  concavity  upon  the  other  side.  The  caecal 
surface  of  the  valve  is  covered  with  a  mucous  membrane  identical  with  the 
general  mucous  lining  of  the  large  intestine.  It  is  evident,  from  an  exami- 
nation of  these  parts,  that  pressure  from  the  ileum  would  open  the  slit  and 
allow  the  easy  passage  of  the  semi-fluid  contents  of  the  intestine  ;  but  press- 
ure from  the  caecal  side  approximates  the  lips  of  the  valve,  and  the  greater 
the  pressure  the  more  firmly  is  the  opening  closed.  The  valve  itself  is  com- 
posed of  folds  formed  of  the  fibrous  tissue  of 
the  intestine,  and  circular  muscular  fibres  from 
both  the  small  and  the  large  intestine,  the  whole 
being  covered  with  mucous  membrane.  The  lips 
of  the  valve  unite  at  either  extremity  of  the  slit 
and  are  prolonged  on  the  inner  surface  of  the 
caecum,  forming  two  raised  bands,  or  bridles  ; 
and  these  become  gradually  effaced  and  are  thus 
continuous  with  the  general  lining  of  the  canal. 
The  posterior  bridle  is  a  little  longer  and  more 
prominent  than  the  anterior.  These  assist  some- 
what in  enabling  the  valve  to  resist  pressure  from 
the  caecal  side.  The  longitudinal  layer  of  mus- 
cular fibres  and  the  peritoneum  pass  directly 
over  the  attached  edge  of  the  valve  and  are  not 

involved    in    its    folds.        These    give    Strength    tO 

the  part,  and  if  they  be  divided  over  the  valve, 

..  ..,  ,      ,  ,., 

gentle  traction  will  suffice  to  draw  out  and  oblit- 

,  i       »   i  n       i         •  •         •, 

erate  the  folds,  leaving  a  simple  and  unprotected 

,•          ,     ,  ,1       -,  1,1 

communication  between  the  large  and  the  small 
intestine. 

Peritoneal  Coat.  —  Like  most  of  the  other  abdominal  viscera,  the  large 
intestine  is  covered  by  peritoneum.  The  caecum  is  covered  by  this  mem- 
brane only  anteriorly  and  laterally.  It  usually  is  bound  down  closely  to  the 
subjacent  parts,  and  its  posterior  surface  is  without  a  serous  investment; 
although  sometimes  it  is  completely  covered,  and  there  may  be  even  a  short 
mesocaecum.  The  ascending  colon  is  likewise  covered  with  peritoneum  only 
in  front,  and  is  closely  attached  to  the  subjacent  parts.  The  same  arrange- 


ttne  mto  the  cwcum  (Le  Bon). 

small   intestine;    2,  ileo-csecal 

valve  ;  a,  caecum  ;  4.  opening  of 

the   appendix  vermiformis  ;   5, 

mucous  fold  at  the  opening  of 

the  appendix  ;  6,  large  intestine  ; 

7,  r,  folds  of  the  mucous  mem- 


260  INTESTINAL  DIGESTION. 

ment  is  found  in  the  descending  colon.  The  transverse  colon  is  almost  com- 
pletely invested  with  peritoneum ;  and  the  two  folds  forming  the  transverse 
mesocolon  separate  to  pass  over  the  tube  above  and  below,  uniting  again  in 
front,  to  form  the  great  omentum.  The  transverse  col'on  is  consequently 
quite  movable.  In  the  course  of  the  colon  and  the  upper  part  of  the  rectum, 
particularly  on  the  transverse  colon,  are  found  a  number  of  little,  sacculated 
pouches  filled  with  fat,  called  the  appendices  epiploicae.  The  sigmoid  flexure 
of  the  colon  is  covered  by  peritoneum,  except  at  the  attachment  of  the  iliac 
mesocolon.  This  division  of  the  intestine  is  quite  movable.  The  upper  por- 
tion of  the  rectum  is  almost  completely  covered  by  peritoneum  and  is  but 
loosely  held  in  place.  The  middle  portion  is  closely  bound  down,  and  is 
covered  by  peritoneum  only  anteriorly  and  laterally.  The  lowest  portion  of 
the  rectum  has  no  peritoneal  covering. 

Muscular  Coat. — The  muscular  fibres  of  the  large  intestine  have  an 
arrangement  quite  different  from  that  which  exists  in  the  small  intestine. 
The  external,  longitudinal  layer,  instead  of  extending  over  the  whole  tube, 
is  arranged  in  three  distinct  bands,  which  begin  in  the  csecum  at  the  vermi- 
form appendix.  Passing  along  the  ascending  colon,  one  of  the  bands  is  sit- 
uated anteriorly,  and  the  others,  latero-posteriorly.  In  the  transverse  colon 
the  anterior  band  becomes  inferior  and  the  two  latero-posterior  bands 
become  respectively  postero-superior  and  postero-inferior.  In  the  descend- 
ing colon  and  the  sigmoid  flexure  the  muscular  bands  resume  the  relative 
position  which  they  had  in  the  ascending  colon.  As  these  longitudinal 
fibres  pass  to  the  rectum,  the  anterior  and  the  external  bands  unite  to  pass 
down  on  the  anterior  surface  of  the  canal,  while  the  posterior  band  passes 
down  on  its  posterior  surface.  Thus  the  three  bands  here  become  two. 
These  two  bands  as  they  pass  downward,  though  remaining  distinct,  become 
much  wider  ;  and  longitudinal  muscular  fibres  beginning  at  the  rectum  are 
situated  between  them,  so  that  this  part  of  the  canal,  especially  in  its  lower 
portion,  is  covered  with  longitudinal  fibres  in  a  nearly  uniform  layer. 

Mucous  Coat. — The  mucous  lining  of  the  large  intestine  presents  several 
important  points  of  difference  from  the  corresponding  membrane  in  the  small 
intestine.  It  is  paler,  somewhat  thicker  and  firmer,  and  is  more  closely  ad- 
herent to  the  subjacent  parts.  In  no  part  of  this  membrane  are  there  any 
folds,  like  those  which  form  the  valvulae  conniventes  of  the  small  intestine ; 
and  the  surface  is  smooth  and  free  from  villi. 

Throughout  the  entire  mucous  membrane,  from  the  ileo-cgecal  valve  to 
the  anus,  are  orifices  which  lead  to  simple  follicular  glands.  These  struct- 
ures resemble  in  all  respects  the  follicles  of  the  small  intestine,  except  that 
they  are  a  little  longer,  owing  to  the  greater  thickness  of  the  membrane,  are 
wider  and  rather  more  abundant.  Among  these  small  follicular  openings 
are  found,  scattered  irregularly  throughout  the  membrane,  larger  openings 
which  lead  to  utricular  glands,  resembling  the  closed  follicles,  in  general 
structure,  except  that  they  have  an  orifice  opening  into  the  cavity  of  the  in- 
testine, which  is  sometimes  so  large  as  to  be  visible  to  the  naked  eye.  The 
.  number  of  these  glands  is  very  variable,  and  they  exist  throughout  the  intes- 


PHYSIOLOGICAL  ANATOMY  OF  THE  LARGE  INTESTINE.     261 

tine,  together  with  the  closed  follicles,  except  in  the  rectum.  In  the  caecum 
and  colon,  isolated  closed  follicles  are  generally  found,  which  are  identical 
in  structure  with  the  solitary  glands  of  the  small  intestine.  These  are  very 
variable,  both  in  number  and  size. 

The  mucous  membrane  of  the  rectum,  in  the  upper  three-fourths  of  its 
extent,  does  not  differ  materially  from  that  of  the  colon.  In  the  lower  fourth, 
the  fibrous  tissue  by  which  the  lining  membrane  is  united  to  the  subjacent 
muscular  coat  is  loose,  and  the  membrane,  when  the  canal  is  empty,  is  thrown 
into  a  great  number  of  irregular  folds.  At  the  site  of  the  internal  sphincter, 
five  or  six  little,  semilunar  valves  have  been  observed,  with  their  concavities 
directed  toward  the  colon.  These  form  an  irregular,  festooned  line,  which 
surrounds  the  canal ;  their  folds,  however,  are  small  and  have  no  tendency  to 
obstruct  the  passage  of  faecal  matters.  The  simple  follicles  are  particularly 
abundant  in  the  rectum,  and  the  membrane  is  constantly  covered  with  a  thin 
coating  of  mucus.  Another  peculiarity  to  be  noted  in  the  mucous  membrane 
of  the  lower  portion  of  the  rectum  is  its  great  vascularity,  the  veins,  espe- 
cially, being  very  abundant. 

The  rectum  terminates  in  the  anus,  a  button-hole  orifice,  situated  a  little 
in  front  of  the  coccyx,  which  is  kept  closed  and  somewhat  retracted,  except 
during  the  passage  of  the  faeces,  by  the  powerful  external  sphincter.  This 
muscle  is  composed  entirely  of  striated  fibres,  which  are  arranged  in  the  form 
of  an  ellipse,  its  long  diameter  being  antero-posterior. 

It  is  now  almost  universally  admitted  that  the  digestion  of  all  classes  of 
alimentary  substances  is  completed  either  in  the  stomach  or  in  the  small  in- 
testine, and  that  the  mucous  membrane  of  the  large  intestine  does  not  secrete 
a  fluid  endowed  with  any  well  marked  digestive  properties.  The  simple  fol- 
licles, the  closed  follicles,  and  the  utricular  glands,  produce  a  glairy  mucus, 
which,  as  far  as  is  known,  serves  merely  to  lubricate  the  canal.  This  has 
never  been  obtained  in  sufficient  quantity  to  admit  of  any  accurate  investiga- 
tion into  its  properties. 

In  studying  the  changes  which  the  alimentary  mass  undergoes  in  its  pas- 
sage through  the  small  intestine,  it  has  been  seen  that  in  this  portion  of  the 
canal,  the  greatest  part  of  all  the  nutritive  material  is  not  only  liquefied 
but  is  absorbed.  Sometimes  fragments  of  muscular  fibre,  oil-globules,  and 
other  matters  in  a  state  of  partial  disintegration,  may  be  detected  in  the 
faeces ;  but  generally  this  is  either  the  result  of  the  ingestion  of  an  excessive 
quantity  of  these  substances  or  it  depends  upon  some  derangement  of  the 
digestive  apparatus.  When  intestinal  digestion  takes  place  with  regularity, 
the  transformation  of  the  alimentary  residue  into  faecal  matter  is  slow  and 
gradual.  As  the  contents  of  the  stomach  are  passed  little  by  little  into  the 
duodenum,  the  mass  becomes  of  a  bright-yellow  color,  and  its  fluidity  is  in- 
creased, from  the  admixture  of  bile  and  pancreatic  fluid.  In  passing  along 
the  canal,  the  consistence  of  the  mass  gradually  diminishes  on  account  of 
absorption  of  its  liquid  portions,  and  the  color  becomes  darker ;  and  by  the 
time  that  the  contents  of  the  ileum  are  ready  to  pass  into  the  caecum,  the 
greatest  part  of  those  substances  recognized  as  alimentary  has  become 


262  INTESTINAL  DIGESTION. 

changed  and  absorbed.  The  various  forms  of  starchy  and  saccharine  matters, 
unless  they  have  been  taken  in  excessive  quantity,  soon  disappear  from  the 
intestine ;  and  the  glucose,  which  is  the  result  of  their  digestion,  may  be  rec- 
ognized in  the  portal  blood.  As  a  rule,  fatty  matters  are  not  found  in  the 
lower  part  of  the  ileum,  having  passed  into  the  lacteals,  in  the  form  of  an 
emulsion.  Neither  fibrin,  albumen  nor  caseine,  can  be  detected  in  the  ileum ; 
and  the  muscular  substance,  as  recognized  by  its  microscopical  characters, 
becomes  gradually  disintegrated  and  is  lost — except  a  few  isolated  fragments 
deeply  colored  with  bile — some  time  before  the  indigestible  residue  passes 
into  the  large  intestine. 

In  the  human  subject  those  portions  of  the  food  which  resist  the  succes- 
sive and  combined  action  of  the  different  digestive  secretions  are  derived 
chiefly  from  the  vegetable  kingdom.  Hard,  vegetable  seeds,  the  cortex  of 
the  cereals,  spiral  vessels,  and,  indeed,  all  parts  which  are  composed  largely 
of  cellulose,  pass  through  the  intestinal  canal  without  much  change.  These 
substances  form,  in  the  faeces,  the  greatest  part  of  what  can  be  recognized  as 
the  residue  of  matters  taken  as  food.  It  is  well  known  that  an  exclusively 
animal  diet,  particularly  if  the  nutritious  matters  be  taken  in  a  concen- 
trated and  readily  assimilable  form,  leaves  very  little  undigested  matter  to 
pass  into  the  large  intestine,  and  gives  to  the  faces  a  character  quite  different 
from  that  which  is  observed  in  herbivorous  animals  or  in  man  when  subjected 
to  an  exclusively  vegetable  diet.  The  characters  of  the  residue  of  the  diges- 
tion of  albuminoid  substances  are  not  very  distinct.  As  a  rule,  none  of  the 
albuminoids  are  to  be  recognized  in  the  healthy  fasces  by  the  ordinary  tests. 

Absorption  of  various  articles  of  food  in.  a  liquid  form  may  take  place 
with  great  activity  in  the  large  intestine,  although  it  has  not  been  shown  that 
the  secretions  in  this  part  of  the  alimentary  canal  have  any  distinct  digestive 
properties ;  still,  as  is  shown  in  rectal  alimentation,  eggs,  milk  and  meat-ex- 
tracts may  be  taken  up  by  the  mucous  membrane,  and  they  enter  the  circu- 
lation in  such  a  form  that  they  contribute  to  the  nutrition  of  the  body. 

Processes  of  Fermentation  in  the  Intestinal  Canal. — The  processes  of 
fermentation  in  the  intestines  are  not  properly  digestive  and  are  to  a  great 
extent  due  to  the  action  of  micro-organisms,  which  exist  here  in  great  num- 
bers and  variety.  It  is  possible,  however,  that  future  researches  may  show 
that  micro-organisms  play  an  important  part  in  actual  digestion,  as  is  fore- 
shadowed in  a  recent  article  by  Pasteur  (August,  1887).  Pasteur  has  isolated 
seventeen  different  micro-organisms  of  the  mouth.  Some  of  these  dissolved 
albumen,  gluten  and  caseine,  and  some  transformed  starch  into  glucose.  The 
micro-organisms  described  were  not  destroyed  by  the  action  of  the  gastric 
juice.  These  observations  are  very  suggestive,  and  they  seem  to  open  a  new 
field  of  inquiry  as  regards  certain  of  the  processes  of  digestion.  Most  of  the 
fermentations  in  the  small  intestine  are  either  putrefactive  or  of  a  nature 
analogous  to  fermentation,  and  the  processes  are  continued  with  increased 
activity  in  the  large  intestine. 

Some  of  the  substances  resulting  from  intestinal  fermentations  have 
already  been  described.  Indol,  skatol,  phenol  etc.,  seem  to  be  produced  by 


CONTENTS  OF  THE  LAEGE  INTESTINE.  263 

the  action  of  micro-organisms ;  but  the  effect  of  these  products  is  to  kill  the 
micro-organisms  and  thus  to  limit  the  putrefactive  processes.  The  produc- 
tion of  indol,  skatol  and  phenol  is  arrested  by  the  action  of  certain  drugs, 
such  as  calomel,  salicylic  acid  and  other  so-called  antiseptics.  The  fermenta- 
tive changes  in  the  intestines  involve  the  production  of  certain  gases,  which 
will  be  described  at  the  close  of  this  chapter. 

CONTEXTS  OF  THE  LARGE  INTESTINE. 

When  the  contents  of  the  small  intestine  have  passed  the  ileo-csecal  valve, 
they  become  changed  in  their  general  character,  partly  from  admixture  with 
the  secretions  of  this  portion  of  the  canal,  and  are  then  known  as  the  fgeces. 
The  most  notable  changes  relate  to  consistence,  color  and  odor.  The  odor, 
especially,  of  normal  ftecal  matter  is  characteristic. 

Faecal  matter  has  a  much  firmer  consistence  than  the  contents  of  the 
ileum,  which  is  due  to  a  constant  absorption  of  the  liquid  portions.  As  a 
rule,  the  consistence  is  great  in  proportion  to  the  length  of  time  that  the 
faeces  remain  in  the  large  intestine ;  and  this  is  variable  in  different  persons, 
and  in  the  same  person,  in  health,  depending  somewhat  upon  the  character 
of  the  food.  The  color  changes  from  the  yellow,  more  or  less  bright,  which 
is  observed  in  the  ileum,  to  the  dark  yellowish-brown  characteristic  of  the 
faeces.  Although  the  bile-pigment  can  not  usually  be  recognized  by  the  ordi- 
nary tests,  it  is  this  which  gives  to  the  contents  of  the  large  intestine  their 
peculiar  color,  which  is  lost  when  the  bile  is  not  discharged  into  the  duode- 
num. In  a  specimen  of  healthy  human  faeces,  which  had  been  dried,  ex- 
tracted with  alcohol,  the  alcoholic  extract  precipitated  with  ether  and  the 
precipitate  dissolved  in  distilled  water,  it  was  impossible  to  detect  the  biliary 
salts  by  Pettenkofer's  test.  In  a  watery  extract  of  the  same  faeces,  the  addi- 
tion of  nitric  acid  failed  to  show  the  reaction  of  the  coloring  matter  of  the 
bile  (Flint,  1862).  The  color  of  the  faeces,  however,  varies  considerably 
under  different  forms  of  diet.  With  a  mixed  diet  the  color  is  yellowish- 
brown  ;  with  an  exclusively  flesh-diet  it  is  much  darker ;  and  with  a  milk- 
diet  it  is  more  yellow  (Wehsarg). 

The  odor  of  the  faeces,  which  is  characteristic  and  quite  different  from 
that  of  the  contents  of  the  ileum,  is  variable  and  is  due  in  part  to  the  pecul- 
iar decomposition  of  the  residue  of  the  food,  in  part  to  the  decomposition  of 
the  bile  and  in  part  to  matters  secreted  by  the  mucous  membrane  of  the 
colon  and  of  the  glands  near  the  anus. 

The  entire  quantity  of  faeces  in  the  twenty-four  hours,  according  to  Weh- 
sarg, is  about  4-6  ounces  (128  grammes).  This  was  the  mean  of  seventeen 
observations ;  the  largest  quantity  being  10'8  ounces  (306  grammes),  and  the 
smallest,  2'4  ounces  (68  grammes). 

The  reaction  of  the  fasces  is  variable,  depending  chiefly  upon  the  char- 
acter of  the  food.  Marcet  found  the  human  excrements  always  alkaline. 
Wehsarg,  on  the  other  hand,  found  the  reaction  generally  acid,  but  very  fre- 
quently it  was  alkaline  or  neutral. 

The  proportions  of  water  and  solid  matter  in  the  faeces  are  variable.    Ber- 


264  INTESTINAL  DIGESTION. 

zelius  found  in  the  healthy  human  faeces,  73-3  parts  of  water  and  26*7  parts 
of  solid  residue.  The  average  of  seventeen  observations  by  Wehsarg  was 
precisely  the  same.  In  the  observations  of  Wehsarg,  the  mean  quantity  of 
solid  matter  discharged  in  the  faeces  in  the  twenty-four  hours  was  463  grains 
(30  grammes),  the  extremes  being  882*8  grains  (57'2  grammes),  and  251-6 
grains  (16*28  grammes).  The  proportion  of  undigested  matters  in  the  solid 
residue  was  very  small,  averaging  but  little  more  than  ten  per  cent.,  the  mean 
quantity  in  the  twenty-four  hours  in  ten  observations  being  but  52*5  grains 
(3-4  grammes).  This  was  found,  however,  to  be  very  variable ;  the  largest 
quantity  being  126*5  grains  (8*2  grammes),  and  the  smallest,  12*5  grains  (0-81 
gramme). 

Microscopical  examination  of  the  faeces  reveals  various  vegetable  and  ani- 
mal structures  which  have  escaped  the  action  of  the  digestive  fluids.  Weh- 
sarg also  found  a  "  finely  divided  fascal  matter  "  of  indefinite  structure,  but 
containing  partly  disintegrated  intestinal  epithelium.  Crystals  of  cholester- 
ine  were  never  observed.  Whenever  the  matter  is  neutral  or  alkaline,  crys- 
tals of  ammonio-magnesian  phosphate  are  found.  Mucus  is  also  found 
in  variable  quantity  in  the  fasces,  with  desquamated  epithelium  and  a  few 
leucocytes.  In  addition,  recent  microscopical  researches  have  shown  the 
presence  of  spores  of  yeast  and  a  great  variety  of  bacteria,  which  latter  exist 
in  the  fasces  in  great  abundance.  These  organisms  probably  excite  many 
of  the  so-called  putrefactive  changes  in  the  intestinal  contents,  which  result 
in  the  formation  of  indol,  phenol,  skatol,  cresol  etc.  According  to  Senator, 

-  'i  ii  ^  i  i«  ©  a  <***       these  putref ac- 

i  |\/}>  2  ^o  /*•  '  «a&«aS3^      donotoccurin 

the  meconium. 
The     quantity 
of      inorganic 
/         W  salts     in     the 

FIG.  80. — Micro-organisms  of  the  large  intestine  (Landois).  f  86068      is      not 
1,  bacterium  coli  commune  :  2,  bacterium  lactis  aerogenes  :  3,  4,  the  large  bacilli 

of  Bienstock,  with  partial  endogenous  spore-formation  ;  5,  the  various  stages  of  great.       In    ad- 

the  development  of  the  bacillus  which  causes  the  fermentation  of  albumen.  ° . 

dition  to  the 

ammonio-magnesian  phosphate,  magnesium  phosphate,  calcium  phosphate 
and  a  small  quantity  of  iron  have  been  found.  The  chlorides  are  either  ab- 
sent or  are  present  only  in  small  quantity. 

Marcet  has  pretty  generally  found  in  the  human  faeces  a  substance  pos- 
sessing the  characters  of  margaric  acid,  and  volatile  fatty  acids ;  the  latter 
free,  however,  from  butyric  acid.  He  also  found  a  coloring  matter,  which  is 
probably  a  modification  of  bile-pigment.  Cystine  is  mentioned  as  an  occa- 
sional constituent  of  the  faeces. 

In  addition  to  the  matters  just  enumerated,  the  following  substances  have 
been  extracted  from  the  normal  faeces : 

Excretine  and  Excretoleic  Acid. — Excretine  was  obtained  from  the  nor- 
mal faeces,  by  Marcet,  in  1854.  This  substance  crystalizes  from  an  ethereal 
solution  in  two  or  three  days,  in  the  form  of  long,  silky  crystals.  Examined 


CONTENTS  OF  THE  LARGE  INTESTINE.  265 

with  the  microscope,  these  are  found  to  consist  of  acicular,  four-sided  prisms 
of  variable  size.  Excretine  is  insoluble  in  water,  slightly  soluble  in  cold  alco- 
hol, but  very  soluble  in  ether  and  in  hot  alcohol.  Its  alcoholic  solutions  are 
faintly  though  distinctly  alkaline.  Its  fusing-point  is  between  203°  and  205° 
Fahr.  (95°  and  96°  C.).  It  may  be  boiled  with  potassium  hydrate  for  hours 
without  undergoing  saponification.  The  quantity  of  excretine  contained  in 
the  faeces  is  not  large.  Only  12-6  grains  (0-816  gramme)  were  obtained  by 
Marcet  from  nine  evacuations. 

There  exists  very  little  definite  information  concerning  the  production 
of  excretine.  Marcet  examined  on  one  occasion  the  contents  of  the  small 
intestine  of  a  man  who  had  died  of  disease  of  the  heart,  without  finding  any 
excretine.  It  is  probable  that  this  substance  is  formed  in  the  large  intestine, 
although  farther  observations  are  wanting  on  this  point. 

The  substance  called  excretoleic  acid  is  very  indefinite  in  its  composition 
and  properties.  It  is  described  as  an  olive-colored,  fatty  acid,  insoluble  in 
water,  non-saponifiable,  and  very  soluble  in  ether  and  in  hot  alcohol.  It 
fuses  between  77°  and  79°  Fahr.  (25°  and  26-11°  C.). 

Stercorine. — This  substance,  discovered  in  the  faeces  in  1862  (Flint),  was 
described  by  Boudet  in  1833,  as  existing  in  minute  quantity  in  the  serum  of 
the  blood,  and  was  called  seroline.  As  it  is  one  of  the  most  abundant  and 
characteristic  constituents  of  the  stercoraceous  matter,  it  may  properly  be 
called  stercorine,  particularly  as  observations  have  led  to  the  opinion  that 
it  really  does  not  exist  in  the  serum,  but  is  formed  from  cholesterine  by  the 
processes  employed  for  its  extraction  from  the  blood  (Flint). 

Stercorine  may  be  extracted  in  the  following  way :  The  faeces  are  first 
evaporated  to  dryness,  pulverized  and  treated  with  ether.  The  ether-extract 
is  then  passed  through  animal  charcoal,  fresh  ether  being  added  until  the 
original  quantity  of  the  ether-extract  has  passed  through.  It  is  impossible 
to  entirely  decolorize  the  solution  by  this  process ;  but  it  should  pass  through 
perfectly  clear  and  of  a  pale-amber  color.  The  ether  is  then  evaporated  and 
the  residue  is  extracted  with  boiling  alcohol.  This  alcoholic  solution  is 
evaporated,  and  the  residue  is  treated  with  a  solution  of  potassium  hydrate 
for  one  or  two  hours  at  a  temperature  a  little  below  the  boiling-point,  by 
which  all  the  saponifiable  fats  are  dissolved.  The  mixture  is  then  largely 
diluted  with  water,  thrown  upon  a  filter,  and  washed  until  the  fluid  which 
passes  through  is  neutral  and  perfectly  clear.  The  filter  is  then  dried  and 
the  residue  is  washed  out  with  ether.  The  ether-solution  is  then  evaporated, 
extracted  with  boiling  alcohol,  and  the  alcoholic  solution  is  evaporated.  The 
residue  of  this  last  evaporation  is  pure  stercorine. 

When  first  obtained,  stercoriue  is  a  clear,  slightly  amber,  oily  substance,  of 
about  the  consistence  of  Canada  balsam  used  in  microscopical  preparations. 
In  four  or  five  days  it  begins  to  show  the  characteristic  crystals.  These  are 
few  in  number  at  first,  but  soon  the  entire  mass  assumes  a  crystalline  form. 
In  one  analysis,  from  seven  and  a  half  ounces  (202-5  grammes)  of  normal 
human  fasces  (the  entire  quantity  for  the  twenty-four  hours),  10-417  grains 
(0-675  gramme)  of  stercorine  were  obtained,  the  extract  consisting  entirely 


266 


INTESTINAL  DIGESTION. 


of  crystals.  This  was  all  the  stercorine  to  be  extracted  from  the  regular, 
daily  evacuation  of  a  healthy  male  twenty-six  years  of  age  and  weighing  about 
one  hundred  and  sixty  pounds  (72'58  kilos.).  In  the  absence  of  other  inves- 
tigations, the  daily  quantity  of  this  substance  excreted  may  be  assumed  to  be 
not  far  from  ten  grains  (0*648  gramme). 

In  many  regards  stercorine  bears  a  close  resemblance  to  cholesterine.  It 
is  neutral,  inodorous,  and  insoluble  in  water  and  in  a  solution  of  potassium 
hydrate.  It  is  soluble  in  ether  and  in  hot  alcohol,  but  is  almost  insoluble  in 
cold  alcohol.  A  red  color  is  produced  when  it  is  treated  with  strong  sul- 
phuric acid.  It  may  be  easily  distinguished  from  cholesterine,  however,  by 
the  form  of  its  crystals.  It  fuses  at  a  low  temperature,  96'8°  Fahr.  (36°  C.), 
while  cholesterine  fuses  at  293°  Fahr.  (145°  C.). 

Stercorine  crystallizes  in  the  form  of  thin,  delicate  needles,  frequently 
mixed  with  clear,  rounded  globules,  which  are  probably  composed  of  the 
same  substance  in  a  non-crystalline  form.  When  the  crystals  are  of  consid- 
erable size,  the  borders  near  their  ex- 
tremities are  split  longitudinally  for  a 
short  distance.  The  crystals  are  fre- 
quently arranged  in  bundles.  They 
are  not  to  be  confounded  with  excre- 
tine,  which  crystallizes  in  the  form 
of  regular,  four-sided  prisms,  or  with 
the  thin,  rhomboidal  or  rectangular 
tablets  of  cholesterine.  They  are 
identical  with  the  crystals  of  seroline, 
figured  by  Eobin  and  Verdiel. 

There  can  be  no  doubt  with  regard 
to  the  origin  of  the  stercorine  which 
exists  in  the  faeces.  Whenever  the  bile 
is  not  discharged  into  the  duodenum, 
as  is  probably  the  case  for  a  time  in 
icterus  accompanied  with  clay-colored  evacuations,  stercorine  is  not  to  be  dis- 
covered in  'the  dejections.  In  one  case  of  this  kind,  in  which  the  faeces  were 
subjected  to  examination,  the  matters  extracted  with  hot  alcohol  were  entirely 
dissolved  by  boiling  for  fifteen  minutes  with  a  solution  of  potassium  hydrate, 
showing  the  absence  of  cholesterine  and  stercorine.  In  another  examination 
of  the  fgeces  from  this  patient,  made  nineteen  days  after,  when  the  icterus 
had  almost  entirely  disappeared  and  the  evacuations  had  become  normal, 
stercorine  was  discovered.  These  facts  show  that  the  cholesterine  of  the 
bile,  in  its  passage  through  the  intestine,  is  changed  into  stercorine.  Both 
of  these  substances  are  crystallizable,  non-saponifiable,  are  extracted  by  the 
same  chemical  manipulations,  and  behave  in  the  same  way  when  treated  with 
sulphuric  acid.  Stercorine  must  be  regarded  as  a  modification  of  cholesterine, 
which  is  the  excrementitious  constituent  of  the  bile. 

The  change  of  cholesterine  into  stercorine  is  directly  connected  with  the 
process  of  intestinal  digestion.  If  an  animal  be  kept  for  some  days  without 


FIG.  81. — Stercorine  from  the  human  faeces. 


MOVEMENTS  OF  THE  LARGE  INTESTINE.  267 

food,  cholesterine  will  be  found  in  the  fasces,  although,  for  a  few  days,  ster- 
corine  is  also  present.  It  is  a  fact  generally  recognized  by  those  who  have 
analyzed  the  faeces,  that  cholesterine  does  not  exist  in  the  normal  evacu- 
ations; but  whenever  digestion  is  arrested,  the  bile  being  constantly  dis- 
charged into  the  duodenum,  cholesterine  is  found  in  large  quantity.  For 
example,  in  hibernating  animals,  cholesterine  is  always  present  in  the  fasces. 
The  same  is  true  of  the  contents  of  the  intestines  during  f O3tal  life ;  the  me- 
conium  always  containing  a  large  quantity  of  cholesterine,  which  disappears 
from  the  evacuations  when  the  digestive  function  becomes  established.  Ster- 
corine  has  not  been  subjected  to  ultimate  analysis.  Its  physiological  relations 
will  be  considered  in  connection  with  the  excretory  office  of  the  liver. 

Indol,  Skatol,  Phenol  etc. — The  so-called  putrefactive  processes,  which 
begin  in  the  small  intestine,  are  more  marked  in  the  large  intestine  and  give 
rise  to  certain  products  which  have  the  characteristic  faecal  odor.  Certain  of 
these  substances  may  be  produced  by  the  prolonged  action,  out  of  the  body, 
of  the  pancreatic  juice  upon  albuminoids.  The  pancreatic  juice,  in  an  alka- 
line medium,  changes  the  trypsine-peptones  into  leucine,  tyrosine,  hypoxan- 
thine  and  asparaginic  acid.  By  still  farther  prolonging  this  action,  indol 
(C8H7N),  skatol  (CgH^N)  and  phenol  (C6HgO),  with  some  other  analogous 
substances  and  volatile  fatty  acids,  are  formed,  and  there  is  an  evolution  of 
certain  gases.  It  is  probable  that  these  products  are  formed  in  abnormal 
quantities  in  the  small  intestine  in  certain  cases  of  intestinal  dyspepsia. 
The  relations  of  the  substances  just  mentioned  to  the  general  process  of  nu- 
trition are  not  understood. 

Movements  of  the  Large  Intestine. — Movements  of  the  general  character 
noted  in  the  small  intestine  occur  in  the  large  intestine,  although  the  pecul- 
iarities in  the  arrangement  of  the  muscular  fibres  and  the  more  solid  consist- 
ence of  the  contents  render  these  movements  in  the  large  intestine  somewhat 
distinctive.  In  all  instances  where  the  movements  have  been  observed  in  the 
human  subject  or  in  the  lower  animals,  they  have  been  found  to  be  less  vig- 
orous and  rapid  than  the  contractions  of  the  small  intestine.  Indeed,  when 
the  abdominal  organs  are  exposed,  either  in  a  living  animal  or  immediately 
after  death,  movements  of  the  large  intestine  are  generally  not  observed, 
except  on  the  application  of  mechanical  or  electric  stimulation  ;  and  they  are 
then  more  circumscribed  and  much  less  marked  than  in  any  other  part  of 
the  alimentary  canal.  That  the  faeces  remain  for  a  considerable  time  in  some 
of  the  sacculated  pouches  of  the  colon,  is  evident  from  the  appearance  which 
they  sometimes  present  of  having  been  moulded  to  the  shape  of  the  canal. 
This  appearance  is  frequently  observed  in  the  dejections,  which  are  then  said 
to  be  "  figured." 

In  the  caecum,  the  pressure  of  matters  received  from  the  ileum  forces  the 
mass  onward  into  the  ascending  colon,  and  the  contractions  of  its  muscular 
fibres  are  probably  slight  and  inefficient.  Once  in  the  colon,  it  is  easy  to 
see  how  the  contractions  of  the  muscular  structure — the  longitudinal  bands 
shortening  the  canal,  and  the  transverse  fibres  contracting  below  and  relax- 
ing above — are  capable  of  passing  the  fascal  mass  slowly  onward.  Although 


268  INTESTINAL  DIGESTION. 

the  transverse  fibres  are  thin  and  apparently  of  little  power,  their  contraction 
is  undoubtedly  sufficient  to  empty  the  sacculi,  when  assisted  by  the  move- 
ments of  the  longitudinal  fibres,  especially  as  the  canal  is  never,  completely 
filled  and  the  fasces  are  frequently  in  the  form  of  small,  moulded  lumps.  By 
these  slow  and  gradual  movements,  the  contents  of  the  large  intestine  are 
passed  toward  the  sigmoid  flexure  of  the  colon,  where  they  are  arrested  until 
the  period  arrives  for  their  final  discharge.  The  time  occupied  in  the  pas- 
sage of  the  faeces  through  the  ascending,  transverse  and  descending  colon  is 
undoubtedly  variable  in  different  persons,  as  great  variations  are  observed  in 
the  intervals  between  the  acts  of  defascation.  During  their  passage  along 
the  colon,  the  contents  of  the  canal  assume  more  and  more  of  the  normal 
faecal  consistence  and  odor  and  become  slightly  coated  with  the  mucous  secre- 
tion of  the  parts. 

The  accumulation  of  faeces  generally  takes  place  in  the  sigmoid  flexure  of 
the  colon ;  and  under  normal  conditions,  the  rectum  is  found  empty  and 
contracted.  This  part  of  the  colon  is  much  more  movable  than  other  por- 
tions of  the  large  intestine.  At  certain  tolerably  regular  intervals,  the  faecal 
matter  is  passed  into  the  rectum  and  is  then  almost  immediately  discharged 
from  the  body. 

DefcBcation. — In  health,  expulsion  of  faecal  matters  takes  place  with  regu- 
larity generally  once  in  the  twenty-four  hours.  This  rule,  however,  is  by  no 
means  invariable,  and  dejections  may  habitually  occur  twice  in  the  day  or 
every  second  or  third  day,  within  the  limits  of  health.  At  the  time  when 
defaecation  ordinarily  takes  place,  a  peculiar  sensation  is  experienced  calling 
for  an  evacuation  of  the  bowels ;  and  if  this  be  disregarded,  the  desire  may 
pass  away,  after  a  little  time  the  act  becoming  impossible.  It  is  probable 
that  the  faeces  are  then  passed  out  of  the  rectum  by  antiperistaltic  action. 

The  condition  which  immediately  precedes  the  desire  for  defaecation  is 
probably  the  descent  of  the  contents  of  the  sigmoid  flexure  of  the  colon  into 
the  rectum.  It  was  formerly  thought  that  the  faeces  constantly  accumulated 
in  the  dilated  portion  of  the  rectum,  where  they  remained  until  an  evacua- 
tion took  place ;  but  the  arguments  of  O'Beirne  against  such  a  view  are 
conclusive.  He  demonstrated,  by  explorations  in  the  human  subject,  that 
under  ordinary  conditions,  the  rectum  is  contracted  and  contains  neither 
faeces  nor  gas.  It  is,  indeed,  a  fact  familiar  to  every  surgeon,  that  the  rec- 
tum usually  contains  nothing  which  can  be  reached  by  the  finger  in  physi- 
cal examinations,  and  that  paralysis  or  section  of  the  muscles  which  close 
the  anus  by  no  means  involves,  necessarily,  a  constant  passage  of  faecal  mat- 
ter. O'Beirne  not  only  found  the  rectum  empty  and  presenting  a  certain 
degree  of  resistance  to  the  passage  of  injected  fluids,  but  on  passing  a  stom- 
ach-tube into  the  bowel,  after  penetrating  six  to  eight  inches  (15  to  20  cen- 
timetres), it  passed  into  a  space  in  which  its  extremity  could  be  moved  with 
great  freedom,  and  there  was  instantly  a  rush  of  flatus,  of  fluid  faeces,  or  of 
both,  through  the  tube.  In  some  instances  in  which  nothing  escaped  through 
the  tube,  the  instrument  conveyed  to  the  hand  an  impression  of  having  en- 
tered a  solid  mass ;  and  on  being  withdrawn  it  contained  solid  faeces  in  its 


DEFJECATION.  269 

upper  portion.  The  sensation  which  leads  to  an  effort  to  discharge  the  f asces 
is  due  to  the  accumulation  of  matters  in  the  sigmoid  flexure,  which  finally 
present  at  the  contracted,  upper  portion  of  the  rectum.  This  constriction, 
situated  at  the  most  superior  portion  of  the  rectum,  is  sometimes  called  the 
sphincter  of  O'Beirne. 

The  above  is  the  mechanism  of  the  descent  of  faecal  matter  into  the  rec- 
tum in  defaecation,  as  the  act  is  usually  performed ;  but  under  certain  condi- 
tions, faeces  must  accumulate  in  the  dilated  portion  of  the  rectum.  Ordina- 
rily, the  discharge  of  faeces  takes  place  only  after  the  efforts  have  been  con- 
tinued for  a  certain  time,  and  when  the  evacuation  is  "  figured,"  the  whole 
length  discharged  frequently  exceeds  so  much  the  length  of  the  rectum,  that 
it  is  evident  that  a  portion  of  it  must  have  come  from  the  colon ;  but  in 
cases  in  which  the  faeces  are  very  fluid,  or  when  the  call  for  an  evacuation 
has  not  been  regarded  and  has  become  imperative,  the  immediate  discharge 
of  matters  when  the  sphincter  is  relaxed  shows  that  the  rectum  has  been 
more  or  less  distended. 

In  the  process  of  defaecation,  the  first  act  is  the  passage,  by  peristaltic 
contractions,  of  the  contents  of  the  sigmoid  flexure  of  the  colon  through  the 
slightly  constricted  opening  of  the  rectum  into  its  dilated  portion  below. 
The  faecal  matter,  however,  is  not  allowed  to  remain  in  this  situation,  but  it 
passes  into  the  lower  portion  of  the  rectum,  in  obedience  to  the  contractions 
of  its  muscular  coat,  assisted  by  the  action  of  the  abdominal  muscles  and  the 
diaphragm.  The  circular  fibres  of  the  rectum  undergo  the  ordinary  peri- 
staltic contraction ;  and  the  action  of  the  longitudinal  fibres  is  to  render  the 
rectum  shorter  and  more  nearly  straight.  The  internal  and  the  external 
sphincters  present  a  certain  resistance  to  the  discharge  of  the  faeces,  particu- 
larly the  external  sphincter,  which  is  a  striated  muscle  of  considerable  power. 
There  is  always,  however,  a  voluntary  relaxation  of  this  muscle,  or  rather  a 
cessation  of  its  semi-voluntary  contraction,  which  immediately  precedes  the 
expulsive  act.  The  dilatation  of  the  anus  is  also  facilitated  by  the  action  of 
the  levator  ani,  which  arises  from  the  posterior  surface  of  the  body  and 
ramus  of  the  pubis,  the  inner  surface  of  the  spine  of  the  ischium,  and  a  line 
of  fascia  between  these  two  points,  passes  downward,  and  is  inserted  into 
the  median  raphe  of  the  perineum  and  the  sides  of  the  rectum,  the  fibres 
uniting  with  those  of  the  sphincter.  While  this  muscle  forms  a  support  for 
the  pelvic  organs  during  the  act  of  straining,  it  steadies  the  end  of  the  rec- 
tum, and  by  its  contractions,  favors  the  relaxation  of  the  sphincter  and 
draws  the  anus  forward. 

The  diaphragm  and  the  abdominal  muscles  merely  compress  the  abdom- 
inal organs,  and  consequently  those  contained  in  the  pelvis,  and  assist  in  the 
expulsion  of  the  contents  of  the  rectum.  The  diaphragm  is  the  most  im- 
portant of  the  voluntary  muscles  concerned  in  this  process ;  and  during  the 
act  of  straining,  the  lungs  are  moderately  filled  and  respiration  is  inter- 
rupted. The  vigor  of  these  efforts  depends  greatly  upon  the  consistence  of 
the  fascal  mass,  very  violent  contractions  being  frequently  required  for  the 
expulsion  of  hardened  faeces  after  long  constipation.  Although  more  or  less 
19 


270  INTESTINAL  DIGESTION. 

straining  generally  takes  place,  the  contractions  of  the  muscular  coats  of  the 
rectum  frequently  are  competent  of  themselves  to  expel  the  faeces,  especially 
when  they  are  soft. 

By  a  combination  of  the  movements  above  described,  the  floor  of  the 
perineum  is  pressed  outward,  the  anus  is  dilated,  the  sharp  bend  in  the 
lower  part  of  the  rectum  is  brought  more  into  line  with  the  rest  of  the  canal, 
and  a  portion  of  the  contents  of  the  rectum  is  expelled.  Very  soon,  however, 
the  passage  of  faeces  is  interrupted  by  a  contraction  of  the  levator  ani  and  the 
sphincter,  by  which  the  anus  is  suddenly  and  rather  forcibly  retracted.  This 
muscular  action  may  be  effected  voluntarily ;  but  after  the  sphincter  has  been 
dilated  for  a  time,  the  evacuation  is  interrupted  in  this  way,  notwithstanding 
all  efforts  to  oppose  it.  After  a  time,  another  portion  of  fasces  is  discharged, 
until  the  matters  have  ceased  to  pass  out  of  the  sigmoid  flexure  and  the  rec- 
.tum  has  been  emptied. 

Very  little  need  be  said  concerning  the  influence  of  the  nervous  system 
on  the  movements  concerned  in  defrecation.  The  non-striated  muscular 
fibres  which  form  the  muscular  coat  of  the  rectum  are  supplied  with  nerves 
from  the  sympathetic  system ;  and  to  the  external  sphincter  are  distributed 
filaments  from  the  last  sacral  pair  of  spinal  nerves.  These  nerves  bring  the 
sphincter  in  a  certain  degree  under  the  control  of  the  will,  and  impart  like- 
wise the  property  of  tonic  contraction,  by  which  the  anus  is  kept  constantly 
closed.  The  nerve-centre  for  defaecation  in  the  dog,  or  the  ano-spinal 
centre,  is  in  the  spinal  cord,  at  the  site  of  the  fifth  lumbar  vertebra  (Budge). 

GASES  FOUND  IN  THE  ALIMENTARY  CANAL. 

The  gases  in  the  stomach  appear  to  have  no  definite  office.  They  gener- 
:ally  exist  in  very  small  quantity  and  they  are  sometimes  absent.  The  oxy- 
gen and  nitrogen  are  derived  from  the  little  bubbles  of  air  which  are  incor- 
porated with  the  alimentary  bolus  during  mastication  and  insalivation. 
The  other  gases  are  probably  evolved  from  the  food  during  digestion ;  at 
least,  there  is  no  satisfactory  evidence  that  they  are  produced  in  any  other 
way.  Magendie  and  Chevreul  collected  and  analyzed  a  small  quantity  of  gas 
from  the  stomach  of  an  executed  criminal  a  short  time  after  death  and  as- 
certained that  it  had  the  following  composition  : 

GASES    CONTAINED    IN   THE   STOMACH. 

Oxygen 11-00 

Carbon  dioxide . 14-00 

Pure  hydrogen 3'55 

Nitrogen 71-45 

100-00 

Magendie  and  Ohevreul  found  three  different  gases  in  the  small  intes- 
tine. Their  examinations  were  made  u-pon  three  criminals  soon  after  execu- 
tion. The  first  was  twenty-four  years  of  age,  and  two  hours  before  execu- 
tion, he  had  eaten  bread  and  Gruyere  cheese  and  had  drunk  red  wine  and 
water.  The  second,  who  was  executed  at  the  same  time,  was  twenty-three 


GASES  FOUND  IN  THE  ALIMENTAEY  CANAL. 


271 


years  of  age,  and  the  conditions  as  regards  digestion  were  the  same.  The 
third  was  twenty-eight  years  of  age,  and  four  hours  before  death,  he  ate 
bread,  beef  and  lentils,  and  drank  red  wine  and  water.  The  following  was 
the  result  of  the  analyses  : 

GASES   CONTAINED    IN   THE   SMALL   INTESTINE. 


First  criminal. 

Second  criminal. 

Third  criminal. 

Carbon  dioxide  

24-39 

40-00 

25-00 

Pure  hydrogen  

55-53 

51-15 

8-40 

Nitrogen  

20-08 

8'85 

66-60 

100-00 

100-00 

100-00 

No  oxygen  was  found  in  either  of  the  examinations,  and  the  quantities  of 
the  other  gases  were  so  variable  as  to  lead  to  the  supposition  that  their  pro- 
portion is  not  at  all  definite.  Reference  has  already  been  made  to  the 
mechanical  office  of  these  gases  in  intestinal  digestion. 

In  the  large  intestine,  the  constitution  of  the  gases  presented  the  same 
variability  as  in  the  small  intestine.  Carburetted  hydrogen  was  found  in  all 
of  the  analyses.  In  the  large  intestine  of  the  first  criminal  and  in  the  rec- 
tum of  the  third,  were  found  traces  of  hydrogen  monosulphide.  The  follow- 
ing is  the  result  of  the  analyses  in  the  cases  just  cited.  In  the  third,  the 
gaseous  contents  of  the  caecum  and  the  rectum  were  analyzed  separately : 

GASES    CONTAINED    IN   THE    LARGE    INTESTINE. 


First  criminal. 

Second  criminal. 

Third  criminal. 

Third  criminal. 

Carbon  dioxide  

43-50 

70-00 

Caecum. 
12*50 

Rectum. 

xo.of! 

Carburetted  hydrogen  and  traces 
of  hydrogen  monosulphide  
Pure  hydrogen  and  Carburetted 
hydrogen  

5-47 

11-60 

U'lfl 

Pure  hydrogen  

7-50 

Carburetted  hydrogen  

12-50 

N  itrogen  

51-03 

18-40 

67-50 

A^-QR 

100-00 

100-00 

100-00 

100-00 

Origin  of  the  Intestinal  Gases.— The  most  reasonable  view  to  take  of  the 
origin  of  the  gases  normally  found  in  the  intestines  is  that  they  are  given  off 
from  the  articles  of  food  in  their  various  stages  of  digestion  and  decomposi- 
tion. That  this  is  the  principal  source  of  the  intestinal  gases,  there  can  be 
no  doubt ;  and  it  is  well  known  that  certain  articles  of  food,  particularly  vege- 
tables, generate  much  more  gas  than  others.  The  principal  gases  found  in 
the  intestinal  canal  may  all  be  obtained  from  the  food.  Some  of  them,  as 
hydrogen  and  Carburetted  hydrogen,  do  not  exist  in  the  blood ;  and  it  is 
difficult  to  conceive  how  they  can  be  generated  in  the  intestine  except  by 
decomposition  of  certain  of  the  articles  of  food.  Gases  do  not  exist  in  the 
alimentary  canal  of  the  foetus. 


272  ABSORPTION— LYMPH  AND  CHYLE. 

CHAPTER  X. 

ABSORPTION— LYMPH  AND   CHYLE. 

Absorption  by  blood-vessels — Absorption  by  lacteal  and  lymphatic  vessels— Physiological  anatomy  of  the 
lacteal  and  lymphatic  vessels — Lymphatic  glands —Absorption  by  the  lacteals— Absorption  by  the 
skin— Absorption  by  the  respiratory  surface— Absorption  from  closed  cavities,  reservoirs  of  glands, 
etc. — Absorption  of  fats  and  insoluble  substances— Variations  and  modifications  of  absorption — 
Mechanism  of  the  passage  of  liquids  through  membranes —Lymph  and  chyle— Properties  and  composi- 
tion of  lymph — Origin  and  uses  of  the  lymph— Composition  of  the  chyle— Microscopical  characters  of 
the  chyle— Movements  of  the  lymph  and  chyle. 

DIGESTION  has  two  great  objects :  one  is  to  liquefy  the  different  aliment- 
ary substances;  and  the  other,  to  begin  the  series  of  transformations  by 
which  these  are  rendered  capable  of  nourishing  the  organism.  The  matters 
thus  acted  upon  are  taken  into  the  blood  as  fast  as  the  requisite  changes  in 
their  constitution  are  effected ;  and  once  received  into  the  circulation,  they 
become  part  of  the  nutritive  fluid,  supplying  the  loss  which  the  constant 
regeneration  of  the  tissues  from  matters  furnished  by  the  blood  necessarily 
involves.  The  only  constituents  of  food  which  possibly  do  not  obey  this 
general  law,  as  regards  their  absorption,  are  the  fats.  Although  a  small  por- 
tion of  the  fat  taken  as  food  may  pass  directly  into  the  blood-vessels  of  the 
intestinal  canal,  by  far  the  greatest  part  finds  its  way  into  the  circulation  by 
means  of  special  absorbent  vessels  which  empty  into  large  veins.  In  what- 
ever way  fat  enters  the  mood,  it  is  not  dissolved  but  is  reduced  to  the  condi- 
tion of  a  fine  emulsion. 

ABSORPTION  BY  BLOOD-VESSELS. 

That  substances  in  solution  can  pass  through  the  walls  of  the  capillaries 
and  of  the  small  veins,  and  that  absorption  actually  takes  place  in  great  part 
by  blood-vessels,  are  facts  which  hardly  demand  discussion  at  the  present 
day.  Soluble  substances  which  have  disappeared  from  the  alimentary  canal 
have  been  repeatedly  found  in  the  blood  coming  from  this  part,  even  when 
the  lymphatics  have  been  divided  and  communication  existed  only  through 
the  blood-vessels ;  and  it  has  been  shown  that  during  absorption,  the  blood 
of  the  portal  vein  is  rich  in  albuminoids,  sugar  and  other  matters  resulting 
from  digestion. 

In  the  mouth  and  oasophagus,  the  sojourn  of  alimentary  matters  is  so 
brief  and  the  changes  which  they  undergo  are  so  slight,  that  no  considerable 
absorption  can  take  place.  It  is  evident,  however,  that  the  mucous  mem- 
brane of  the  mouth  is  capable  of  absorbing  certain  soluble  matters,  from  the 
effects  which  are  constantly  observed  when  the  smoke  or  the  juice  of  tobac- 
co is  retained  in  the  mouth,  even  for  a  short  time.  In  the  stomach,  how- 
ever, absorption  takes  place  with  great  activity.  A  large  proportion  of  the 
ingested  liquids  and  of  those  constituents  of  food  which  are  dissolved  by  the 
gastric  juice  and  converted  into  peptones  is  taken  up  directly  by  the  blood- 
vessels of  the  stomach.  It  may,  indeed,  be  assumed,  as  a  general  law,  that 
alimentary  matters  are  in  great  part  absorbed  as  soon  as  their  digestive 
transformations  in  the  alimentary  canal  have  been  completed. 


ABSORPTION  BY  LACTEAL  AND  LYMPHATIC  VESSELS.    273 

In  the  passage  of  the  food  along  the  intestinal  canal,  as  the  digestion  of 
the  albuminoids  is  completed,  these  matters  are  absorbed,  and  their  passage 
into  the  mass  of  blood  is  indicated  by  an  increase  in  its  proportion  of  albu- 
minoid constituents.  The  greatest  part  of  the  food  is  absorbed  by  the  intes- 
tinal mucous  membrane,  and  with  the  alimentary  substances  proper,  a  large 
quantity  of  secreted  fluid  is  reabsorbed.  This  fact  is  particularly  marked  as 
regards  the  bile.  The  biliary  salts  disappear  as  the  alimentary  mass  passes 
down  the  intestine,  and  undoubtedly  are  absorbed,  although  they  are  so 
changed  that  they  can  not  be  detected  in  the  blood  by  the  ordinary  tests. 
In  this  portion  of  the  alimentary  canal,  it  will  be  remembered,  an  immense 
absorbing  surface  is  provided  by  the  arrangement  of  the  mucous  membrane 
in  folds,  forming  the  valvulae  conniventes,  and  by  the  presence  of  villi,  which 
are  found  throughout  the  small  intestine.  A  certain  portion  of  the  gaseous 
contents  of  the  intestines  is  also  taken  up,  although  it  is  not  easily  ascer- 
tained what  particular  gases  are  thus  absorbed. 

ABSOBPTION  BY  LACTEAL  AND  LYMPHATIC  VESSELS. 

The  history  of  the  discovery  of  what  is  ordinarily  termed  the  absorbent 
system  of  vessels,  from  the  vague  allusions  of  Hippocrates,  Galen,  Aristotle 
and  others,  to  the  description  of  the  thoracic  duct  in  the  middle  of  the  six- 
teenth century,  by  Eustachius,  and  finally  to  the  discovery  of  the  lacteals  by 
Asellius,  in  1622,  is  more  interesting  in  an  anatomical  than  in  a  physiologi- 
cal point  of  view.  The  history  of  the  anatomy  of  the  absorbent  system  dates 
from  the  discovery  of  the  thoracic  duct ;  but  from  the  discovery  of  the  lac- 
teals,  by  Asellius,  dates  the  history  of  these  vessels  as  the  carriers  of  nutritive 
matters  from  the  intestinal  canal  to  the  general  system. 

In  1649,  Pecquet  discovered  the  receptaculum  chyli  and  demonstrated 
that  the  lacteals  did  not  pass  to  the  liver,  but  emptied  the  chyle  into  the 
thoracic  duct,  by  which  it  is  finally  conveyed  into  the  venous  system.  In 
1650-'51,  the  anatomical  history  of  the  absorbent  vessels  was  completed  by 
the  discovery,  by  Rudbeck,  of  vessels  carrying  a  colorless  fluid,  in  the  liver 
and  finally  in  almost  all  parts  of  the  body.  Rudbeck  demonstrated  the  ana- 
tomical identity  of  these  vessels  with  the  lacteals.  They  were  afterward 
studied  by  Bartholinus,  who  gave  them  the  name  of  lymphatics. 

The  idea,  which  dates  from  the  discoveries  of  Asellius  and  Pecquet,  that 
the  lacteals  absorb  all  the  products  of  digestion,  was  disproven  by  the  exper- 
iments of  Magendie  and  of  those  who  experimented  after  him  upon  vascu- 
lar absorption.  It  is  now  known  that  fats  in  the  form  of  a  very  fine  emul- 
sion are  absorbed  by  the  lacteals,  and  that  these  are  the  only  constituents  of 
food  taken  up  in  great  quantity  by  this  system  of  vessels.  It  becomes  an 
important  question  to  determine,  however,  whether  the  lacteals  be  not  con- 
cerned, to  some  extent,  in  the  absorption  of  drinks,  the  albuminoids,  saline 
and  saccharine  matters,  etc.  This  question  will  be  taken  up  after  a  consid- 
eration of  certain  points  in  the  anatomy  of  the  lymphatic  system. 

Physiological  Anatomy  of  the  Lacteal  and  Lymphatic  Vessels. — The 
lacteals  are  the  intestinal  lymphatics ;  and  during  the  intervals  of  intestinal 


274 


ABSOEPTION--LYMPH   AND   CHYLE. 


absorption  they  carry  a  liquid  which  is  identical  with  the  contents  of  other 
lymphatic  vessels.  In  their  structure,  also,  the  lacteals  are  identical  with 
the  general  lymphatics. 

Owing  to  the  exceeding  tenuity  of  the  walls  of  the  small  lymphatics  and 
the  existence  of  great  numbers  of  valves  which  prevent  injection  from  the 
large  trunks,  the  anatomy  of  these  vessels  is  studied  with  some  difficulty ; 
and  still  greater  difficulty  is  presented  in  the  study  of  the  vessels  of  origin  of 
the  lymphatic  system  in  different  tissues  and  organs.  The  origin  of  the 
lymphatics  in  the  intestinal  villi  has  already  been  considered,  and  it  remains 
to  study  the  origin  of  these  vessels  in  other  parts. 

Comparatively  recent  investigations,  particularly  those  of  Von  Reckling- 
hausen  and  his  followers,  have  entirely  changed  the  views  of  anatomists 
with  regard  to  the  mode  of  origin  of  the  lymphatics  of  various  parts ;  but 
the  results  of  these  investigations  are  so  definite  and  positive  and  have  been 
so  fully  confirmed,  that  they  are  now  almost  universally  adopted.  Accord- 
ing to  these  results,  the  lymphatics  have  several  modes  of  origin. 

In  the  connective  tissues,  which  are  so  widely  distributed  in  the  body, 
there  are  always  found,  irregularly  shaped,  stellate  spaces,  which  communicate 


FIG.  82. — Origin  of  lymphatics  (Landois). 

I.  From  the  central  tendon  of  the  diaphragm  of  the  rabbit  (semi-diagrammatic) :  s,  lymph-canals  com- 

municating by  x  with  the  lymphatic  vessel  L  ;  A,  origin  of  the  lymphatic  by  a  union  of  lymph- 
canals  ;  E,  E,  endothelium. 

II.  Perivascular  canal. 

with  each  other  by  branching  canals,  that  can  properly  be  called  lymph- 
spaces,  or  "juice-canals."  These  spaces  contain  a  liquid  and  large  numbers 
of  leucocytes.  The  leucocytes  in  these  spaces  may  be  called  lymph-corpus- 
cles, as  they  eventually  find  their  way  into  the  true  lymphatic  vessels ;  but 
they  are  thought  to  be  white  blood-corpuscles  which  have  passed  through  the 
stomata  of  the  capillary  blood-vessels.  The  connective-tissue  lymph-spaces, 
by  certain  of  their  branches,  finally  communicate  with  the  so-called  lymph- 


ANATOMY  OF  THE  LACTEAL  AND  LYMPHATIC  VESSELS.  275 

capillaries,  through  what  have  been  regarded  as  the  stomata  of  these  vessels. 
These  anatomical  data  have  led  to  the  following  view  with  regard  to  the  re- 
lations between  the  blood,  the  lymph  and  the  tissues. 

Nutrient  matters  are  supplied  to  the  parts  by  transudation  through  the 
walls  of  the  capillary  blood-vessels;  and  the  effete  matters  pass  from  the 
lymph-spaces  into  the  true  lymphatic  vessels,  to  be  finally  carried  to  the 
venous  system.  In  certain  tissues  and  organs,  however,  such  as  the  cornea 
and  fibrous  membranes,  the  lymph -spaces  or  canals  supply  the  nutrient 
fluid ;  and  in  the  glands  they  probably  supply  part  of  the  material  used  in 
the  formation  of  the  secretions. 

In  the  serous  membranes  and  in  other  analogous  structures,  there  are 
large  numbers  of  openings  into  the  cavities ;  and  the  peritoneum,  pleura, 
pericardium,  tunica  vaginalis  testis,  chambers  of  the  eye,  labyrinth  of  the  in- 
ternal ear  and  subarachnoid  space  are  to  be  regarded  as  great  lymph-sacs,  the 
contained  fluids  being  lymph,  without,  however,  presenting  the  so-called 
lymph-corpuscles. 

The  relations  between  the  blood-vessels  and  the  smallest  lymphatics  are 
very  close  in  certain  parts.  In  the  cerebro-spinal  centres,  Robin  and  His 
have  demonstrated  a  system  of  canals  which  surround  the  small  blood-ves- 
sels and  are  connected  with  the  lymphatic-trunks  or  reservoirs  described  by 
Fohmann  and  found  under  the  pia  mater.  The  capillary  blood-vessels 
thus  float  in  surrounding  vessels  filled  with  liquid.  These  vessels  surround- 
ing the  blood-vessels  are  called  perivascular  canals,  and  the  contained  liquid 
is  true  lymph,  containing  leucocytes,  or  lymph-corpuscles.  They  exceed  .the 
blood-vessels  in  diameter  by  y^V?r  to  ^-J^-  of  an  inch  (20  to  62/i).  Since  the 
perivascular  canals  of  the  nerve-centres  have  been  described,  similar  vessels 
have  been  found  in  the  retina  and  in  the  liver. 

The  true  capillary  lymphatics  have  been  studied  in  various  parts  by 
means  of  mercurial  injections,  but  the  presence  of  valves  in  the  small  trunks 
renders  it  necessary  to  make  these  injections  from  the  periphery.  The  ves- 
sels have  been  injected  in  certain  situations  with  mercury,  by  simply  punct- 
uring with  a  fine-pointed  canula  the  parts  in  which  the  plexus  is  supposed 
to  exist,  and  allowing  the  liquid  to  gently  diffuse  itself.  Following  the 
course  of  the  vessels,  the  injection  passes  into  the  larger  trunks  and  thence 
to  the  lymphatic  glands.  The  regularity  of  the  plexus  through  which  the 
liquid  is  first  diffused  and  the  passage  of  the  injection  through  the  larger 
vessels  to  the  glands  are  proof  that  the  lymphatics  have  been  penetrated  and 
that  the  appearances  observed  are  not  the  result  of  mere  infiltration  in  the 
tissue.  It  does  not  appear  that  the  vessels  composing  this  plexus  vary  much 
in  size.  They  are  quite  elastic,  and  after  distention  by  injection,  they  return 
to  a  very  small  diameter  when  the  fluid  is  allowed  to  escape. 

By  the  method  above  indicated,  it  is  possible  to  inject  the  superficial 
lymphatics  of  the  skin,  the  deeper  vessels  situated  just  beneath  the  skin,  and 
vessels  in  the  serous  membranes,  glandular  organs,  lungs,  tendons  etc.,  in 
addition  to  the  larger  trunks,  such  as  the  thoracic  duct.  The  lacteal  system 
presents  essentially  the  same  anatomical  characters  as  the  general  lymphatics, 


276 


ABSORPTION— LYMPH  AND  CHYLE. 


and  the  vessels  are  filled  with  colorless  lymph  during  the  intervals  of  diges- 
tion. In  many  situations  the  lymphatics  present  in  their  course  little,  solid 
structures,  called  lymphatic  glands,  although,  as  regards  structure  and  office, 
they  are  not  true  glandular  organs.  The  smallest  capillary  lymphatics  have 
a  diameter  of  about  -5^  of  an  inch  (83  /*).  This  may  be  taken  as  their  aver- 
age diameter  in  the  primitive  plexus.  This  plexus,  when  the  vessels  are 
abundant,  as  they  are  in  certain  parts  of  the  cutaneous  surface,  resembles  an 
ordinary  plexus  of  capillary  blood-vessels,  except  that  the  walls  of  the  vessels 


FIG.  83. — Lymphatic  plexus,  showing  the  endothelium  (Belaieff  j. 

are  thinner  and  their  diameter  is  greater.  The  vessels  are  lined  by  endo- 
thelial  cells,  the  borders  of  which  are  brought  into  view  by  the  action  of  sil- 
ver nitrate,  as  is  shown  in  Fig.  83. 

The  smallest  lymphatic  vessels  are  by  far  the  most  abundant.  They  are 
arranged  in  the  form  of  a  fine  plexus,  very  superficially  situated  in  the  skin. 
A  second  plexus  exists  just  beneath  the  skin,  composed  of  vessels  of  much 
greater  diameter.  The  skin  is  thus  enclosed  between  two  plexuses  of  capil- 
lary lymphatics.  A  plexus  analogous  to  the  superficial  plexus  of  the  skin  is 
found  just  beneath  the  surface  of  the  mucous  membranes.  These  may,  in- 
deed, be  classed  with  the  superficial  lymphatics.  The  deep  lymphatics  are 
much  larger  and  less  abundant,  and  their  origin  is  less  easily  made  out. 
These  accompany  the  deeper  veins  in  their  course.  They  receive  the  lymph 
from  the  superficial  vessels. 

No  valvular  arrangement  is  found  in  the  smallest  lymphatics ;  but  the 
vessels  coming  from  the  primitive  plexuses,  as  well  as  the  large  vessels,  con- 
tain valves  in  great  numbers.  These  valves,  being  so  closely  set  in  the  ves- 
sels, give  to  them,  when  filled  with  injection,  a  peculiar  and  characteristic 
beaded  appearance. 


ANATOMY  OF  THE  LACTEAL  AND  LYMPHATIC  VESSELS.  277 


The  course  of  the  lymphatics  is  generally  direct.     As  they  pass  toward 
the  great  trunks  by  which  they  communicate  with  the  venous  system,  they 


FIG.  8i.—  Superficial  lym- 
phatics  of  the  skin  of 
the  palmar  surface  of 
the  finger  (Sappey). 


FlG-  ^  -Deep  lymphatics  of  the  skin  of  the  FlQ  gg  _  Same  finger,  lat- 

finger  (bappey).  erai  view,  showing  lym- 

1,  1,  deep  net-work  of  cutaneous  lymphatics  ;  phatic  trunks  connected 

2,  2,  2,  2,  lymphatic  trunks  connected  with  with  the  superficial  net- 

this  net-work.  work  (Sappey). 


present  a  peculiar  anastomosis  with  the  adjacent  vessels,  called  anastomosis 
by  bifurcation  ;  that  is,  as  a  vessel  passes  along  with  other  vessels  nearly 
parallel  with  it,  it  bifurcates,  and  the  two  branches  pass  into  the  nearest  ves- 
sels on  either  side.  These  anastomoses  are  quite  frequent,  and  they  generally 
occur  between  vessels  of  equal  size.  In  their  course,  the  vessels  pass  through 
the  so-called  lymphatic  glands. 

A  notable  peculiarity  in  the  lymphatic  vessels  is  that  they  vary  very  little 
in  size,  being  nearly  as  large  at  the  extremities  as  they  are  near  the  trunk. 
In  their  course,  they  are  always  much  smaller  than  the  veins  and  do  not  pro- 
gressively enlarge  as  they  pass  on  to  the  great  lymphatic  trunks.  The  largest 
vessels  that  pass  from  the  skin  are  ^  to  -^  of  an  inch  (1  to  2  mm.)  in  diame- 
ter, and  the  larger  vessels,  in  their  course,  have  a  diameter  of  ^  to  %  of  an 
inch  (2  to  3  mm.).  As  in  the  case  of  the  smallest  lymphatics  of  the  primi- 
tive plexuses,  the  elasticity  of  the  walls  of  the  vessels  renders  their  diame- 
ter greatly  dependent  upon  the  pressure  of  fluid  in  their  interior.  Many 
anatomists  have  noticed  that  vessels  which  are  hardly  perceptible  while  emp- 
ty are  capable  of  being  dilated  to  the  diameter  of  half  a  line  (about  1  mm.) 


278 


ABSORPTION— LYMPH  AND  CHYLE. 


or  more,  returning  to  their  original  size  as  soon  as  the  distending  fluid  is 

removed. 

In  the  lymphatics  of  the  skin,  the  only  important  peculiarity  which  has 

not  yet  been  mentioned  is. 
that  the  vessels  appear  to 
be  very  unequally  distrib- 
uted in  different  parts  of 
the  surface.  According  to 
Sappey,  they  are  particularly 
abundant  in  the  scalp  over 
the  biparietal  suture,  the 
soles  of  the  feet  and  the 
palms  of  the  hand,  the  fin- 
gers at  the  lateral  portion  of 
the  last  phalanges,  and  the 
scrotum.  In  the  median 
portion  of  the  scrotum  they 
attain  their  highest  degree 
of  development.  They  are 
also  found,  though  in  less 
number,  originating  from 
around  the  median  line  on 
the  anterior  and  posterior 
surface  of  the  trunk,  the 
posterior  median  portion  of 
the  extremities,  the  skin 
over  the  mammae,  and  around 
the  orifices  of  the  mucous 
passages.  Sappey  has  in- 
jected lymphatic  vessels  in 
the  anterior  portion  of  the 
forearm,  the  thigh  and  the 
leg,  and  in  the  middle  por- 

^on    Qf    fae    face      although 

they  are  demonstrated  with 
difficulty  in  these  situations.  If  they  exist  at  all  in  other  portions  of  the  cu- 
taneous surface,  they  are  not  abundant. 

In  the  mucous  membranes  the  lymphatics  are  very  abundant.  Here  are 
found,  as  in  the  skin,  two  distinct  layers  which  enclose  between  them  the 
entire  thickness  of  the  mucous  membrane.  The  more  superficial  of  these 
layers  is  composed  of  a  rich  plexus  of  small  vessels,  and  beneath  the  mucous 
membrane,  is  a  plexus  consisting  of  vessels  of  larger  size.  The  superficial 
plexus  is  very  rich  in  the  mixed  structure  which  forms  the  lips  and  the  glans 
penis,  and  around  the  orifices  of  the  mouth,  the  nares,  the  vagina  and  the 
anus.  There  are  certain  mucous  membranes  in  which  the  lymphatics  have 
never  been  injected.  In  the  serous  membranes,  lymphatics  have  been  demon- 


FIG.  S7.  -Superficial  lymphatics 
of  the  arm  (Sappey). 


FIG    8S.-Superficial    lym- 
phatics  of  the  leg  (Sappey). 


ANATOMY  OF  THE  LACTEAL  AND  LYMPHATIC  VESSELS.  279 

strated  in  great  abundance.  Lymphatics  have  been  demonstrated  taking 
their  origin  in  the  voluntary  muscles,  the  diaphragm,  the  heart  and  the  non- 
striated  muscular  coats  of  the  hollow  viscera,  although  their  investigation  in 
these  situations  is  difficult. 

Lymphatics  are  found  coming  from  the  lungs  in  great  numbers.  These 
arise  in  the  walls  of  the  air-cells  and  surround  each  pulmonary  lobule  with  a 
close  plexus.  The  deep  vessels  follow  the  course  of  the  bronchial  tubes, 
passing  through  the  bronchial  glands  and  the  glands  at  the  bifurcation  of  the 
trachea,  to  empty  into  the  thoracic  duct  and  the  great  lymphatic  duct  of  the 
right  side. 

In  the  glandular  system,  including  the  ductless  glands,  and  in  the  ovaries, 
the  lymphatic  vessels  are,  as  a  rule,  more  abundant  than  in  any  other  parts 
of  the  body.  They  are  especially  abundant  in  the  testicles,  the  ovaries,  the 
liver  and  the  kidneys. 

The  lymphatic  vessels  from  the  superficial  and  deep  portions  of  the  head 
and  face  on  the  right  side,  and  those  from  the  superficial  and  deep  portions 
of  the  right  arm,  the  right  half  of  the  chest,  and  the  mammary  gland,  with  a 
few  vessels  from  the  lungs,  pass  into  the  great  lymphatic  duct,  ductus  lym- 
phaticus  dexter,  which  empties  into  the  venous  system  at  the  junction  of 
the  right  subclavian  with  the  internal  jugular.  This  vessel  is  about  an  inch 
(2o-4  mm.)  in  length  and  one-twelfth  to  one-eighth  of  an  inch  ('2  to  3  mm.) 
in  diameter.  It  is  provided  with  a  pair  of  semilunar  valves  at  its  opening 
into  the  veins,  which  effectually  prevent  the  ingress  of  blood.  The  vessels 
from  the  inferior  extremities,  and  those  from  the  lower  portions  of  the 
trunk,  the  pelvic  viscera,  the  abdominal  organs  generally  and  the  left  half 
of  the  body  above  the  abdomen  empty  into  the  thoracic  duct. 

In  their  course,  all  of  the  lymphatics  pass  through  the  small,  flattened, 
oval  bodies,  called  the  lymphatic  glands,  which  are  so  abundant  in  the  groin, 
the  axilla,  the  pelvis  and  in  some  other  parts.  Two  to  six  vessels,  called  the 
va*;i  afferentia,  penetrate  each  gland,  having  first  broken  up  into  a  number 
of  smaller  vessels  just  before  they  enter.  They  pass  out  by  a  number  of 
small  vessels  which  unite  to  form  one,  two  or  three  trunks,  generally  of  larger 
size  than  the  vasa  afferentia.  The  vessels  which  thus  emerge  from  the 
glands  are  called  vasa  efferentia. 

The  lymphatics  of  the  small  intestine,  called  lacteals,  pass  from  the  intes- 
tine between  the  folds  of  the  mesentery  to  empty,  sometimes  by  one  and 
sometimes  by  four  or  five  trunks,  into  the  receptaculum  chyli.  In  their 
course,  the  lacteals  pass  through  several  sets  of  lymphatic  glands,  which  are 
here  called  mesenteric  glands. 

The  thoracic  duct,  into  which  most  of  the  lymphatic  vessels  empty,  is  a 
vessel  with  very  delicate  walls  and  about  the  size  of  a  goose-quill.  It  begins 
by  a  dilatation,  more  or  less  marked,  called  the  receptaculum  chyli.  This  is 
situated  upon  the  second  lumbar  vertebra.  The  canal  passes  upward  in  the 
median  line  for  the  inferior  half  of  its  length.  It  then  inclines  to  the  left 
side,  forms  a  semicircular  curve  something  like  the  arch  of  the  aorta,  and 
empties  at  the  junction  of  the  left  subclavian  with  the  internal  jugular  vein. 


280 


ABSORPTION— LYMPH  AND  CHYLE. 


It  diminishes  in  size  from  the  receptaculum  to  its  middle  portion  and  be- 
comes larger  again  near  its  termination.  It  occasionally  bifurcates  near  the 
middle  of  the  thorax,  but  the  branches  become  reunited  a  short  distance 
above.  At  its  opening  into  the  venous  system,  there  is  generally  a  valvular 
fold,  but  according  to  Sappey,  this  is  not  constant.  There  is  always,  how- 
ever, a  pair  of  semilunar  valves  in  the  duct,  three-quarters  of  an  inch  to  an 


FIG.  89.—  Stomach,  intestine  and  mrsnutery,  ii.itli  the  mesenteric  blood-vessels  and  lacteals  (copied  and 
slightly  reduced  from  a  figure  in  the  original  work  of  Asellius.  published  in  1628). 

A,  A.  A,  A,  A,  mesenteric  arteries  and  veins  :  B,  B,  B,  B,  B,  B,  B,  B,  B,  B,  lacteals  ;  C.  C,  C,  C,  mesen- 
tery ;  D,  D,  stomach  :  E,  pyloric  portion  of  the  stomach  :  F,  duodenum  :  G,  G,  G,  jejunum  ;  H,  H, 
H,  H,  H,  ileum  ;  I,  artery  and  vein  on  the  fundus  of  the  stomach  ;  K,  portion  of  the  omentum. 


ANATOMY  OF  THE  LACTEAL  AND  LYMPHATIC  VESSELS.  281 


inch  (19  to  25  mm.)  from  its  termination,  which  effectually  prevent  the 
entrance  of  blood  from  the  venous  system. 

The  foregoing  sketch  of  the  descriptive  anatomy  of  what  has  been  called 
the  absorbent  system  of  vessels  shows  that  they  may  collect  fluids,  not  only 
from  the  intestinal  canal  during  digestion,  but  from  nearly  every  tissue  and 
organ  in  the  body,  and  that  these  fluids  are  finally  received  into  the  venous 
circulation. 

Structure  of  the  Lacteal  and  Lymphatic  Vessels. — The  lymphatic  vessels, 
even  those  of  largest  size,  are  remarkable  for  the  delicacy  and  transparency 
of  their  Avails.  This  is  well  illustrated  in  the  case  of  the  lacteals,  which  are 
hardly  visible  in  the  transparent  mesentery,  unless  they  be  filled  with  the 
opaque  chyle. 

From  the  difficulty  in  studying  the  lymphatics  at  their  origin,  except  by 
means  of  injections  or  by  reagents  which  stain  the  vessels,  investigations  into 
the  structure  of  the  smallest  vessels  have  not  been  very  satisfactory.  It  is 
supposed,  however,  that  the 
vessels  here  consist  of  a  single 
coat,  resembling,  in  this  re- 
gard, the  capillary  blood-ves- 
sels. Belaieff  has  described  in 
the  capillary  lymphatics  of  the 
penis  a  lining  of  endothelial 
cells  arranged  in  a  single  layer. 
These  cells  are  oval,  polygonal, 
fusiform  or  dentated,  with 
their  long  diameter  in  the  di- 
rection of  the  axis  of  the  ves- 
sels. 

In  all  but  the  capillary  lym- 
phatics, although  the  walls  are 
very  thin,  three  distinct  coats 
can  be  distinguished.  The  in- 
ternal coat  consists  of  an  elas- 
tic membrane  lined  with  ob- 
long, endothelial  cells.  This 
coat  readily  gives  way  when 
the  vessels  are  forcibly  dis- 
tended. The  middle  coat  is 
composed  of  longitudinal  fibres 
of  connective  tissue,  with  deli- 
cate elastic  fibres,  and  non- 
striated  muscular  fibres  ar- 
ranged transversely.  The  external  coat  is  composed  of  the  same  structures 
as  the  middle  coat,  but  most  of  the  fibres  are  arranged  longitudinally.  In 
this  coat  the  muscular  fibres  do  not  form  a  continuous  sheet,  but  are  col- 
lected into  separate  fasciculi,  which  have  a  direction  either  longitudinal  or 


FIG.  90.— Thoracic  duct  (Maseagni). 

1,  thoracic  duct ;  2,  great  lymphatic  duct :  3,  receptaculum 
chyli :  4,  curve  of  the  thoracic  duct  just  before  ft  empties 
into  the  venous  system. 


282 


ABSORPTION— LYMPH  AND  CHYLE. 


oblique.  The  fibres  of  connective  tissue  are  very  abundant  and  unite  the 
vessels  to  the  surrounding  parts.  The  internal  and  the  middle  coats  are 
closely  adherent  to  each  other ;  but  the  external  coat  may  readily  be  separated 
from  the  others.  Blood-vessels  have  been  found  in  the  walls  of  the  lym- 
phatics, and  the  existence  of  vaso-motor  nerves  is  probable. 

The  walls  of  the  lymphatic  vessels  are  very  closely  adherent  to  the  sur- 
rounding tissues ;  so  closely,  indeed,  that  even  a  small  portion  of  a  vessel  is 
detached  with  great  difficulty,  and  the  vessels,  even  those  of  large  size,  can 
not  be  followed  out  and  isolated  for  any  considerable  distance. 

In  all  the  lymphatic  vessels,  beginning  a  short  distance  from  their  plexus 
of  origin,  are  semilunar  valves,  generally  arranged  in  pairs,  with  their  con- 
cavities looking  toward  the  larger  trunks.  These  folds  are  formed  of  the 
middle  and  inner  coats ;  but  the  fold  formed  from  the  lining  membrane  is  by 
far  the  wider,  so  that  the  free  edges  of  the  valves  are  considerably  thinner 
than  that  portion  which  is  attached  directly  to  the  vessel.  The  valves  are 
most  abundant  in  the  superficial  vessels.  The  distance  between  the  valves  is 
one-twelfth  to  one-eighth  of  an  inch  (2  to  3  mm.),  near  the  origin  of  the  ves- 
sels, and  one-quarter  to  one-third  of  an  inch  (6  to  8  mm.),  in  their  course. 
In  the  lymphatics  situated  between  the  muscles  the  valves  are  less  abun- 
dant. They  are  always  relatively  few  in  the  vessels  of  the 
head  and  neck  and  in  all  that  have  a  direction  from  above 
downward.  Although  there  are  a  number  of  valves  in  the 
thoracic  duct,  they  are  not  so  abundant  here  as  in  the 
smaller  vessels. 

In  their  anatomy  and  general  properties,  the  lymphatics 
bear  a  close  resemblance  to  the  veins.  Although  much 
thinner  and  more  transparent,  their  coats  have  nearly  the 
same  arrangement.  The  arrangement  of  valves  is  entirely 
the  same ;  and  in  both  systems,  the  folds  prevent  the  reflux 
of  fluids  when  the  vessels  are  subjected  to  pressure. 

The  lymphatics  are  very  elastic ;  and  it  is  generally 
admitted  that  the  larger  vessels  and  those  of  medium  size 
are  contractile,  although  the  action  of  their  muscular  fibres, 
like  that  of  all  fibres  of  the  non-striated  variety,  is  slow 
and  gradual. 

One  of  the  most  important  points  in  connection  with 
the  physiological  anatomy  of  the  lymphatic  vessels  is  the 
question  of  the  existence  of  orifices  in  their  walls,  which 
might  allow  the  passage  of  solid  particles  or  of  emulsions. 
Anatomical  observations  have  indicated  the  existence  of 
stomata,  of  variable  size  and  irregular  shape,  in  the  small- 
est vessels ;  and  a  strong  argument  in  favor  of  the  existence  of  these  orifices 
has  been  the  fact  of  the  actual  passage,  through  the  walls  of  the  vessels,  of 
fatty  particles,  the  entrance  of  which  can  not  be  explained  by  the  well  known 
laws  of  endosmosis.  The  anatomical  evidence  of  the  existence  of  openings 
is  derived  mainly  from  preparations  stained  with  silver  nitrate,  It  is  assumed 


FIG.  91.— Valves  of 
the  lymphatics 
(Sappey). 


ANATOMY   OF  THE  LACTEAL  AND  LYMPHATIC  VESSELS.  283 


that  silver  nitrate  stains  the  solid  parts  of  tissues  and  the  borders  of  the  en- 
dothelial  cells,  and  that  non-nucleated  areas  which  do  not  present  any  stain- 
ing are  necessarily  open.  In  preparations  of  the  lymphatics,  the  solution  of 
silver  is  seen  staining  the  tissues  and  the  borders  of  the  cells  lining  the  ves- 
sels ;  but  there  are  areas  between  these  cells  where  no  staining  is  observed 
and  in  which  no  nuclei  are  brought  out  by  staining  with  carmine. 

Lymphatic  Glands. — In  the  course  of  the  lymphatic  vessels,  are  small, 
lenticular  bodies,  called  lymphatic  glands.  The  number  of  these  is  very 
great,  although  it  is  estimated  with  difficulty,  from  the  fact  that  many  of 
them  are  very  small  and  are 
consequently  liable  to  escape 
observation.  It  may  be  stated 
as  an  approximation  that  there 
are  six  or  seven  hundred  lym- 
phatic glands  in  the  body. 
Their  size  and  form  are  also 
very  variable  within  the  lim- 
its of  health.  They  generally 
are  flattened  and  lenticular, 
some  as  large  as  a  bean  and 
others  as  small  as  a  small  pea 
or  even  a  pin's-head.  They 
are  arranged  in  two  sets ;  one 
superficial  and  corresponding 
with  the  superficial  lymphatic 
vessels,  and  a  deep  set,  corre- 
sponding with  the  deep  ves- 
sels. The  superficial  glands 
are  most  abundant  in  the 
folds  at  the  flexures  of  the 
great  joints  and  about  the 
great  vessels  of  the  head  and 
neck.  The  deep-seated  glands 
are  most  abundant  around  the 
vessels  coming  from  the  great 
glandular  viscera.  A  distinct 
set  of  large  glands  is  found 

connected  with  the  lymphatic  vessels  between  the  folds  of  the  mesentery. 
These  are  known  as  the  mesenteric  glands.  All  of  the  lymphatic  vessels  pass 
through  glands  before  they  empty  into  the  great  lymphatic  trunks,  and  most 
of  them  pass  through  several  glands  in  their  course. 

The  perfect,  healthy  glands  are  of  a  grayish-white  or  reddish  color,  of 
about  the  consistence  of  the  liver,  presenting  a  hilum  where  the  larger  blood- 
vessels enter  and  the  efferent  vessels  emerge,  and  are  covered,  except  at  the 
hilum,  with  a  delicate  membrane  composed  of  inelastic  fibres,  a  few  elastic 
fibres  and  non-striated  muscular  fibres.  Their  exterior  is  somewhat  tuber- 


FIG.  92.—  Lymphatics  and  lymphatic  glandx  (Sappey). 
1,  upper  extremity  of  the  thoracic  duct,  passing  behind  the 
internal  jugular  vein  ;  2,  opening  of  the  thoracic  duct 
into  the  internal  jugular  and  left  subclavian  vein.    The 
lymphatic  glands  are  seen  in  the  course  of  the  vessels. 


284 


ABSORPTION— LYMPH  AND  CHYLE. 


culated,  from  the  projections  of  the  follicles  just  beneath  the  investing  mem- 
brane. The  interior  of  the  glands  is  soft  and  pulpy.  It  presents  a  coarsely 
granular,  cortical  substance,  of  a  reddish- white  or  gray  color,  which  is  one- 
sixth  to  one-fourth  of  an  inch  (4  to  6  mm.)  in  thickness  in  the  largest 
glands.  The  medullary  portion,  which  comes  to  the  surface  at  the  hilum,  is 
lighter  colored  and  coarser  than  the  cortical  substance.  Throughout  the 
gland,  are  found  delicate  fasciculi  of  fibrous  tissue  connected  with  the  in- 
vesting membrane,  which  serve  as  a  fibrous  skeleton  for  the  gland  and  divide 
its  substance  into  little  alveoli.  The  structure  is  far  more  delicate  in  the 
cortical  than  in  the  medullary  portion. 

Within  the  alveoli,  are  irregularly  oval,  closed  follicles,  about  T£¥  of  an 
inch  (100  fi.)  in  diameter,  filled  with  a  fluid  and  with  cells  like  those  con- 
tained in  the  solitary  glands  of  the  intestines  and  the  patches  of  Peyer.  These 
follicles  do  not  seem  to  occupy  the  medullary  portion  of  the  glands,  which, 
according  to  Kolliker,  is  composed  chiefly  of  a  net- work  of  lymphatic  capil- 
laries, mixed  with  rather  coarse  bands  of  fibrous  tissue.  The  follicular  struct- 
ures in  the  lymphatic  glands  resemble  the  closed  follicles  in  the  mucous  mem- 
brane of  the  intestinal  canal  and  the  Malpighian  bodies  of  the  spleen. 

According  to  Von  Recklinghausen,  there  exist  in  the  substance  of  the 
lymphatic  glands  great  numbers  of  lymph-spaces  or  canals,  which  are  proba- 
bly lined  with  endothelium; 
and  these  spaces  communicate 
with  the  efferent  vessels,  by 
the  stomata.  The  afferent 
vessels,  two  to  six  in  number, 
penetrate  the  gland,  and  prob- 
ably empty  their  contents  into 
the  lymph-spaces.  The  lymph 
is  then  collected  from  the 
lymph  -  spaces,  by  the  vasa 
efferentia,  one  to  three  in 
number,  which  are  always 
larger  than  the  afferent  ves- 
sels. 

The  lymphatic  glands  are 
supplied  with  blood,  some- 
times by  one  but  generally  by 
several  small  arteries,  which 
penetrate  at  the  hilum.  These 
vessels  pass  directly  to  the 

no.  gl-wren*  varieties  of  lvmphatic  glands  (Sappey).     medullary  portion  and  there 

break  up  into  several  coarse 

branches  to  be  distributed  to  the  cortical  substance,  where  they  ramify  in  a 
delicate,  capillary  net-work  with  rather  wide  meshes,  in  the  closed  follicles 
found  in  this  portion  of  the  gland.  This  capillary  plexus  also  receives 
branches  from  small  arterial  twigs  which  penetrate  the  capsule  of  the  gland 


ABSORPTION  BY  THE  LACTEALS.  285 

at  different  points.  Returning  on  themselves  in  loops,  the  vessels  unite  to 
form  one  or  more  large  veins,  which  generally  emerge  at  the  hilum. 

Very  little  is  known  regarding  the  distribution  of  nerves  in  the  lymphatic 
glands.  A  few  filaments  from  the  sympathetic  system  enter  with  the  arteries, 
but  they  have  never  been  traced  to  their  final  distribution.  The  entrance  of 
filaments  from  the  cerebro-spinal  system  has  never  been  demonstrated. 

It  is  evident,  from  the  structure  of  the  lymphatic  glands,  that  they  must 
materially  retard  the  passage  of  the  lymph  toward  the  great  trunks ;  and  it 
is  well  known  in  pathology  that  morbid  matters  taken  up  by  the  absorbents 
are  frequently  arrested  and  retained  in  the  nearest  glands. 

The  uses  of  the  lymphatic  glands  are  somewhat  obscure.  They  are  sup- 
posed, however,  to  have  an  important  office  in  the  elaboration  of  the  corpus- 
cular elements  of  the  lymph  and  chyle ;  and  it  has  been  observed  that  the 
lymph  contained  in  vessels  which  have  passed  through  no  glands  is  relatively 
poor  in  corpuscles,  while  the  large  trunks  and  the  efferent  vessels  contain 
them  in  large  numbers. 

Absorption  of  Albuminoids  by  the  Lacteals. — Comparative  analyses  of  the 
lymph  and  chyle  always  show  in  the  latter  fluid  an  excess  of  albuminoid 
matters ;  and  it  is  natural  to  infer  that  the  excess  of  nitrogenized  matters  in 
the  chyle  is  due  to  absorption  of  albuminoids  from  the  intestinal  canal. 
Lane  collected  the  chyle  from  the  lacteals  of  a  donkey,  seven  and  a  half  hours 
after  a  full  meal  of  oats  and  beans,  and  compared  its  composition  with  that 
of  the  lymph.  The  analyses  were  made  by  Rees,  who  found  that  the  chyle 
contained  about  three  times  as  much  albumin  and  fibrin  as  the  lymph. 
While  by  far  the  greatest  part  of  the  products  of  digestion  of  the  albuminoids 
is  absorbed  by  the  blood-vessels,  there  can  be  no  doubt  that  a  small  portion 
is  also  taken  up  by  the  lacteals. 

Absorption  of  Glucose  and  Salts  by  the  Lacteals. — What  has  just  been 
stated  regarding  the  absorption  of  albuminoids  applies  to  saccharine  matters 
and  the  inorganic  salts.  Small  quantities  of  sugar  and  sometimes  lactic  acid 
have  been  detected  in  the  chyle  from  the  thoracic  duct  in  the  herbivora ;  and 
the  presence  of  sugar  in  both  the  lymph  and  the  chyle  has  been  determined 
by  Colin.  While  the  products  of  the  digestion  of  saccharine  and  amylaceous 
matters  are  taken  up  mainly  by  the  blood-vessels,  a  small  quantity  is  also  ab- 
sorbed by  the  lacteals.  In  the  comparative  analyses  of  the  chyle  and  lymph  by 
Rees,  the  proportion  of  inorganic  salts  was  found  to  be  considerably  greater  in 
the  chyle.  The  great  excess  in  the  quantity  of  blood  coming  from  the  intes- 
tine, and  the  rapidity  of  its  circulation,  as  compared  with  the  chyle,  will  ex- 
plain the  more  rapid  penetration  by  endosmosis  of  the  soluble  products  of  di- 
gestion. 

Absorption  of  Water  by  the  Lacteals. — There  can  be  no  doubt  that  a  small 
portion  of  the  liquids  taken  as  drink  finds  its  way  into  the  circulation  by  the 
lacteals,  although  the  greatest  part  passes  directly  into  the  blood-vessels.  This 
has  been  proved  by  experiments  of  a  most  positive  character.  When  an  ani- 
mal has  taken  solid  food  only  and  is  killed  during  digestion,  the  thoracic  duct 
contains  a  very  small  quantity  of  chyle  ;  but  when  the  animal  has  taken  liq- 
20 


286  ABSORPTION— LYMPH  AND  CHYLE. 

uids  with  the  food,  the  thoracic  duct  and  the  lacteals  are  very  much  distended 
(Leuret  and  Lassaigne).  In  an  experiment  by  Ernest  Burdach,  a  dog  was  de- 
prived of  food  and  drink  for  twenty-four  hours,  after  which  he  was  allowed  to 
drink  water,  and  in  addition,  half  a  pound(227  c.  c.)  Avas  injected  into  the 
stomach.  The  animal  was  killed  a  half-hour  after,  and  the  thoracic  duct 
was  found  engorged  with  watery  lymph,  which  contained  a  very  few  lymph- 
corpuscles. 

Aside  from  the  entrance  of  gases  into  the  blood  from  the  pulmonary  sur- 
face, physiological  absorption  is  almost  entirely  confined  to  the  mucous  mem- 
brane of  the  alimentary  canal.  It  is  true  that  liquids  may  find  their  way  in- 
to the  circulation  through  the  skin,  the  lining  membrane  of  the  air-passages, 
the  reservoirs,  ducts  and  parenchyma  of  glands,  the  serous  and  other  closed 
cavities,  the  areolar  tissue,  the  conjunctiva,  the  muscular  tissue,  and,  in  fact, 
all  parts  which  are  supplied  with  blood-vessels ;  but  here  the  absorption  of 
foreign  matters  is  occasional  or  accidental  and  is  not  connected  with  the  gen- 
•eral  process  of  nutrition.  It  is  now  well  known  that  all  parts  of  the  body, 
except  the  epidermis  and  its  appendages,  the  epithelium,  and  some  other 
^structures  which  are  regularly  desquamated,  are  constantly  undergoing  change, 
.and  the  effete  matters  which  result  from  their  disassimilation  are  taken  up 
by  what  is  called  interstitial  absorption,  and  are  carried  by  the  blood  to  the 
proper  organs,  to  be  excreted.  It  seems  probable  that  the  vessels  of  these 
parts  would  also  be  capable  of  absorbing  soluble  foreign  substances  ;  and  this 
is,  indeed,  the  fact  with  regard  to  all  parts  in  which  the  nutritive  processes 
.are  even  moderately  active  or  where  the  structures  covering  the  vascular 
parts  are  permeable. 

Absorption  by  the  Skin. — It  is  universally  admitted  that  absorption  can 
take  place  from  the  general  surface,  although  at  one  time  this  was  a  question 
much  discussed  by  physiologists.  The  proofs,  however,  of  the  entrance  of 
certain  medicinal  preparations  from  the  surface  of  the  body  are  now  entirely 
conclusive ;  and  the  constitutional  effects  of  medicines  administered  in  this 
way  are  frequently  as  marked  as  when  they  are  taken  into  the  alimentary  canal. 
The  question  which  is  of  most  importance  in  this  connection  relates  to  the 
normal  action  of  the  skin  as  an  absorbing  surface.  Looking  at  this  subject 
from  a  purely  physiological  point  of  view,  absorption  from  the  skin,  under 
ordinary  conditions,  must  be  very  slight,  if,  indeed,  it  take  place  at  all.  There 
are,  nevertheless,  facts  which  render  it  certain  that  water  may  be  absorbed 
by  the  skin.  In  a  series  of  experiments  by  Collard  de  Martigny,  in  1821,  it 
was  shown  that  water  could  be  absorbed  in  small  quantity  by  the  skin  of  the 
palm  of  the  hand.  In  one  experiment,  a  small  bell-glass  filled  with  water  was 
applied  hermetically  to  the  palm.  This  was  connected  with  a  tube  bent  in 
the  form  of  a  siphon,  also  filled  with  water,  the  long  branch  of  which  was 
placed  in  a  vessel  of  mercury.  After  the  apparatus  had  been  applied  for  an 
hour  and  three-quarters,  the  mercury  was  found  sensibly  elevated  in  the  tube, 
showing  that  a  certain  quantity  of  the  water  had  disappeared.  In  a  series  of 
observations  upon  the  absorption  of  water  and  soluble  substances,  by  Wille- 


ABSORPTION  BY  THE  SKIN  ETC.  287 

min  (1863),  it  was  shown  that  water  is  absorbed  in  a  bath,  and  that  various 
medicinal  substances  may  be  taken  up  by  the  skin  in  this  way  and  can  be 
detected  afterward  in  the  urine. 

It  has  been  frequently  remarked  that  the  sensation  of  thirst  is  always  least 
pressing  in  a  moist  atmosphere,  and  that  it  may  be  allayed  to  a  certain  extent 
by  baths.  It  is  true  that  in  a  moist  atmosphere  the  cutaneous  exhalations 
are  diminished,  and  this  might  account  for  the  maintenance  of  the  normal  pro- 
portion of  fluids  in  the  body  with  a  less  amount  of  drink  than  ordinary ;  but 
one  could  hardly  account  for  an  actual  alleviation  of  thirst  by  immersion  of 
the  body  in  water,  unless  it  were  assumed  that  a  certain  quantity  of  water 
had  been  absorbed.  A  striking  example  of  relief  of  thirst  in  this  way  is  given 
by  Captain  Kennedy,  in  the  narrative  of  his  sufferings  after  shipwreck,  when 
he  and  his  men  were  exposed  for  a  long  time  without  water,  in  an  open  boat. 
With  regard  to  his  sufferings  from  thirst,  he  says :  "  I  can  not  conclude  without 
making  mention  of  the  great  advantage  I  derived  from  soaking  my  clothes 
twice  a  day  in  salt-water,  and  putting  them  on  without  wringing.  .  .  .  There 
is  one  very  remarkable  circumstance,  and  worthy  of  notice,  which  was,  that 
we  daily  made  the  same  quantity  of  urine  as  if  we  had  drunk  moderately  of 
any  liquid,  which  must  be  owing  to  a  body  of  water  absorbed  through  the 
pores  of  the  skin.  ...  So  very  great  advantage  did  we  derive  from  this 
practice,  that  the  violent  drought  went  off,  the  parched  tongue  was  cured  in 
a  few  minutes  after  bathing  and  washing  our  clothes ;  at  the  same  time  we 
found  ourselves  as  much  refreshed  as  if  we  had  received  some  actual  nour- 
ishment." 

Absorption  by  the  Respiratory  Surface. — Animal  and  vegetable  emana- 
tions may  be  taken  into  the  blood  by  the  lungs  and  produce  certain  well 
marked  pathological  conditions.  Many  contagious  diseases  are  propagated 
in  this  way,  as  well  as  some  fevers  and  other  general  diseases  which  are  not 
contagious.  With  regard  to  certain  poisonous  gases  and  volatile  matters, 
the  effects  of  their  absorption  by  the  lungs  are  even  more  striking.  Carbon 
monoxide  and  arsenious  hydride  produce  death  almost  instantly,  even 
when  inhaled  in  small  quantity.  The  vapor  of  pure  hydrocyanic  acid  acts 
frequently  with  great  promptness  through  the  lungs.  Turpentine,  iodine 
and  many  medicinal  substances  may  be  introduced  with  great  rapidity  by  in- 
halation of  their  vapors  ;  and  the  serious  effects  produced  by  the  emanations 
from  lead  or  mercury,  in  persons  who  work  in  these  articles,  are  well  known. 
Not  only  have  vapors  introduced  in  this  way  been  recognized  in  the  blood, 
but  many  of  the  matters  thus  absorbed  are  excreted  by  the  kidneys  and  may 
be  detected  by  their  characteristic  reactions  in  the  urine. 

As  would  naturally  be  expected,  water  and  substances  in  solution,  when 
injected  into  the  respiratory  passages,  are  rapidly  absorbed,  and  poisons  ad- 
ministered in  this  way  manifest  their  peculiar  effects  with  great  promptness. 
Experimenters  on  this  subject  have  shown  the  facility  with  which  liquids 
may  be  absorbed  from  the  lungs  and  the  air-passages,  but  it  must  be  remem- 
bered that  the  natural  conditions  are  never  such  as  to  admit  of  this  action. 
The  normal  office  of  the  lungs  is  to  absorb  oxygen  and  sometimes  a  little  ni- 


288  ABSORPTION— LYMPH  AND  CHYLE. 

trogen  from  the  air  ;  and  the  absorption  of  any  thing  else  by  these  surfaces 
is  unnatural  and  generally  deleterious. 

Absorption  from  Closed  Cavities,  Reservoirs  of  Glands,  6tfc.— Facts  in 
pathology,  showing  absorption  from  closed  cavities,  the  areolar  tissue,  the 
muscular  and  nervous  tissues,  the  conjunctiva  and  other  parts,  are  sufficient- 
ly well  known.  In  cases  of  effusion  of  serum  into  the  pleural,  peritoneal,  per- 
icardial  or  synovial  cavities,  in  which  recovery  takes  place,  the  liquid  becomes 
absorbed.  It  has  been  shown  by  experiment  that  warm  water  injected  into 
these  cavities  is  disposed  of  in  the  same  way.  Effusions  into  the  areolar  tis- 
sue are  generally  removed  by  absorption.  In  cases  of  penetration  of  air  into 
the  pleura  or  the  general  areolar  tissue,  absorption  likewise  takes  place ;  show- 
ing that  gases  may  be  taken  up  in  this  way  as  well  as  liquids.  Effusions  of 
blood  beneath  the  skin  or  the  conjunctiva  or  in  the  muscular  or  nervous  tis- 
sue may  become  entirely  or  in  part  absorbed.  It  is  true  that  these  are  path- 
ological conditions,  but  in  the  closed  cavities,  the  processes  of  exhalation  and 
absorption  are  constantly  going  on,  although  not  very  actively.  As  regards 
absorption  from  the  areolar  tissue,  the  administration  of  remedies  by  the  hy- 
podermatic method  is  a  familiar  evidence  of  the  facility  with  which  soluble 
substances  are  taken  into  the  blood,  when  introduced  beneath  the  skin. 

Under  some  conditions,  absorption  takes  place  from  the  reservoirs  of  the 
various  glands,  the  watery  portions  of  the  secretions  being  generally  taken 
up,  leaving  the  solid  and  the  organic  matters.  It  is  supposed  that  the  bile 
becomes  somewhat  inspissated  when  it  has  remained  for  a  time  in  the  gall- 
bladder, even  when  the  natural  flow  of  the  secretion  is  not  interrupted.  Cer- 
tainly, when  the  duct  is  in  any  way  obstructed,  absorption  of  a  portion  of  the 
bile  takes  place,  as  is  shown  by  coloration  of  the  conjunctiva  and  even  of  the 
general  surface.  The  serum  of  the  blood,  under  these  conditions,  is  always 
strongly  colored  with  bile.  It  is  probable,  also,  that  some  of  the  watery  por- 
tions of  the  urine  are  reabsorbed  by  the  mucous  membrane  of  the  urinary 
bladder  when  the  urine  has  been  long  confined  in  its  cavity,  although  this 
reabsorption  is  ordinarily  very  slight.  Absorption  may  take  place  from  the 
ducts  and  the  parenchyma  of  glands,  although  this  occurs  chiefly  when  for- 
eign substances  have  been  injected  into  these  parts. 

ABSORPTION  OF  FATS  AND  INSOLUBLE  SUBSTANCES. 

The  general  proposition  that  all  substances  capable  of  being  absorbed  are 
soluble  in  water  or  in  the  digestive  fluids  must  be  modified  in  the  case  of  the  fats. 
These  are  never  dissolved  in  any  considerable  quantity  in  digestion,  the  only 
change  which  they  undergo  being  a  minute  subdivision  in  the  form  of  a  very 
fine  emulsion.  In  this  condition  the  fats  are  taken  up  by  the  lacteals  and 
may  be  absorbed  in  small  quantity  by  the  blood-vessels. 

In  studying  the  mechanism  of  the  penetration  of  fatty  particles  into  the 
intestinal  villi,  it  has  been  ascertained  that  the  epithelial  cells  covering  the 
villi  play  an  important  part  in  this  process.  During  the  digestion  of  fat, 
these  cells  become  filled  with  fatty  granules  (Goodsir).  Funke,  in  his  atlas  of 
physiological  chemistry,  figures  the  appearances  of  the  intestinal  epithelium 


ABSORPTION  OF  FATS  AND  INSOLUBLE  SUBSTANCES.      289 


during  the  digestion  of  fat,  as  contrasted  with  the  epithelium  observed  dur- 
ing the  intervals  of  digestion,  showing  the  cells,  during  absorption,  filled  with 
fatty  granules. 

It  has  not  been  demonstrated  exactly  how  the  fatty  particles  penetrate  the 
epithelium  of  the  villi,  but  the  fact  of  such  penetration  is  undoubted.  From 
the  epithelium,  the  particles  of  emulsion 
pass  into  the  substance  of  the  villi — 
probably  into  the  lymph-spaces  and  ca- 
nals— and  from  these  they  readily  find 
their  way  into  the  lymphatic  capillaries. 
It  has  been  shown  that  fatty  emulsion 
will  pass  more  easily  through  porous 
septa  that  have  been  moistened  with 
bile;  and  it  is  probably  in  this  way 
mainly  that  the  bile  aids  in  the  passage 
of  the  fine  particles  of  fat  into  the  Jac- 
teals. 

As  a  general  law,  insoluble  substan- 
ces, with  the  exception  of  the  fats,  are 
never  regularly  absorbed,  no  matter  how 
finely  they  may  be  divided.  The  appar- 
ent exceptions  to  this  are  mercury  in  a  state  of  minute  subdivision  like 
an  emulsion,  and  carbonaceous  particles.  As  regards  mercury,  it  is  well 
known  that  minute  particles  in  the  form  of  unguents  may  be  introduced  into 
the  system  by  prolonged  frictions.;  but  this  can  not  be  taken  as  an  instance 
of  physiological  absorption.  The  passage  of  small,  carbonaceous  particles 
through  the  pulmonary  membrane  seems  to  be  purely  mechanical.  The  same 
thing  may  possibly  occur  when  fine,  sharp  particles  of  carbon  are  introduced 


FIG.  94. — Epithelium  of  the  small  intestine  of 
the  rabbit  (Funke). 


1'iG.  95.—  Epithelium  from  the  duodenum  of  a 
rabbit,  two  hours  after  having  been  fed 
with  melted  butter  (Funke). 


Fio.  96.— Villi  filled  with  fat,  from  the  small 
intestine  of  an  executed  criminal,  one  hour 
after  death  (Funke). 


into  the  alimentary  canal ;  but  the  experiments  of  Mialhe  with  pulverized 
charcoal,  and  particularly  those  of  Berard,  Robin  and  Bernard  with  lamp- 


290  ABSORPTION— LYMPH  AND  CHYLE. 

black  introduced  into  the  intestinal  canal  of  animals,  showed  that  although 
the  intestinal  mucous  membrane  became  of  a  deep  black,  this  could  easily  be 
removed  by  a  stream  of  water  and  no  carbonaceous  particles  could  be  dis- 
covered in  the  mesenteric  veins,  the  lacteals  or  the  mesenteric  glands.  When 
the  carbon  is  used  in  the  form  of  lamp-black,  the  particles  are  very  minute 
and  rounded,  and  they  do  not  present  the  sharp  points  and  edges  which 
sometimes  enable  the  grains  of  pulverized  charcoal  to  penetrate  the  vessels 
mechanically. 

VARIATIONS  AND  MODIFICATIONS  OF  ABSORPTION. 

Very  little  is  known  concerning  the  variations  in  lacteal  or  lymphatic  ab- 
sorption ;  but  in  absorption  by  blood-vessels,  important  modifications  occur, 
due,  on  the  one  hand,  to  different  conditions  of  the  fluids  to  be  absorbed,  and 
on  the  other,  to  differences  in  the  constitution  of  the  blood  and  in  the  con- 
ditions of  the  vessels. 

The  different  conditions  of  the  fluids  to  be  absorbed  apparently  do  not 
always  have  the  same  influence  in  physiological  absorption  as  in  endosmotic 
experiments  made  out  of  the  body.  Saccharine  solutions  of  different  densi- 
ties confined  in  distinct  portions  of  the  intestinal  canal  of  a  living  animal  do 
not  present  any  marked  variations  in  the  rapidity  of  their  absorption,  and 
they  are  taken  up  by  the  blood,  even  when  their  density  is  greater  than 
that  of  the  blood-plasma.  Solutions  of  potassium  nitrate  and  of  sodium  sul- 
phate, of  greater  density  than  the  serum,  which  would,  therefore,  attract  the 
endosmotic  current  in  an  endosmometer,  are  readily  taken  up  by  the  blood- 
vessels in  a  living  animal.  Indeed,  nearly  all  soluble  substances,  whatever 
be  the  density  of  their  solutions,  may  be  taken  up  by  the  various  absorbing 
surfaces  during  life.  The  curare  poison  and  most  of  the  venoms  are  remark- 
able exceptions  to  this  rule.  In  a  series  of  experiments  upon  the  absorption 
of  curare,  Bernard  has  shown  that  this  poison,  Avhich  is  absorbed  so  readily 
from  wounds  or  when  injected  under  the  skin,  generally  produces  no  effect 
when  introduced  into  the  stomach,  the  small  intestine  or  the  urinary  bladder. 
This  result,  however,  is  not  invariable,  for  poisonous  effects  are  produced 
when  curare  is  introduced  into  the  stomach  of  a  fasting  animal.  This  pecul- 
iarity in  the  absorption  of  many  of  the  animal  poisons  has  long  been  ob- 
served ;  and  it  is  well  known  that  the  flesh  of  animals  poisoned  with  curare 
may  be  eaten  with  impunity.  It  is  curious,  however,  to  see  an  animal  carry- 
ing in  the  stomach  without  danger  a  fluid  which  would  produce  death  if  in- 
troduced under  the  skin ;  and  the  explanation  of  this  is  not  readily  apparent. 
The  poison  is  not  neutralized  by  the  digestive  fluids,  for  curare  digested  for 
a  long  time  in  gastric  juice,  or  taken  from  the  stomach  of  a  dog,  is  found  to 
possess  all  its  toxic  properties.  This  may  be  shown  by  poisoning  a  pigeon 
with  curare  drawn  by  a  fistula  from  the  stomach  of  a  living  dog  (Bernard). 
If  the  absorption  of  this  poison  be  recognized  simply  by  its  effects  upon  the 
system,  it  must  be  assumed  that  during  digestion,  it  can  not  be  absorbed  by 
the  mucous  membrane  of  the  stomach  and  small  intestine,  notwithstanding 
its  solubility. 


VARIATIONS  AND   MODIFICATIONS  OF  ABSORPTION.        291 

It  has  been  shown  that  liquids  which  immediately  disorganize  the  tissues, 
such  as  concentrated  nitric  or  sulphuric  acid,  can  not  be  absorbed.  Another 
important  peculiarity  in  absorption  is  that  solutions  which  readily  coagulate 
the  albumen  of  the  circulating  fluids  are  absorbed  very  slowly  (Miahle). 
This  is  explained  by  the  supposition  that  there  is  a  coagulation  of  the  albu- 
minous fluids  with  which  the  absorbing  membrane  is  permeated,  which  in- 
terferes with  the  passage  of  liquids.  These  substancs  are  nevertheless  taken 
up  by  the  blood-vessels,  though  rather  slowly. 

Influence  of  the  Condition  of  the  Blood  and  of  the  Vessels  on  Absolution. 
— After  loss  of  blood  or  deterioration  of  the  nutritive  fluid  from  prolonged 
abstinence,  absorption  generally  takes  place  with  great  activity.  This  is  well 
known,  both  as  regards  the  entrance  of  water  and  alimentary  substances  and 
the  absorption  of  medicines.  It  was  at  one  time  quite  a  common  practice  to 
bleed  before  administering  certain  remedies,  in  order  to  produce  their  more 
speedy  action  upon  the  system. 

The  rapidity  of  the  circulation  has  an  important  influence  in  facilitating 
absorption,  and  this  process  is  generally  active  in  proportion  to  the  vascu- 
larity  of  different  parts.  During  intestinal  absorption,  the  increase  in  the 
activity  of  the  circulation  in  the  mucous  membrane  is  very  marked  and  un- 
doubtedly has  an  influence  upon  the  rapidity  with  which  the  products  of  di- 
gestion are  taken  up  by  the  blood. 

Influence  of  the  Nervous  System  on  Absorption. — It  is  certain  that  ab- 
sorption, especially  in  the  stomach,  is  subject  to  certain  variations,  which  can 
hardly  be  dependent  upon  anything  but  nervous  action.  Water  and  other 
liquids,  which  usually  are  readily  absorbed  from  the  stomach,  are  sometimes 
retained  for  a  time,  and  are  afterward  rejected  in  nearly  the  condition  in 
which  they  were  taken.  It  is  probable,  however,  that  the  most  important 
influences  thus  exerted  by  the  nervous  system  are  effected  through  the  circu- 
lation. The  experiments  of  Bernard  and  others  upon  the  vaso-motor  nerves, 
by  the  action  of  which  the  supply  of  blood  in  different  parts  is  regulated, 
point  out  a  line  of  experimentation  which  would  probably  throw  much  light 
upon  some  of  the  important  variations  in  absorption.  When  it  is  remem- 
bered that  the  small  arteries  may  become  so  contracted  under  the  influence 
of  the  vaso-motor  nerves  that  their  caliber  is  almost  obliterated,  of  course  re- 
tarding in  a  corresponding  degree  the  capillary  and  venous  circulation  in  the 
parts,  and  again,  that  the  same  vessels  may  be  so  dilated  as  to  admit  to  a.  par- 
ticular part  many  times  more  blood  than  it  ordinarily  receives,  it  becomes 
apparent  that  absorption  may  be  profoundly  affected  through  this  system  of 
nerves.  It  has  been  ascertained  that  while  a  section  of  some  of  the  nerves 
distributed  to  the  alimentary  canal  will  slightly  retard  the  absorption  of  the 
poisonous  substances,  the  process  is  never  entirely  arrested. 

IMBIBITION  AND  ENDOSMOSIS. 

If  liquids  pass  through  the  substance  of  an  animal  membrane,  it  is  evident 
that  the  membrane  itself  must  be  capable  of  taking  up  a  certain  portion  by 
imbibition ;  and  this  must  be  considered  as  the  starting-point  in  absorption. 


292  ABSORPTION-LYMPH  AND  CHYLE. 

Imbibition  is,  indeed,  a  property  common  to  all  animal  tissues.  It  is  a  well 
known  fact,  however,  that  the  tissues  do  not  imbibe  all  solutions  with  the 
same  degree  of  activity.  Distilled  water  is  the  liquid  which  is  always  taken 
up  in  greatest  quantity,  and  saline  solutions  enter  the  substance  of  the  tissues 
in  an  inverse  ratio  to  their  density.  This  is  also  the  fact  with  regard  to 
mix!  ares  of  alcohol  and  water,  imbibition  always  being  in  an  inverse  propor- 
tion to  the  quantity  of  alcohol  present  in  the  liquid.  Among  the  other  con- 
ditions which  have  a  marked  influence  upon  imbibition,  is  temperature.  It 
is  a  familiar  fact  that  dried  animal  membranes  may  be  more  rapidly  softened 
in  warm  than  in  cold  water ;  and  with  regard  to  the  imbibition  of  liquids  by 
sand,  the  researches  of  Matteucci  and  Cima  have  shown  a  considerable  in- 
crease at  a  moderately  elevated  temperature.  While  nearly  all  the  structures 
of  the  body,  after  desiccation,  will  imbibe  liquids,  the  membranes  through 
which  the  processes  of  absorption  are  most  active  are,  as  a  rule,  most  easily 
permeated ;  and  the  character  of  the  liquid,  the  temperature  etc.,  have  a 
great  influence  upon  the  activity  of  this  process.  For  example,  all  liquids 
which  have  a  tendency  to  harden  the  tissues,  such  as  saline  solutions,  alcohol 
etc.,,  pass  through  with  much  less  rapidity  than  pure  water. 

Mechanism  of  the  Passage  of  Liquids  through  Membranes. — The  passage 
of  liquids  through  membranes  is  called  osmosis.  In  the  case  of  two  liquids 
passing  in  opposite  directions,  the  stronger  current  is  called  endosmotic  and 
the  weaker  current  is  called  exosmotic.  In  the  passage  of  liquids  into  the 
vessels,  in  physiological  absorption,  the  process  is  generally  called  endosmosis. 
The  attention  of  physiologists  was  first  directed  to  these  phenomena  by  the 
researches  of  Dutrochet,  published  in  1826. 

It  is  now  definitely  ascertained  that  the  following  conditions  are  necessary 
for  the  operation  of  endosmosis  and  exosmosis : 

1.  That  both  liquids  be  capable  of  "  wetting  "  the  interposed  membrane, 
or  in  other  words,  that  the  membrane  be  capable  of  imbibing  both  liquids. 
If  but  one  of  the  liquids  can  wet  the  membrane,  the  current  takes  place  in 
only  one  direction. 

2.  That  the  liquids  be  miscible  with  each  other  and  be  differently  consti- 
tuted.    Although  it  is  found  that  the  currents  are  most  active  when  the 
liquids 'are  of  different  densities,  this  condition  is  not  indispensable ;  for  cur- 
rents will  take  place  between  solutions  of  different  substances,  such  as  salt, 
sugar  or  albumen,  when  they  have  precisely  the  same  density. 

The  physiological  applications  of  the  laws  of  endosmosis  can  now  be  more 
fully  appreciated,  as  it  is  evident  that  the  above  conditions  are  fulfilled  when- 
ever absorption  takes  place,  with  the  single  exception  of  the  absorption  of 
fats,  which  has  been  specially  considered.  For  example,  all  substances  are 
dissolved  or  liquefied  before  they  are  absorbed,  and  in  this  condition,  they 
are  capable  of  "  wetting  "  the  walls  of  the  blood-vessels.  All  the  liquids  ab- 
sorbed are  capable,  also,  of  mixing  with  the  plasma  of  the  blood.  What 
makes  this  application  still  more  complete,  is  the  behavior  of  albumin  in 
endosmotic  experiments.  In  physiological  absorption,  there  is  always  a  great 
predominance  of  the  endosmotic  current,  and  there  is  very  little  transudation, 


IMBIBITION  AND  ENDOSMOSIS. 


293 


or  exosmosis,  of  the  albuminoid  constituents  of  the  blood.  On  the  other 
hand,  there  is  a  constant  absorption  of  peptones,  which  are  destined  to  be 
converted  into  the  albuminoid  constituents  of  the  blood. 

Recognizing  the  fact  that  albumin  is  capable  of  inducing  a  more  power- 
ful endosmotic  current  than  almost  any  other  liquid,  it  has  been  shown  that 
it  never  itself  passes  through  membranes  in  the  exosmotic  current,  but  that 
albuminoids,  after  transformation  by  digestion  into  peptones,  or  albumin 
mixed  with  gastric  juice,  pass  through  animal  membranes  with  great  facility. 
The  experiments  by  which  these  facts  are  demonstrated  are  of  the  highest 
physiological  importance.  On  removing  part  of  the  shell  of  an  egg,  so  as  to 
expose  its  membranes,  and  immersing  it  in  pure  water,  the  passage  of  water 
into  the  egg  is  rendered  evident  by  the  projection  of  the  distended  mem- 
branes ;  but  although  the  surrounding  liquid  becomes  alkaline  and  the  appro- 
priate tests  reveal  the  presence  of  some  of  the  inorganic  constituents  of  the 
egg,  the  presence  of  albumin  can  not  be  detected.  When  the  contents  of  the 
egg  are  replaced  by  the  serum  of  the  blood,  the  same  result  follows.  "  After 
six  or  eight  hours  of  immersion,  the  serum  had  yielded  to  the  water  in  the  ves- 
sel all  its  saline  elements,  chlorides,  sulphates,  phosphates,  which  were  easily 
recognized  by  their  peculiar  reactions,  but  not  a  trace  of  albumin  "  (Dutrochet). 

A  very  simple  apparatus  for  illustrating  endosmotic  action  can  be  con- 
structed in  the  following  way :  Remove  carefully  a  circular  portion,  about 
an  inch  (25'4  mm.)  in  diameter,  of  the  shell  from  one 
end  of  an  egg,  which  may  be  done  without  injuring  the 
membranes,  by  cracking  the  shell  into  small  pieces,  which 
are  picked  off  with  forceps.  A  small,  glass  tube  is  then 
introduced  through  an  opening  in  the  shell  and  mem- 
branes of  the  other  end  of  the  egg,  and  is  secured  in  a 
vertical  position  by  wax  or  plaster  of  Paris,  the  tube 
penetrating  the  yelk.  The  egg  is  then  placed  in  a  wine- 
glass partly  filled  with  water.  In  the  course  of  a  few 
minutes  the  water  will  have  penetrated  the  exposed 
membrane,  and  the  yelk  will  rise  in  the  tube. 

The  force  with  which  liquids  pass  through  mem- 
branes, called  endosmotic  or  osmotic  force,  is  to  a  great 
degree  dependent  upon  the  influence  of  the  membranes 
themselves.  This  influence  is  always  purely  physical,  in 
experiments  made  out  of  the  body;  and  physiological  ab- 
sorption can  be  explained,  to  a  certain  extent,  by  the  same 
laws.  It  must  be  remembered,  however,  that  the  prop- 
erties of  organic  structures,  which  are  manifested  only  in 
living  bodies,  are  capable  of  modifying  these  physical  phe- 
nomena in  a  remarkable  degree.  For  example,  all  living 
tissues  are  capable  of  selecting  and  appropriating  from 
the  nutritive  fluids  the  materials  necessary  for  their  regeneration  ;  and  the 
secreting  structures  of  glands  also  select  from  the  blood  certain  constituents 
which  are  used  in  the  formation  of  their  secretions.  These  phenomena  and 


FIG.  97. — Egg  prepared 
so  as  to  illustrate 
endosmotic  action. 


294  ABSORPTION  -LYMPH  AND  CHYLE. 

their  modifications  through  the  nervous  system  can  not  be  fully  explained. 
This  is  true,  also,  of  many  of  the  phenomena  of  absorption  and  their  modi- 
fications, which  are  probably  dependent  upon  the  same  kind  of  action. 

It  is  not  necessary  to  assume  the  existence  of  infinitely  small  openings 
in  homogeneous  membranes  through  which  osmotic  currents  can  be  made  to 
take  place,  in  order  to  explain  the  mechanism  of  these  currents.  In  the  case 
of  two  liquids  capable  of  diffusing  with  each  other  and  separated  by  an  ani- 
mal membrane,  the  mechanism  of  the  endosmotic  and  exosmotic  currents  is 
very  simple.  In  the  first  place,  the  membrane  imbibes  both  the  liquids,  but 
one  is  always  taken  up  in  greater  quantity  than  the  other.  If  water  and  a 
solution  of  common  salt  be  employed,  the  surface  of  the  membrane  exposed 
to  the  water  will  imbibe  more  than  the  surface  exposed  to  the  saline  solution ; 
but  both  liquids  will  meet  in  its  substance.  The  first  step,  therefore,  in  the 
production  of  the  currents  is  imbibition.  Once  in  contact  with  each  other, 
the  liquids  diffuse,  the  water  passing  to  the  saline  solution,  and  vice  versa. 
This  takes  place  by  precisely  the  same  mechanism  as  that  of  the  passage  of 
liquids  through  porous  septa. 

In  no  experiments  performed  out  of  the  body,  can  the  conditions  favor- 
able to  the  passage  of  liquids  through  membranes  in  accordance  with  purely 
physical  laws  be  realized  as  they  exist  in  the  living  organism.  The  great  ex- 
tent of  the  absorbing  surfaces ;  the  delicacy  and  permeability  of  the  mem- 
branes ;  the  rapidity  with  which  substances  are  carried  on  by  the  torrent  of 
the  circulation,  as  soon  as  they  pass  through  these  membranes  ;  the  uniform- 
ity of  the  pressure,  notwithstanding  the  penetration  of  liquids ;  all  these 
favor  the  physical  phenomena  of  absorption  in  a  way  which  can  not  be  imi- 
tated in  artificially  constructed  apparatus.  Within  the  blood-vessels,  the 
albuminoid  matters  exist  in  a  form  which  does  not  permit  them  to  pass 
through  membranes,  while  the  peptones  are  highly  osmotic.  The  sugars, 
also,  pass  through  the  walls  of  the  vessels  with  facility,  as  well  as  various 
salts  and  medicinal  substances  in  solution.  The  fats,  as  has  been  stated,  pass 
mainly  into  the  lacteals,  by  a  process  which  has  already  been  described  and 
which  can  not  be  fully  explained  by  the  laws  of  endosmosis. 

LYMPH  AND  CHYLE. 

To  complete  the  history  of  physiological  absorption,  it  will  be  necessary 
to  treat  of  the  origin,  composition  and  properties  of  the  lymph  and  chyle. 
It  is  only  within  a  few  years  that  physiologists  have  been  able  to  appreciate 
the  importance  of  the  lymph,  for  the  experiments  indicating  the  great  quan- 
tity of  this  liquid  which  is  continually  passing  into  the  blood  are  of  com- 
paratively recent  date. 

The  first  successful  experiments  in  which  the  lymph  and  chyle  were 
obtained  in  quantity  were  made  by  Colin.  This  observer,  in  operating  upon 
large  animals,  particularly  the  ruminants,  experienced  no  great  difficulty  in 
isolating  the  thoracic  duct  near  its  junction  with  the  subclavian  vein  and 
introducing  a  metallic  tube  of  sufficient  size  to  allow  the  free  discharge  of 
fluid.  These  experiments,  made  upon  horses  and  the  larger  ruminants,  were 


PROPERTIES  AND  COMPOSITION  OF  LYMPH.  295 

the  first  to  give  any  clear  idea  of  the  quantity  of  liquids — lymph  and  chyle — 
which  pass  through  the  thoracic  duct.  In  an  observation  upon  a  cow  of 
medium  size,  he  succeeded  in  collecting,  in  the  course  of  twelve  hours,  105 -3 
Ibs.  (47,963  grammes) ;  and  he  stated  that  a  very  much  greater  quantity  can 
be  obtained  by  operating  upon  ruminants  of  larger  size. 

According  to  the  estimates  of  Dalton,  deduced  from  his  own  observations 
upon  dogs  and  the  experiments  of  Colin  upon  horses,  the  total  quantity  of 
lymph  and  chyle  produced  in  the  twenty-four  hours  in  a  man  weighing  one 
hundred  and  forty-three  pounds  (65  kilos.)  is  about  6*6  pounds  (3,000 
grammes).  And  again,  reasoning  from  experiments  made  upon  dogs  thir- 
teen hours  after  feeding,  when  the  fluid  which  passes  up  the  thoracic  duct 
may  be  assumed  to  be  pure,  unmixed  lymph,  the  total  quantity  of  lymph 
alone,  produced  in  the  twenty-four  hours  by  a  man  of  ordinary  weight, 
would  be  about  4-4  pounds  (2,000  grammes).  These  estimates  can  be  accepted 
only  as  approximate,  and  they  do  not  indicate  the  entire  quantity  of  lymph 
actually  contained  in  the  organism. 

There  are  110  very  satisfactory  recent  researches  with  regard  to  the  physi- 
ological variations  in  the  quantity  of  lymph.  Collard  de  Martigny  found 
the  lymphatics  always  distended  with  fluid  in  dogs  killed  after  two  days  of 
total  deprivation  of  food.  This  condition  continued  during  the  first  week 
of  starvation ;  but  after  that  time,  the  quantity  in  the  vessels  gradually 
diminished,  and  a  few  hours  before  death,  the  lymphatics  and  the  thoracic 
duct  were  nearly  empty.  In  comparing  the  quantity  of  fluid  in  the  lymphat- 
ics of  the  neck,  during  digestion  and  absorption,  with  the  quantity  which  they 
contained  soon  after  digestion  was  completed,  the  same  observer  found  that 
while  digestion  and  absorption  were  going  on  actively,  the  vessels  of  the 
neck  contained  scarcely  any  fluid ;  but  the  quantity  gradually  increased  after 
these  processes  were  completed. 

Properties  and  Composition  of  Lymph. — Lymph  taken  from  the  vessels 
in  various  parts  of  the  system,  or  the  fluid  which  is  discharged  from  the 
thoracic  duct  during  the  intervals  of  digestion,  is  either  perfectly  transpar- 
ent and  colorless  or  of  a  slightly  yellowish  or  greenish  hue.  When  allowed 
to  stand  for  a  short  time,  it  becomes  faintly  tinged  with  red,  and  frequently 
it  has  a  pale  rose-color  when  first  discharged.  Microscopical  examination 
shows  that  this  reddish  color  is  dependent  upon  the  presence  of  a  few  red 
blood-corpuscles,  which  are  entangled  in  the  clot  as  the  lymph  coagulates, 
thus  accounting  for  the  deepening  of  the  color  when  the  fluid  has  been 
allowed  to  stand. 

Lymph  has  no  decided  or  characteristic  odor.  It  is  very  slightly  saline 
in  taste,  being  almost  insipid.  Its  specific  gravity  is  much  lower  than  that 
of  the  blood.  Magendie  found  the  specific  gravity  in  the  dog  to  be  about 
1022.  According  to  Robin,  the  specific  gravity  of  the  defibrinated  serum  of 
lymph  is  1009.  In  analyses  by  Diihnhardt,  of  the  lymph  taken  from  dilated 
vessels  in  the  leg,  in  the  human  subject,  the  specific  gravity  was  1007. 

A  few  minutes  after  discharge  from  the  vessels,  both  the  lymph  and 
chyle  undergo  coagulation.  This  process,  as  regards  the  chemical  changes 


296  ABSORPTION— LYMPH  AND  CHYLE. 

involved,  is  identical  with  the  coagulation  of  the  blood,  in  which  the  leuco- 
cytes play  an  important  part.  According  to  Colin,  the  fluid  collected 
from  the  thoracic  duct  in  the  large  ruminants  coagulates  at  the  end  of 
five,  ten  or  twelve  minutes,  and  sets  into  a  mass  having  exactly  the  form 
of  the  vessel  in  which  it  is  contained.  The  clot  is  tolerably  consistent,  but 
there  is  never  any  spontaneous  separation  of  serum  (Colin).  This  may  be 
the  fact  with  regard  to  the  lymph  and  the  chyle  of  the  large  ruminants, 
but  in  the  observations  of  Dalton,  who  operated  upon  dogs  and  goats,  after  a 
few  hours'  exposure,  the  clot  contracted  to  about  half  its  original  size,  pre- 
cisely like  coagulated  blood,  expressing  a  considerable  quantity  of  serum.  In 
one  instance,  in  the  dog,  the  volume  of  serum,  after  twenty-four  hours  of  re- 
pose, was  about  twice  that  of  the  contracted  clot. 

Although  many  analyses  have  been  made  of  lymph  from  the  human  sub- 
ject, the  conditions  under  which  the  fluid  has  been  obtained  render  it  proba- 
ble that  in  the  majority  of  instances  it  was  not  entirely  normal.  It  will  be 
necessary,  therefore,  to  compare  these  analyses  with  observations  made  upon 
the  lymph  of  the  inferior  animals ;  as  in  the  latter,  this  fluid  has  been  col- 
lected under  conditions  which  leave  no  doubt  as  to  its  normal  character.  In 
the  experiments  of  Colin  especially,  the  fluids  taken  from  the  thoracic  duct, 
during  the  intervals  of  digestion  undoubtedly  represented  the  normal,  mixed 
lymph  collected  from  nearly  all  parts  of  the  body ;  and  the  operative  proced- 
ure in  the  large  ruminants  is  so  simple  as  to  produce  little  if  any  general  dis- 
turbance. The  following  is  an  analysis  by  Lassaigne  of  specimens  of  lymph 
collected  by  Colin  from  the  thoracic  duct  of  a  cow,  under  the  most  favorable 
conditions : 

COMPOSITION    OF    LYMPH    FROM    A    COW. 

Water 964-0 

Fibrin 09 

Albumin 28-0 

Patty  matter 0'4 

Sodium  chloride 5-0 

Sodium  carbonate,  sodium  phosphate  and  sodium  sulphate 1-2 

Calcium  phosphate 0-5 


1,000-0 

The  proportions  given  in  the  table  are  by  no  means  invariable,  the  differ- 
ences in  coagulability  indicating  differences  in  the  proportion  of  fibrin-fac- 
tors, and  the  degree  of  lactescence  showing  great  variations  in  the  quantity 
of  fatty  matters.  The  table  may  be  taken,  however,  as  an  approximation  of 
the  average  composition  of  the  lymph  of  these  animals,  during  the  intervals 
of  digestion. 

The  analysis  of  human  lymph  which  seems  to  be  the  most  reliable,  and 
in  which  the  fluid  was  apparently  pure  and  normal,  is  that  of  Gubler  and 
Quevenne.  The  lymph  in  this  case  was  collected  by  Desjardins  from  a 
female  who  suffered  from  a  varicose  dilatation  of  the  lymphatic  vessels  in  the 
anterior  and  superior  portion  of  the  left  thigh.  These  vessels  occasionally 
ruptured,  and  the  lymph  could  then  be  obtained  in  considerable  quantity. 


PROPERTIES  AND  COMPOSITION  OF  LYMPH.  297 

When  an  opening  existed,  the  discharge  of  fluid  could  be  arrested  at  will  by 
flexing  the  trunk  upon  the  thigh.  Gubler  and  Quevenne  made  analyses  of 
two  different  specimens  of  the  fluid,  with  the  following  results : 

COMPOSITION    OF    HUMAN    LYMPH. 

First  analysis.        Second  analysis. 

Water 939'87  934-77 

Fibrin 0-56  0-63 

Caseous  matter  (with  earthy  phosphates  and  traces  of 
iron) 42-75  42-80 

Fatty  matter  (in  the  second  analysis,  fusible  at  102-3° 
Fahr.,  or  39°  C) 3-82  9'20 

Hydro-alcoholic  extract  (containing  sugar,  and  leaving, 
after  incineration,  sodium  chloride,  with  sodium  phos- 
phate and  sodium  carbonate) 13-00  12-60 


1,000-00  1,000-00 

The  above  analyses  show  a  much  larger  proportion  of  solid  constituents 
than  was  found  by  Lassaigne  in  the  lymph  of  the  cow.  This  excess  is  pretty 
uniformly  distributed  throughout  all  the  constituents,  with  the  exception  of 
the  fatty  matters  and  fibrin ;  the  former  existing  largely  in  excess  in  the 
human  lymph,  especially  in  the  second  analysis,  while  the  latter  is  smaller 
in  quantity  than  in  the  lymph  of  the  cow.  It  is  evident,  however,  from  a 
comparison  of  the  two  analyses  by  Gubler  and  Quevenne,  that  the  composi- 
tion of  the  lymph,  even  when  it  is  unmixed  with  chyle,  is  subject  to  great 
variations.  The  caseous  matter  given  by  Gubler  and  Quevenne  is  probably 
equivalent  to  the  albuminous  matter  mentioned  by  other  chemists. 

The  distinctive  characters  of  the  different  constituents  of  the  lymph  do 
not  demand  extended  consideration,  inasmuch  as  most  of  them  have  already 
been  treated  of  in  connection  with  the  blood.  In  comparing,  however,  the 
composition  of  the  lymph  with  that  of  the  blood,  the  great  excess  of  solid 
constituents  in  the  latter  fluid  is  at  once  apparent. 

In  nearly  all  analyses  the  organic  nitrogenized  constituents  have  been 
found  to  be  very  much  less  in  the  lymph  than  in  the  blood.  This  is  gener- 
ally most  marked  with  regard  to  the  fibrin-factors;  but  as  before  stated, 
the  proportion  of  all  these  substances  is  quite  variable.  On  account  of  this 
deficiency,  lymph  is  much  inferior  to  the  blood  in  coagulability,  and  the 
coagulum,  when  it  is  formed,  is  soft  and  friable.  There  does  not  appear, 
however,  to  be  any  actual  difference  between  the  coagulating  constituents  of 
the  lymph  and  of  the  blood. 

Fatty  matters  have  generally  been  found  to  be  more  abundant  in  the 
lymph  than  in  the  blood ;  but  their  proportion  is  even  more  variable  than 
that  of  the  albuminoid  constituents. 

Very  little  remains  to  be  said  concerning  the  ordinary  inorganic  constitu- 
ents of  the  lymph.  The  analyses  of  Dahnhardt  have  shown  that  nearly  if 
not  all  of  the  inorganic  matters  which  have  been  demonstrated  in  the  blood 
are  contained  in  the  lymph ;  and  a  small '  proportion  of  iron  is  given  in  the 
analyses  by  Gubler  and  Quevenne. 


298 


ABSORPTION— LYMPH  AND  CHYLE. 


These  facts  indicate  a  remarkable  correspondence  in  composition  between 
the  lymph  and  the  blood.  All  of  the  constituents  of  the  blood,  except  the 
red  corpuscles,  exist  in  the  lymph,  the  only  difference  being  in  their  relative 
proportions. 

In  addition  to  the  constituents  of  the  lymph  ordinarily  given,  the  presence 
of  glucose,  and  more  lately,  the  existence  of  a  certain  proportion  of  urea,  have 
been  demonstrated  in  this  fluid.  It  has  not  been  ascertained  how  the  sugar 
contained  in  the  lymph  takes  its  origin. 

The  presence  of  urea  in  considerable  quantity  in  both  the  chyle  and  the 
lymph  has  been  determined  by  Wurtz ;  and  it  is  thought  by  Bernard  that  the 
lymph  is  the  principal  fluid,  if  not  the  only  one,  by  which  this  excrementi- 
tious  substance  is  taken  up  from  the  tissues.  Although  urea  always  exists  in 
the  blood,  its  quantity  is  less  than  in  the  lymph. 

According  to  Ludwig  and  Hammersten,  the  lymph  of  the  dog  contains 
about  forty  parts  per  hundred  in  volume  of  carbon  dioxide,  of  which  seven- 
teen parts  may  be  extracted  by  the  air-pump  and  twenty-three  parts,  by  acids. 

In  addition,  the  lymph  contains  a  trace 
of  oxygen  and  one  or  two  parts  of  ni- 
trogen. 

Corpuscular  Elements  of  the  Lymph. 
—In  every  part  of  the  lymphatic  system, 
in  addition  to  a  few  very  minute  fatty 
granules,  there  are  found  certain  cor- 
puscular elements  known  as  lymph-cor- 
puscles. These  exist,  not  only  in  the 
clear  lymph,  but  in  the  opaque  fluid 
contained  in  the  lacteals  during  absorp- 
tion. They  are  now  regarded  as  identi- 
cal with  the  white  blood-corpuscles,  or 
leucocytes.  Eight  thousand  two  hun- 
dred leucocytes  have  been  counted  in 
0-061  cubic  inch  (1  c.  c.)  of  lymph  from 
a  dog  (Hitter). 

The  leucocytes  found  in  the  lymph  and  chyle  are  rather  less  uniform  in 
size  and  general  appearance  than  the  white  corpuscles  of  the  blood.  Their 
average  diameter  is  about  -3-^  of  an  inch  (10  /*.) ;  but  some  are  larger,  and 
others  are  as  small  as  -^^  of  an  inch  (5  /x..).  Some  of  these  corpuscles  are 
quite  clear  and  transparent,  presenting  but  few  granulations  and  an  indistinct 
nuclear  appearance  in  their  centre ;  but  others  are  granular  and  quite  opaque. 
They  present  the  same  adhesive  character  in  the  lymph  as  in  the  blood,  and 
frequently  they  are  found  collected  in  masses  in  different  parts  of  the  lym- 
phatic system.  In  all  other  regards,  these  bodies  present  the  same  charac- 
ters as  the  leucocytes  of  the  blood,  and  they  need  not,  therefore,  be  farther 
described. 

In  addition  to  the  ordinary  leucocytes  and  a  certain  number  of  fatty  gran- 
ules, a  few  small,  clear  globules  or  granules,  about  T^gVs  of  an  inch  (3-3  /*.) 


FIG. 


. — Chyle  taken  from  the  lacteals  and 
thoracic  duct  of  a  criminal  executed  dur- 
ing digestion  (Funke). 


ORIGIN  AND  USES  OF  THE  LYMPH.  299 

IB  diameter,  called  sometimes  globulins,  are  almost  constantly  present  in  the 
lymph.  These  are  insoluble  in  ether  and  acetic  acid  but  are  dissolved  by 
ammonia.  They  were  regarded  by  Robin  as  a  variety  of  leucocytes  and 
described  by  him  as  free  nuclei. 

Origin  and  Uses  of  the  Lymph. — There  can  hardly  be  any  doubt  concern- 
ing the  source  of  most  of  the  liquid  portions  of  the  lymph,  for  they  can  be 
derived  only  from  the  blood.  Although  the  exact  relations  between  the 
smallest  lymphatics  and  the  blood-vessels  have  not  been  made  out  in  all  parts 
of  the  system,  there  is  manifestly  no  anatomical  reason  why  the  water,  mixed 
with  albuminoid  matters  and  holding  salts  in  solution,  should  not  pass  from 
the  blood  into  the  lymphatics ;  and  this  is  rendered  nearly  certain  by  the  fact 
that  the  lymphatics  surround  many  of  the  blood-vessels.  In  comparing  the 
composition  of  the  lymph  with  that  of  the  plasma  of  the  blood,  it  is  seen  that 
the  constituents  of  these  fluids  are  nearly  if  not  quite  identical ;  the  only 
variations  being  in  their  relative  proportions.  This  is  another  argument  in 
favor  of  the  passage  of  most  of  the  constituents  of  the  blood  into  the  lymph. 

One  of  the  most  important  physiological  facts  in  the  chemical  history  of 
the  lymph  is  the  constant  existence  of  a  considerable  proportion  of  urea. 
This  can  not  .be  derived  from  the  blood,  for  its  proportion  is  greater  in  the 
lymph,  notwithstanding  the  fact  that  this  fluid  is  being  constantly  discharged 
into  the  blood-vessels.  The  urea  which  exists  in  the  lymph  is  derived  from 
the  tissues ;  it  is  discharged  then  into  the  blood,  and  is  constantly  being 
removed  from  this  fluid  by  the  kidneys. 

The  positive  facts  upon  which  to  base  any  precise  ideas  with  regard  to  the 
general  office  of  the  lymph  are  not  very  many.  From  the  composition  of 
this  fluid,  its  mode  of  circulation,  and  the  fact  that  it  is  being  constantly  dis- 
charged into  the  blood,  it  would  not  seem  to  have  an  important  use  in  the 
active  processes  of  nutrition.  The  experiments  of  Collard  de  Martigny  sus- 
tain this  view,  inasmuch  as  the  quantity  and  the  proportion  of  solid  constitu- 
ents of  the  lymph  were  rather  increased  than  diminished  in  animals  that  had 
been  deprived  of  food  and  drink  for  several  days ;  while  it  is  well  known  that 
starvation  always  impoverishes  the  blood  from  the  first.  On  the  other  hand, 
urea,  one  of  the  most  important  of  the  products  of  disassimilation,  is  undoubt- 
edly taken  up  by  the  lymph  and  conveyed  in  this  fluid  to  the  blood.  It 
remains  for  future  investigations  to  determine  whether  other  excrementitious 
matters  may  not  be  taken  up  from  the  tissues  in  the  same  way — a  question 
of  importance  in  its  relations  to  the  mechanism  of  excretion. 

What  is  positively  known  with  regard  to  the  uses  of  the  lymph  may  be 
summed  up  in  a  very  few  words  :  A  great  part  of  its  constituents  is  evidently 
derived  from  the  blood,  and  the  relations  of  these  to  nutrition  are  not  under- 
stood. The  same  may  be  said  of  sugar,  which  is  a  constant  constituent  of 
the  lymph.  Urea  and  perhaps  other  excrementitious  matters  are  taken  up 
from  the  tissues  by  the  lymph,  and  are  discharged  into  the  blood,  to  be  re- 
moved from  the  system  by  the  appropriate  organs. 

Properties  and  Composition  of  Chyle. — During  the  intervals  of  digestion, 
the  intestinal  lymphatics  and  the  thoracic  duct  carry  ordinary  lymph ;  but 


300  ABSOEPTION— LYMPH  AND  CHYLE. 

as  soon  as  absorption  of  alimentary  matters  begins,  certain  nutritive  matters 
are  taken  up  in  quantity  by  these  vessels,  and  their  contents  are  known  under 
the  name  of  chyle. 

In  the  human  subject  and  in  carnivorous  animals,  the  chyle,  taken  from 
the  lacteals  near  the  intestine,  where  it  is  nearly  pure,  or  from  the  thoracic 
duct,  when  it  is  mixed  with  lymph,  is  a  white,  opaque,  milky  fluid,  of  a 
slightly  saline  taste  and  an  odor  which  is  said  to  resemble  that  of  the  semen. 
The  odor  is  also  said  to  be  characteristic  of  the  animal  from  which  the  fluid 
is  taken ;  although  this  is  not  very  marked,  except  on  the  addition  of  a  con- 
centrated acid,  the  process  employed  by  Barreul  to  develop  the  characteristic 
odor  in  the  fluids  from  different  animals.  Bouisson  has  found  that  the 
peculiar  odor  of  the  dog  was  thus  developed  in  fresh  chyle  taken  from  the 
thoracic  duct. 

The  reaction  of  the  chyle  is  either  alkaline  or  neutral.  Dalton  noted  an 
alkaline  reaction  in  the  chyle  of  the  goat  and  of  the  dog ;  and  a  specimen  of 
chyle  taken  from  a  criminal  immediately  after  execution,  examined  by  Eees, 
was  neutral.  Leuret  and  Lassaigne  obtained  the  fluid  from  the  receptaculum 
chyli  in  a  man  that  had  died  of  cerebral  inflammation,  and  found  its  reaction 
to  be  alkaline. 

The  specific  gravity  of  the  chyle  is  always  less  than  that  of  the  blood ;  but 
it  is  very  variable  and  depends  upon  the  quality  of  the  food  and  particularly 
upon  the  quantity  of  liquids  ingested.  Lassaigne  found  the  specific  gravity 
of  a  specimen  of  pure  chyle  taken  from  the  mesenteric  lacteals  of  a  bull  to 
be  1013,  and  the  specific  gravity  of  the  specimen  of  human  chyle  examined 
by  Rees  was  1024. 

The  differences  in  the  appearance  of  the  chyle  in  different  animals  depend 
chiefly  upon  the  food.  Colin  found  the  chyle  milky  in  the  carnivora,  espe- 
cially after  fats  had  been  taken  in  quantity ;  while  in  dogs  that  were  nour- 
ished with  articles  containing  but  little  fat,  its  appearance  was  hardly  lac- 
tescent. Tiedemann  and  Gmeliii  found  the  chyle  almost  transparent  in 
herbivora  fed  with  hay  or  straw.  They  also  observed  that  the  chyle  was 
nearly  transparent  in  dogs  fed  with  liquid  albumen,  fibrin,  gelatine,  starch 
and  gluten ;  while  it  was  white  in  the  same  animals  fed  with  milk,  meat, 
bones  etc. 

It  is  impossible  to  give  an  accurate  estimate  of  the  entire  quantity  of 
pure  chyle  taken  up  by  the  lacteal  vessels.  When  it  finds  its  way  into  the 
thoracic  duct,  it  is  mingled  immediately  with  all  the  lymph  from  the  lower 
extremities ;  and  the  large  quantities  of  fluid  which  have  been  collected  from 
this  vessel  by  Colin  and  others  give  no  idea  of  the  quantity  of  chyle  absorbed 
from  the  intestinal  canal.  No  attempt  will  be  made,  therefore,  to  give  even 
an  approximate  estimate  of  the  absolute  quantity  of  chyle ;  but  it  is  evident 
that  this  is  variable,  depending  upon  the  nature  of  the  food  and  the  quantity 
of  liquids  ingested. 

Like  the  lymph,  the  chyle,  when  removed  from  the  vessels,  undergoes 
coagulation.  Different  specimens  of  the  fluid  vary  very  much  as  regards  the 
rapidity  with  which  coagulation  takes  place.  The  chyle  from  the  thoracic 


PROPERTIES   AND  COMPOSITION  OF  CHYLE.  301 

duct  generally  coagulates  in  a  few  minutes.  The  first  portion  of  the  fluid 
collected  from  the  human  subject  by  Eees — the  chyle  was  collected  in  this 
case  in  two  portions — coagulated  in.  an  hour.  Received  into  an  ordinary 
glass  vessel,  the  chyle  generally  separates  more  or  less  completely  after  coagu- 
lation, into  clot  and  serum.  The  serum  is  quite  variable  in  quantity  and  is 
never  clear.  Its  milkiness  does  not  depend  entirely  upon  the  presence  of 
particles  of  emulsified  fat,  and  it  is  not  rendered  transparent  by  ether.  It 
contains,  also,  a  number  of  leucocytes  and  organic  granules. 

Observations  have  been  made  with  reference  to  the  influence  of  different 
kinds  of  food  upon  the  chyle ;  but  these  have  not  been  followed  by  any  defi- 
nite results  that  can  be  applied  to  the  human  subject.  It  is  usual  to  find  the 
chyle  fluid  in  the  lacteals  and  in  the  thoracic  duct  for  many  hours  after 
death ;  but  it  soon  coagulates  after  exposure  to  the  air.  Although  the  entire 
lacteal  system  is  sometimes  found,  in  the  human  subject  and  in  the  inferior 
animals,  filled  with  perfectly  opaque,  coagulated  chyle,  the  fluid  does  not 
often  coagulate  in  the  vessels. 

Composition  of  the  Chyle. — Analyses  of  the  milky  fluid  taken  from  the 
thoracic  duct  during  full  digestion  by  no  means  represent  the  composition  of 
pure  chyle ;  and  it  is  only  by  collecting  the  fluid  from  the  mesenteric  lacteals, 
that  it  can  be  obtained  without  a  very  large  admixture  of  lymph.  In  the 
human  subject,  it  is  rare  even  to  have  an  opportunity  of  taking  the  fluid 
from  the  thoracic  duct  in  cases  of  sudden  death  during  digestion ;  and  in 
most  of  the  inferior  animals  which  have  been  operated  upon,  it  is  difficult  to 
obtain  fluid  from  the  small  lacteals  in  quantity  sufficient  for  accurate  analy- 
sis. In  operating  upon  the  ox,  however,  Colin  has  succeeded  in  collecting 
pure  chyle  in  considerable  quantity. 

In  the  analysis  by  Rees,  the  fluid  was  taken  from  the  thoracic  duct  of  a 
vigorous  man,  a  little  more  than  an  hour  after  his  execution  by  hanging. 
The  subject  was  apparently  in  perfect  health  to  the  moment  of  his  death. 
The  evening  before,  he  ate  two  ounces  (56-7  grammes)  of  bread  and  four 
ounces  (113-4  grammes)  of  meat.  At  seven  A.  M.,  precisely  one  hour  before 
death,  he  took  two  cups  of  tea  and  a  piece  of  toast ;  and  he  drank  a  glass  of 
wine  just  before  mounting  the  scaffold.  When  the  dissection  was  made,  the 
body  was  yet  warm,  although  the  weather  was  quite  cold.  The  thoracic 
duct  was  rapidly  exposed  and  divided,  and  about  six  fluidrachms  (22-2  c.  c.) 
of  milky  chyle  were  collected.  The  fluid  was  neutral  and  had  a  specific 
gravity  of  1024.  The  following  was  its  approximate  composition : 

COMPOSITION   OF   HUMAN   CHYLE   FROM  THE  THORACIC   DUCT. 

Water 904-8 

Albumin,  with  traces  of  fibrinous  matter 70-8 

Aqueous  extractive 5*6 

Alcoholic  extractive,  or  osmazome 5'2 

Alkaline  chlorides,  carbonates  and  sulphates,  with  traces  of  alkaline  phos- 
phates and  oxides  of  iron 4'4 

Fatty  matters 9'2 

1,000-0 

21 


302  ABSORPTION— LYMPH  AND  CHYLE. 

Of  the  constituents  of  the  chyle  not  given  in  the  ordinary  analyses,  the 
most  important  are  the  urea,  which  in  all  probability  is  derived  exclusively 
from  the  lymph,  and  sugar,  coming  from  the  saccharine  and  amylaceous  arti- 
cles of  food  during  digestion. 

The  difference  in  chemical  composition  between  the  unmixed  lymph  and 
the  chyle  is  illustrated  in  a  comparative  examination  of  these  two  fluids  taken 
from  a  donkey.  The  fluids  were  collected  by  Lane,  the  chyle  being  taken 
from  the  lacteals  before  reaching  the  thoracic  duct.  The  animal  was  killed 
seven  hours  after  a  full  meal  of  oats  and  beans.  The  following  analyses  of 
the  fluids  were  made  by  Rees  : 

COMPOSITION    OF    CHYLE   AND    LYMPH    BEFORE    REACHING   THE   THORACIC 

DUCT. 

Chyle.  Lymph. 

Water 902-37  965-36 

Albuminous  matter 35-16  12-00 

Fibrinous  matter 3-70  1-20 

Animal  extractive  matter  soluble  in  water  and  alcohol 3-32  2'40 

Animal  extractive  matter  soluble  in  water  only 12-33  13-19 

Fatty  matter 36-01  a  trace 

Salts  -i  Alkaline  chlorides,  sulphates  and  carbonates,  with  )          ~ ....  r.e~ 
'  (      traces  of  alkaline  phosphates  and  oxide  of  iron .  ) 

1,000-00         1,000-00 

The  above  analyses  show  a  very  marked  difference  in  the  proportion  of 
solid  constituents  in  the  two  fluids.  The  chyle  contains  about  three  times  as 
much  albumen  and  fibrin  as  the  lymph,  with  a  larger  proportion  of  salts. 
The  proportion  of  fatty  matters  in  the  chyle  is  very  great,  while  in  the  lymph 
there  exists  only  a  trace.  The  individual  constituents  of  the  chyle  given  in 
the  above  tables  do  not  demand  any  farther  consideration  than  they  have 
already  received  under  the  head  of  lymph.  The  albuminoid  matters  are  in 
part  derived  from  the  food,  and  in  part  from  the  blood,  through  the  admixt- 
ure of  the  chyle  with  lymph.  The  fatty  matters  are  derived  in  greatest  part 
from  the  food.  As  far  as  has  been  ascertained  by  analyses  of  the  chyle  for 
salts,  this  fluid  has  been  found  to  contain  essentially  the  same  inorganic  con- 
stituents as  the  plasma  of  the  blood. 

The  presence  of  sugar  in  the  chyle  was  first  mentioned  by  Brande,  who 
described  it,  however,  rather  indefinitely.  Glucose  was  first  distinctly  recog- 
nized in  the  chyle  by  Trommer,  and  its  existence  in  many  of  the  higher  orders 
of  animals  has  since  been  fully  established  by  Colin. 

Microscopical  Characters  of  the  Chyle. — The  milky  appearance  of  the 
chyle  as  contrasted  with  the  lymph  is  due  to  the  presence,  of  a  large  number 
of  very  minute  fatty  granules.  The  liquid  becomes  much  less  opaque  when 
treated  with  ether,  which  dissolves  many  of  the  fatty  particles.  In  fact,  the 
chyle  of  the  thoracic  duct  is  nothing  more  than  lymph  to  which  an  emulsion 
of  fat  in  a  liquid  containing  albuminoid  matters  and  salts  is  temporarily 
added  during  the  process  of  intestinal  absorption.  The  quantity  of  fatty 
granules  in  the  chyle  varies  considerably  with  the  diet,  and  it  generally  di- 


MOVEMENTS  OF  THE  LYMPH  AND  CHYLE.       303 

minishes  progressively  from  the  smaller  to  the  larger  vessels,  on  account 
of  the  constant  admixture  of  lymph.  The  size  of  the  granules  is  pretty 
uniformly  -^^  to  T2^T  of  an  inch  (1  to  2  p.).  They  are  much  smaller 
and  more  uniform  in  size  in  the  lacteals  than  in  the  cavity  of  the 
intestine.  Their  constitution  is  not  constant;  and  they  are  composed  of 
the  different  varieties  of  fat  which  are  taken  as  food,  mixed  with  each 
other  in  various  proportions.  The  ordinary  corpuscular  elements  of  the 
lymph,  leucocytes  and  globulins,  are  also  found  in  variable  quantity  in  the 
chyle. 

MOVEMENTS  OF  THE  LYMPH  AND  THE  CHYLE. 

Compared  with  the  current  of  blood,  the  movements  of  the  lymph  and 
chyle  are  feeble  and  irregular ;  and  the  character  of  these  movements  is  such 
that  they  are  evidently  due  to  a  variety  of  causes.  As  regards  those  constitu- 
ents which  are  derived  directly  from  the  blood,  the  lymph  may  be  said  to  un- 
dergo a  true  circulation  ;  inasmuch  as  there  is  a  constant  transudation  at  the 
peripheral  portion  of  the  vascular  system,  of  fluids  which  are  returned  to  the 
circulating  blood  by  the  communications  of  the  lymphatic  system  with  the 
great  veins.  The  constituents  of  the  lymph,  however,  are  not  derived  entirely 
from  the  blood,  a  considerable  portion  resulting  from  interstitial  absorption 
in  the  general  lymphatic  system ;  and  the  chyle  contains  certain  nutritive 
matters  absorbed  by  the  lacteal  vessels.  These  are,  physiologically,  the  most 
important  constituents  of  the  lymph  and  chyle ;  and  they  are  taken  up  sim- 
ply to  be  carried  to  the  blood  and  do  not  pass  again  from  the  general  vascular 
system  into  the  lymphatics. 

As  far  as  the  mode  of  origin  of  the  lymph  and  chyle  has  any  bearing  upon 
the  movements  of  these  fluids  in  the  lymphatic  vessels,  there  is  no  difference 
between  the  imbibition  of  new  matters  from  the  tissues  or  from  the  intestinal 
canal  and  the  transudation  of  the  liquid  portions  of  the  blood;  for  the 
mechanism  of  the  passage  of  liquids  from  the  blood-vessels  is  such  that  the 
motive  power  of  the  blood  can  not  be  felt.  An  illustration  of  this  is  in  the 
mechanism  of  the  transudation  of  the  liquid  portions  of  the  secretions.  The 
force  with  which  fluids  are  discharged  into  the  ducts  of  the  glands  is  very 
great  and  is  independent  of  the  action  of  the  heart,  being  due  entirely  to  the 
processes  of  transudation  and  secretion.  This  is  combined  with  the  force  of 
imbibition,  and  with  it  forms  one  of  the  important  agents  in  the  movements 
of  the  lymph  and  chyle.  These  movements  are  studied  with  great  difficulty. 
One  of  the  first  peculiarities  to  be  observed  is  that  under  normal  conditions, 
the  vessels  are  seldom  distended,  and  the  quantity  of  fluid  which  they  con- 
tain is  subject  to  considerable  variation.  As  far  as  the  flow  in  the  vessels  of 
medium  size  is  concerned,  the  movement  is  probably  continuous,  subject  only 
to  certain  momentary  obstructions  or  accelerations  from  various  causes ;  but 
in  the  large  vessels  situated  near  the  thorax  and  in  those  within  the  chest,  the 
movements  are  in  a  marked  degree  remittent,  or  they  may  even  be  intermit- 
tent. All  experimenters  who  have  observed  the  flow  of  lymph  or  chyle  from 
a  fistula  into  the  thoracic  duct  have  noted  a  constant  acceleration  with  each 


304  ABSORPTION-LYMPH  AND  CHYLE. 

act  of  expiration ;  and  an  impulse  synchronous  with  the  pulsations  of  the 
heart  has  frequently  been  observed. 

The  fact  that  the  lymphatic  system  is  never  distended,  and  the  existence 
of  the  valves,  by  which  different  portions  may  become  isolated,  render  it  im- 
possible to  estimate  the  general  pressure  of  fluid  in  these  vessels.  This  is 
undoubtedly  subject  to  great  variations  in  the  same  vessels  at  different  times, 
as  well  as  in  different  parts  of  the  lymphatic  system.  It  is  well  known,  for 
example,  that  the  degree  of  distention  of  the  thoracic  duct  is  very  variable, 
its  capacity  not  infrequently  being  many  times  increased  during  active  ab- 
sorption. At  the  same  time  it  is  difficult  to  attach  a  manometer  to  any  part 
of  the  lymphatic  system  without  seriously  obstructing  the  circulation  and 
consequently  exaggerating  the  normal  pressure ;  but  the  force  with  which 
liquids  penetrate  these  vessels  is  very  great.  This  is  illustrated  by  the  ex- 
periment of  tying  the  thoracic  duct ;  for  after  this  operation,  unless  com- 
municating vessels  exist  by  which  the  fluids  can  be  discharged  into  the 
venous  system,  their  accumulation  is  frequently  sufficient  to  rupture  the 
vessel. 

The  general  rapidity  of  the  current  in  the  lymphatic  vessels  has  never 
been  accurately  estimated.  As  a  natural  consequence  of  the  variations  in  the 
distention  of  these  vessels,  the  rapidity  of  the  circulation  must  be  subject  to 
constant  modifications.  Beclard,  making  his  calculation  from  the  experi- 
ments of  Colin,  who  noted  the  quantity  of  fluid  discharged  in  a  given  time 
from  fistulous  openings  into  the  thoracic  duct,  estimated  that  the  rapidity  of 
the  flow  in  this  vessel  was  about  one  inch  (25-4  mm.)  per  second.  This  esti- 
mate, however,  can  be  only  approximate;  and  it  is  evident  that  the  flow 
must  be  much  less  rapid  in  the  vessels  near  the  periphery  than  in  the  large 
trunks,  as  the  liquid  moves  in  a  space  which  becomes  rapidly  contracted  as  it 
approaches  the  openings  into  the  venous  system. 

Various  influences  combine  to  produce  the  movements  of  fluids  in  the 
lymphatic  system,  some  being  constant  in  their  operation,  and  others,  inter- 
mittent or  occasional.  These  will  be  considered,  as  nearly  as  possible,  in  the 
order  of  their  relative  importance. 

The  forces  of  endosmosis  and  transudation  are  undoubtedly  the  main 
causes  of  the  lymphatic  circulation,  more  or  less  modified,  however,  by  influ- 
ences which  may  accelerate  or  retard  the  current ;  but  this  action  is  capable 
in  itself  of  producing  the  regular  movement  of  the  lymph  and  chyle.  It  is 
a  force  which  is  in  constant  operation,  as  is  seen  in  cases  of  ligation  of  the 
thoracic  duct,  a  procedure  which  must  finally  abolish  all  other  forces  which 
aid  in  producing  the  lymphatic  circulation.  When  the  receptaculum  chyli 
is  ruptured  as  a  consequence  of  obstruction  of  the  thoracic  duct,  the  vessel 
gives  way  as  the  result  of  the  constant  endosmotic  action,  in  the  same  way 
that  the  exposed  membranes  of  an  egg  may  be  ruptured  by  endosmosis,  when 
immersed  in  water. 

The  situations  in  which  the  endosmotic  force  originates  are  at  the  periph- 
ery, where  the  single  wall  of  the  vessels  is  very  thin,  and  where  the  extent  of 
absorbing  surface  is  large.  If  liquids  can  penetrate  with  such  rapidity  and 


MOVEMENTS  OF  THE  LYMPH  AND  CHYLE.       305 

force  through  the  walls  of  the  blood-vessels,  where  their  entrance  is  opposed 
by  the  pressure  of  the  fluids  already  in  their  interior,  they  certainly  must 
pass  without  difficulty  through  the  walls  of  the  lymphatics,  where  there  is 
no  lateral  pressure  to  oppose  their  entrance,  except  that  produced  by  the 
weight  of  the  column  of  liquid.  This  pressure  is  readily  overcome ;  and  the 
valves  in  the  lymphatic  system  effectually  prevent  any  backward  current. 

In  describing  the  anatomy  of  the  lymphatic  system,  it  has  already  been 
stated  that  the  large  vessels  and  those  of  medium  size  are  provided  with 
non-striated  muscular  fibres  and  are  endowed  with  contractility.  This  fact 
has  been  demonstrated  by  physiological  as  well  as  anatomical  investigations. 
Beclard  stated  that  he  often  produced  contractions  of  the  thoracic  duct 
by  the  application  of  the  two  poles  of  an  inductive  apparatus.  It  is  not  un- 
common to  see  the  lacteals  become  reduced  in  size  to  a  mere  thread,  even 
while  under  observation.  Although  experiments  have  generally  failed  to 
demonstrate  any  regular,  rhythmical  contractions  in  the  lymphatic  system,  it 
is  probable  that  the  vessels  contract  upon  their  contents,  when  they  are  un- 
usually distended,  and  thus  assist  the  circulation,  the  action  of  the  valves 
opposing  a  regurgitating  current.  This  action,  however,  can  not  have  any 
considerable  and  regular  influence  upon  the  general  current. 

Contractions  of  the  ordinary  voluntary  muscles,  compression  of  the 
abdominal  organs  by  contraction  of  the  abdominal  muscles,  peristaltic  move- 
ments of  the  intestines  and  pulsations  of  large  arteries  situated  against  the 
lymphatic  trunks,  particularly  the  thoracic  aorta,  are  all  capable  of  increas- 
ing the  rapidity  of  the  circulation  of  the  lymph  and  chyle. 

The  contractions  of  voluntary  muscles  assist  the  lymphatic  circulation  in 
precisely  the  way  in  which  they  influence  the  flow  of  blood  in  the  venous 
system ;  and  there  is  nothing  to  be  added  regarding  this  action  to  what  has 
already  been  said  on  this  subject  in  connection  with  the  description  of  the 
venous  circulation. 

Increase  in  the  flow  of  chyle  in  the  thoracic  duct,  as  the  result  of  com- 
pression of  the  abdominal  organs  or  of  kneading  the  abdomen  with  the 
hands,  was  observed  by  Magendie,  and  the  fact  has  been  confirmed  in  all 
recent  experiments  on  this  subject.  The  same  effect,  though  probably  less 
in  degree,  is  produced  by  the  peristaltic  contractions  of  the  intestines. 

When  a  tube  is  introduced  into  the  upper  part  of  the  thoracic  duct,  it  is 
frequently  the  case  that  the  fluid  is  discharged  with  increased  force  at  each 
pulsation  of  the  heart.  This  was  frequently  observed  by  Dalton  in  his  exper- 
iments on  the  thoracic  duct,  and  he  described  the  jets  as  being  "  like  blood 
coming  from  a  small  artery  when  the  circulation  is  somewhat  impeded." 
This  impulse  is  due  to  compression  of  the  thoracic  duct  as  it  passes  under 
the  arch  of  the  aorta.  Its  influence  upon  the  general  current  of  the  lymph 
and  chyle  is  probably  insignificant. 

While  the  vis  a  teryo  must  be  regarded  as  by  far  the  most  important 
agent  in  the  production  of  the  lymphatic  circulation,  the  movements  of 
fluids  in  the  thoracic  duct  receive  constant  and  important  aid  from  the 
respiratory  acts.  This  fact  has  long  been  recognized ;  and  in  the  works  of 


306  SECRETION. 

Haller  there  is  a  full  discussion  of  the  influence  of  the  diaphragm  and  of  the 
movements  of  the  thorax  upon  the  circulation  of  chyle.  Colin  always  found 
marked  impulses  in  the  flow  of  chyle  from  a  fistula  into  the  thoracic  duct, 
which  were  synchronous  with  the  movements  of  respiration.  With  each  act 
of  expiration  the  fluid  was  forcibly  ejected,  and  with  inspiration  the  flow 
was  very  much  diminished  or  even  arrested.  These  impulses  became  much 
more  marked  when  respiration  was  interfered  with  and  the  efforts  became 
violent.  The  impulses  were  sometimes  so  decided,  that  the  pulsations  were 
repeated  in  a  long  elastic  tube  attached  to  the  canula  for  the  purpose  of  col- 
lecting the  fluid. 

From  all  these  considerations,  it  is  evident  that  although  there  are  many 
conditions  capable  of  modifying  the  currents  in  the  lymphatic  system,  the 
regular  flow  of  the  lymph  and  chyle  depends  chiefly  upon  the  vis  a  tergo  ; 
but  the  vessels  themselves  sometimes  undergo  contraction,  and  they  are  sub- 
ject to  occasional  compression  from  surrounding  parts,  which,  from  the  exist- 
ence of  valves  in  the  vessels,  must  favor  the  current  toward  the  venous  sys- 
tem. The  alternate  dilatation  and  compression  of  the  thoracic  duct  with 
the  acts  of  respiration  likewise  aid  the  circulation,  and  they  are  more  effi- 
cient than  any  other  force,  except  the  vis  a  tergo.  The  action  of  the  valves 
is  precisely  the  same  in  the  lymphatic  as  in  the  venous  system. 


CHAPTER  XL 

SECRETION. 

Classification  of  the  secretions— Mechanism  of  the  production  of  the  true  secretions— Mechanism  of  the 
production  of  the  excretions — Influence  of  the  composition  and  pressure  of  the  blood  on  secretion — • 
Influence  of  the  nervous  system  on  secretion— Anatomical  classification  of  glandular  organs— Classifi- 
cation of  the  secreted  fluids— Synovial  membranes  and  synovia— Mucous  membrSiies  and  mucus- 
Physiological  anatomy  of  the  sebaceous,  ceruminous  and  Meibomian  glands— Ordinary  sebaceous  matter 
— Smegma  of  the  prepuce  and  of  the  labia  minora — Vernix  caseosa — Cerumen — Meibomian  secretion — 
Mammary  secretion— Physiological  anatomy  of  the  mammary  glands— Mechanism  of  the  secretion  of 
milk— Conditions  which  modify  the  lacteal  secretion— Quantity  of  milk— Properties  and  composition  of 
milk— Microscopical  characters  of  milk— Composition  of  milk — Variations  in  the  composition  of  milk- 
Colostrum— Lacteal  secretion  in  the  newly-born— Secretory  nerve-centres. 

THE  processes  of  secretion  are  intimately  connected  with  general  nutri- 
tion. In  the  sense  in  which  the  term  secretion  is  usually  received,  it  em- 
braces most  of  the  processes  in  which  there  is  a  separation  of  matters  from 
the  blood  by  glandular  organs  or  a  formation  of  a  new  fluid  out  of  materials 
furnished  by  the  blood.  The  blood  itself,  the  lymph  and  the  chyle,  are  in 
no  sense  to  be  regarded  as  secretions.  These  fluids,  like  the  tissues,  are  per- 
manent parts  of  the  organism,  undergoing  those  changes  only  that  are  neces- 
sary to  their  proper  regeneration.  They  are  likewise  characterized  by  the 
presence  of  certain  formed  anatomical  elements,  which  themselves  undergo 
processes  of  molecular  destruction  and  regeneration.  These  characters  are 


CLASSIFICATION  OF  THE  SECRETIONS.  307 

not  possessed  by  the  secretions.  As  a  rule,,  the  latter  are  homogeneous  fluids, 
without  formed  anatomical  elements,  except  as  accidental  constituents,  such 
as  the  desquamated  epithelium  in  mucus  or  in  sebaceous  matter.  The  secre- 
tions are  either  discharged  from  the  body,  when  they  are  called  excretions, 
or  after  having  performed  their  proper  office  as  secretions,  are  absorbed  in  a 
more  or  less  modified  form  by  the  blood. 

Physiologists  now  regard  secretion  as  the  act  by  which  fluids,  holding 
certain  substances  in  solution,  and  sometimes  containing  peculiar  ferments 
but  not  necessarily  possessing  formed  anatomical  elements,  are  separated 
from  the  blood  or  are  formed  by  special  organs  out  of  materials  furnished  by 
the  blood.  These  organs  may  be  membranes,  follicles  or  collections  of  folli- 
cles, or  tubes.  In  the  latter  instances  they  are  called  glands.  The  liquids 
thus  formed  are  called  secretions ;  and  they  may  be  destined  to  perform 
some  office  connected  with  nutrition  or  may  be  simply  discharged  from  the 
organism. 

It  is  not  strictly  correct  to  speak  of  formed  anatomical  elements  as  prod- 
ucts of  secretion,  except  in  the  instance  of  the  fatty  particles  in  the  milk. 
The  leucocytes  found  in  pus,  the  spermatozoids  of  the  seminal  fluid,  and  the 
ovum,  which  are  sometimes  spoken  of  as  products  of  secretion,  are  anatomi- 
cal elements  developed  in  the  way  in  which  such  structures  are  ordinarily 
formed.  For  example,  leucocytes,  or  pus-corpuscles,  may  be  developed  Avith- 
out  the  intervention  of  any  special  secreting  organ ;  and  spermatozoids  and 
ova  are  generated  in  the  testicles  and  the  ovaries,  by  a  process  entirely  differ- 
ent from  ordinary  secretion.  It  is  important  to  recognize  these  facts  in 
studying  the  mechanism  by  which  the  secretions  are  produced. 

Classification  of  the  Secretions. — Certain  secretions  are  formed  by  special 
organs  and  have  important  uses  which  do  not  involve  their  discharge  from 
the  body.  These  may  be  classed  as  the  true  secretions  ;  and  the  most  strik- 
ing examples  of  such  'are  the  digestive  fluids.  Each  one  of  these  fluids  is 
formed  by  a  special  gland  or  set  of  glands,  which  generally  has  no  other 
office ;  and  they  are  never  produced  by  any  other  part.  It  is  the  gland  which 
produces  the  characteristic  constituent  or  constituents  of  the  true  secretions, 
out  of  materials  furnished  by  the  blood ;  and  the  matters  thus  formed  never 
pre-exist  in  the  circulating  fluid.  The  office  which  these  fluids  have  to  per- 
form is  generally  not  continuous ;  and  when  this  is  the  case,  the  flow  of  the 
secretion  is  intermittent,  taking  place  only  when  its  action  is  required.  When 
the  parts  which  produce  one  of  the  true  secretions  are  destroyed,  as  is  some- 
times done  in  experiments  upon  living  animals,  the  characteristic  constituents 
of  this  particular  secretion  never  accumulate  in  the  blood  nor  are  they  formed 
vicariously  by  other  organs.  The  simple  effect  of  such  an  experiment  is 
absence  of  the  secretion,  with  the  disturbances  consequent  upon  the  loss  of 
its  physiological  action. 

Certain  other  of  the  fluids  are  composed  of  water,  holding  one  or  more 
characteristic  constituents  in  solution,  which  result  from  the  physiological 
wear  of  the  tissues.  These  matters  have  no  office  to  perform  in  the  animal 
economy  and  are  simply  separated  from  the  blood  to  be  discharged  from  the 


308  SECRETION. 

body.  These  may  be  classed  as  excretions,  the  urine  being  the  type  of  fluids 
of  this  kind.  The  characteristic  constituents  of  the  excrementitious  fluids 
are  formed  in  the  tissues,  as  one  of  the  results  of  the  constant  changes  going 
on  in  all  organized,  living  structures.  They  always  pre-exist  in  the  circulating 
fluid  and  may  be  eliminated,  either  constantly  or  occasionally,  by  a  number 
of  organs.  As  they  are  produced  continually  in  the  substance  of  the  tissues 
and  are  taken  up  by  the  blood,  they  are  constantly  separated  from  the  blood 
by  the  proper  eliminating  organs.  When  the  glands  which  thus  eliminate 
these  substances  are  destroyed  or  when  their  action  is  seriously  impaired,  the 
excrementitious  matters  may  accumulate  in  the  blood  and  give  rise  to  certain 
toxic  phenomena.  These  effects,  however,  are  often  retarded  by  the  vicarious 
action  of  other  organs. 

There  are  some  fluids,  as  the  bile,  which  have  important  uses  as  secre- 
tions, and  which  nevertheless  contain  certain  excrementitious  matters.  In 
these  instances,  it  is  only  the  excrementitious  matters  that  are  discharged 
from  the  organism. 

In  the  sheaths  of  some  tendons  and  of  muscles,  in  the  substance  of  mus- 
cles and  in  some  other  situations,  fluids  are  found  which  simply  moisten  the 
parts  and  which  contain  very  little  organic  matter,  with  but  a  small  propor- 
tion of  inorganic  salts.  Although  these  are  frequently  spoken  of  as  secretions, 
they  are  produced  generally  by  a  simple,  mechanical  transudation  of  certain 
of  the  constituents  of  the  blood  through  the  walls  of  the  vessels.  Still,  it  is 
difficult  to  draw  a  line  rigorously  between  transudation  and  some  of  the  phe- 
nomena of  secretion ;  particularly  as  experiments  upon  dialysis  have  shown 
that  simple,  osmotic  membranes  are  capable  of  separating  complex  solutions, 
allowing  certain  constituents  to  pass  much  more  freely  than  others.  This 
fact  explains  why  the  transuded  fluids  do  not  contain  all  the  soluble  con- 
stituents of  the  blood  in  the  proportions  in  which  they  exist  in  the  plasma. 
All  the  secreted  fluids,  both  the  true  secretions  and  the  excretions,  contain 
many  of  the  inorganic  salts  of  the  blood-plasma. 

Mechanism  of  the  Production  of  the  True  Secretions. — Although  the 
characteristic  constituents  of  the  true  secretions  are  not  to  be  found  in  the 
blood  or  in  any  other  of  the  animal  fluids,  they  can  generally  be  extracted 
from  the  glands,  particularly  during  their  intervals  of  so-called  repose.  This 
fact  has  been  repeatedly  demonstrated  with  regard  to  many  of  the  digestive 
fluids,  as  the  saliva,  the  gastric  juice  and  the  pancreatic  juice ;  and  artificial 
fluids,  possessing  certain  of  the  physiological  properties  of  the  natural  secre- 
tions, have  been  prepared  by  simply  extracting  the  glandular  tissue  with  water. 
There  can  be  no  doubt,  therefore,  that  during  the  periods  when  the  secre- 
tions are  not  discharged,  the  glands  are  taking  from  the  blood  matters  which 
are  to  be  transformed  into  the  characteristic  constituents  of  the  individual 
secretions,  and  that  this  process  is  constant,  bearing  a  close  resemblance  to 
the  general  act  of  nutrition.  There  are  certain  anatomical  elements  in  the 
glands,  which  have  the  power  of  selecting  the  proper  materials  from  the 
blood  and  causing  them  to  undergo  peculiar  transformations ;  in  the  same 
way  that  the  muscular  tissue  takes  from  the  nutritive  fluid  albuminoid  mat- 


PRODUCTION  OF  THE  SECRETIONS.  309 

ters  and  transforms  them  into  its  own  substance.  The  exact  nature  of  this 
property  is  unexplained. 

In  all  of  the  secreting  organs,  epithelium  is  found  which  seems  to  possess 
the  power  of  forming  the  peculiar  constituents  of  the  different  secretions. 
The  epithelial  cells  lining  the  tubes  or  follicles  of  the  glands  constitute  the 
only  peculiar  structures  of  these  parts,  the  rest  being  made  up  of  basement- 
membrane,  connective  tissue,  blood-vessels,  nerves,  and  other  structures  which 
are  distributed  generally  in  the  economy ;  and  these  cells  alone  contain  the 
constituents  of  the  secretions.  It  has  been  found,  for  example,  that  the 
liver-cells  contain  the  glycogen  formed  by  the  liver ;  and  it  has  been  farther 
shown  that  when  the  cellular  structures  of  the  pancreas  have  been  destroyed, 
the  secretion  is  no  longer  produced.  There  can  be  hardly  any  doubt  with 
regard  to  the  application  of  this  principle  to  the  glands  generally,  both  secre- 
tory and  excretory.  Indeed,  it  is  well  known  to  pathologists,  that  when  the 
tubes  of  the  kidney  have  become  denuded  of  their  epithelium,  they  are  no 
longer  capable  of  separating  from  the  blood  the  peculiar  constituents  of  the 
urine. 

With  regard  to  the  origin  of  the  characteristic  constituents  to  the  true 
secretions,  it  is  impossible  to  entertain  any  other  view  than  that  they  are  pro- 
duced in  the  epithelial  structures  of  the  glands.  While  the  secretions  con- 
tain inorganic  salts  in  solution  transuded  from  the  blood,  the  organic  con- 
stituents, such  as  ptyaline,  pepsine,  trypsine  etc.,  are  readily  distinguished 
from  all  other  albuminoid  substances,  by  their  peculiar  physiological  proper- 
ties. 

It  may  be  stated,  then,  as  a  general  proposition,  that  the  characteristic 
constituents  of  the  true  secretions,  as  contradistinguished  from  the  excre- 
tions, are  formed  by  the  epithelial  structures  of  the  glands,  out  of  materials 
furnished  mainly  by  the  blood.  Their  formation  is  by  no  means  confined  to 
what  is  usually  termed  the  period  of  activity  of  the  glands,  or  the  time  when 
the  secretions  are  poured  out,  but  it  takes  place  more  or  less  constantly  when 
no  fluid  is  discharged.  It  is  more  than  probable,  indeed,  that  the  formation 
of  the  peculiar  and  characteristic  constituents  of  the  secretions  takes  place 
with  as  much  activity  in  the  intervals  of  secretion  as  during  the  discharge 
of  fluid ;  and  most  of  the  glands  connected  with  the  digestive  system  seem 
to  require  certain  intervals  of  repose  and  are  capable  of  discharging  their 
secretions  for  a  limited  time  only. 

When  a  secreting  organ  is  called  into  activity — like  the  gastric  mucous 
membrane  or  the  pancreas,  upon  the  introduction  of  food  into  the  aliment- 
ary canal — a  marked  change  in  its  condition  takes  place.  The  circulation 
in  the  part  is  then  very  much  increased  in  activity,  thus  furnishing  water 
and  the  inorganic  constituents  of  the  secretion.  This  difference  in  the  quan- 
tity of  blood  in  the  glands  during  their  activity  is  very  marked  when  the 
organs  are  exposed  in  a  living  animal,  and  is  one  of  the  important  facts  bear- 
ing upon  the  mechanism  of  secretion. 

In  all  the  secretions  proper,  there  are  intervals,  either  of  complete  re- 
pose, as  is  the  case  with  the  gastric  juice  or  the  pancreatic  juice,  or  periods 


310  SECRETION. 

when  the  activity  of  the  secretion  is  very  greatly  diminished,  as  in  the  saliva. 
These  periods  of  repose  seem  to  be  necessary  to  the  proper  action  of  the 
secreting  glands ;  forming  a  marked  contrast  with  the  constant .  action  of 
organs  of  excretion.  It  is  well  known,  for  example,  that  digestion  is  seri- 
ously disturbed  when  the  act  is  too  prolonged  on  account  of  the  habitual  in- 
gestion  of  an  excessive  quantity  of  food. 

From  the  considerations  already  mentioned,  it  is  evident  that  the  charac- 
teristic constituents  of  the  true  secretions  are  formed  by  the  epithelial 
structures  of  the  glands.  While  the  mechanism  of  this  process  is  not  under- 
stood in  all  its  details  as  regards  all  of  the  secretions,  in  some  of  the  glands 
the  processes  have  been  studied  with  tolerably  definite  results.  In  some  of 
the  salivary  glands,  in  the  peptic  cells  and  in  the  cells  of  the  pancreas,  it 
has  been  shown  that  the  so-called  ferments  are  not  formed  directly. 
The  secreting  cells  are  apparently  divided  into  two  portions,  or  zones ;  an 
outer  zone,  which  is  next  the  tubular  membrane,  and  an  inner  zone,  next 
the  lumen  of  the  tube  or  follicle.  In  the  inner  zone,  during  the  intervals 
of  actual  secretion,  there  appears  a  substance,  which  at  the  time  when  the 
secretion  is  formed  and  is  poured  out,  is  changed  into  the  true  ferment, 
or  active  principle  of  the  secretion ;  so  that  there  is  probably  a  zymogenic, 
or  ferment-forming  substance,  first  produced  by  the  cells.  The  substance, 
if  such  a  substance  exists,  out  of  which  ptyaline  is  formed,  has  not  been 
described  ;  but  in  the  viscid  forms  of  saliva,  there  appears  to  be  first  formed 
a  substance  called  mucinogen,  afterward  changed  into  mucine,  upon  which 
the  viscidity  of  the  fluid  depends. 

In  the  salivary  glands  which  produce  viscid  secretions,  the  submaxillary 
and  sublingual,  the  parenchyma  presents  two  kinds  of  acini,  serous  and 
mucous.  The  so-called  serous  acini  are  the  more  abundant  and  are  thought 
to  produce  the  true  saliva,  while  the  mucous  acini  secrete  the  viscid  con- 
stituents of  the  saliva. 

In  the  production  of  pepsine,  the  inner  zone  of  the  peptic  cells  first 
forms  pepsinogen,  which  is  changed  into  pepsine  as  it  is  discharged  from 
the  glands.  In  the  pancreas,  trypsinogen  is  formed  in  the  inner  zone  of  the 
cells,  and  this  is  changed  into  trypsine.  The  general  name  zymogen  has 
been  given  to  the  substances  which  are  changed  into  the  digestive  ferments  ; 
although,  as  is  evident,  this  substance  is  not  identical  in  the  different  glands. 
The  formation  of  the  ferments  of  the  true  secretions  is  analogous  in  its  na- 
ture to  certain  of  the  nutritive  processes. 

The  theory  that  the  discharge  of  the  secretions  is  due  simply  to  mechan- 
ical causes  and  is  attributable  solely  to  the  increase  in  the  pressure  of  blood 
can  not  be  sustained.  Pressure  undoubtedly  has  considerable  influence  upon 
the  activity  of  secretion ;  but  the  flow  will  not  always  take  place  in  obedi- 
ence to  simple  pressure,  and  secretion  may  be  excited  for  a  limited  time 
without  any  increase  in  the  quantity  of  blood  circulating  in  the  gland. 

The  glands  possess  a  peculiar  excitability,  which  is  manifested  by  their 
action  in  response  to  proper  stimulation.  During  secretion,  they  generally 
receive  an  increased  quantity  of  blood ;  but  this  is  not  indispensable,  and 


PRODUCTION  OF  THE  EXCRETIONS.  311 

secretion  may  be  excited  without  any  modification  of  the  circulation.  This 
excitability  will  disappear  Avhen  the  artery  supplying  the  part  with  blood  is 
tied  for  a  number  of  hours ;  and  secretion  can  not  then  be  excited  even 
when  the  blood  is  again  allowed  to  circulate.  If  the  gland  be  not  deprived 
of  blood  for  too  long  a  period,  the  excitability  is  soon  restored ;  but  it  may- 
be permanently  destroyed  by  depriving  the  part  of  blood  for  a  long  time. 
These  facts  show  a  certain  similarity  between  glandular  and  muscular  excita- 
bility, although  these  properties  are  manifested  in  very  different  ways. 

Mechanism  of  the  Production  of  the  Excretions. — Certain  of  the  glands 
separate  from  the  blood  excrementitious  matters  which  are  of  no  use  in  the 
economy  and  are  simply  discharged  from  the  body.  These  matters,  which 
will  be  fully  considered,  both  in  connection  with  the  fluids  of  which  they 
form  a  part  and  under  the  head  of  nutrition,  are  entirely  different  in  their 
mode  of  production  from  the  characteristic  constituents  of  the  secretions. 
The  formation  of  excrementitious  matters  takes  place  in  the  tissues  and  is 
connected  with  the  general  process  of  nutrition;  and  in  the  excreting 
glands  there  is  simply  a  separation  of  products  already  formed.  The  action 
of  the  excreting  organs  is  constant,  and  there  is  not  that  regular,  periodic 
increase  in  the  activity  of  the  circulation  which  is  observed  in  secreting 
organs  ;  but  it  has  been  observed  that  the  blood  which  comes  from  the  kid- 
neys is  nearly  as  red  as  arterial  blood,  showing  that  the  quantity  of  blood 
which  these  organs  receive  is  greater  than  is  required  for  mere  nutrition,  the 
excess,  as  in  the  secreting  organs,  furnishing  the  water  and  inorganic  salts 
that  are  found  in  the  urine.  It  has  also  been  shown  that  when  the  secre- 
tion of  urine  is  interrupted,  the  blood  of  the  renal  veins  becomes  dark  like 
the  blood  in  the  general  venous  system. 

Excretion  is  not,  under  all  conditions,  confined  to  the  ordinary  excre- 
tory organs,  When  their  action  is  disturbed,  certain  of  the  secreting  glands, 
as  the  follicles  of  the  stomach  and  intestine,  may  for  a  time  eliminate  excre- 
mentitious matters ;  but  this  is  abnormal  and  is  analogous  to  the  elimination 
of  foreign  matters  from  the  blood  by  the  glands. 

Influence  of  the  Composition  and  Pressure  of  the  Blood  upon  Secretion. — 
Under  normal  conditions,  the  composition  of  the  blood  has  little  to  do  with 
the  action  of  the  secreting  organs,  as  it  simply  furnishes  the  materials  out  of 
which  the  characteristic  constituents  of  the  secretions  are  formed ;  but  when 
certain  foreign  matters  are  taken  into  the  system  or  are  injected  into  the 
blood-vessels,  they  are  eliminated  by  the  different  glandular  organs,  both 
secretory  and  excretory.  These  organs  seem  to  possess  a  power  of  selection 
in  the  elimination  of  different  substances.  Thus,  sugar  and  potassium  fer- 
rocyanide  are  eliminated  in  greatest  quantity  by  the  kidneys ;  the  salts  of 
iron,  by  the  kidneys  and  the  gastric  tubules ;  and  iodine,  by  the  salivary 
glands. 

The  discharge  of  secretions  is  almost  always  accompanied  with  an  in- 
crease in  the  pressure  of  blood  in  the  vessels  supplying  the  glands ;  and  it 
has  been  shown,  on  the  other  hand,  that  an  exaggeration  in  the  pressure,  if 
the  nerves  of  the  glands  do  not  exert  an  opposing  influence,  increases  the 


312  SECRETION. 

activity  of  secretion.  The  experiments  of  Bernard  on  this  point  show  the 
influence  of  pressure  upon  the  salivary  and  renal  secretions,  particularly  the 
latter.  After  inserting  a  tube  into  one  of  the  ureters  of  a  living  animal,  so 
that  the  activity  of  the  renal  secretion  could  be  accurately  observed,  the 
pressure  in  the  renal  artery  was  increased  by  tying  the  crural  and  the 
brachial.  It  was  then  found  that  the  flow  of  urine  was  markedly  increased. 
The  pressure  was  afterward  diminished  by  the  abstraction  of  blood,  which 
was  followed  by  a  corresponding  diminution  in  the  quantity  of  urine.  The 
same  phenomena  were  observed  in  analogous  experiments  upon  the  submax- 
illary  secretion.  These  facts,  however,  do  not  demonstrate  that  secretion  is 
due  simply  to  an  increase  in  the  pressure  of  blood  in  the  glands,  although 
this  undoubtedly  exerts  an  important  influence.  It  is  necessary  that  every 
condition  should  be  favorable  to  the  act  of  secretion  for  this  influence  to  be 
effective.  Experiments  have  shown  that  pain  may  completely  arrest  the 
secretion  of  urine,  operating  undoubtedly  through  the  nervous  system.  If 
the  flow  of  urine  be  arrested  by  pain,  an  increase  in  the  pressure  of  blood  in 
the  part  falls  to  excite  the  secretion. 

Influence  of  the  Nervous  System  on  Secretion. — The  fact  that  the  secre- 
tions are  generally  intermittent  in  their  flow,  being  discharged  in  obedi- 
ence to  impressions  which  are  made  only  when  there  is  a  demand  for  their 
physiological  action,  would  naturally  lead  to  the  supposition  that  they  are 
regulated,  to  a  great  extent,  through  the  nervous  system ;  particularly  as  it 
is  now  well  established  that  the  nerves  are  capable  of  modifying  and  regulat- 
ing local  circulations.  The  same  facts  apply,  to  a  certain  extent,  to  the 
excretions,  which  are  also  subject  to  considerable  modifications. 

It  is  evident  that  the  nervous  system  has  an  important  influence  in  the 
production  of  the  secretions ;  and  this  is  exerted  largely  through  modifica- 
tions in  the  activity  of  the  circulation  in  the  glands.  This  takes  place  in 
greatest  part  through  vaso-motor  nerves  distributed  to  the  muscular  coats  of 
the  arteries  of  supply.  When  these  nerves  are  divided,  the  circulation  is  in- 
creased here,  as  in  other  situations,  and  secretion  is  the  result ;  and  if  the 
extremity  of  the  nerve  connected  with  the  gland  be  stimulated,  contraction 
of  the  vessels  follows,  and  the  secretion  is  arrested. 

"With  regard  to  many  of  the  glands,  it  has  been  shown  that  the  influence 
of  the  vaso-motor  nerves  is  antagonized  by  certain  other  nerves,  which  latter 
are  called  the  motor  nerves  of  the  glands.  The  motor  nerve  of  the  submax- 
illary  is  the  chorda  tympani ;  and  as  both  this  nerve  and  the  sympathetic, 
which  latter  contains  the  vaso-motor  filaments,  together  with  the  excretory 
duct  of  the  gland,  can  be  easily  exposed  and  operated  upon  in  a  living  animal, 
many  experiments  have  been  performed  upon  this  gland.  When  all  these 
parts  are  exposed  and  a  tube  is  introduced  into  the  salivary  duct,  division  of 
the  sympathetic  induces  secretion,  with  an  increase  in  the  circulation  in  the 
gland,  the  blood  in  the  vein  becoming  red.  On  the  other  hand,  division 
of  the  chorda  tympani,  the  sympathetic  being  intact,  arrests  secretion,  and 
the  venous  blood  coming  from  the  gland  becomes  dark.  If  the  nerves  be  now 
stimulated  alternately,  it  will  be  found  that  stimulation  of  the  sympathetic 


INFLUENCE  OF  THE  NERVOUS  SYSTEM  ON  SECRETION.      313 

produces  contraction  of  the  vessels  of  the  gland  and  arrests  secretion,  while  a 
stimulus  applied  to  the  chorda  tympani  increases  the  circulation  and  excites 
secretion  (Bernard).  Enough  is  known  of  the  nervous  influences  which 
modify  secretion,  to  admit  of  the  inference  that  all  the  glands  are  supplied 
with  nerves  through  which  certain  reflex  phenomena,  affecting  their  secre- 
tions, take  place. 

As  reflex  phenomena  involve  the  action  of  nerve-centres,  it  becomes  a 
question  to  determine  whether  any  particular  parts  of  the  central  nervous 
system  preside  over  the  various  secretions.  Experiments  showing  the  exist- 
ence of  such  centres  are  not  wanting,  but  it  will  be  more  convenient  to  treat 
of  these  in  connection  with  the  physiology  of  the  individual  secretions. 

Mental  emotions,  pain,  and  various  conditions,  the  influence  of  which 
upon  secretion  has  long  been  observed,  operate  through  the  nervous  system. 
Many  familiar  instances  of  this  kind  are  mentioned  in  works  on  physiology : 
such  as  the  secretion  of  tears ;  arrest  or  production  of  the  salivary  secretions ; 
sudden  arrest  of  the  secretion  of  the  mammary  glands,  from  violent  emotion ; 
increase  in  the  secretion  of  the  kidneys  or  of  the  intestinal  tract,  from  fear 
or  anxiety ;  with  other  examples  which  it  is  unnecessary  to  enumerate. 

Paralytic  Secretion  ly  Glands. — The  effects  of  destruction  of  the  nerves 
distributed  to  the  parenchyma  of  some  of  the  glandular  organs  are  very  re- 
markable. Miiller  and  Peipers  destroyed  the  nerves  distributed  to  the  kidney 
and  found  that  not  only  was  the  secretion  arrested  in  the  great  majority  of 
instances,  but  the  renal  tissue  became  softened  and  broken  down.  Ber- 
nard found  that  animals  operated  upon  in  this  way  died,  and  that  the  tissue 
of  the  kidney  was  broken  doAvn  into  a  fetid,  semi-fluid  mass.  After  division 
of  the  nerves  of  the  salivary  glands,  the  organs  became  atrophied,  but  they 
did  not  undergo  the  peculiar  putrefactive  change  which  was  observed  in  the 
kidneys.  The  same  effect  was  produced  when  the  nerves  were  paralyzed  by 
introducing  a  few  drops  of  a  solution  of  curare  at  the  origin  of  the  little 
artery  which  is  distributed  to  the  submaxillary  gland.  It  is  possible  that 
other  glands  have  so-called  motor-nerves,  stimulation  of  which  excites  secre- 
tion, but  such  nerves  have  been  most  satisfactorily  isolated  and  studied  in 
connection  with  the  salivary  secretions.  When  the  motor-nerves  of  the  sali- 
vary glands  are  divided,  in  the  course  of  a  day  or  two,  the  secretion  becomes 
abundant  and  watery,  losing  its  normal  characters.  After  about  eight  days, 
the  secretion  begins  to  diminish  and  the  glands  undergo  atrophy.  The  in- 
creased secretion  first  observed  has  been  called  "paralytic."  The  watery 
secretion  discharged  from  a  permanent  pancreatic  fistula  is  thought  to  be 
paralytic ;  and  certainly  it  does  not  present  the  physiological  properties  of 
normal  pancreatic  juice. 

Anatomical  Classification  of  Glandular  Organs. — The  organs  which 
produce  the  different  secretions  are  susceptible  of  a  classification  according 
to  their  anatomical  peculiarities,  which  greatly  facilitates  their  study.  They 
may  be  divided  as  follows : 

1.  Secreting  membranes. — Examples  of  these  are  the  synovial  mem- 
branes. 


3U  SECRETION. 

2.  Follicular  glands. — Examples  of  these  are  the  simple  mucous  follicles, 
the  follicles  of  Lieberklihn  and  the  uterine  follicles. 

3.  Tubular  glands. — Examples  of  these  are  the  ceruminous  glands,  the 
sudoriparous  glands  and  the  kidneys. 

4.  Racemose  glands,  simple  and  compound. — Examples  of  the  simple 
racemose  glands  are  the  sebaceous  and  Meibomian   glands,  the  tracheal 
glands  and  the  glands  of  Brunner.     Examples  of  the  compound  racemose 
glands  are  the  salivary  glands,  the  pancreas,  the  lachrymal  glands  and  the 
mammary  glands. 

5.  Ductless,  or  blood-glands. — Examples  of  these  are  the  thymus,  the 
thyroid,  the  suprarenal  capsules  and  the  spleen. 

The  liver  is  a  glandular  organ  which  can  not  be  placed  in  any  one  of  the 
above  divisions.  The  lymphatic  glands  and  other  parts  connected  with  the 
lymphatic  and  the  lacteal  system  are  not  true  glandular  organs ;  and  these 
are  sometimes  called  conglobate  glands. 

The  general  structure  of  secreting  membranes  and  of  the  follicular 
glands  is  very  simple.  The  secreting  parts  consist  of  a  membrane,  gen- 
erally homogeneous,  covered  on  the  secreting  surface  with  epithelial  cells. 
Beneath  this  membrane,  ramify  the  blood-vessels  which  furnish  materials 
for  the  secretions.  The  follicular  glands  are  simply  digital  inversions  of 
this  structure,  with  rounded,  blind  extremities,  the  epithelium  lining  the  fol- 
licles. 

The  tubular  glands  have  essentially  the  same  structure  as  the  follicles, 
except  that  the  tubes  are  long  and  are  more  or  less  convoluted.  The  more 
complex  of  these  organs  contain  connective  tissue,  blood-vessels,  nerves  and 
lymphatics. 

The  compound  racemose  glands  are  composed  of  branching  ducts,  around 
the  extremities  of  which  are  arranged  collections  of  rounded  follicles,  like 
bunches  of  grapes.  In  addition  to  the  epithelium,  basement-membrane  and 
blood-vessels,  these  organs  contain  connective  tissue,  lymphatics,  non-striated 
muscular  fibres,  and  nerves.  In  the  simple  racemose  glands  the  excretory 
duct  does  not  branch. 

The  ductless  glands  contain  blood-vessels,  lymphatics,  nerves,  sometimes 
non-striated  muscular  fibres,  and  a  peculiar  structure  called  pulp,  which  is 
composed  of  fluid  with  cells  and  occasionally  with  closed  vesicles.  These 
are  sometimes  called  blood-glands,  because  they  are  supposed  to  modify  the 
blood  as  it  passes  through  their  substance. 

The  testicles  and  the  ovaries  are  not  simply  glandular  organs;  for  in 
addition  to  the  production  of  mucous  or  watery  secretions,  their  principal 
office  is  to  develop  certain  anatomical  elements,  the  spermatozoids  and  the 
ova.  The  physiology  of  these  organs  will  be  considered  in  connection  with 
the  physiology  of  generation. 

Classification  of  the  Secreted  Fluids.— The  products  of  the  various  glands 
may  be  divided,  according  to  their  uses,  into  secretions  proper  and  excretions. 
Some  of  the  true  secretions  have  certain  mechanical  uses,  and  some,  like 
mucus,  are  thrown  off  in  small  quantity  without  being  actually  excremen- 


SYNOVIAL  MEMBRANES  AND  SYNOVIA.  315 

titious ;  while  others,  like  most  of  the  digestive  fluids,  are  produced  at  certain 
intervals  and  are  taken  up  again  by  the  blood. 

TABULAR   VIEW   OF   THE   SECRETED    FLUIDS. 
Secretions  Proper. 


Synovia. 

Mucus,  in  many  varieties. 

Sebaceous  matter. 

Cerumen,  the  waxy  secretion  of  the  external 

auditory  meatus. 
Meibomian  fluid. 
Milk  and  colostrum. 
Tears. 


Saliva. 

Gastric  juice. 
Pancreatic  juice. 

Secretion  of  the  glands  of  Brunner. 
Secretion  of  the  follicles  of  Lieberkiihn. 
Secretion  of  the  follicles  of  the  large  intes- 
tine. 
Bile  (also  an  excretion). 


Excretions. 


Perspiration  and  the  secretion  of  the  axillary 
glands. 


Urine. 

Bile  (also  a  secretion). 


Fluids  containing  Formed  Anatomical  Elements. 
Seminal  fluid,  containing,  in  addition  to  spermatozoids,  the  secretions  of  a  number  of 

glandular  structures. 
Fluid  of  the  Graaflan  follicles. 

The  serous  cavities  are  now  regarded  as  sacs  connected  with  the  lym- 
phatic system,  and  the  liquids  of  these  cavities  are  not  classed  with  the  secre- 
tions. 

Synovial  Membranes  and  Synovia. — The  true  synovial  membranes  are 
found  in  the  diarthrodial,  or  movable  articulations ;  but  in  various  parts  of 
the  body  are  found  closed  sacs,  sheaths  etc.,  which  resemble  synovial  mem- 
branes both  in  structure  and  in  their  office.  Every  movable  joint  is  envel- 
oped in  a  capsule,  which  is  closely  adherent  to  the  edges  of  the  articular 
cartilage  and  is  even  reflected  upon  its  surface  for  a  short  distance ;  but  it  is 
now  the  general  opinion  that  the  cartilage  which  incrusts  the  articulating 
extremities  of  the  bones,  though  bathed  in  synovial  fluid,  is  not  itself  cov- 
ered by  a  distinct  membrane. 

The  fibrous  portion  of  the  synovial  membranes  is  dense  and  resisting.  It 
is  composed  of  ordinary  fibrous  tissue,  with  a  few  elastic  fibres,  and  blood- 
vessels. The  internal  surface  is  lined  with  small  cells  of  flattened  endothe- 
lium  with  rather  large,  rounded  nuclei.  These  cells  exist  in  one,  two,  three 
or  sometimes  four  layers. 

In  most  of  the  joints,  especially  those  of  large  size,  as  the  knee  and  the 
hip,  the  synovial  membrane  is  thrown  into  folds  which  contain  adipose  tis- 
sue. In  nearly  all  the  joints,  the  membrane  presents  fringed,  vascular  pro- 
cesses, called  synovial  fringes.  These  are  composed  of  looped  vessels  of  con- 
siderable size ;  and  when  injected  they  bear  a  certain  resemblance  to  the 
choroid  plexus.  The  edges  of  these  fringes  present  a  number  of  leaf-like, 
membranous  appendages,  of  a  great  variety  of  curious  forms.  They  are  gen- 
erally situated  near  the  attachment  of  the  membrane  to  the  cartilage. 

The  arrangement  of  the  synovial  bursse  is  very  simple.  Wherever  a  ten- 
don plays  over  a  bony  surface,  there  is  a  delicate  membrane  in  the  form  of 


316  SECEETION. 

an  irregularly  shaped,  closed  sac,  one  layer  of  which  is  attached  to  the  ten- 
don, and  the  other,  to  the  bone.  These  sacs  are  lined  with  an  endothelium 
like  that  found  in  the  synovial  cavities,  and  they  secrete  a  true  synovial  fluid. 
Btirsse  are  also  found  beneath  the  skin,  especially  in  parts  where  the  integu- 
ment moves  over  bony  prominences,  as  the  olecranon,  the  patella  and  the 
tuberosities  of  the  ischium.  These  sacs,  sometimes  called  bursse  mucosaa,  are 
much  more  common  in  man  than  in  the  inferior  animals,  and  they  have  essen- 
tially the  same  uses  as  the  deep-seated  bursae.  The  form  of  both  the  super- 
ficial and  deep-seated  bursae  is  very  irregular,  and  their  interior  is  frequently 
traversed  by  small  bands  of  fibrous  tissue.  The  synovial  sheaths,  or  vaginal 
processes,  line  the  canals  in  which  the  long  tendons  play,  particularly  the 
tendons  of  the  flexors  and  extensors  of  the  fingers  and  toes.  They  have 
essentially  the  same  structure  as  the  bursae,  and  present  two  layers,  one  of 
which  lines  the  canal,  while  the  other  is  reflected  over  the  tendon.  The  vas- 
cular folds,  described  in  connection  with  the  articular  synovial  membranes, 
are  found  in  many  of  the  bursas  and  the  synovial  sheaths. 

The  quantity  of  synovia  in  the  joints  is  sufficient  to  lubricate  freely  the 
articulating  surfaces.  In  a  horse  of  medium  size  and  in  good  condition, 
examined  immediately  after  death,  Colin  found  1*6  fluidrachm  (6  c.  c.)  in 
the  shoulder-joint ;  1-9  drachm  (7  c.  c.)  in  the  elbow-joint ;  1-6  drachm  (6 
c.  c.)  in  the  coxo-femoral  articulation ;  2'2  drachms  (8  c.  c.)  in  the  femoro- 
tibial  articulation ;  and  1-9  drachm  (7  c.  c.)  in  the  tibio-tarsal  articulation. 

When  perfectly  normal,  the  synovial  fluid  is  either  colorless  or  of  a  pale, 
yellowish  tinge.  It  is  so  viscid  that  it  is  with  difficulty  poured  from  one  ves- 
sel into  another.  This  peculiar  character  is  due  to  the  presence  of  an  organic 
substance  called  synovine.  When  this  organic  matter  has  been  extracted 
and  mixed  with  water,  it  gives  to  the  fluid  the  peculiar  viscidity  of  the  syno- 
vial secretion.  The  reaction  of  the  fluid  is  faintly  alkaline,  on  account  of  the 
presence  of  a  small  proportion  of  sodium  carbonate.  The  fluid,  especially 
when  the  joints  have  been  much  used,  usually  contains  in  suspension  pale 
endothelial  cells  and  a  few  leucocytes.  According  to  Robin,  the  synovia  of 
the  human  subject  contains  about  sixty-four  parts  per  thousand  of  organic 
matter,  with  sodium  chloride,  sodium  carbonate,  calcium  phosphate  and  am- 
monio-magnesian  phosphate. 

The  synovial  secretion  is  produced  by  the  general  surface  of  the  mem- 
brane and  not  by  any  special  organs.  The  folds  and  fringes  which  have  been 
described  were  at  one  time  supposed  to  be  most  active  in  secreting  the  organic 
matter,  but  there  is  no  evidence  that  they  have  any  such  special  office. 

Mucous  Membranes  and  Mucus. — A  distinct  anatomical  division  of  the 
mucous  membranes  may  be  made  into  two  classes ;  first,  those  provided  with 
squamous  epithelium,  and  second,  those  provided  with  columnar  or  conoidal 
epithelium.  All  of  the  mucous  membranes  line  cavities  or  tubes  communica- 
ting with  the  exterior  by  the  different  openings  in  the  body. 

The  following  are  the  principal  situations  in  which  the  first  variety 
of  mucous  membranes,  covered  with  squamous  epithelium,  is  found:  the 
mouth,  the  lower  part  of  the  pharynx,  the  oesophagus,  the  conjunctiva,  the 


MUCOUS  MEMBRANES  AND  MUCUS.          317 

female  urethra  and  the  vagina.  In  these  situations  the  membrane  is  com- 
posed of  a  chorion  made  up  of  inelastic  and  elastic  fibrous  tissue,  with  capil- 
laries, lymphatics  and  nerves.  The  elastic  fibres  are  small  and  quite  abun- 
dant. The  membrane  itself  is  loosely  united  to  the  subjacent  parts.  The 
chorion  is  provided  with  vascular  papilla?,  more  or  less  marked ;  but  in  all 
situations,  except  in  the  pharynx,  the  epithelial  covering  fills  up  the  spaces 
between  these  papillae,  so  that  the  membrane  presents  a  smooth  surface. 
Between  the  chorion  and  the  epithelium,  is  an  amorphous  basement-mem- 
brane. The  mucous  glands  open  upon  the  surface  of  the  membrane  by  their 
ducts,  but  the  glandular  structure  is  situated  in  the  submucous  tissue.  Certain 
of  these  glands  have  been  described  in  connection  with  the  anatomy  of  the 
mucous  membrane  of  the  mouth,  pharynx  and  oesophagus.  They  generally 
are  simple  racemose  glands,  presenting  a  collection  of  follicles  arranged  around 
the  extremity  of  a  single  excretory  duct,  and  lined  or  filled  with  rounded, 
nucleated  epithelium.  The  squamous  epithelium  covering  these  membranes 
exists  generally  in  several  layers  and  presents  great  variety,  both  in  form  and 
size.  The  most  superficial  layers  are  of  large  size,  flattened  and  irregularly 
polygonal.  The  deeper  layers  are  smaller  and  more  rounded.  The  size  of 
these  cells  is  2g*0o  to  -^  of  an  inch  (10  to  83  p).  The  cells  are  pale  and 
slightly  granular,  each  with  a  small,  ovoid  nucleus  and  one  or  two  nucleoli. 

The  second  variety  of  mucous  membranes,  covered  with  columnar  epi- 
thelium, is  found  lining  the  alimentary  canal  below  the  cardiac  orifice  of  the 
stomach,  the  biliary  passages,  the  excretory  ducts  of  all  the  glands,  the  nasal 
passages,  the  upper  part  of  the  pharynx,  the  uterus  and  Fallopian  tubes, 
the  bronchia,  the  Eustachian  tubes  and  the  male  urethra.  In  certain  situ- 
ations this  variety  of  epithelium  is  provided  on  its  free  surface  with  little 
hair-like  processes  called  cilia.  During  life  the  cilia  are  in  constant  motion, 
producing  a  current  generally  in  the  direction  of  the  mucous  orifices.  Ciliated 
epithelium  is  found  throughout  the  nasal  passages,  beginning  about  three- 
quarters  of  an  inch  (19'1  mm.)  within  the  nose;  in  the  upper  part  of  the 
pharynx ;  the  posterior  surface  of  the  soft  palate ;  the  Eustachian  tube  ;  the 
tympanic  cavity ;  the  larynx,  trachea,  and  bronchial  tubes,  until  they  become 
less  than  -1$  of  an  inch  (Oo  mm.)  in  diameter;  the  neck  and  body  of  the 
uterus ;  the  Fallopian  tubes ;  the  internal  surface  of  the  eyelids ;  and  the 
ventricles  of  the  brain.  Mucous  membranes  of  this  variety  are  formed  of  a 
chorion,  a  basement-membrane  and  epithelium.  The  chorion  is  composed  of 
inelastic  and  elastic  fibres,  a  few  non-striated  muscular  fibres,  amorphous  mat- 
ter, blood-vessels,  nerves  and  lymphatics.  It  is  less  dense  and  less  elastic 
than  the  chorion  of  the  first  variety  and  generally  is  more  closely  united  to 
the  subjacent  tissue.  The  surface  of  these  membranes  is  generally  smooth, 
the  only  exception  being  the  mucous  membrane  of  the  pyloric  portion  of  the 
stomach  and  the  small  intestines.  These  membranes  are  provided  with  fol- 
licular  glands,  extending  through  their  entire  thickness  and  terminating  in 
rounded  extremities,  sometimes  single  and  sometimes  double,  Avhich  rest  upon 
the  submucous  structure.  Many  of  them  are  provided  also  with  simple  race- 
mose glands,  the  ducts  passing  through  the  membrane,  and  the  glandular 
22 


318  SECRETION. 

structure  being  situated  in  the  submucous  areolar  tissue.  The  columnar  epi- 
thelium covering  these  membranes  rests  upon  an  amorphous  structure  called 
basement-membrane.  The  epithelium  generally  presents  but  few  layers,  and 
sometimes,  as  in  the  intestinal  canal,  there  is  only  a  single  layer.  The  cells 
are  prismoidal,  with  a  large,  free  extremity,  and  a  pointed  end  which  is  at- 
tached. The  cells  of  the  lower  strata  are  shorter  and  more  rounded  than 
those  in  the  superficial  layer.  The  cells  are  pale  and  very  closely  adherent 
to  each  other  by  their  sides,  each  with  a  moderate-sized,  oval  nucleus  and  one 
or  two  nucleoli.  The  length  of  the  cells  is  -^  to  g-J¥  of  an  inch  (30  to  40  /z,), 
and  their  diameter,  ?T5Vo  to  ^^THT  °f  an  incn  (8  to  10  /*).  When  villosities 
exist  on  the  surface  of  the  membranes,  the  cells  follow  the  elevations  and  do 
not  fill  up  the  spaces  between  them,  as  in  most  of  the  membranes  covered 
with  squamous  epithelium. 

The  mucous  membrane  of  the  urinary  bladder,  of  the  ureters  and  of  the 
pelvis  of  the  kidneys  can  not  be  classed  in  either  of  the  above  divisions.  In 
these  situations  the  membrane  is  covered  with  mixed  epithelium,  presenting 
all  varieties  of  form  between  the  squamous  and  the  columnar,  some  of  the 
cells  being  caudate  and  quite  irregular  in  shape. 

Mechanism  of  the  Secretion  of  Mucus. — Nearly  every  one  of  the  many 
fluids  known  under  the  name  of  mucus  is  composed  of  the  products  of  sev- 
eral different  glandular  structures.  Certain  membranes  which  do  not  possess 
glands,  as  the  mucous  lining  of  the  ureters  and  of  a  great  portion  of  the 
urinary  bladder,  are  capable  of  secreting  mucus.  The  mucous  membrane  of 
.the  stomach  produces  an  alkaline,  viscid  secretion,  during  the  intervals  of  di- 
gestion, when  the  gastric  glands  do  not  act ;  and  the  gastric  glands,  during 
digestion,  secrete  a  fluid  of  an  entirely  different  character.  The  fluid  pro- 
duced by  the  follicles  of  the  small  intestine  likewise  has  peculiar  digestive 
properties.  These  considerations  and  the  fact  that  the  entire  extent  of  the 
mucous  membranes  is  covered  with  more  or  less  secretion  show  that  the  gen- 
eral epithelial  covering  of  these  membranes  is  capable  of  secreting  a  fluid 
which  forms  one  of  the  constituents  of  what  is  ordinarily  recognized  as 
mucus.  It  is  impossible,  however,  to  separate  the  secretion  of  the  superficial 
layer  of  cells  from  the  other  fluids  that  are  found  on  the  mucous  membranes ; 
and  it  will  be  more  convenient  to  regard  as  mucus,  the  secretion  which  is 
found  upon  mucous  membranes,  except  when,  as  in  the  case  of  the  gastric  or 
the  intestinal  juice,  a  special  fluid  can  be  recognized  by  certain  distinctive 
physiological  properties. 

In  the  membranes  covered  with  columnar  epithelium,  which  are  usually 
provided  with  simple  follicles,  the  secretion  is  produced  mainly  by  these  fol- 
licles, but  in  part  by  the  epithelium  covering  the  general  surface.  The 
membranes  covered  with  squamous  epithelium  usually  contain  but  few  folli- 
cles and  are  provided  with  simple  racemose  glands  situated  in  the  submucous 
structure,  which  are  to  be  regarded  as  appendages  to  the  membrane.  The 
secretion  is  here  produced  by  the  epithelium  on  the  free  surface  and  is 
always  mixed  with  fluids  resulting  from  the  action  of  the  mucous  glands. 

There  is  nothing  to  be  said  with  regard  to  the  mechanism  of  the  secre- 


COMPOSITION  AND  VARIETIES  OF  MUCUS.  319 

tion  of  mucus  in  addition  to  what  has  already  been  stated  in  connection  with 
the  general  mechanism  of  secretion.  All  the  mucous  membranes  are  quite 
Tascular,  and  the  cells  covering  the  membrane  and  lining  the  follicles  and 
glands  attached  to  it  have  the  property  of  taking  from  the  blood  the  materi- 
als necessary  for  the  formation  of  the  secretion.  These  matters  pass  out  of 
the  cells  upon  the  surface  of  the  membrane,  in  connection  with  water  and 
inorganic  salts  in  variable  proportions.  Many  of  the  cells  themselves  are 
thrown  off  and  are  found  in  the  secretion,  together  with  a  few  leucocytes, 
which  latter  are  produced  upon  mucous  surfaces  with  great  facility. 

Composition  and  Varieties  of  Mucus. — All  the  varieties  of  mucus  are  more 
or  less  viscid ;  but  this  character  is  very  variable  in  the  secretions  from  differ- 
ent membranes,  in  some  of  them  the  secretion  being  quite  fluid,  and  in  others, 
almost  semi-solid.  The  different  kinds  of  mucus  vary  considerably  in  gen- 
eral appearance.  Some  of  them  are  perfectly  clear  and  colorless ;  but  the 
secretion  is  generally  grayish  and  semi-transparent.  Examined  by  the  mi- 
croscope, in  addition  to  the  mixture  of  epithelium  and  the  occasional  leuco- 
cytes, which  give  to  the  fluid  its  semi-opaque  character,  the  mass  of  the  secre- 
tion presents  a  very  finely  striated  appearance,  as  though  it  were  composed 
of  thin  layers  of  nearly  transparent  substance  with  many  folds.  These  deli- 
cate striae  do  not  usually  interlace  with  each  other,  and  they  are  rendered 
more  distinct  by  the  action  of  acetic  acid.  This  appearance,  with  the  pecul- 
iar effect  of  the  acid,  is  characteristic  of  mucus.  Some  varieties  of  mucus 
present  very  fine,  pale  granulations  and  a  few  small  globules  of  oil. 

On  the  addition  of  water,  mucus  is  somewhat  swollen  but  is  not  dissolved. 
An  exception  to  this  is  the  secretion  of  the  conjunct! val  mucous  membrane, 
which  is  coagulated  on  the  addition  of  water.  As  a  rule  the  reaction  of 
mucus  is  alkaline ;  the  only  exception  to  this  being  the  vaginal  mucus, 
which  is  very  fluid  and  is  distinctly  acid. 

It  is  difficult  to  get  an  exact  idea  of  the  composition  of  normal  mucus, 
from  the  fact  that  the  quantity  secreted  by  the  membranes  in  their  natural 
condition  is  very  small,  being  just  sufficient  to  lubricate  their  surface.  All 
varieties,  however,  contain  a  peculiar  organic  matter,  called  mucine,  which 
gives  to  the  fluid  its  peculiar  viscidity.  They  likewise  present  a  consid- 
erable variety  of  inorganic  salts,  as  sodium  chloride,  potassium  chloride, 
alkaline  lactates,  sodium  carbonate,  calcium  phosphate,  a  small  propor- 
tion of  the  sulphates,  and  in  some  varieties,  traces  of  iron  and  of  silica.  Of 
all  these  constituents,  mucine  is  the  most  important,  as  it  gives  to  the 
secretion  its  characteristic  properties.  Like  all  other  organic  nitrogenized 
substances,  mucine  is  coagulable  by  various  reagents.  It  is  imperfectly  coag- 
ulated by  heat ;  and  after  desiccation  it  can  be  made  to  assume  its  peculiar 
consistence  by  the  addition  of  a  small  quantity  of  water.  It  is  coagulated 
by  acetic  acid  and  by  a  small  quantity  of  the  strong  mineral  acids,  being 
redissolved  in  an  excess  of  the  latter.  It  is  also  coagulated  by  strong  alcohol, 
forming  a  fibrinous  clot  soluble  in  hot  and  cold  water.  Mucine  may  be 
readily  isolated  by  adding  water  to  a  specimen  of  normal  mucus,  filtering, 
and  precipitating  with  an  excess  of  alcohol.  If  this  precipitate,  after  having 


320  SECRETION. 

been  dried,  be  exposed  to  water,  it  assumes  the  viscid  consistence  peculiar  to 
mucine.  This  property  serves  to  distinguish  it  from  albumin  and  other  or- 
ganic nitrogenized  matters. 

General  Uses  of  Mucus. — The  smooth,  viscid  and  adhesive  character  of 
mucus,  forming,  as  this  fluid  does,  a  coating  for  the  mucous  membranes, 
serves  to  protect  these  parts,  enables  their  surfaces  to  move  freely  one  upon 
the  other,  and  modifies  to  a  certain  extent  the  process  of  absorption.  Aside 
from  these  mechanical  uses,  it  has  been  shown  that  mucus,  in  connection 
with  the  epithelial  covering  of  the  mucous  membranes,  is  capable  of  prevent- 
ing the  absorption  of  certain  substances.  It  is  well  known,  for  example, 
that  venoms  may  be  applied  with  impunity  to  certain  mucous  surfaces, 
while  they  produce  poisonous  effects  if  introduced  into  the  circulation. 
These  agents  are  not  neutralized  by  the  secretions  of  the  parts,  for  they 
will  produce  their  characteristic  effects  upon  the  system  when  removed  from 
the  mucous  surfaces  and  introduced  into  the  circulation ;  and  it  is  reasonable 
to  suppose  that  the  mucous  membranes  are  capable  of  resisting  their  absorp- 
tion. This  fact  is  illustrated  by  the  following  experiment : 

Let  an  endosmometer  be  constructed,  using  a  fresh  mucous  membrane,  on 
the  surface  of  which  the  epithelium  and  layer  of  mucus  remain  intact,  and 
in  the  interior  of  the  apparatus,  place  a  saccharine  solution  and  let  the  mem- 
brane be  exposed  to  a  solution  containing  some  venomous  fluid.  The  liquid 
will  mount  in  the  interior  of  the  apparatus,  but  the  poison  will  not  pene- 
trate the  membrane.  If  the  mucus  and  epithelium  be  now  removed 
with  the  finger-nail  from  even  a  small  portion  of  the  membrane,  the  poison 
will  immediately  pass  through  that  part  of  the  membrane,  and  an  animal 
may  be  killed  with  the  fluid  which  now  penetrates  into  the  interior  of  the 
endosmometer  (Kobin). 

These  facts  show  that  mucus  is  an  important  secretion.  It  not  only  has 
a  useful  mechanical  office,  but  it  is  in  all  probability  closely  connected  with 
some  of  the  phenomena  of  elective  absorption  which  are  so  often  observed, 
particularly  in  the  alimentary  canal. 

Physiological  Anatomy  of  the  Sebaceous,  Ceruminous  and  Meibomian 
Glands. — The  true  sebaceous  glands  are  found  in  all  parts  of  the  skin  that 
are  provided  with  hair ;  and  as  nearly  every  part  of  the  general  surface  pre- 
sents either  the  long,  the  short  or  the  downy  hairs,  these  glands  are  very 
generally  distributed.  They  exist,  indeed,  in  greater  or  less  numbers  in  all 
parts  of  the  skin,  except  the  palms  of  the  hands  and  the  soles  of  the  feet. 
In  the  labia  minora  in  the  female,  and  in  portions  of  the  prepuce  and  glans 
penis  of  the  male,  parts  not  provided  with  hair,  small,  racemose  sebaceous 
glands  are  found,  which  produce  secretions  differing  somewhat  from  that 
formed  by  the  ordinary  glands.  The  glands  in  the  areola  of  the  nipple  in 
the  female  are  very  large  and  are  connected  with  small,  downy  hairs. 

Nearly  all  of  the  sebaceous  glands  are  either  simple  racemose  glands,  that 
is,  presenting  a  number  of  follicles  connected  with  a  single  excretory  duct,  or 
compound  racemose  glands,  presenting  several  ducts,  with  their  follicles, 
opening  by  a  common  tube.  Although  there  is  this  variation  in  the  size  and 


SEBACEOUS  GLANDS. 


321 


arrangement  of  the  glands  of  the  general  surface,  they  secrete  essentially  the 
same  fluid,  and  their  anatomical  differences  consist  simply  in  a  multiplication 
of  follicles. 

The  differences  in  the  size  of  the  sebaceous  glands  bear  a  certain  relation 
to  the  size  of  the  hairs  with  which  they  are  connected ;  and  as  a  rule,  the 

B  .    D 


FIG.  99.— Sebaceous  glands  (Sappey). 

A,  a  gland  in  its  most  rudimentary  form  :  1,  rudimentary  hair-follicle  ;  2,  downy  hair  ;  3,  simple  seba- 

ceous follicle. 

B,  a  gland  more  developed  :  1,  hair-follicle  ;  2,  simple  sebaceous  follicle. 

C,  a  gland  with  two  follicles  :  1,  hair-follicle  ;  2,  simple  follicle  :  3,  follicle  imperfectly  divided. 

D,  a  compound  gland  :  1,  hair-follicle  ;  2.  lobule  with  three  follicles  :  3,  lobule  with  four  follicles. 

E,  a  gland  with  four  lobules :  1.  hair-follicle  ;  2,  2,  first  lobule  ;  3,  second  lobule  ;  4,  4,  third  lobule  ;  5, 

fourth  lobule  ;  6,  excretory  duct  with  a  hair  passing  through  it. 

F,  a  gland  with  four  lobules  :  I,  hair-follicle  ;  2, 2,  first  lobule  ;  3,  second  lobule  ;  4,  third  lobule  ;  5,  fourth 

lobule  ;  6,  excretory  duct. 

largest  glands  are  connected  with  the  small,  downy  hairs.  These  distinctions 
in  size  are  so  marked,  that  the  glands  may  be  divided  into  two  classes ;  viz., 
those  connected  with  the  long  hairs  of  the  head,  face,  chest,  axilla  and  geni- 
tal organs  and  with  the  coarse,  short  hairs,  and  those  connected  with  the 
fine,  downy  hairs. 

The  glands  connected  with  the  larger  hair-follicles  are  of  the  simple  race- 
mose variety  and  are  -^  to  ^  of  an  inch  (0-21  to  0*64  mm.)  in  diameter. 
Two  to  five  of  these  glands  are  generally  found  arranged  around  each  hair- 
follicle.  They  discharge  their  secretion  at  about  the  junction  of  the  upper 


322 


SECRETION. 


third  with  the  lower  two-thirds  of  the  hair-follicle.  The  follicles  of  the  long 
hairs  of  the  scalp  are  generally  provided  each  with  a  pair  of  sebaceous  glands, 
measuring  T|7  to  -fa  of  an  inch  (0-21  to  O34  mm.)  in  diameter.  Encircling 
the  hairs  of  the  beard,  the  chest,  axilla  and  genital  organs,  are  large  glands, 
some  of  them  -fa  of  an  inch  (0-64  mm.)  in  diameter,  arranged  in  groups  of 
four  to  eight. 

The  glands  connected  with  the  follicles  of  the  small,  downy  hairs  are  so 
large,  as  compared  with  the  hair-follicles,  that  the  latter  seem  rather  as  ap- 
pendages to  the  glandular  structures.  These  glands  are  of  the  compound 
racemose  variety  and  present  sometimes^  as  many  as  fifteen  culs-de-sac.  The 
largest  are  found  on  the  nose,  the  ear,  the  curuncula  lachrymalis,  the  penis 
and  the  areola  of  the  nipple,  where  they  measure  -£$  to  -^  of  an  inch  (0-51 
to  2*1  mm.).  The  glands  connected  with  the  downy  hairs  of  other  parts 
usually  are  smaller.  The  glands  of  Tyson,  situated  upon  the  corona  and 
cervix  of  the  glans  penis,  are  sebaceous  glands  of  the  compound  racemose 
variety. 

The  minute  structure  of  the  sebaceous  glands  is  very  simple.  The  folli- 
cles which  compose  the  simple  glands  and  the  follicular  terminations  of  the 
simple  and  compound  racemose  glands  are  formed  of  a  delicate,  structureless 
or  slightly  granular  membrane,  with  an  external  layer  of  inelastic  and  small 
elastic  fibres,  and  are  lined  by  cells.  Next  the  membrane,  the  cells  are  poly- 
hedric,  pale  and  granular,  most  of  them  presenting  a  nucleus  and  a  nucle- 

olus ;  but  the  follicle 
itself  contains  fatty 
granules  and  the  other 
constituents  of  the 
sebaceous  matter,  with 
cells  filled  with  fatty 
particles.  These  cells 
abound  in  the  seba- 
ceous matter  as  it  is 
discharged  from  the 
duct.  The  great  quan- 
tity of  fatty  granules 
and  globules  found 
in  the  ducts  and  fol- 
licles of  the  sebaceous 
glands  renders  them 
dark  and  opaque  when 
examined  with  the 
microscope  by  trans- 
mitted light,  and  their 
appearance  is  quite 
distinctive.  The  larger  glands  are  surrounded  with  capillary  blood-vessels. 
The  ceruminous  glands  produce  a  secretion  resembling  the  sebaceous 
matter  in  many  regards,  but  in  their  anatonjy  they  are  almost  identical  with 


FIG.  100.— Cerumin&us  glands  (Sappey). 

Vertical  section  of  the  skin  of  the  external  auditory  meatus :  1,1,  epi- 
dermis ;  2,  2,  derma  ;  3,  3,  series  of  hair-follicles  lodged  in  the  sub- 
stance of  the  skin  ;  4,  4,  series  of  sebaceous  glands  attached  to  these 
follicles  ;  5.  5,  subcutaneous  areolar  layer  ;  6.  6,  ceruminous  glands  ; 
7,  7,  ceruminous  glands  with  the  ducts  divided  ;  8,  8,  adipose  vesicles. 


MEIBOMIAN  GLANDS. 


323 


Ihe  sudoriparous  glands.  They  belong  to  the  variety  of  glands  called  tubu- 
lar, and  they  consist  of  a  nearly  straight  tube  which  penetrates  the  skin,  and 
a  rounded  or  ovoid  coil  situated  in  the  subcutaneous  structure.  These  glands 
are  found  only  in  the  cartilaginous  portion  of  the  external  auditory  meatus, 
where  they  exist  in  great  numbers. 

The  ducts  of  the  ceruminous  glands  are  short  and  nearly  straight,  sim- 
ply penetrating  the  different  layers  of  the  skin,  and  are  T¥¥  to  -%fa  of  an 
inch  (36  to  50  ft)  in  diameter.  Their  openings  are  rounded  and  about 
j^fg  of  an  inch  (93  ft)  in  diameter.  They  sometimes  terminate  in  the  upper 
part  of  one  of  the  hair-follicles.  They  present  an  external  coat  of  fibrous 
tissue  and  are  lined  with  several  layers  of  small,  pale,  nucleated  epithelial 
cells. 

The  glandular  coil  is  an  ovoid  or  rounded,  brownish  mass,  j-J-g-  to  -^  or  -fa 
of  an  inch  (0-21  to  0'51  or  1-6  mm.)  in  diameter.  It  is  simply  a  convoluted 
tube,  continuous  with  the  excretory  duct  and  terminating  in  a  somewhat 
dilated,  rounded  extremity.  It  occasionally  presents  small,  lateral  protru- 
sions. The  diameter  of  the  tube  is  -g-J^  to  ^-^  of  an  inch  (83  to  100  p.).  It 
has  a  fibrous  coat,  with  a  longitudinal 
layer  of  non-striated  muscular  fibres,  and 
externally  a  few  elastic  fibres.  It  is 
lined  by  a  single  layer  of  irregularly 
polygonal  cells,  which  are  ^-gVo  to  7^75- 
of  an  inch  (12  to  20  p.)  in  diameter. 
These  cells  contain  a  number  of  brown- 
ish or  yellowish  pigmentary  granules. 
The  tube  forming  the  gland  contains  a 
clear  fluid  mixed  with  a  granular  sub- 
stance containing  cells. 

In  addition  to  the  ceruminous  glands, 
sebaceous  follicles  are  found  connected 
with  the  hair-follicles.  The  arrange- 
ment of  the  ordinary  sebaceous  glands 
and  the  ceruminous  glands,  which  are 
situated  in  diiferent  planes  in  the  subcu- 
taneous structure,  is  shown  in  Fig.  100. 

The  Meibomian  glands  have  essen- 
tially the  same  structure  as  the  ordinary 
sebaceous  glands.  Their  ducts,  however, 
are  longer,  and  the  terminal  follicles 
are  arranged  in  a  peculiar  manner  by 
the  sides  of  the  tubes  along  their  entire 
length.  These  glands  are  situated  part- 
ly in  the  substance  of  the  tarsal  carti- 
lages, between  their  posterior  surfaces 
and  the  conjunctival  mucous  membrane.  They  are  placed  at  right  angles  to 
the  free  border  of  the  eyelids,  opening  upon  the  inner  edge  and  occupying 


FIG.  101. — Meibomian  glands  of  the  upper  lid  ; 
magnified  1  diameters  (Sappeyj. 

1,  1,  free  border  of  the  lid ;  2,  2,  anterior  lip 
penetrated  by  the  eyelashes  ;  3,  3,  posteri- 
or lip,  with  the  openings  of  the  Meibomian 
glands  ;  4,  a  gland  passing  obliquely  at  the 
summit ;  5,  another  gland  bent  upon  itself  ; 
6,  6,  two  glands  in  the  form  of  racemose 

f  lands  at  their  origin  ;  7,  a  very  small  gland; 
,  a  medium-sized  gland. 


324  SECRETION. 

the  entire  width  of  the  cartilages.  Twenty-five  to  thirty  glands  are  found  in 
the  upper  lid,  and  twenty  to  twenty-five,  in  the  lower  lid. 

Each  Meibomian  gland  consists  of  a  nearly  straight  excretory  duct,  -^fa  to 
•jfg-  of  an  inch  (83  to  100  p.)  in  diameter,  communicating  laterally  with  com- 
pound racemose  acini,  or  collections  of  follicles,  measuring  ^-^  to  T^7  of  an 
inch  (83  to  200  /*).  Fifteen  or  twenty  of  these  collections  of  follicles  are 
found  on  either  side  of  the  duct  in  glands  of  medium  length.  Most  of  the 
excretory  ducts  are  nearly  straight,  but  some  are  turned  upon  themselves 
near  their  upper  extremity.  The  general  arrangement  of  these  glands  is 
shown  in  Fig.  101. 

In  general  structure  there  is  little  if  any  difference  between  the  terminal 
follicles  of  the  Meibomian  glands  and  the  follicles  of  the  ordinary  sebaceous 
glands.  They  are  lined  with  cells  ¥^g~o  to  -j-g^  of  an  inch  (10  to  20  p.)  in 
diameter.  The  cells  contain  fatty  globules,  but  these  do  not  coalesce  into 
large  drops,  such  as  are  often  seen  in  the  ordinary  sebaceous  cells.  The  folli- 
cles and  ducts  are  filled  with  the  whitish,  oleaginous  matter  which  consti- 
tutes the  Meibomian  secretion,  or  the  sebum  palpebrale. 

In  addition  to  the  Meibomian  secretion,  the  edges  of  the  palpebral  orifice 
receive  a  small  quantity  of  secretion  from  ordinary  sebaceous  glands  of  the 
compound  racemose  variety  (ciliary  glands),  which  are  appended  in  pairs  to 
each  of  the  follicles  of  the  eyelashes,  and  from  the  sebaceous  glands  attached 
to  the  small  hairs  of  the  caruncula  lachrymalis. 

Ordinary  Sebaceous  Matter. — Although  it  may  be  inferred,  from  the 
great  number  of  sebaceous  glands  opening  upon  the  cutaneous  surface,  that 
the  amount  of  sebaceous  matter  must  be  considerable,  it  has  been  impossible 
to  collect  the  normal  fluid  in  quantity  sufficient  for  ultimate  analysis.  In 
some  parts,  as  the  skin  of  the  nose,  where  the  glands  are  particularly  abun- 
dant, a  certain  quantity  of  oily  secretion  is  sometimes  observed,  giving  to  the 
surface  a  greasy,  glistening  aspect.  This  may  be  absorbed  by  paper,  giving 
it  the  well  known  appearance  produced  by  oily  matters,  and  it  may  be  col- 
lected in  small  quantity  upon  a  glass  slide  and  examined  microscopically.  It 
then  presents  a  number  of  strongly  refracting  fatty  globules,  with  a  few 
epithelial  cells.  The  cells,  however,  are  not  abundant  in  the  fluid  as  it  is 
discharged  upon  the  general  surface ;  but  if  the  contents  of  the  ducts  and 
follicles  be  examined,  cells  will  here  be  found  in  great  number.  Most  of  the 
cells,  indeed,  remain  in  the  glands,  and  the  oily  matter  only  is  discharged. 
The  object  of  this  secretion  is  to  lubricate  the  general  cutaneous  surface  and 
to  give  to  the  hairs  that  softness  which  is  characteristic  of  them  when  in  a 
perfectly  healthy  condition. 

The  chemical  constituents  of  the  sebaceous  matter  are  largely  fatty.  In 
an  analysis  made  by  Lutz,  in  a  case  of  general  hypertrophy  of  the  seba- 
ceous system,  the  proportion  of  water  was  only  357  parts  per  1000.  The 
solid  matters  consisted  of  oleine,  270  parts,  palmitine,  135  parts,  caseous 
matter,  129  parts,  gelatine,  87  parts,  a  little  albumin,  butyric  acid  and  so- 
dium butyrate,  with  sodium  phosphate,  sodium  chloride,  sodium  sulphate 
and  traces  of  calcium  phosphate.  Cholesterine,  which  is  present  so  fre- 


SEBACEOUS  MATTER.  325 

quently  in  the  contents  of  sebaceous  cysts,  does  not  exist  in  the  normal  se- 
cretion. 

During  the  later  months  of  pregnancy  and  during  lactation,  the  sebaceous 
glands  of  the  areola  of  the  nipple  become  considerably  distended  with  a 
grayish-white,  opaque  secretion,  containing  oily  globules  and  granules.  Fre- 
quently the  fluid  contains  also  a  large  number  of  epithelial  cells.  During  the 
periods  above  indicated,  the  secretion  here  is  always  much  more  abundant 
than  in  the  ordinary  sebaceous  glands. 

Smegma  of  the  Prepuce  and  of  the  Labia  Minora. — In  the  folds  of  the 
prepuce  of  the  male  and  on  the  inner  surface  and  folds  of  the  labia  minora 
in  the  female,  a  small  quantity  of  a  whitish,  grumous  matter,  of  a  cheesy 
consistence,  is  sometimes  found,  particularly  when  proper  attention  is  not 
paid  to  cleanliness.  The  matter  which  thus  collects  in  the  folds  of  the  pre- 
puce has  really  little  analogy  with  the  ordinary  sebaceous  secretion.  Exami- 
nation with  the  microscope  shows  that  it  is  composed  almost  entirely  of 
irregular  scales  of  epithelium,  which  do  not  present  the  fatty  granules  and 
globules  usually  observed  in  the  cells  derived  from  the  sebaceous  glands. 
The  production  of  this  substance  is  probably  independent  of  the  secretion  of 
sebaceous  matter,  as  it  is  formed  chiefly  in  parts  of  the  prepuce  in  which  the 
sebaceous  glands  are  wanting. 

The  smegma  of  the  labia  minora  is  of  the  same  character  as  the  smegma 
preputiale ;  but  it  contains  drops  of  oil  and  the  other  products  of  the  seba- 
ceous glands  found  in  these  parts. 

Vernix  Caseosa. — The  surface  of  the  foetus  at  birth  and  near  the  end  of 
utero-gestation  is  generally  covered  with  a  whitish  coating,  or  smegma,  called 
the  vernix  caseosa.  This  is  most  abundant  in  the  folds  of  the  skin ;  but  it 
usually  covers  the  entire  surface  with  a  coating  of  greater  or  less  thickness 
and  of  about  the  consistence  of  lard.  There  are  great  differences  in  foetuses 
at  term  as  regards  the  quantity  of  the  vernix  caseosa,  In  some  the  coating 
is  so  slight  that  it  is  observed  only  on  close  inspection.  There  are  few  analy- 
ses which  give  accurately  the  chemical  composition  of  this  substance ;  and 
the  best  idea  of  its  constitution  and  mode  of  formation  can  be  formed  from 
microscopical  examinations.  If  a  small  quantity  be  scraped  from  the  surface 
and  be  spread  out  upon  a  glass  slide  with  a  little  glycerine  and  water,  it  will 
be  found  on  microscopical  examination,  to  consist  of  a  large  number  of  epi- 
thelial cells  with  a  very  few  small,  fatty  granules.  These  cells,  after  desicca- 
tion, constitute  about  ten  per  cent,  of  the  entire  mass.  The  fatty  granula- 
tions are  very  few  and  do  not  seem  to  be  necessary  constituents  of  the  vernix, 
as  they  are  of  the  sebaceous  matter.  In  fact,  the  vernix  caseosa  must  be  re- 
garded as  the  residue  of  the  secretion  of  the  sebaceous  glands,  rather  than 
an  accumulation  of  true  sebaceous  matter. 

The  office  of  the  vernix  caseosa  is  undoubtedly  protective.  In  making  a 
microscopical  preparation  of  the  cells  with  water,  it  becomes  evident  that 
the  coating  is  penetrated  by  the  liquid  with  very  great  difficulty,  even  when 
mixed  with  it  as  thoroughly  as  possible.  The  protecting  coat  of  vernix  cas- 
eosa allows  the  skin  to  perform  its  office  in  utero,  and  at  birth,  when  this 


326  SECRETION. 

coating  is  removed,  the  surface  is  found  in  a  condition  perfectly  adapted  to 
extraiiterine  existence.  It  is  not  probable  that  the  vernix  caseosa  is  necessa- 
ry to  facilitate  the  passage  of  the  child  into  the  world,  for  the  parts  of  the 
mother  are  always  sufficiently  lubricated  with  mucous  secretion. 

Cerumen. — A  peculiar  substance  of  a  waxy  consistence  is  secreted  by  the 
glands  that  have  been  described  in  the  external  auditory  meatus,  under  the 
name  of  ceruminous  glands,  mixed  with  the  secretion  of  sebaceous  glands 
connected  with  the  short  hairs  in  this  situation.  It  is  difficult  to  ascertain 
what  share  these  two  sets  of  glands  have  in  the  formation  of  the  cerumen. 
According  to  Robin,  the  waxy  portion  of  the  secretion  is  produced  entirely  by 
the  sebaceous  glands,  and  the  convoluted  glands,  commonly  known  as  the  ce- 
ruminous glands,  produce  a  secretion  like  the  perspiration.  This  view  is  to 
a  certain  extent  reasonable ;  for  the  sebaceous  matter  is  not  removed  from 
the  meatus  by  friction,  as  in  other  situations,  and  would  have  a  natural  ten- 
dency to  accumulate;  but  the  contents  of  the  ducts  of  the  ceruminous 
glands  differ  materially  from  the  fluid  found  in  the  ducts  of  the  ordinary 
sudoriparous  glands,  containing  granules  and  fatty  globules  such  as  exist  in 
the  cerumen.  Although  the  glands  of  the  ear  are  analogous  in  structure, 
and  to  a  certain  extent,  in  the  character  of  their  secretion,  to  the  sudoripa- 
rous glands,  the  fluid  which  they  produce  is  peculiar.  The  perspiratory 
glands  of  the  axilla  and  of  some  other  parts  also  produce  secretions  differing 
somewhat  from  ordinary  perspiration.  As  far  as  can  be  ascertained,  the  cer- 
umen is  produced  by  both  sets  of  glands.  The  sebaceous  glands  attached  to 
the  hair-follicles  probably  secrete  most  of  the  oleaginous  and  waxy  matter, 
while  the  so-called  ceruminous  glands  produce  a  secretion  of  much  greater 
fluidity,  but  containing  a  certain  quantity  of  granular  and  fatty  matter. 

The  consistence  and  general  appearance  of  cerumen  are  quite  variable 
within  the  limits  of  health.  When  first  secreted,  it  is  of  a  yellowish  color 
and  about  the  consistence  of  honey,  becoming  darker  and  much  more  viscid 
upon  exposure  to  the  air.  It  has  a  very  decided  and  bitter  taste.  It  readily 
forms  a  sort  of  emulsive  mixture  with  water. 

Examined  microscopically,  the  cerumen  is  found  to  contain  semi-solid, 
dark  granulations  of  an  irregularly  polyhedric  shape,  with  epithelium  from  the 
sebaceous  glands,  and  epidermic  scales,  both  isolated  and  in  layers.  Some- 
times, also,  a  few  crystals  of  cholesterine  are  found. 

Chemical  examination  shows  that  the  cerumen  is  composed  of  oily  mat- 
ters fusible  at  a  low  temperature,  a  peculiar  organic  matter  resembling 
mucine,  with  sodium  salts  and  a  certain  quantity  of  calcium  phosphate. 
The  yellow  coloring  matter  is  soluble  in  alcohol ;  and  the  residue  after  evap- 
oration of  the  alcohol  is  very  soluble  in  water  and  may  be  precipitated  from 
its  watery  solution  by  neutral  lead  acetate  or  tin  chloride.  This  extract  has 
a  very  bitter  taste. 

The  cerumen  lubricates  the  external  meatus,  accumulating  in  the  canal 
around  the  hairs.  Its  peculiar  bitter  taste  is  supposed  to  be  useful  in  prevent- 
ing the  entrance  of  insects. 

Meibomian  Secretion. — Very  little  is  known  concerning  any  special  prop- 


ANATOMY  OF  THE  MAMMARY  GLANDS.  327 

erties  of  the  Meibomian  fluid,  except  that  it  mixes  in  the  form  of  an  emulsion 
with  water  more  readily  than  the  other  sebaceous  secretions.  It  is  produced 
in  small  quantity,  mixed  with  mucus  and  the  secretion  from  the  ordinary  se- 
baceous glands  attached  to  the  eyelashes  and  the  glands  of  the  caruncula 
lachrymalis,  and  smears  the  edges  of  the  palpebral  orifice.  This  oily  coating 
on  the  edges  of  the  lids,  unless  the  tears  be  produced  in  excessive  quantity, 
prevents  their  overflow  upon  the  cheeks,  and  the  excess  of  fluid  passes  into 
the  nasal  duct. 

MAMMARY  SECRETION. 

The  mammary  glands  are  among  the  most  remarkable  organs  in  the  econ- 
omy ;  not  only  on  account  of  the  peculiar  character  of  their  secretion,  which 
is  unlike  the  product  of  any  other  of  the  glands,  but  from  the  great  changes 
which  they  undergo  at  different  periods,  both  in  size  and  structure.  Kudi- 
mentary  in  early  life  and  in  the  male  at  all  periods  of  life,  these  organs  are 
fully  developed  in  the  adult  female  only  in  the  later  months  of  pregnancy 
and  during  lactation.  In  the  female,  after  puberty,  the  mammary  glands 
undergo  a  marked  and  rapid  increase  in  size ;  but  even  then  they  are  not  ful- 
ly developed. 

Physiological  Anatomy  of  the  Mammary  Glands. — The  form,  size  and 
situation  of  the  mammaB  in  the  adult  female  are  too  well  known  to  de- 
mand more  than  a  passing  mention.  These  organs  are  almost  invariably 
double  and  are  situated  on  the  anterior  portion  of  the  thorax,  over  the  great 
pectoral  muscles.  In  women  who  have  never  borne  children,  they  gener- 
ally are  firm  and  nearly  hemispherical,  with  the  nipple  at  the  most  promi- 
nent point.  In  women  who  have  borne  children,  the  glands  during  the 
intervals  of  lactation  usually  are  larger,  are  held  more  loosely  to  the  sub- 
jacent parts  and  are  often  flabby  and  pendulous.  The  areola  of  the  nipple, 
also,  is  darker. 

In  both  sexes  the  mammary  glands  are  nearly  as  fully  developed  at  birth 
as  at  any  time  before  puberty.  They  make  their  appearance  at  about  the 
fourth  month,  in  the  form  of  little  elevations  of  the  structure  of  the  true 
skin,  which  soon  begin  to  send  off  processes  beneath  the  skin,  which  are  des- 
tined to  be  developed  into  the  lobes  of  the  glands.  In  the  foetus  at  term 
the  glands  measure  hardly  more  than  one-third  of  an  inch  (8'5  mm.)  in  di- 
ameter. At  this  time  there  are  twelve  to  fifteen  lobes  in  each  gland,  and  each 
lobe  is  penetrated  by  a  duct,  with  but  few  branches,  composed  of  fibrous  tis- 
sue and  lined  with  cylindrical  epithelium.  The  ends  of  these  ducts  are  fre- 
quently somewhat  dilated ;  but  what  have  been  called  the  gland-vesicles  do 
not  make  their  appearance  before  puberty.  In  the  adult  male  the  glands 
are  half  an  inch  to  two  inches  (12'7  to  50'8  mm.)  broad,  and  ^  to  £  of  an 
inch  (2~l  to  6'4  mm.)  in  thickness.  In  their  structure,  however,  they  pre- 
sent little  if  any  difference  from  the  rudimentary  glands  of  the  infant. 

As  the  time  of  puberty  approaches  in  the  female,  the  rudimentary  ducts 
of  the  different  lobes  become  more  and  more  ramified.  Instead  of  each  duct 
having  but  two  or  three  branches,  the  different  lobes,  as  the  gland  enlarges, 


328  SECRETION. 

are  penetrated  by  innumerable  ramifications  which  have  gradually  been  devel- 
oped as  processes  from  the  main  duct.  It  is  important  to  remember,  how- 
ever, that  these  branches  are  never  so  abundant  or  so  long  during  the  inter- 
vals of  lactation  as  they  are  when  the  gland  is  in  full  activity. 

Between  the  fourth  and  fifth  months  of  utero-gestation  the  mammary 
glands  of  the  mother  begin  to  increase  in  size ;  and  at  term  they  are  very 
much  larger  than  during  the  unimpregnated  state.  At  this  'time  the  breasts 
become  quite  hard,  and  the  surface  near  the  areola  is  somewhat  uneven, 
from  the  great  development  of  the  ducts.  The  nipple  itself  is  increased  in 
size,  the  papillse  upon  its  surface  and  upon  the  areola  are  more  largely  devel- 
oped, and  the  areola  becomes  larger,  darker  and  thicker.  The  glandular 
structure  of  the  breasts  during  the  latter  half  of  pregnancy  becomes  so  far  de- 
veloped, that  if  the  child  be  born  at  the  seventh  month,  the  lacteal  secretion 
may  be  established  at  the  usual  time  after  parturition.  Even  when  parturi- 
tion takes  place  at  term,  a  few  days  elapse  before  secretion  is  fully  established, 
and  the  first  product  of  the  glands,  called  colostrum,  is  very  different  from 
the  fully  formed  milk. 

The  only  parts  of  the  covering  of  the  breasts  that  present  any  peculiarities 
are  the  areola  and  the  nipple.  The  surface  of  the  nipple  is  covered  with  pa- 
pillae, which  are  very  largely  developed  near  the  summit.  It  is  covered  by 
epithelium  in  several  layers,  the  lower  strata  being  filled  with  pigmentary 
granules.  The  true  skin  covering  the  nipples  is  composed  of  inelastic  and 
elastic  fibres,  containing  a  large  number  of  sebaceous  glands,  but  no  hair-fol- 
licles or  sudoriparous  glands.  These  glands  are  always  of  the  racemose  va- 
riety, and  they  never  exist  in  the  form  of  simple  follicles  (Sappey).  The 
nipple  contains  the  lactiferous  ducts,  fibres  of  inelastic  and  elastic  tissue, 
with  a  large  number  of  non-striated  muscular  fibres.  The  muscular  fibres 
have  no  definite  direction,  but  are  so  abundant  that  when  they  are  contracted 
the  nipple  becomes  very  firm  and  hard. 

The  areola  does  not  lie,  like  the  general  integument  covering  the  gland, 
upon  a  bed  of  adipose  tissue,  but  it  is  closely  adherent  to  the  subjacent  gland- 
ular structure.  The  skin  here  is  much  thinner  and  more  delicate  than 
in  other  parts,  and  the  pigmentary  granules  are  very  abundant  in  some  of 
the  lower  strata  of  epidermic  cells,  particularly  during  pregnancy.  The 
true  skin  of  the  areola  is  composed  of  inelastic  and  elastic  fibres  and  lies 
upon  a  distinct  layer  of  non-striated  muscular  fibres.  The  arrangement  of 
the  muscular  fibres — sometimes  called  the  subareolar  muscle — is  quite  regular, 
forming  concentric  rings  around  the  nipple.  These  fibres  are  supposed  to 
be  useful  in  compressing  the  ducts  during  the  discharge  of  milk.  The 
areolar  presents  the  following  structures ;  papillae,  considerably  smaller  than 
those  upon  the  nipple ;  hair-follicles,  containing  small,  rudimentary  hairs ; 
sudoriparous  glands ;  and  sebaceous  glands  connected  with  the  hair-follicles. 
The  sebaceous  glands  are  very  large,  and  their  situation  is  indicated  by  little 
prominences  on  the  surface  of  the  areola,  which  are  especially  marked  dur- 
ing pregnancy. 

The  mammary  gland  itself  is  of  the  compound  racemose  variety.     It  is 


ANATOMY  OF  THE  MAMMAEY  GLANDS. 


329 


covered  in  front  by  a  subcutaneous  layer  of  fat,  and  posteriorly  it  is  envel- 
oped in  a  fibrous  membrane  loosely  attached  to  the  pectoralis  major  muscle. 
A  considerable  quantity  of  adipose  tissue  is  also  found  in  the  substance  of 
the  gland  between  the  lobes. 

Separated  from  the  adipose  and  fibrous  tissue,  the  mammary  gland  is 
found  divided  into  lobes,  fifteen  to  twenty-four  in  number.  These  are 
subdivided  into  lobules  made  up  of  a  greater  or  less  number  of  acini,  or 
culs-de-sac.  The  secreting  structure  is  of  a  reddish-yellow  color  and  is 
distinctly  granular,  presenting  a  decided  contrast  to  the  pale  and  uniformly 
fibrous  appearance  of  the  gland  during  the  intervals  of  lactation.  If  the 
ducts  be  injected  from  the  nipple  and  be  followed  into  the  substance  of  the 
gland,  each  one  will  be  found  distributing  its  branches  to  a  distinct  lobe ;  so 
that  the  organ  is  really  made  up  of  a  number  of  glands  identical  in  structure. 

The  canals  which  discharge  the  milk  at  the  nipple  are  called  lactiferous 
or  galactophorous  ducts.  They  are  ten  to  fourteen  in  number.  The  open- 
ings of  the  ducts  at  the  nipple  are  very  small,  measuring  only  -fa  to  -fa  of  an 
inch  (O42  to  0'64  mm.).  As  each  duct  passes  downward,  it  enlarges  in  the 
nipple  to  2*5  or  -^  of  an  inch  (1  or  2  mm.)  in  diameter,  and  beneath  the  are- 
ola  it  presents  an  elon- 
gated dilatation,  £  to  -J- 
of  an  inch  (4*2  to  8*5 
mm.)  in  diameter,  called 
the  sinus  of  the  duct. 
During  lactation  a  con- 
siderable quantity  of  milk 
collects  in  these  sinuses, 
which  serve  as  reservoirs. 
Beyond  the  sinuses,  the 
caliber  of  the  ducts  meas- 
ures ^  to  %  of  an  inch 
(2-1  to  4-2  mm.).  The 
ducts  penetrate  the  dif- 
ferent lobes,  branching 
and  subdividing,  to  ter- 
minate finally  in  the  col- 
lections of  culs-de-sac 
which  form  the  acini. 
There  is  no  anastomosis 
between  the  different  lac- 
tiferous ducts,  and  each 
one  is  distributed  inde- 
pendently to  one  or  more 
lobes. 

The  lactiferous  ducts  have  three  distinct  coats.  The  external  coat  is 
composed  of  anastomosing  fibres  of  elastic  tissue  with  some  inelastic  fibres. 
The  middle  coat  is  composed  of  non-striated  muscular  fibres,  arranged  Ion- 


FIG.  102.— Mammary  gland  of  the  human  female  (Liegeois). 
a,  nipple,  the  central  portion  of  which  is  retracted;  6,  areola  ;  c,  c, 
c,  c,  c,  lobules  of  the  gland:  1.  sinus,  or  dilated  portion  of  one  of 
the  lactiferous  ducts  ;  2,  extremities  of  the  lactiferous  ducts. 


330  SECRETION. 

gitudinally  and  existing  throughout  the  duct,  from  its  opening  at  the  nipple 
to  the  secreting  culs-de-sac.  The  internal  coat  is  an  amorphous  membrane, 
lined  with  flat,  polygonal  cells  during  the  intervals  of  lactation  and  even  dur- 
ing pregnancy,  the  cells  being  cylindrical  in  form  and  frequently  presenting 
multiple  nuclei,  when  milk  is  secreted. 

The  acini  of  the  gland,  which  are  very  abundant,  are  visible  to  the  naked 
eye,  in  the  form  of  small,  rounded  granules  of  a  reddish-yellow  color.  Be- 
tween these  acini,  there  exists  a  certain  quantity  of  the  ordinary  white  fibrous 
tissue,  with  quite  a  number  of  adipose  vesicles.  The  presence  of  adipose 
tissue  in  considerable  quantity  in  the  substance  of  the  glandular  structure  is 
peculiar  to  the  mammary  glands.  Each  acinus  is  made  up  of  twenty  to 
forty  secreting  vesicles.  These  vesicles  are  irregular  in  form,  often  varicose, 
and  sometimes  they  are  enlarged  and  imperfectly  bifurcated  at  their  termi- 
nal extremities.  During  lactation  their  diameter  is  j-J^  to  -g-i-g-  of  an  inch 
(60  to  80/t). 

During  the  intervals  of  lactation,  as  the  lactiferous  ducts  become  re- 
tracted, the  glandular  culs-de-sac  disappear ;  and  in  pregnancy,  as  the  gland 
takes  on  its  full  development,  the  ducts  branch  and  extend  themselves,  and 
the  vesicles  are  gradually  developed  around  their  extremities. 

Mechanism  of  the  Secretion  of  Milk. — With  the  exception  of  water  and 
inorganic  matters,  all  the  important  and  characteristic  constituents  of  the 
milk  are  formed  in  the  substance  of  the  mammary  glands.  The  secreting 
structures  have  the  property  of  separating  from  the  blood  a  great  variety  of 
inorganic  salts ;  and  the  milk  furnishes  all  the  inorganic  matter  necessary 
for  the  nutrition  of  the  infant,  even  containing  a  small  quantity  of  iron. 

The  lactose,  or  sugar  of  milk,  the  caseine,  and  the  fatty  particles,  are  all 
produced  in  the  gland.  The  peculiar  kind  of  sugar  here  found  does  not 
exist  anywhere  else  in  the  organism.  Even  when  the  secretion  of  milk  is 
most  active,  different  varieties  of  sugar,  such  as  glucose  or  cane-sugar,  in- 
jected into  the  blood-vessels  of  a  living  animal,  are  never  eliminated  by  the 
mammary  glands,  as  they  are  by  the  kidneys ;  and  their  presence  in  the 
blood  does  not  influence  the  quantity  of  lactose  found  in  the  milk. 

Caseine  is  produced  in  the  mammary  glands,  probably  by  a  peculiar 
transformation  of  the  albuminoid  constituents  of  the  blood.  The  fatty  par- 
ticles of  the  milk  are  likewise  produced  in  the  substance  of  the  gland,  and 
the  peculiar  kind  of  fat  which  exists  in  this  secretion  is  not  found  in  the 
blood.  The  mechanism  of  the  production  of  fat  in  the  mammary  glands  is 
somewhat  obscure.  The  particles  are  produced  in  the  cells,  probably  by  a 
process  analogous  to  that  which  takes  place  in  the  formation  of  the  fatty 
particles  found  in  the  sebaceous  matter. 

As  regards  the  mechanism  of  the  formation  of  the  peculiar  and  character- 
istic constituents  of  the  milk,  the  mammary  glands  are  to  be  classed  among 
the  organs  of  secretion  and  not  with  those  of  elimination  or  excretion ;  for 
none  of  these  elements  pre-exist  in  the  blood,  and  they  all  appear  first  in  the 
substance  of  the  glands. 

During  the  period  of  secretion,  the  glands  receive  a  much  larger  supply 


SECRETION  OF  MILK.  331 

of  blood  than  at  other  times.  Pregnancy  favors  the  development  of  the 
secreting  portions  of  the  glands  but  does  not  induce  secretion.  On  the  other 
hand,  when  pregnancy  occurs  during  lactation,  it  diminishes  and  modifies, 
and  it  may  arrest  the  secretion  of  milk.  The  secreting  action  of  the  mam- 
mary glands  is  nearly  continuous.  When  the  secretion  of  milk  has  become 
fully  established,  while  there  may  be  certain  times  when  it  is  formed  in 
greater  quantity  than  at  others,  there  is  no  actual  intermission  in  its  pro- 
duction. 

General  Conditions  which  modify  the  Lacteal  Secretion. — Very  little  is 
known  concerning  the  physiological  conditions  which  modify  the  secretion 
of  milk.  When  lactation  is  fully  established,  the  quantity  and  quality  of  the 
milk  secreted  become  adapted  to  the  requirements  of  the  child  at  different 
periods  of  its  existence.  In  studying  the  composition  of  the  milk,  therefore, 
it  will  be  found  to  vary  considerably  in  the  different  stages  of  lactation. 
It  is  evident  that  as  the  development  of  the  child  advances,  a  constant  in- 
crease of  nourishment  is  demanded ;  and  as  a  rule,  the  mother  is  capable  of 
supplying  all  the  nutritive  requirements  of  the  infant  for  eight  to  twenty 
months. 

During  the  time  when  such  an  amount  of  nutritive  matter  is  furnished 
to  the  child,  the  quantity  of  food  taken  by  the  mother  is  sensibly  increased ; 
but  observations  have  shown  that  the  secretion  of  milk  is  not  much  influ- 
enced by  the  character  of  the  food.  It  is  necessary  that  the  mother  should  be 
supplied  with  good,  nutritious  articles ;  but  as  far  as  solid  food  is  concerned, 
there  seems  to  be  no  great  difference  between  a  coarse  and  a  delicate  ali- 
mentation, and  the  milk  of  females  in  the  lower  walks  of  life,  when  the  gen- 
eral condition  is  normal,  is  fully  as  good  as  in  women  who  are  able  to  live 
luxuriously.  It  is,  indeed,  a  fact  generally  recognized  by  physiologists,  that 
the  secretion  of  milk  is  little  influenced  by  any  special  diet,  provided  the  ali- 
mentation be  sufficient  and  of  the  quality  ordinarily  required  by  the  system 
and  that  it  contain  none  of  the  few  articles  of  food  which  are  known  to  have 
a  special  influence  upon  lactation.  It  is  very  common,  however,  for  women 
to  become  quite  fat  during  lactation ;  which  shows  that  the  fatty  constituents 
of  the  food  do  not  pass  exclusively  into  the  milk,  but  that  there  is  a  tendency, 
at  the  same  time,  to  a  deposition  of  adipose  tissue  in  the  situations  in  which 
it  is  ordinarily  found.  It  is  a  matter  of  common  experience,  that  certain 
articles,  such  as  acids  and  fermentable  substances,  often  disturb  the  digestive 
organs  of  the  child  without  producing  any  change  in  the  milk,  that  can  be 
recognized  by  chemical  analysis.  The  individual  differences  in  women,  in 
this  regard,  are  very  great. 

The  statements  with  regard  to  solid  food  do  not  apply  to  liquids.  Dur- 
ing lactation  there  is  always  an  increased  demand  for  water  and  for  liq- 
uids generally;  and  if  these  be  not  supplied  in  sufficient  quantity,  the 
secretion  of  milk  is  diminished  and  its  quality  is  almost  always  impaired. 
It  is  a  curious  fact,  which  has  been  fully  established  by  observations  upon 
the  human  subject  and  the  inferior  animals,  that  while  the  quantity  of  milk 
is  increased  by  taking  a  large  amount  of  simple  water,  the  solid  constituents 


332  SECRETION. 

are  also  increased,  and  the  milk  retains  all  of  its  qualities  as  a  nutritive 
fluid. 

Alcohol,  especially  when  largely  diluted,  as  in  malt-liquors  and  other  mild 
beverages,  is  well  known  to  exert  an  influence  upon  the  secretion  of  milk. 
Drinks  of  this  kind  almost  always  temporarily  increase  the  activity  of  the  se- 
cretion, and  sometimes  they  produce  a  certain  effect  upon  the  child ;  but  di- 
rect and  accurate  observations  on  the  actual  passage  of  alcohol  into  the  milk 
are  wanting.  During  lactation  the  moderate  use  of  drinks  containing  a 
small  proportion  of  alcohol  is  frequently  beneficial,  particularly  in  assisting 
the  mother  to  sustain  the  unusual  drain  upon  the  system.  There  are,  how- 
ever, few  instances  of  normal  lactation  in  which  their  use  is  absolutely  ne- 
cessary. 

It  is  well  known  that  the  secretion  of  milk  may  be  profoundly  affected 
by  violent  mental  emotions.  This  is  the  case  in  many  other  secretions,  as  the 
saliva  and  the  gastric  juice.  It  is  hardly  necessary,  however,  to  cite  many 
instances  of  modification  or  arrest  of  the  secretion  from  this  cause,  which  are 
quoted  by  authors.  Vernois  and  Becquerel  reported  a  case,  in  which  a 
hospital  wet-nurse,  who  lost  her  only  child  from  pneumonic  fever,  became 
violently  affected  with  grief  and  presented,  as  a  consequence,  an  immediate 
diminution  in  the  quantity  of  her  milk,  with  a  great  reduction  in  the  propor- 
tion of  salts,  sugar  and  butter.  In  this  case  the  proportion  of  caseine  was 
increased.  Astley  Cooper  reported  fyvo  cases  in  which  the  secretion  of  milk 
was  instantaneously  and  permanently  arrested  by  terror.  These  cases  are 
types  of  many  others,  which  have  been  cited  by  writers,  of  the  effects  of 
mental  emotions  upon  secretion. 

Direct  observations  upon  the  influence  of  the  nerves  upon  the  mammary 
glands  are  few  and  unsatisfactory.  The  operation  of  dividing  the  nerves 
distributed  to  these  glands,  which  has  occasionally  been  practised  upon  ani- 
mals in  lactation,  has  not  been  observed  to  produce  any  sensible  diminution 
in  the  quantity  of  the  secretion.  It  is  difficult,  however,  to  operate  upon  all 
the  nerves  distributed  to  these  organs.  There  are  no  observations  indicating 
the  situation  of  a  nerve-centre  presiding  over  the  secretion  of  milk,  although 
such  a  centre  may  exist. 

Quantity  of  Milk. — It  is  difficult  to  form  a  reliable  estimate  of  the  aver- 
age quantity  of  milk  secreted  by  the  human  female  in  the  twenty-four  hours. 
The  quantity  undoubtedly  varies  very  much  in  different  persons ;  some  women 
being  able  to  nourish  two  children,  while  others,  though  apparently  in  per- 
fect health,  furnish  hardly  enough  food  for  one.  Astley  Cooper,  as  the  result 
of  direct  observation,  stated  that  the  quantity  that  can  be  drawn  from  a  full 
breast  is  usually  about  two  fluidounces  (60  grammes).  This  may  be  assumed 
to  be  about  the  quantity  contained  in  the  lactiferous  ducts  when  they  are 
moderately  distended.  Lehmann,  taking  for  the  basis  of  his  calculations  the 
observations  of  Lamperierre,  who  found,  as  the  result  of  sixty-seven  experi- 
ments, that  between  1'7  and  2  ounces  (50  and  60  grammes)  of  milk  were 
secreted  in  two  hours,  estimated  that  the  average  quantity  discharged  in 
twenty-four  hours  is  about  44-5  fluidounces  (1,320  grammes).  Taking  into 


PROPERTIES  AND  COMPOSITION  OF  MILK.  333 

consideration  the  variations  in  the  quantity  of  milk  secreted  by  different 
women,  it  may  be  assumed  that  the  daily  production  is  between  two  and  three 
pints  (950  and  1,420  grammes). 

Certain  conditions  of  the  female  are  capable  of  materially  influencing  the 
quantity  of  milk  secreted.  It  is  evident  that  the  secretion  is  usually  some- 
what increased  within  the  first  few  months  of  lactation,  when  the  progressive 
development  of  the  child  demands  an  increase  in  the  quantity  of  nourish- 
ment. If  the  menstrual  function  become  re-established  during  lactation,  the 
milk  usually  is  diminished  in  quantity  during  the  periods,  but  sometimes  it 
is  not  affected,  either  in  its  quantity  or  composition.  Should  the  female 
become  pregnant,  there  generally  is  a  great  diminution  in  the  quantity  of 
milk,  and  that  which  it  secreted  is  ordinarily  regarded  as  possessing  little 
nutritive  power.  In  obedience  to  a  popular  prejudice,  apparently  well  founded, 
the  child  is  usually  taken  from  the  breast  as  soon  as  pregnancy  is  recognized. 
No  marked  and  constant  variations  have  been  observed  in  the  quantity  of 
milk  in  females  of  different  ages. 

Properties  and  Composition  of  Milk. — The  general  appearance  and  char- 
acters of  ordinary  cow's  milk  are  sufficiently  familiar.  Human  milk  is  nei- 
ther so  white  nor  so  opaque  as  cow's  milk,  having  ordinarily  a  slightly 
bluish  tinge.  After  the  secretion  has  become  fully  established,  the  fluid 
possesses  no  viscidity  and  is  nearly  opaque.  It  is  almost  inodorous,  of  a 
peculiar  soft  and  sweetish  taste,  and  when  perfectly  fresh  it  has  a  decidedly 
alkaline  reaction.  The  taste  of  human  milk  is  sweeter  than  that  of  cow's 
milk.  A  short  time  after  its  discharge  from  the  gland,  the  reaction  of  milk 
becomes  faintly  acid;  but  this  change  takes  place  more  slowly  in  human 
milk  than  in  the  milk  of  most  of  the  inferior  animals. 

The  average  specific  gravity  of  human  milk  is  1032 ;  although  this  is 
subject  to  considerable  variation,  the  minimum  of  eighty-nine  observations 
being  1025,  and  the  maximum,  1046  (Vernois  and  Becquerel).  The  observa- 
tions of  most  physiological  chemists  have  shown  that  this  average  is  nearly 
correct. 

Milk  is  not  coagulated  by  'heat,  even  after  prolonged  boiling;  but  a 
thin  pellicle  then  forms  on  the  surface,  which  is  probably  due  to  the  com- 
bined action  of  heat  and  the  atmosphere  upon  the  caseine.  Although  a 
small  quantity  of  albumin  exists  in  the  milk,  this  does  not  coagulate  on 
the  surface  by  the  action  of  the  heat,  for  the  scum  does  not  form  when  the 
fluid  is  heated  in  a  vacuum  or  in  an  atmosphere  of  carbon  dioxide  or  of 
hydrogen. 

When  the  milk  is  coagulated  by  any  substance  acting  upon  the  caseine 
or  when  it  coagulates  spontaneously  it  separates  into  a  curd,  composed  of 
caseine  with  most  of  the  fatty  particles,  and  a  nearly  clear,  greenish-yellow 
serum,  called  whey.  This  separation  occurs  spontaneously  at  a  variable  time 
after  the  discharge  of  the  milk,  taking  place  much  sooner  in  warm  than  in 
cold  weather.  It  is  a  curious  fact  that  fresh  milk  frequently  is  coagulated 
during  a  thunder-storm,  a  phenomenon  which  has  never  been  satisfactorily 
explained. 

23 


334: 


SECRETION. 


On  being  allowed  to  stand  for  a  short  time,  the  milk  separates,  without 
coagulating,  into  two  tolerably  distinct  portions.  A  large  proportion  of  the 
globules  rises  to  the  top,  forming  a  yellowish-white  and  very  opaque  fluid, 
called  cream,  leaving  the  lower  portion  poorer  in  globules  and  of  a  decidedly 
bluish  tint.  In  healthy  milk  the  stratum  of  cream  forms  one-fifth  to  one- 
third  of  the  entire  mass  of  the  milk.  In  the  human  subject  the  skim-milk  is 
not  white  and  opaque,  but  it  is  nearly  as  transparent  as  the  whey.  The  spe- 
cific gravity  of  the  cream  from  milk  of  the  average  specific  gravity  of  1032  is 
about  1024.  The  specific  gravity  of  skim-milk  is  about  1034. 

Microscopical  Characters  of  the  Milk. — Milk  contains  an  immense  num- 
ber of  minute,  spherical  globules,  of  highly  refractive  power,  held  in  sus- 
pension in  a  clear  fluid.  These  are  known  under  the  name  of  milk-glob- 
ules and  are  composed  of  palmitine,  oleine,  and  fatty  matters  peculiar  to 
milk. 

The  human  milk-globules  are  -g-^^  *°  T^TTT  °f  an  incn  (1  to  20  fi)  in 
diameter.  They  usually  are  distinct  from  each  other,  but  they  may  occasion- 
ally become  collected  into  groups,  without  indicating  any  thing  abnormal. 
In  a  perfectly  normal  condition  of  the  glands,  when  the  lacteal  secretion  has 

become  fully  established,  the  milk  con- 
tains nothing  but  a  clear  fluid  with 
these  globules  in  suspension.  The  pro- 
portion of  fatty  matters  in  the  milk  is 
twenty -five  to  forty -eight  parts  per 
thousand ;  and  this  gives  an  idea  of  the 
proportion  of  globules  which  are  seen 
on  microscopical  examination. 

In  some  regards  milk  does  not  pre- 
sent the  characters  of  a  simple  emulsion. 
If  it  be  shaken  with  ether,  the  mixture 
remains  opaque ;  but  the  fatty  matters 
are  dissolved  on  the  addition  of  potassi- 
um hydrate.  Dilute  acetic  acid  added 
to  milk  causes  the  globules  to  run  to- 
gether. These  reactions  have  led  to  the 
view  that  the  milk-globules  have  a  membrane  which  is  dissolved  by  potassi- 
um hydrate  and  by  acetic  acid.  It  is  probable  that  the  butter  in  normal 
milk  does  not  exist  precisely  in  the  form  of  a  simple  emulsion,  but  that  the 
globules  have  a  very  thin,  caseous  coating.  In  view  of  the  action  of  reagents 
upon  the  globules,  the  only  alternative,  if  the  existence  of  a  caseous  coating 
be  denied,  is  the  opinion  that  the  addition  of  potassium  hydrate  or  of  acetic 
acid  renders  the  caseine  incapable  of  holding  the  fat  in  the  condition  of  an 
emulsion.  There  is  actually  little  more  than  a  verbal  difference  between 
these  two  opinions. 

Composition  of  the  Milk.  —  The  following  table,  compiled  by  Robin 
from  the  analyses  of  various  chemists,  gives  the  constituents  of  human 
milk: 


FIG.  103.—  Human  milk-globules,  from  a  healthy 
lying-in  woman,  eight  days  after  delivery 
(Funke). 


PROPERTIES  AND  COMPOSITION  OF  MILK.  335 

COMPOSITION    OF    HUMAN"    MILK. 

Water 902-717  to  863-149 

Caseine  (desiccated) 29-000  "  39-000 

Lactoproteine 1-000  "  2'770 

Albumin  traces  "  0-880 

r  Palmitine , 17-000  "  25-840 

Butter,  25  to  38  )  Oleine 7-500  "  11-400 

(  Butyrine,  caprine,  caprome,  caprilene  etc.  0-500  "  0-760 

Sugar  of  milk  (lactose) 37-000  "  49-000 

Sodium  lactate  (?) 0-420  "  0-450 

Sodium  chloride 0-240  "  0-340 

Potassium  chloride 1-440  "  1-830 

Sodium  carbonate 0-053  "  0-056 

Calcium  carbonate 0-069  "  0-070 

Calcium  phosphate 2-310  "  3-440 

Magnesium  phosphate 0'420  "  0-640 

Sodium  phosphate 0-225  "  0-230 

Ferric  phosphate  (?) 0-032  "  0-070 

Sodium  sulphate 0-074  "  0-075 

Potassium  sulphate traces. 

1,000-000         1,000-000 

t  Oxygen 1-29  ) 

Gases  in  solution  <  Nitrogen 12-17  £  30  parts  per  1,000  in  volume.  (Hoppe.) 

(  Carbon  dioxide.  16-54  ) 

The  proportion  of  water  in  milk  is  subject  to  certain  changes,  but  these 
are  not  so  considerable  as  might  be  expected  from  the  great  variations  in 
the  entire  quantity  of  the  secretion.  As  regards  the  quantity  of  milk  in  the 
twenty- four  hours,  the  influence  of  drinks,  even  when  nothing  but  pure  water 
is  taken,  is  very  marked ;  and  although  the  activity  of  the  secretion  is  much 
increased  by  fluid  ingesta,  the  quality  of  the  milk  usually  is  not  affected,  and 
the  proportion  of  water  to  the  solid  matters  remains  about  the  same. 

Nitrogenized  Constituents  of  Milk. — Very  little  remains  to  be  said  con- 
cerning the  nitrogenized  constituents  of  human  milk,  after  what  has  been 
stated  in  connection  with  alimentation.  The  different  constituents  of  this 
class  undoubtedly  have  the  same  nutritive  office  and  they  appear  to  be  iden- 
tical in  all  varieties  of  milk,  the  only  difference  being  in  their  relative  pro- 
portions. It  js  a  matter  of  common  experience,  indeed,  that  the  milk  of 
many  of  the  lower  animals  will  take  the  place  of  human  milk,  when  prepared 
so  as  to  make  the  proportions  of  its  different  constituents  approximate  the 
composition  of  the  natural  food  of  the  child.  A  comparison  of  the  composi- 
tion of  human  milk  and  of  cow's  milk  shows  that  the  former  is  poorer  in  nitro- 
genized matters  and  richer  in  butter  and  sugar ;  and  consequently,  the  upper 
strata  of  cow's  milk,  properly  sweetened  and  diluted  with  water,  very  nearly 
represents  the  ordinary  breast-milk. 

Caseine  is  by  far  the  most  important  of  the  nitrogenized  constituents  of 
milk,  and  it  supplies  nearly  all  of  this  kind  of  nutritive  matter  demanded  by 
the  child.  Lactoproteine,  described  by  Millon  and  Commaille,  is  not  so  well 
denned,  and  albumin  exists  in  the  milk  in  very  small  quantity. 


336  SECRETION. 

The  coagulation  of  milk  depends  upon  the  reduction  of  caseine  from  a 
liquid  to  a  semi-solid  condition.  When  milk  is  allowed  to  coagulate  spon- 
taneously, the  change  is  effected  by  the  action  of  the  lactic  acid  which  results 
from  a  transformation  of  a  portion  of  the  sugar  of  milk.  Caseine,  in  fact,  is 
coagulated  by  any  of  the  acids,  even  the  feeble  acids  of  organic  origin.  It 
differs  from  albumen  in  this  regard  and  in  the  fact  that  it  is  not  coagulated 
by  heat.  If  fresh  milk  be  slightly  raised  in  temperature  and  be  treated  with 
an  infusion  of  the  gastric  mucous  membrane  of  the  calf,  coagulation  Avill 
take  place  in  five  or  ten  minutes,  the  clear  liquid  still  retaining  its  alkaline 
reaction.  Simon  has  observed  that  the  mucous  membrane  of  the  stomach  of 
an  infant  a  few  days  old,  that  had  recently  died,  coagulated  woman's  milk 
more  readily  than  the  mucous  membrane  of  the  stomach  of  the  calf. 

Non-Nitrogenized  Constituents  of  Milk. — Non-nitrogenized  matters  exist 
in  abundance  in  the  milk.  The  liquid  caseine  and  the  water  hold  the  fats 
in  the  condition  of  a  fine  and  permanent  emulsion.  This  fat  may  easily  be 
separated  from  the  milk,  and  is  known  under  the  name  of  butter.  In  human 
milk,  the  butter  is  much  softer  than  in  the  milk  of  many  of  the  inferior 
animals,  particularly  the  cow;  but  it  is  composed  of  essentially  the  same 
constituents,  although  in  different  proportions.  In  different  animals,  there 
are  developed,  even  after  the  discharge  of  the  milk,  certain  odorous  matters, 
which  are  more  or  less  characteristic  of  the  animal  from  which  the  butter  is 
taken. 

•  The  greatest  part  of  the  butter  consists  of  palmitine.  Butter  contains 
in  addition,  oleine,  and  a  small  proportion  of  peculiar  fats,  which  have  not 
been  very  well  determined,  called  butyrine,  caprine,  caprome,  capriline,  with 
some  other  analogous  substances.  Palmitine  and  oleine  are  found  in  the  fat 
throughout  the  body;  but  the  last-named  substances  are  peculiar  to  the 
milk.  These  are  especially  liable  to  acidification,  and  the  acids  resulting 
from  their  decomposition  give  the  peculiar  odor  and  flavor  to  rancid  butter. 

Sugar  of  milk,  or  lactose,  is  the  most  abundant  of  the  solid  constituents 
of  the  mammary  secretion.  It  is  this  that  gives  to  the  milk  its  peculiar 
sweetish  taste,  although  this  variety  of  sugar  is  much  less  sweet  than  cane- 
sugar.  The  chief  peculiarities  of  milk-sugar  are  that  it  readily  undergoes 
change  into  lactic  acid  in  the  presence  of  nitrogenized  ferments,  and  that 
it  takes  on  alcoholic  fermentation  slowly  and  with  difficulty.  In  the  fer- 
mentation of  milk,  the  lactose  is  changed  first  into  galactose,  and  then  into 
alcohol  and  carbon  dioxide.  In  some  parts  of  the  world,  alcoholic  beverages 
made  from  milk  are  in  common  use. 

Inorganic  Constituents  of  Milk. — It  is  probable  that  many  inorganic  salts 
exist  in  the  milk,  which  are  not  given  in  the  table ;  and  the  separation  of 
these  from  their  combinations  with  organic  matters  is  one  of  the  most  diffi- 
cult problems  in  physiological*chemistry.  This  must  be  the  case,  for  during 
the  first  months  of  extraiiterine  existence,  the  child  derives  all  the  inorganic 
as  well  as  the  organic  matters  necessary  to  nutrition  and  development,  from 
the  breast  of  the  mother.  The  reaction  of  the  milk  depends  upon  the  pres- 
ence of  the  alkaline  carbonates,  and  these  are  important  in  preserving  the 


VAKIATIONS  IN  THE  COMPOSITION  OF  MILK.  337 

fluidity  of  the  caseine.  It  is  not  determined  precisely  in  what  form  iron 
exists  in  the  milk,  but  its  presence  here  is  undoubted.  A  comparison  of  the 
composition  of  the  milk  with  that  of  the  blood  shows  that  most  of  the  impor- 
tant inorganic  matters  found  in  the  latter  fluid  exist  also  in  the  milk. 

Hoppe  has  indicated  the  presence  of  carbon  dioxide,  nitrogen  and  oxygen, 
in  solution  in  milk.  Of  these  gases,  carbon  dioxide  is  the  most  abundant. 
It  is  well  known  that  the  presence  of  gases  in  solution  in  liquids  renders  them 
more  agreeable  to  the  taste,  and  carbon  dioxide  increases  very  materially 
their  solvent  properties.  Aside  from  these  considerations,  the  uses  of  the 
gaseous  constituents  of  the  milk  are  not  apparent. 

Iii  addition  to  the  constituents  given  in  the  table  of  composition,  the 
rnilk  contains  small  quantities  of  peptone,  nucleine,  dextrine,  urea,  lecithine, 
hypoxanthine,  fluorine  and  silica. 

A  study  of  the  composition  of  the  milk  fully  confirms  the  fact  that  this 
is  a  typical  alimentary  fluid  and  presents  in  itself  the  proper  proportion  and 
variety  of  material  for  the  nourishment  of  the  body  during  the  period  when 
the  development  of  the  system  is  going  on  with  its  maximum  of  activity. 
The  form  in  which  its  different  nutritive  constituents  exist  is  such  that  they 
are  easily  digested  and  are  assimilated  with  great  rapidity. 

Variations  in  the  Composition  of  Milk. — If  the  composition  of  the  milk 
be  compared  at  different  periods  of  lactation,  it  will  be  found  to  undergo 
great  changes  during  the  first  few  days.  In  fact,  the  first  fluid  secreted  after 
parturition  is  so  different  from  ordinary  milk,  that  it  has  been  called  by  an- 
other name.  It  is  then  known  as  colostrum,  the  peculiar  properties  of  which 
will  be  considered  more  fully  under  a  distinct  head.  As  the  secretion  of  milk 
becomes  established,  the  fluid,  from  the  first  to  the  fifteenth  day,  becomes 
gradually  diminished  in  density  and  in  its  proportion  of  water  and  of  sugar, 
while  there  is  a  progressive  increase  in  the  proportion  of  most  of  the  other 
constituents ;  viz.,  butter,  caseine  and  the  inorganic  salts.  The  milk,  there- 
fore, as  far  as  one  can  judge  from  its  composition,  as  it  increases  in  quantity 
during  the  first  few  days  of  lactation,  is  constantly  increasing  in  its  nutritive 
properties. 

The  differences  in  the  composition  of  the  milk,  taken  from  month  to 
month  during  the  entire  period  of  lactation,  are  not  so  distinctly  marked. 
It  is  difficult,  indeed,  to  indicate  any  constant  variations  of  sufficient  impor- 
tance to  lead  to  the  view  that  the  milk  varies  much  in  its  nutritive  properties 
at  different  times,  during  the  ordinary  period  of  lactation.  The  differences 
between  the  milk  of  primiparae  and  multiparae  are  slight  and  unimportant. 
As  a  rule,  however,  the  milk  of  primiparse  approaches  more  nearly  the  normal 
standard. 

In  normal  lactation,  there  is  no  marked  and  constant  difference  in  com- 
position between  milk  that  has  been  secreted  in  great  abundance  and  milk 
which  is  produced  in  comparatively  small  quantity ;  and  the  difference  be- 
tween the  fluid  first  drawn  from  the  breast  and  that  taken  when  the  ducts 
are  nearly  empty,  which  is  observed  in  the  milk  of  the  cow,  has  not  been 
noted  in  human  milk. 


338 


SECRETION. 


COLOSTKUM. 

Near  the  end  of  utero-gestation,  during  a  period  which  varies  considera- 
bly in  different  women  and  has  not  been  accurately  determined,  a  small 
quantity  of  a  thickish,  stringy  fluid  may  frequently  be  drawn  from  the  mam- 
mary glands.  This  bears  little  resemblance  to  perfectly  formed  milk.  It  is 
small  in  quantity  and  is  usually  more  abundant  in  multipart  than  in  primi- 
parae.  This  fluid,  as  well  as  that  secreted  for  the  first  few  days  after  delivery, 
is  called  colostrum.  It  is  yellowish,  semi-opaque,  of  a  distinctly  alkaline  re- 
action and  is  somewhat  mucilaginous  in  its  consistence.  Its  specific  gravity 
is  considerably  above  that  of  the  ordinary  milk,  being  between  1040  and  1060. 
As  lactation  progresses,  the  character  of  the  secretion  rapidly  changes,  until 
the  fluid  becomes  filled  with  true  milk-globules  and  assumes  the  characters 
of  ordinary  milk. 

The  opacity  of  the  colostrum  is  due  to  the  presence  of  a  number  of  differ- 
ent corpuscular  elements.  Milk-globules,  very  variable  in  size  and  number, 
are  to  be  found  in  the  secretion  from  the  first.  These,  however,  do  not  exist 
in  sufficient  quantity  to  render  the  fluid  very  opaque,  and  they  are  frequently 
aggregated  in  rounded  and  irregular  masses,  held  together,  apparently,  by 
some  glutinous  matter.  Peculiar  corpuscles,  supposed  to  be  characteristic  of 

the  colostrum,  always  exist  in  this  fluid. 
These  are  known  as  colostrum-corpus- 
cles. They  are  spherical,  varying  in 
size  between  2^06  and  -^J-^-  of  an  inch 
(10  and  50  /*.),  are  sometimes  pale,  but 
more  frequently  quite  granular,  and 
they  contain  very  often  a  large  number 
of  fatty  particles.  They  behave  in  all 
respects  like  leucocytes  and  are  de- 
scribed as  a  variety  of  these  bodies. 
Many  of  them  are  precisely  like  the 
leucocytes  found  in  the  blood,  lymph 
or  pus.  In  addition  to  these  corpuscu- 
lar elements,  a  small  quantity  of  mucine 
may  frequently  be  observed  in  the  co- 
lostrum on  microscopical  examination. 
On  the  addition  of  ether  to  a  speci- 
men of  colostrum  under  the  microscope, 
most  of  the  fatty  particles,  both  within 
and  without  the  colostrum-corpuscles, 
are  dissolved.  Ammonia  added  to  the  fluid  renders  it  stringy,  and  sometimes 
the  entire  mass  assumes  a  gelatinous  consistence. 

In  its  composition,  colostrum  presents  many  points  of  difference  from 
true  milk.  It  is  sweeter  to  the  taste  and  contains  a  greater  proportion  of 
sugar  and  of  the  inorganic  salts.  The  proportion  of  fat  is  at  least  equal  to 
the  proportion  in  the  milk  and  is  generally  greater.  Instead  of  caseine,  pure 


FIG.  104. — Colostrum,  from  a  healthy  lying-in 
woman,  twelve  hours  after  delivery  (Funke). 

The  smaller  globules  are  globules  of  milk.  The 
larger  globules,  a,  a,  filled  with  granula- 
tions, are  colostrum-corpuscles.  As  lacta- 
tion advances,  the  colostrum  -  corpuscles 
gradually  disappear,  and  the  milk-globules 
become  more  abundant,  smaller  and  more 
nearly  uniform  in  size. 


COLOSTEUM.  339 

colostrum  contains  a  large  proportion  of  serum-albumin ;  and  as  the  charac- 
ter of  the  secretion  changes  in  the  process  of  lactation,  the  albumin  becomes 
gradually  reduced  in  quantity  and  caseine  takes  its  place. 

The  following,  deduced  from  the  analyses  of  Clemm,  may  be  taken  as  the 
ordinary  composition  of  colostrum  of  the  human  female : 

COMPOSITION    OF    COLOSTRUM. 

Water 945-24 

Albumin,  and  salts  insoluble  in  alcohol 29-81 

Butter 7-07 

Sugar  of  milk,  extractive  matter,  and  salts  soluble  in  alcohol 17'27 

Loss . .  0-61 


1,000-00 

Colostrum  ordinarily  decomposes  much  more  readily  than  milk  and  takes 
on  putrefactive  changes  very  rapidly.  If  it  be  allowed  to  stand  for  twelve 
to  twenty-four  hours,  it  separates  into  a  thick,  opaque,  yellowish  cream  and 
a  serous  fluid.  In  an  observation  by  Astley  Cooper,  nine  measures  of  colos- 
trum, taken  soon  after  parturition,  after  twenty-four  hours  of  repose,  gave 
six  parts  of  cream  to  three  of  milk. 

The  peculiar  constitution  of  the  colostrum,  particularly  the  presence  of 
an  excess  of  sugar  and  inorganic  salts,  renders  it  somewhat  laxative  in  its 
effects,  and  it  is  supposed  to  be  useful,  during  the  first  few  days  after  deliv- 
ery, in  assisting  to  relieve  the  infant  of  the  accumulation  of  meconium. 

As  the  quantity  of  colostrum  that  may  be  pressed  from  the  mammary 
glands  during  the  latter  periods  of  utero-gestation,  particularly  the  last 
month,  is  very  variable,  it  becomes  an  important  question  to  determine 
whether  this  secretion  have  any  relation  to  the  quantity  of  milk  that  may  be 
expected  after  delivery.  This  question  has  been  studied  by  Donne,  who  ar- 
rived at  the  following  conclusions : 

In  women  in  whom  the  secretion  of  colostrum  is  almost  absent,  the  fluid 
being  in  exceedingly  small  quantity,  viscid,  and  containing  hardly  any  cor- 
puscular elements,  there  is  hardly  any  milk  produced  after  delivery. 

In  women  who,  before  delivery,  present  a  moderate  quantity  of  colostrum, 
containing  very  few  milk-globules  and  a  number  of  colostrum-corpuscles, 
after  delivery  the  milk  will  be  scanty  or  it  may  be  abundant,  but  it  is  always 
of  poor  quality. 

When  the  quantity  of  colostrum  produced  is  considerable,  the  secretion 
being  quite  fluid  and  rich  in  corpuscular  elements,  particularly  milk-globules, 
the  milk  after  delivery  is  always  abundant  and  of  good  quality. 

From  these  observations,  it  would  seem  that  the  production  of  colostrum 
is  an  indication  of  the  proper  development  of  the  mammary  glands ;  and 
the  early  production  of  fatty  granules,  which  are  first  formed  by  the  cells 
lining  the  secreting  vesicles,  indicates  the  probable  activity  in  the  secretion 
of  milk  after  lactation  shall  have  become  fully  established. 

The  secretion  of  the  mammary  glands  preserves  the  characters  of  colos- 
trum until  toward  the  end  of  the  so-called  milk-fever,  when  the  colostrum- 


340  SECRETION. 

corpuscles  rapidly  disappear,  and  the  milk-globules  become  more  abundant, 
regular  and  uniform  in  size.  It  may  be  stated,  in  general  terms,  that  the 
secretion  of  milk  becomes  fully  established  and  all  the  characters  of  the 
colostrum  disappear  between  the  eighth  and  the  tenth  day  after  delivery.  A 
few  colostrum-corpuscles  and  masses  of  agglutinated  milk-globules  may 
sometimes  be  discovered  after  the  tenth  day,  but  they  are  rare.  After  the 
fifteenth  day,  the  milk  does  not  sensibly  change  in  its  microscopical  or  its 
chemical  characters. 

LACTEAL  SECRETION  IN  THE  NEWLY-BORN. 

In  infants  of  both  sexes  there  is  generally  a  certain  amount  of  secretion 
from  the  mammary  glands,  beginning  at  birth  or  two  or  three  days  after, 
and  continuing  sometimes  for  two  or  three  weeks.  The  quantity  of  fluid 
that  may  be  pressed  out  at  the  nipples  at  this  time  is  very  variable.  Some- 
times only  a  few  drops  can  be  obtained,  but  occasionally  the  fluid  amounts 
to  one  or  two  drachms  (3'7  or  7'4  grammes.)  Although  it  is  impossible  to 
indicate  the  object  of  this  secretion,  which  takes  place  when  the  glands  are 
in  a  rudimentary  condition,  it  has  been  so  often  observed  and  described  by 
physiologists,  that  there  can  be  no  doubt  with  regard  to  the  nature  of  the 
fluid  and  the  fact  that  the  secretion  is  almost  always  produced  in  greater  or 
less  quantity.  The  following  is  an  analysis  by  Quevenne  of  the  secretion 
obtained  by  Gubler.  The  observations  of  Gubler  were  made  upon  about 
twelve  hundred  children.  The  secretion  rarely  continued  for  more  than 
four  weeks,  but  in  four  instances  it  persisted  for  two  months. 

COMPOSITION    OF   THE   MILK    OF    THE    INFANT. 

Water 894-00 

Caseine    26-40 

Sugar  of  milk 62.20 

Butter 14-00 

Earthy  phosphates 1-20 

Soluble  salts  (with  a  small  quantity  of  insoluble  phosphates) 2-20 


1,000-00 

This  fluid  does  not  differ  much  in  its  composition  from  ordinary  milk. 
The  proportion  of  butter  is  much  less,  but  the  proportion  of  sugar  is  greater, 
and  the  quantity  of  caseine  is  nearly  the  same. 

Of  the  other  fluids  which  are  enumerated  in  the  list  of  secretions,  the 
saliva,  gastric  juice,  pancreatic  juice  and  the  intestinal  fluids  have  already 
been  described  in  connection  with  the  physiology  of  digestion.  The  physi- 
ology of  the  lachrymal  secretion  will  be  taken  up  in  connection  with  the  eye, 
and  the  bile  will  be  treated  of  fully  under  the  head  of  excretion. 

Secretory  Nerve- Centres. — It  remains  now  to  consider  the  influence  of 
nerve-centres  upon  certain  secretions.  Cerebro-spinal  centres  presiding  over 
secretion  have  not  been  determined  for  all  of  the  glands,  although  they  may 
exist.  No  cerebro-spinal  centres  have  been  described  for  the  secretions  of 


DIFFEKENCES  BETWEEN  SECRETIONS  AND  EXCRETIONS.  341 

mucous  membranes,  the  gastric  juice,  the  intestinal  juice,  the  sebaceous 
fluids,  the  milk  or  the  lachrymal  fluid. 

The  centres  for  the  salivary  secretions  are  in  the  medulla  oblongata,  near 
the  points  of  origin  of  the  facial  and  glosso-pharyngeal  nerves.  The  centre 
for  the  pancreatic  secretion  is  also  in  the  medulla  oblongata.  The  centres 
which  act  upon  the  liver  and  upon  certain  excretions  will  be  treated  of  in 
connection  with  the  physiology  of  the  liver,  kidneys  and  skin. 


CHAPTER  XII. 

EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

Differences  between  the  secretions  proper  and  the  excretions— Physiological  anatomy  of  the  skin — Physio- 
logical anatomy  of  the  nails— Physiological  anatomy  of  the  hairs— Sudden  blanching  of  the  hair— Per- 
spiration—Sudoriparous  glands— Mechanism  of  the  secretion  of  sweat— Properties  and  composition  of 
the  sweat— Peculiarities  of  the  sweat  in  certain  parts — Physiological  anatomy  of  the  kidneys— Mechan- 
ism of  the  production  and  discharge  of  urine— Influence  of  blood-pressure,  the  nervous  system  etc., 
upon  the  secretion  of  urine— Physiological  anatomy  of  the  urinary  passages— Mechanism  of  the  dis- 
•  charge  of  urine— Properties  and  composition  of  the  urine— Influence  of  ingesta  upon  the  composition 
of  the  urine  and  upon  the  elimination  of  nitrogen— Influence  of  muscular  exercise  upon  the  elimination 
of  nitrogen— Water  regarded  as  a  product  of  excretion— Variations  in  the  composition  of  the  urine. 

IN  entering  upon  the  study  of  the  elimination  of  effete  matters,  it  is  ne- 
cessary to  appreciate  fully  the  distinctions  between  the  secretions  proper  and 
the  excretions,  in  their  composition,  the  mechanism  of  their  production,  and 
their  destination.  The  urine  may  be  taken  as  the  type  of  the  excrementi- 
tious  fluids.  None  of  its  normal  constituents  belong  to  the  class  of  non-crys- 
tallizable,  organic  nitrogenized  matters,  but  it  is  composed  entirely  of  crys- 
tallizable  matters,  simply  held  in  solution  in  water.  The  solid  constituents 
of  the  urine  represent  the  ultimate  physiological  changes  of  certain  parts  of 
the  organism,  and  they  are  in  such  a  condition  that  they  are  of  no  farther 
use  in  the  economy  and  are  simply  discharged  from  the  body.  Certain  in- 
organic matters  are  found  in  the  excrementitious  fluids,  are  discharged  with 
the  products  of  excretion,  and  are  thus  associated  with  the  organic  constitu- 
ents of  the  body  in  their  physiological  changes  as  well  as  in  their  deposition 
in  the  tissues.  Coagulable  organic  matters,  or  albuminoids,  never  exist  in 
the  excrementitious  fluids  under  normal  conditions  ;  except  as  the  products 
of  other  glands  may  become  accidentally  or  constantly  mixed  with  the  ex- 
crementitious fluids  proper.  The  same  remark  applies  to  the  non-nitrogen- 
ized  matters,  sugars  and  fats,  which,  whether  formed  in  the  organism  or 
taken  as  food,  are  consumed  in  the  organism.  The  production  of  the  excre- 
tions is  constant,  being  subject  only  to  certain  modifications  in  activity, 
which  are  dependent  upon  varying  conditions  of  the  system.  All  of  the 
elements  of  excretion  pre-exist  in  the  blood,  either  in  the  condition  in 
which  they  are  discharged  or  in  some  slightly  modified  form. 

The  urine  is  a  purely  excrementitious  fluid.     The  perspiration  and  the 


342  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

secretion  of  the  axillary  glands  are  excrementitious  fluids,  but  they  contain  a 
certain  quantity  of  the  secretion  of  the  sebaceous  glands.  Certain  excre- 
mentitious matters  are  found  in  the  bile,  but  at  the  same  time,  this  fluid  con- 
tains substances  that  are  formed  in  the  liver,  and  it  has  an  important  office 
as  a  secretion,  in  connection  with  the  processes  of  digestion. 

PHYSIOLOGICAL  ANATOMY  OF  THE  SKIN. 

The  skin  is  one  of  the  most  complex  and  important  structures  in  the 
body,  and  it  has  a  variety  of  uses.  In  the  first  place,  it  forms  a  protect- 
ive covering  for  the  general  surface.  It  is  quite  thick  over  the  parts  most 
subject  to  pressure  and  friction,  is  elastic  over  movable  parts  and  those  liable 
to  variations  in  size,  and  in  many  situations,  is  covered  with  hair,  which 
affords  an  additional  protection  to  the  subjacent  structures.  The  skin  and 
its  appendages  are  imperfect  conductors  of  caloric,  are  capable  of  resisting 
very  considerable  variations  in  temperature,  and  they  thus  tend  to  maintain 
the  normal  standard  of  the  animal  heat.  As  an  organ  of  sensibility,  the  skin 
has  important  uses,  being  abundantly  supplied  with  sensory  nerves,  some  of 
which  present  an  arrangement  peculiarly  adapted  to  the  nice  appreciation  of 
tactile  impressions.  The  skin  assists  in  preserving  the  external  forms  of  the 
muscles.  It  also  relieves  the  abrupt  projections  and  depressions  of  the  gen- 
eral surface  and  gives  roundness  and  grace  to  the  contours  of  the  body.  In 
some  parts  it  is  very  closely  attached  to  the  subjacent  structures,  while  in 
others  it  is  less  adherent  and  is  provided  with  a  layer  of  adipose  tissue. 

As  an  organ  of  excretion,  the  skin  is  very  important ;  and  although  the 
quantity  of  excrementitious  matter  exhaled  from  it  is  not  very  great,  the 
evaporation  of  water  from  the  general  surface  is  always  considerable  and  is 
subject  to  such  modifications  as  may  become  necessary  from  the  varied  con- 
ditions of  the  animal  temperature.  Thus,  while  the  skin  protects  the  body 
from  external  influences,  its  office  is  important  in  regulating  the  heat  pro- 
duced as  one  of  the  phenomena  attendant  upon  the  general  process  of  nu- 
trition. 

As  the  skin  presents  such  a  variety  of  uses,  its  physiological  anatomy  is 
most  conveniently  considered  in  connection  with  different  divisions  of  the 
subject  of  physiology.  For  example,  under  the  head  of  secretion,  the  struct- 
ure of  the  different  varieties  of  sebaceous  glands  has  already  been  described  ; 
and  the  anatomy  of  the  skin  as  an  organ  of  touch  will  be  most  appropriately 
considered  in  connection  with  the  physiology  of  the  nervous  system.  In 
connection  with  the  excreting  organs  found  in  the  skin,  it  will  be  convenient 
to  describe  briefly  its  general  structure  and  the  most  important  points  in  the 
anatomy  of  the  epidermic  appendages.  A  full  and  connected  description  of 
the  skin  and  its  appendages  belongs  properly  to  works  upon  anatomy. 

Extent  and  Thickness  of  the  Skin. — Sappey  has  made  a  number  of  obser- 
vations upon  the  extent  of  the  surface  of  the  skin.  Without  detailing  the 
measurements  of  different  parts,  it  may  be  stated,  as  the  general  result  of  his 
observations,  that  the  cutaneous  surface  in  a  good-sized  man  is  equal  to  a  lit- 
tle more  than  sixteen  square  feet  (15,000  square  centimetres) ;  and  in  men  of 


PHYSIOLOGICAL  ANATOMY  OF  THE  SKIN.  343 

more  than  ordinary  size,  it  may  extend  to  twenty-one  or  twenty-two  square 
feet  (2  square  metres).  In  women  of  medium  size,  as  the  mean  result  of 
three  observations,  the  surface  was  found  to  equal  about  twelve  and  a  half 
square  feet  (11,500  square  centimetres). 

The  thickness  of  the  skin  varies  very  much  in  different  parts.  Where  it 
is  exposed  to  constant  pressure  and  friction,  as  on  the  soles  of  the  feet  or  the 
palms  of  the  hands,  the  epidermis  becomes  very  much  thickened,  and  in  this 
way  the  more  delicate  structure  of  the  true  skin  is  protected.  It  is  well 
known  that  the  development  of  the  epidermis,  under  these  conditions,  varies 
in  different  persons,  with  the  pressure  and  friction  to  which  the  surface  is 
habitually  subjected.  The  true  skin  is  fa  to  £  of  an  inch  (2-1  to  3-2  mm.) 
in  thickness ;  but  in  certain  parts,  particularly  in  the  external  auditory  mea- 
tus,  the  lips  and  the  glans  penis,  it  frequently  measures  not  more  than  y^  of 
an  inch  (0^254  mm.). 

Layers  of  the  Skin. — The  skin  is  naturally  divided  into  two  principal  lay- 
ers, which  may  be  readily  separated  from  each  other  by  maceration.  These 
are  the  true  skin — cutis  vera,  derma,  or  corium — and  the  epidermis,  cuticle, 
or  scarf-skin.  The  true  skin  is  more  or  less  closely  attached  to  the  subjacent 
structures  by  a  fibrous  structure  called  the  subcutaneous  areolar  tissue,  in  the 
meshes  of  which  there  is  usually  a  certain  quantity  of  adipose  tissue.  This 
layer  is  sometimes  described  under  the  name  of  the  panniculus  adiposus.  The 
thickness  of  the  adipose  layer  varies  very  much  in  different  parts  of  the  general 
surface  and  in  different  persons.  There  is  no  fat  beneath  the  skin  of  the 
eyelids,  the  upper  and  outer  part  of  the  ear,  the  penis  and  the  scrotum.  Be- 
neath the  skin  of  the  cranium,  the  nose,  the  neck,  the  dorsum  of  the  hand 
and  foot,  the  knee  and  the  elbow,  the  fatty  layer  is  about  fa  of  an  inch  (2'1 
mm.)  in  thickness.  In  other  parts  it  usually  measures  £  to  |-  of  an  inch  (4*2 
to  12'7  mm.).  In  very  fat  persons  it  may  measure  an  inch  (25-4  mm.)  or 
more.  Upon  the  head  and  the  neck,  in  the  human  subject,  are  muscles  at- 
tached more  or  less  closely  to  the  skin.  These  are  capable  of  moving  the 
skin  to  a  slight  extent.  Muscles  of  this  kind  are  largely  developed  and  quite 
extensively  distributed  in  some  of  the  lower  animals. 

There  is  no  sharply  defined  line  of  demarcation  between  the  cutis  and  the 
subcutaneous  areolar  tissue ;  and  the  under  surface  of  the  skin  is  always  ir- 
regular, from  the  presence  of  fibres  which  are  necessarily  divided  in  detach- 
ing it  from  the  subjacent  structures.  The  fibres  which  enter  into  the  com- 
position of  the  skin  become  looser  in  their  arrangement  near  its  under  surface, 
the  change  taking  place  rather  abruptly,  until  they  present  large  alveoli,  which 
generally  contain  a  certain  quantity  of  adipose  tissue. 

The  layer  called  the  true  skin  is  subdivided  into  a  deep,  reticulated  or 
fibrous  layer,  and  a  superficial  portion,  called  the  papillary  layer.  The  epi- ' 
dermis  is  also  divided  into  two  layers,  as  follows  :  an  external  layer,  called  the 
horny  layer ;  and  an  internal  layer,  called  the  Malpighian,  or  the  mucous 
layer,  which  is  in  contact  with  the  papillary  layer  of  the  corium. 

The  Corium,  or  True  Skin. — The  reticulated  and  the  papillary  layers  of 
the  true  skin  are  quite  distinct.  The  lower  stratum,  the  reticulated  layer,  is 


344  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

much  thicker  than  the  papillary  layer  and  is  dense,  resisting,  quite  elastic 
and  slightly  contractile.  It  is  composed  of  bundles  of  fibrous  tissue,  inter- 
lacing with  each  other  in  every  direction,  generally  at  acute  angles.  Distrib- 
uted throughout  this  layer,  are  found  anastomosing  elastic  fibres  of  the  small 
variety,  and  with  them  a  number  of  non-striated  muscular  fibres.  This  por- 
tion of  the  skin  contains,  in  addition,  a  considerable  quantity  of  amorphous 
matter,  which  serves  to  hold  the  fibres  together.  The  muscular  fibres  are 
particularly  abundant  about  the  hair-follicles  and  the  sebaceous  glands  con- 
nected with  them,  and  their  arrangement  is  such  that  when  they  are  excited 
to  contraction  by  cold  or  by  electricity,  the  follicles  are  drawn  up,  projecting 
upon  the  general  surface  and  producing  the  appearance  known  as  "  goose- 
flesh."  Contraction  of  these  fibres  is  particularly  marked  about  the  nipple, 
producing  the  so-called  erection  of  this  organ,  and  about  the  scrotum  and 
penis,  wrinkling  the  skin  of  these  parts.  The  peculiar  arrangement  of  the 
little  muscles  around  the  hair-follicles,  forming  little  bands  attached  to  the 
surface  of  the  true  skin  and  the  base  of  the  follicles,  explains  fully  the  man- 
ner in  which  the  "  goose-flesh  "  is  produced.  (See  Fig.  107,  page  349.)  Con- 
traction of  the  skin,  under  the  stimulus  of  electricity,  has  been  repeatedly 
demonstrated,  both  in  the  living  subject  and  in  executed  criminals  immedi- 
ately after  death. 

The  papillary  layer  of  the  skin  passes  insensibly  into  the  subjacent  struct- 
ure without  any  marked  line  of  division.  It  is  composed  chiefly  of  amor- 
phous matter  like  that  which  exists  in  the  reticulated  layer.  The  papillae 
themselves  appear  to  be  simple  elevations  of  this  amorphous  matter,  although 
they  contain  a  few  fibres,  connective-tissue  nuclei  and  little  corpuscular 
bodies  called  cytoblastions  (Robin). 

As  regards  their  form,  the  papillae  may  be  divided  into  two  varieties ;  the 
simple  and  the  compound.  The  simple  papillse  are  conical,  rounded  or 
club-shaped  elevations  of  the  amorphous  matter  and  are  irregularly  distrib- 
uted on  the  general  surface.  The  smallest  are  y^-g-  to  ^^  of  an  inch  (36  to 
62  /A)  in  length  and  are  found  chiefly  upon  the  face.  The  largest  are  on  the 
palms  of  the  hands,  the  soles  of  the  feet,  and  the  nipple.  These  measure 
-z^-o  to  -zfa  °f  an  incn  (100  to  125  /x).  Large  papillae,  regularly  arranged  in 
a  longitudinal  direction,  are  found  beneath  the  nails.  The  regular,  curved 
lines  observed  upon  the  palms  of  the  hands  and  the  soles  of  the  feet,  particu- 
larly the  palmar  surfaces  of  the  last  phalanges,  are  formed  by  double  rows  of 
compound  papillae,  which  present  two,  three  or  four  elevations  attached  to  a 
single  base.  In  the  centre  of  each  of  these  double  rows  of  papillae,  is  a  fine 
and  shallow  groove,  in  which  are  found  the  orifices  of  the  sudoriferous  ducts. 

The  papillae  are  abundantly  supplied  Avith  blood-vessels  terminating  in 
looped  capillary  plexuses  and  with  nerves.  The  termination  of  the  nerves  is 
peculiar  and  will  be  fully  described  in  connection  with  the  organs  of  touch. 
The  arrangement  of  the  lymphatics,  which  are  very  abundant  in  the  skin, 
has  already  been  indicated  in  the  general  description  of  the  lymphatic  system. 

The  Epidermis  and  its  Appendages. — The  epidermis,  or  external  layer  of 
the  skin,  is  composed  of  cells.  It  has  neither  blood-vessels,  nerves  nor  lym- 


PHYSIOLOGICAL  ANATOMY  OF  THE  NAILS.  345 

phatics.  Its  external  surface  is  marked  by  shallow  grooves,  which  correspond 
to  the  deep  furrows  between  the  papillae  of  the  derma.  Its  internal  surface 
is  applied  directly  to  the  papillary  layer  of  the  true  skin  and  follows  closely 
all  its  inequalities.  This  portion  of  the  skin  is  subdivided  into  two  tolerably 
distinct  layers.  The  internal  layer  is  called  the  rete  mucosum,  or  the  Mal- 
pighian  layer,  and  the  external  is  called  the  horny  layer.  These  two  layers 
present  certain  important  distinctive  characters. 

The  Malpighian  layer  is  composed  of  a  single  stratum  of  prismoidal,  nu- 
cleated cells,  containing  pigmentary  matter,  which  are  applied  directly  to  all 
the  inequalities  of  the  derma,  and  of  a  number  of  layers  of  rounded  cells 
containing  no  pigment.  The  upper  layers  of  cells,  with  the  scales  of  the 
horny  layer,  are  semi-transparent  and  nearly  colorless ;  and  it  is  the  pigment- 
ary layer  chiefly  which  gives  to  the  skin  its  characteristic  color  and  the  pe- 
culiarities in  the  complexion  of  different  races  and  of  different  individuals. 
All  the  epidermic  cells  are  somewhat  colored  in  the  dark  races,  but  the  upper 
layers  contain  no  pigmentary  granules.  The  thickness  of  the  rete  mucosum 
is  J^VT  to  -fa  of  an  inch  (15  to  333  p). 

The  horny  layer  is  composed  of  a  number  of  strata  of  hard,  flattened  cells, 
irregularly  polygonal  in  shape  and  generally  without  nuclei.  The  deeper 
cells  are  thicker  and  more  rounded  than  those  of  the  superficial  layers. 

The  epidermis  serves  as  a  protection  to  the  more  delicate  structure  of  the 
true  skin,  and  its  thickness  is  in  proportion  to  the  exposure  of  the  different 
parts.  It  is  consequently  much  thicker  upon  the  soles  of  the  feet  and  the 
palms  of  the  hands  than  in  other  portions  of  the  general  surface,  and  its 
thickness  is  very  much  increased  in  those  who  are  habitually  engaged  in 
manual  labor.  Upon  the  face  and  eyelids,  and  in  the  external  auditory  pas- 
sages, the  epidermis  is  most  delicate.  The  variations  in  thickness  depend 
entirely  upon  the  development  of  the  horny  layer.  The  thickness  of  the 
rete  mucosum,  although  it  varies  in  different  parts,  is  rather  more  uniform. 

There  is  constantly  more  or  less  desquamation  of  the  epidermis,  particu- 
larly of  the  horny  layer,  and  the  cells  are  regenerated  from  the  subjacent 
parts.  It  is  probable  that  there  is  a  constant  formation  of  cells  in  the  deeper 
strata  of  the  horny  layer,  which  become  flattened  as  they  near  the  surface ; 
but  there  is  no  direct  evidence  that  the  cells  of  the  rete  mucosum  undergo 
transformation  into  the  hard,  flattened  scales  of  the  horny  layer. 

Physiological  Anatomy  of  the  Nails. — The  nails  are  situated  on  the  dor- 
sal surfaces  of  the  distal  phalanges  of  the  fingers  and  toes.  They  serve  to 
protect  these  parts,  and  in  the  fingers,  they  are  quite  important  in  prehen- 
sion. The  general  appearance  of  the  nails  is  sufficiently  familiar.  In  their 
description,  anatomists  have  distinguished  a  root,  a  body  and  a  free  border. 

The  root  of  the  nail  is  thin  and  soft,  terminating  in  rather  a  jagged  edge, 
which  is  turned  slightly  upward  and  is  received  into  a  fold  of  the  skin,  ex- 
tending around  the  nail  to  its  free  edge.  The  length  of  the  root  varies  with 
the  size  of  the  nail,  but  it  is  generally  one-fourth  to  one-third  of  the  length 
of  the  body. 

The  body  of  the  nail  extends  from  the  fold  of  skin  which  covers  the  root, 


EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 


to  the  free  border.  This  portion  of  the  nail,  with  the  root,  is  closely  adher- 
ent by  its  under  surface  to  the  true  skin.  It  is  marked  by  fine  but  distinct 

longitudinal  striae 
and  very  faint 
transverse  lines. 
It  usually  is  red- 
dish in  color  on  ac- 
count of  the  great 
vascularity  of  the 
subjacent  struct- 
ure. At  the  pos- 
terior part,  is  a 
whitish  portion,  of 

FIG.  105  —Anatomy  of  the  nails  (Sappey).  .. 

A,  nail  in  situ:  1,  cutaneous  fold  covering  the  root  of  the  nail ;  2,  section    ^  Semilunar  Sliape, 

of  this  fold,  turned  back  to  show  the  root  of  the  nail ;  3,  lunula  ;  4,  nail.     nollf,/l     tVio    Irmula 

B,  concave  or  adherent  surface  of  the  nail :  1,  border  of  the  root;  2,  lunula    <J"11  uid, 

and  root ;  3,  body  ;  4.  free  border.  wViinh    >in«   fhic  an 

C,  longitudinal  section  of  the  nail :  1,  2,  epidermis  ;  3,  superficial  layer  of    wnl 

the  nail ;  4,  epidermis  of  the  pulp  of  the  finger  ;  5,  6,  true  skin  :  7,  11,  -nparanpp 

bed  of  the  nail ;  8,  Malpighian  layer  of  the  pulp  of  the  finger  ;  9,  10,  true  rVt 

skin  on  the  dorsal  surface  of  the  finger  ;  12,  true  skin  of  the  pulp  of  the  f  rnm    -I- IIP    fir>f 
finger  ;  13,  last  phalanx  of  the  finger. 

the  corium  in  this 

part  is  less  vascular  and  the  papillae  are  not  so  regular  as  in  the  rest  of  the 
body.  That  portion  of  the  skin  situated  beneath  the  root  and  the  body  of 
the  nail  is  called  the  matrix.  It  presents  highly  vascular  papillae,  arranged 
in  regular,  longitudinal  rows,  and  it  receives  into  its  grooves  corresponding 
ridges  on  the  under  surface  of  the  nail. 

The  free  border  of  the  nail  begins  where  the  nail  becomes  detached  from 
the  skin.  This  is  generally  cut  or  worn  away  and  is  constantly  growing ; 
but  if  left  to  itself,  it  attains  in  time  a  definite  length,  which  may  be  stated, 
in  general  terms,  to  be  an  inch  and  a  half  to  two  inches  (40  to  50  mm.). 

On  examining  the  nail  in  a  longitudinal  section,  the  horny  layer,  which  is 
usually  regarded  as  the  true  nail,  is  found  to  increase  progressively  in  thick- 
ness from  the  root  to  near  the  free  border.  If  the  nail  be  examined  in  a 
transverse  section,  it  will  also  be  found  much  thicker  in  the  central  portion 
than  near  the  edge,  and  that  part  which  is  received  into  the  lateral  portions 
of  the  fold  becomes  excessively  thin  like  the  rest  of  the  root.  The  nail  be- 
comes somewhat  thinner  at  and  near  the  free  border. 

Sections  of  the  nails  show  that  they  are  composed  of  two  layers,  which 
correspond  to  the  Malpighian  and  the  horny  layers  of  the  epidermis,  although 
they  are  much  more  distinct.  The  Malpighian  layer  is  applied  directly  to 
the  ridges  of  the  bed  of  the  nail  and  presents  upon  its  upper  surface  ridges 
much  less  strongly  marked  than  those  of  the  underlying  true  skin.  This 
layer  is  rather  thinner  than  the  horny  layer,  is  whitish  in  color,  and  is  com- 
posed of  a  number  of  strata  of  elongated,  prismoidal,  nucleated  cells,  arranged 
perpendicularly  to  the  matrix. 

The  horny  layer,  which  constitutes  the  true  nail,  is  applied  by  its  under 
surface  directly  to  the  ridges  of  the  Malpighian  layer.  It  is  dense  and  brittle 
and  is  composed  of  strata  of  flattened  cells  which  can  not  be  isolated  without 


PHYSIOLOGICAL  ANATOMY  OF  THE  NAILS. 


34T 


the  use  of  reagents.  If  the  different  strata  of  this  portion  of  the  nail  be 
studied  after  boiling  in  a  dilute  solution  of  sodium  or  potassium  hydrate, 
it  becomes  evident  that  here,  as 

in  the  horny  layer  of  the  epider-     F"  i 

mis,  the  lower  cells  are  rounded, 
while  those  nearer  the  surface 
are  flattened.  These  cells  are 
nearly  all  nucleated.  The  thick- 
ness of  this  layer  varies  in  differ- 
ent portions  of  the  nail,  while 
that  of  the  Malpighian  layer  is 
nearly  uniform.  This  layer  is 
constantly  growing,  and  it  con- 
stitutes the  entire  substance  of 
the  free  borders  of  the  nails. 

The  connections  of  the  nails 
with  the  true  skin  resemble  those 
of  the  epidermis;  but  the  rela- 
tions of  these  structures  to  the 
epidermis  itself  are  somewhat 
peculiar.  Before  the  fourth 
month  of  foetal  life,  the  epider- 
mis covering  the  dorsal  surfaces 
of  the  last  phalanges  of  the  fin- 
gers and  toes  does  not  present 
any  marked  peculiarities ;  but  at 
about  the  fourth  month,  the  pe- 
culiar hard  cells  of  the 
layer  of  the  nails  make  their  ap- 

.  B,  cells  of  the  superficial  layer,  lateru,  .,.. 

pearaiice  between  the    Malplglll-   C,  cells  of  the  superficial  layer,  flat  view. 

D,  cells  of  the  deep  layer. 

an  and  the  horny  layer  of  the 

epidermis,  and  at  the  same  time  the  Malpighian  layer  beneath  this  plate, 
which  is  destined  to  become  the  Malpighian  layer  of  the  nails,  is  thickened 
and  the  cells  assume  a  more  elongated  form.  The  horny  layer  of  the  nails 
constantly  thickens  from  this  time ;  but  until  the  end  of  the  fifth  month, 
it  is  covered  by  the  horny  layer  of  the  epidermis.  After  the  fifth  month, 
the  epidermis  breaks  away  and  disappears  from  the  surface ;  and  at  the 
seventh  month,  the  nails  begin  to  increase  in  length.  Thus,  at  one  time, 
the  nails  are  actually  included  between  the  two  layers  of  the  epidermis ;  but 
after  they  have  become  developed,  they  are  simply  covered  at  their  roots  by  a 
narrow  border  of  the  horny  layer.  The  nails  are  therefore  to  be  regarded  as 
modifications  of  the  horny  layer  of  the  epidermis,  possessing  certain  anatom- 
ical and  chemical  peculiarities.  The  Malpighian  layer  of  the  nails  is  con- 
tinuous with  the  same  layer  of  the  epidermis,  but  the  horny  layers  are  dis- 
tinct. 

One  of  the   most   striking  peculiarities  of  the  nails  is   their  mode  of 


A          .  na.VX.-S**ton  of  the  nail  tie.  (Sappey). 
A,  section  of  the  nail :  1,  1,  superficial  layer  ;  2,  deep  layer ; 
homy          3-  3<  4.  4»  section  of  the  grooves  on  the  attached  sur- 
J  face  ;  5,  5,  union  of  the  superficial  with  the  deep  layer  ; 

<  dark  line  between  the  two  layers. 

arview. 


34:8  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

growth.  The  Malpighian  layer  is  stationary,  but  the  horny  layer  is  con- 
stantly growing,  if  the  nails  be  cut,  from  the  root  and  bed.  It  is  evident  that 
the  nails  grow  from  the  bed,  as  their  thickness  progressively  increases  in  the 
body  from  the  root  to  near  the  free  border ;  but  their  longitudinal  growth  is 
by  far  the  more  rapid.  Indeed,  the  nails  are  constantly  pushing  forward, 
increasing  in  thickness  as  they  advance.  Near  the  end  of  the  body  of  the 
nail,  as  the  horny  layer  becomes  thinner,  the  growth  from  below  is  dimin- 
ished. 

Physiological  Anatomy  of  the  Hairs. — Hairs,  varying  greatly  in  size, 
cover  nearly  every  portion  of  the  cutaneous  surface.  The  only  parts  in 
which  they  are  not  found  are  the  palms  of  the  hands  and  soles  of  the  feet,  the 
palmar  surfaces  of  the  fingers  and  toes,  the  dorsal  surfaces  of  the  last  phalanges 
of  the  fingers  and  toes,  the  lips,  the  upper  eyelids,  the  lining  of  the  prepuce 
and  the  glans  penis.  Some  of  the  hairs  are  long,  others  are  short  and  stiff, 
and  others  are  fine  and  downy.  These  differences  have  led  to  a  division  of 
the  hairs  into  three  varieties : 

The  first  variety  includes  the  long,  soft  hairs,  which  are  found  on  the 
head,  on  the  face  in  the  adult  male,  around  the  genital  organs  and  under  the 
arms  in  both  the  male  and  the  female,  and  sometimes  upon  the  breast  and 
over  the  general  surface  of  the  body  and  extremities,  particularly  in  the  male. 

The  second  variety,  the  short,  stiff  hairs,  is  found  just  within  the  nostrils, 
upon  the  edges  of  the  eyelids  and  upon  the  eyebrows. 

The  third  variety,  the  short,  soft,  downy  hairs,  is  found  on  parts  of  the 
general  surface  not  occupied  by  the  long  hairs,  and  in  the  caruncula  lachry- 
malis.  In  early  life,  and  ordinarily  in  the  female  at  all  ages,  the  trunk  and 
extremities  are  covered  with  downy  hairs ;  but  in  the  adult  male,  these  fre- 
quently become  developed  into  long,  soft  hairs. 

The  hairs  are  usually  set  obliquely  in  the  skin  and  take  a  definite  direc- 
tion as  they  lie  upon  the  surface.  Upon  the  head  and  face,  and,  indeed,  the 
entire  surface  of  the  body,  the  general  course  of  the  hairs  may  be  followed 
out,  and  they  present  currents  or  sweeps  that  have  nearly  always  the  same 
directions  in  different  persons. 

The  diameter  and  length  of  the  hairs  are  variable  in  different  persons,  es- 
pecially in  the  long,  soft  hairs  of  the  head  and  beard.  It  may  be  stated  in 
general  terms  that  the  long  hairs  attain  the  length  of  twenty  inches  to 
three  feet  (500  to  900  mm.)  in  women,  and  considerably  less  in  men.  Like 
the  nails,  the  hair,  when  left  to  itself,  attains  in  three  or  four  years  a  definite 
length,  but  when  it  is  habitually  cut  it  grows  constantly.  The  short, 
stiff  hairs  are  £  to  £  of  an  inch  (6'4  to  12'7  mm.)  in  length.  The 
soft,  downy  hairs  measure  ordinarily  -fa  to  £  of  an  inch  (2'1  to  12'7  mm.)  in 
length. 

Of  the  long  hairs,  the  finest  are  upon  the  head,  where  they  average  about 
j-J-g-  of  an  inch  (64  //.)  in  diameter.  The  hair  ordinarily  is  coarser  in  women 
than  in  men.  Dark  hair  is  generally  coarser  than  light  hair  ;  and  upon  the 
same  head  the  extremes  of  variation  are  sometimes  observed.  The  hairs  of 
the  beard  and  the  long  hairs  of  the  body  are  coarser  than  the  hairs  of  the 


PHYSIOLOGICAL  ANATOMY   OF   THE   HAIRS. 


349 


head.  The  average  number  of  hairs  upon  a  square  inch  of  the  scalp  is  about 
1,000  (155  in  a  square  centimetre)  and  the  number  upon  the  entire  head, 
about  120,000  (Wilson). 

When  the  hairs  are  in  a  perfectly  normal  condition,  they  are  very  elastic 
and  may  be  stretched  to  one-fifth  or  one-third  more  than  their  original 


FIG.  107.— Hair  and  hair-follicle  (Sappey). 
1,  root  of  the  hair  ;  2,  bulb  of  the  hair  ;  3,  internal  root- 
sheath  :  4,  external  root-sheath  ;  5,  membrane  of 
the  hair-follicle  (the  internal,  amorphous  mem- 
brane of  the  follicle  is  very  delicate  and  is  not  rep- 
resented in  the  figure*  :  fi.  external  membrane  of 
the  follicle  ;  7,  7.  muscular  band-i  attached  to  the 
follicle  ;  8,  8,  extremities  of  these  bands  passing  to 
the  skin  ;  9,  compound  sebaceous  gland,  with  its 
duct  (10)  opening  into  the  upper  third  of  the  fol- 
licle :  11.  simple  sebaceous  gland  ;  12,  opening  of 
the  hair-follicle. 


FIG.  108.— Root  of  the  hair  (Sappey). 
1,  root  of  the  hair  ;  2,  hair-bulb  :  3,  papilla  of 
the  follicle  ;  4,  opening  of  the  follicle  ;  5, 
5,  internal  root-sheath  ;  6,  external  root- 
sheath  ;  7,  7,  sebaceous  glands  :  8,  8,  ex- 
cretory ducts  of  the  sebaceous  glands. 


length.  Their  strength  varies  with  their  thickness,  but  an  ordinary  hair  from 
the  head  will  bear  a  weight  of  six  to  seven  ounces  (170  to  200  grammes).  A 
well  known  property  of  the  hair  is  that  of  becoming  strongly  electric  by 


350  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

friction ;  and  this  is  particularly  marked  when  the  weather  is  cold  and  dry. 
The  electricity  thus  excited  is  negative.  Sections  of  the  shaft  of  the  hairs 
show  that  they  are  oval,  but  their  shape  is  very  variable,  straight  hairs  being 
nearly  round,  while  curled  hairs  are  quite  flat.  Another  peculiarity  of  the 
hairs  is  that  they  are  strongly  hygrornetric.  They  readily  absorb  moisture 
and  become  sensibly  elongated,  a  property  which  has  been  made  use  of  by 
physicists  in  the  construction  of  delicate  hygrometers. 

Roots  of  the  Hairs,  and  Hair-follicles. — The  roots  of  the  hairs  are  em- 
bedded in  follicular  openings  in  the  skin,  which  differ  in  the  different  vari- 
eties only  in  the  depth  to  which  they  penetrate  the  cutaneous  structure.  In 
the  downy  hairs,  the  roots  pass  only  into  the  superficial  layers  of  the  true 
skin  ;  but  in  the  thicker  hairs,  the  roots  pass  through  the  skin  and  penetrate 
the  subcutaneous  cellulo-adipose  tissue. 

The  root  of  the  hair  is  softer,  rounder  and  a  little  larger  than  the  shaft. 
It  becomes  enlarged  into  a  rounded  bulb  at  the  bottom  of  the  follicle,  and  rests 
upon  a  fungiform  papilla,  constricted  at  its  base,  to  which  the  hair  is  closely 
attached. 

The  hair-follicles  are  tubular  inversions  of  the  structures  that  compose  the 
corium,  and  their  walls  present  three  membranes.  Their  length  is  ^  to  ^  of 
an  inch  (2-1  to  6-4  mm.).  The  membrane  that  forms  the  external  coat  of  the 
follicles  is  composed  of  inelastic  fibres,  generally  arranged  longitudinally.  It 
is  provided  with  blood-vessels,  a  few  nerves  and  some  connective-tissue  ele- 
ments, but  no  elastic  tissue.  This  is  the  thickest  of  the  three  membranes  and 
is  closely  connected  with  the  corium.  Next  to  this,  is  a  fibrous  membrane 
composed  of  fusiform,  nucleated  fibres  arranged  transversely.  These  re- 
semble non-striated  muscular  fibres.  The  internal  membrane  is  structureless 
and  corresponds  to  the  amorphous  layer  of  the  true  skin.  The  papilla  at  the 
bottom  of  the  hair-sac  varies  in  size  with  the  size  of  the  hairs  and  is  con- 
nected with  the  fibrous  layers  of  the  walls  of  the  follicle.  It  is  composed  of 
amorphous  matter,  with  a  few  granules  and  nuclei,  and  it  probably  contains 
blood-vessels  and  nerves,  although  these  are  not  very  distinct. 

Although  the  different  membranes  of  the  hair-follicles  are  sufficiently  rec- 
ognizable, it  is  evident  that  the  hair-sac  is  nothing  more  than  an  inversion  of 
the  corium,  with  certain  modifications  in  the  character  and  arrangement 
of  its  anatomical  elements.  The  fibrous  membranes  correspond  to  the  deeper 
layers  of  the  true  skin,  without  the  elastic  elements ;  and  they  present  a  pecul- 
iar arrangement  of  its  inelastic  fibres,  the  external  fibres  being  longitudinal 
and  the  internal  fibres  transverse.  The  structureless  membrane  corresponds 
to  the  upper  layers  of  the  true  skin,  which  are  composed  chiefly  of  amorphous 
matter.  The  hair-papilla  corresponds  to  the  papillae  on  the  general  surface 
of  the  corium. 

The  investment  of  the  root  of  the  hair  presents  two  distinct  layers 
called  the  external  and  internal  root-sheaths.  The  external  root-sheath  is 
three  or  four  times  as  thick  as  the  inner  membrane,  and  it  corresponds  ex- 
actly with  the  Malpighian  layer  of  the  epidermis.  This  sheath  is  continu- 
ous with  the  bulb  of  the  hair.  The  internal  root-sheath  is  a  transparent 


PHYSIOLOGICAL  ANATOMY  OF  THE  HAIRS. 


351 


membrane,  composed  of  flattened  cells,  generally  without  nuclei.  This 
extends  from  the  bottom  of  the  hair-follicle  and  covers  the  lower  two-thirds 
of  the  root. 

Structure  of  the  Hairs. — The  different  varieties  of  hairs  present  certain 
peculiarities  in  their  anatomy,  but  all  of  them  are  composed  of  a  fibrous 
structure  forming  the  greater  part  of  their  substance,  covered  by  a  thin  layer 


United  States  Army  Medical  Museum). 


This  figure  shows  the  imbricated  arrangement  of 
the  epidermis  of  the  hair. 

of  imbricated  cells.  In  the  short,  stiff  hairs,  and  in  the  long,  white  hairs, 
there  is  a  distinct  medullary  substance ;  but  this  is  wanting  in  the  downy 
hairs  and  is  indistinct  in  many  of  the  long,  dark  hairs. 

The  fibrous  substance  of  the  hairs  is  composed  of  hard,  elongated,  longi- 
tudinal fibres,  which  can  not  be  isolated  without  the  aid  of  reagents.  They 
may  be  separated,  however,  by  maceration  in  warm  sulphuric  acid,  when 
they  present  themselves  in  the  form  of  dark,  irregular,  spindle-shaped  plates. 
These  contain  pigmentary  matter  of  various  shades  of  color,  occasional  cavi- 
ties filled  with  air,  and  a  few  nuclei.  The  pigment  may  be  of  any  shade, 
between  a  light  yellow  and  an  intense  black ;  and  it  is  this  substance  that 
gives  to  the  hair  the  great  variety  in  color  which  is  observed  in  different 
persons.  In  the  lower  part  of  the  root  the  fibres  are  much  shorter,  and  at 
the  bulb  they  become  transformed,  as  it  were,  into  the  soft,  rounded  cells 
found  in  this  situation,  covering  the  papilla. 

The  epidermis  of  the  hair  is  very  thin  and  is  composed  of  flattened, 
quadrangular  plates,  overlying  each  other  from  below  upward.  These  scales, 
or  plates,  are  without  nuclei,  and  they  exist  in  a  single  layer  over  the  shaft 
of  the  hair  and  the  upper  part  of  its  root ;  but  in  the  lower  part  of  the  root, 
the  cells  are  thicker,  softer,  are  frequently  nucleated,  and  they  exist  in  two 
layers. 

The  medulla  is  found  in  the  short,  stiff  hairs,  and  it  is  often  very  distinct 


352  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

in  the  long,  white  hairs  of  the  head.  It  occupies  one-fourth  to  one-third  of 
the  diameter  of  the  hair.  The  medulla  can  be  traced,  under  favorable  con- 
ditions, from  just  above  the  bulb  to  near  the  pointed  extremity  of  the  hair. 
It  is  composed  of  small,  rounded,  nucleated  cells,  which  frequently  contain 
dark  granules  of  pigmentary  matter.  Mixed  with  these  cells  are  air-glob- 
ules ;  and  frequently  the  cells  are  interrupted  for  a  short  distance  and  the 
space  is  filled  with  air.  The  medulla  likewise  contains  a  glutinous  fluid  be- 
tween the  cells  and  surrounding  the  air-globules. 

Growth  of  the  Hairs. — Although  not  provided  with  blood  and  devoid 
of  sensibility,  the  hairs  are  connected  with  vascular  parts  and  are  nourished 
by  imbibition  from  the  papillae.  Each  hair  is  first  developed  in  a  closed 
sac,  and  at  about  the  sixth  month  of  intrauterine  life,  its  pointed  extremity 
perforates  the  epidermis.  These  first-formed  hairs  are  afterward  shed,  like 
the  milk-teeth,  being  pushed  out  by  new  hairs  from  below,  which  latter  arise 
from  a  second  and  a  more  deeply  seated  papilla.  This  shedding  of  the  hairs 
usually  takes  place  between  the  second  and  the  eighth  month  after  birth. 

The  difference  in  the  color  of  the  hair  depends  upon  differences  in  the 
quantity  and  the  tint  of  the  pigmentary  matter ;  and  in  old  age  the  hair  be- 
comes white  or  gray  from  a  blanching  of  the  cortex  and  medulla. 

Sudden  Blanching  of  the  Hair. — There  are  a  few  instances  on  record  in 
which  sudden  blanching  of  the  hair  has  been  observed  and  the  causes  of  this 
remarkable  phenomenon  fully  investigated  by  competent  observers ;  and  it 
is  almost  unnecessary  to  say  that  a  single,  well  authenticated  case  of  this  kind 
demonstrates  the  possibility  of  its  occurrence  and  is  important  in  connection 
with  the  reported  instances  which  have  not  been  subjected  to  proper  investi- 
gation. One  of  these  cases  has  been  reported  by  Landois.  In  this  instance 
the  blanching  of  the  hair  occurred  in  a  hospital  in  a  single  night,  while  the 
patient,  who  had  an  acute  attack  of  delirium  tremens,  was  under  the  daily 
observation  of  the  visiting  physician. 

The  microscopical  examinations  by  Landois  and  others  leave  no  doubt  as 
to  the  cause  of  the  white  color  of  the  hair  in  cases  of  sudden  blanching ;  and 
the  fact  of  the  occurrence  of  this  phenomenon  can  no  longer  be  called  in 
question.  All  are  agreed  that  there  is  no  diminution  in  the  pigment,  but 
that  the  greater  part  of  the  medulla  becomes  filled  with  air,  small  globules 
being  also  found  in  the  cortical  substance.  The  hair  in  these  cases  presents 
a  marked  contrast  with  hair  that  has  gradually  become  gray  from  old  age, 
when  there  is  always  a  loss  of  pigment  in  the  cortex  and  medulla.  How  the 
air  finds  its  way  into  the  hair  in  sudden  blanching,  it  is  difficult  to  under- 
stand ;  and  the  views  that  have  been  expressed  on  this  subject  by  different 
authors  are  entirely  theoretical. 

The  fact  that  the  hair  may  become  white  or  gray  in  the  course  of  a  few 
hours  renders  it  probable  that  many  of  the  cases  reported  upon  unscientific 
authority  actually  occurred ;  and  these  have  all  been  supposed  to  be  con- 
nected with  intense  grief  or  terror.  The  terror  was  very  marked  in  the  case 
reported  by  Landois.  In  the  great  majority  of  recorded  observations,  the 
sudden  blanching  of  the  hair  has  been  apparently  connected  with  intense 


PERSPIEATION.  353 

mental  emotion ;  but  this  is  all  that  can  be  said  on  the  subject  of  causation, 
and  the  mechanism  of  the  change  is  not  understood. 

Uses  of  the  Hair. — The  hairs  serve  an  important  purpose  in  the  protec- 
tion of  the  general  surface  and  in  guarding  certain  of  the  orifices  of  the  body. 
The  hair  upon  the  head  and  the  face  protects  from  cold  and  shields  the  head 
from  the  rays  of  the  sun  during  exposure  in  hot  climates.  Although  the 
quantity  of  hair  upon  the  general  surface  is  small,  as  it  is  a  very  imperfect 
conductor  of  caloric,  it  serves  in  a  degree  to  maintain  the  heat  of  the  body. 
It  also  moderates  the  friction  upon  the  surface.  The  eyebrows  prevent  the 
perspiration  from  running  from  the  forehead  upon  the  lids ;  the  eyelashes 
protect  the  surface  of  the  conj  tinctiva  from  dust  and  other  foreign  matters ; 
the  mustache  protects  the  lungs  from  dust,  which  is.  very  important  in  per- 
sons exposed  to  dust  in  long  journeys  or  in  their  daily  work ;  and  the  short, 
stiff  hairs  at  the  openings  of  the  ears  and  nose  protect  these  orifices.  It  is 
difficult  to  assign  any  special  office  to  the  hairs  in  some  other  situations,  but 
their  general  uses  are  sufficiently  evident. 

PERSPIRATION. 

In  the  fullest  acceptation  of  the  term,  perspiration  embraces  the  entire 
action  of  the  skin  as  an  excreting  organ  and  includes  the  exhalation  of  carbon 
dioxide  as  well  as  of  watery  vapor  and  organic  matters.  The  office  of  the 
skin  as  an  eliminator  is  undoubtedly  very  important ;  but  the  quantity  of 
excrementitious  matters  with  the  properties  of  which  physiologists  are  well 
acquainted,  such  as  carbon  dioxide  and  urea,  thrown  off  from  the  general 
surface,  is  small  as  compared  with  what  is  exhaled  by  the  lungs  and  discharged 
by  the  kidneys.  If  the  surface  of  the  body  be  covered  with  an  impermeable 
coating,  death  occurs  in  a  very  short  time ;  but  the  phenomena  which  precede 
the  fatal  result  are  difficult  to  explain.  All  that  can  be  said  upon  this  point 
is  that  death  takes  place  when  the  heat  of  the  body  has  been  reduced  to  about 
70°  Fahr.  (21°  C.),  and  that  suppression  of  the  action  of  the  skin  in  this  way 
is  always  followed  by  a  depression  of  the  animal  temperature.  Warm-blooded 
animals  die  usually  when  more  than  one-half  of  the  general  surface  has  been 
varnished.  Kabbits  die  when  one-fourth  of  the  surface  has  been  covered 
with  an  impermeable  coating  (Laschkewitsch).  Valentin  and  Laschkewitsch 
found  that  when  the  temperature  was  kept  at  about  the  normal  standard  by 
artificial  means,  no  morbid  symptoms  were  developed.  The  cause  of  death 
in  these  experiments  has  never  been  satisfactorily  explained ;  and  it  is  not 
easy  to  understand  why  coating  the  surface  should  be  followed  by  such  a 
rapid  diminution  in  the  general  temperature.  The  experimental  facts,  how- 
ever, indicate  that  the  skin  probably  possesses  important  uses  with  which 
physiologists  are  unacquainted.  Urea  and  some  other  effete  products  have 
been  detected  in  the  perspiration,  but  it  is  probable  that  some  volatile  mat- 
ters are  eliminated  by  the  general  surface,  which  have  thus  far  escaped  ob- 
servation. 

Sudoriparous  Glands. — With  few  exceptions,  every  portion  of  the  skin 
is  provided  with  sudoriparous  glands.  They  are  not  found,  however,  in  the 


354 


EXCRETION   BY  THE  SKIN  AND  KIDNEYS. 


skin  covering  the  concave  surface  of  the  concha  of  the  ear,  the  glans  penis, 
the  inner  lamella  of  the  prepuce,  and  unless  the  ceruminous  glands  be  re- 
garded as  sudoriparous  organs,  in  the  external  auditory  meatus. 

On  examining  the  surface  of  the  skin  with  a  low  magnifying  power,  espe- 
cially on  the  palms  of  the  hands  and  the  soles  of  the  feet,  the  orifices  of  the 

sudoriferous  ducts  may  be  seen  in  the  mid- 
dle of  the  papillary  ridges,  forming  a  regu- 
lar line  in  the  shallow  groove  between  the 
two  rows  of  papillse.  The  tubes  always 
open  upon  the  surface  obliquely.  In  a  thin 
section  of  the  skin,  the  ducts  are  seen  pass- 
ing through  the  different  layers  and  ter- 
minating in  rounded,  convoluted  coils  in 
the  subcutaneous  structure.  These  little, 
rounded  or  ovoid  bodies,  which  are  the  su- 
doriparous, or  sweat-producing  structures, 
maybe  seen  attached  to  the  under  surface 

».i          i  •          i  -J.TV  j   £ 

of  the  skin  when  it  has  been  removed  from 
the  subjacent  parts  by  maceration.  A  per- 


FIG.  111.—  Surfaceof  the  palm  of  the  hand, 

a  portion  of  the  skin  about  one-half  an 

inch  (127  mm.)  square  ;  magnified  4  di- 


oriferous  ducts; 

of  the  sfkif  ro°ves  between  the  PaPillae  spiratory  gland  consists,  indeed,  of  a  simple 

tube,  presenting  a  coiled  mass,  the  sudorip- 

.-arous  portion,  beneath  the  skin,  and  a  tube  of  greater  or  less  length,  in  pro- 
portion to  the  thickness  of  the  cutaneous  layers,  which  is  the  excretory  duct, 
•  or  the  sudoriferous  portion. 

The  glandular  coils  are  y^-j  to  ^  of  an  inch  (0-2  to  1  mm.)  in  diameter  ; 
the  smallest  coils  being  found  beneath  the  skin  of  the  penis,  the  scrotum,  the 
eyelids,  the  nose  and  the  convex  surface  of  the  concha  of  the  ear,  and  the 
largest,  on  the  areola  of  the  nipple  and  the  perineum.  Very  large  glands  are 
found  mixed  with  smaller  ones  in  the  axilla,  and  these  produce  a  peculiar 
secretion.  The  coiled  portion  of  the  tube  is  about  ^-5-  of  an  inch  (0'07'mm.) 
in  diameter,  and  presents  six  to  twelve  turns.  It  consists  of  a  sharply  defined, 
strong,  external  membrane,  which  is  very  transparent,  uniformly  granular  and 
sometimes  indistinctly  striated.  The  tube  is  of  uniform  diameter  throughout 
the  coil  and  terminates  in  a  very  slightly  dilated,  rounded,  blind  extremity. 
It  is  filled  with  epithelium  in  the  form  of  finely  granular  matter,  usually  not 
segmented  into  cells,  and  is  provided  with  small,  oval  nuclei.  The  glandular 
mass  is  surrounded  by  a  plexus  of  capillary  blood-vessels,  which  send  a  few 
small  branches  between  the  convolutions  of  the  coil.  Sometimes  the  coil  is 
enclosed  in  a  delicate  fibrous  envelope. 

The  excretory  duct  is  simply  a  continuation  of  the  glandular  coil.  Its 
course  through  the  layers  of  the  true  skin  is  nearly  straight.  It  then  passes 
into  the  epidermis,  between  the  papillae  of  the  corium,  and  presents,  in  this 
layer,  a  number  of  spiral  turns.  The  spirals  vary  in  number  according  to 
the  thickness  of  the  epidermis.  Six  to  ten  are  found  in  the  palms  of  the 
hands  and  twelve  to  fifteen  in  the  soles  of  the  feet  (Sappey).  As  it  emerges 
from  the  glandular  coil,  the  excretory  duct  is  somewhat  narrower  than  the 


MECHANISM  OF  THE  SECRETION  OF  SWEAT. 


355 


tube  in  the  secreting  portion ;  but  as  it  passes  through  the  epidermis,  it  again 
becomes  larger.  It  possesses  the  same  external  membrane  as  the  glandular 
coil  and  is  lined  generally  by  two  layers  of  cells. 

In  a  section  of  the  skin  and  the  subcutaneous  tissue,  involving  several  of 
the  sudoriparous  glands  with  their  ducts,  it  is  seen  that  the  glandular  coils 
generally  are  situated  at  different  planes  be- 
neath the  skin,  as  is  indicated  in  Fig.  112. 

Sudoriparous  glands  in  the  axilla  have  been 
described  which  do  not  differ  so  much  from 
the  glands  in  other  parts  in  their  anatomy  as 
in  the  character  of  their  secretion.*  The  coil 
in  these  glands  is  much  larger  than  in  other 
parts,  measuring  -fa  to  ^  of  an  inch  (1  to  2 
mm.) ;  the  walls  of  the  tube  are  thicker,  and 
they  present  an  investment  of  fibrous  tissue 
with  an  internal  layer  of  longitudinal,  non- 
striated  muscular  fibres ;  and  finally,  the  tubes 
of  the  coil  itself  are  lined  with  cells  of  epithe- 
lium. These  glands  are  very  abundant  in  the 
axilla,  forming  a  continuous  layer  beneath  the 
skin.  Mixed  with  these,  are  a  few  glands  of 
the  ordinary  variety. 

Estimates  have  been  made  of  the  number 
of  sudoriparous  glands  in  the  body  and  the 
probable  extent  of  the  exhalant  surface  of  the 
skin,  but  they  are  to  be  taken  as  merely  approx-  FIG.  112.— sudoriparous  glands ;  mag- 

T7-  „  ,  ,     -,.„,  .,  nified  20  diameters  (Sappey). 

imate.     Jvrause  round  great  differences  in  the 

number  of  perspiratory  openings  in  different 

portions  of  the  skin ;   but  taking  an  average 

for  the   entire   surface,  it  was  estimated  that 

the  entire  number   of   perspiratory  glands  is 

2,381,248;  and  assuming  that  each  coil  when  unravelled  measures  about  -^ 

of  an  inch  (1-8  mm.),  the  entire  length  of  the  secreting  tubes  is  about  2£ 

miles  (3f  kilometres).     It  must  be  remembered,  however,  that  the  length  of 

the  secreting  coil  only  is  given,  and  that  the  excretory  ducts  are  not  included. 

Mechanism  of  the  Secretion  of  Sweat. — The  action  of  the  skin  as  a  glandu- 
Lir  organ  is  continuous  and  not  intermittent;  but  under  ordinary  conditions, 
the  sv/eat  is  exhaled  from  the  general  surface  in  the  form  of  vapor.  With 
regard  to  the  mechanism  of  its  separation  from  the  blood,  nothing  is  to  be 
said  in  addition  to  the  general  remarks  upon  the  subject  of  secretion ;  and 
it  is  probable  that  the  epithelium  of  the  secreting  coils  is  the  active  agent  in 
the  selection  of  the  peculiar  matters  which  enter  into  its  composition.  There 
are  no  examples  of  the  separation  by  glandular  organs  of  vapor  from  the 
blood,  and  the  perspiration  is  secreted  as  a  liquid,  which  becomes  vaporous 
as  it  is  discharged  upon  the  surface. 

The  influence  of  the  nervous  system  upon  the  secretion  of  sweat  is  impor- 


1,  epidermis  ;  2,  2,  mucous  layer ; 
3,  3,  papillae  ;  4,  4,  derma  :  5,  5,  sub- 
cutaneous areolar  tissue  ;  6,  6,  6,  6, 
sudoriparous  glands  ;  7,  7,  adipose 
vesicles  ;  8,  8,  excretory  ducts  in 
the  derma ;  9,  9,  excretory  ducts 
divided. 


356  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

tant.  It  is  well  known,  for  example,  that  an  abundant  production  of  per- 
spiration is  frequently  the  result  of  mental  emotions.  Bernard  has  shown 
that  the  nervous  influence  may  be  exerted  through  the  sympathetic  system. 
He  divided  the  sympathetic  in  the  neck  of  a  horse,  producing  as  a  conse- 
quence an  elevation  in  temperature  and  an  increase  in  the  arterial  pressure 
in  the  part  supplied  with  branches  of  the  nerve.  He  found,  also,  that  the 
skin  of  the  part  became  covered  with  a  copious  perspiration.  Upon  stimu- 
lating the  divided  extremity  of  the  nerve,  the  secretion  of  sweat  was  arrested. 
The  local  secretion  of  sweat  after  division  of  the  sympathetic  in  the  neck  of 
the  horse  was  first  observed  by  Dupuy,  in  1816. 

The  stimulation  as  well  as  the  division  of  certain  nerves  induces  local 
secretion  of  sweat,  but  this  is  nearly  always  associated  with  dilatation  of  the 
blood-vessels  of  the  part ;  still,  sweat  is  frequently  secreted  when  the  surface 
is  pale  and  bloodless,  showing  that  dilatation  of  the  blood-vessels  is  not  an 
indispensable  condition.  The  action  of  the  so-called  vaso-dilator  nerves  will 
be  treated  of  in  connection  with  the  physiology  of  the  nervous  system.  In 
experiments  upon  the  cat,  excito-secretory  fibres  have  been  found  to  exist  in 
the  oerebro-spinal  nerves  going  to  the  anterior  extremities.  The  fibres  for 
the  posterior  extremities  are  in  the  sheath  of  the  sciatic  nerve.  In  all  in- 
stances the  action  of  these  nerves  is  direct  and  not  reflex.  Experiments  upon 
the  cat  have  been  very  satisfactory,  as  this  animal  sweats  only  on  the  soles  of 
the  feet,  and  the  secretion  can  be  readily  observed. 

The  so-called  sweat-centres  are  in  the  lower  part  of  the  dorsal  region  of 
the  spinal  cord,  for  the  posterior  extremities,  and  in  the  lower  part  of  the 
cervical  region  of  the  cord,  for  the  anterior  extremities.  According  to  Adam- 
kiewicz,  both  of  these  centres  are  subordinate  to  the  principal  sweat-centre, 
which  is  situated  in  the  medulla  oblongata.  Ott  has  collected  a  number  of 
cases  of  disease  of  the  cord  in  the  human  subject,  which  go  far  to  confirm 
the  results  of  experiments  on  the  inferior  animals,  with  regard  to  the  action 
of  excito-secretory  nerves  and  sweat-centres. 

When  the  skin  is  in  a  normal  condition,  after  exercise  or  whenever  there 
is  a  tendency  to  elevation  of  the  animal  temperature,  there  is  a  determination 
of  blood  to  the  surface,  accompanied  with  an  increase  in  the  secretion  of 
sweat.  This  is  the  case  when  the  body  is  exposed  to  a  high  temperature ; 
and  it  is  by  an  increase  in  the  transpiration  from  the  surface  that  the  animal 
heat  is  maintained  at  the  normal  standard. 

Quantity  of  Cutaneous  Exhalation. — The  quantity  of  cutaneous  exhala- 
tion is  subject  to  great  variations,  depending  upon  conditions  of  temperature 
and  moisture,  exercise,  the  quantity  and  character  of  the  ingesta,  etc.  Most 
of  these  variations  relate  to  the  action  of  the  skin  in  regulating  the  tempera- 
ture of  the  body ;  and  it  is  probable  that  the  elimination  of  excrementitious 
matters  by  the  skin  is  not  subject,  under  normal  conditions,  to  the  same 
modifications,  although  positive  experiments  upon  this  point  are  wanting. 
When  there  is  such  a  wide  range  of  variation  in  different  individuals  and  in 
the  same  person  under  different  conditions  of  season,  climate  etc.,  it  is  pos- 
sible only  to  give  approximate  estimates  of  the  quantity  of  sweat  secreted 


PROPERTIES  AND  COMPOSITION  OF  THE  SWEAT.          357 

and  exhaled  in  the  twenty-four  hours.  Seguin  and  Lavoisier  (1790)  esti- 
mated the  daily  quantity  of  cutaneous  transpiration  at  one  pound  and  four- 
teen ounces  (850  grammes),  and  the  results  of  their  observations  have  been 
fully  confirmed  by  recent  investigations.  It  may  be  assumed  that  the  aver- 
age quantity  is  nearly  two  pounds,  or  about  900  grammes. 

Under  violent  and  prolonged  exercise,  the  loss  of  weight  by  exhalation 
from  the  skin  and  lungs  may  become  very  considerable.  It  is  stated  by 
Maclaren,  the  author  of  a  work  on  training,  that  in  one  hour's  energetic 
fencing,  the  loss  by  perspiration  and  respiration,  taking  the  average  of  six 
consecutive  clays,  was  forty  ounces  (1,130  grammes),  with  a  range  of  variation 
of  eight  ounces  (227  grammes). 

When  the  body  is  exposed  to  a  high  temperature,  the  exhalation  from  the 
surface  is  largely  increased  ;  and  it  is  by  this  rapid  evaporation  that  persons 
have  been  able  to  endure  for  several  minutes  a  dry  heat  considerably  exceed- 
ing that  of  boiling  water.  Southwood  Smith  made  a  series  of  observations 
with  regard  to  this  point  upon  workmen  employed  about  the  furnaces  of  gas- 
works and  exposed  to  intense  heat ;  and  he  found  that  in  an  hour,  the  loss  of 
weight  was  two  to  four  pounds  (907  to  1,814  grammes),  this  being  chiefly  by 
exhalation  of  watery  vapor  from  the  skin.  In  such  instances  the  loss  of  water 
by  transpiration  is  compensated  by  the  ingestion  of  large  quantities  of  liquid. 

Properties  and  Composition  of  the  Sweat. — An  analysis  of  the  sweat  was 
made  by  Favre,  in  1853.  After  taking  every  precaution  to  obtain  the  secre- 
tion in  a  perfectly  pure  state,  he  collected  a  very  large  quantity,  nearly  thirty 
pints  (14  litres),  the  result  of  six  transpirations  from  one  person,  which  he 
assumed  to  represent  about  the  average  in  composition.  The  liquid  was  per- 
fectly limpid,  colorless,  and  of  a  feeble  but  characteristic  odor.  Almost  all 
observers  have  found  the  reaction  of  the  sweat  to  be  acid ;  but  it  readily  be- 
comes alkaline  on  being  subjected  to  evaporation,  showing  that  it  contains 
some  of  the  volatile  acids.  Favre  found  that  the  fluid  collected  during  the 
first  half -hour  of  the  observation  was  acid ;  during  the  second  half -hour  it 
was  neutral  or  feebly  alkaline  ;  and  during  the  third  half-hour,  it  was  con- 
stantly alkaline.  The  specific  gravity  of  the  sweat  is  1003  to  1004.  The  fol- 
lowing is  the  composition  of  the  fluid  collected  by  Favre  : 

COMPOSITION    OF    THE    SWEAT. 

Water 995-573 

Urea  •. 0-043 

Fatty  matters 0-014 

Alkaline  lactates 0-317 

Alkaline  sudorates 1-562 

Sodium  chloride,           ]   2-230 

Potassium  chloride,       I   • 0-244 

Alkaline  sulphates,       I  soluble  in  water 0-012 

Alkaline  phosphates,        a  trace 

Alkaline  albuminates,  J 0-005 

Alkaline  earthy  phosphates  (soluble  in  acidulated  water) a  trace 

Epidermic  debris  (insoluble) a  trace 

1,000-000 


358  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

The  sweat  is  exhaled  usually  in  the  form  of  vapor,  when  it  is  known  as 
insensible  perspiration.  When  from  any  cause  it  collects  on  the  surface,  in 
the  form  of  a  liquid,  it  is  called  sensible  perspiration. 

The  peculiar  constituents  of  the  sweat  have  been  more  carefully  and  suc- 
cessfully studied  since  the  analyses  of  Favre.  The  neutral  fats  are  probably 
derived  in  great  part  from  the  sebaceous  glands,  although  certain  fats,  palmi- 
tine  and  stearine,  have  been  found  in  the  secretion  of  the  palms  of  the  hands, 
which  contain  no  sebaceous  glands.  The  volatile  fatty  acids  are  formic, 
butyric,  caproic,  capric,  acetic  etc.,  some  of  which  exist  also  in  milk.  These 
give  to  the  sweat  its  peculiar  odor.  Urea  is  always  present  in  small  quan- 
tity, and  its  proportion  may  be  largely  increased  when  there  is  a  deficiency  of 
elimination  by  the  kidneys.  It  is  a  matter,  also,  of  common  as  well  as  df 
scientific  observation  that  the  sweat  is  more  abundant  when  the  kidneys  are 
comparatively  inactive,  and  vice  versa.  Generally,  however,  conditions  oper- 
ate to  increase  the  quantity  of  sweat,  and  the  quantity  of  urine  is  proportion- 
ally diminished.  The  skin  is  undoubtedly  an  important  organ  of  excretion, 
and  it  may  eliminate  excrementitious  matters  of  a  character  as  yet  unknown. 
The  action  of  the  skin  as  a  respiratory  organ  has  already  been  considered. 
With  regard  to  the  inorganic  constituents  of  the  sweat,  there  is  no  great  inter- 
est attached  to  any  but  the  sodium  chloride,  which  exists  in  a  proportion 
many  times  greater  than  that  of  all  the  other  inorganic  salts  combined. 

Peculiarities  of  the  Sweat  in  Certain  Parts.—  In  the  axilla,  the  inguino- 
scrotal  region  in  the  male,  and  the  inguino-vulvar  region  in  the  female,  and 
between  the  toes,  the  sweat  always  has  a  peculiar  odor,  more  or  less  marked, 
which  in  some  persons  is  excessively  disagreeable.  Donne  has  shown  that 
whenever  the  secretion  has  an  odor  of  this  kind  its  reaction  is  distinctly  alka- 
line ;  and  he  is  disposed  to  regard  its  peculiar  characters  as  due  to  a  mixture 
of  the  secretion  of  the  other  follicles  found  in  these  situations.  Sometimes 
the  sweat  about  the  nose  has  an  alkaline  reaction.  In  the  axillary  region 
the  secretion  is  rather  less  fluid  than  on  the  general  surface  and  frequently 
has  a  yellowish  color,  so  marked,  sometimes,  as  to  stain  the  clothing. 

PHYSIOLOGICAL  ANATOMY  OF  THE  KIDNEYS. 

The  kidneys  are  symmetrical  organs,  situated  in  the  lumbar  region,  be- 
neath the  peritoneum,  invested  by  a  proper  fibrous  coat,  and  always  sur- 
rounded by  more  or  less  adipose  tissue.  They  usually  extend  from  the 
eleventh  or  twelfth  rib  downward  to  near  the  crest  of  the  iliurn,  and  the 
right  is  always  a  little  lower  than  the  left.  In  shape  the  kidney  is  very 
appropriately  compared  to  a  bean ;  and  the  concavity,  the  deep,  central  por- 
tion of  which  is  called  the  hilum,  looks  inward  toward  the  spinal  column. 
The  weight  of  each  kidney  is  four  to  six  ounces  (113  to  170  grammes),  usu- 
ally about  half  an  ounce  (14  grammes)  less  in  the  female  than  in  the  male. 
The  left  kidney  is  nearly  always  a  little  heavier  than  the  right. 

Outside  of  the  proper  coat  of  the  kidney,  is  a  certain  quantity  of  adipose 
tissue  enclosed  in  a  loose,  fibrous  structure.  This  is  sometimes  called  the 
adipose  capsule ;  but  the  proper  coat  consists  of  a  close  net- work  of  ordinary 


PHYSIOLOGICAL  ANATOMY  OF  THE  KIDNEYS. 


359 


fibrous  tissiie,  interlaced  with  small  elastic  fibres.  This  coat  is  thin  and 
smooth  and  may  be  readily  removed  from  the  surface  of  the  organ,  At  the 
hilum  it  is  continued  inward  to  line  the  pelvis  of  the  kidney,  covering  the 
calices  and  blood-vessels. 

The  kidney  in  a  vertical  section  presents  a  cavity  at  the  hilum,  which  is 
bounded  internally  by  the  dilated  origin  of  the  ureter.  This  is  called  the 
pelvis.  It  is  lined  by  a  smooth  membrane,  which  is  simply  a  continuation 
of  the  proper  coat  of  the  kidney,  and  which  forms  little  cylinders,  called 
calices,  into  which  the  apices  of  the  pyramids  are  received.  Some  of  the 
calices  receive  the  apex  of  a  single  pyramid,  while  others  are  larger  and  re- 
ceive two  or  three.  The  calices  unite  into  three  short,  funnel-shaped  tubes, 
called  infimdibula,  corresponding  respectively  to  the  superior,  middle  and 
inferior  portions  of  the  kidney.  These  finally  open  into  the  common  cavity, 
or  pelvis.  The  substance  of  the  kid- 
ney is  composed  of  two  distinctly 
marker!  portions,  called  the  cortical 
substance,  and  the  medullary,  or  py- 
ramidal substance. 

The  cortical  substance  is  reddish 
and  granular,  rather  softer  than  the 
pyramidal  substance,  and  is  about  one- 
sixth  of  an  inch  (4-2  mm.)  in  thick- 
ness. This  occupies  the  exterior  of 
the  kidney  and  sends  little  prolonga- 
tions, called  the  columns  of  Bertin,  be-  i. 
tween  the  pyramids.  The  surface  of 
the  kidney  is  marked  by  little,  poly- 
gonal divisions,  giving  it  a  lobulated 
appearance.  This,  however,  is  mainly 
due  to  the  arrangement  of  the  super- 
ficial blood-vessels.  The  medullary 
substance  is  arranged  in  the  form  of 
pyramids,  sometimes  called  the  pyra- 
mids of  Malpighi,  twelve,  fifteen  or 
eighteen  in  numbor,  their  bases  pre- 

3    .  .  Fio.  113.—  Vertical  section  of  the  kidney  (Sappey). 

senting  toward  the  cortical  substance,  i,  i,  2, 2, 
and  their  apices  being  received  into        roun 
the  culices,  at  the  pelvis.    Ferrein  sub- 
divided the  pyramids  of  Malpighi  into 

smaller  pyramids,  called  the  pyramids  of  Ferrein,  each  formed  by  about  one 
hundred  tubes  radiating  from  the  openings  at  the  summit  of  the  pyramids, 
toward  their  bases.  The  tubes  composing  these  pyramids  pass  into  the  cor- 
tical substance,  forming  corresponding  pyramids  of  convoluted  tubes,  thus 
dividing  this  portion  of  the  kidney  into  lobules,  more  or  less  distinct. 

The  medullary  substance  is  firm,  .of  a  darker  red  color  than  the  cortical 
substance,  and  is  marked  by  tolerably  distinct  strias,  which  take  a  nearly 


Be" 
8' upper  extremi' 


360 


EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 


straight  course  from  the  bases  to  the  apices  of  the  pyramids.  As  these  stria? 
indicate  the  direction  of  the  little  tubes  that  constitute  the  greatest  part  of 
the  medullary  substance,  this  is  sometimes  called  the  tubular  portion  of  the 
kidney. 

From  the  arrangement  of  the  secreting  portion  of  the  kidneys,  these 
organs  are  classed  among  the  tubular  glands,  presenting  a  system  of  tubes, 
or  canals,  some  of  which  are  supposed  simply  to  carry  off  the  urine,  while 
others  separate  the  excrementitious  constituents  of  this  fluid  from  the  blood. 
It  is  difficult  to  determine  precisely  where  the  secreting  tubes  merge  into  the 
excretory  ducts,  but  it  is  the  common  idea,  which  is  probably  correct,  that 
the  cortical  substance  is  the  active  portion,  while  the  tubes  of  the  pyramidal 
portion  simply  carry  off  the  excretion. 

Pyramidal  Substance. — Each  papilla,  as  it  projects  into  the  pelvis  of  the 
kidney,  presents  ten  to  twenty-five  little  openings,  -^  to  -fa  of  an  inch  (85 
to  425  p.)  in  diameter.  The  tubes  leading  from  the  pelvis  immediately 


FIG.  114. — Longitudinal  section  of  the  py- 
ramidal substance  of  the  kidney  of  the 
foetus  (Sappey). 

1,  trunk  of  a  large  uriniferous  tube  ;  2,  2, 
primary  branches  of  this  tube  ;  3,  3,  3, 
secondary  branches  ;  4,  4,  5,  5,  6.  6,  7,  7. 
7,  7,  branches  becoming  smaller  and 
smaller  ;  8,  8,  8,  8,  loops  of  the  tubes  of 
Henle. 


FIQ.  115.—  Longitudinal  section  of  the  cortical  sub- 
stance of  the  same  kidney  (Sappey). 

1,  1,  limit  of  the  cortical  substance  and  base  of  the  pyr- 
amids ;  2,  2,  2,  tubes  passing  toward  the  surface  of 
the  kidne.y  ;  3,  3.  3,  8,  8,  8,  convoluted  tubes  ;  4,  4  4, 
4.  S^Malpighian  bodies  ;  6,  6.  artery,  with  its  branch- 
es (7,  7,  7) ;  9,  9,  fibrous  covering  of  the  kidney. 


PHYSIOLOGICAL  ANATOMY  OF  THE  KIDNEYS.  361 

divide  at  very  acute  angles,  generally  dichotomously,  until  a  bundle  of  tubes 
arises,  as  it  were,  from  each  opening.  These  bundles  constitute  the  pyra- 
mids of  Ferrein.  In  their  course  the  tubes  are  slightly  wavy  and  are  nearly 
parallel  to  each  other.  These  are  called  the  straight  tubes  of  the  kidney, 
or  the  tubes  of  Bellini.  They  extend  from  the  apices  of  the  pyramids  to 
their  bases  and  pass  then  into  the  cortical  substance.  The  pyramids  contain, 
in  addition  to  the  straight  tubes,  a  delicate,  fibrous  matrix  and  blood-vessels, 
which  latter  generally  pass  beyond  the  pyramids,  to  be  finally  distributed  in 
the  cortical  substance.  Small  tubes,  continuous  with  the  convoluted  tubes 
of  the  cortical  substance,  dip  down  into  the  pyramids,  returning  to  the  corti- 
cal substance  in  the  form  of  loops.  This  arrangement  will  be  fully  described 
in  connection  with  the  cortical  substance. 

The  tubes  of  the  pyramidal  substance  are  composed  of  a  strong,  struct- 
ureless basement-membrane,  lined  with  granular,  nucleated  cells.  Accord- 
ing to  Bowman,  the  tubes  measure  -^  to  -^  of  an  inch  (85  to  127  /A),  in 
diameter  at  the  apices,  and  near  the  bases  of  the  pyramids  their  diameter  is 
about  -g-^  of  an  inch  (42  fi). 

The  cells  lining  the  straight  tubes  exist  in  a  single  layer  applied  to  the 
basement-membrane.  They  are  thick  and  irregularly  polygonal  in  shape,  with 
abundant  albuminoid  granules.  They  present  one,  and  occasionally,  though 
rarely,  two  granular  nuclei,  with  one  or  two  nucleoli.  They  readily  undergo 
alteration  and  are  seen  in  their  normal  condition  only  in  a  perfectly  fresh, 
healthy  kidney.  Their  diameter  is  about  r-gW  °f  an  incn  (I?  /*)•  The  ca^~ 
her  of  the  tubes  is  reduced  by  the  thickness  of  their  lining  epithelium  to  -$$-$ 
or  -g-J-g-  of  an  inch  (28  or  30  /*). 

Cortical  Substance. — In  the  cortical  portion  of  the  kidney,  are  found 
tubes,  differing  somewhat  from  the  tubes  of  the  pyramidal  portion  in  their 
size  and  in  the  character  of  their  epithelial  lining,  but  presenting  the  most 
marked  difference  in  their  direction.  These  tubes  are  rather  larger  than  the 
tubes  of  the  pyramidal  substance,  and  are  very  much  convoluted,  interlacing 
with  each  other  in  every  direction.  Scattered  pretty  uniformly  throughout 
this  portion  of  the  kidney,  are  rounded  or  ovoid  bodies,  about  four  times  the 
diameter  of  the  convoluted  tubes,  known  as  the  Malphigian  bodies.  These 
are  simply  flask-like,  terminal  dilatations  of  the  tubes  themselves. 

The  cortical  portion  of  the  kidney  presents  a  delicate,  fibrous  matrix, 
which  forms  a  support  for  the  secreting  portion  and  its  blood-vessels.  The 
tubes  of  the  cortical  substance  present  considerable  variations  in  size,  and 
three  well  defined  varieties  can  be  distinguished : 

1.  The  ordinary  convoluted  tubes,  directly  connected  with  the  Malpig- 
hian  bodies.  2.  Small  tubes,  continuous  with  the  convoluted  tubes,  dipping 
down  into  the  pyramids  and  returning  to  the  cortical  portion  in  the  form  of 
loops.  3.  Communicating  tubes,  forming  a  plexus  connecting  the  different 
varieties  of  tubes  with  each  other  and  finally  with  the  straight  tubes  of  the 
pyramidal  portion. 

In  tracing  out  the  course  of  the  tubes,  it  will  be  found  most  convenient 
to  begin  with  a  description  of  the  Malpighian  bodies  and  to  follow  the  tubes 


362  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

from  these  bodies  to  their  connections  with  the  straight  tubes  of  the  pyram- 
idal substance. 

Malpighian  Bodies. — These  are  ovoid  or  rounded,  terminal  dilatations  of 
the  convoluted  tubes,  and  are  ^|7  to  jfa  of  an  inch  (100  to  250  /u),  in  diam- 
eter. They  are  composed  of  a  membrane,  which  is  continuous  with  the  ex- 
ternal membrane  of  the  convoluted  tubes,  and  is  of  the  same  homogeneous 
character,  but  somewhat  thicker.  This  sac,  called  the  capsule  of  Miiller  or 
of  Bowman,  encloses  a  mass  of  convoluted  blood-vessels  and  is  lined  with  a 
layer  of  nucleated  epithelial  cells.  In  addition  to  the  cells  lining  the  cap- 
sule, there  are  other  cells  which  are  applied  to  the  blood-vessels. 

The  cells  attached  to  the  capsule  of  Miiller  are  smaller  and  more  trans- 
parent than  those  lining  the  convoluted  tubes.  They  are  ovoid,  nucleated 
and  finely  granular.  The  cells  covering  the  vessels,  however,  are  larger  and 
more  opaque,  and  they  resemble  the  epithelium  lining  the  tubes.  They 
measure  T3V¥  to  10*06  of  an  inch  (1G  to  25  /A),  in  diameter,  by  about  -g-gVo  of 
an  inch  (10 /A)  in  thickness. 

Tubes  of  the  Cortical  Substance. — Passing  from  the  Malpighian  bodies, 
the  tubes  present  first  a  short,  constricted  portion,  called  the  neck  of  the 
capsule,  which  soon  dilates  to  the  diameter  of  about  -^  of  an  inch  (50  p], 
when  their  course  becomes  quite  intricate  and  convoluted.  These  are  what 
are  known  as  the  convoluted  tubes  of  the  kidney.  The  membrane  of  these 
tubes  is  transparent  and  homogeneous,  but  quite  firm  and  resisting.  It  is 
lined  throughout  with  a  single  layer  of  epithelial  cells,  14^6  to  TTJiinr  of  an 
inch  (16  to  25  /A)  in  diameter,  somewhat  larger,  consequently,  than  the  cells 
lining  the  straight  tubes.  The  cells  lining  the  convoluted  tubes  present  two 
tolerably  distinct  portions.  The  inner  portion  or  zone,  which  is  next  the 
lumen  of  the  tube,  is  finely  granular,  with  sometimes  a  few  small  oil-glob- 
ules. The  outer  zone  presents  little  fibrils  or  rods,  which  are  perpendicular 
to  the  tubular  membrane.  These  are  called  "  rodded  "  cells,  and  a  similar 
appearance  is  presented  by  some  of  the  cells  of  the  pancreas  and  of  the  sali- 
vary glands.  The  nucleus  is  usually  situated  between  the  granular  and  the 
rodded  zones. 

The  researches  of  Heidenhain  and  others  have  shown  that  the  greatest 
part  of  the  solid  excrementitious  constituents  of  the  urine,  such  as  urea 
and  the  urates,  is  separated  from  the  blood  by  the  cells  of  the  convoluted 
tubes  of  the  cortical  substance  and  perhaps  by  the  dilated  portions  of  the 
tubes  of  Henle,  while  the  water  and  a  certain  portion  of  the  inorganic  salts 
of  the  urine  transude  through  the  blood-vessels  in  the  Malpighian  bodies. 
This  view  was  first  advanced  by  Bowman,  in  1842. 

Narrow  Tubes  of  Henle. — The  convoluted  tubes  above  described,  after  a 
tortuous  course  in  the  cortical  substance,  become  continuous,  near  the  pyra- 
mids, with  the  tubes  of  much  smaller  diameter,  which  form  loops  extending 
to  a  greater  or  less  depth  into  the  pyramids.  The  loops  formed  by  these 
canals  (the  narrow  tubes  of  Henle),  are  nearly  parallel  with  the  tubes  of  Bel- 
lini and  are  much  greater  in  number  near  the  bases  of  the  pyramids  than 
toward  the  apices.  The  diameter  of  these  tubes  is  very  variable,  and  they 


PHYSIOLOGICAL  ANATOMY  OF  THE  KIDNEYS. 


363 


present  enlargements  at  irregular  intervals  in  their  course.     The  narrow  por- 
tions are  about  ^oVo"  °f  an  incn  (12  /*)  in  diameter,  and  the  wide  portions, 


FIG.  116.—  Structure  of  the  kidney  (Landois). 

I,  blood-vessels  and  tubes  (semi-diagrammatic).    A,  capillaries  of  the  cortical  substance  ;  B,  capillaries 

of  the  medullary  substance  :   1.  artery  penetrating  a  Malpighian  body :  2,  vein  emerging  from  a 

Malpighian  body  ;  R,  arteriolro  rectae  ;  c.  venae  rectse  ;  v,  v,  interlobular  veins  ;  s,  stellate  veins ; 

i,  i.  capsules  of  Miiller  ;  x,  x,  convoluted  tubes  ;  T,  T,  T.  tubes  of  Henle  ;  N,  N,  N,  N,  communicating 

tubes  ;  p,  o,  straight  tubes  ;  O,  opening  into  the  pelvis  of  the  kidney. 

IT,  Malpighian  body.    A,  artery  ;  E,  vein  ;  c,  capillaries  ;  K,  epithelium  of  the  capsule  ;  H,  beginning  of 
a  convoluted  tube. 

III,  rodded  cells  from  a  convoluted  tube.    1,  view  from  the  surface  ;  2,  side  view  (G,  granular  zone). 

IV,  cells  lining  the  tubes  of  Henle. 

V,  cells  lining  the  communicating  tubes. 

VI,  section  of  a  straight  tube. 

about  twice  this   size.      The  narrow  portion  is  lined  by  small,  clear  cells 
with  very  prominent  nuclei.     The  wider  portions  are  lined  by  larger,  gran- 


364  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

ular  cells.  Near  the  bases  of  the  pyramids  the  wide  portion  sometimes 
forms  the  loop,  but  near  the  apices  the  loop  is  always  narrow.  The  differ- 
ence in  the  size  of  the  epithelium  is  such,  that  while  the  diameter  of  the 
tube  is  variable,  its  caliber  remains  nearly  uniform.  The  membrane  of  these 
tubes  is  quite  thick,  thicker,  even,  than  the  membrane  of  the  tubes  of  Bel- 
lini. 

Intermediate  Tubes. — After  the  narrow  tubes  of  Henle  have  returned  to 
the  cortical  substance,  they  communicate  with  a  system  of  flattened,  ribbon- 
shaped,  anastomosing  canals,  jf^jr  to  TTjVir  of  an  inch  (21  to  25  /*)  in  diam- 
eter, with  very  thin  walls,  lined  by  rodded  epithelium.  These  tubes  take  an 
irregular  and  somewhat  angular  course  between  the  true  convoluted  tubes 
and  finally  empty  into  the  branches  of  the  straight  tubes  of  Bellini,  thus  es- 
tablishing a  communication  between  the  tubes  coming  from  the  Malpighian 
bodies  and  the  tubes  of  the  pyramidal  substance.  They  are  called  the  inter- 
mediate tubes,  or  the  canals  of  communication. 

The  tubes  into  which  the  intermediate  canals  open  join  with  others  gen- 
erally two  by  two,  and  then  pass  in  a  nearly  straight  direction  into  the  pyra- 
mids, where  they  continue  to  unite  with  each  other  in  their  course,  becoming, 
consequently,  reduced  in  number  until  they  open  at  the  apices  of  the  pyra- 
mids, into  the  infundibula  and  the  pelvis  of  the  kidney. 

Distribution  of  Blood-vessels  in  the  Kidney. — The  renal  artery,  which  is 
quite  voluminous  in  proportion  to  the  size  of  the  kidney,  enters  at  the  hilum 
and  divides  into  four  branches.  A  number  of  smaller  branches  penetrate 
between  the  pyramids  and  ramify  in  the  columns  of  cortical  substance  which 
occupy  the  spaces  between  the  pyramids  (columns  of  Berlin).  The  main 
vessels,  which  are  generally  two  in  number,  occupy  the  centre  of  the  columns 
of  Berlin,  sending  off  in  their  course,  at  short  intervals,  regular  branches  on 
either  side,  toward  the  pyramids.  When  Ihese  branches  reach  the  boundary 
of  the  cortical  substance,  they  turn  upward  and  follow  the  periphery  of  the 
pyramid  to  its  base.  Here  the  vessels  form  an  arched,  anastomosing  plexus, 
the  arterial  arcade,  situated  between  Ihe  rounded  base  of  the  pyramid  and 
the  cortical  substance.  This  plexus  presents  a  convexity  looking  toward  Ihe 
cortical  subslance,  and  a  concavity,  toward  the  pyramid.  It  is  so  arranged 
that  the  interstices  are  just  large  enough  lo  admil  Ihe  collections  of  tubes 
thai  form  Ihe  so-called  pyramids  of  Ferrein. 

From  Ihe  arterial  arcade,  branches  are  given  off  in  Iwo  opposite  direc- 
lions.  From  its  concavity,  small  branches,  measuring  at  first  Y^Q-Q  to  T^F  of 
an  inch  (21  to  34  p.)  in  diameter,  pass  downward  toward  the  papillae,  giving 
off  small  ramifications  at  very  acute  angles,  and  becoming  reduced  in  size  to 
about  g^^  of  an  inch  (10  /*).  These  vessels,  called  sometimes  Ihe  arteri- 
olse  recta?,  surround  the  straighl  lubes,  and  pass  into  capillaries  in  Ihe  sub- 
stance of  the  pyramids  and  at  their  apices. 

From  the  convex  surface  of  Ihe  arterial  arcade,  branches  are  given  off  at 
nearly  right  angles.  These  pass  into  Ihe  cortical  substance,  breaking  up  into 
a  large  number  of  lillle  arterial  twigs,  y^r  to  irJTr  of  an  inch  (17  to  40  p)  in 
diameter,  each  one  of  which  penetrates  a  Malpighian  body  al  a  point  oppo- 


PHYSIOLOGICAL  ANATOMY   OF  THE  KIDNEYS. 


365 


site  the  neck  of  the  capsule.  Once  within  the  capsule,  the  arteriole  breaks 
up  into  five  to  eight  branches,  which  then  divide  dichotomously  into  vessels 
measuring  SoiQQ  to  3-^  of  an  inch  (8  to  17  /*)  in  diameter,  arranged  in  the 
form  of  coils  and  loops,  constituting  a  dense,  rounded  mass  (the  Malpighian 
coil,  or  glomerulus),  filling  the  capsule. 
These  vessels  break  up  into  capillaries 
without  anastomoses. 

The  blood  is  collected  from  the  vessels 
of  the  Malpighian  bodies  by  veins,  some- 
times one  and  frequently  three  or  four, 
which  pass  out  of  the  capsule  and  form 
a  second  capillary  plexus  surrounding  the 
convoluted  tubes.  When  there  is  but  one 
vein,  it  generally  emerges  from  the  cap- 
sule near  the  point  of  penetration  of  the 
arteriole. 

The  efferent  vessels,  immediately  after 
their  emergence  from  the  capsule,  break 
up  into  a  very  fine  and  delicate  plexus  of 
capillaries,  closely  surrounding  the  con- 
voluted tubes.  These  form  a  true  plexus, 
the  branches  anastomosing  freely  in  every 
direction ;  and  the  distribution  of  vessels 
in  this  part  resembles  essentially  the  vas- 
cular arrangement  in  most  of  the  glands. 
Bowman  has  called  the  branches  which 
connect  together  the  vessels  of  the  Mal- 
pighian tuft  and  the  capillary  plexus  sur- 
rounding the  tubes,  the  portal  system  of 
the  kidney.  These  intermediate  vessels 
form  a  coarse  plexus  surrounding  the  pro- 
longations of  the  pyramids  of  Ferrein  into 
the  cortical  substance. 

The  renal,  or  emulgent  vein  takes  its 
origin  in  part  from  the  capillary  plexus  FIG.  in.—Biood-vesseisofth? 

v  ,1  i    i   j  j_i_         '     a.« 

surrounding  the  convoluted  tubes  and  in 

rmrt,   from    flip    vp««pl<5    rliurviVmWl    in    fVio 

pyramidal  substance.  A  few  branches 
come  from  vessels  in  the  envelopes  of  the 
kidney,  but  these  are  comparatively  un- 
important. The  plexus  surrounding  the 
convoluted  tubes  empties  into  venous  rad- 
icles which  pass  to  the  surface  of  the  kidney,  and  these  present  a  number  of 
little  radiating  groups,  each  converging.toward  a  central  vessel.  This  arrange- 
ment gives  to  the  vessels  of  the  fibrous  envelope  of  the  kidney  a  peculiar,  stel- 
late appearance,  forming  what  are  sometimes  called  the  stars  of  Verheyn.  The 
25 


bodies  and  convoluted  tubes  of  the  kidney 
(Sappey). 

1, 1,  Malpighian  bodies  surrounded  by  the  cap- 
sules of  Miiller  :  2,  2.  2.  convoluted  tubes 
connected  with  the  Malpighian  bodies  ;  3, 
artery  branching  to  go  to  the  Malpighian 
bodies  :  4,  4,  4,  branches  of  the  artery  ;  6. 
6,  Malpighian  bodies  from  which  a  portion 
of  the  capsules  has  been  removed  :  7,  7,  7, 
vessels  passing  out  of  the  Malpighian  bod- 
ies :  8,  vessel,  the  branches  of  which  (9) 
pass  to  the  capillary  plexus  (10). 


366  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

large  trunks  which  form  the  centres  of  these  stars  then  pass  through  the  corti- 
cal substance  to  the  rounded  bases  of  the  pyramids,  where  they  form  a  vaulted, 
venous  plexus  corresponding  to  the  arterial  plexus  already  described.  The 
vessels  distributed  upon  the  straight  tubes  of  the  pyramidal  substance  form  a 
loose  plexus  around  these  tubes,  except  at  the  papillae,  where  the  network  is 
much  closer.  They  then  pass  into  the  plexus  at  the  bases  of  the  pyramids  to 
join  with  the  veins  from  the  cortical  substance.  From  this  plexus  a  number 
of  larger  trunks  arise  and  pass  toward  the  hilum,  in  the  axis  of  the  inter- 
pyramidal  substance,  enveloped  in  the  same  sheath  with  the  arteries.  Passing 
thus  to  the  pelvis  of  the  kidney,  the  veins  converge  into  three  or  four  great 
branches,  which  unite  to  form  the  renal,  or  emulgent  vein.  A  preparation  of 
all  the  vessels  of  the  kidneys  shows  that  the  veins  are  much  more  volu- 
minous than  the  arteries. 

The  capsule  of  the  kidney  has  a  lymphatic  plexus  connected  with  lymph- 
spaces  below  ;  and  lymph-spaces,  in  the  form  of  large  slits,  exist  between  and 
around  the  convoluted  tubes. 

The  nerves  are  quite  abundant  and  are  derived  from  the  solar  plexus,  their 
filaments  following  the  renal  artery  in  its  distribution  in  the  interior  of  the 
organ,  and  ramifying  upon  the  walls  of  the  vessels. 

MECHANISM  OF  THE  PRODUCTION  AND  DISCHARGE  OF  URINE. 

The  most  important  constituent  of  the  urine  is  urea — CO(lSrH!1).2 — ,  a  crys- 
tallizable,  nitrogenized  substance,  which  is  discharged  by  the  skin  as  well  as 
by  the  kidneys.  This  has  long  been  recognized  as  an  excrementitious  sub- 
stance ;  but  the  first  observations  that  gave  any  definite  idea  of  the  mechanism 
of  its  production  were  made  by  Prevost  and  Dumas,  in  1821.  At  the  time  these 
experiments  were  made,  chemists  were  not  able  to  detect  urea  in  the  normal 
blood  ;  but  Prevost  and  Dumas  extirpated  the  kidneys  from  living  animals, 
dogs  and  cats,  and  found  an  abundance  of  urea  in  the  blood,  after  certain 
symptoms  of  blood-poisoning  had  been  developed.  For  the  first  two  or 
three  days  after  the  operation  there  were  no  symptoms  of  blood-poisoning ;  but 
finally  stupor  and  other  marked  evidences  of  nervous  disturbance  supervened, 
when  the  presence  of  urea  in  the  blood  could  be  easily  determined.  These  ob- 
servations were  confirmed  and  extended  by  Segalas  and  Vauquelin,  in  1822. 
Since  that  time,  as  the  processes  for  the  determination  of  urea  in  the  animal 
fluids  have  been  improved,  this  substance  has  been  detected  in  minute  quan- 
tity in  the  normal  blood.  Picard  (1856)  estimated  and  compared  the  propor- 
tions of  urea  in  the  renal  artery  and  the  renal  vein,  and  he  found  that  the 
quantity  in  the  blood  was  diminished  by  about  one-half  in  its  passage  through 
the  kidneys.  Still  later,  urea  has  been  found  in  the  lymph  and  chyle,  in 
larger  quantity,  even,  than  in  the  blood(Wurtz). 

Bernard  and  Barreswil  (1847)  found  that  animals  from  which  both  kid- 
neys had  been  removed  did  not  usually  present  any  distinctive  symptoms  for 
a  day  or  two  after,  except  that  they  vomited  and  passed  an  unusual  quantity 
of  liquid  from  the  intestinal  canal.  During  this  time  the  blood  never  con- 
tained an  abnormal  quantity  of  urea ;  but  the  contents  of  the  stomach  and 


MECHANISM  OF  THE  PRODUCTION  OF  URINE.  367 

intestine  were  found  to  be  highly  ammoniacal,  and  the  secretions  from  these 
parts,  particularly  the  stomach,  became  continuous  as  well  as  increased  in 
quantity.  Animals  operated  upon  in  this  way  usually  live  for  four  or  five 
days,  and  they  then  die  in  coma  following  convulsions.  Toward  the  end  of 
life,  the  secretion  of  gastric  and  intestinal  fluids  becomes  arrested,  probably 
from  the  irritating  effects  of  ammoniacal  decomposition  of  their  contents, 
and  then,  and  then  only,  urea  is  found  to  accumulate  in  the  blood. 

The  results  obtained  by  other  experimenters  have  generally  corresponded 
with  those  of  Bernard  and  Barreswil.  It  has  also  been  ascertained,  as  was 
shown  by  Segalas  and  Vauquelin,  that  urea  is  an  active  diuretic  when  inject- 
ed in  small  quantity  into  the  veins  of  a  healthy  animal ;  and  that  in  this  case, 
it  does  not  produce  any  poisonous  effects,  but  is  immediately  eliminated. 
When  urea  is  injected  into  the  vascular  system  of  a  nephrotomized  animal, 
it  produces  death  in  a  very  short  time,  with  the  characteristic  symptoms  of 
urEemic  poisoning. 

Experiments  which  were  supposed  to  show  that  urea  and  the  urates  are 
formed  in  the  kidneys  have  been  made  with  the  view  of  comparing  the  effects 
of  removal  of  both  kidneys  with  those  produced  by  tying  the  ureters.  Ac- 
cording to  these  observations,  the  blood  contains  much  more  urea  after  the 
ureters  are  tied  than  after  removal  of  the  kidneys.  These  experiments, 
which  are  directly  opposed  in  their  results  to  the  observations  of  Prevost  and 
Dumas,  Bernard  and  Barreswil,  Segalas,  and  many  others,  can  not  be  accepted 
unless  it  be  certain  that  all  the  necessary  physiological  conditions  were  fulfilled. 
In  the  first  place,  it  was  demonstrated,  as  early  as  1847,  that  urea  does  not 
accumulate  in  the  blood  immediately  after  removal  of  the  kidneys,  but  that 
this  occurs  only  toward  the  end  of  life,  and  then  urea  is  found  in  large  quan- 
tity. In  the  second  place,  it  is  well  known  that  the  operation  of  tying  the 
ureters  is  followed  by  a  greatly  increased  pressure  of  urine  in  the  kidneys, 
which  not  only  disturbs  the  eliminative  action  of  these  organs  but  affects 
most  seriously  the  general  functions.  Since  the  influence  of  the  nervous  sys- 
tem upon  the  secretions  has  been  closely  studied,  it  is  evident  that  the  pain 
and  disturbance  consequent  upon  the  accumulation  of  urine  above  the  ligat- 
ed  ureters  must  have  an  important  reflex  action  upon  the  secretions ;  and 
this  would  probably  interfere  with  the  vicarious  elimination  of  urea  and  of 
other  excrementitious  substances  by  the  stomach  and  intestines.  It  is  well 
known  that  an  arrest  of  these  secretions,  in  cases  of  organic  disease  of  the 
kidneys,  is  liable  to  be  followed  immediately  by  evidences  of  uraemia,  and 
that  grave  urasmic  symptoms  are  frequently  relieved  by  the  administration  of 
remedies  that  act  promptly  and  powerfully  upon  the  intestinal  canal. 

From  a  careful  review  of  the  important  facts  bearing  upon  the  question 
under  consideration,  there  does  not  seem  to  be  any  valid  ground  for  a  change 
in  the  ideas  of  physiologists  concerning  the  mode  of  elimination  of  urea  and 
the  other  important  excrementitious  constituents  of  the  urine.  There  is  every 
reason  to  suppose  that  these  substances  are  produced  in  various  tissues  and 
organs  of  the  body  during  the  process  of  disassimilation,  are  taken  up  by  the 
blood  and  are  simply  separated  from  the  blood  by  the  kidneys. 


368  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

Extirpation  of  one  kidney  from  a  living  animal  is  not  necessarily  fatal. 
If  the  operation  be  carefully  performed,  the  wound  will  generally  heal  with- 
out difficulty,  and  in  most  instances  the  remaining  kidney  seems  sufficient 
for  the  elimination  of  urine  for  an  indefinite  period.  In  a  large  number  of  ex- 
periments, the  animals  killed  long  after  the  wound  had  healed  never  pre- 
sented any  marked  symptoms  of  retention  of  excrementitious  matters  in  the 
blood,  except  in  one  or  two  instances.  It  is  a  noticeable  fact,  however,  that 
in  many  instances  they  showed  a  marked  change  in  disposition,  and  the  ap- 
petite became  voracious  and  unnatural.  These  animals  would  sometimes  eat 
faeces,  the  flesh  of  dogs,  etc.,  and,  in  short,  presented  certain  of  the  phenom- 
ena so  frequently  observed  after  extirpation  of  the  spleen  (Flint).  After 
extirpation  of  one  kidney,  it  has  been  observed  that  the  remaining  kidney 
increases  in  weight,  although  investigations  have  shown  that  this  is  due 
mainly  to  an  increase  in  the  quantity  of  blood,  lymph  and  urinary  matters, 
and  not  to  a  new  development  of  renal  tissue.  The  following  is  an  excep- 
tional experiment  in  which  the  animal  died  after  extirpation  of  one  kidney  : 
One  kidney  was  removed  from  a  small  cur-dog,  about  nine  months  old,  by 
an  incision  in  the  lumbar  region.  The  animal  did  not  appear  to  suffer  from 
the  operation,  and  the  wound  healed  kindly.  The  only  marked  effects  were 
great  irritability  of  disposition  and  an  exaggerated  and  perverted  appetite. 
He  would  attack  the  other  dogs  in  the  laboratory  without  provocation,  and 
would  eat  with  avidity,  fasces,  putrid  dog's  flesh  and  articles  which  the  other 
animals  would  not  touch  and  which  he  did  not  eat  before  the  operation. 
Forty-three  days  after  the  operation,  the  dog  appeared  to  be  uneasy,  cried 
frequently,  and  went  into  convulsions,  which  continued  for  about  three 
hours,  when  he  died  (Flint,  1864).  In  one  other  instance,  in  which  a  dog 
was  kept  for  more  than  a  year  after  extirpation  of  one  kidney,  it  was  occa- 
sionally observed  that  the  animal  was  rather  quiet  and  indisposed  to  move 
for  a  day  or  two,  but  this  always  passed  off,  and  when  he  was  killed  he  was 
as  well  as  before  the  operation. 

Influence  of  Blood-pressure,  the  Nervous  System  etc.,  upon  the  Secre- 
tion of  Urine. — There  are  many  instances  in  which  very  marked  and  sudden 
modifications  in  the  action  of  the  kidneys  take  place  under  the  influence  of 
fear,  anxiety,  hysteria  etc.,  which  must  operate  through  the  nervous  system. 
Although  little  is  known  of  the  final  distribution  of  the  nerves  in  the  kidney, 
it  has  been  ascertained  that  here,  as  elsewhere,  vaso-motor  nerves  are  distrib- 
uted to  the  walls  of  the  blood-vessels,  and  they  are  capable  of  modifying  the 
quantity  and  the  pressure  of  blood  in  these  organs. 

It  may  be  stated  as  a  general  proposition,  that  an  increase  in  the  pressure 
of  blood  in  the  kidneys  increases  the  flow  of  urine,  and  that  when  the  blood- 
pressure  is  lowered,  the  flow  of  urine  is  correspondingly  diminished.  This 
will  in  a  measure  account  for  the  increase  in  the  flow  of  urine  during  diges- 
tion ;  but  it  can  not  serve  to  explain  all  of  the  modifications  that  may  take 
place  in  the  action  of  the  kidneys.  Bernard  measured  the  pressure  of  blood 
in  the  carotid  artery  of  a  dog  and  noted  the  quantity  of  urine  discharged  in 
the  course  of  a  minute  from  one  of  the  ureters.  Afterward,  by  tying  the 


PHYSIOLOGICAL  ANATOMY  OF  THE  URINARY  PASSAGES.     3G9 

two  crural,  the  two  brachial  and  the  two  carotid  arteries,  he  increased  the 
blood-pressure  about  one-half,  and  the  quantity  of  urine  discharged  in  a  min- 
ute was  immediately  increased  by  a  little  more  than  fifty  per  cent.  In 
another  animal,  he  diminished  the  pressure  by  taking  blood  from  the  jugu- 
lar vein,  and  the  quantity  of  urine  was  immediately  reduced  about  one-half. 
He  also  showed  that  the  increase  in  the  quantity  of  urine  produced  by  ex- 
aggerated pressure  of  blood  in  the  kidneys  could  be  modified  through  the 
nervous  system.  The  nerves  going  to  one  kidney  were  divided,  which  pro- 
duced, an  increase  in  the  arterial  pressure  and  a  consequent  exaggeration  in 
the  quantity  of  urine  from  the  ureter  on  that  side.  The  pressure  was  then 
farther  increased  by  stopping  the  nostrils  of  the  animal.  The  quantity  of 
urine  was  increased  by  this  on  the  side  on  which  the  nerves  had  been  divided, 
but  the  pain  and  distress  from  want  of  air  arrested  the  secretion  upon  the 
sound  side. 

When  irritation  is  applied  to  the  floor  of  the  fourth  ventricle,  in  the  median 
line,  exactly  in  the  middle  of  the  space  between  the  origin  of  the  pneumo- 
gastrics  and  the  auditory  nerves,  the  urine  is  increased  in  quantity  and  be- 
comes strongly  saccharine.  When  the  irritation  is  applied  a  little  above 
this  point,  the  urine  is  simply  increased  in  quantity,  but  it  contains  no  sugar ; 
and  when  a  puncture  is  made  a  little  below,  sugar  appears  in  the  urine, 
without  any  increase  in  the  quantity  of  the  secretion  (Bernard).  It  has  also 
been  observed  that  section  of  the  spinal  cord  in  the  upper  part  of  the  dor- 
sal region  arrests,  for  a  time,  the  secretion  of  urine. 

Other  physiological  conditions  that  affect  the  urinary  excretion  influence 
the  composition  of  the  urine  and  the  quantity  of  excrementitious  matters  sep- 
arated by  the  kidneys.  These  will  be  fully  considered  in  another  place.  It 
is  sufficient  to  remark,  in  this  connection,  that  during  digestion,  when  the 
composition  of  the  blood  is  modified  by  the  absorption  of  nutritive  matters, 
the  quantity  of  urine  usually  is  increased.  This  is  particularly  marked  when 
a  large  quantity  of  liquid  has  been  taken. 

Inasmuch  as  the  excrementitious  matters  eliminated  by  the  kidneys  are 
being  constantly  produced  in  the  tissues  by  the  process  of  disassimilation, 
the  formation  of  urine  is  constant,  presenting,  in  this  regard,  a  marked 
contrast  with  the  intermittent  flow  of  most  of  the  secretions  proper  as  distin- 
guished from  the  excretions.  It  was  noted  by  Erichsen,  in  a  case  of  extro- 
version of  the  bladder,  and  it  has  been  farther  shown  by  experiments  upon 
dogs,  that  there  is  an  alternation  in  the  action  of  the  kidneys  upon  the  two 
sides.  Bernard  exposed  the  ureters  in  a  living  animal  and  fixed  a  small,  silver 
tube  in  each,  so  that  the  secretion  from  either  kidney  could  be  readily  ob- 
served ;  and  he  noted  that  a  large  quantity  of  fluid  was  discharged  from  one 
side  for  fifteen  to  thirty  minutes,  while  the  flow  from  the  other  side  was  slight 
arid  in  some  instances  was  arrested.  The  flow  then  began  with  activity  upon 
the  other  side,  while  the  discharge  from  the  opposite  ureter  was  diminished 
or  arrested. 

Physiological  Anatomy  of  the  Urinary  Passages. — The  excretory  ducts 
of  the  kidneys,  the  ureters,  begin  each  by  a  funnel-shaped  portion,  which  is 


370  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

applied  to  the  kidney  at  the  hilum.  The  ureters  themselves  are  membranous 
tubes  of  about  the  diameter  of  a  goose-quill,  becoming  much  reduced  in  cali- 
ber as  they  penetrate  the  coats  of  the  bladder.  They  are  sixteen  to  eighteen 
inches  (40  to  46  centimetres)  in  length,  and  pass  from  the  kidneys  to  the 
bladder,  behind  the  peritoneum.  They  have  three  distinct  coats  :  an  external 
coat,  composed  of  ordinary  fibrous  tissue,  with  small  elastic  fibres ;  a  middle 
coat,  composed  of  non-striated  muscular  fibres ;  and  a  mucous  coat. 

The  external  coat  requires  no  special  description.  It  is  prolonged  into 
the  calices  and  is  continuous  with  the  fibrous  coat  of  the  kidney. 

The  fibres  of  the  muscular  coat,  in  the  greatest  part  of  the  length  of  the 
ureters,  interlace  with  each  other  in  every  direction  and  are  not  arranged  in 
distinct  layers ;  but  near  the  bladder,  is  an  internal  layer,  in  which  the  direc- 
tion of  the  fibres  is  longitudinal. 

The  mucous  lining  is  thin,  smooth  and  without  any  follicular  glands.  It 
is  thrown  into  narrow,  longitudinal  folds,  when  the  tube  is  flaccid,  which  are 
easily  effaced  by  distention.  The  epithelium  exists  in  several  layers  and  is 
remarkable  for  the  irregular  shape  of  the  cells.  These  present,  usually,  dark 
granulations  and  one  or  two  clear  nuclei  with  distinct  nucleoli.  Some  of  the 
cells  are  flattened,  some  are  rounded,  and  some  are  caudate  with  one  or  two 
prolongations. 

Passing  to  the  base  of  the  bladder,  the  ureters  become  constricted,  pene- 
trate the  coats  of  this  organ  obliquely,  their  course  in  its  walls  being  a  little 
less  than  an  inch  (25  mm.)  in  length.  This  valvular  opening  allows  the 
free  passage  of  the  urine  from  the  ureters,  but  compression  or  distention  of 
the  bladder  closes  the  orifices  and  renders  a  return  of  the  fluid  impossible. 

The  bladder,  which  serves  as  a  reservoir  for  the  urine,  varies  in  its  rela- 
tions to  the  pelvic  and  abdominal  organs  as  it  is  empty  or  more  or  less 
distended.  When  empty,  it  lies  deeply  in  the  pelvic  cavity  and  is  then  a 
small  sac,  of  an  irregularly  triangular  form.  As  it  becomes  filled,  it  assumes 
a  globular  or  ovoid  form,  rises  up  in  the  pelvic  cavity,  and  when  excessively 
distended,  it  may  extend  partly  into  the  abdomen.  When  the  urine  is  voided 
at  normal  intervals,  the  bladder,  when  filled,  contains  about  a  pint  (nearly 
500  c.  c.)  of  liquid ;  but  under  pathological  conditions  it  may  become  dis- 
tended so  as  to  contain  ten  or  twelve  pints  (about  4  or  5  litres),  and  in  some 
instances  of  obstruction  it  has  been  found  to  contain  even  more.  The  blad- 
der is  usually  more  capacious -in  the  female  than  in  the  male. 

The  coats  of  the  bladder  are  three  in  number.  The  external  coat  is  sim- 
ply a  reflection  of  the  peritoneum,  covering  the  posterior  portion  completely, 
from  the  openings  of  the  ureters  to  the  summit,  about  one-third  of  the  lateral 
portion  and  a  small  part  of  the  anterior  portion. 

The  middle  or  muscular  coat  consists  of  non-striated  fibres,  arranged  in 
three  tolerably  distinct  layers :  The  external  muscular  layer  is  composed  of 
longitudinal  fibres,  which  arise  from  parts  adjacent  to  the  neck,  and  pass 
anteriorly,  posteriorly  and  laterally  over  the  organ,  so  that  when  they  are 
contracted  they  diminish  its  capacity  chiefly  by  shortening  its  vertical  diam- 
eter. The  fibres  of  the  external  layer  are  of  a  pinkish  hue,  being  much  more 


MECHANISM  OF  THE  DISCHARGE  OF   URINE.  371 

highly  colored  than  the  other  layers.  The  middle  layer  is  formed  of  circular 
fibres,  arranged,  on  the  anterior  surface  of  the  bladder,  in  distinct  bands  at 
right  angles  to  the  superficial  fibres.  They  are  thinner  and  less  strongly 
marked  on  the  posterior  and  lateral  surfaces.  The  internal  layer  is  composed 
of  pale  fibres  arranged  in  longitudinal  fasciculi,  the  anterior  and  lateral  bun- 
dles anastomosing  with  each  other,  as  they  descend  toward  the  neck  of  the 
bladder,  by  oblique  bands  of  communication,  and  the  posterior  bundles  inter- 
lacing in  every  direction,  forming  an  irregular  plexus.  Here  they  are  not  to 
be  distinguished  from  the  fibres  of  the  middle  layer.  This  is  sometimes  called 
the  plexiform  layer,  and  it  gives  to  the  interior  of  the  bladder  its  reticulated 
appearance.  This  layer  is  continuous  with  the  muscular  fibres  of  the  urachus, 
the  ureters  and  the  urethra. 

The  sphincter  vesicae  is  a  band  of  non-striated  fibres,  about  half  an  inch 
(12-7  mm.)  in  breadth  and  one-eighth  of  an  inch  (3 -2  mm.)  in  thickness, 
embracing  the  neck  of  the  bladder  and  the  posterior  half  of  the  prostatic 
portion  of  the  urethra.  The  tonic  contraction  of  these  fibres  prevents  the 
flow  of  urine,  and  during  the  ejaculation  of  the  seminal  fluid,  it  offers  an 
obstruction  to  its  passage  into  the  bladder. 

The  mucous  membrane  of  the  bladder  is  smooth,  rather  pale,  thick,  and 
loosely  adherent  to  the  submucous  tissue,  except  over  the  corpus  trigonum. 
The  epithelium  is  stratified  and  presents  the  same  diversity  in  form  as  that 
observed  in  the  pelvis  of  the  kidney  and  the  ureters ;  viz.,  the  deeper  cells  are 
elongated  and  resemble  columnar  epithelium,  while  the  cells  on  the  surface 
are  flattened.  In  the  neck  and  fundus  of  the  bladder,  are  a  few  mucous 
glands,  some  in  the  form  of  simple  follicles  and  others  collected  to  form 
glands  of  the  simple  racemose  variety. 

The  corpus  trigonum  is  a  triangular  body,  lying  just  beneath  the  mucous 
membrane,  at  the  base  of  the  bladder,  and  extending  from  the  urethra  in  front, 
to  the  openings  of  the  ureters.  It  is  composed  of  ordinary  fibrous  tissue, 
with  a  few  elastic  and  muscular  fibres.  At  the  opening  of  the  urethra,  it 
presents  a  small,  projecting  fold  of  mucous  membrane,  which  is  sometimes 
called  the  uvula  vesicae.  Over  the  whole  of  the  surface  of  the  trigone,  the 
mucous  membrane  is  very  closely  adherent,  and  it  is  never  thrown  into  folds, 
even  when  the  bladder  is  entirely  empty. 

The  blood-vessels  going  to  the  bladder  are  ultimately  distributed  to  its 
mucous  membrane.  They  are  not  very  abundant  except  at  the  fundus,  where 
the  mucous  membrane  is  quite  vascular.  Lymphatics  have  been  described  as 
existing  in  the  walls  of  the  bladder,  but  Sappey  has  failed  to  demonstrate 
them  in  this  situation.  The  nerves  of  the  bladder  are  derived  from  the  hypo- 
gastric  plexus. 

The  urethra  is  provided  with  muscular  fibres,  and  it  is  lined  by  a  mucous 
membrane,  the  anatomy  of  which  will  be  more  fully  considered  in  connection 
with  the  physiology  of  generation.  In  the  female  the  epithelium  of  the  ure- 
thra is  like  that  of  the  bladder.  In  the  male  the  epithelial  cells  are  small, 
pale  and  of  the  columnar  variety. 

Mechanism  of  the  Discharge  of  Urine. — In  the  human  subject  the  urine 


372 


EXCRETION  BY  THE  SKIN   AND  KIDNEYS. 


is  discharged  into  the  pelves  of  the  kidneys  and  the  ureters  by  pressure  due 
to  the  act  of  separation  of  fluid  from  the  blood.  Once  discharged  into  the 
ureters,  the  course  of  the  urine  is  determined  in  part  by  the  vis  a  tergo,  and 
in  part,  probably,  by  the  action  of  the  muscular  coats  of  these  canals.  Miiller 
has  found  that  the  ureters  can  be  made  to  undergo  a  powerful  local  contrac- 
tion by  the  application  of  a  Faradic  current ;  and  Bernard  has  shown  that 
this  may  be  produced  by  stimulation  of  the  anterior  roots  of  the  eleventh 
dorsal  nerves. 

When  the  urine  has  accumulated  to  a  certain  extent  in  the  bladder,  a  pe- 
culiar sensation  is  felt  which  leads  to  the  act  for  its  expulsion.  The  intervals 
at  which  it  is  experienced  are  very  variable.  The  urine  is  usually  voided 
before  retiring  to  rest  and  upon  rising  in  the  morning,  and  generally  two  or 
three  times,  in  addition,  during  the  day.  The  frequency  of  micturition,  how- 
ever, depends  very  much  upon  habit,  upon  the  quantity  of  liquids  ingested 
and  upon  the  degree  of  activity  of  the  skin. 

Evacuation  of  the  bladder  is  accomplished  by  the  muscular  walls  of  the 
organ  itself,  aided  by  contractions  of  the  diaphragm  and  the  abdominal  mus- 
cles with  certain  muscles  which  oper- 
ate upon  the  urethra,  and  it  is  accom- 
panied by  relaxation  of  the  sphincter 
vesicas.  This  act  is  at  first  voluntary, 
but  once  begun,  it  may  be  continued 
by  the  involuntary  contraction  of  the 
bladder  alone.  During  the  first  part 
of  the  process,  the  distended  bladder 
is  compressed  by  contraction  of  the  di- 
aphraghm  and  the  abdominal  mus- 
cles ;  and  this  after  a  time  excites  the 
action  of  the  bladder  itself.  A  cer- 
tain time  usually  elapses  then  before 
the  urine  begins  to  flow.  When  the 
bladder  contracts,  aided  by  the  mus- 
cles of  the  abdomen  and  the  dia- 
phragm, the  resistance  of  the  sphinc- 
ter is  overcome,  and  a  jet  of  urine 
flows  from  the  urethra.  All  voluntary 
may  then  cease  for  a  time,  and 
bladder  will  nearly  empty  itself ; 
the  force  of  the  jet  may  be  con- 
siderably increased  by  voluntary  effort. 

Toward  the  end  of  the  expulsive  act,  when  the  quantity  of  liquid  remain- 
ing in  the  bladder  is  small,  the  diaphragm  and  the  abdominal  muscles  are 
again  called  into  action,  and  there  is  a  convulsive,  interrupted  discharge  of 
the  small  quantity  of  urine  that  remains.  At  this  time  the  impulse  from  the 
bladder,  and,  indeed,  the  influence  of  the  abdominal  muscles  and  diaphragm, 
are  very  slight,  and  the  flow  of  urine  along  the  urethra  is  aided  by  the  con- 


FIG.  118.—  Diagram  shmving  the  mechanism  of  mic- 
turition (Ktiss.). 

1,  bladder  distended  with  liquid  ;  by  the  contrac- 
tion of  its  walls  it  assumes  successively  the  po- 
sitions 2,  3, 4,  5  ;  but  the  walls  can  not  approach 
nearer  the  base  without  the  aid  of  the  abdom- 
inal muscles,  which,  by  a  voluntary  effort,  bring 
summit  to  the  position  indicated  by  the 


PROPERTIES  AND  COMPOSITION  OF  THE  URINE.  373 

tractions  of  its  muscular  walls  and  the  action  of  some  of  the  perineal  mus- 
cles, the  most  efficient  being  the  accelerator  urinae ;  but  with  all  this  muscu- 
lar action,  a  few  drops  of  urine  generally  remain  in  the  male  urethra  after  the 
act  of  urination  has  been  accomplished.  The  process  of  evacuation  of  urine 
in  the  female  is  essentially  the  same  as  in  the  male,  with  the  exception  of 
the  slight  modifications  due  to  differences  in  the  direction  and  length  of  the 
urethra. 

According  to  Budge,  the  influence  of  the  nervous  system  on  the  bladder 
operates  through  the  sympathetic ;  and  he  has  described  a  centre  in  the  spinal 
cord,  which  presides  over  the  contractions  of  the  lower  part  of  the  intestinal 
canal,  the  bladder  and  the  vasa  deferentia.  This  is  called  the  genito-spinal 
centre,  and  it  has  been  located,  in  experiments  upon  rabbits,  in  the  spinal 
cord,  at  a  point  opposite  the  fourth  lumbar  vertebra.  From  this  centre  the 
nervous  filaments  pass  through  the  sympathetic  nerve,  communicating  with 
the  ganglion  which  corresponds  to  the  fifth  lumbar  vertebra. 

PROPERTIES  AND  COMPOSITION  OF  THE  URINE. 

The  color  of  the  urine  is  very  variable  within  the  limits  of  health,  and  it 
depends  to  a  considerable  extent  upon  the  character  of  the  food,  the  quantity 
of  drink  and  the  activity  of  the  skin.  As  a  rule  the  color  is  yellowish  or 
amber,  with  more  or  less  of  a  reddish  tint.  The  fluid  is  perfectly  transpar- 
ent, free  from  viscidity,  and  exhales,  when  first  passed,  a  peculiar,  aromatic 
odor,  which  is  by  no  means  disagreeable.  Soon  after  the  urine  cools,  it  loses 
this  peculiar  odor  and  has  the  odor  known  as  urinous.  This  odor  remains 
until  the  liquid  begins  to  undergo  decomposition.  The  color  and  odor  of 
the  urine  usually  are  modified  by  the  same  physiological  conditions.  AVhen 
the  fluid  contains  a  large  proportion  of  solid  matters,  the  color  is  more  intense 
and  the  urinous  odor  is  more  penetrating ;  and  when  its  quantity  is  increased 
by  an  excess  of  water,  the  specific  gravity  is  low,  the  color  is  pale  and  the 
odor  is  faint.  The  first  urine  passed  in  the  morning,  immediately  after 
rising,  usually  is  more  intense  in  color  than  that  passed  during  the  day,  and 
contains  a  relatively  larger  proportion  of  solids  in  solution. 

The  temperature  of  the  urine  at  the  moment  of  its  emission,  under  physio- 
logical conditions,  varies  but  a  very  small  fraction  of  a  degree  from  100° 
Fahr.  (37'78°  C.).  This  estimate  is  the  result  of  an  extended  series  of  obser- 
vations, by  Byasson,  in  1868. 

In  estimating  the  total  quantity  of  urine  discharged  in  the  twenty-four 
hours,  it  is  important  to  take  into  consideration  the  specific  gravity,  as  an 
indication  of  the  amount  of  solid  matter  excreted  by  the  kidneys.  Variations 
in  quantity  constantly  occur  in  health,  depending  upon  the  proportion  of 
water ;  but  the  quantity  of  solid  matters  excreted  is  usually  more  nearly  uni- 
form. It  must  also  be  taken  into  account  that  differences  in  climate,  habits 
of  life,  etc.,  in  different  countries,  have  an  important  influence  upon  the  daily 
quantity  of  urine.  Parkes  collected  the  results  of  twenty-six  series  of  observa- 
tions made  in  America,  England,  France  and  Germany,  and  found  the  aver- 
age daily  quantity  of  urine  in  healthy  male  adults,  between  twenty  and  forty 


374  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

years  of  age,  to  be  fifty-two  and  a  half  fluidounces  (1,552-6  c.  c.),  the  average 
quantity  per  hour  being  two  and  one-tenth  fluidounces  (62  c.  c.).  The 
extremes  were  thirty-five  ounces  and  eighty-one  ounces  (1,035  and  2,395 
c.  c.).  The  average  quantity  may  be  assumed  to  be  about  fifty-one  fluid- 
ounces  (1,500  c.  c.).  The  normal  range  of  variation  is  between  thirty  and 
sixty  ounces  (about  900  and  1,775  c.  c.).  The  conditions  which  lead  to  a 
diminution  in  the  quantity  of  urine  usually  are  more  efficient  in  their  opera- 
tion than  those  which  tend  to  an  increase ;  and  the  range  below  the  normal 
standard  is  rather  wider  than  it  is  above.  More  urine  usually  is  secreted 
during  the  day  than  at  night.  The  quantity  of  water  discharged  by  the 
kidneys  in  the  twenty-four  hours  is  a  little  greater  in  the  female  than  in  the 
male ;  but  in  the  female  the  specific  gravity  is  lower,  and  the  quantity  of  solid 
constituents  is  relatively  and  absolutely  less  (Becquerel). 

The  specific  gravity  of  the  urine  should  be  estimated  in  connection  with 
the  absolute  quantity  in  the  twenty-four  hours.  Those  who  assume  that  the 
daily  quantity  is  about  fifty-one  ounces  (1,500  c.  c.),  give  the  ordinary  specific 
gravity  of  the  mixed  urine  of  the  twenty-four  hours  as  about  1020.  The 
specific  gravity  is  liable  to  the  same  variations  as  the  proportion  of  water,  and 
the  density  is  increased  as  the  water  is  diminished.  The  ordinary  range  of 
variation  in  specific  gravity  is  between  1015  and  1025  ;  but  without  positively 
indicating  any  pathological  condition,  it  may  be  as  low  as  1005  or  as  high 
as  1030. 

The  reaction  of  the  urine  is  acid  in  the  carnivora  and  alkaline  in  the 
herbivora.  In  the  human  subject  it  usually  is  acid  at  the  moment  of  its 
discharge  from  the  bladder;  although  at  certain  times  of  the  day  it  may 
be  neutral  or  feebly  alkaline,  the  reaction  depending  upon  the  character 
of  the  food.  The  acidity  may  be  measured  by  neutralizing  the  urine  with 
an  alkali  in  a  solution  that  has  previously  been  graduated  with  a  solution 
of  oxalic  acid  of  known  strength ;  and  the  degree  of  acidity  is  usually  ex- 
pressed by  calling  it  equivalent  to  so  many  grains  of  crystallized  oxalic 
acid. 

As  the  result  of  a  large  number  of  observations  made  by  Vogel  and  under 
his  direction,  the  total  quantity  of  acid  in  the  urine  of  the  twenty-four  hours 
in  a  healthy  adult  male  is  equal  to  between  thirty  and  sixty  grains  (2  and  4 
grammes)  of  oxalic  acid.  The  hourly  quantity  in  these  observations  was 
equal,  in  round  numbers,  to  between  one  and  a  half  and  three  grains  (O'l  and 
0'2  gramme)  of  acid.  The  proportion  of  acid  was  found  to  be  very  variable 
in  the  same  person  at  different  times  of  the  day.  The  urine  contains  no  free 
acid,  but  its  acidity  under  an  animal  or  a  mixed  diet  depends  upon  the  pres- 
ence of  acid  salts,  of  which  the  principal  one  is  acid  sodium  phosphate,  with 
possibly  a  little  acid  calcium  phosphate. 

Composition  of  the  Urine. — Eegarding  the  excrementitious  constituents 
of  the  urine  as  a  measure,  to  a  certain  extent,  of  the  general  process  of  dis- 
similation, it  is  more  important  to  recognize  the  quantities  of  these  products 
discharged  in  a  definite  time  than  to  learn  simply  their  proportions  in  the 
urine ;  and  in  the  following  table  of  composition  of  the  urine,  the  absolute 


PROPERTIES  AND  COMPOSITION  OF  THE  URINE.  375 

quantities  of  its  different  constituents,  excreted  in  twenty-four  hours,  have 
been  given  when  practicable. 

COMPOSITION    OF   THE    HUMAN    URINE. 
Water  (in  24  hours,  27  to  50  fluidounces,  800  to  1,480  c.  c.— Becquerel) . .  96?47  to  940-36 

Urea  (in  24  hours,  355  to  463  grains,  23  to  30  grammes— Robin) 15-00   "     23-00 

Uric  acid,  accidental,  or  traces 

Sodium  urate,  neutral  and  acid 1      (In  24  hours.  6  to  9  grs.,  0-39 


Ammonium  urate,  neutral  and  acid  (in 


to  0-58  gramme,  of  uric  acid 


small  quantity) !  — Becquerel — or  9  to  14  grs 


Potassium  urate . 
Calcium  urate , 


0-58  to  0-9  gramme,  of  urates, 
estimated  as  neutral  urate  of 


Magnesium  urate J  soda) 1*00   "        1'GO 

1      (In  24  hours,  about  7-5  grs.,  0-486  gramme, 

Sodium  hippurate 

V.  !  of  hippunc  acid — Thudichum — equivalent 

Potassium  hippurate > 

n  ,  •        .-  to  about  8-7  grs.,  0-o66  gramme,  of  sodium 

Calcium  hippurate 

J  hippurate) I'OO   " 

Sodium  lactate | 

Potassium  lactate >-      (Daily  quantity  not  estimated) 1'50   "       2'60 

Calcium  lactate I 

Creatine /      (In  24  hours,  about  11-5   grains,  0-74.5 

Creatinine )  gramme,  of  both — Thudichum) 1*60   "       3'00 

Calcium  oxalate  (daily  quantity  not  estimated) traces   "       1*10 

Xanthine not  estimated. 

Margarine,  oleine  and  other  fatty  matters 0-10  to      0-20 

Sodium  chloride  (in  24  hours,  about  154  grains,  10  grammes — Robin)  . . .       3-00   "       8'00 

Potassium  chloride traces. 

Ammonium  chloride 1'50  to      2'20 

(In  24  hours,  23  to  38  grains,  1-5  to  2-5 
grammes,  of  sulphuric  acid — Thudichum. 


Sodium  sulphate , 


About  equal  parts  of  sodium  sulphate  and 


Potassium  sulphate Y  potassium  sulphate-Robin-equivalent  to 

Calcium  sulphate  (traces)..      22.~  to  3?.5  grains>  ^45  to  2-43  grammes 

J  of  each) 3-00"       7-00 

Sodium  phosphate,  neutral  )      (Dail    quantity  not  estimated)  . . .  2'50   "       4'30 

Sodium  phosphate,  acid  . .   ) 

Magnesium   phosphate  (in   24  hours,  7'7  to  11 -8  grains,  0-5    to  0-768 

gramme — Neubauer) 0'50   "       I'OO 

Calcium  phosphate,  acid ..   1      (In  24  hours,  4-7  to  5-7  grains,  0-307  to 

Calcium  phosphate,  basic..  )  0'372  gramme — Neubauer) 0-20   "       1-30 

Ammonio-magnesian  phosphate  (daily  quantity  not  estimated) 1-50   "       2-40 

(Daily  excretion  of  phosphoric  acid,  about  56  grains,  3-629  grammes — 

Thudichum.) 

Silicic  acid ... 0-03   "       0-04 

Urochrome ^  0.10   «       0-50 

Mucus  from  the  bladder  . . 


1,000-00     1,000-00 
Proportion  of  solid  constituents,  32-63  to  59'89  parts  per  1,000. 

Gases  of  the  Urine.    (Parts  per  1,000,  in  volume.) 

Oxygen  in  solution 0-90  to  I'OO 

Nitrogen  in  solution 7*00   "  10-00 

Carbon  dioxide  in  solution . .                             '45   "  SO'OO 


376  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

Urea. — As  regards  quantity,  and  probably  as  a  measure  of  the  activity 
of  the  general  process  of  disassimilation,  urea — CO(NH2)2 — is  the  most  im- 
portant of  the  urinary  constituents.  Regarding  the  daily  excretion  of  urea 
as  a  measure  of  the  physiological  wear  of  certain  tissues,  its  consideration 
would  come  properly  under  the  head  of  nutrition,  in  connection  with  other 
substances  known  to  be  the  results  of  disassimilation  ;  but  it  is  convenient  to 
treat  of  its  general  physiological  properties  and  some  of  its  variations  in 
common  with  other  excrementitious  principles  separated  by  the  kidneys,  in 
connection  with  the  composition  of  the  urine. 

The  formula  for  urea,  showing  the  presence  of  a  large  proportion  of 
nitrogen,  would  lead  to  the  supposition  that  this  substance  is  one  of  the  prod- 
ucts of  the  wear  of  the  nitrogenized  constituents  of  the  body.  It  is  found, 
under  normal  conditions,  in  the  urine,  the  lymph  and  chyle,  the  blood,  the 
sweat,  the  vitreous  humor,  and  a  trace  in  the  saliva.  Its  presence  has  been 
demonstrated,  also,  in  the  substance  of  the  healthy  liver  in  both  carnivorous 
and  herbivorous  animals ;  and  it  has  been  shown  that  it  exists  in  minute 
quantity  in  the  muscular  juice  (Zalesky).  Under  pathological  conditions, 
urea  finds  its  way  into  various  other  fluids,  such  as  the  secretion  from  the 
stomach,  the  serous  fluids  etc. 

Urea  is  one  of  the  few  organic  substances  that  have  been  produced  artifi- 
cially. In  1828,  Wohler  obtained  urea  by  adding  ammonium  sulphate  to  a 
solution  of  potassium  cyanate.  The  products  of  this  combination  are  potas- 
sium sulphate,  with  cyanic  acid  and  am- 
monium in  a  form  to  constitute  urea. 
Ammonium  cyanate  is  isomeric  with 
urea,  and  the  change  is  -effected  by  a 
re-arrangement  of  its  elements.  It  has 
long  been  known  that  urea  is  readily 
convertible  into  ammonium  carbonate  ; 
and  ammonium  carbonate,  when  heated 
in  sealed  tubes  to  the  temperature  at 
which  urea  begins  to  decompose,  is  con- 
verted into  urea  (Kolbe). 

Urea  may  readily  be  extracted  from 
the  urine,  by  processes  fully  described  in 
works   upon    physiological    chemistry; 
FIG.  119.— Urea  crystallized  from  an  aqueous     and  its  proportion  mav  now  easily  be 

solution  (Funke).  .  ,    ,  ,  .  ,      ,          „ 

estimated  by  the  various   methods  ot 

volumetric  analysis.  It  is  not  so  easy,  however,  to  separate  it  from  the  blood 
or  from  the  substance  of  any  of  the  tissues,  on  account  of  -the  difficulty  in 
getting  rid  of  other  organic  matters  and  the  readiness  with  which  it  under- 
goes decomposition. 

When  perfectly  pure,  urea  crystallizes  in  the  form  of  long,  four-sided, 
coloiless  and  transparent  prisms,  which  are  without  odor,  neutral,  and  in 
taste  resemble  saltpetre.  These  crystals  are  very  soluble  in  water  and  in 
alcohol,  but  they  are  entirely  insoluble  in  ether.  In  its  behavior  with  reagents, 


ORIGIN  OF  UEEA.  377 

urea  acts  as  a  base,  combining  readily  with  certain  acids,  particularly  nitric 
and  oxalic.  It  also  forms  combinations  with  certain  salts,  such  as  mercuric 
oxide,  sodium  chloride  etc.  It  exists  in  the  economy  in  a  state  of  watery 
solution,  with  perhaps  a  small  portion  modified  by  the  presence  of  sodium 
chloride. 

Origin  of  Urea. — It  is  now  universally  admitted  by  physiologists  that 
urea  is  not  formed  in  the  kidneys  but  pre-exists  in  the  blood.  It  finds  its  way 
into  the  blood,  in  part  directly  from  the  tissues,  and  in  part  from  the  lymph, 
which  contains  a  greater  proportion  of  urea  than  is  found  in  the  blood  itself. 
The  quantity  of  urea  in  the  blood  is  kept  down  by  the  eliminating  action  of 
the  kidneys.  Although  a  great  part  of  the  lymph  is  probably  derived  from 
the  blood,  it  is  not  probable  that  the  blood  gives  to  the  lymph  all  of  the  urea 
contained  in  the  latter  fluid ;  and  it  must  be  assumed  that  a  part  of  the  urea 
of  the  lymph  passes  from  the  tissues  into  the  lymph-spaces  and  canals, 
although  a  certain  quantity  may  be  produced  by  the  lymphatic  glands. 

As  an  outcome  of  many  contradictory  experiments  and  opinions  on  the 
subject,  it  must  now  be  considered  as  proved  that  the  liver  produces  urea  in 
large  quantity.  If  defibrinated  blood  be  passed  several  times  through  a  per- 
fectly fresh  liver,  it  gains  urea.  This  observation,  which  was  first  made  by 
Cyon,  in  1870,  has  been  repeatedly  confirmed.  In  certain  cases  of  struct- 
ural disease  of  the  liver,  the  excretion  of  urea  is  much  diminished,  and  this 
substance  may  disappear  from  the  urine.  A  number  of  cases  illustrating 
this  fact  has  been  reported  by  Brouardel. 

Assuming  that  urea  is  the  most  abundant  and  important  of  the  nitrogen- 
ized  excrementitious  products — which  is  fully  justified  by  physiological  facts — 
it  is  difficult  to  avoid  the  conclusion  that  this  substance  represents,  to  a  great 
extent,  the  disassimilation  of  the  nitrogenized  parts  of  the  tissues,  and  neces- 
sarily the  physiological  wear  of  the  muscular  substance.  The  fact  that  urea 
exists  in  very  minute  quantity  in  the  muscles — and  some  chemists  state  that 
it  is  absent — is  probably  due  to  its  constant  removal  by  the  blood  and  lymph. 

Uric  acid,  creatine,  creatinine,  xanthine,  hypoxanthine,  leucine,  tyrosine 
and  some  other  analogous  substances  are  to  be  regarded  as  formations  ante- 
cedent to  urea,  urea  being  the  final  and  perfect  excrementitious  product. 

It  is  convenient,  in  this  connection,  to  consider  the  principal  conditions 
which  influence  the  formation  and  elimination  of  urea,  or  in  order  to  com- 
pare this  substance  with  certain  constituents  of  food,  the  elimination  of 
excrementitious  nitrogen  from  the  body. 

Influence  of  Ingesta  upon  the  Composition  of  the  Urine  and  upon  the 
Elimination  of  Nitrogen. — Water  and  other  liquid  ingesta  usually  increase 
the  proportion  of  water  in  the  urine  and  diminish  its  specific  gravity.  This 
is  so  marked  after  the  ingestion  of  large  quantities  of  liquids,  that  the  urine 
passed  under  these  conditions  is  sometimes  spoken  of  by  physiologists  as  the 
urina  potus ;  but  when  an  excess  of  water  has  been  taken  for  purposes  of  ex- 
periment, the  diet  being  carefully  regulated,  the  absolute  quantity  of  solid 
matters  excreted  is  considerably  increased.  This  is  particularly  marked  as 
regards  urea,  but  it  is  noticeable  in  the  sulphates  and  phosphates,  though  not 


378  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

to  any  great  extent  in  the  chlorides.  The  results  of  experiments  upon  this 
point  seem  to  show  that  water  taken  in  excess  increases  the  activity  of  disas- 
similation. 

The  ordinary  meals  increase  the  solid  constituents  of  the  urine,  the  most 
constant  and  uniform  increase  being  in  the  proportion  of  urea.  This,  how- 
ever, depends  to  a  great  extent  upon  the  kind  of  food  taken.  The  increase 
is  usually  noted  during  the  first  hour  after  a  meal,  and  it  attains  its  maxi- 
mum at  the  third  or  fourth  hour.  The  inorganic  matters  are  increased  as 
well  as  the  excrementitious  substances  proper.  The  urine  passed  after  food, 
has  been  called  urina  cibi,  under  the  idea  that  it  is  to  be  distinguished  from 
the  urine  supposed  to  be  derived  exclusively  from  disassimilation  of  the  tis- 
sues, which  is  called  the  urina  sanguinis. 

It  is  an  important  question,  to  determine  the  influence  of  different  kinds 
of  food  upon  the  composition  of  the  urine,  particularly  the  comparative 
effects  of  a  nitrogenized  and  a  non-nitrogenized  diet.  •  Lehmann  has  made  a 
number  of  observations  upon  this  point,  and  his  results  have  been  confirmed 
by  many  other  physiologists.  Without  discussing  fully  all  of  these  observa- 
tions, it  is  sufficient  to  state  that  the  ingestion  of  an  excess  of  nitrogenized 
food  always  produced  a  great  increase  in  the  proportion  of  the  nitrogenized 
constituents  of  the  urine,  particularly  the  urea.  On  a  non-nitrogenized  diet, 
the  proportion  of  urea  was  found  to  be  diminished  more  than  one-half.  The 
general  results  of  the  experiments  of  Lehmann  are  embodied  in  the  following 
quotation  : 

"  My  experiments  show  that  the  amount  of  urea  which  is  excreted  is  ex- 
tremely dependent  on  the  nature  of  the  food  which  has  been  previously  taken. 
On  a  purely  animal  diet,  or  on  food  very  rich  in  nitrogen,  there  were  often 
two-fifths  more  urea  excreted  than  on  a  mixed  diet ;  while,  on  a  mixed  diet, 
there  was  almost  one-third  more  than  on  a  purely  vegetable  diet;  while, 
finally,  on  a  non-nitrogenous  diet,  the  amount  of  urea  was  less  than  half  the 
quantity  excreted  during  an  ordinary  mixed  diet." 

The  influence  of  food  is  not  absolutely  confined  to  the  period  when  any 
particular  kind  of  food  is  taken,  but  is  continued  for  many  hours  after  a  re- 
turn to  the  ordinary  diet. 

With  regard  to  the  influence  of  food  upon  the  inorganic  constituents  of 
the  urine,  it  may  be  stated  in  general  terms  that  the  ingestion  of  mineral 
substances  increases  their  proportion  in  the  excretions. 

There  are  certain  articles  which,  when  taken  into  the  system,  the  diet 
being  regular,  seem  to  retard  the  process  of  disassimilation  ;  or  at  least  they 
diminish,  in  a  marked  manner,  the  quantity  of  matters  excreted,  particularly 
urea.  Alcohol  has  a  very  decided  influence  of  this  kind.  Its  action  may  be 
modified  by  the  presence  of  salts  and  other  matters  in  the  different  alcoholic 
beverages,  but  in  nearly  all  direct  experiments,  alcohol  either  taken  under 
normal  conditions  of  diet,  when  the  diet  is  deficient  or  when  it  is  in  excess, 
diminishes  the  excretion  of  urea.  The  same  may  be  stated  in  general  terms 
of  tea  and  coffee. 

Influence  of  Muscular  Exercise  upon  the  Elimination  of  Nitrogen. — In 


ELIMINATION  OF  NITKOGEN.  379 

all  observations  with  regard  to  the  influence  of  muscular  exercise  upon  the 
elimination  of  nitrogen,  account  should  be  taken  of  the  influence  of  diet ;  and 
those  observations  are  most  valuable  which  have  given  the  proportion  of  nitro- 
gen eliminated  to  the  nitrogen  of  food.  The  observations  of  Fick  and  Wisli- 
cenus  (1866)  showed  a  diminution  in  the  elimination  of  nitrogen  during  work; 
but  during  the  time  of  the  muscular  work,  no  nitrogenized  food  was  taken. 
The  same  conditions  obtained  in  certain  of  the  observations  of  Parkes.  In 
a  series  of  observations  made  in  1870  (Flint),  on  a  person  who  walked  317£ 
miles  (about  510  kilometres)  in  five  consecutive  days,  the  diet  was  normal, 
and  the  proportionate  quantity  of  nitrogen  was  calculated  for  three  periods  of 
five  days  each,  with  the  following  results  : 

For  the  five  days  before  the  walk,  with  an  average  exercise  of  about  eight 
miles  (13  kilometres)  daily,  the  nitrogen  eliminated  was  92-82  parts  for  100 
parts  of  nitrogen  ingested.  For  the  five  days  of  the  walk,  for  every  hundred 
parts  of  nitrogen  ingested,  there  were  discharged  153*99  parts.  For  the  five 
days  after  the  walk,  when  there  was  hardly  any  exercise,  for  every  hundred 
parts  of  nitrogen  ingested,  there  were  discharged  84*63  parts.  During  the 
walk,  the  nitrogen  excreted  was  in  direct  ratio  to  the  amount  of  work; 
and  the  excess  of  nitrogen  eliminated,  over  the  nitrogen  of  food,  almost  ex- 
actly corresponded  with  a  calculation  of  the  nitrogen  of  the  muscular  tissue 
consumed,  as  estimated  from  the  loss  of  weight  of  the  body.  In  1876,  a  similar 
series  of  observations  was  made  upon  the  same  person  by  Pavy.  In  these  ob- 
servations, the  subject  of  the  experiment  walked  450  miles  (724-21  kilometres) 
in  six  consecutive  days.  During  this  period,  the  proportionate  elimination  of 
nitrogen  was  increased,  but  not  to  the  extent  observed  in  1870.  Similar  re- 
sults, although  the  experiments  were  made  on  a  less  extended  scale,  were  ob- 
tained by  North,  in  1878.  These  results  are  opposed  to  the  views  of  many 
physiologists,  since  the  experiments  of  Fick  and  Wislicenus,  who  regard  the 
elimination  of  nitrogen  under  ordinary  conditions  as  dependent  mainly  upon 
the  diet  and  not  upon  the  muscular  work  performed.  The  observations  of 
Voit,  indeed,  are  favorable  to  this  view. 

Notwithstanding  the  results  obtained  by  Fick  and  Wislicenus,  Frankland, 
Haughton,  Voit  and  others,  the  fact  remains  that  excessively  severe  and 
prolonged  muscular  work  increases  the  elimination  of  nitrogen  over  and 
above  the  quantity  to  be  accounted  for  by  the  nitrogenized  food  taken.  Ac- 
tual observations  (Flint,  Pavy  and  others)  are  conclusive  as  regards  this 
simple  fact ;  but  it  is  well  known  that  muscular  exercise  largely  increases 
the  elimination  of  carbon  dioxide  and  the  consumption  of  oxygen.  In  exer- 
cise so  violent  as  to  produce  dyspnoea,  the  distress  in  breathing  is  probably 
due  to  the  impossibility  of  supplying  by  the  lungs  sufficient  oxygen  to  meet 
the  increased  demand  on  the  part  of  the  muscular  system,  and  the  possible 
amount  of  muscular  work  is  thereby  limited. 

The  observations  and  conclusions  of  Oppenheim  (1880)  go  far  to  harmon- 
ize the  results  obtained  by  different  experimenters.  Oppenheim  concludes 
that  muscular  work,  when  not  carried  to  the  extent  of  producing  shortness  of 
breath  or  when  moderate  and  extending  over  a  considerable  length  of  time, 


380 


EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 


does  not  increase  the  elimination  of  urea ;  but  that  even  less  work,  when  vio- 
lent and  attended  with  shortness  of  breath,  increases  the  discharge  of  urea. 
According  to  this  view,  moderate  work  draws  upon  the  oxygen  supplied  to 
the  body  and  at  once  largely  increases  the  elimination  of  carbon  dioxide ;  but 
the  less  active  processes  which  result  in  the  production  of  urea  are  not  so 
promptly  affected.  Violent  muscular  work,  however,  or  work  which  is  ex- 
cessively prolonged,  consumes  those  parts  of  the  tissues  the  destruction  of 
which  is  represented  by  the  discharge  of  urea.  This  view,  if  accepted,  har- 
monizes the  apparently  contradictory  experiments  upon  the  influence  of 
muscular  work  on  the  elimination  of  nitrogen. 

The  daily  quantity  of  urea  excreted  is  subject  to  very  great  variations. 
It  is  given  in  the  table  as  355  to  463  grains  (23  to  30  grammes).  This  is 
less  than  the  estimates  frequently  given ;  but  when  the  quantity  has  been 
very  large,  it  has  generally  depended  upon  an  unusual  amount  of  nitrogen- 
ized  food,  or  the  weight  of  the  body  has  been  above  the  average.  Parkes 
has  given  the  results  of  twenty-five  different  series  of  observations  upon  this 
point.  The  lowest  estimate  was  286-1  grains  (18-24  grammes),  and  the 
highest,  688-4  grains  (44-61  grammes). 

Uric  Acid  and  its  Compounds. — Uric  acid  (C5H4N403)  seldom  if  ever 
exists  in  a  free  state  in  normal  urine.  It  is  very  insoluble,  requiring  four- 
teen to  fifteen  thousand  times  its  volume  of  cold  water  or  eighteen  to  nine- 
teen hundred  parts  of  boiling  water  for  its  solution.  Its  presence  uncom- 
bined  in  the  urine  must  be  regarded  as  a  pathological  condition. 

In  normal  urine,  uric  acid  is  combined  with  sodium,  ammonium,  potas- 
sium, calcium  and  magnesium.  Of  these  combinations,  the  sodium  urate 


FIG.  130.— Crystals  of  uric  acid,  obtained  partly 
by  the  solution  and  subsequent  precipita- 
tion of  chemically  pure  acid,  and  partly  by 
decomposition  of  the  urates  by  nitric  or 
acetic  acid  (Funke). 


FIG.  121.— Sodium  urate  (Funke). 


and  ammonium  urate  are  by  far  the  most  important,  and  they  constitute  the 
great  proportion  of  the  urates,  potassium,  calcium  and  magnesium  urates 
existing  only  in  minute  traces.  Sodium  urate  is  very  much  more  abundant 
than  ammonium  urate.  The  union  of  uric  acid  with  the  bases  is  very  feeble. 


HIPPURIC  ACID,  HIPPURATES  AND  LACTATES.  381 

If  from  any  cause  the  urine  become  excessively  acid  after  its  emission,  a 
deposit  of  uric  acid  is  likely  to  occur.  The  addition  of  a  very  small  quantity 
of  almost  any  acid  is  sufficient  to  decompose  the  urates,  when  the  uric  acid 
appears,  after  a  few  hours,  in  a  crystalline  form. 

Uric  acid,  probably  in  combination  with  bases,  was  found  in  the  substance 
of  the  liver  in  large  quantity  by  Cloetta  (1858),  and  his  observations  have 
been  confirmed  by  recent  authorities.  The  urates  also  exist  in  the  blood  in 
very  small  quantity  and  pass  ready-formed  into  the  urine.  The  fact  that 
the  urates  exist  in  the  liver  has  led  to  the  opinion  that  this  organ  is  the  prin- 
cipal seat  of  the  formation  of  uric  acid  (Meissner).  However  this  may  be,  uric 
acid  certainly  is  not  formed  in  the  kidneys,  but  is  simply  separated  by  these  or- 
gans from  the  blood.  Meissner  did  not  succeed  in  finding  uric  acid  in  the  mus- 
cular tissue,  although  the  specimens  were  taken  from  animals  in  which  he  had 
found  large  quantities  in  the  liver.  The  urates,  particularly  sodium  urate, 
are  products  of  disassimilation  of  the  nitrogenized  constituents  of  the  body. 

The  daily  excretion  of  uric  acid,  given  in  the  table,  is  six  to  nine  grains 
(0-39  to  O58  gramme),  the  equivalent  of  nine  to  fourteen  grains  (0-58  to  0-9 
gramme)  of  urates  estimated  as  neutral  sodium  urate.  Like  urea,  the  pro- 
portion of  the  urates  in  the  urine  is  subject  to  certain  physiological  varia- 
tions. 

Hippuric  Acid,  Hippurates  and  Lactates. — The  compounds  of  hippuric 
acid  (C9H9N03),  which  are  so  abundant  in  the  urine  of  the  herbivora,  are 
now  known  to  be  constant  constituents  of  the  human  urine.  Hippuric  acid 
is  always  to  be  found  in  the  urine  of  children,  but  it  is  sometimes  absent 
temporarily  in  the  adult.  The  hippurates  have  been  detected  in  the  blood 
of  the  ox  by  Verdeil  and  Dolfuss,  and  they  have  since  been  found  in  the  blood 
of  the  human  subject.  There  can  be  scarcely  any  doubt  that  they  pass, 
ready-formed,  from  the  blood  into  the  urine.  As  to  the  exact  mode  of  origin 
of  the  hippurates,  there  is  even  less  information  than  with  regard  to  the 
origin  of  the  other  urinary  constituents  already  considered.  Experiments 
have  shown  that  the  proportion  of  hippuric  acid  in  the  urine  is  greatest  after 
taking  vegetable  food ;  but  it  is  found  after  a  purely  animal  diet,  and  proba- 
bly it  also  exists  during  fasting.  The  daily  excretion  of  hippuric  acid  is 
about  7-5  grains  (0*486  gramme),  which  is  equivalent  to  about  8-7  grains 
(0-566  gramme)  of  sodium  hippurate. 

Hippuric  acid  itself,  unlike  uric  acid,  is  soluble  in  water  and  in  a  mixture 
of  hydrochloric  acid.  It  requires  six  hundred  parts  of  cold  water  for  its 
solution,  and  a  much  smaller  proportion  of  warm  water.  Under  pathological 
conditions  it  is  sometimes  found  free  in  solution  in  the  urine. 

Sodium,  potassium  and  calcium  lactates  exist  in  considerable  quantity  in 
the  normal  urine.  They  are  undoubtedly  derived  immediately  from  the 
blood,  passing  ready- formed  into  the  urine,  where  they  exist  in  simple  watery 
solution.  According  to  Robin,  the  lactates  are  formed  in  the  muscles,  in  the 
substance  of  which  they  can  readily  be  detected.  Physiologists  have  little 
positive  information  with  regard  to  the  precise  mode  of  formation  of  these 
salts.  It  is  probable,  however,  that  the  lactic  acid  is  the  result  of  transforma- 
26 


382 


EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 


tion  of  glucose!  The  lactic  acid  contained  in  the  lactates  extracted  from  the 
muscular  substance  is  not  identical  with  the  acid  resulting  from  the  trans- 
formation of  the  sugars.  .  The  former 
have  been  called  sarcolactates,  and  they 
contain  one  equivalent  of  water  less 
than  the  ordinary  lactates.  The  com- 
pounds of  lactic  acid  in  the  urine  are  in 
the  form  of  sarcolactates  (Robin). 

Creatine  and  Creatinine. — Creatine 
(C4HgN302)  and  creatinine  (C4H7N30) 
are  probably  identical  in  their  relations 
to  the  general  process  of  disassimilation, 
for  one  is  easily  converted  into  the 
other,  out  of  the  body,  by  very  simple 
chemical  means ;  and  there  is  every  rea- 
son to  suppose  that  in  the  organism, 
they  are  the  products  of  physiological 
These  substances  have  been  found  in  the 
urine,  blood,  muscular  tissue  and  brain.  Scherer  has  demonstrated  the  pres- 
ence of  creatine  in  the  amniotic  fluid.  By  certain  chemical  manipulatioiis, 
both  creatine  and  creatinine  may  be  converted  into  urea.  Verdeil  and  Mar- 
cet  have  found  both  creatine  and  creatinine  in  the  blood ;  and  these  sub- 
stances are  now  regarded  as  excrementitious  matters,  taken  from  the  tissues 
by  the  blood,  to  be  eliminated  by  the  kidneys. 

Creatine  has  a  bitter  taste,  is  quite  soluble  in  cold  water  (one  part  in  sev- 
enty-five), and  is  much  more  soluble  in  hot  water,  from  which  it  separates  in 


FIG.  122.— Crystals  of  hippuric  acid  (Funke). 


wear  of  the  same  tissue  or  tissues. 


FIG.  123.— Creatine,  extracted  from  the  muscu- 
lar tissue,  and  crystallized  from  a  hot,  wa- 
tery solution  (Funke). 


FIG.  124.— Creatinine,  formed  from  creatine  by 
digestion  with  hydrochloric  acid,  and  crys- 
tallized from  a  hot,  watery  solution  (Funke). 


a  crystalline  form  on  cooling.  It  is  slightly  soluble  in  alcohol  and  is  insolu- 
ble in  ether.  A  watery  solution  of  creatine  is  neutral.  It  does  not  readily 
form  combinations  as  a  base ;  but  it  has  lately  been  made  to  form  crystalline 
compounds  with  some  of  the  strong  mineral  acids,  nitric,  hydrochloric  and 


CALCIUM  OXALATE. 


383 


sulphuric.  When  boiled  for  a  long  time  with  barium  hydrate,  it  is  changed 
into  urea  and  sarcosine.  When  boiled  with  the  strong  acids,  creatine  loses 
an  atom  of  water  and  is  converted  into  creatinine.  This  change  takes  place 
very  readily  in  decomposing  urine,  which  contains  neither  urea  nor  creatine, 
but  a  large  quantity  of  creatinine,  when  far  advanced  in  putrefaction. 

Creatinine  is  more  soluble  than  creatine,  and  its  watery  solution  has  a 
strongly  alkaline  reaction.  It  is  dissolved  by  eleven  parts  of  cold  water  and 
is  even  more  soluble  in  boiling  water.  It  is  slightly  soluble  in  ether  and  is 
dissolved  by  one  hundred  parts  of  alcohol.  This  substance  is  one  of  the  most 
powerful  of  the  organic  bases,  1'eadily  forming  crystalline  combinations  with 
a  number  of  acids.  According  to  Thudichum,  creatine  is  the  original  excre- 
mentitious  substance  produced  in  the  muscular  substance,  and  creatinine  is 
formed  in  the  blood  by  a  transformation  of  a  portion  of  the  creatine,  some- 
where between  the  muscles  and  the  kidneys ;  "  for,  in  the  muscle,  creatine 
has  by  far  the  preponderance  over  creatinine ;  in  the  urine,  creatinine  over 
creatine."  The  fact  that  creatine  has  been  found  in  the  brain  would  lead  to 
the  supposition  that  it  is  also  one  of  the  products  of  disassimilation  of  the 
nervous  tissue. 

The  average  daily  excretion  of  creatine  and  creatinine  was  estimated  by 
Thudichum  at  about  11-5  grains  (0*745  gramme).  Of  this  he  estimated  that 
4-5  grains  (0-292  gramme)  consisted  of  creatine,  and  7  grains  (0-453  gramme) 
of  creatinine. 

Calcium  Oxalate. — Calcium  oxalate  (oxalic  acid,  C2H204)  is  not  constantly 
present  in  normal  human  urine,  although  it  may  exist  in  certain  quantity 


FIG.  125.— Crystals  of  calcium  oxalate,  depos- 
ited from  the  normal  human  urine,  on  the 
addition  of  ammonium  oxalate  to  the  urine 
(Funke). 


FIG.  126.— Crystals  of  leucine  (Funke). 


without  indicating  any  pathological  condition.  It  is  exceedingly  insoluble, 
and  the  appearance  of  its  crystals,  which  are  commonly  in  the  form  of  small, 
regular  octahedra,  is  quite  characteristic.  According  to  Neubauer,  a  small 
quantity  may  be  retained  in  solution  by  the  acid  sodium  phosphate  in  the 
urine.  Calcium  oxalate  may  find  its  way  out  of  the  system  by  the  kidneys, 


384: 


EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 


after  it  has  been  taken  with  vegetable  food  or  with  certain  medicinal  sub- 
stances. The  ordinary  rhubarb,  or  pie-plant,  contains  a  large  quantity  of  cal- 
cium oxalate,  which,  when  this  article  is  taken,  will  pass  into  the  urine.  It 
is  probable,  however,  that  a  certain  quantity  may  be  formed  in  the  organism. 

Inasmuch  as  pathological  facts  have  shown  pretty  conclusively  that  oxalic 
acid  may  appear  in  the  system  without  having  been  introduced  with  the  food, 
some  physiologists  have  endeavored  to  show  how  it  may  originate  from  a 
change  in  certain  other  substances  from  which  it  can  be  produced  artifi- 
cially out  of  the  body.  One  of  the  substances  from  which  oxalic  acid  can  be 
thus  formed  is  uric  acid.  Woehler  and  Frerichs  injected  into  the  jugular 
vein  of  a  dog  a  solution  containing  about  twenty- three  grains  (T5  gramme) 
of  ammonium  urate.  In  the  urine  taken  a  short  time  after,  there  was  no 
deposit  of  uric  acid,  but  there  appeared  a  large  number  of  crystals  of  calcium 
oxalate.  The  same  result  followed  in  the  human  subject,  on  the  adminis- 
tration of  sixty-seven  grains  (4'34  grammes)  of  ammonium  urate  by  the 
mouth.  These  questions  have  more  pathological  than  physiological  impor- 
tance ;  for  the  quantity  of  calcium  oxalate  in  the  normal  urine  is  insig- 
nificant, and  this  salt  does  not  seem  to  be  connected  with  any  of  the  well 
known  processes  of  disassimilation. 

Xantliine,  Hypoxanthine,  Leucine,  Tyrosine  and  Taurine. — Traces  of 
xanthine  (C5H4N402)  have  been  found  in  the  normal  human  urine,  but  its  pro- 


FIG.  127. — Crystals  of  tyrosine  (Funke). 


FIG.  128. — Crystals  of  taurine  (Funke). 


portion  has  not  been  estimated,  and  observers  are  as  yet  but  imperfectly 
acquainted  with  its  physiological  relations.  It  has  been  found  in  the  liver, 
spleen,  thymus,  pancreas,  muscles  and  brain.  It  is  insoluble  in  water  but  is 
soluble  in  both  acid  and  alkaline  fluids.  Hypoxanthine  (C5H4N40)  has  never 
been  found  in  normal  urine,  although  it  exists  in  the  muscles,  liver,  spleen  and 
thymus.  Leucine  (C6H13N02)  exists  in  the  pancreas,  salivary  glands,  thyroid, 
thymus,  suprarenal  capsules,  lymphatic  glands,  liver,  lungs,  kidneys  and  the 
gray  substance  of  the  brain.  It  has  never  been  detected  in  the  normal  urine. 
The  same  remarks  apply  to  tyrosine  (C9HnN03),  although  it  is  not  so  exten- 
sively distributed  in  the  economy,  to  taurine  (C2H7N03S)  and  to  cystine 


INORGANIC  CONSTITUENTS  OF  THE  URINE. 


385 


(C3H7NS02).  The  last  two,  however,  contain  sulphur,  and  they  may  have 
peculiar  physiological  and  pathological  relations  that  are  not  at  present  un- 
derstood. 

These  various  substances  are  mentioned,  although  some  of  them  have  not 
been  found  in  the  normal  urine,  for  the  reason  that  there  is  evidently  much 
to  be  learned  with  regard  to  the  various  products  of  disassimilation  as  they 
are  represented  by  the  composition  of  the  urine.  While  some  of  them  may 
not  be  actual  constituents  of  the  urine,  but  substances  produced  by  the  pro- 
cesses employed  for  their  extraction,  some,  which  have  thus  far  been  discov- 
ered only  under  pathological  conditions,  may  yet  be  found  in  health,  and 
they  represent,  perhaps,  important  physiological  processes. 

Fatty  Matters.— F&t  and  fatty  acids  are  said  to  exist  in  the  normal  urine 
in  certain  quantity.  Their  proportion,  however,  is  small,  and  the  mere  fact 
of  their  presence,  only,  is  of  physiological  interest. 

Inorganic  Constituents  of  the  Urine. — It  is  by  the  kidneys  that  the 
greatest  quantity  and  variety  of  inorganic  salts  are  discharged  from  the 
organism ;  and  it  is  probable  that  even  now  physiological  •  chemists  are  not 
acquainted  with  the  exact  proportion  and  condition  of  all  the  constituents 
of  this  class  found  in  the  urine.  In  all  the  processes  of  nutrition,  it  is 
found  that  the  inorganic  constituents  of  the  blood  and  tissues  accompany 
the  organic  matters  in  their  various  transformations,  although  they  are  them- 
selves unchanged.  Indeed,  the  condition  of  union  of  inorganic  with  organic 
matters  is  so  intimate,  that  they  can  not  be  completely  separated  without  in- 
cineration. In  view  of  these  facts,  it  is  evident  that  a  certain  proportion,  at 
least,  of  the  inorganic  salts  of  the  urine  is  derived  from  the  tissues,  of  which, 
in  combination  with  organic  matters,  they  have  formed  a  constituent  part. 
As  the  kidneys  frequently  eliminate  from  the  blood  foreign  matters  taken 
into  the  system,  and  are  capable  sometimes  of  throwing  off  an  excess  of  the 
normal  constituents,  which  may  be  in- 
troduced into  the  circulation,  it  can 
readily  be  understood  how  a  large  pro- 
portion of  some  of  the  inorganic  con- 
stituents of  the  urine  may  be  derived 
from  the  food. 

Chlorides. — Almost  all  of  the  chlo- 
rine in  the  urine  is  in  the  form  of  so- 
dium chloride,  the  quantity  of  potassi- 
um chloride  being  insignificant  and  not 
of  any  special  physiological  importance. 
By  reference  to  the  table  of  the  compo- 
sition of  the  urine,  it  is  seen  that  the 
proportion  of  sodium  chloride  is  subject 
to  very  great  variations,  the  range  being 
between  three  and  eight  parts  per  thou- 
sand. This  at  once  suggests  the  idea  that  the  quantity  excreted  is  dependent 
to  a  considerable  extent  upon  the  quantity  taken  in  with  the  food ;  and,  in- 


FIG.  129.— Crystals  of  sodium  chloride  (Funke)- 


38G  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

deed,  it  has  been  shown  by  direct  observations  that  this  is  the  fact.  The  pro- 
portion of  sodium  chloride  in  the  blood  seems  to  be  tolerably  constant ;  and 
any  excess  that  may  be  introduced  is  thrown  off,  chiefly  by  the  kidneys.  As 
the  chlorides  are  deposited  with  the  organic  matters  in  all  the  acts  of  nutri- 
tion, they  are  found  to  be  eliminated  constantly  with  the  products  of  dis- 
assimilation  of  the  nitrogenized  parts,  and  their  absence  from  the  food  does 
not  completely  arrest  their  discharge  in  the  urine.  According  to  Robin,  by 
suppressing  salt  in  the  food,  its  daily  excretion  may  be  reduced  to  between 
thirty  and  forty-five  grains  (1-9  and  2-9  grammes).  This  quantity  is  less 
than  that  ordinarily  contained  in  the  ingesta,  and  under  these  conditions 
there  is  a  gradual  diminution  in  the  general  nutritive  activity.  In  nearly  all 
acute  febrile  disorders  the  chlorine  in  the  urine  rapidly  diminishes  and  is 
frequently  reduced  to  one-hundredth  of  the  normal  proportion.  The  quan- 
tity rapidly  increases  to  the  normal  standard  during  convalescence.  Most  of 
the  chlorides  of  the  urine  are  in  simple  watery  solution ;  but  a  certain  pro- 
portion of  sodium  chloride  exists  in  combination  with  urea. 

The  daily  elimination  of  sodium  chloride  is  about  one  hundred  and  fifty- 
four  grains  (10  grammes.)  The  great  variations  in  its  proportion  in  the 
urine,  under  different  conditions  of  alimentation,  etc.,  will  explain  the  differ- 
ences in  the  estimates  given  by  various  authorities. 

Sulphates. — There  is  very  little  to  be  said  regarding  the  sulphates,  in 
:  addition  to  the  general  statements  already  made  concerning  the  inorganic 
constituents  of  the  urine.  The  proportion  of  these  salts  in  the  urine  is  very 
much  greater  than  in  the  blood,  in  which  there  exist  only  about  O28  of  a 
part  per  thousand.  Inasmuch  as  the  proportion  in  the  urine  is  three  to 
seven  parts  per  thousand,  it  seems  probable  that  the  kidneys  eliminate  these 
rsalts  as  fast  as  they  find  their  way  into  the  circulating  fluid  either  from  the 
food  or  from  the  tissues.  Like  other  constituents  derived  in  great  part  from 
the  food,  the  normal  variations  in  the  proportion  of  sulphates  in  the  urine 
are  very  great.  It  is  unnecessary  to  consider  in  detail  the  variations  in  the 
quantity  of  sulphates  discharged  in  the  urine,  depending  upon  the  ingestion 
of  different  salts  or  upon  diet,  for  all  recorded  observations  have  given  the 
same  results,  and  they  show  that  the  ingestion  of  sulphates  in  quantity  is 
followed  by  a  corresponding  increase  in  the  proportion  eliminated. 

Thudichum  estimated  the  daily  excretion  of  sulphuric  acid  at  23  to  38 
grains  (1-5  to  2'5  grammes).  Assuming  that  the  sulphates  consist  of  about 
equal  parts  of  potassium  sulphate  and  sodium  sulphate  with  traces  of  calcium 
sulphate,  the  quantity  of  salts  would  be  22'5  to  37*5  grains  (T46  to  2-23 
grammes)  of  potassium  sulphate,  with  an  equal  quantity  of  sodium  sul- 
phate. 

Phosphates. — The  urine  contains  phosphates  in  a  variety  of  forms ;  but 
inasmuch  as  it  is  not  known  that  any  one  of  the  different  combinations  pos- 
sesses peculiar  relations  to  the  processes  of  disassimilation,  as  distinguished 
from  the  other  phosphates,  the  phosphatic  salts  may  be  considered  together. 

The  phosphates  exist  constantly  in  the  urine  and  are  derived  in  part  from 
the  food  and  in  part  from  the  tissues.  Like  other  inorganic  matters,  they  are 


INOEGANIG  CONSTITUENTS  OF  THE  URINE.  387 

united  with  the  nitrogenized  constituents  of  the  organism,  and  when  these 
are  changed  into  excrementitious  substances  and  are  separated  from  the  blood 
by  the  kidneys,  they  pass  with  them  and  are  discharged  from  the  body. 

It  is  a  question  of  some  importance  to  consider  how  far  the  phosphates 
are  derived  from  the  tissues  and  what  proportion  comes  directly  from  the 
food.  All  observers  agree  that  the  quantity  of  phosphates  in  the  urine  is  in 
direct  relation  to  the  proportion  in  the  food,  and  that  an  excess  of  phos- 
phates taken  into  the  stomach  is  immediately  thrown  off  by  the  kidneys.  It 
is  a  familiar  fact,  indeed,  that  the  phosphates  are  deficient  and  the  carbonates 
predominate  in  the  urine  of  the  herbivora,  while  the  reverse  obtains  in  the 
carnivora,  and  that  variations,  in  this  respect,  in  the  urine,  may  be  produced 
by  feeding  animals  with  different  kinds  of  food.  Deprivation  of  food 
diminishes  the  quantity  of  phosphates  in  the  urine,  but  a  certain  proportion 
is  discharged,  which  is  derived  exclusively  from  the  tissues. 

In  connection  with  the  fact  that  phosphorus  exists  in  the  nervous  mat- 
ter, it  has  been  assumed  that  mental  exertion  is  always  attended  with  an  in- 
crease in  the  elimination  of  phosphates ;  and  this  has  been  advanced  to  sup- 
port the  view  that  these  salts  are  specially  derived  from  disassimilation  of  the 
brain-substance.  Experiments  show  that  it  is  not  alone  the  phosphates  that 
are  increased  in  quantity  by  mental  work,  but  urea,  the  chlorides,  sulphates 
and  inorganic  matters  generally;  and  in  point  of  fact,  any  physiological 
conditions  which  increase  the  proportion  of  nitrogenized  excrementitious 
matters  increase  as  well  the  elimination  of  inorganic  salts.  It  can  not  be 
assumed,  therefore,  that  the  discharge  of  phosphates  is  specially  connected 
with  the  activity  of  the  brain.  Little  has  been  learned  upon  this  point  from 
pathology,  for  although  many  observations  have  been  made  upon  the  excre- 
tion of  phosphoric  acid  in  disease  —  Vogel  having  made  about  one  thou- 
sand different  analyses  in  various  affections — no  definite  results  have  been 
obtained.  From  these  facts  it  is  seen  that  there  is  no  physiological  reason 
why  the  elimination  of  the  phosphates  should  be  specially  connected  with 
the  disassimilation  of  any  particular  tissue  or  organ,  especially  as  these  salts 
in  some  form  are  universally  distributed  in  the  organism. 

Observations  have  been  made  upon  the  hourly  variations  in  the  discharge 
of  phosphoric  acid  at  different  times  of  the  day  ;  but  these  do  not  appear  to 
bear  any  definite  relation  to  known  physiological  conditions,  not  even  to  the 
process  of  digestion. 

Of  the  different  phosphatic  salts  of  the  urine,  the  most  important  are 
those  in  which  the  acid  is  combined  with  sodium.  These  exist  in  the  form 
of  the  neutral  and  acid  phosphates.  The  acid  salt  is  supposed  to  be  the 
source  of  the  acidity  of  the  urine  at  the  moment  of  its  emission.  The  so- 
called  neutral  salt  is  slightly  alkaline.  The  proportion  of  the  sodium  phos- 
phates in  the  urine  is  larger  than  that  of  any  of  the  other  phosphatic  salts, 
but  the  daily  quantity  excreted  has  not  been  estimated.  According  to  Robin, 
there  always  exists  in  the  urine  a  small  quantity  of  the  ammonio-magnesian 
phosphate,  but  it  never,  in  health,  exists  in  sufficient  quantity  to  form  a  crys- 
talline deposit.  The  daily  excretion  of  the  phosphates  is  subject  to  great 


388  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

variations,  but  the  average  quantity  of  phosphoric  acid  excreted  daily  may 
be  estimated  at  about  fifty-six  grains  (3-629  grammes). 

The  urine  contains,  in  addition  to  the  inorganic  salts  that  have  been 
mentioned,  a  small  quantity  of  silicic  acid ;  but  as  far  as  is  known,  this  has 
no  physiological  importance. 

Coloring  Matter  and  Mucus. — The  peculiar  color  of  the  urine  is  due  to 
the  presence  of  a  nitrogenized  substance  called  urochrome.  This  is  also  called 
urohaematine,  uroxanthine  and  purpurine.  There  is  no  accurate  account  of 
its  composition,  and  all  that  is  known  is  that  it  contains  carbon,  oxygen, 
hydrogen  and  nitrogen,  and  probably  iron.  Although  its  exact  chemical 
composition  is  not  absolutely  determined,  its  elements  are  supposed  to  be 
nearly  the  same  as  those  of  the  coloring  matter  of  the  blood,  the  proportion 
of  oxygen  being  much  greater.  These  facts  point  to  the  probability  of  the 
formation  of  urochrome  from  haemaglobine. 

The  quantity  of  coloring  matter  in  the  normal  urine  is  very  small.  It  is 
subject  to  considerable  variation  in  disease,  and  almost  always  it  is  fixed  by 
deposits  and  calculi  of  uric  acid  or  the  urates,  giving  them  their  peculiar 
color.  This  substance  first  makes  its  appearance  in  the  urine  and  is  probably 
formed  in  the  kidneys.  So  little  is  known  of  its  physiological  or  pathologi- 
cal relations  to  the  organism,  that  it  does  not  seem  necessary  to  follow  out 
all  of  the  chemical  details  of  its  behavior  in  the  presence  of  different  re- 
agents. 

The  normal  urine  always  contains  a  small  quantity  of  mucus,  with  more 
or  less  epithelium  from  the  urinary  passages  and  a  few  leucocytes.  These 
form  a  faint  cloud  in  the  lower  strata  of  healthy  urine  after  a  few  hours' 
repose.  The  properties  of  the  different  kinds  of  mucus  have  already  been 
considered.  An  important  peculiarity,  however,  of  the  mucus  contained  in 
normal  urine  is  that  it  does  not  seem  to  excite  decomposition  of  the  urea, 
and  that  the  urine  may  remain  for  a,  long  time  in  the  bladder  without  under- 
going putrefactive  changes. 

Gases  of  the  Urine. — In  the  process  of  separation  of  the  urine  from  the 
blood  by  the  kidneys,  a  certain  proportion  of  the  gases  in  solution  in  the 
circulating  fluid  is  also  removed.  For  a  long  time,  indeed,  it  has  been  known 
that  the  normal  human  urine  contained  different  gases ;  but  observations  on 
this  subject  have  been  made  by  Morin  (1864),  in  which  the  proportions  of 
the  free  gases  in  solution  have  been  accurately  estimated.  By  using  the 
method  employed  by  Magnus  in  estimating  the  gases  of  the  blood,  Morin 
was  able  to  extract  ab'out  two  and  a  half  volumes  of  gas  from  a  hundred 
parts  of  urine.  He  ascertained,  however,  that  a  certain  quantity  of  gas 
remained  in  the  urine  and  could  not  be  extracted  by  the  ordinary  process. 
This  was  about  one-fifth  of  the  whole  volume  of  gas.  Adding  this  to  the 
quantity  of  gas  extracted,  he  obtained  the  following  proportions  to  one  litre 
of  urine,  in  cubic  centimetres  (one  part  per  thousand  in  volume) : 

Oxygen 0-824 

Nitrogen 9-589 

Carbon  dioxide  . .  19-620 


WATER  REGARDED  AS  A  PRODUCT  OF  EXCRETION.   389 

These  proportions  represent  the  average  of  fifteen  observations  upon  the 
urine  secreted  during  the  night. 

The  proportion  of  these  gases  was  found  by  Morin  to  be  subject  to  certain 
variations.  For  example,  after  the  ingestion  of  a  considerable  quantity  of 
water  or  any  other  liquid,  the  proportion  of  oxygen  was  considerably  increased 
(from  0-824  to  1-024),  and  the  carbon  dioxide  was  diminished  more  than  one- 
half.  The  most  important  variations,  however,  were  in  connection  with 
muscular  exercise.  After  walking  a  long  distance,  the  exercise  being  taken 
both  before  and  after  eating,  the  quantity  of  carbon  dioxide  was  found  to  be 
double  that  contained  in  the  urine  after  repose.  The  proportion  of  oxygen 
was  very  slightly  diminished,  and  the  nitrogen  was  somewhat  increased ;  but 
the  variations  of  these  gases  were  insignificant. 

It  is  not  probable  that  the  kidneys  are  very  important  as  eliminators  of 
carbon  dioxide,  but  it  is  certain  that  the  presence  of  this  gas  in  the  urine 
assists  in  the  solution  of  some  of  the  saline  constituents  of  this  fluid,  notably 
the  phosphates. 

Water  regarded  as  a  Product  of  Excretion. — It  has  been  shown  by  indi- 
rect observations  that  a  large  proportion  of  the  hydrogen  introduced  as  an 
ingredient  of  food,  about  eighty-five  per  cent.,  is  not  accounted  for  by  the 
hydrogen  of  the  excreta.  Direct  observations  have  shown,  also,  that  under 
certain  conditions,  an  excess  of  water  over  that  introduced  with  food  and 
drink  is  discharged  from  the  body.  One  of  these  conditions  is  abstinence 
from  food  (Flint,  1878).  The  elimination  of  water  is  very  much  increased 
by  muscular  work  (Pettenkofer  and  Voit,  1868 ;  Flint,  1879).  These  facts 
point  to  the  actual  production  of  water  in  the  body  by  a  union  of  oxygen 
with  hydrogen. 

While  it  is  not  certain  that  water  is  constantly  produced  in  the  body, 
there  can  be  no  doubt  with  regard  to  its  formation  under  some  conditions, 
and  the  oxidation  of  hydrogen  is  important  as  one  of  the  factors  in  the  pro- 
duction of  animal  heat.  If  a  certain  proportion  of  the  water  discharged  by 
the  lungs,  skin  and  kidneys  be  regarded  as  a  product  of  oxidation  within  the 
body,  the  relations  which  it  bears  to  nutrition  are  probably  the  same  as  those 
of  some  of  the  excretions,  especially  carbon  dioxide,  and  are  subject  to  nearly 
the  same  laws.  It  has  not  been  shown,  however,  that  water  is  produced 
constantly,  like  those  substances  universally  regarded  as  true  excretions ;  and 
it  gives  rise  to  no  direct  toxic  phenomena  when  retained  in  the  system  or 
when  its  production  is  diminished  pathologically.  Water  also  has  important 
physiological  uses,  particularly  as  a  solvent.  Still,  carbon  dioxide,  with 
which  water  may  be  compared  as  regards  its  mode  of  production,  is  not  in 
itself  poisonous,  its  retention  in  the  blood  simply  interfering  with  the  absorp- 
tion of  oxygen ;  and  carbon  dioxide  probably  is  useful  in  increasing  the  solvent 
properties  of  the  liquids  of  the  organism.  The  relations  of  the  formation  of 
water  in  the  body  to  the  production  of  animal  heat  will  be  fully  considered 
in  connection  with  the  physiology  of  nutrition  and  calorification. 

Variations  in  the  Composition  of  the  Urine. — The  urine  not  only  repre- 
sents, in  its  varied  constituents,  a  great  part  of  the  physiological  disintegra- 


390  EXCRETION  BY  THE  SKIN  AND  KIDNEYS. 

tion  of  the  organism,  but  it  contains  matters  evidently  derived  from  the 
food.  Its  constitution  is  varying  with  every  different  condition  of  nutrition, 
with  exercise,  bodily  and  mental,  with  sleep,  age,  sex,  diet,  respiratory 
activity,  the  quantity  of  cutaneous  exhalation,  and,  indeed,  with  every  con- 
dition that  affects  any  part  of  the  system.  There  is  no  fluid  in  the  body 
that  presents  such  a  variety  of  constituents  as  a  constant  condition,  but  in 
which  the  proportion  of  these  constituents  is  so  variable.  It  is  for  this 
reason  that  in  the  table  of  the  composition  of  the  urine,  the  ordinary  limits 
of  variation  of  its  different  constituents  have  been  given ;  and  it  has  been 
found  necessary,  in  treating  of  the  individual  excrementitious  products,  to 
refer  to  some  of  the  variations  in  their  proportion  in  the  urine. 

Variations  with  Age  and  Sex, — There  are  decided  differences  in  the 
composition  of  the  urine  at  different  periods  of  life  and  in  the  sexes.  These 
undoubtedly  depend  in  part  upon  the  different  conditions  of  nutrition  and 
exercise  and  in  part  upon  differences  in  the  food.  Although  the  quantities 
of  excrementitious  matters  present  great  variations,  their  relations  to  the 
organism  are  not  materially  modified,  except,  perhaps,  at  an  early  age ;  and 
the  influence  of  sex  and  age  operates  merely  as  these  conditions  affect  the 
diet  and  the  general  habits  of  life. 

It  has  been  stated  that  urea  does  not  exist  in  the  urine  of  the  foetus ;  but 
in  a  specimen  of  urine  taken  from  a  still-born  child  delivered  with  forceps, 
examined  by  Elliot  and  Isaacs,  the  presence  of  urea  was  determined.  Beale 
found  urea  in  a  specimen  taken  at  the  seventh  month.  Observations  upon 
children  between  the  ages  of  three  and  seven  have  shown  that  at  this  period 
of  life,  the  urea  excreted  in  proportion  to  the  weight  of  the  body  is  about 
double  the  quantity  excreted  in  the  adult.  The  chlorine  in  the  urine  of  chil- 
dren is  about  three  times  the  quantity  in  the  adult ;  and  the  quantities  of 
other  solid  matters  are  also  greater.  The  quantity  of  water  excreted  by  the 
kidneys  in  children,  in  proportion  to  the  weight  of  the  body,  is  very  much 
greater  than  in  the  adult,  being  more  than  double.  Between  the  ages  of  eight 
and  eighteen  years,  the  urinary  excretion  gradually  approximates  the  stand- 
ard in  the  adult.  It  has  been  observed  that  crystals  of  calcium  oxalate  are 
much  more  frequent  in  the  urine  of  children  between  four  and  fourteen 
years  of  age  than  in  the  adult. 

There  are  not  many  definite  observations  on  record  upon  the  composition 
of  the  urine  in  the  later  periods  of  life.  It  has  been  shown,  however,  that 
there  is  a  decided  diminution,  at  this  time,  in  the  excretion  of  urea,  and  that 
the  absolute  quantity  of  urine  is  somewhat  less. 

The  absolute  quantity  of  the  urinary  excretion  in  women  is  less  than  in 
men,  and  the  same  is  true  of  the  quantity  in  proportion  to  the  weight  of  the 
body ;  still,  the  differences  are  not  very  marked,  and  the  proportion  of  the 
urinary  constituents  being  subject  to  modifications  from  the  same  causes  as 
in  men,  the  small  deficiency,  in  the  few  direct  observations  on  record,  may 
be  in  part  if  not  entirely  explained  by  the  fact  that  women  usually  perform 
less  mental  and  physical  work  than  men,  and  that  their  digestive  system  is 
generally  not  so  active. 


VAKIATIONS  IN  THE  COMPOSITION  OF  THE  URINE.        391 

Variations  at  Different  Seasons  and  at  Different  Periods  of  the  Day. — 
The  changes  in  the  quantity  and  composition  of  the  urine  which  may  be 
directly  referred  to  the  conditions  of  digestion,  temperature,  sleep,  exercise 
etc.,  have  long  been  recognized  by  physiologists ;  but  it  is  difficult  so  to  sepa- 
rate these  influences  that  the  true  modifying  value  of  each  can  be  fully 
appreciated.  For  example,  there  is  nothing  which  produces  such  marked 
variations  in  the  composition  of  the  urine  as  the  digestion  of  food.  Under 
strictly  physiological  conditions,  the  modifying  influence  of  digestion  must 
always  complicate  observations  upon  the  effects  of  exercise,  sleep,  season, 
period  of  the  day  etc. ;  and  the  urine  is  continually  varying  in  health,  with 
the  physiological  modifications  in  the  various  processes  and  conditions  of 
life. 

At  different  seasons  of  the  year  and  in  different  climates,  the  urine  pre- 
sents certain  variations  in  its  quantity  and  composition.  It  seems  necessary 
that  a  tolerably  definite  quantity  of  water  should  be  discharged  from  the 
body  at  all  times ;  and  when  the  temperature  or  the  hygrometric  condition  of 
the  atmosphere  is  favorable  to  the  action  or  the  skin,  as  in  a  warm,  dry  cli- 
mate, the  quantity  of  water  in  the  urine  is  diminished  and  its  proportion  of 
solid  matters  is  correspondingly  increased.  On  the  other  hand,  the  reverse 
obtains  when  the  action  of  the  skin  is  diminished  from  any  cause.  • 

At  different  times  of  the  day,  the  urine  presents  certain  important  varia- 
tions. It  is  evident  that  the  specific  gravity  must  be  constantly  varying 
with  the  relative  proportions  of  water  and  of  solid  constituents.  According 
to  Dalton,  the  urine  first  discharged  in  the  morning  is  dense  and  highly 
colored ;  that  passed  during  the  forenoon  is  pale  and  of  a  low  specific  gravity; 
and  in  the  afternoon  and  evening  it  is  again  deeply  colored,  and  its  specific 
gravity  is  increased.  The  acidity  is  also  subject  to  certain  variations,  which 
have  already  been  mentioned. 

Influence  of  Mental  Exertion. — Although  the  influence  of  mental  exer- 
tion upon  the  composition  of  the  urine  has  not  been  very  closely  studied,  the 
results  of  the  investigations  which  have  been  made  upon  this  subject  are  in 
many  regards  quite  satisfactory.  It  is  a  matter  of  common  remark  that  the 
secretion  of  urine  is  often  modified  to  a  considerable  extent  through  the 
nervous  system.  Fear,  anger,  and  various  violent  emotions,  sometimes  pro- 
duce a  sudden  and  copious  secretion  of  urine  containing  a  large  proportion  of 
water,  and  this  is  often  observed  in  cases  of  hysteria.  Intense  mental  exer- 
tion will  occasionally  produce  the  same  result.  In  studying  the  influence 
of  cerebral  activity  upon  the  composition  of  the  urine,  Byasson  found  that 
by  mental  exertion  the  quantity  of  urine  was  increased ;  the  urea  was  also 
increased ;  the  phosphoric  acid  was  increased  about  one-third  ;  the  sulphuric 
acid  was  more  than  doubled  ;  and  the  chlorine  was  nearly  doubled. 

The  products  of  spontaneous  decomposition  of  the  urine  have  a  certain 
chemical  interest  but  are  of  no  physiological  importance. 


392  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

CHAPTER  XIII. 

USES  OF  THE  LIVER-DUCTLESS   GLANDS. 

Physiological  anatomy  of  the  liver — Distribution  of  the  portal  vein,  the  hepatic  artery  and  the  hepatic  duct — > 
Structure  of  a  lobule  of  the  liver — Arrangement  of  the  bile-ducts  in  the  lobules — Anatomy  of  the  excre- 
tory biliary  passages — Nerves  and  lymphatics  of  the  liver — Mechanism  of  the  secretion  and  discharge  of 
bile— Quantity  of  bile— Uses  of  the  bile — Properties  and  composition  of  the  bile— Biliary  salts— Choles- 
terine — Tests  for  bile — Excretory  action  of  the  liver — Formation  of  glycogen  in  the  liver— Change  of 
glycogen  into  sugar — Conditions  which  influence  the  quantity  of  sugar  in  the  blood — Summary  of  the 
glycogenic  action  of  the  liver — Probable  office  of  the  ductless  glands— Physiological  anatomy  of  the 
spleen— Suprarenal  capsules— Addison's  disease— Thyroid  gland— Myxeedema — Thymus— Pituitary  body 
and  pineal  gland. 

PHYSIOLOGICAL  ANATOMY  OF  THE  LIVER. 

THE  liver  has  several  uses  in  the  economy,  which  are  more  or  less  dis- 
tinct from  each  other.  It  secretes  bile,  a  fluid  concerned  in  digestion  and 
containing  at  least  one  excrementitious  product.  Another  office  is  the  for- 
mation of  glycogen,  in  which  it  acts  as  a  ductless  gland. 

It  is  unnecessary,  in  this  connection,  to  dwell  upon  the  ordinary  descrip- 
tive anatomy  of  the  liver.  It  is  sufficient  to  state  that  it  is  situated  just  be- 
low the  diaphragm,  in  the  right  hypochondriac  region,  and  is  the  largest 
gland  in  the  body,  weighing,  when  moderately  filled  with  blood,  about  four 
and  a  half  pounds  (2  kilos.).  Its  weight  is  somewhat  variable,  but  in  a  per- 
son of  ordinary  adipose  development,  its  proportion  to  the  weight  of  the  body 
is  about  as  one  to  thirty-two.  In  early  life  the  liver  is  relatively  larger,  its 
proportion  to  the  weight  of  the  body,  in  the  new-born  child,  being  as  one  to 
eighteen  or  twenty  (Sappey). 

The  liver  is  covered  externally  by  peritoneum,  folds  or  duplicatures  of 
this  membrane  being  formed  as  it  passes  from  the  surface  of  the  liver  to  the 
adjacent  parts.  These  constitute  four  of  the  so-called  ligaments  that  hold 
the  liver  in  place.  The  proper  coat  is  a  thin  but  dense  and  resisting  fibrous 
membrane,  adherent  to  the  substance  of  the  organ,  but  detached  without 
much  difficulty,  and  very  closely  united  to  the  peritoneum.  This  membrane 
is  of  variable  thickness  at  different  parts  of  the  liver,  being  especially  thin 
in  the  groove  for  the  vena  cava.  At  the  transverse  fissure,  it  surrounds  the 
duct,  blood-vessels  and  nerves,  and  it  penetrates  the  substance  of  the  organ 
in  the  form  of  a  vagina,  or  sheath,  investing  the  vessels,  and  branching  with 
them.  This  membrane,  as  it  ramifies  in  the  substance  of  the  liver,  is  called 
the  capsule  of  Glisson.  It  will  be  more  fully  described  in  connection  with 
the  arrangement  and  distribution  of  the  hepatic  vessels. 

The  substance  of  the  liver  is  made  up  of  lobules,  of  an  irregularly  ovoid 
or  rounded  form,  and  about  -fa  of  an  inch  (1  mm.)  in  diameter.  The  space 
Avhich  separates  these  lobules  is  about  one-quarter  of  the  diameter  of  the 
lobule  and  is  occupied  by  the  blood-vessels,  nerves  and  ramifications  of  the 
hepatic  duct.  In  certain  animals,  the  pig  and  the  polar  bear,  the  division  of 
the  hepatic  substance  can  be  readily  made  out  with  the  naked  eye  ;  but  in 
man  and  in  most  of  the  mammalia,  the  lobules  are  not  so  distinct,  although 
their  arrangement  is  essentially  the  same.  The  lobules  are  intimately  con- 


PHYSIOLOGICAL  ANATOMY  OF  THE  LIVER  393 

nected  with  each  other,  and  branches  going  to  a  number  of  different  lobules 
are  given  off  from  the  same  inteiiobular  vessels ;  but  they  are  sufficiently 
distinct  to  represent,  each  one,  the  general  anatomy  of  the  secreting  portion 
of  the  liver. 

At  the  transverse  fissure,  the  portal  vein,  collecting  the  blood  from  the 
abdominal  organs,  and  the  hepatic  artery,  which  is  a  branch  of  the  coeliac 
axis,  penetrate  the  substance  of  the  liver,  with  the  hepatic  duct,  nerves  and 
lymphatics,  all  enveloped  in  the  fibrous  vagina,  or  sheath,  known  as  the  cap- 
sule of  Glisson.  The  portal  vein  is  by  far  the  larger  of  the  two  blood-vessels, 
and  its  caliber  may  be  roughly  estimated  as  eight  to  ten  times  that  of  the 
artery. 

The  vagina,  or  capsule  of  Glisson,  is  composed  of  fibrous  tissue  in  the 
form  of  a  dense  membrane,  closely  adherent  to  the  adjacent  structure  of  the 
liver,  and  enveloping  the  vessels  and  nerves,  to  which  it  is  attached  by  a  loose, 
areolar  tissue.  The  attachment  of  the  blood-vessels  to  the  sheath  is  so  loose 
that  the  branches  of  the  portal  vein  are  collapsed  when  not  filled  with  blood ; 
presenting  a  striking  contrast  to  the  hepatic  veins,  which  are  closely  adher- 
ent to  the  substance  of  the  liver  and  remain  open  when  they  are  cut  across. 
This  sheath  is  prolonged  over  the  vessels  as  they  branch  and  it  follows  them 
in  their  subdivisions.  It  varies  considerably  in  thickness  in  different  animals. 
In  man  and  in  the  mammalia  generally,  it  is  rather  thin,  becoming  more  and 
more  delicate  as  the  vessels  subdivide,  and  it  is  entirely  lost  before  the  ves- 
sels are  distributed  between  the  lobules. 

The  vessels  distributed  in  the  liver  are  the  following : 

The  portal  vein,  the  hepatic  artery  and  the  hepatic  duct,  passing  in  at 
the  transverse  fissure,  to  be  distributed  in  the  lobules.  The  blood-vessels 
are  continuous  in  the  lobules  with  the  radicles  of  the  hepatic  veins.  The 
duct  is  to  be  followed  to  its  branches  of  origin  in  the  lobules. 

The  hepatic  veins ;  vessels  that  originate  in  the  lobules,  and  collect  the 
blood  distributed  in  their  substance  by  branches  of  the  portal  vein  and  of  the 
hepatic  artery. 

Branches  of  the  Portal  Vein,  the  Hepatic  Artery  and  the  Hepatic  Duct. 
—These  vessels  follow  out  the  branches  of  the  capsule  of  Glisson,  become 
smaller  and  smaller,  and  they  finally  pass  directly  between  the  lobules.  In 
their  course,  however,  they  send  off  lateral  branches  to  the  sheath,  forming 
the  so-called  vaginal  plexus.  The  arrangement  of  the  vessels  in  the  sheath  is 
not  in  the  form  of  a  true  anastomosing  plexus,  although  branches  pass  from 
this  so-called  vaginal  plexus  between  the  lobules.  These  vessels  do  not  anas- 
tomose or  communicate  with  each  other  in  the  sheath. 

The  portal  vein  does  not  present  any  important  peculiarity  in  its  course 
from  the  transverse  fissure  to  the  interlobular  spaces.  It  subdivides,  enclosed 
in  its  sheath,  until  its  small  branches  go  directly  between  the  lobules,  and  in 
its  course,  it  sends  branches  to  the  sheath  (vaginal  vessels),  which  afterward 
go  between  the  lobules.  The  hepatic  artery  has  three  sets  of  branches.  As 
soon  as  it  enters  the  sheath  with  the  other  vessels,  it  sends  off  minute 
branches  (vasa  vasorum)  to  the  walls  of  the  portal  vein,  to  the  larger 


394 


USES  OF  THE  LIVER-DUCTLESS  GLANDS. 


FIG.  130. — Lobules  of  the  liver,  interlobular  vessels  and  intralobular  veins 

(Sappey). 
1, 


branches  of  the  artery  itself,  to  the  walls  of  the  hepatic,  veins,  and  a  very  rich 
net-work  of  branches  to  the  hepatic  duct.  In  its  course,  the  hepatic  artery 

also  sends  branches 
to  the  capsule  of 
Glisson  (capsular 
branches),  which, 
with  branches  of 
the  portal  vein, 
go  to  form  the  so- 
called  vaginal  plex- 

'  ^'^"JStffc&BMr ,  us.  From  these  ves- 
sels, a  few  arterial 
branches  are  given 
off,  which  pass  be- 
tween the  lobules. 
The  hepatic  artery 
can  not  be  followed 
beyond  the  inter- 

1,  1,  1,  3,  4,  lobules  ;  2,  2.  2,  2,  intralobular  veins  injected  with  white  ;  5, 5,      InVmluT-  voocolo     Tlio 
5,  5,  5,  interlobular  vessels  filled  with  a  dark  injection.  ji°'    J 

terminal  branches 

of  the  hepatic  artery  are  not  directly  connected  with  the  radicles  of  the 
hepatic  veins,  but  they  empty  into  small  branches  of  the  portal  vein  within 
the  capsule  of  Glisson. 

Interlobular  Vessels. — Branches  of  the  portal  vein,  coming  from  the  ter- 
minal ramifications  of  the  vessel  within  the  capsule  and  from  the  branches 
in  the  walls  of  the  capsule,  are  distributed  between  the  lobules,  constituting 
the  greatest  part  of  the  so-called  interlobular  plexus.  These  are  situated 
between  the  lobules  and  surround  them;  each  vessel,  however,  giving  off 
branches  to  two  or  three  lobules,  and  never  to  one  alone.  They  do  not 
anastomose,  and  consequently  they  are  not  in  the  form  of  a  true  plexus.  The 
diameter  of  these  interlobular  vessels  varies  between  -^TS  an(^  -fihr  °f  an  incn 
(17  and  34  /*.).  In  this  distribution,  the  blood-vessels  are  followed  by  branches 
of  the  duct,  which  are  much  fewer  and  smaller,  measuring  only  ^-gVrr  °f  an 
inch  (10  /u,),  and  some,  even,  have  been  measured  that  are  not  more  than 
J^OQ-  °f  an  inch  (8  p)  in  diameter. 

Lobular  Vessels. — From  the  interlobular  veins,  eight  or  ten  branches  are 
given  off  which  penetrate  the  lobule.  As  the  interlobular  vessels  are  situated 
between  different  lobules,  each  one  sends  branches  into  two  and  sometimes 
three  of  these  lobules ;  so  that,  as  far  as  vascular  supply  is  concerned,  these 
divisions  of  the  liver  are  never  absolutely  distinct. 

After  passing  from  the  interlobular  plexus  into  the  lobules,  the  vessels 
immediately  break  up  into  an  elongated  net-work  of  capillaries,  -j^nr  to  ^Vr 
of  an  inch  (8  to  11  //,)  in  diameter,  which  occupy  the  lobules  with  a  true 
plexus.  These  vessels  are  very  abundant.  The  blood,  having  been  distrib- 
uted in  the  lobules  by  this  lobular  plexus,  is  collected  by  three  or  four  venous 
radicles  into  a  single  central  vessel  situated  in  the  long  axis  of  the  lobule, 


PHYSIOLOGICAL  ANATOMY  OF  THE  LIVER. 


395 


FlG  isi.—  Transverse  section  of  a  single  hepatic  lobule  (Sappey). 


called  the  intralobular  vein.     A  single  lobule,  surrounded  by  an  interlobular 

vessel,  showing  the  lobular  capillary  plexus,  and  the  central  vein  (the  intra- 

lobular vein)  cut  across, 

is  represented  in  Fig.  .  ;  -    sv  /;'  .          ••"";, 

131. 

Intralobular  Veins. 
—The  capillaries  of 
the  lobules  converge 
into  three  or  four  ve- 
nous radicles  (2,  2,  2,  2, 
in  Fig.  131),  which 
empty  into  a  central 
vessel.  This  is  the  in- 
tralobular vein.  If  a 
liver  be  carefully  in- 
jected from  the  he- 
patic veins,  and  if  sec- 
tions be  made  in  van- 

OUS    directions,    it    will    1,  intralobular  vein,  cut  across  ;  2,  2,  2,  2,  afferent  branches  of  the  intra- 
.  lobular  vein  ;  3,  3.  3,  3,  3,  3,  3,  3,  3,  interlobular  branches  of  the  portal 

06    Seen  that  the  intra-  vein,  with  its  capillary  branches,  forming  the  lobular  plexus,  ex- 

tending to  the  radicles  of  the  iutralobular  vein. 

lobular  veins  follow  the 

long  axis  of  the  lobules,  receiving  vessels  in  their  course,  until  they  empty 
into  a  larger  vessel  situated  at  what  may  be  called  the  base  of  the  lobules. 
These  latter  are  the  sublobular  veins.  They  collect  the  blood  in  the  manner 
just  described,  from  all  parts  of  the  liver,  unite  with  others,  becoming  larger 
and  larger,  until  finally  they  form  the  three  hepatic  veins,  which  discharge 
the  blood  from  the  liver  into  the  vena  cava  ascendens. 

The  hepatic  veins  differ  somewhat  in  their  structure  from  other  portions 
of  the  venous  system.  Their  walls  are  thinner  than  those  of  the  portal  veins, 
they  are  not  enclosed  in  a  sheath,  and  they  are  very  closely  adherent  to  the 
hepatic  tissue  It  has  also  been  noted  that  the  hepatic  veins  possess  a  well 
marked  muscular  tunic,  very  thin  in  man,  but  well  developed  in  the  pig,  the 
ox  and  the  horse,  and  composed  of  non-striated  muscular  fibres  interlacing 
with  each  other  in  every  direction. 

In  addition  to  the  blood-vessels  just  described,  the  liver  receives  venous 
blood  from  vessels  which  have  been  called  accessory  portal  veins,  coming 
from  the  gastro-hepatic  omentum,  the  surface  of  the  gall-bladder,  the  dia- 
phragm and  from  the  anterior  abdominal  walls.  These  vessels  penetrate  at 
different  points  on  the  surface  of  the  liver,  and  they  may  serve  as  deriva- 
tives, when  the  circulation  through  the  portal  vein  is  obstructed. 

Structure  of  a  Lobule  of  the  Liver.  —  Each  hepatic  lobule,  bounded  and 
more  or  less  distinctly  separated  from  the  others  by  the  interlobular  vessels, 
contains  blood-vessels,  radicles  of  the  hepatic  ducts  and  the  so-called  hepatic 
cells.  The  arrangement  of  the  blood-vessels  has  just  been  described  ;  but 
in  all  preparations  made  by  artificial  injection,  the  space  occupied  by  the 
blood-vessels  is  exaggerated  by  excessive  distention,  and  the  difficulties  in 


396 


USES  OF  THE  LIVEE— DUCTLESS  GLANDS. 


FIG.  132.— Liver-cells  from  a  human,  fatty  liver 
(Funke). 


the  study  of  the  relations  of  the  ducts  and  the  liver-cells  are  thereby  much 
increased. 

Hepatic  Cells. — If  a  scraping  from  the  cut  surface  of  a  fresh. liver  be  ex- 
amined with  a  moderately  high  magnifying  power,  the  field  of  view  will  be 
found  filled  with  rounded,  ovoid  or  irregularly  polygonal  cells,  measuring 
rsW  ^°  T^OT  °f  an  i110^  (16  to  25  /A)  in  diameter.  In  their  natural  condition 

they  are  more  frequently  ovoid  than 
polygonal ;  and  when  they  have  the 
latter  form  the  corners  are  always 
rounded.  These  cells  present  one  and 
occasionally  two  nuclei,  sometimes  with 
and  sometimes  without  nucleoli.  The 
presence  of  small,  pigmentary  granules 
gives  to  the  cells  a  peculiar  and  char- 
acteristic appearance ;  and  in  addition, 
nearly  all  of  them  contain  a  few  gran- 
ules or  small  globules  of  fat.  Some- 
times the  fatty  and  pigmentary  gran- 
ules are  so  abundant  as  to  obscure  the 
nuclei.  The  addition  of  acetic  acid 
renders  the  cells  pale  and  the  nuclei 
become  more  distinct.  The  cells  also 
contain  more  or  less  glycogen  in  the  form  of  granules  surrounding  the  nu- 
clei. • 

Arrangement  of  the  Bile-ducts  in  the  Lobules. — In  the  substance  of  the 
lobules  is  a  fine  and  regular  net- work  of  vessels  of  nearly  uniform  size,  about 
Io^00  of  an  inch  (2  or  3  p.)  in  diame- 
ter, which  surround  the  liver-cells,  each 
cell  lying  in  a  space  bounded  by  inos- 
culating branches  of  these  canals.  This 
plexus  is  entirely  independent  of  the 
blood-vessels,  and  it  seems  to  enclose 
in  its  meshes  each  individual  cell,  ex- 
tending from  the  periphery  of  the  lob- 
ule to  the  intralobular  vein. 

The  reticulated  bile-ducts  were  dis- 
covered in  the  substance  of  the  lobules, 
near  their  borders,  by  Gerlach,  in  1848. 
It  is  evident,  from  an  examination  of 
his  figures  and  description,  that  he 
succeeded  in  filling  with  injection  that 

portion    Of   the    loblllar    net- Work    near    FIG.  133.—  Portion  of  a  transverse  section  of  an 
a  . !       ill  j-uj  hepatic  lobule  of  the   rabbit ;  magnified  400 

the  borders  of  the  lobules,  and  he  dem-        diameters  (Ksmker). 

onstrated  the  continuity  of  these  ves-  ft-  6> 6'  MpJ|j£§,J!£f  ^ffff if4£ceV'  capiUary 

sels  with  the  interlobular  ducts ;  but  he 

did  not  recognize  the  vessels  nearer  the  centre  of  the  lobule.     It  is  now 


ANATOMY  OF  THE  EXCRETORY  BILIARY  PASSAGES.       397 


known  that  there  are  either  canals  or  interspaces  between  the  liver-cells  in 
the  lobules,  and  that  these  open  into  the  interlobular  hepatic  ducts.  It  is 
still  a  question,  however,  whether  these  passages  be  simple  spaces  between 
the  cells  or  true  vessels  lined  with  a  membrane. 

Anatomy  of  the  Excretory  Biliary  Passages. — Between  the  lobules  the 
ducts  are  very  small,  the  smallest  measuring  about  -^fa  of  an  inch  (8  /*)  in 
diameter.  They  are  composed  of  a  delicate  membrane  lined  with  epithe- 
lium. The  ducts  larger  than  y^Vrr  °^  an  inch  (about  20  /*,)  have  a  fibrous 
coat,  formed  of  inelastic  with  a  few  elastic  elements,  and  in  the  larger  ducts, 
there  are,  in  addition,  a  few  non-striated  muscular  fibres.  The  epithelium 
lining  these  ducts  is  of  the  columnar  variety,  the  cells  gradually  undergoing 
a  transition  from  the  pavement-form  as  the  ducts  increase  in  size.  In  the 
largest  ducts  there  is  a  distinct  mucous  membrane  with  mucous  glands. 

Throughout  the  extent  of  the  biliary  passages,  from  the  interlobular  canals 
to  the  ductus  choledochus,  are  little  utricular  or  racemose  glands,  varying  in 
size  in  different  portions  of  the  liver.  These  are  situated,  at  short  intervals, 
by  the  sides  of  the  canals.  The  glands  connected  with  the  smallest  ducts  are 
simple  follicles,  -$%-$  to  y^  of  an  inch  (31  to  62  /n)  long.  The  larger  glands 
are  formed  of  groups  of  these  follicles,  and  they  measure  -^  or  yfg-  of  an 
inch  (100  or  250  /*)  in  diameter.  The  glands  are  only  found  connected  with 
the  ducts  ramify- 
ing in  the  sub- 
stance of  the  liver, 
and  they  do  not  ex- 
ist in  the  hepatic, 
cystic  and  common 
ducts.  They  are 
composed  of  a  ho- 
mogeneous mem- 
brane, lined  with 
small,  pale  cells  of 
epithelium.  If  the 
ducts  in  the  sub- 
stance of  the  liver 
be  isolated,  they  are 
found  covered  with 

these    little    groups    Fi«-  134.—  Racemose  glands  attached  to  the  biliary  ducts  of  the  pig;  mag- 

of  follicles  and  have 
the  appearance  of 
an  ordinary  race- 
mose gland,  except 
that  the  acini  are 

relatively  small  and  scattered.     This  appearance  is  represented  in  Fig.  134. 
The  excretory  biliary  ducts,  from  the  interlobular  vessels  to  the  point  of 
emergence  of  the  hepatic  duct,  present  frequent  anastomoses  with  each  other 
in  their  course. 
27 


nified  18  diameters  (Sappey). 
branch  of  an  hepatic  duct,  with  the  surface  almost  entirely  covered 
with  racemose  glands  opening  into  its  cavity ;  2,  branch  in  which  the 
glands  are  smaller  and  less  abundant ;  3,  3,  3,  branches  of  the  duct  with 
still  simpler  glands  ;  4,  4,  4,  4,  biliary  ducts  with  simple  follicles  at- 
tached :  5.  5.  5,  5,  the  same,  with  fewer  follicles ;  6.  6,  6,  6,  6,  anasto- 
moses in  arches  ;  7,  7,  7,  angular  anastomoses  ;  8,  8,  8,  8,  anastomoses 
by  transverse  branches. 


398 


USES  OF  THE  LIVER— DUCTLESS  GLANDS. 


Vasa  Aberrantia. — In  the  livers  of  old  persons,  and  occasionally  in  the 
adult,  certain  vessels  are  found  ramifying  on  the  surface  of  the  liver,  but 
always  opening  into  the  biliary  ducts,  which  have  been  called  vasa  aberrantia. 
These  are  never  found  in  the  foetus  or  in  children.  They  are  appendages  of 
the  excretory  system  of  the  liver,  and  are  analogous  in  their  structure  to  the 
ducts,  but  are  apparently  hypertrophied,  with  thickened,  fibrous  walls,  and 
present  in  their  course  irregular  constrictions  not  found  in  the  normal  ducts. 
The  racemose  glands  attached  to  them  are  always  very  much  atrophied. 

Gall-bladder,  Hepatic,  Cystic  and  Common  Ducts. — The  hepatic  duct  is 
formed  by  the  union  of  two  ducts,  one  from  the  right  and  the  other  from 
the  left  lobe  of  the  liver.  It  is  about  an  inch  and  a  half  (38  mm.)  in  length 
and  joins  at  an  acute  angle  with  the  cystic  duct,  to  form  the  ductus  coin- 
munis  choledochus.  The  common  duct  is  about  three  inches  (76  mm.)  in 
length,  of  the  diameter  of  a  goose-quill,  and  it  opens  into  the  descending 
portion  of  the  duodenum.  It  passes  obliquely  through  the  coats  of  the  in- 
testine, and  opens  into  its  cavity,  in  connection  with  the  principal  pancreatic 


20  12   19 


Fin.  135.— Gall-bladder,  hepatic,  cystic  and  common  ducts  (Sappey). 

1,  2,  3.  duodenum  ;  4,  4,  5,  6,  7,  7,  8,  pancreas  and  pancreatic  ducts  ;  9.  10,  11,  12,  13,  liver ;  14,  flall-blrid- 
der ;  15,  hepatic  duct ;  16,  cystic  duct ;  17,  common  duct ;  18,  portal  vein  ;  19,  branch  from  the  cceliac 
axis  :  20.  hepatic  artery  ;  21,  coronary  artery  of  the  stomach  :  22,  cardiac  portion  of  the  stomach  ; 
23,  splenic  artery  ;  24,  spleen  ;  25,  left  kidney  ;  26,  right  kidney  ;  27,  superior  mesenteric  artery  and 
vein  ;  28,  inferior  vena  cava. 

duct.     The  cystic  duct  is  about  an  inch  (25  mm.)  in  length,  and  is  the 
smallest  of  the  three  canals. 

The  structure  of  these  ducts  is  essentially  the  same.  They  have  a  proper 
coat  formed  of  ordinary  fibrous  tissue,  a  few  elastic  fibres  and  non-striated 
muscular  fibres.  The  muscular  tissue  is  not  sufficiently  distinct  to  form  a 
separate  coat.  The  mucous  membrane  is  always  found  tinged  yellow  with 


NERVES  AND  LYMPHATICS  OF  THE  LIVER.  399 

the  bile,  even  in  living  animals.  It  is  marked  by  a  large  number  of  minute 
excavations  and  is  covered  with  cells  of  columnar  epithelium.  This  mem- 
brane contains  a  large  number  of  mucous  glands. 

The  gall-bladder  is  an  ovoid  or  pear-shaped  sac,  about  four  inches  (10 
centimetres)  in  length,  one  inch  (25  mm.)  in  breadth  at  its  widest  portion, 
and  capable  of  holding  an  ounce  to  an  ounce  and  a  half  (30  to  45  c.  c.)  of 
fluid.  Its  f  undus  is  covered  entirely  with  peritoneum,  but  this  membrane 
passes  only  over  the  lower  surface  of  its  body. 

The  proper  coat  of  the  gall-bladder  is  composed  of  ordinary  fibrous  tissue 
with  a  few  elastic  fibres.  In  some  of  the  lower  animals  there  is  a  distinct 
muscular  coat,  but  a  few  scattered  fibres  only  are  found  in  the  human  sub- 
ject. The  mucous  coat  is  of  a  yellowish  color,  with  very  small,  interlacing 
folds  which  are  very  vascular.  The  mucous  membrane  of  the  gall-bladder 
has  a  general  lining  of  columnar  epithelium  with  a  few  goblet-cells.  In  the 
gall-bladder  are  found  small,  racemose  glands,  formed  of  four  to  eight  folli- 
cles lodged  in  the  submucous  structure.  These  are  essentially  the  same  as 
the  glands  opening  into  the  ducts  in  the  substance  of  the  liver,  and  they 
secrete  a  mucus  which  is  mixed  with  the  bile. 

Nerves  and  Lymphatics  of  the  Liver. — The  nerves  of  the  liver  are  derived 
from  the  pneumogastric,  the  phrenic,  and  the  solar  plexus  of  the  sympathetic. 
The  branches  of  the  left  pneumogastric  penetrate  with  the  portal  vein,  while 
the  branches  from  the  right  pneumogastric,  the  phrenic  and  the  sympathetic, 
surround  the  hepatic  artery  and  the  hepatic  duct.  All  of  these  nerves  pene- 
trate at  the  transverse  fissure  and  follow  the  blood-vessels  in  their  distribu- 
tion. They  have  not  been  traced  farther  than  the  final  ramifications  of  the 
capsule  of  Glisson,  and  their  exact  mode  of  termination  is  unknown. 

The  lymphatics  of  the  liver  are  very  abundant.  They  are  divided  into 
two  layers ;  the  superficial  layer,  situated  just  beneath  the  serous  membrane, 
and  the  deep  layer.  The  superficial  lymphatics  from  the  under  surface  of 
the  liver,  and  that  portion  of  the  deep  lymphatics  which  follows  the  hepatic 
veins  out  of  the  liver,  pass  through  the  diaphragm  and  are  connected  with 
the  thoracic  glands.  Some  of  the  lymphatics  from  the  superior,  or  convex 
surface  join  the  deep  vessels  that  emerge  at  the  transverse  fissure  and  pass 
into  glands  below  the  diaphragm,  while  others  pass  into  the  thoracic  cavity. 

The  mode  of  origin  of  the  lymphatics  is  peculiar.  The  superficial  lym- 
phatics are  subperitoneal  and  are  connected  with  spaces  or  canals  in  the 
general  connective  tissue  of  the  liver.  The  deep  lymphatics  are  supposed  to 
originate  by  perivascular  canals  surrounding  the  blood-vessels  of  the  lobules, 
which  are  connected  with  vessels  in  the  walls  of  small  branches  of  the  hepatic 
and  portal  veins,  afterward  surrounding  the  larger  vessels. 

Mechanism  of  the  Secretion  and  Discharge  of  Bile. — In  its  anatomy  the 
liver  differs  greatly  from  other  glandular  organs,  both  secretory  and  excretory. 
The  liver-cells  are  not  enclosed  in  ducts,  but  are  surrounded  by  a  plexus  of 
exceedingly  small  vessels  which  undoubtedly  receive  the  bile  as  it  is  formed. 
The  liver,  also,  is  supplied  with  both  venous  and  arterial  blood,  the  venous 
blood  largely  predominating.  In  addition  it  is  now  recognized  that  the  bile 


400  USES  OF  THE  LIVER-DUCTLESS  GLANDS. 

is  necessary  to  intestinal  digestion,  that  it  contains  excrementitious  matters 
and  that  the  cells  constantly  produce  glycogen.  The  liver  produces  urea, 
which  is  excreted,  however,  chiefly  by  the  kidneys.  It  may  also  effect  certain 
changes  in  digested  and  foreign  matters  that  are  absorbed  from  the  aliment- 
ary canal.  As  regards  its  varied  uses,  therefore,  as  well  as  in  its  anatomy,  it 
has  no  analogue  in  the  glandular  system,  and  the  mechanism  of  its  action  is 
necessarily  complex. 

As  regards  the  secretion  of  bile,  the  only  view  that  is  consistent  with 
actual  knowledge  is  that  this  fluid  is  produced  by  the  liver-cells  and  is  taken 
up  by  the  plexus  of  bile-ducts  which  surrounds  these  cells.  The  little  gland- 
ular organs  that  are  attached  to  the  larger  branches  of  the  duct  secrete  mucus 
which  gives  the  viscidity  observed  in  the  bile  of  some  animals.  The  bile, 
indeed,  is  viscid  in  different  animals  in  proportion  to  the  development  of 
these  mucous  glands  ;  and  in  the  rabbit,  in  which  the  glands  do  not  exist,  the 
bile  has  no  viscidity  (Sappey).  The  passage  of  excrementitious  substances 
from  the  blood  into  the  bile  will  be  discussed  in  connection  with  the  action 
of  the  liver  as  an  organ  of  excretion,  and  the  formation  of  glycogen  will  be 
considered  in  its  proper  place. 

Of  course  the  circulation  of  blood  in  the  liver  is  a  condition  necessary  to 
the  secretion  of  bile.  As  regards  the  question  of  the  production  of  bile  from 
venous  or  arterial  blood,  it  has  been  shown  that  the  materials  out  of  which 
the  bile  is  formed  may  be  supplied  by  either  the  hepatic  artery  or  the  portal 
vein.  Bile  is  secreted  after  the  hepatic  artery  has  been  tied,  and  also  after 
the  portal  vein  has  been  gradually  obliterated,  the  hepatic  artery  being  intact 
(Ore).  Bile  is  produced  in  the  liver  from  the  blood  distributed  in  its  sub- 
stance by  the  portal  vein  and  the  hepatic  artery,  and  not  from  the  blood  of 
either  of  these  vessels  exclusively ;  and  bile  may  continue  to  be  secreted,  if 
either  one  of  these  vessels  be  obliterated,  provided  the  supply  of  blood  be 
sufficient. 

Some  of  the  variations  in  the  discharge  of  bile  have  been  described  in 
connection  with  the  physiology  of  digestion;  but  although  the  bile  is 
poured  out  much  more  abundantly  during  intestinal  digestion  than  at  other 
times,  its  production  and  discharge  are  constant.  The  bile  is  stored  up  in 
the  gall-bladder  to  a  considerable  extent  during  the  intervals  of  digestion. 
If  an  animal  be  killed  at  this  time,  the  gall-bladder  is  always  distended ;  but 
it  is  found  empty,  or  nearly  so,  in  animals  killed  during  digestion. 

The  influence  of  the  nervous  system  on  the  secretion  of  bile  has  been 
very  little  studied,  and  the  question  is  one  of  great  difficulty  and  obscurity. 
The  liver  is  supplied  very  abundantly  with  nerves,  both  cerebro-spinal  and 
sympathetic,  and  some  observations  have  been  made  upon  the  influence  of 
the  nerves  upon  its  glycogenic  action ;  but  with  regard  to  the  secretion  of 
bile,  there  is  little  to  be  said  beyond  what  has  already  been  stated  concerning 
the  influence  of  the  nervous  system  on  other  secretions. 

The  bile  is  discharged  through  the  hepatic  ducts  like  the  secretion  of  any 
other  gland.  During  digestion  the  fluid  accumulated  in  the  gall-bladder 
passes  into  the  ductus  communis,  in  part  by  contractions  of  its  walls,  and  in 


PROPERTIES  AND  COMPOSITION  OF  THE  BILE.  401 

part,  probably,  by  compression  exerted  by  the  distended  and  congested  diges- 
tive organs  adjacent  to  it.  It  seems  that  this  fluid,  which  is  necessarily  pro- 
duced by  the  liver  without  intermission,  separating  from  the  blood  certain 
excrementitious  matters,  is  retained  in  the  gall-bladder  for  use  during  diges- 
tion. 

Quantity  of  Bile. — The  estimates  of  the  daily  quantity  of  bile  in  the 
human  subject  must  be  merely  approximate ;  and  the  ideas  of  physiologists 
on  this  point  are  derived  chiefly  from  experiments  upon  the  inferior  animals. 
The  most  complete  and  reliable  observations  upon  this  subject  are  those  of 
Bidder  and  Schmidt,  which  were  made  upon  animals  with  a  fistula  into  the 
gall-bladder,  the  cluctus  communis  having  been  tied.  These  observers  found 
great  variations  in  the  daily  quantity  in  different  classes  of  animals,  the  quan- 
tity in  the  carnivora  being  the  smallest.  Applying  their  results  to  the  human 
subject,  assuming  that  the  amount  is  about  equal  to  the  quantity  secreted  by 
the  carnivora,  the  daily  secretion  in  a  man  weighing  one  hundred  and  forty 
pounds  (63-5  kilos.)  would  be  about  two  and  a  half  pounds  (1,134  grammes). 

USES  OF  THE  BILE. 

The  uses  of  the  bile  in  digestion  have  already  been  fully  described  ;  but 
before  considering  its  characters  as  an  excretion,  it  will  be  necessary  to  study 
its  general  properties  and  composition. 

Properties  and  Composition  of  the  Bile. — The  secretion  as  it  comes 
directly  from  the  liver  is  somewhat  viscid ;  but  after  it  has  passed  into  the 
gall-bladder,  its  viscidity  is  much  increased  by  a  farther  admixture  of  mucus. 

The  color  of  the  bile  is  very  variable  within  the  limits  of  health.  It  may 
be  of  any  shade  between  a  dark,  yellowish-green  and  a  reddish-brown.  It  is 
semi-transparent,  except  when  the  color  is  very  dark.  In  different  classes  of 
animals  the  variations  in  color  are  very  great.  In  the  pig  it  is  bright-yellow ; 
in  the  dog  it  is  dark-brown ;  and  in  the  ox  it  is  greenish-yellow.  As  a  rule 
the  bile  is  dark-green  in  the  carnivora  and  greenish-yellow  in  the  herbivora. 

The  specific  gravity  of  the  human  bile  is  1020  to  1026.  When  the  bile 
is  perfectly  fresh  it  is  almost  inodorous,  but  it  readily  undergoes  putrefactive 
changes.  It  has  a  disagreeable  and  bitter  taste.  It  is  not  coagulated  by  heat. 
When  mixed  with  water  and  shaken,  it  becomes  frothy,  probably  on  account 
of  the  tenacious  mucus  and  its  saponaceous  constituents. 

It  is  generally  stated  that  the  bile  is  alkaline.  This  is  true  of  the  fluid 
discharged  from  the  hepatic  duct,  although  the  alkalinity  is  not  strongly 
marked ;  but  the  reaction  varies  after  it  has  passed  into  the  gall-bladder. 
Bernard  found  it  sometimes  acid  and  sometimes  alkaline  in  the  gall-bladder, 
in  animals  (dogs  and  rabbits)  killed  under  various  conditions ;  but  many  of 
these  animals  were  suffering  from  the  effects  of  severe  operations.  In  the 
hepatic  ducts  the  reaction  is  always  alkaline ;  and  there  are  no  observations 
on  human  bile  that  show  that  the  fluid  is  not  alkaline  in  all  of  the  biliary 
passages. 

The  epithelium  of  the  biliary  passages  is  strongly  tinged  with  yellow,  even 
in  living  animals.  This  is  due  to  the  facility  with  which  the  coloring  mat- 


4:02  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

ter  of  the  bile  stains  the  animal  tissues.  This  is  very  well  illustrated  in 
icterus,  when  even  a  small  quantity  of  this  coloring  matter  finds  its  way  into 
the  circulation. 

Perfectly  normal  and  fresh  bile,  examined  with  the  microscope,  presents 
a  certain  quantity  of  mucus,  the  characters  of  which  have  already  been  de- 
scribed. There  are  no  formed  anatomical  elements  characteristic  of  this 
fluid.  The  fatty  and  coloring  matters  are  in  solution  and  not  in  the  form  of 
globules  or  granules. 

COMPOSITION    OF   HUMAN    BILE.       (KOBIX.) 

Water 916-00  to  819-00 

Sodium  taurocholate ...  56-50   "   106-00 

Sodium  glycoeholate traces. 

Cholesterine 0-62  to      2-66 

Bilirubin 14-00   "     30-00 

Lecithene 

Palmitine,  oleine  and  traces  of  soaps. 

Choline traces. 

Sodium  chloride 2-77  to      3-50 

Sodium  phosphate 1-60   "       2-50 

Potassium  phosphate 0-75   "       1-50 

Calcium  phosphate  0-50   "       1  -35 

Magnesium  phosphate 0-45   "       0-80 

Salts  of  iron 0-15   "       0-30 

Salts  of  manganese traces    "       0-12 

Silicic  acid 0-03   "       0'06 

Mucine traces. 

Loss. .  3-43  to      1-21 


3-20   "     31-00 

5.  .    .' 


1,000-00     1,000-00 

There  are  no  peculiarities  in  the  composition  of  the  bile,  in  respect  to  its 
inorganic  constituents,  which  demand  more  than  a  passing  mention.  It  con- 
tains no  coagulable  organic  matters  except  mucine,  and  all  of  its  constitu- 
ents are  simply  solids  in  solution.  The  quantity  of  solid  matter  is  very  large, 
and  the  proportion  of  water  is  relatively  small.  Among  the  inorganic  salts, 
sodium  chloride  exists  in  considerable  quantity,  with  a  large  proportion  of 
phosphates.  There  exist,  also,  salts  of  iron  and  of  manganese,  with  a  small 
quantity  of  silicic  acid. 

The  fatty  and  saponaceous  constituents  demand  hardly  any  more  extended 
consideration.  A  small  quantity  of  palmitine  and  oleine  are  held  in  solu- 
tion, partly  by  the  soaps,  but  chiefly  by  the  sodium  taurocholate.  The  fats 
sometimes  exist  in  larger  quantity,  when  they  may  be  discovered  in  the  form  of 
globules.  The  proportion  of  soaps  is  very  small.  Lecithene  (C44H90NP09) 
is  a  neutral,  fatty  substance  extracted  from  the  bile,  and  may  be  decomposed 
into  phosphoric  acid  and  glycerine.  Choline  (C5Ha5N02)  is  an  alkaloid 
found  in  the  bile  in  exceedingly  minute  quantity. 

Biliary  Salts. — In  human  bile  the  characteristic  biliary  salt  is  a  combi- 
nation of  taurocholic  acid  (C26H45NS07)  with  sodium.  A  very  small  quantity 
of  sodium  exists  in  combination  with  glycocholic  acid  (C26H43N06).  These 


COMPOSITION  OF  THE  BILE.  403 

two  salts  were  discovered  in  the  bile  of  the  ox,  by  Strecker,  in  1848.  Sodi- 
um glycocholate  exists  in  quantity  in  ox-gall.  Both  of  these  salts  may  be 
precipitated  from  an  alcoholic  extract  of  bile  by  an  excess  of  ether.  The 
taurocholate  is  precipitated  in  the  form  of  dark,  resinous  drops  which  crys- 
tallize with  difficulty.  The  glycocholate  is  readily  crystallizable.  The  bil- 
iary salts  are  very  soluble  in  water  and  in  alcohol.  Their  reaction  is  neutral. 

There  can  be  no  doubt  that  the  biliary  salts  are  products  of  secretion  and 
are  formed  in  the  substance  of  the  liver.  In  no  instance  have  they  ever 
been  discovered  in  the  blood  in  health ;  and  although  they  present  certain 
points  of  resemblance  with  some  of  the  constituents  of  the  urine,  they  have 
never  been  found  in  the  excreta.  In  experiments  made  by  M  tiller,  Kunde, 
Lehmann  and  Moleschott,  on  frogs,  in  which  the  liver  was  removed  and 
the  animal  survived  several  days — and  in  the  observations  of  Moleschott,  be- 
tween two  and  three  weeks — it  was  found  impossible  to  determine  the  pres- 
ence of  the  biliary  salts  in  the  blood.  There  is  no  reason,  therefore,  for  sup- 
posing that  these  salts  are  products  of  disassimilation.  Once  discharged 
into  the  intestine,  they  undergo  certain  changes  and  can  no  longer  be  recog- 
nized by  the  usual  tests ;  but  experiments  have  shown  that,  changed  or  un- 
changed, they  are  absorbed  with  the  products  of  digestion.  They  are  prob- 
ably concerned  in  the  digestive  action  of  the  bile. 

Cholesterine. — Cholesterine  (Cgell^O)  is  a  normal  constituent  of  various 
of  the  tissues  and  fluids  of  the  body.  Most  authors  state  that  it  is  found  in 
the  bile,  blood,  liver,  nervous  tissue,  crystalline  lens,  meconium  and  faecal 
matter.  It  is  to  be  found  in  all  these  situations,  with  the  exception  of  the 
faeces,  where  it  does  not  exist  normally,  being  transformed  into  stercorine  in 
its  passage  down  the  intestinal  canal. 

In  the  fluids  of  the  body  cholesterine  exists  in  solution ;  but  by  virtue  of 
what  constituents  it  is  held  in  this  condition,  is  a  question  that  is  not  en- 
tirely settled.  It  is  stated  that  the  biliary  salts  have  the  power  of  holding 
cholesterine  in  solution  in  the  bile,  and  that  the  small  quantity  of  fatty  acids 
contained  in  the  blood  holds  it  in  solution  in  that  fluid ;  but  direct  experi- 
ments on  this  point  are  wanting.  In  the  nervous  tissue  and  in  the  crys- 
talline lens,  it  is  united  with  the  other  substances  which  go  to  make  up 
these  parts.  After  it  is  discharged  into  the  intestinal  canal,  when  it  is  not 
changed  into  stercorine  it  is  to  be  found  in  a  crystalline  form,  as  in  the 
meconium,  and  in  the  faeces  of  certain  animals  in  a  state  of  hibernation.  In 
pathological  fluids  and  in  tumors,  it  is  found  in  a  crystalline  form  and  may 
be  detected  by  microscopical  examination. 

Cholesterine  is  usually  described  as  an  alcohol,  having  many  of  the  prop- 
erties of  the  fats,  but  not  that  of  saponification  with  the  alkalies.  It  is  neu- 
tral, inodorous,  crystallizable,  insoluble  in  water,  soluble  in  ether  and  very 
soluble  in  hot  alcohol,  though  sparingly  soluble  in  cold  alcohol.  It  is  in- 
flammable and  burns  with  a  bright  flame.  It  is  not  attacked  by  the  alkalies 
even  after  prolonged  boiling.  When  treated  with  strong  sulphuric  acid  it 
strikes  a  peculiar  red  color. 

Cholesterine  may  easily  and  certainly  be  recognized  under  the  microscope 


404: 


USES  OF  THE  LIVER— DUCTLESS  GLANDS. 


by  the  form  of  its  crystals.  They  are  rectangular  or  rhomboidal,  very  thin 
and  transparent,  of  variable  size,  with  distinct  and  generally  regular  borders, 
and  frequently  arranged  in  layers,  with  the  borders  of  the  lower  strata  show- 
ing through  those  which  are  super- 
imposed. The  plates  of  cholesterine 
are  often  marked  by  a  cleavage  at 
one  corner,  the  lines  running  par- 
allel to  the  borders.  Frequently  the 
plates  are  rectangular,  and  some- 
times they  are  almost  lozenge-shaped. 
Crystals  of  cholesterine  melt  at  293° 
Fahr.  (145°  C.),  but  they  are  formed 
again  when  the  temperature  falls  be- 
low that  point. 

The  proportion  of  cholesterine  in 
the  bile  is  not  very  large.  In  the 
table,  it  is  estimated  at  0-62  to  2*66 

FIG.  m.-Cholesterine  extracted  from  the  bile.         partg  per  thousand<      In  a  single  ex_ 

amination  of  the  human  bile,  the  proportion  was  0-618  of  a  part  per  thou- 
sand (Flint). 

The  origin  and  destination  of  cholesterine  involve  an  office  of  the  liver 
which  has  not  been  generally  recognized  by  physiologists ;  and  these  questions 
will  be  considered  specially,  under  the  head  of  the  excretory  action  of  the 
liver. 

BiliruUn. — The  coloring  matter  of  the  bile,  bilirubin  (Cagl^T^C),;), 
bears  a  certain  resemblance  to  the  coloring  matter  of  the  blood  and  is  sup- 
posed to  be  formed  from  it  in  the  liver.  It  gives  to  the  bile  its  peculiar  tint 
and  has  the  property  of  coloring  the  tissues  with  which  it  comes  in  contact. 
Whenever  the  flow  of  bile  is  obstructed  for  any  considerable  time,  the  color- 
ing matter  is  absorbed  by  the  blood  and  can  be  readily  detected  in  the  serum 
and  in  the  urine.  It  also  colors  the  skin  and  the  conjunctiva.  It  is  soluble 
in  chloroform,  by  which  it  is  distinguished  from  biliverdine,  and  forms  sol- 
uble combinations  with  alkalies,  in  which  form  it  is  thought  to  exist  in  the 
bile.  It  probably  is  formed  in  the  liver  from  the  haemoglobine  of  the  red 
blood-corpuscles.  When  exposed  to  the  air  or  to  the  influence  of  certain  ox- 
idizing agents,  it  assumes  a  greenish  color  and  is  changed  into  biliverdine. 
It  is  unnecessary  to  follow  the  various  other  changes  produced  by  spontane- 
ous decomposition  or  by  the  action  of  reagents. 

Tests  for  Bile. — A  simple  test  for  bile-pigment  is  the  following  :  A  thin 
stratum  of  the  liquid  to  be  tested  is  placed  upon  a  white  surface,  as  a  porce- 
lain plate,  and  to  this  is  added  a  drop  of  nitroso-nitric  acid.  If  the  coloring 
matter  of  the  bile  be  present,  a  play  of  colors  will  be  observed  surrounding 
the  drop  of  acid.  The  color  will  rapidly  change  from  green  to  blue,  red, 
orange,  purple  and  finally  to  yellow.  This  test  is  applicable  only  to  the  col- 
oring matter  and  does  not  detect  the  biliary  salts. 

A  very  delicate  test  for  the  biliary  salts  in  a  clear  solution  not  contain- 


EXCRETORY  ACTION  OF  THE  LIVER.  405 

ing  albumen  is  what  is  known  as  Pettenkofer's  test :  To  the  suspected 
liquid  are  added  a  few  drops  of  a  strong  solution  of  cane-sugar.  Sulphuric 
acid  is  then  slowly  added,  to  the  extent  of  about  two-thirds  of  the  bulk  of  the 
liquid.  It  is  recommended  to  add  the  acid  slowly,  so  that  the  temperature 
shall  be  but  little  raised.  If  a  large  quantity  of  the  biliary  salts  be  present, 
a  red  color  shows  itself  almost  immediately  at  the  bottom  of  the  test-tube, 
and  this  soon  extends  through  the  entire  liquid,  rapidly  deepening  until  it 
becomes  dark  lake  or  purple.  If  the  biliary  matters  exist  in  very  small  pro- 
portion, it  may  be  several  minutes  before  a  red  color  makes  its  appearance, 
and  the  change  to  a  purple  is  correspondingly  slow,  the  whole  process  occu- 
pying fifteen  to  twenty  minutes. 

EXCKETOKY   ACTION    OF   THE   LlVER. 

Although  the  liver  produces  a  greater  or  less  quantity  of  urea,  this  sub- 
stance is  discharged  from  the  body  chiefly  in  the  urine  and  mere  traces  exist 
in  the  bile.  The  excretory  action  of  the  liver  will  be  considered,  in  this  con- 
nection, with  reference  to  the  bile  itself.  At  the  present  day  it  is  generally 
admitted  that  the  bile  is  an  excretion  as  well  as  a  secretion. ;  and  this  ques- 
tion has  been  fully  discussed  in  connection  with  the  physiology  of  digestion. 
The  confusion  that  has  arisen  with  regard  to  this  point  has  been  due  to  the 
fact  that  those  who  adopted  the  view  that  the  bile  was  simply  an  excretion 
denied  to  it  any  digestive  properties ;  while  on  the  other  hand,  those  who 
believed  it  to  be  concerned  in  digestion  would  not  admit  that  it  was  an  excre- 
tion. It  will  be  useful,  as  'bearing  upon  the  probable  office  of  the  bile  as  an 
excretion,  to  apply  to  this  fluid  the  general  law  of  the  distinctions  between 
secretions  and  excretions. 

Cells  of  glandular  epithelium  are  constantly  forming,  out  of  materials 
furnished  by  the  blood,  the  characteristic  constituents  of  the  true  secre- 
ions ;  but  these  do  not  pre-exist  in  the  blood,  they  appear  first  in  the  secret- 
ting  organ,  and  they  never  accumulate  in  the  system  when  the  action  of  the 
secreting  organ  is  disturbed.  Again,  the  true  secretions  are  not  discharged 
from  the  body,  but  they  have  an  office  to  perform  in  the  economy,  and  are 
poured  out  by  the  glands  intermittently,  at  the  times  when  this  office  is  called 
into  action.  As  far  as  the  biliary  salts,  sodium  taurocholate  and  sodium 
glycocholate,  are  concerned,  the  bile  corresponds  entirely  to  the  true  secre- 
tions. These  salts  are  formed  in  the  liver,  they  do  not  pre-exist  in  the  blood, 
and  they  do  not  accumulate  in  the  blood  when  their  formation  in  the  liver  is 
disturbed.  The  researches  of  Bidder  and  Schmidt  and  others  have  shown 
that  although  the  biliary  salts  can  not  be  detected  in  the  blood  or  chyle 
coming  from  the  intestine,  they  are  not  discharged  in  the  faeces.  These  facts 
point  to  an  important  office  of  the  bile  as  a  secretion.  It  is  true  that  the 
bile  is  discharged  constantly,  but  during  digestion  its  flow  is  very  much  more 
abundant  than  at  any  other  time.  It  is  pretty  well  established  that  during 
the  intervals  of  the  flow  of  the  secretions,  the  glands  are  forming  the  materi- 
als of  secretion,  which  are  washed  out,  as  it  were,  in  the  great  afflux  of  blood 
which  takes  place  during  what  has  been  called  the  activity  of  the  gland. 


406  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

The  constant  and  invariable  presence  of  cholesterine  in  the  bile  assimi- 
lates it  in  every  regard  to  the  excretions,  of  which  the  urine  may  be  taken  as 
the  type.  Cholesterine  always  exists  in  the  blood  and  in  certain  of  the  tissues 
of  the  body.  It  is  not  produced  in  the  substance  of  the  liver,  but  is  merely 
separated  from  the  blood  by  this  organ.  It  is  constantly  passed  into  the 
intestine,  and  is  discharged,  although  in  a  modified  form,  in  the  faeces. 
Physiologists  know  of  no  office  which  it  has  to  perform  in  the  economy,  any 
more  than  urea  or  any  other  of  the  excrementitious  constituents  of  the  .urine. 
It  accumulates  in  the  blood  in  certain  cases  of  organic  disease  of  the  liver 
and  gives  rise  to  symptoms  of  blood-poisoning. 

Origin  of  Cholesterine. — Cholesterine  exists  in  largest  quantity  in  the  sub- 
stance of  the  brain  and  nerves.  It  is  also  found  in  the  substance  of  the  liver 
— probably  in  the  bile  contained  in  this  organ — the  crystalline  lens  and  the 
spleen ;  but  with  these  exceptions,  it  is  found  only  in  the  nervous  tissue  and 
blood.  It  is  either  deposited  in  the  nervous  matter  from  the  blood  or  it  is 
formed  in  the  brain  and  taken  up  by  the  blood.  This  is  a  question,  however, 
which  can  be  settled  experimentally. 

In  a  series  of  experiments  made  in  1862,  it  was  invariably  found  that  the 
proportion  of  cholesterine  in  the  blood  of  the  internal  jugular  vein  and  the 
femoral  vein  was  greater  than  in  the  arterial  blood.  In  experiments  made 
on  dogs  not  etherized,  the  blood  of  the  jugular  vein  contained,  in  one  in- 
stance 23*3  and  in  another  59-8  per  cent,  more  cholesterine  than  the  arterial 
blood  of  the  same  animals.  The  blood  of  the  femoral  vein  contained  about 
6-3  per  cent,  more  cholesterine  than  arterial  blood.  In  three  cases  of  hemi- 
plegia,  cholesterine  was  found  in  normal  quantity  in  blood  taken  from  the 
arm  of  the  sound  side,  while  blood  from  the  paralyzed  side  contained  no 
cholesterine  (Flint). 

These  observations  point  to  the  production  of  cholesterine  in  the  tissues ; 
and  the  fact  of  its  existence,  under  normal  conditions,  in  the  nervous  tissue 
renders  it  probable  that  the  chief  seat  of  its  production  is  the  substance  of 
the  nerve-centres  and  nerves.  The  question  of  its  formation  in  the  spleen  is 
one  that  has  not  been  investigated. 

In  another  series  of  experiments,  it  was  shown  that  the  blood  lost  cho- 
lesterine in  passing  through  the  liver.  In  one  observation  it  was  found  that 
the  arterial  blood  lost  a  little  more  than  23  per  cent,  and  the  portal  blood, 
about  4£  per  cent.,  in  passing  through  the  liver  (Flint). 

The  portal  blood,  as  it  goes  into  the  liver,  contains  but  a  small  percent- 
age of  cholesterine  over  the  blood  of  the  hepatic  vein,  while  the  percentage 
in  the  arterial  blood  is  large.  The  arterial  blood  is  the  mixed  blood  of  the 
entire  system ;  and  as  it  probably  passes  through  no  organ  which  diminishes 
its  cholesterine  before  it  goes  to  the  liver,  it  contains  a  quantity  of  this  sub- 
stance which  must  be  removed.  The  portal  blood,  coming  from  a  limited 
part  of  the  system,  contains  less  cholesterine,  although  it  gives  up  a  certain 
quantity.  In  the  circulation  in  the  liver,  the  portal  system  largely  predomi- 
nates and  is  necessary  to  other  important  actions  of  this  organ,  such  as  the 
production  of  glycogen ;  but  soon  after  the  portal  vein  enters  the  liver,  its 


EXCRETORY  ACTION  OF  THE  LIVER.  407 

blood  becomes  mixed  with  that  from  the  hepatic  artery,  and  from  this  mixt- 
ure the  cholesterine  is  separated.  It  is  necessary  only  that  blood,  contain- 
ing a  certain  quantity  of  cholesterine,  should  come  in  contact  with  the  bile- 
secreting  cells,  in  order  that  this  substance  shall  be  separated.  The  fact  that 
it  is  eliminated  by  the  liver  is  proved  with  much  less  difficulty  than  that  it 
is  formed  in  the  nervous  system.  In  fact,  its  presence  in  the  bile,  and  the 
necessity  of  its  constant  removal  from  the  blood,  consequent  on  its  constant 
formation  and  absorption  by  this  fluid,  are  almost  sufficient  in  themselves 
to  warrant  the  conclusion  that  it  is  eliminated  by  the  liver. 

In  treating  of  the  composition  of  the  faeces,  the  changes  which  the  choles- 
terine of  the  bile  undergoes  in  its  passages  down  the  intestinal  canal  have 
been  so  fully  considered  that  it  is  not  necessary  to  refer  to  this  portion  of 
the  subject  again.  But  one  examination  only  was  made  of  the  quantity  of 
stercorine  contained  in  the  daily  faecal  evacuation ;  and  assuming  that 
the  quantity  of  cholesterine  excreted  by  the  liver  is  equal  to  the  stercorine 
found  in  the  evacuations,  the  quantity  in  twenty-four  hours  is  about  ten  and 
a  half  grains  (0*68  gramme).  This  corresponds  with  the  estimates  of  the 
daily  quantity  of  cholesterine  excreted,  calculated  from  its  proportion  in  the 
bile  and  the  estimated  daily  quantity  of  bile  produced  by  the  liver. 

To  complete  the  chain  of  the  evidence  leading  to  the  conclusion  that 
cholesterine  is  an  excrementitious  product  which  is  formed  in  certain  of  the 
tissues  and  eliminated  by  the  liver,  it  is  necessary  only  to  show  that  it  may 
accumulate  in  the  blood  when  the  eliminating  action  of  the  liver  is  inter- 
rupted. 

In  a  case  of  simple  jaundice  from  duodenitis,  in  which  there  was  no 
great  disturbance  of  the  system,  a  specimen  of  blood  taken  from  the  arm 
presented  undoubted  evidences  of  the  coloring  matter  of  the  bile,  but  the 
proportion  of  cholesterine  was  not  increased,  being  only  0-508  of  a  part  per 
thousand.  The  faeces  contained  a  large  proportion  of  saponfiable  fat,  but  no 
cholesterine  or  stercorine. 

In  a  case  of  cirrhosis  with  jaundice,  there  was  ascites,  with  great  general 
prostration.  This  patient  died  a  few  days  after  the  blood  and  faeces  had 
been  examined,  and  the  liver  was  found  in  a  condition  of  cirrhosis,  with  the 
liver-cells  shrunken  and  the  gall-bladder  contracted.  In  this  case  the  blood 
contained  1'85  of  a  part  of  cholesterine  per  thousand,  more  than  double  the 
largest  quantity  found  in  health.  The  faeces  contained  a  small  quantity  of 
stercorine. 

Inasmuch  as  cases  frequently  present  themselves  in  which  there  are  evi- 
dences of  cirrhosis  of  the  liver  with  little  if  any  constitutional  disturbance, 
while  others  are  attended  with  grave  nervous  symptoms,  it  seemed  an  inter- 
esting question  to  determine  whether  it  be  possible  for  cholesterine  to  accu- 
mulate in  the  blood  without  the  ordinary  evidence  of  jaundice.  An  oppor- 
tunity occurred  of  examining  the  blood  in  two  strongly  contrasted  cases  of 
cirrhosis,  in  neither  of  which  was  there  jaundice.  One  of  these  patients  had 
been  tapped  repeatedly — about  thirty  times — but  the  ascites  was  the  only 
troublesome  symptom  and  the  general  health  was  little  impaired.  In  this 


408  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

case  the  proportion  of  cholesterine  in  the  blood  was  only  0-246  of  a  part  per 
thousand,  considerably  below  the  quantity  ordinarily  found  in  health.  The 
other  patient  had  cirrhosis,  but  he  was  confined  to  the  bed  and  was  very  feeble. 
The  proportion  of  cholesterine  in  the  blood  in  this  case  was  0-922  of  a  part  per 
thousand,  a  little  above  the  largest  proportion  found  in  health.  A  few  other 
pathological  observations  of  this  kind  are  on  record.  Picot,  in  1872,  re- 
ported a  fatal  case  of  "  grave  jaundice,"  in  which  he  determined  a  great  in- 
crease in  the  quantity  of  cholesterine  in  the  blood,  the  proportion  being 
1-804  per  1000. 

It  is  probable  that  organic  disease  of  the  liver,  accompanied  with  grave 
symptoms  generally  affecting  the  nervous  system,  does  not  differ  in  its  pathol- 
ogy from  cases  of  simple  jaundice  in  the  fact  of  retention  of  the  biliary  salts 
in  the  blood ;  but  these  grave  symptoms,  it  is  more  than  probable,  are  due  to 
a  deficiency  in  the  elimination  of  cholesterine  and  its  consequent  accumula- 
tion in  the  system.  Like  the  accumulation  of  urea  in  structural  disease  of 
the  kidney,  this  produces  blood-poisoning ;  and  this  condition  may  be  char- 
acterized by  the  name  Cholesteraemia,  a  term  expressing  a  pathological  con- 
dition, but  at  the  same  time  indicating  the  physiological  relations  of  choles- 
terine. 

Koloman  Miiller,  in  1873,  succeeded  in  injecting  cholesterine  into  the 
blood-vessels  without  producing  any  effects  due  to  mechanical  obstruction  of 
the  circulation.  He  made  a  preparation  by  rubbing  cholesterine  with  glyc- 
erine and  mixing  the  mass  with  soap  and  water.  He  injected  into  the  veins  of 
dogs,  2-16  fluidounces  (about  64  c.  c.)  of  this  solution,  containing  about 
69  grains  (4-5  grammes)  of  cholesterine.  In  five  experiments  of  this  kind,  he 
produced  a  complete  representation  of  the  phenomena  of  "  grave  jaundice." 

In  view  of  all  these  facts,  an  excretory  action  of  the  liver,  involving  the 
separation  of  cholesterine  from  the  blood  and  its  discharge  in  the  fasces  in 
the  form  of  stercorine,  must  be  regarded  as  established,  as  well  as  the  exist- 
ence of  cholesteraemia  as  a  definite  pathological  condition. 

FORMATION  OF  GLYCOGEN  IN  THE  LIVER. 

In  addition  to  the  uses  of  the  liver  already  described,  this  organ  con- 
stantly produces  in  health  a  substance  resembling  starch,  called  glycogen, 
which  is  converted  into  glucose  and  is  carried  into  the  circulation  by  the 
hepatic  veins.  In  this  way  the  liver  acts  as  a  ductless  gland,  glycogen  being 
formed  by  the  liver-cells  in  precisely  the  manner  that  the  various  constitu- 
ents of  the  secretions  are  produced  by  other  glands.  The  discovery  of  this, 
which  was  first  called  the  sugar-producing  office  of  the  liver,  was  made  by 
Bernard,  in  1848.  During  the  present  century  there  have  been  few  dis- 
coveries which  have  attracted  so  much  attention,  and  Bernard's  experiments 
have  been  repeated  and  extended  by  physiologists  in  different  parts  of  the 
world.  In  1857,  Bernard  discovered  glycogen  in  the  liver  and  showed  that 
the  production  of  this  substance  precedes  the  formation  of  sugar.  In  study- 
ing, then,  the  mechanism  of  sugar-production  in  animals,  it  will  be  necessary 
to  begin  with  the  physiological  history  of  glycogen. 


FORMATION  OF  GLYCOGEN  IN  THE  LIVER.  409 

Glycogen  (C6H1005)  belongs  to  the  class  of  carbohydrates  and  is  iso- 
meric  with  starch.  It  is  readily  converted  into  glucose  (C6Hi806).  In  nearly 
all  regards  it  has  the  properties  of  starch,  but  it  gives  a  deep  red  color  with 
iodine  instead  of  a  blue.  In  the  liver-cells  it  exists  in  the  form  of  amor- 
phous granules  surrounding  the  nuclei.  It  may  be  extracted  from  a  decoc- 
tion of  the  liver-substance,  by  precipitating  the  albuminoids  by  adding  alter- 
nately dilute  hydrochloric  acid  and  potassio-mercuric  iodide,  filtering  and 
treating  the  filtrate  with  an  excess  of  alcohol.  The  alcoholic  precipitate, 
washed  with  alcohol  and  dried  rapidly,  is  in  the  form  of  a  white  powder, 
which  will  keep  indefinitely.  In  the  adult,  glycogen  is  most  abundant  in 
the  liver ;  but  it  has  been  found  in  small  quantity  in  the  muscular  substance, 
in  cartilage  and  in  certain  cells  in  process  of  development.  In  the  early 
months  of  foetal  life  it  exists  in  nearly  all  the  tissues.  It  is  found,  also,  in 
cells  attached  to  the  villi  of  the  placenta. 

The  most  important  of  the  conditions  which  influence  the  quantity  of 
glycogen  in  the  liver  relate  to  alimentation  and  digestion.  The  liver  always 
contains  more  glycogen  during  digestion  than  in  fasting  animals.  After  a 
few  days  of  starvation,  glycogen  may  almost  or  quite  disappear  from  the 
liver.  This  also  occurs  in  animals  fed  for  a  time  exclusively  with  fats,  and 
the  quantity  is  diminished  by  a  purely  albuminous  diet  as  contrasted  with  a 
mixed  diet.  Still,  as  was  shown  by  Bernard,  glycogen  is  invariably  present 
in  the  livers  of  healthy  carnivorous  animals  that  have  always  been  fed  with 
meat  alone. 

A  very  great  increase  in  the  quantity  of  glycogen  in  the  liver  is  produced 
by  feeding  animals  largely  with  carbohydrates.  Not  only  are  the  starches 
apparently  stored  up  for  a  time  in  the  form  of  glycogen  in  the  liver,  but 
sugars  seem  to  undergo  a  change  into  glycogen  which  accumulates  in  the 
liver.  This  is  to  be  expected,  as  the  starches  are  changed  into  sugar  before 
they  are  absorbed,  and  all  the  carbohydrates  behave  in  the  same  way  as 
regards  general  nutrition.  Very  abundant  alimentation  with  carbohydrates 
sometimes  produces  a  temporary  diabetes,  the  quantity  of  sugar  in  the  blood 
increasing  to  such  an  extent  that  sugar  is  discharged  in  the  urine.  This  is 
due  either  to  the  passage  of  a  certain  quantity  of  sugar  unchanged  through 
the  liver  or  to  an  excessive  formation  of  glycogen,  which  is  more  actively 
changed  into  sugar  than  under  normal  conditions. 

As  far  as  regards  the  influence  of  alimentation  upon  the  formation  of 
glycogen,  it  seems  probable  that  in  the  herbivora  and  in  man  the  chief  source^ 
of  hepatic  glycogen  is  the  class  of  alimentary  substances  called  carbohydrates ; 
but  the  fact  that  glycogen  exists  in  the  livers  of  the  carnivora,  and  probably 
in  man,  under  a  nitrogenized  diet,  shows  that  the  liver  is  capable  of  forming 
glycogen  from  the  albuminoids. 

Change  of  Glycogen  into  Sugar. — It  is  almost  certain  that  the  liver  does 
not  contain  sugar  during  life.  Many  years  ago  (1858)  this  fact  was  recog- 
nized by  Pavy,  and  it  has  since  been  confirmed  by  other  physiologists.  Pavy, 
however,  assumed  that  there  was  no  such  thing  as  sugar-formation  by  the 
liver,  under  absolutely  normal  conditions.  He  regarded  the  sugar  found  in 


410  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

the  substance  of  the  liver  and  in  the  blood  of  the  hepatic  veins  as  due  to  post- 
mortem action,  and  his  observations  seemed  to  be  directly  opposed  to  those 
of  Bernard.  The  views  of  these  two  observers  and  their  followers  seemed  to 
be  harmonized  by  a  series  of  experiments  made  in  1868.  If  the  abdomen  of 
a  dog,  perfectly  quiet  and  not  under  the  influence  of  an  anaesthetic,  be  opened, 
and  a  portion  of  the  liver  be  excised,  rinsed  in  cold  water  and  rapidly  cut  up 
into  boiling  water,  the  extract  will  show  no  reaction  with  Fehling's  test  for 
sugar.  In  one  experiment,  in  which  twenty-eight  seconds  elapsed  between 
the  time  of  opening  the  abdomen  and  the  action  of  the  boiling  water,  the 
reaction  with  Fehling's  test  was  doubtful.  In  an  experiment  in  which  the 
time  was  only  ten  seconds,  there  was  no  trace  of  sugar  in  the  extract  from 
the  liver  (Flint).  l)alton,  however,  in  1871,  found  small  quantities  of  sugar 
in  extracts  of  portions  of  liver  taken  from  an  animal  in  an  average  time  of 
6£  seconds ;  but  it  is  possible  that  the  sugar  may  have  been  in  blood  retained 
in  the  liver.  All  observers,  however,  are  now  agreed  that  sugar  is  formed  in 
the  liver  very  rapidly  after  death. 

If  the  view  be  correct,  that  the  glycogen  of  the  liver  is  being  constantly 
transformed  into  sugar  during  life,  and  that  this  sugar  is  carried  away 
in  the  blood-current,  as  fast  as  it  is  formed,  sugar  would  not  necessarily  be 
contained  in  the  liver  under  normal  conditions ;  and  there  is  no  actual  antag- 
onism between  the  results  obtained  by  Bernard  and  the  fact  that  sugar  itself 
is  not  a  normal  constituent  of  the  liver,  as  is  asserted  by  Pavy,  McDonnell, 
Meissner,  Eitter  and  others. 

If  the  liver  be  washed  by  a  stream  of  water  passed  through  its  vessels 
until  it  is  free  from  sugar,  and  if  it  be  kept  at  the  temperature  of  the  body 
for  a  few  hours,  sugar  will  appear  in  abundance  (Bernard,  1855).  This  is 
due  to  a  conversion  of  the  glycogen  of  the  liver  into  sugar  by  a  ferment,  which 
has  been  extracted  and  isolated  by  Bernard  and  others  by  a  process  analogous 
to  that  by  which  similar  ferments  have  been  extracted  from  the  saliva  and 
the  pancreatic  juice.  This  ferment  probably  exists  originally  in  the  liver 
and  does  not  appear  first  in  the  blood. 

The  question  of  the  transformation  of  glycogen  into  sugar  during  life 
depends  upon  the  comparative  quantities  of  sugar  in  the  blood  going  to  and 
coming  from  the  liver.  Bernard  always  found  sugar  in  quantity  in  the  blood 
of  the  hepatic  veins  taken  immediately  after  death,  and  it  exists  in  blood 
drawn  during  life  by  a  catheter  introduced  into  the  right  cavities  of  the 
heart ;  while  in  the  carnivora,  under  a  purely  animal  diet,  no  sugar  is  con- 
tained in  the  blood  of  the  portal  system.  The  normal  blood  contains,  per- 
haps, a  small  quantity  of  sugar — 0*5  to  1  part  per  1,000 — but  the  proportion 
is  always  greater  in  the  blood  of  the  hepatic  veins. 

The  characters  of  animal  sugar  do  not  materially  differ  from  those  of  glu- 
cose, except  that  it  ferments  more  readily  and  is  destroyed  in  the  system 
with  great  facility.  This  property  of  the  sugar  which  results  from  the  gly- 
cogen formed  in  the  liver  is  probably  of  great  importance.  The  sugar  which 
results  from  digestion  is  all  carried  to  the  liver.  Here  it  is  changed  into 
glycogen ;  and  it  is  probable  that  without  this  change  into  glycogen  and  its 


FORMATION  OF  GLYCOGEN  IN  THE  LIVER.  411 

subsequent  transformation  into  what  is  called  liver-sugar,  it  is  not  perfectly 
adapted  to  the  purposes  of  nutrition.  In  many  cases  of  diabetes,  a  possible 
explanation  of  the  glycosuria  is  that  the  carbohydrates  pass  unchanged  into 
the  vena  cava  and  do  not  undergo  the  changes  which  take  place  normally 
in  the  liver,  at  the  same  time  being  received  into  the  general  circulation  sud- 
denly and  in  large  quantity,  instead  of  gradually,  as  when  they  are  changed 
into  glycogen  and  afterward  into  liver-sugar.  When  an  excess  of  sugar  finds 
its  way  into  the  blood,  it  is  probable  that  the  liver,  under  normal  conditions, 
retains  it  for  a  time  in  the  form  of  glycogen. 

The  sugar  which  is  discharged  into  the  venous  system  by  the  hepatic 
veins  is  usually  lost  in  the  passage  of  the  blood  through  the  lungs.  The  ques- 
tion of  the  final  destination  of  sugar  will  be  taken  up  again  in  connection 
with  the  physiology  of  nutrition. 

Conditions  ivhich  influence  the  Quantity  of  Sugart  in  the  Blood. — It  is 
probable  that  disturbances  of  the  circulation  in  the  liver  are  the  most  impor- 
tant conditions  influencing  the  discharge  of  sugar  by  the 
hepatic  veins,  and  these  operate  mainly  through  the  nervous 
system. 

The  most  remarkable  experiment  upon  the  influence  of/ 
the  nervous  system  on  the  liver  is  the  one  in  which  artificial 
diabetes  is  produced  by  irritation  of  the  floor  of  the  fourth 
ventricle  (Bernard).  This  operation  is  not  difficult.  The 
instrument  used  is  a  delicate  stilet,  with  a  flat,  cutting  ex- 
tremity, and  a  small,  projecting  point  about  ^  of  an  inch 
(1  mm.)  long.  In  performing  the  operation  upon  a  rabbit, 
the  head  of  the  animal  is  firmly  held  in  the  left  hand,  and 
the  skull  is  penetrated  in  the  median  line,  just  behind  the 
superior  occipital  protuberance.  This  can  easily  be  done  by 
a  few  lateral  movements  of  the  instrument.  Once  within 
the  cranium,  the  instrument  is  passed  obliquely  downward 
and  forward,  so  as  to  cross  an  imaginary  line  drawn  be- 
tween the  two  auditory  canals,  until  its  point  reaches  the 
basilar  process  of  the  occipital  bone.  The  point  then  pene- 
trates the  medulla  oblongata,  between  the  roots  of  the  audi- 
tory nerves  and  the  pneumogastrics,  and  by  its  projection 
it  serves  to  protect  the  nervous  centre  from  more  serious 
injury  from  the  cutting  edge.  The  instrument  is  then  care- 
fully withdrawn  and  the  operation  is  completed.  This  ex- 
periment is  almost  painless,  and  it  is  not  desirable  to  ad- 
minister an  anaesthetic,  as  this,  in  itself,  would  disturb  the 
glycogenic  process.  The  urine  may  be  drawn  before  the  op-  FIQ  13?  _  Ingtrw_ 
eration,  by  pressing  the  lower  part  of  the  abdomen,  taking  care  ^thenS^onhe 
not  to  allow  the  bladder  to  pass  up  above  the  point  of  press-  ^rth  ventricle 
ure,  and  it  will  be  found  turbid,  alkaline  and  without  sugar. 
In  one  or  two  hours  after  the  operation,  the  urine  will  have  become  clear  and 
acid,  and  it  will  react  readily  with  any  of  the  copper-tests.  When  this  opera- 


412  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

tion  is  performed  without  injuring  the  adjacent  organs,  the  presence  of  sugar 
in  the  urine  is  temporary,  and  the  next  day  the  secretion  will  have  returned 
to  its  normal  condition.  The  production  of  diabetes  in  this  way,  in  animals, 
is  important  in  its  relations  to  certain  cases  of  the  disease  in  the  human 
subject,  in  which  the  affection  is  traumatic  and  directly  attributable  to  injury 
near  the  medulla.  Its  mechanism  is  difficult  to  explain.  The  irritation  is 
not  propagated  through  the  pneumogastric  nerves,  for  the  experiment  suc- 
ceeds after  both  of  these  nerves  have  been  divided  ;  nevertheless,  the  pneumo- 
gastrics  have  an  important  influence  upon  glycogenesis.  If  both  of  these 
nerves  be  divided  in  the  neck,  in  a  few  hours  or  days,  depending  upon  the 
length  of  time  that  the  animal  survives  the  operation,  no  sugar  is  to  be  found 
in  the  liver,  and  there  is  reason  to  believe  that  the  glycogenic  action  has  been 
arrested.  After  division  of  the  nerves  in  the  neck,  stimulation  of  their  periph- 
eral ends  does  not  affect  the  production  of  sugar ;  but  stimulation  of  the  cen- 
tral ends  produces  an  impression  which  is  conveyed  to  the  nervous  centre,  is 
reflected  to  the  liver  and  gives  rise  to  an  increased  production  of  sugar. 

With  regard  to 
the  influence  of  the 

•^  fi^l HVltu  >.  sympathetic  nerves 

upon  glycogenic 
action,  there  have 
been  few  if  any  ex- 
periments which 
lead  to  conclusions 
of  any  great  value. 
It  has  been  ob- 

1 -^M&sm  Served  that  the  in- 

halation of  anaes- 
thetics and  irrita- 
ting vapors  pro- 
duces  temporary 
diabetes ;  and  this 
has  been  attributed 

FIG.  138. — Section  of  the  head  of  a  rabbit,  showing  the  operation  of  punct-    j._  QT,  i^vif  otirvn  r>r»r> 

uring  the  floor  of  the  fourth  ventricle  (Bernard), 
o,  cerebellum  :  6,  origin  of  the  seventh  pair  of  nerves  ;  c,  spinal  cord  ;  rf,    yeved  bv  the  pneu- 

prigin  of  the  p_neumogastric  ;  e,  opening  of  entrance  of  the  instrument         J  J. 

into  the  cranial  cavity  ;  /,  instrument ;  g,  fifth  pair  of  nerves  ;  h,  audi-    mOffastl'icS    to    the 

tory  canal ;  <',  extremity  of  the  instrument  upon  the  spinal  cord,  after  it 

has  penetrated  the  cerebellum  ;  fc,  occipital  venous  sinus ;  I,  tubercula    nerve-Centre,      and 

quadrigemina  ;  TO,  cerebrum  ;  n,  section  of  the  atlas. 

reflected,  in  the 

form  of  a  stimulus,  to  the  liver.  It  is  for  this  reason  that  the  administration  of 
anaesthetics  should  be  avoided  in  all  accurate  experiments  on  glycogenic  action. 

The  following  summary  expresses  what  is  known  with  regard  to  the  pro- 
duction of  glycogen  by  the  liver  and  its  conversion  into  sugar : 

A  substance  exists  in  the  healthy  liver,  which  is  readily  convertible  into 
sugar;  and  inasmuch  as  this  is  changed  into  sugar  during  life,  the  sugar 
being  washed  away  by  the  blood  passing  through  the  liver,  it  is  proper  to 
call  it  glycogen,  or  sugar-forming  matter. 


PHYSIOLOGICAL  ANATOMY  OF  THE  SPLEEN.  413 

The  liver  has  a  glycogenic  action,  which  consists  in  the  constant  forma- 
tion of  sugar  out  of  the  glycogen,  the  sugar  being  carried  away  by  the  blood 
of  the  hepatic  veins,,  which  always  contains  sugar  in  a  certain  proportion. 
This  production  of  sugar  takes  place  in  the  carnivora,  as  well  as  in  those 
animals  that  take  sugar  and  starch  as  food ;  and  it  is  to  a  certain  extent  in- 
dependent of  the  kind  of  food  taken. 

During  life  the  liver  contains  glycogen  only  and  no  sugar,  because  the 
blood  which  is  constantly  passing  through  this  organ  washes  out  the  sugar  as 
fast  as  it  is  formed ;  but  after  death  or  when  the  circulation  is  interfered 
with,  the  transformation  of  glycogen  into  sugar  continues.  The  sugar  is  not 
removed  under  these  conditions,  and  it  can  then  be  detected  in  the  substance 
of  the  liver. 

The  liver  serves  as  a  receptacle  for  the  carbohydrates,  which,  under  nor- 
mal conditions  of  alimentation  and  nutrition,  are  all  converted  into  glycogen. 
The  glycogen  is  then  converted  into  sugar,  which  is  supplied  to  the  system 
as  the  nutritive  requirements  demand. 

In  addition  to  the  varied  uses  of  the  liver  which  have  been  described,  it  is 
thought  that  this  organ  either  arrests  or  in  some  way  influences  the  condition 
of  certain  foreign  and  poisonous  substances  which  may  be  absorbed  from  the 
alimentary  canal;  but  a  study  of  this  action  does  not  properly  belong  to 
physiology. 

DUCTLESS  GLANDS. 

Certain  organs  in  the  body,  with  a  structure  resembling,  in  some  regards, 
the  true  glands,  but  without  excretory  ducts,  have  long  been  the  subject  of 
physiological  speculation ;  and  the  most  extravagant  notions  concerning  their 
uses  have  prevailed  in  the  early  history  of  physiology.  The  discovery  of  the 
action  of  the  liver,  which  consists  in  modifications  in  the  composition  of  the 
blood  passing  through  its  substance,  has  foreshadowed  the  probable  mode  of 
action  of  the  ductless  glands  ;  for  as  far  as  the  production  of  glycogen  is  con- 
cerned, the  liver  belongs  to  this  class.  Indeed,  the  supposition  that  the 
ductless  glands  effect  certain  changes  in  the  blood  is  now  regarded  by  physi- 
ologists as  the  most  reasonable  of  the  many  theories  that  have  been  entertained 
concerning  their  uses  in  the  economy.  Under  this  idea,  these  organs  have 
been  called  blood-glands  or  vascular  glands.  Under  the  head  of  ductless 
glands,  are  classed  the  spleen,  the  suprarenal  capsules,  the  thyroid  gland,  the 
thymus,  and  sometimes  the  pituitary  body  and  the  pineal  gland. 

PHYSIOLOGICAL  ANATOMY  OF  THE  SPLEEN. 

The  spleen  is  situated  in  the  left  hypochondriac  region,  next  the  cardiac 
extremity  of  the  stomach.  Its  color  is  a  dark  bluish-red  and  its  consistence 
is  rather  soft  and  friable.  It  is  shaped  somewhat  like  the  tongue  of  a  dog, 
presenting  above,  a  rather  thickened  extremity,  which  is  in  relation  with 
the  diaphragm,  and  below,  a  pointed  extremity,  in  relation  with  the  trans- 
verse colon.  Its  external  surface  is  convex.  Its  internal  surface  is  concave, 
presenting  a  vertical  fissure,  the  hilum,  which  gives  passage  to  the  vessels  and 
28 


414  USES  OF  THE  LIVER -DUCTLESS  GLANDS. 

nerves.  It  is  connected  with  the  stomach  by  the  gastro-splenic  omentum  and 
is  still  farther  fixed  by  a  fold  of  peritoneum  passing  to  the  diaphragm.  It  is 
about  five  inches  (127mm.)  in  length,  three  to  four  inches  (75  to  100  mm.)  in 
breadth,  and  a  little  more  than  an  inch  (25*4  mm.)  in  thickness.  Its  weight  is 
six  to  seven  ounces  (170  to  198  grammes).  In  the  adult  it  attains  its  maxi- 
mum of  development,  and  it  diminishes  slightly  in  size  and  weight  in  old  age. 
In  early  life  it  bears  about  the  same  relation  to  the  weight  of  the  body  as  in 
the  adult. 

The  external  coat  of  the  spleen  is  the  peritoneum,  which  is  very  closely  ad- 
herent to  the  subjacent  fibrous  structure.  The  proper  coat  is  dense  and  resist- 
ing, but  in  the  human  subject  it  is  quite  thin  and  somewhat  translucent.  It 
is  composed  of  ordinary  fibrous  tissue  mixed  with  abundant  small  fibres  of 
.elastic  tissue  and  a  few  non-striated  muscular  fibres. 

At  the  hilum  the  fibrous  coat  penetrates  the  substance  of  the  spleen  in 
the  form  of  sheaths  for  the  vessels  and  nerves.  The  number  of  the  sheaths  in 
the  spleen  is  equal  to  the  number  of  arteries  that  penstrate  the  organ.  This 
membrane  is  sometimes  called  the  capsule  of  Malpighi.  The  fibrous  sheaths 
are  closely  adherent  to  the  surrounding  substance  but  they  are  united  to  the 
vessels  by  a  loose,  fibrous  net-work.  They  follow  the  vessels  in  their  ramifi- 
cations to  the  smallest  branches  and  are  lost  in  the  spleen-pulp.  Between 
the  sheath  and  the  outer  coat,  are  bands,  or  trabeculae,  presenting  the  same 
structure  as  the  fibrous  coat.  The  presence  of  elastic  fibres  in  the  trabeculas 
can  be  easily  demonstrated,  and  this  kind  of  tissue  is  very  abundant  in  the  her- 
bivora.  In  the  carnivora  the  muscular  tissue  is  particularly  abundant  and 
can  be  readily  demonstrated ;  but  in  man  this  is  not  so  easy,  and  the  fibres 
are  less  abundant.  These  peculiarities  in  the  fibrous  structure  are  important 
in  their  relations  to  certain  physiological  changes  in  the  size  of  the  spleen. 
Its  contractility  may  be  easily  demonstrated  in  the  dog,  by  the  application  of 
a  Faradic  current  to  the  nerves  as  they  enter  at  the  hilum.  This  is  followed 
by  a  prompt  and  enegetic  contraction  of  the  organ.  Contractions  may  be  pro- 
duced, though  they  are  much  more  feeble,  by  applying  the  current  directly 
to  the  spleen. 

The  substance  of  the  spleen  is  soft  and  friable ;  and  a  portion  of  it,  the 
spleen-pulp,  may  be  easily  pressed  out  with  the  fingers  or  even  washed  away 
by  a  stream  of  water.  Aside  from  the  vessels  and  nerves,  it  presents  for 
study :  1,  an  arrangement  of  fibrous  bands,  or  trabeculae,  by  which  it  is 
divided  into  communicating  spaces ;  2,  closed  vesicles,  called  Malpighian 
bodies,  attached  to  the  walls  of  the  blood-vessels ;  3,  a  soft,  reddish  substance, 
containing  large  numbers  of  cells  and  free  nuclei,  called  the  spleen-pulp. 

Fibrous  Structure  of  the  Spleen  (Trabeculce). — From  the  internal  face  of 
the  investing  membrane  of  the  spleen  and  from  the  fibrous  sheath  of  the  ves- 
sels (capsule  of  Malpighi),  are  bands,  or  trabeculae,  which,  by  their  interlace- 
ment, divide  the  substance  of  the  organ  into  irregularly  shaped,  communi- 
cating cavities.  These  bands  are  -£%  to  ^  of  an  inch  (1  to  1-7  mm.)  broad,  and 
are  composed,  like  the  proper  coat,  of  ordinary  fibrous  tissue  with  elastic 
fibres  and  probably  a  few  non-striated  muscular  fibres.  They  pass  off  from 


PHYSIOLOGICAL  ANATOMY  OF  THE  SPLEEN. 


415 


the  capsule  of  Malpighi  and  the  fibrous  coat  at  right  angles,  very  soon  branch, 
interlace,  and  unite  with  each  other,  becoming  smaller  and  smaller,  until 
they  measure  ^fg-  to  -^  of  an  inch  (0*1  to  0*42  mm.).  This  fibrous  net-work 
serves  as  a  support  for  the  softer  and  more  delicate  parts. 

Malpighian  Bodies. — These  bodies  are  sometimes  called  the.  splenic  cor- 
puscles or  glands.  They  are  rounded  or  slightly  ovoid,  about  -fa  of  an  inch 
(0-5  mm.)  in  diameter,  and  are  filled  with  what  are  thought  to  be  lymph- 
corpuscles,  and  free  nuclei.  The  Malpighian  bodies  have  no  investing  mem- 
brane. With  this  difference,  they  resemble  in  structure  the  solitary  glands 
of  the  intestine.  Both  the  cells  and  the  free  nuclei  of  the  splenic  corpuscles 
bear  a  close  resemblance  to  cells  and  nuclei  found  in  the  spleen-pulp.  The 
corpuscles  are  surrounded  by  blood- 
vessels— which  send  branches  into 
the  interior,  to  form  a  delicate,  capil- 
lary plexus — and  by  what  is  thought 
to  be  a  lymphatic  space  or  sinus. 

The  number  of  the  Malpighian 
corpuscles  in  a  spleen  of  ordinary 
size  has  been  estimated  at  about  ten 
thousand  (Sappey).  They  are  readi- 
ly made  out  in  the  ox  and  sheep 
but  are  frequently  not  to  be  discov- 
ered in  the  human  subject.  The 
occasional  absence  of  these  bodies 
constitutes  another  point  of  resem- 
blance to  the  Solitary  glands  Of  the  Flo.  m.-Malpighian  corpuscle'of  the  spleen  of  the 

small  intestine.  cat  ccadiat). 

A,  artery  around  which  the  corpuscle  is  placed  ;  B, 
The    Malpighian    bodies    are    at-  meshes  of  the  pulp,  injected  ;  c,  the  artery  of  the 

.  .  corpuscle  ramifying  in  the  lymphatic  tissue. 

tached   to  arteries   measuring  -JW  to    The  clear  space  around  the  corpuscle  is  the  lymphat- 

ic  sinus 

^j-  of  an  inch  (O32  to  0-42  mm.)  or 

less  in  diameter  (Sappey).     They  are  often  found  in  the  notch  formed  by 

the  branching  of  an  artery,  but  they  usually  lie  by  the  sides  of  the  vessel. 

Spleen-pulp. — The  spleen-pulp  is  a  dark,  reddish,  semi-fluid  substance,  its 
color  varying  in  intensity  in  different  specimens.  It  is  so  soft  that  it  may  be 
washed  by  a  stream  of  water  from  a  thin  section,  and  it  readily  decomposes, 
becoming  then  nearly  fluid.  It  is  contained  in  the  cavities  bounded  by  the 
fibrous  trabeculae,  and  it  contains  itself  microscopic  bands  of  fibres  arranged 
in  the  same  way.  It  surrounds  the  Malpighian  bodies  and  contains  the  termi- 
nal branches  of  the  blood-vessels,  nerves  and  lymphatics.  Upon  microscopi- 
cal examination,  it  presents  free  nuclei  and  cells  like  those  described  in  the  Mal- 
pighian bodies ;  but  the  nuclei  are  here  relatively  much  more  abundant.  In 
addition  are  found,  red  blood-corpuscles,  some  natural  in  form  and  size  and 
others  more  or  less  altered,  with  pigmentary  granules,  both  free  and  en- 
closed in  cells. 

Blood-vessels,  Nerves  and  Lymphatics  of  the  Spleen. — The  quantity  of  blood 
which  the  spleen  receives  is  very  large  in  proportion  to  the  size  of  the  organ. 


416  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

The  splenic  artery  is  the  largest  branch  of  the  cceliac  axis.  It  is  a  vessel  of  con- 
siderable length  and  is  remarkable  for  its  tortuous  course.  In  an  observation 
by  Sappey,  in  a  man  between  forty  and  fifty  years  of  age,  the  vessel  measured 
about  five  inches  (12  centimetres),  without  taking  account  of  its  deflections; 
and  a  thread  placed  on  the  vessel  so  as  to  follow  exactly  all  its  windings  meas- 
ured a  little  more  than  eight  inches  (21  centimetres).  The  large  caliber  of 
this  vessel  and  its  tortuous  course  are  important  points  in  connection  with 
the  great  variations  in  the  size  of  the  spleen  under  various  conditions  in  health 
and  disease.  The  artery  gives  off  several  branches  to  the  adjacent  viscera  in 
its  course,  and  as  it  passes  to  the  hilum,  it  divides  into  three  or  four  branches, 
which  again  divide  so  as  to  form  six  to  ten  vessels.  These  penetrate  the  sub- 
stance of  the  spleen,  with  the  veins,  nerves  and  lymphatics,  enveloped  in 
fibrous  sheaths.  In  the  substance  of  the  spleen  the  arteries  branch  rather 
peculiarly,  giving  off  many  small  ramifications  in  their  course,  generally  at 
right  angles  to  the  parent  trunk.  These  are  accompanied  by  the  veins  until 
they  are  reduced  to  -fa  or  ^  of  an  inch  (0-32  or  0-42  mm.)  in  diameter.  The 
two  classes  of  vessels  then  separate,  and  the  arteries  have  attached  to  them  the 
corpuscles  of  Malpighi.  It  is  also  a  noticeable  fact  that  the  arteries  passing 
in  at  the  hilum  have  no  inosculations  with  each  other  in  the  substance  of  the 
spleen,  so  that  the  organ  is  divided  up  into  six  to  ten  vascular  compartments. 

The  veins  join  the  small  branches  of  the  arteries  in  the  spleen-pulp  and 
pass  out  of  the  spleen  in  the  same  sheath.  They  anastomose  quite  freely  in 
their  larger  as  well  as  their  smaller  branches.  Their  caliber  is  estimated  as 
about  twice  that  of  the  arteries  (Sappey).  The  estimates  which  have  put 
the  caliber  of  the  veins  at  four  or  five  times  that  of  the  arteries  are  probably 
much  exaggerated.  The  number  of  veins  emerging  from  the  spleen  is  equal 
to  the  number  of  arteries  of  supply. 

By  most  anatomists  two  sets  of  lymphatic  vessels  have  been  recognized, 
the  superficial  and  the  deep.  The  superficial  lymphatics  are  in  the  investing 
membrane  of  the  spleen  and  probably  are  connected  with  the  deep  lym- 
phatics. The  origin  of  the  deep  vessels  is  somewhat  obscure.  Lymphatic 
spaces  or  sinuses  surround  the  Malpighian  bodies,  and  there  is  probably  a 
perivascular  canal-system,  the  exact  origin  of  which  is  unknown.  At  the 
hilum  the  deep  lymphatics  are  joined  by  vessels  from  the  surface.  The  ves- 
sels, numbering  five  or  six,  then  pass  into  small  lymphatic  glands  and  empty 
into  the  thoracic  duct  opposite  the  eleventh  or  twelfth  dorsal  vertebra.  No 
lymphatic  vessels  have  been  observed  going  to  the  spleen. 

The  nerves  of  the  spleen  are  derived  from  the  solar  plexus.  They  follow 
the  vessels  in  their  distribution  and  are  enclosed  with  them  in  the  capsule 
of  Malpighi.  They  are  distributed  ultimately  in  the  spleen-pulp,  but  nothing 
definite  is  known  of  their  mode  of  termination.  When  these  nerves  are 
stimulated,  the  non-striated  muscles  in  the  substance  of  the  spleen  are  thrown 
into  contraction. 

Some  Points  in  the  Chemical  Constitution  of  the  Spleen. — Very  little  has 
been  learned  with  regard  to  the  probable  uses  of  the  spleen  from  analyses  of 
its  substance ;  and  it  would  therefore  be  out  of  place  to  discuss  its  chemical 


VARIATIONS  IN  THE  VOLUME  OF  THE  SPLEEN.  417 

constitution  very  fully.  Cholesterine  has  been  found  to  exist  in  the  spleen 
constantly  and  in  considerable  quantity,  and  the  same  may  be  said  of  uric 
acid.  In  addition,  chemists  have  extracted  from  the  substance  of  the  spleen, 
hypoxanthine,  leucine,  tyrosine,  a  peculiar  crystallizable  substance  called,  by 
Scherer,  lienine,  crystals  of  hsematoidine,  lactic  acid,  acetic  acid,  butyric  acid, 
inosite,  amyloid  matter  and  some  indefinite  fatty  matters. 

Variations  in  the  Volume  of  the  Spleen. — One  of  the  theories  with  regard 
to  the  uses  of  the  spleen,  which  merits  some  consideration,  is  that  it  serves 
as  a  diverticulum  for  the  blood  when  there  is  a  tendency  to  congestion  of  the 
other  abdominal  viscera. 

It  has  been  shown  that  the  spleen  is  greatly  enlarged  in  dogs  four  or  five 
hours  after  feeding,  that  its  enlargement  is  at  its  maximum  at  about  the  fifth 
hour,  and  that  it  gradually  diminishes  to  its  original  size  during  the  succeed- 
ing twelve  hours ;  but  it  is  not  apparent  how  far  these  changes  are  important 
or  essential  to  normal  digestion  and  absorption.  Experiments  have  shown 
that  animals  may  live,  digest,  and  absorb  alimentary  matters  after  the  spleen 
has  been  removed,  and  this  has  been  observed  even  in  the  human  subject. 
In  view  of  these  facts,  it  can  not  be  assumed  that  the  office  of  the  spleen, 
as  a  diverticulum  for  the  blood,  is  essential  to  the  proper  action  of  the  other 
abdominal  organs. 

Changes  in  the  volume  of  the  spleen  may  be  produced  by  operating  on 
the  nervous  system,  chiefly  through  the  vaso-motor  nerves.  Section  of  the 
nerves  at  the  hilum  increases  the  size  of  the  spleen  by  increasing  the  quantity 
of  blood  which  it  receives ;  and  stimulation  of  these  nerves  produces  contrac- 
tion of  the  spleen.  It  is  stated  that  stimulation  of  the  medulla  oblongata 
diminishes  the  size  of  the  spleen,  and  that  the  same  result  can  be  produced 
by  reflex  action,  stimulating  the  central  ends  of  the  pneumogastrics  or  of 
various  sensory  nerves,  provided  that  the  splanchnic  nerves  be  intact.  Start- 
ing from  the  medulla  oblongata,  the  nerve-fibres  which  influence  the  size  of 
the  spleen  pass  down  the  spinal  cord  to  the  lower  dorsal  region,  enter  the 
semilunar  ganglion  by  the  left  splanchnic,  and  are  distributed  to  the  spleen 
through  the  splenic  plexus. 

Extirpation  of  the  Spleen. — There  is  one  experimental  fact  that  has  pre- 
sented itself  in  opposition  to  nearly  every  theory  advanced  with  regard  to 
the  uses  of  the  spleen,  which  is  that  the  organ  may  be  removed  from  a  liv- 
ing animal  and  yet  all  the  processes  of  life  go  on  apparently  as  before.  The 
spleen  is  certainly  not  necessary  to  life,  nor,  as  far  as  is  known,  is  it  essential 
to  any  of  the  important  general  functions.  It  has  been  removed  from  dogs, 
cats,  and  even  from  the  human  subject,  and  its  absence  is  attended  with  no 
constant  and  definite  changes  in  the  phenomena  of  life.  If  it  act  as  a  diver- 
ticulum, this  is  not  essential  to  normal  digestion  and  absorption ;  and  if  its 
office  be  the  destruction  or  the  formation  of  the  blood-corpuscles,  the  forma- 
tion of  leucocytes,  of  uric  acid,  cholesterine  or  of  any  excrementitious  matter, 
there  are  other  organs  which  may  perform  these  acts.  Extirpation  of  the 
spleen  is  an  old  and  a  very  common  experiment.  In  the  works  of  Malpighi, 
published  in  1687,  is  an  account  of  an  experiment  on  a  dog,  in  which  the 


418  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

spleen  was  destroyed  and  the  operation  was  followed  by  no  serious  results. 
Since  then  it  has  been  removed  so  often,  and  the  experiments  have  been  so 
universally  negative  in  their  results,  that  it  is  hardly  necessary  to  cite  authori- 
ties upon  the  subject.  There  are  many  instances,  also,  in  which  it  has  been 
in  part  or  entirely  removed  from  the  human  subject,  which  it  is  unnecessary 
to  refer  to  in  detail.  One  of  the  phenomena  following  extirpation  of  the 
spleen  is  a  modification  of  the  appetite.  Great  voracity  in  animals  after 
removal  of  the  spleen  was  noted  by  the  earlier  observers.  Later  experiment- 
ers have  observed  this  change  in  the  appetite  and  have  noted  that  digestion 
and  assimilation  do  not  appear  to  be  disturbed,  the  animals  becoming  unusu- 
ally fat.  Dalton  has  also  observed  that  the  animals,  particularly  dogs,  some- 
times present  a  remarkable  change  in  their  disposition,  becoming  unnaturally 
ferocious  and  aggressive. 

In  the  following  observation  these  phenomena  were  very  well  marked : 

The  spleen  was  removed  from  a  young  dog  weighing  twenty-two  pounds 
(about  10  kilos.).  Before  the  operation  the  dog  presented  nothing  unusual, 
either  in  his  appetite  or  disposition.  The  wound  healed  rapidly,  and  after 
recovery  had  taken  place,  the  animal  was  fed  moderately  once  a  day.  It  was 
noticed,  however,  that  the  appetite  was  voracious.  The  dog  became  so  irrita- 
ble and  ferocious  that  it  was  dangerous  to  approach  him,  and  it  became  neces- 
sary to  separate  him  from  the  other  animals  in  the  laboratory.  He  would 
eat  refuse  from  the  dissecting-room,  the  flesh  of  dogs,  fasces  etc.  About  six 
weeks  after  the  operation,  having  been  well  fed  twenty-four  hours  before,  the 
dog  ate  at  one  time  a  little  more  than  four  pounds  (1,814  grammes)  of  beef- 
heart,  nearly  one-fifth  of  his  weight.  This  he  digested  well,  and  the  appetite 
was  undiminished  on  the  following  day.  This  dog  had  a  remarkably  sleek 
and  well  nourished  appearance  (Flint,  1861). 

The  above  is  a  striking  example  of  the  change  in  the  appetite  and  dis- 
position of  animals  after  extirpation  of  the  spleen ;  but  these  results  are  by 
no  means  invariable.  In  many  instances  of  removal  of  the  spleen  from  dogs, 
the  animals  were  kept  for  several  months  and  nothing  unusual  was  observed. 
On  the  other  hand,  the  change  in  disposition  and  the  development  of  an 
unnatural  appetite  were  observed  in  animals  after  removal  of  one  kidney. 
These  effects  were  also  very  well  marked  in  an  animal  with  biliary  fistula, 
that  lived  for  thirty-eight  days.  In  the  latter  instance,  the  voracity  could 
be  accounted  for  by  the  disturbance  in  digestion  and  assimilation  produced 
by  shutting  off  the  bile  from  the  intestine ;  but  these  phenomena  occurring 
after  removal  of  one  kidney  are  not  so  readily  explained. 

Cases  are  on  record  of  congenital  absence  of  the  spleen  in  the  human  sub- 
ject, in  which  no  special  phenomena  had  been  observed  during  life. 

Aside  from  certain  uses  which  are  connected  with  changes  in  its  volume, 
it  is  certain  that  the  spleen  has  some  relation  to  the  formation  of  the  blood- 
corpuscles,  both  white  and  red.  In  certain  cases  of  leucocythaemia,  the  spleen 
is  in  a  condition  of  hyperplastic  enlargement.  The  blood  coming  from  the 
spleen  is  peculiarly  rich  in  leucocytes,  but  the  proportion  of  its  red  corpuscles 
is  diminished.  It  may  be  that  the  spleen  destroys  a  certain  number  of  red 


SUPRARENAL  CAPSULES.  419 

corpuscles,  the  coloring  matter  being  changed  into  other  pigmentary  matters, 
and  that  it  also  produces  new  red  corpuscles.  After  removal  of  the  spleen, 
the  red  blood-corpuscles  are  diminished  in  number,  and  the  proportion  of 
leucocytes  is  increased.  This  condition  continues  for  about  six  months,  but 
after  that  time,  in  dogs,  the  marrow  of  the  long  bones,  which  normally  is 
yellow,  becomes  red,  assuming  the  character  of  the  marrow  concerned  in  the 
formation  of  red  corpuscles.  Temporary  diminution  of  red  corpuscles  and 
increase  of  leucocytes  have  been  observed  in  the  blood  in  cases  of  extirpation 
of  the  spleen  in  the  human  subject. 

Whatever  uses  the  spleen  has  in  connection  with  the  development  of  red 
and  of  white  blood-corpuscles  it  shares  with  the  red  marrow  of  the  bones 
and  the  so-called  lymphatic  glands. 

The  above  expresses  about  all  that  is  known  with  regard  to  the  physiology 
of  the  spleen. 

SUPRARENAL  CAPSULES. 

The  suprarenal  capsules,  as  their  name  implies,  are  situated  above  the 
kidneys.  They  are  small,  triangular,  flattened  bodies,  situated  behind  the 
peritoneum  and  capping  the  kidneys  at  the  anterior  portion  of  their  superior 
ends.  The  left  capsule  is  a  little  larger  than  the  right  and  is  rather  semi- 
lunar  in  form,  the  right  being  more  nearly  triangular.  Their  size  and 
weight  are  very  variable  in  diiferent  individuals.  It  may  be  stated,  as  an 
average,  that  each  capsule  weighs  about  one  hundred  grains  (6-5  grammes). 
The  capsules  are  about  an  inch  and  a  half  (38  mm.)  in  length,  a  little  less  in 
width,  and  a  little  less  than  one-fourth  of  an  inch  (G'4  mm.)  in  thickness. 

The  weight  of  the  capsules,  in  proportion  to  the  weight  of  the  kidneys, 
presents  great  variations  at  different  periods  of  life.  They  are  relatively  much 
larger  in  the  foetus  than  after  birth.  They  are  easily  distinguished  in  the 
foetus  of  two  months  ;  at  the  end  of  the  third  month  they  are  a  little  larger 
and  heavier  than  the  kidneys ;  they  are  equal  in  size  to  the  kidneys — though 
a  little  lighter — at  four  months ;  and  at  the  beginning  of  the  sixth  month 
they  are  to  the  kidneys  as  two  to  five  (Meckel).  In  the  f  oat  us  at  term  the 
proportion  is  as  one  to  three,  and  in  the  adult,  as  one  to  twenty-three. 

The  color  of  the  capsules  is  whitish-yellow.  They  are  completely  cov- 
ered by  a  thin,  fibrous  coat,  which  penetrates  their  interior,  in  the  form  of 
trabeculae.  Upon  section  they  present  a  cortical  and  a  medullary  substance. 
The  cortex  is  yellowish  and  ^  to  -^  of  an  inch  (1  to  2  mm.)  in  thickness.  It 
surrounds  the  capsule  completely  and  constitutes  about  two-thirds  of  its  sub- 
stance. The  medullary  substance  is  whitish,  very  vascular,  and  is  remark- 
ably prone  to  decomposition,  so  that  it  is  desirable  to  study  the  anatomy  of 
these  bodies  in  specimens  that  are  perfectly  fresh. 

Cortical  Substance. — The  cortical  substance  is  divided  into  two  layers. 
The  external  layer  is  pale-yellow  and  is  composed  of  closed  vesicles,  rounded 
or  ovoid  in  form,  containing  an  albuminoid  fluid,  cells,  nuclei  and  fatty  glob- 
ules. This  layer  is  very  thin.  The  greater  part  of  the  cortical  substance  is  of 
a  reddish-brown  color  and  is  composed  either  of  closed  tubes  containing 


420 


USES  OF  THE  LIVER— DUCTLESS  GLANDS. 


cells  or  of  columns  of  cells  surrounded  by  delicate,  fibrous  trabeculae.  On 
making  thin  sections  through  the  cortical  substance  previously  hardened  in 
chromic  acid  and  rendered  clear  by  glycerine,  rows  of  cells  are  seen,  arranged 
with  great  regularity,  and  extending,  apparently,  from  the  investing  mem- 
brane to  the  medullary  substance.  The  cells  appear  to  be  enclosed  in  tubes 
measuring  T^QTF  t°  -JOT  °^  an  ^ncn  (25  to  80  /x,)  in  diameter.  They  are  gran- 
ular, with  a  distinct  nucleus  and  nucleolus  and  a  variable  number  of  oil- 
globules.  They  measure  y^g-g-  to  T^Vo  °f  an  inch  (14  to  25  /*)  in  diameter. 
Between  the  rows  of  cells  of  the  cortical  substance,  are  bands  of  fibrous  tissue 
connected  with  the  investing  membrane  of  the  capsule. 

Medullary  Substance. — The  medullary  substance  is  much  paler  and  more 
transparent  than  the  cortex.  In  its  centre  are  openings  which  mark 
the  passage  of  its  venous  sinuses.  It  is  penetrated  in  every  direction  by  very 
delicate  bands  of  fibrous  tissue,  which  enclose  blood-vessels,  nerves,  and  elon- 
gated, closed  vesicles  containing  cells,  nuclei  and  granular  matter.  These 
vesicles,  which  are  -^  of  an  inch  (0*32  mm.)  long  and  about  T^  of  an  inch 
(64/t)  broad,  have  been  demonstrated  in  the  ox  and  in  the  human  subject. 
The  cells  in  the  human  subject  are  -^fanr  to  y^nr  °f  an  incn  (15  to  20  /z.)  in 
diameter.  They  are  isolated  with  difficulty  and  are  very  irregular  in  their 

form.     The  nuclei  measure  about   2g*6<)  of 
an  inch  (10  /t).     The  medullary  substance  is 
S  peculiarly  rich  in  vessels  and  nerves. 

Vessels  and  Nerves. — The  blood-vessels 
going  to  the  suprarenal  capsules  are  very 
abundant  and  are  derived  from  the  aorta, 
the  phrenic  artery,  the  coeliac  axis  and  the 
renal  artery.  Sometimes  as  many  as  twenty 
distinct  vessels  penetrate  each  capsule.  In 
the  cortical  substance  the  capillaries  are  ar- 
ranged in  elongated  meshes,  anastomosing 
freely  and  surrounding  the  tubes  but  never 
penetrating  them.  In  the  medullary  sub- 
stance the  meshes  are  more  rounded,  and 
here  the  vessels  form  a  very  rich  capillary 
plexus.  Two  large  veins  pass  out,  to  empty, 
on  the  right  side,  into  the  vena  cava,  and  on 
the  left,  into  the  renal  vein.  Other  smaller 
veins  empty  into  the  vena  cava,  the  renal 
and  the  phrenic  veins. 

The  nerves  are  very  abundant  and  are 
derived  from  the  semilunar  ganglia,  the  re- 
nal plexus,  the  pneumogastric  and  the  phren- 
ic. Kolliker  counted  in  the  human  subject 

medullary  substance  ;D,biood-ves-  thirty-three    nervous    trunks   entering  the 

right  suprarenal  capsule.     The  nerves  prob- 
ably pass  directly  to  the  medullary  substance,  but  here  their  mode  of  distri- 


FiG.  140. — Section  of  a  human  suprarenal 

capsule  (Cadiat). 

A,  fibrous  coat;  B,  cells  of  the  cortical  sub- 
stance, arranged  in  rows;  c,  vesicles  of 


THYROID  GLAND.  421 

• 

bution  is  unknown.     In  the  medullary  substance,  however,  there  are  two 
ganglia  situated  close  to  the  central  vein. 

Nothing  is  known  of  lymphatics  in  the  suprarenal  capsules,  and  the  exist- 
ence of  such  vessels  is  doubtful. 

Chemical  Reactions  of  the  Suprarenal  Capsules. — Vulpian  has  described 
(185G),  in  the  medullary  portion  of  the  suprarenal  capsules,  a  peculiar  sub- 
stance, soluble  in  water  and  in  alcohol,  which  gave  a  greenish  reaction  with 
the  salts  of  iron  and  a  peculiar  rose-tint  on  the  addition  of  iodine.  He 
could  not  determine  the  same  reaction  with  extracts  from  any  other  parts. 
Later,  in  conjunction  with  Cloez,  he  discovered  hippuric  and  taurocholic 
acid  in  the  capsules  of  some  of  the  herbivora.  These  bodies  contain  in 
addition,  leucine,  hypoxanthine,  taurine,  fats  and  inorganic  salts,  the  latter 
chiefly  phosphates  and  salts  of  potassium. 

The  suprarenal  capsules  are  not  essential  to  life.  If  care  be  taken  to 
avoid  injury  of  the  semilunar  ganglia,  they  may  be  removed  from  animals 
and  the  operation  apparently  has  no  remote  effects.  In  Addison's  disease,  a 
disorder  attended  with  bronzing  of  the  skin  and  serious  and  finally  fatal  dis- 
order of  nutrition,  there  usually  is  disorganization  of  the  suprarenal  capsules, 
but  this  is  not  invariable.  It  is  not  established  that  disorganization  of  the 
capsules  stands  in  a  causative  relation  to  the  discoloration  of  the  skin  or  to 
the  constitutional  disturbance.  Investigations  into  these  diseased  conditions 
have  developed  little  or  nothing  of  importance  concerning  the  physiology  of 
the  suprarenal  capsules. 

THYROID  GLAND. 

The  thyroid  gland  is  attached  to  the  lower  part  of  the  larynx  and  follows 
it  in  its  movements.  Its  color  is  brownish-red.  The  anterior  face  is  convex 
and  is  covered  by  certain  of  the  muscles  of  the  neck.  The  posterior  surface 
is  concave  and  is  applied  to  the  larynx  and  trachea.  It  presents  two  lateral 
lobes,  each  with  a  rounded,  thickened  base  below,  and  a  long,  pointed  extrem- 
ity extending  upward,  the  lobes  being  connected  by  an  isthmus  (see  Fig.  141, 
page  424).  Each  of  these  lobes  is  about  two  inches  (50  mm.)  in  length, 
three-quarters  of  an  inch  (19  mm.)  in  breadth,  and  about  the  same  in  thick- 
ness at  its  thickest  portion.  The  isthmus  connects  the  lower  portion  of  the 
lateral  lobes,  covers  the  second  and  third  tracheal  rings,  and  is  about  half  an 
inch  (12  mm.)  wide  and  one-third  of  an  inch  (8'5  mm.)  thick.  From  the 
left  side  of  the  isthmus,  and  sometimes  from  the  left  lobe,  is  a  portion  pro- 
jecting upward,  called  the  pyramid.  The  weight  of  the  thyroid  gland, 
according  to  Sappey,  is  three  hundred  and  fifty  to  three  hundred  and  eighty 
grains  (22  to  24  grammes).  It  is  usually  stated  by  anatomical  writers  that 
it  is  relatively  larger  in  the  f O3tus  and  in  early  life  than  in  the  adult ;  but 
according  to  Sappey,  its  weight,  in  proportion  to  the  weight  of  the  adjacent 
organs,  does  not  vary  with  age.  It  is  a  little  larger  and  more  prominent  in 
the  female  than  in  the  male. 

Structure  of  the  Thyroid  Gland. — The  thyroid  gland  is  covered  with  a 
thin  but  resisting  coat  of  ordinary  fibrous  tissue,  which  is  loosely  connected 


422  USES  OF  THE  LIVER— DUCTLESS  GLANDS. 

with  the  surrounding  parts.  From  the  internal  surface  of  this  membrane, 
are  fibrous  bands,  or  trabeculge,  giving  off,  as  they  pass  through  the  gland, 
secondary  trabeculae,  and  then  subdividing  until  they  become  of  microscopic 
size.  By  this  arrangement  the  gland  is  divided  up  into  small,  communicat- 
ing cells.  The  trabeculae  contain  many  small,  elastic  fibres.  Throughout 
the  substance  of  the  gland,  lodged  in  the  meshes  of  the  trabeculge,  are 
rounded  or  ovoid,  closed  vesicles,  measuring  -g-J^  to  ^^  of  an  inch  (40  to 
100  p.}.  These  are  formed  of  a  structureless  membrane  and  are  lined  by 
a  single  layer  of  pale,  granular,  nucleated  cells,  3 0*6  0  to  joVo  °f  an  in°h 
(8  to  12  /*)  in  diameter.  The  layer  of  cells  sometimes  lines  the  vesicle  com- 
pletely, sometimes  it  is  incomplete,  and  sometimes  it  is  wanting.  The  con- 
tents of  the  vesicles  are  a  clear,  yellowish,  slightly  viscid,  albuminoid  fluid, 
with  a  few  granules,  pale  cells,  and  nuclei.  The  vesicles  are  arranged  in  the 
form  of  lobules,  and  between  them  are  the  great  veins. 

Vessels  and  Nerves. — The  blood-vessels  of  the  thyroid  gland  are  very 
abundant,  this  organ  being  supplied  by  the  superior  and  inferior  thyroid 
arteries  and  sometimes  by  a  branch  from  the  innominata.  The  arteries 
break  up  into  a  close,  capillary  plexus,  surrounding  the  vesicles  with  a  rich 
net-work,  but  never  penetrating  their  interior.  The  veins  are  large,  and 
like  the  hepatic  veins,  they  are  so  closely  adherent  to  the  surrounding  tissue 
that  they  do  not  collapse  when  cut  across.  The  veins  emerging  from  the 
gland  form  a  plexus  over  its  surface  and  the  surface  of  the  trachea,  and  they 
then  go  to  form  the  superior,  middle  and  inferior  thyroid  veins.  The  nerves 
are  derived  from  the  pneumogastrics  and  from  the  cervical  sympathetic  gan- 
glia. The  lymphatics  are  abundant  but  are  difficult  to  inject.  The  exact 
distribution  of  the  nerves  and  the  origin  of  the  lymphatics  are  not  well  un- 
derstood. 

What  little  is  known  with  regard  to  the  chemical  constitution  of  the 
thyroid  gland  is  embodied  in  the  statement  that  it  contains  leucine,  xanthine, 
lactic  acid,  succinic  acid  and  some  volatile  fatty  acids.  The  blood  of  the 
thyroid  veins  has  been  analyzed,  but  the  changes  in  its  composition  in  pass- 
ing through  the  gland  are  slight  and  indefinite.  It  has  been  asserted  that 
one  of  the  uses  of  the  thyroid  gland  is  to  regulate  the  blood-circulation  in  the 
brain,  but  the  observations  in  support  of  this  view  are  not  very  satisfactory. 

Myxcedema. — Important  facts  have  lately  been  developed  showing  a  con- 
nection between  the  thyroid  gland  and  a  disease  characterized  by  infiltration 
of  the  connective  tissues  with  a  gelatinous  substance  containing  mucine. 
This  disease  has  been  described  by  Ord,  under  the  name  of  myxosdema.  It 
is  attended  with  marked  impairment  of  the  mental  faculties,  and  a  condition 
like  cretinism.  This  is  usually  associated  with  disease  of  the  thyroid  gland. 

Complete  excision  of  the  thyroid  gland  in  the  human  subject  has  been 
followed  by  the  peculiar  mental  condition  characteristic  of  cretinism.  In 
the  lower  animals  the  operation  of  complete  extirpation  is  fatal.  The  ex- 
periments of  Horsley,  upon  dogs  and  monkeys,  show  great  differences  in  the 
results,  depending  upon  age.  In  young  animals  death  usually  occurs  in  a 
few  days,  while  old  animals  survive  the  operation  four,  five,  or  six  months. 


THYMUS  GLAND.  423 

As  far  as  could  be  ascertained  from  these  experiments  upon  the  lower  ani- 
mals— dogs  and  monkeys — the  conditions,  including  the  mental  phenomena, 
resembled  those  observed  in  cases  of  myxoedema  in  the  human  subject,  The 
animals  operated  upon  were  found  to  be  exceedingly  sensitive  to  cold.  If  put 
in  a  hot-air  bath  at  a  temperature  of  105°  Fahr.  (40-5°  C.)  after  the  general 
symptoms  made  their  appearance,  the  animals  could  be  kept  alive  for  several 
months.  Horsley  described  the  symptoms  in  monkeys,  after  three  to  seven 
weeks,  as  "  commencing  hebetude  and  mucinoid  degeneration  of  the  connect- 
ive tissues,"  and  after  five  to  eight  weeks,  "  complete  imbecility  and  atrophy 
of  all  tissues,  especially  muscles." 

It  is  difficult  to  draw,  from  these  observations,  absolutely  definite  conclu- 
sions with  regard  to  the  physiological  relations  of  the  thyroid  gland.  This 
organ  seems  essential  to  life,  and  its  removal  profoundly  affects  the  general 
processes  of  nutrition.  It  influences  the  quantity  of  mucine  in  the  body,  but 
precisely  in  what  way,  it  is  difficult  to  determine. 

THYMUS  GLAND. 

In  its  anatomy  the  thymus  resembles  the  ductless  glands,*but  its  office, 
whatever  this  may  be,  is  confined  to  early  life.  In  the  adult  the  organ  is 
wanting,  traces,  only,  of  fibrous  tissue  with  a  little  fat  existing  after  puberty 
in  the  situation  previously  occupied  by  this  gland.  As  there  never  has  been 
a  plausible  theory,  even,  of  the  uses  of  this  organ,  the  existence  of  which  is 
confined  to  the  first  two  or  three  years  of  life,  it  seems  necessary  only  to  give 
a  brief  sketch  of  its  structure. 

The  thymus  appears  at  about  the  third  month  of  foetal  life  and  gradually 
increases  in  size  until  about  the  end  of  the  second  year.  It  then  undergoes 
atrophy  and  it  disappears  almost  entirely  at  the  age  of  puberty.  It  is  situ- 
ated partly  in  the  thorax  and  partly  in  the  neck.  The  thoracic  portion  is  in 
the  anterior  mediastinum,  resting  upon  the  pericardium,  extending  as  low  as 
the  fourth  costal  cartilage.  The  cervical  portion  extends  upward  as  far  as  the 
lower  border  of  the  thyroid  gland.  The  whole  gland  is  about  two  inches 
(50-8  mm.)  in  length,  an  inch  and  a  half  (38  mm.)  broad  at  its  lower  por- 
tion, and  about  one-quarter  of  an  inch  (6-4  mm.)  thick.  Its  color  is  grayish 
with  a  slightly  rosy  tint.  It  is  usually  in  the  form  of  two  lateral  lobes  lying 
in  apposition  in  the  median  line,  although  sometimes  there  exists  but  a 
single  lobe.  It  is  composed  of  a  number  of  lobules  held  together  by  con- 
nective tissue 

The  proper  coat  of  the  thymus  is  a  delicate,  fibrous  membrane  sending 
processes  into  the  interior  of  the  organ.  Its  fibrous  structure,  however,  is 
loose,  so  that  the  lobules  can  be  separated  with  little  difficulty.  Portions  of 
the  gland  may  be,  as  it  were,  unravelled,  by  loosening  the  interstitial  fibrous 
tissue.  In  this  way  it  is  found  to  be  composed  of  little  lobular  masses  at- 
tached to  a  continuous  cord.  This  arrangement  is  more  distinct  in  the  in- 
ferior animals  of  large  size  than  in  man.  The  lobules  are  composed  of 
rounded  vesicles,  ten  to  fifteen  in  number,  and  y^-g-  to  -^  of  an  inch  (200 
to  600  p.)  in  diameter.  The  walls  of  these  vesicles  are  thin,  finely  granular 


424 


USES  OF  THE  LIVER-DUCTLESS  GLANDS. 


and  very  fragile.     The  vesicles  contain  a  small  quantity  of  an  albuminoid 
fluid,  with  cells  and  free  nuclei.     The  cells  are  small  and  transparent,  and 


FIG.  141.— Thyroid  and  thymus  glands  (Sappey). 

A.  1,  right  lobe  of  the  thymus  ;  2,  left  lobe  ;  3,  groove  between  the  two  lobes  ;  4,  lungs,  the  anterior  bor- 
ders raised  to  show'  the  thymus  ;   5,  terminal  branch  of  the  internal  mammary  vein  ;  6,  thyroid 
gland  ;  7,  median  inferior  thyroid  veins;  8,  lateral  inferior  thyroid  veins;  9,  common  carotid  artery; 
10.  internal  jugular  vein  ;  11,  pneumogastric  nerve. 

B.  Right  lobe  of  the  thymus  with  the  investing  membrane  removed.    1,  upper  extremity  of  the  lobe  ;  2, 

lower  extremity  ;  3,  external  border  :  4,  internal  border. 

C.  Arrangement  or  the  lobules  of  the  same  lobe,  around  the  central  cord.    1,  upper  extremity  of  the 

lobe  ;  2,  lower  extremity  ;  3,  3,  3,  lobules  ;  4,  4,  central  cord. 

the  nuclei  are  spherical,  relatively  large,  and  contain  one  to  three  nucleoli. 
The  free  nuclei  are  also  rounded  and  contain  several  distinct  nucleoli.  These 
vesicles  are  easily  ruptured,  when  their  contents  exude  in  the  form  of  an 
opalescent  fluid,  which  is  sometimes  called  the  thymic  juice. 

Anatomists  are  somewhat  divided  in  their  opinions  with  regard  to  the 
structure  of  the  central  cord  and  the  lobules.  Some  adopt  the  view  advanced 
by  Astley  Cooper,  that  the  cord  has  a  central  canal  connected  with  cavities 
in  the  lobules ;  while  others  believe  that  the  cavities  thus  described  are  pro- 
duced artificially  by  the  processes  employed  in  anatomical  investigation. 
The  latter  opinion  is  probably  correct. 

The  blood-vessels  of  the  thymus  are  abundant,  but  their  caliber  is  small 
and  the  gland  is  not  very  vascular.  They  are  derived  chiefly  from  the  in- 
ternal mammary  artery,  a  few  coming  from  the  inferior  thyroid,  with  occa- 


PITUITARY  BODY  AND  PINEAL  GLAND.  425 

sional  branches  from  the  superior  diaphragmatic  or  the  pericardial.  They 
pass  between  the  lobules,  surround  and  penetrate  the  vesicles  and  form  a 
capillary  plexus  in  their  interior.  The  vesicles  in  this  respect  bear  a  certain 
resemblance  to  the  closed  follicles  of  the  intestine.  The  veins  are  also  abun- 
dant but  they  do  not  follow  the  course  of  the  arteries.  The  principal  vein 
emerges  at  about  the  centre  of  the  gland  posteriorly  and  empties  into  the  left 
brachio-cephalic.  Other  small  veins  empty  into  the  internal  mammary,  the 
superior  diaphragmatic  and  the  pericardial.  A  few  nervous  filaments  from  the 
sympathetic  surround  the  principal  thymic  artery  and  penetrate  the  gland. 
Their  ultimate  distribution  is  uncertain.  The  lymphatics  are  very  abundant. 

As  regards  its  chemical  constitution,  it  may  be  stated  in  general  terms 
that  the  thymus  contains  matters  of  about  the  same  character  as  those  found 
in  the  other  ductless  glands. 

Inasmuch  as  the  thymus  is  peculiar  to  early  life,  one  of  the  most  impor- 
tant points  in  its  anatomical  history  relates  to  its  mode  of  development. 
This,  however,  does  not  present  any  great  physiological  interest  and  is  fully 
treated  of  in  works  upon  anatomy. 

PITUITARY  BODY  AND  PINEAL  GLAND. 

These  little  bodies,  situated  at  the  base  of  the  brain,  are  quite  vascular, 
contain  closed  vesicles  and  but  few  nervous  elements,  and  are  sometimes 
classed  with  the  ductless  glands.  Physiologists  have  no  definite  idea  of  their 
uses. 

The  pituitary  body  is  of  an  ovoid  form,  a  reddish-gray  color,  weighs  five 
to  ten  grains  (0-324  to  0-648  grammes),  and  is  situated  on  the  sella  Turcica  of 
the  sphenoid  bone.  It  is  said  to  be  larger  in  the  foetus  than  in  the  adult,  and 
in  foetal  life  it  has  a  cavity  communicating  with  the  third  ventricle.  This 
little  body  has  been  studied  by  Grandry,  in  connection  with  the  suprarenal 
capsules.  He  regarded  it  as  essentially  composed  of  closed  vesicles,  with 
fibres  of  connective  tissue  and  blood-vessels.  The  vesicles  are  formed  of  a 
transparent  membrane,  containing  irregularly  polygonal,  nucleated  cells  and 
free  nuclei.  The  nuclei  are  distinct,  with  a  well  marked  nucleolus.  Capillary 
vessels  surround  these  vesicles  without  penetrating  them.  Grandry  did  not 
observe  either  nerve-cells  or  fibres  between  the  vesicles. 

The  pineal  gland  is  situated  just  behind  the  posterior  commissure  of  the 
brain,  between  the  nates,  and  is  enclosed  in  the  velum  interpositum.  It  is  of 
a  conical  shape,  one-third  of  an  inch  (S'5  mm.)  in  length  and  of  nearly  the 
color  of  the  pituitary  body.  It  is  connected  with  the  base  of  the  brain  by 
several  delicate,  commissural  peduncles.  It  presents  a  small  cavity  at  its  base, 
and  frequently  it  contains  in  its  substance  little  calcareous  masses  composed 
of  calcium  phosphate,  calcium  carbonate,  ammonio-magnesian  phosphate 
and  a  small  quantity  of  organic  matter.  It  is  covered  with  a  fibrous  envelope 
which  sends  processes  into  its  interior.  As  the  result  of  the  researches  of 
Grandry,  it  has  been  found  to  present  a  cortical  substance,  analogous  in  its 
structure  to  the  pituitary  body,  and  a  central  portion  composed  of  the  ordi- 
nary nervous  elements  found  in  the  gray  matter  of  the  brain.  Its  structure 


426  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

is  very  like    that    of   the    medullary   portion    of    the    suprarenal    capsules 
(Grandry). 

It  is  difficult  to  classify  organs,  of  the  uses  of  which  physiologists  are  en- 
tirely ignorant;  but  in  structure,  the  little  bodies  just  described  certainly 
resemble  the  ductless  glands. 


CHAPTER  XIV. 

NUTRITION— ANIMAL  HEAT  AND  FORCE. 

Nature  of  the  forces  involved  in  nutrition — Life,  as  represented  in  development  and  nutrition — Substances 
which  pass  through  the  organism — Metabolism — Substances  consumed  in  the  organism — Conditions 
which  influence  nutrition — Animal  heat  and  force — Estimated  quantity  of  heat  produced  by  the  body 
— Limits  of  variation  in  the  normal  temperature  in  man — Variations  with  external  temperature — Varia- 
tions in  different  parts  of  the  body — Variations  at  different  periods  of  life  etc.— Influence  of  exercise 
etc.,  upon  the  heat  of  the  body— Influence  of  the  nervous  system  upon  the  production  of  animal  heat 
(heat-centres)— Mechanism  of  the  production  of  animal  heat— Equalization  of  the  animal  temperature- 
Relations  of  heat  to  force. 

NUTRITION  proper,  in  the  light  in  which  it  is  proposed  to  consider  it  in 
this  chapter,  is  the  process  by  which  the  physiological  wear  of  the  tissues  and 
fluids  of  the  body  is  compensated  by  the  appropriation  of  new  matter.  All 
of  the  physiological  operations  that  have  thus  far  been  described,  including 
the  circulation  of  the  blood,  respiration,  alimentation,  digestion,  absorption 
and  secretion,  are  to  be  regarded  as  means  directed  to  a  single  end ;  and  the 
great  end,  to  which  all  of  the  functions  enumerated  are  subservient,  is  the 
general  process  of  nutrition. 

The  nature  of  the  main  forces  involved  in  nutrition,  be  it  in  a  highly 
organized  part,  like  the  brain  or  muscles,  or  in  a  tissue  called  extra- vascular, 
like  the  cartilages  or  nails,  is  unknown.  The  phenomena  attending  the  gen- 
eral process,  however,  have  been  carefully  studied,  and  certain  important 
positive  results  have  been  attained ;  but  there  is  really  no  more  satisfactory 
explanation  of  the  nature  of  the  causative  force  of  nutrition  to  be  found  in 
the  doctrines  of  to-day  than  in  the  speculative  theories  of  the  past. 

The  blood  contains  all  the  matters  that  enter  into  the  composition  of  the 
tissues  and  secretions,  either  identical  with  them  in  form  and  composition, 
as  is  the  case  in  most  of  the  inorganic  matters,  or  in  a  condition  which 
admits  of  their  transformation  into  the  characteristic  constituents  of  the  tis- 
sues, as  in  the  organic  substances  proper.  These  matters  are  supplied  to  the 
tissues,  in  the  required  quantity,  through  the  circulatory  apparatus ;  and  oxy- 
gen, which  is  immediately  indispensable  to  all  the  operations  of  life,  is  intro- 
duced by  respiration.  The  great  nutritive  fluid,  being  constantly  drawn  upon 
by  the  tissues  for  materials  for  their  regeneration,  is  kept  at  the  proper  stand- 
ard by  the  introduction  of  new  matter  into  the  system  in  alimentation,  its 
elaborate  preparation  by  digestion,  and  its  appropriation  by  the  fluids  by 
absorption.  Many  of  these  processes  require  the  action  of  certain  secretions. 


GENERAL  PROCESSES  OF  NUTRITION.  427 

The  introduction  of  new  matter,  so  essential  to  the  continuance  of  the  phe- 
nomena of  life,  is  demanded,  on  account  of  the  change  o'f  the  substance  of 
the  tissues  into  what  is  called  effete  matter ;  and  this  is  discharged  from  the 
animal  organism,  to  be  appropriated  by  vegetables  and  thus  maintain  the 
equilibrium  between  the  animal  and  the  vegetable  kingdoms. 

It  is  a  well  established  fact  that  nearly  all  of  the  tissues  undergo  disassimi- 
lation,  or  conversion  into  effete  matter,  during  their  physiological  wear  in  the 
living  organism,  while  others,  like  the  epidermis  and  its  appendages,  are 
gradually  desquamated,  and  when  once  formed,  do  not  pass  through  any 
farther  changes.  The  whole  question  of  the  essence  and  nature  of  the  nutri- 
tive property  or  force  resolves  itself  into  vitality.  Life  is  always  attended 
with  what  are  known  as  the  phenomena  of  nutrition,  and  nutrition  does  not 
exist  except  in  living  organisms.  At  present,  physiologists  have  been  able 
to  define  life  only  by  a  recital  of  certain  of  its  invariable  and  characteristic 
attendant  conditions ;  and  yet  there  are  few  if  any  definitions  of  life — re- 
garding life  as  the  sum  of  the  phenomena  peculiar  to  living  organisms — that 
are  not  open  to  grave  objections. 

If  life  be  regarded  as  a  principle,  it  stands  in  the  relation  of  a  cause  to 
the  vital  phenomena ;  if  it  be  regarded  as  the  totality  of  these  phenomena,  it 
is  an  effect. 

In  the  study  of  the  development  of  a  fecundated  ovum,  life  seems  to  be 
a  principle,  giving  the  property  of  appropriating  matter  from  without,  until 
the  germ  becomes  changed,  from  a  globule  of  microscopic  size  and  compara- 
tively simple  structure,  into  a  complete  organism  with  highly  elaborated  parts. 
This  organism  has  a  definite  form  and  size,  a  definite  period  of  existence,  and 
it  produces,  at  a  certain  time,  generative  elements,  capable  of  perpetuating 
its  life  in  new  beings.  It  may  be  said  that  an  organism  dies  physiologically 
because  the  vital  principle,  if  such  a  principle  be  admitted,  has  a  limited 
term  of  existence ;  but  on  the  other  hand,  the  fully  developed  living  organ- 
ism, called  an  animal,  presents  many  distinct  parts,  each  endowed  with 
an  independent  property  called  vital,  that  property  recognized  by  Haller 
in  various  tissues,  under  the  name  of  irritability;  and  it  is  the  co-ordinated 
association  of  these  vitalities  that  constitutes  the  perfect  being.  These  are 
more  or  less  distinct ;  and  a  sudden  and  simultaneous  arrest  of  the  physio- 
logical properties  in  all  the  tissues,  in  what  is  called  death,  is  not  often  ob- 
served. For  example,  the  nerves  may  die  before  the  muscles,  or  the  muscles, 
before  the  nerves.  It  is  found,  also,  that  physiological  properties,  apparently 
lost  or  destroyed,  may  be  made  to  return ;  as  in  resuscitation  after  asphyxia 
or  in  the  restoration  of  muscular  or  nervous  excitability  by  injection  of  blood. 

The  life  of  a  fecundated  ovum  is  the  property  which  enables  it  to  undergo 
development  when  placed  under  favorable  conditions ;  and  by  the  surround- 
ing conditions,  its  development  may  be  arrested,  suspended  or  modified. 
The  life  of  a  non-fecundated  ovum  is  like  that  of  any  ordinary  anatomical 
element. 

The  life  of  an  anatomical  element  or  tissud  in  process  of  development  is 
the  property  by  virtue  of  which  it  arrives  at  its  perfection  of  organization 


428  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

and  performs  certain  denned  offices,  as  far  as  its  organization  will  permit. 
This  can  also  be  destroyed,  suspended  or  modified  by  surrounding  conditions. 

The  life  of  a  perfected  anatomical  element  or  tissue  is  the  property  which 
enables  it  to  regenerate  itself  and  perform  it  offices,  subject,  also,  to  modifica- 
tions from  surrounding  conditions. 

The  life  of  a  perfect  animal  organism  is  the  sum  of  the  vitalities  of  its 
constituent  parts ;  but  a  being  may  live  with  the  physiological  properties  of 
certain  parts  abolished  or  seriously  modified,  as  a  man  exists  and  preserves 
his  identity  with  a  limb  amputated.  Life  may  continue  for  a  long  time  with- 
out consciousness  or  with  organs  paralyzed ;  but  certain  functions,  such  as 
respiration  and  circulation,  are  indispensable  to  the  nutrition  of  all  parts,  the 
properties  of  the  different  tissues  are  speedily  lo.st  when  these  processes  are 
arrested,  and  the  being  then  ceases  to  exist. 

These  considerations  make  it  evident  that  it  is  difficult  if  not  impossible 
to  give  a  single,  comprehensive  definition  of  life,  a  study  of  the  varied  phe- 
nomena of  which  constitutes  the  science  of  physiology. 

The  general  process  of  nutrition  begins  with  the  introduction  of  matter 
from  without,  called  food.  It  is  carried  on  by  the  appropriation  of  this  mat- 
ter by  the  organism.  It  is  attended  with  the  production  of  excrementitious 
matters  and  the  development  of  certain  phenomena  that  remain  to  be  studied, 
the  most  important  of  which  is  the  production  of  heat. 

The  term  metabolism,  now  used  by  many  English  writers,  seems  destined 
to  become  generally  adopted.  It  was  employed  by  Schwann  to  designate  a 
kind  of  action  by  cells,  resulting  in  a  change  in  the  character  of  substances 
brought  in  contact  with  them.  Modern  writers  use  it  as  a  translation  of  the 
German  word  Stoffivechsel.  The  literal  signification  of  the  Greek  word 
/Aera/3oAi7  is  change.  As  applied  to  nutritive  changes,  metabolism  is  equiva- 
lent to  assimilation ;  and  as  applied  to  the  changes  which  result  in  the  pro- 
duction of  effete  matters,  it  is  equivalent  to  disassimilation,  a  term  much 
used  by  the  French,  and  one  which  well  expresses  changes  that  are  exactly 
the  opposite  of  assimilation.  The  signification  of  the  term  metabolism  seems 
likely  to  be  extended  so  as  to  include  the  acts  of  cells  in  the  production  of 
the  constituents  of  the  secretions,  a  process  which  it  is  difficult  to  express  in 
a  single  word. 

The  behavior  of  various  substances  in  nutrition  has  already  been  treated 
of,  to  some  extent,  in  connection  with  alimentation ;  but  certain  general  rela- 
tions of  nutritive  substances  to  assimilation  remain  to  be  considered.  It  is 
convenient,  as  before,  to  divide  these  substances  into  the  following  classes : 
1,  Inorganic ;  2,  organic  non-nitrogenized ;  3,  organic  nitrogenized.  The 
excrementitious  products  constitute  a  distinct  class  by  themselves. 

SUBSTANCES  WHICH  PASS  THROUGH  THE  ORGANISM. 

All  of  the  inorganic  matters  taken  in  with  the  food  pass  out  of  the  organ- 
ism, generally  in  the  form  in  which  they  enter,  in  the  fseces,  urine  and  per- 
spiration ;  but  it  must  not  be  inferred  from  this  fact  that  they  are  not  useful 
as  constituent  parts  of  the  body.  Some  of  these,  such  as  water  and  the  chlo- 


SUBSTANCES  WHICH  PASS  THEOUGH  THE  ORGANISM.    429 

rides,  have  important  uses  of  a  purely  physical  character.  It  is  necessary,  for 
example,  that  the  blood  should  contain  a  certain  proportion  of  sodium  chlo- 
ride, this  substance  modifying  and  regulating  the  processes  of  absorption  and 
probably  of  assimilation.  In  addition,  however,  the  chlorides  exist  as  con- 
stituent parts  of  every  tissue  and  organ  of  the  body,  and  they  are  so  closely 
united  with  the  nitrogenized  matters  that  they  can  not  be  completely  sepa- 
rated without  incineration.  Those  inorganic  matters,  the  uses  of  which  are 
so  important  in  their  passage  through  the  body,  are  found  largely  as  con- 
stituents of  the  fluids  and  are  less  abundant  in  the  solids.  They  are  con- 
tained in  large  proportion,  also,  in  the  liquid  excretions ;  and  any  excess  over 
the  quantity  actually  required  by  the  system  is  thrown  off  in  this  way.  Other 
inorganic  matters  are  specially  important  as  constituent  parts  of  the  tissues, 
and  they  are  more  abundant  in  the  solids  than  in  the  fluids.  Examples  of 
substances  of  this  class  are  the  calcium  salts,  particularly  the  phosphates. 
These  are  also  in  a  condition  of  intimate  union  with  organic  matters. 

If  certain  simple  chemical  changes  be  excepted,  such  as  the  decomposi- 
tion of  the  bicarbonates,  the  inorganic  constituents  of  food  do  not  necessarily 
undergo  any  modification  in  digestion.  They  are  generally  introduced  already 
in  combination  with  organic  matters,  and  they  accompany  them  in  the 
changes  which  they  pass  through  in  digestion,  assimilation  by  the  blood, 
deposition  in  the  tissues,  and  the  final  transformations  that  result  in  the 
various  excrementitious  products ;  so  that  the  inorganic  salts  are  found  united 
with  the  organic  matter  of  the  food  as  it  enters  the  body,  and  what  seem  to 
be  the  same  substances,  in  connection  with  the  organic  excrementitious  mat- 
ters. Between  these  two  conditions,  however,  are  the  various  operations  of 
assimilation  and  disassimilation,  or  metabolism,  from  which  inorganic  matters 
are  never  absent. 

Inorganic  Constituents  of  the  Body. — The  number  of  inorganic  substances 
now  well  established  as  existing  in  the  human  body  is  about  twenty-one ;  but 
some  are  found  in  small  quantities,  are  not  always  present  and  apparently 
have  no  very  important  uses.  These  will  be  passed  over  rapidly,  as  well  as 
those  which  are  so  intimately  connected  with  some  important  function  as  to 
render  their  full  consideration  in  connection  with  that  function  indispensable. 

Gases. — The  gases  (oxygen,  hydrogen,  nitrogen,  carburetted  hydrogen 
and  hydrogen  monosulphide)  exist  both  in  a  gaseous  state  and  in  solution  in 
some  of  the  fluids  of  the  body.  Oxygen  plays  a  most  important  part  in  the 
function  of  respiration ;  but  the  office  of  the  other  gases  is  by  no  means  so 
essential.  Nitrogen  seems  to  be  formed  by  the  system  in  small  quantity  and 
is  taken  up  by  the  blood  and  exhaled  by  the  lungs,  except  during  inanition, 
when  the  blood  absorbs  a  little  from  the  inspired  air.  It  exists  in  greatest 
quantity  in  the  intestinal  canal.  Carburetted  hydrogen  and  hydrogen  mono- 
sulphide,  with  pure  hydrogen,  are  found  in  minute  quantities  in  the  expired 
air  and  exist  in  a  gaseous  state  in  the  alimentary  canal.  From  the  offensive 
nature  of  the  contents  of  the  large  intestine,  one  would  suspect  the  presence 
of  hydrogen  monosulphide  in  considerable  quantity  ;  but  actual  analysis  has 
shown  that  the  gas  contained  in  the  stomach  and  in  the  small  and  large  in- 
29 


430  NUTRITION— ANIMAL  HEAT  AND  FOECE. 

testines  is  composed  chiefly  of  nitrogen,  with  hydrogen  and  carburetted 
hydrogen  in  about  equal  proportions  (five  to  eleven  parts  per  hundred),  and 
but  a  trace  of  hydrogen  monosulphide.  With  the  exception,  then,  of  oxy- 
gen and  carbon  dioxide,  the  latter  being  an  excretion,  the  gases  do  not  hold 
an  important  place  among  the  constituents  of  the  organism.  At  all  events, 
their  uses,  whether  they  be  important  or  not,  are  but  little  understood. 

Water. — Water  exists  in  all  parts  of  the  body ;  in  the  fluids,  some  of 
which,  as  the  lachrymal  fluid  and  perspiration,  contain  little  else,  and  in  the 
hardest  structures,  as  the  bones  and  the  enamel  of  the  teeth.  In  the  solids 
and  semi-solids  it  does  not  exist  as  water,  but  it  enters  into  their  composition, 
assuming  the  consistence  by  which  the  tissues  are  characterized. 

The  quantity  of  water  which  each  organic  substance  contains  is  impor- 
tant ;  and  it  is  provided  that  this  quantity,  though  indefinite,  shall  not  ex- 
ceed or  fall  below  certain  limits.  All  organs  and  tissues  must  contain  a  tol- 
erably definite  quantity  of  water  to  give  them  proper  consistence.  The 
effects  of  too  great  a  proportion  of  water  in  the  system  are  well  known  to 
physicians.  General  muscular  debility,  loss  of  appetite,  dropsies  and  various 
other  indications  of  imperfect  nutrition  are  among  the  results  of  such  a  con- 
dition ;  while  a  deficiency  of  water  is  immediately  made  known  by  the  sensa- 
tion, of  thirst,  which  leads  to  its  introduction  from  without. 

The  fact  that  water  never  exists  in  any  of  the  fluids,  semi-solids  or  solids, 
without  being  combined  with  inorganic  salts,  especially  sodium  chloride,  is 
one  reason  why  its  proportion  in  various  situations  is  nearly  constant.  The 
presence  of  these  salts  influences,  in  the  semi-solids  at  least,  the  quantity  of 
water  entering  into  their  composition,  and  consequently  it  regulates  their 
consistence.  The  nutrient  fluid  of  the  muscles  during  life  contains  water 
with  just  enough  saline  matter  to  preserve  the  normal  consistence  of  the 
parts.  This  action  of  saline  matters  is  even  more  apparent  in  the  case  of 
the  blood-corpuscles.  If  pure  water  be  added  to  the  blood,  these  bodies 
swell  up  and  are  finally  dissolved ;  while  on  the  addition  of  a  strong  solution 
of  salt,  they  lose  water  and  become  shrunken  and  corrugated.  Their  nat- 
ural form  and  consistence  can  be  restored,  however,  even  after  they  have 
been  completely  dried,  by  adding  water  containing  about  the  proportion  of 
salt  which  exists  in  the  blood-plasma.  It  seems  clear,  then,  that  water  is  a 
a  necessary  part  of  all  tissues  and  is  especially  important  to  the  proper  con- 
stitution of  organic  nitrogenized  substances ;  that  it  enters  into  the  constitu- 
tion of  these  substances,  not  as  pure  water,  but  always  in  connection  with 
certain  inorganic  salts ;  that  its  proportion  is  confined  within  certain  lim- 
its ;  and  that  the  quantity  in  which  it  exists,  in  organic  nitrogenized  sub- 
stances particularly,  is  regulated  by  the  quantity  of  salts  which  enter,  with 
it,  into  the  constitution  of  these  substances. 

The  quantities  of  water  which  can  be  driven  off  by  a  moderate  tempera- 
ture (212°  Fahr..  or  100°  0.),  from  the  different  fluids  and  tissues  of  the 
body,  vary  of  course  very  considerably  according  to  the  consistence  of  the 
parts.  The  following  is  a  list  of  the  quantities  in  the  most  important  fluids 
and  solids  (Robin  and  Verdeil)  : 


r2 


£ 


C£ 


SUBSTANCES  WHICH  PASS  THROUGH  THE  ORGANISM.    431 

TABLE   OF   QUANTITIES   OF   WATER. 

Tarts  per  1.000. 

r  In  the  enamel  of  the  teeth 2 

In  epithelial  desquamation 37 

In  teeth 100 

In  bones 130 

In  tendons  (Burdach) 500 

In  articular  cartilages 550 

In  skin  (Weinholt) 575 

In  liver  (Frommherz  and  Gugert) 618 

In  muscles  of  man  (Bibra) 725 

[  In  ligaments  (Chevreul) 768 

f  In  the  blood  of  man  (Becquerel  and  Rodier) 780 

In  milk  of  the  human  female  (Simon) 887 

In  chyle  of  man  (Rees) 904 

In  bile 905 

3  ,  In  urine 933 

~     In  human  lymph  (Tiedemann  and  Gmelin) 960 

In  human  saliva  (Mitscherlich) 983 

In  gastric  juice 984 

In  perspiration 986 

Lin  tears 990 

Uses  of  Water. — After  what  has  been  stated  with  regard  to  the  condition 
in  which  water  exists  in  the  body,  there  remains  but  little  to  say  concerning 
its  uses.  As  a  constituent  of  organized  tissues,  it  gives  to  cartilage  its  elas-  « 
ticity,  and  to  tendons  their  pliability  and  toughness ;  it  is  necessary  to  the 
power  of  resistance  of  the  bones,  and  it  is  essential  to  the  proper  consistence 
of  all  parts  of  the  body.  It  also  has  other  important  uses,  as  a  solvent. 
Soluble  articles  of  food  are  introduced  in  solution  in  water.  The  excremen- 
titious  products,  which  generally  are  soluble  in  water,  are  dissolved  by  it  in 
the  blood,  are  carried  to  the  organs  of  excretion,  and  are  discharged  in  a 
watery  solution  from  the  body. 

Origin  and  Discharge  of  Water. — It  is  evident  that  a  great  proportion  of 
the  water  in  the  organism  is  introduced  from  without,  in  the  fluids  and  in 
the  watery  constituents  of  all  kinds  of  food ;  but  water  is  also  formed  in  the 
body  by  a  direct  union  of  oxygen  and  hydrogen.  The  evidences  of  forma- 
tion of  water  in  the  body  have  already  been  given,  in  connection  with  the 
question  of  water  considered  as  a  product  of  excretion,  and  will  be  again  dis- 
cussed in  treating  of  the  relations  of  water  to  the  processes  of  calorification. 
In  the  discharge  of  water  by  the  kidneys  and  skin,  it  has  long  been  observed 
that  in  point  of  activity  these  two  emunctoriea  bear  a  certain  relation  to 
each  other.  When  the  skin  is  inactive,  as  in  cold  weather,  the  kidneys  dis- 
charge a  large  quantity  of  water ;  and  when  the  skin  is  active,  the  quantity 
of  water  discharged  by  the  kidneys  is  proportionally  diminished. 

Sodium  Chloride. — Sodium  chloride  is  next  in  importance,  as  an  inor- 
ganic constituent  of  the  organism,  to  water.  It  is  found  in  the  body  at  all 
periods  of  life,  existing  even  in  the  ovum.  It  exists  in  all  the  fluids  and  sol- 
ids of  the  body,  with  the  single  exception  of  the  enamel  of  the  teeth.  The 
exact  quantity  in  the  entire  body  has  never  been  ascertained  ;  nor,  indeed, 


432  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

has  any  accurate  estimate  been  made  of  the  quantity  contained  in  the  vari- 
ous tissues,  for  all  the  chlorides  are  generally  estimated  together.  It  exists 
in  greatest  proportion  in  the  fluids,  giving  to  some  of  them,  as  the  tears  and 
perspiration,  a  distinctly  saline  taste.  The  following  table  gives  the  quanti- 
ties found  in  some  of  the  most  important  of  the  fluids  and  solids : 

TABLE    OF    QUANTITIES    OF    CHLORIDES. 

Parts  per  1,000. 
In  blood,  human  (Leiimann) 4-210 

In  chyle  (Lehrnann) 5-310 

In  lymph  (Nasse) 4-120 

In  milk,  human  (Lehmann) 0-870 

In  saliva,  human  (Lehmann) 1-530 

In  perspiration,  human  (mean  of  three  analyses,  Piutti) 3-433 

In  urine  (maximum)  }  I 7-280 

In  urine  (mean) >  Valentin.  \ 4-610 

In  urine  (minimum)  )  ' 2-400 

In  fascal  matters  (Berzelius) 3-010 

Uses  of  Sodium  Chloride. — The  uses  of  sodium  chloride  are  undoubtedly 
important,  but  are  not  yet  fully  understood.  While  it  enters  into  the  com- 
position of  the  organized  solids  and  semi-solids,  as  an  important  and  essential 
constituent,  it  seems  to  exercise  its  chief  office  in  the  liquids.  It  is  the  so- 
dium chloride  particularly  which  regulates  the  quantity  of  water  entering 
into  the  composition  of  the  blood-corpuscles,  thereby  preserving  their  form 
and  consistence ;  and  it  seems  to  perform  an  analogous  office  with  regard  to 
the  other  semi-solids  of  the  body.  The  following  brief  statement  expresses 
the  general  uses  of  this  substance  in  the  economy  : 

"  Common  salt  is  intermediate  in  certain  general  processes  and  does  not 
participate  by  its  elements  in  the  formation  of  organs  "  (Liebig). 

In  the  first  place,  the  fluids  of  the  body  are  generally  intermediate  in  their 
uses,  containing  nutritious  matters,  which  are  destined  to  be  appropriated  by 
the  tissues  and  organs,  and  excrementitious  matters,  which  are  to  be  separated 
from  the  body.  In  the  blood  and  chyle,  sodium  chloride  is  found  in  greatest 
abundance.  In  the  nutrition  of  tissues  and  organs,  sodium  chloride  is  not 
deposited  in  any  considerable  quantity,  but  it  seems  to  regulate  the  general 
process,  at  least  to  a  certain  extent.  In  all  civilized  countries  salt  is  used  ex- 
tensively as  a  condiment,  and  it  undoubtedly  facilitates  digestion  by  rendering 
the  food  more  savory  and  increasing  the  flow  of  the  digestive  fluids ;  here, 
likewise,  acting  simply  as  an  intermediate  agent.  There  is  nothing  more 
general  among  men  and  animals  than  this  desire  for  common  salt.  In  the 
experiments  made  by  Dailly  on  sheep  and  by  Boussingault  on  bullocks,  de- 
priving these  animals  as  nearly  as  possible  of  common  salt  for  a  number  of 
months,  the  general  nutrition  was  affected  without  any  marked  change  in 
special  tissues  or  organs. 

It  is  significant  that  the  quantity  of  sodium  chloride  existing  in  the  blood 
is  not  subject  to  variation,  but  that  an  excess  introduced  with  the  food  is 
thrown  off  by  the  kidneys.  The  quantity  in  the  urine,  then,  bears  a  relation 
to  the  quantity  introduced  with  food,  but  the  proportion  in  the  blood  is  nearly 


SUBSTANCES  WHICH  PASS  THROUGH  THE  ORGANISM.    433 

constant.  This  is  another  fact  in  favor  of  the  view  that  the  presence  of  a 
definite  quantity  of  common  salt  in  the  circulating  fluid  is  essential  to  normal 
nutrition. 

Origin  and  Discharge  of  Sodium  Chloride. — Sodium  chloride  is  always 
introduced  with  food,  in  the  condition  in  which  it  is  found  in  the  body.  It 
is  contained  in  the  substance  of  all  kinds  of  food,  animal  and  vegetable ;  but 
in  the  herbivora  and  in  man,  this  source  is  not  sufficient  to  supply  the  wants 
of  the  system,  and  it  is  introduced,  therefore,  as  salt.  The  quantity  which  is 
discharged  from  the  body  has  been  estimated  by  Barral  to  be  somewhat  less 
than  the  quantity  introduced,  about  one-fifth  disappearing ;  but  these  esti- 
mates are  not  entirely  accurate,  for  the  quantity  thrown  off  in  the  perspira- 
tion has  never  been  directly  ascertained.  It  exists  in  the  blood  in  connection 
with  potassium  phosphate,  and  a  certain  quantity  is  lost  in  a  double  decom- 
position which  takes  place  between  these  two  salts,  resulting  in  the  forma- 
tion of  potassium  chloride  and  sodium  phosphate.  It  also  is  supposed  to 
furnish  sodium  to  all  the  salts  which  have  a  sodium  base,  and  a  certain  quan- 
tity, therefore,  disappears  in  this  way. 

Existing,  as  it  does,  in  all  the  solids  and  fluids  of  the  body,  sodium  chlo- 
ride is  discharged  in  all  the  excretions,  being  thrown  off  in  the  urine,  faeces, 
perspiration  and  mucus. 

Potassium  Chloride. — Potassium  chloride,  although  neither  so  important 
as  sodium  chloride  nor  so  generally  distributed  in  the  economy,  seems  to 
have  analogous  uses.  It  is  found  in  the  muscles,  liver,  milk,  chyle,  blood, 
mucus,  saliva,  bile,  gastric  juice,  cephalo-rachidian  fluid  and  urine.  It  is 
very  soluble,  and  in  these  situations  it  exists  in  solution  in  the  fluids.  Its 
quantity  in  the  fluids  has  not  been  accurately  ascertained,  as  it  has  gen- 
erally been  estimated  in  connection  with  sodium  chloride.  In  the  muscles 
it  exists,  however,  in  a  larger  proportion  than  common  salt.  In  cow's  milk, 
Berzelius  found  1-7  part  per  1,000.  Pfaff  and  Schwartz  found  T35  per 
1,000  in  cow's  milk  and  0-3  per  1,000  in  human  milk.  Of  the  uses  of  this 
salt,  little  remains  to  be  said  after  what  has  been  stated  with  regard  to  sodi- 
um chloride.  The  uses  of  these  two  salts  are  probably  identical,  although 
sodium  chloride,  on  account  of  its  greater  quantity  in  the  fluids  and  its  uni- 
versal distribution,  is  by  far  the  more  important. 

Origin  and  Discharge  of  Potassium  Chloride. — This  substance  has  two 
sources ;  one  in  the  food,  existing,  as  it  does,  in  muscular  tissue,  milk  etc., 
and  the  other  in  a  chemical  reaction  between  potassium  phosphate  and  sodi- 
um chloride,  forming  potassium  chloride  and  sodium  phosphate.  That  this 
decomposition  takes  place  in  the  body,  is  evident  from  the  fact  that  the  in- 
gestion  of  a  considerable  quantity  of  common  salt  has  been  found,  in  the 
sheep,  to  increase  the  quantity  of  potassium  chloride  in  the  urine,  without 
having  any  influence  upon  the  quantity  of  sodium  chloride.  Potassium  chlo- 
ride is  discharged  from  the  body  in  the  urine  and  in  mucus. 

Calcium  Phosphate. — This  salt  is  found  in  all  the  solids  and  fluids  of  the 
body.  As  it  is  always  united,  in  the  solids,  with  organic  substances  as  an 
important  element  of  constitution,  it  'is  hardly  second  in  importance  to  water. 


434  NUTRITION-ANIMAL  HEAT  AND  FORCE. 

It  differs  in  its  uses  so  essentially  from  the  chlorides,  that  they  are  hardly  to 
be  compared.  It  is  insoluble  in  water,  but  is  held  in  solution  in  the  fluids  of 
the  body  by  virtue  of  free  carbon  dioxide,  the  bicarbonates  and  sodium  chlo- 
ride. In  the  solids  and  semi-solids,  the  condition  of  its  existence  is  the  same 
as  that  of  water ;  i.  e.  it  is  incorporated  with  the  organic  substance  character- 
istic of  the  tissue,  is  one  of  its  essential  constituents,  and  can  not  be  com- 
pletely separated  without  incineration.  Nothing  need  be  added  here  with 
regard  to  this  mode  of  union  in  the  body,  of  organic  and  inorganic  substances, 
after  what  has  been  said  with  regard  to  water. 

The  following  table  gives  the  relative  quantities  of  calcium  phosphate  in 
various  situations : 


TABLE   OF    QUANTITIES   OF    CALCIUM    PHOSPHATE. 

Parts  per  1,000. 

In  arterial  blood.  <pialeandMarchal( 0'79 

In  venous  blood.  (                                          ( 0-76 

In  milk,  human  (Pfaff  and  Schwartz) 2-50 

In  saliva  (Wright) 0-60 

In  urine,  proportion  to  weight  of  ash  (Fleitmann) 25-70 

In  excrements  (Berzelius) 40-00 

In  bone  (Lassaigne) 400-00 

In  the  vertebrae  of  a  rachitic  patient  (Bostoek) 136-00 

In  teeth  of  an  infant  one  day  old  .  ]                      f    510-00 

In  teeth  of  the  adult I                      I   610-00 

In  teeth,  at  eighty-one  years |  Lassalgne-  -j   660-00 

In  the  enamel  of  the  teeth I                      I   885-00 

By  this  table  it  is  seen  that  calcium  phosphate  exists  in  very  small  quan- 
tity in  the  fluids  but  is  abundant  in  the  solids.  In  the  latter,  the  quantity 
is  in  proportion  to  the  hardness  of  the  structure,  the  quantity  in  enamel,  for 
example,  being  more  than  twice  that  in  bone.  The  variations  in  quantity 
with  age  are  very  considerable.  In  the  teeth  of  an  infant  one  day  old,  Las- 
saigne found  510  parts  per  1,000 ;  in  the  teeth  of  an  adult,  610  parts ;  and 
in  the  teeth  of  an  old  man  of  eighty-one  years,  660  parts.  This  increase  in  the 
calcareous  constituents  of  the  bones,  teeth  etc.,  in  old  age  is  very  marked ; 
and  in  extreme  old  age  they  are  deposited  in  considerable  quantity  in  situa- 
tions where  there  existed  but  a  small  proportion  in  adult  life.  The  system 
seems  to  gradually  lose  the  property  of  appropriating  to  itself  organic  mat- 
ters ;  and  although  articles  of  food  may  be  digested  as  well  as  ever,  the  power 
of  assimilation  by  the  tissues  is  diminished.  The  bones  become  brittle,  and 
fractures,  therefore,  are  common  at  this  period  of  life,  when  dislocations  are 
almost  unknown.  Inasmuch  as  the-  efficiency  of  organs  depends  mainly  upon 
organic  matters,  the  system  actually  wears  out,  and  this  progressive  change 
finally  unfits  certain  parts  for  their  various  offices.  An  individual,  if  he 
escape  accidents  and  die  of  old  age,  passes  away  by  a  simple  wearing  out  of 
some  essential  part  or  parts  of  the  organism. 

Uses  of  Calcium  Phosphate. — This  substance,  as  before  remarked,  enters 
largely  into  the  constitution  of  the  solids  of  the  body.  In  the  bones  its  office 
is  most  apparent.  Its  existence,  in  suitable  proportion,  is  necessary  to  the 


SUBSTANCES  WHICH  PASS  THROUGH  THE  ORGANISM.    435 

mechanical  uses  of  these  parts,  giving  them  their  power  of  resistance  without 
rendering  them  too  brittle.  It  is  more  abundant  in  the  bones  of  the  lower 
extremities,  which  have  to  sustain  the  weight  of  the  body,  than  in  the  upper 
extremities ;  and  in  the  ribs,  which  are  elastic  rather  than  resisting,  it  exists 
in  less  quantity  than  in  the  bones  of  the  arm. 

The  necessity  of  a  proper  proportion  of  calcium  phosphate  in  the  bones 
is  made  evident  by  cases  of  disease.  In  rachitis,  where,  as  is  seen  by  the 
table,  its  quantity  is  very  much  diminished,  the  bones  being  unable  to  sus- 
tain the  weight  of  the  body  become  deformed ;  and  finally,  when  calcium 
phosphate  is  deposited,  they  retain  their  distorted  shape. 

Origin  and  Discharge  of  Calcium  Phosphate. — The  origin  of  calcium 
phosphate  is  exclusively  from  the  external  world.  It  enters  into  the  consti- 
tution of  food  and  is  discharged  in  the  faeces,  urine  and  other  matters  thrown 
off  by  the  body.  Its  proportion  in  the  urine  is  very  variable. 

Calcium  Carbonate. — This  salt  exists  in  the  bones,  teeth,  cartilage,  internal 
ear,  blood,  sebaceous  matter  and  sometimes  in  the  urine.  It  exists  as  a  nor- 
mal constituent  of  the  urine  in  some  herbivora  but  not  in  the  carnivora  or 
in  man.  It  is  most  appropriately  considered  immediately  after  calcium  phos- 
phate, because  it  is  the  salt  next  in  importance  in  the  constitution  of  the 
bones  and  teeth.  In  these  structures  it  exists  intimately  combined  with  the 
organic  matter,  under  the  same  conditions  as  the  phosphates,  and  it  has  analo- 
gous uses.  In  the  fluids  it  exists  in  small  quantity  and  is  held  in  solution 
by  virtue  of  free  carbon  dioxide  and  potassium  chloride. 

Calcium  carbonate  is  the  only  example  of  an  inorganic  salt  existing  un- 
combined  and  in  a  crystalline  form  in  the  body.  In  the  internal  ear  it  is 
found  in  this  form  and  has  some  office  connected  with  audition. 

TABLE   OF    QUANTITIES   OF   CALCIUM   CARBONATE. 

Parts  per  1,000. 

In  bone,  human  (Berzelius) 113-00 

"      "          "        (Marchand) 102-00 

';      "          "        (Lassaigne) 76-00 

In  teeth  of  an  infant  one  day  old )  f    140-00 

In  teeth  of  an  adult \  Lassaigne.  -j    100-00 

In  teeth  of  an  old  man,  eighty-one  years  .  )  (    10-00 

In  urine  of  the  horse  (Boussingault) 10-82 

Origin  and  Discharge  of  Calcium  Carbonate. — This  salt  is  introduced  into 
the  body  with  food,  held  in  solution  in  water  by  the  carbon  dioxide,  which  is 
always  present  in  small  quantity.  It  is  also  formed  in  the  body,  particularly 
in  the  herbivora,  by  a  decomposition  of  the  calcium  tartrates,  malates,  citrates 
and  acetates  contained  in  the  food.  These  salts,  meeting  with  carbon  diox- 
ide, are  decomposed  and  calcium  carbonate  is  formed.  It  is  probable  that 
in  the  human  subject  some  of  it  is  changed  into  calcium  phosphate  and  in 
this  form  is  discharged  in  the  urine ;  but  it  has  not  been  definitely  ascertained 
when  and  how  this  change  takes  place. 

Sodium  Carbonate. — This  salt  is  found  in  the  blood  and  saliva,  giving  to 
these  fluids  their  alkalinity ;  in  the  urine  of  the  human  subject  when  it  is 


4:30  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

alkaline  without  being  ammoniacal ;  in  the  urine  of  the  herbivora ;  and  in 
the  lymph,  cephalo-rachidian  fluid  and  bone.  The  analyses  by  different 
chemists,  with  regard  to  this  substance,  are  very  contradictory,  on  account  of 
its  formation  during  the  process  of  incineration ;  but  there  is  no  doubt  that 
it  is  found  in  the  above  situations.  The  following  table  gives  the  quanti- 
ties which  have  been  found  in  some  of  the  fluids  and  solids : 

TABLE   OF   QUANTITIES    OF   SODIUM    CARBONATE. 

Parts  per  1,000. 

In  blood  of  the  ox  (Marcet) 1-62 

In  lymph  (Nasse) 0-56 

In  cephalo-rachidian  fluid  (Lassaigne) 0-60 

In  compact  tissue  of  the  tibia  in  a  male  of  38  years  (Valentin) 2-00 

In  spongy  tissue  of  the  same  (Valentin) 0*70 

Uses  of  Sodium  Carbonate. — This  substance  has  a  tendency  to  maintain 
the  fluidity  of  the  albuminoid  constituents  of  the  blood,  and  it  assists  in  pre- 
serving the  form  and  consistence  of  the  blood-corpuscles.  Its  office  in  nutri- 
tion is  rather  accessory,  like  that  of  sodium  chloride,  than  essential,  like  cal- 
cium phosphate,  in  the  constitution  of  certain  structures. 

Origin  and  Discharge  of  Sodium  Carbonate. — This  substance  is  not  intro- 
duced into  the  body  as  sodium  carbonate,  but  it  is  formed,  as  is  calcium 
carbonate  in  part,  by  a  decomposition  of  the  malates,  tartrates  etc.,  which 
exist  in  fruits.  It  is  discharged  occasionally  in  the  urine  of  the  human  sub- 
ject, and  a  great  part  of  it  is  decomposed  in  the  lungs,  carbon  dioxide  being 
set  free,  which  latter  is  discharged  in  the  expired  air. 

Potassium  Carbonate. — This  salt  exists  particularly  in  herbivorous  ani- 
mals. It  is  found  in  the  human  subject  under  a  vegetable  diet.  Under  the 
heads  of  uses,  origin  and  discharge,  what  has  been  said  with  regard  to  sodium 
carbonate  will  apply  to  potassium  carbonate. 

Magnesium  Carbonate  and  Sodium  Bicarbonate. — It  is  most  convenient 
to  take  up  these  two  salts  in  connection  with  the  other  carbonates,  though 
they  are  among  the  least  important  of  the  inorganic  constituents  of  the 
body.  Traces  of  magnesium  carbonate  have  been  found  in  the  blood  of  man, 
and  it  exists  normally  in  considerable  quantity  in  the  urine  of  herbivora.  In 
the  human  subject  it  is  discharged  in  the  sebaceous  matter. 

Liebig  has  indicated  the  presence  of  sodium  bicarbonate  in  the  blood. 
In  this  form  a  certain  quantity  of  carbon  dioxide  is  carried  to  the  lungs,  to 
be  exhaled  in  the  expired  air. 

Magnesium  Phosphate,  Sodium  Phosphate  (neutral)  and  Potassium 
Phosphate. — These  salts  are  found  in  all  the  fluids  and  solids  of  the  body, 
though  not  in  a  very  large  proportion  as  compared  with  calcium  phosphate. 
In  their  relations  to  organized  structures,  they  are  analogous  to  calcium 
phosphate,  entering  into  the  composition  of  the  tissues  and  existing  there  in 
a  state  of  intimate  combination.  They  are  all  taken  into  the  body  with  food, 
especially  by  the  carnivora,  in  the  fluids  of  which  they  are  found  in  much 
greater  abundance  than  the  carbonates,  which  latter  are  in  great  part  the 
result  of  the  decomposition  by  carbon  dioxide  of  the  malates,  tartrates,  oxa- 


SUBSTANCES  CONSUMED  IN  THE  ORGANISM.  437 

lates  etc.  With  respect  to  their  uses,  it  can  only  be  said  that  with  calcium  phos- 
phate they  go  to  form  the  organized  structures  of  which  they  are  necessary 
constituents.  They  are  discharged  from  the  body  in  the  urine  and  faeces. 

Sodium  Sulphate,  Potassium  Sulphate  and  Calcium  Sulphate. — Sodium 
sulphate  and  potassium  sulphate  are  identical  in  their  situations  and  appar- 
ently in  their  uses.  They  are  found  in  all  the  fluids  and  solids  of  the  body 
except  in  the  milk,  bile  and  gastric  juice.  Their  origin  in  the  body  is  from 
the  food,  in  which  they  are  contained  in  small  quantity,  and  they  are  dis- 
charged in  the  urine.  Their  chief  office  appears  to  be  in  the  blood,  where 
they  tend  to  preserve  the  fluidity  of  the  albuminoid  matters  and  the  form 
and  consistence  of  the  blood-corpuscles.  Calcium  sulphate  is  found  in  the 
blood  and  fasces.  It  is  introduced  into  the  body  in  solution  in  the  water 
which  is  used  as  drink,  and  it  is  discharged  in  the  faeces.  Its  office  is  not 
understood  and  is  probably  not  very  important. 

Ammonium  Chloride. — This  substance  has  simply  been  indicated  by 
chemists  as  existing  in  the  gastric  juice  of  ruminants,  the  saliva,  tears  and 
urine.  It  is  discharged  in  the  urine,  in  which  it  exists  in  the  proportion  of 
0-41  part  per  1,000  (Simon).  Its  origin  and  uses  are  unknown.  Various 
combinations  of  bases  with  organic  acids  taken  as  food,  as  the  acetates,  tar- 
trates  etc.,  found  in  fruits,  undergo  decomposition  in  the  body  and  are  trans- 
formed into  carbonates.  In  this  form  they  behave  precisely  like  the  other 
inorganic  salts. 

SUBSTANCES   CONSUMED    IN   THE    ORGANISM. 

All  of  the  assimilable  organic  matters  taken  as  food  are  consumed  in  the 
organism,  and  none  are  ever  discharged  from  the  body  in  health  in  the  form 
in  which  they  entered.  The  matters  thus  consumed  in  nutrition  have  been 
divided  into  nitrogenized  and  non-nitrogenized  ;  and  although  they  both  dis- 
appear in  the  organism,  they  possess  certain  marked  differences  in  their  prop- 
erties and  probably,  also,  in  their  relations  to  nutrition. 

Nitrogenized  Constituents  of  the  Body  (Albuminoids].  —  The  organic 
constituents  of  the  body  are  composed  of  carbon,  hydrogen,  oxygen,  nitro- 
gen and  sulphur.  The  exact  proportions  of  these  elements  are  not  definitely 
fixed,  and  the  nitrogenized  matters  may  change  in  their  general  characters 
without  undergoing  corresponding  changes  in  their  actual  ultimate  constitu- 
tion, unless  it  be  in  the  arrangement  of  their  atoms.  They  are  coagulable 
and  non-crystallizable.  They  possess  certain  properties  in  common  with 
each  other,  which  have  already  been  described  more  or  less  fully  in  connec- 
tion with  the  physiological  history  of  the  blood,  alimentation,  the  secreted 
fluids  etc.  One  of  these  properties  is  a  tendency  to  decomposition  by  putre- 
faction, under  certain  conditions  of  heat  and  moisture.  They  also  undergo 
certain  changes  under  chemical  manipulation,  analogous  to  those  already 
described  as  effected  by  the  prolonged  action  of  the  pancreatic  juice.  The 
type  of  substances  of  this  class  is  the  albumin  of  white  of  egg,  and  as  a 
class,  they  are  generally  known  as  albuminoids.  Artificial  subdivisions  of 
these  substances  have  been  made  into  proteids  and  albuminoids,  the  latter 


438  NUTRITION-- ANIMAL  HEAT  AND  FORCE. 

name,  in  this  subdivision,  being  restricted  to  certain  albuminoids  which 
closely  resemble  proteids  but  possess  some  distinctive  characters.  Inasmuch 
as  proteine  is  an  hypothetical  compound  and  the  so-called  proteids  do  not 
differ  much  from  other  nitrogenized  substances,  it  seems  better  to  designate 
the  entire  class  as  albuminoids. 

The  so-called  proteids  are  the  albuminoid  constituents  of  the  blood, 
lymph  and  chyle,  and  the  characteristic  albuminoid  constituents  of  the  vari- 
ous tissues.  These  are  sometimes  called  colloids.  They  pass  through  mem- 
branes with  difficulty,  or  are  very  slightly  osmotic.  In  this  regard  they  pre- 
sent a  striking  contrast  to  the  peptones,  which  are  very  osmotic,  passing 
easily  through  animal  membranes.  This  distinction  is  important,  and  it  has 
already  been  fully  described  in  connection  with  the  physiology  of  digestion 
and  absorption. 

Nitrogenized  matters  constitute  an  important  class  of  alimentary  sub- 
stances, and  the  corresponding  constituents  of  the  body  are  all  originally 
derived  from  food.  The  condition  of  existence  of  these  substances  in  the 
body  is  always  one  of  union  with  more  or  less  of  the  class  of  inorganic  mat- 
ters. Nitrogenized  matters  are  found  in  all  of  the  tissues  and  liquids  of  the 
body,  except  the  bile  and  urine.  They  undergo  changes  in  digestion  before 
they  become  a  part  of  the  blood,  they  are  changed  in  the  blood  into  the 
nitrogenized  constituents  of  this  fluid  and  are  again  changed  as  they  are  de- 
posited in  the  tissues  in  the  process  of  nutrition.  They  are  not  discharged 
from  the  body  in  health,  but  are  destroyed  or  changed  into  excrementftious 
matters,  chiefly  urea,  and  in  this  form  are  eliminated  in  the  excretions.  An 
excess  of  these  substances  taken  as  food  is  not  discharged  in  the  faeces,  nor 
does  it  pass  out,  in  the  form  in  which  it  entered,  in  the  urine ;  but  it  under- 
goes digestion,  becomes  absorbed  by  the  blood,  and  increases  the  quantity  of 
nitrogenized  excrementitious  matters  discharged,  particularly  the  urea.  This 
fact  is  shown  by  the  great  increase  in  the  elimination  of  urea  produced  by 
an  excess  of  nitrogenized  food.  Whether  the  nitrogenized  matter  that  is  /iot 
actually  needed  in  nutrition  be  changed  into  urea  in  the  blood,  in  the  so- 
called  luxus-consumption  process,  or  whether  it  be  appropriated  by  the  tissues, 
increasing  the  activity  of  their  disassimilation,  is  a  question  difficult  to  deter- 
mine experimentally.  Certain  it  is,  however,  that  an  excess  of  nitrogen- 
ized food  is  thrown  off  in  nearly  the  same  way  as  an  excess  of  inorganic 
matter  ;  the  difference  being  that  the  latter  passes  out  in  the  form  in  which 
it  has  entered,  and  the  former  is  discharged  in  the  form  of  nitrogenized  ex- 
crementitious matters. 

The  nutrition  of  the  nitrogenized  constituents  of  the  tissues  may  be  greatly 
modified  by  the  supply  of  new  matter.  For  example,  a  diet  composed  of  nitro- 
genized matter  in  a  readily  assimilable  form  will  undoubtedly  affect  favorably 
the  development  of  the  corresponding  tissues  of  the  body ;  and  on  the  other 
hand,  a  deficiency  in  the  supply  will  produce  a  corresponding  diminution  in 
power  and  development.  The  modifications  in  nutrition  due  to  supply  have, 
however,  certain  well  defined  limits.  As  regards  the  muscular  tissue,  proper 
exercise  increases  nutritive  activity,  the  development  and  power  of  muscles 


NON-NITROGENIZED  CONSTITUENTS  OF  THE  BODY.        439 

and  the  capacity  for  muscular  Avork  and  endurance.  The  nutritive  activity 
of  other  parts  and  organs  is  limited  and  is  not  sensibly  affected  by  an  excess 
of  nitrogenized  food. 

In  addition  to  the  albuminoids  of  the  blood,  lymph,  chyle  and  secreted 
fluids,  and  those  which  have  been  described  as  alimentary  matters,  the  fol- 
lowing have  been  found  in  various  tissues  and  organs  of  the  body. 

Cystalline,  a  nitrogenized  substance  in  the  crystalline  lens. 

Myosine,  a  substance  extracted  from  muscular  tissue,  of  which  it  is  the 
chief  nitrogenized  constituent. 

Keratine,  found  in  the  epidermis  and  its  appendages. 

Elastine,  the  nitrogenized  constituent  of  the  elastic  tissues. 

Osseine,  in  bones,  and  chondrine,  in  cartilage. 

Gelatine,  probably  not  a  normal  constituent  of  the  body,  but  a  substance 
formed  from  the  connective  tissues  by  prolonged  boiling  in  water. 

Certain  nitrogenized  substances  containing  phosphorus,  found  in  the 
nervous  tissues,  which  will  be  described  in  connection  with  the  chemistry  of 
the  nervous  system. 

The  changes  involved  in  nutrition,  assimilation,  or  nutritive  metabolism, 
are  apparently  dependent  upon  properties  belonging  to  the  nitrogenized  con- 
stituents of  the  tissues.  When  the  supply  of  new  matter  is  equal  to  the  de- 
structive metabolism,  the  system  is  in  what  is  called  a  condition  of  equilib- 
rium, and  the  body  neither  gains  nor  loses  in  weight.  In  growth,  the  supply 
exceeds  the  waste,  and  in  the  opposite  condition,  the  waste  exceeds  the  supply. 

Certain  liquids  and  tissues  of  the  human  body  may  be  restored  after 
their  destruction.  The  blood  and  its  corpuscles  undergo  regeneration.  Blood- 
vessels, also,  may  be  regenerated,  being  developed  first  as  capillaries  and 
afterward  as  arteries  and  veins.  The  same  is  probably  true  of  lymphatics. 
The  epidermis  and  its  appendages  and  certain  parts  of  the  true  skin  may  be 
regenerated  after  destruction.  Muscular  substance,  after  certain  kinds  of 
degeneration  in  disease,  as  in  fevers,  may  be  restored.  Portions  of  nerves 
may  be  regenerated  after  division  or  exsection.  A  divided  tendon  may  become 
reunited  by  connective  tissue.  Portions  of  cartilage  or  bone  may  be  regen- 
erated, if  the  perichondrium  or  the  periosteum  remain  intact.  When  wounded 
or  lost  parts  are  not  absolutely  restored,  the  divided  tissue  is  reunited  or  the 
lost  tissue  is  supplied  by  what  is  called  cicatricial  connective  tissue. 

Non-Xitroyenized  Constituents  of  the  Body. — Under  the  head  of  alimen- 
tation, the  general  properties  of  non-nitrogenized  matters  (starch,  sugars 
and  fats)  have  been  fully  described.  These  are  important  constituents  of 
food,  but  in  themselves  they  are  incapable  of  supporting  life.  They  are 
introduced  as  food,  but  are  destroyed  in  the  organism  and  are  never  dis- 
charged from  the  body  in  health  in  the  form  in  which  they  entered. 

The  carbohydrates  (starch  and  sugars)  are  all  converted  into  glucose  in  di- 
gestion. As  glucose  they  are  taken  up  by  the  blood  and  carried  to  the  liver, 
where  they  are  in  great  part  and  probably  entirely  converted  into  glycogen. 
The  glycogen  thus  formed  is  stored  up  in  the  liver  and  is  gradually  transformed 
into  animal  sugar,  which  passes  into  the  blood  slowly  and  gradually,  and 


440  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

promptly  disappears  as  sugar,  usually  in  the  passage  of  the  blood  through 
the  lungs.  In  addition  to  the  glycogen  formed  from  the  carbohydrates  of 
food,  the  liver  is  capable  of  forming  glycogen  from  other  substances,  as  is 
shown  by  the  presence  of  glycogen  in  the  liver  of  carnivorous  animals.  It  is 
probable  that  the  glycogen  thus  produced  is  formed  from  albuminoid  matters 
and  not  from  fats.  The  exact  mechanism  of  the  destruction  of  carbohydrates 
in  the  organism  has  not  been  fully  understood,  although  it  is  admitted  that 
these  substances  are  important  factors  in  the  production  of  animal  heat.  The 
presence  of  alcohol  in  very  small  quantity  in  the  normal  blood  has  been 
demonstrated  by  Ford  (1872).  If  this  be  admitted — and  the  accuracy  of  the 
observations  by  Ford  seems  to  have  been  absolute — it  is  reasonable  to  sup- 
pose that  the  small  quantity  of  sugar  constantly  discharged  into  the  blood  by 
the  liver  is  converted  into  alcohol,  which  is  promptly  oxidized,  being  con- 
verted into  carbon  dioxide  and  water.  The  carbohydrates,  in  contributing  to 
calorification,  are  very  important  in  saving  destruction  of  the  albuminoid 
constituents  of  the  body.  In  this  process  the  carbohydrates  and  the  fats  act 
together  and  in  the  same  way ;  and  in  this  action  they  are  capable  of  mutu- 
ally replacing  each  other. 

The  fats  taken  as  food  are  either  consumed  in  the  organism  or  are  de- 
posited in  the  form  of  adipose  tissue.  That  the  fats  are  consumed,  there  can 
be  no  doubt ;  for  in  the  normal  alimentation  of  man,  fat  is  a  constant  article, 
and  it  is  never  discharged  from  the  body.  For  a  time,  during  absorption, 
fat  may  exist  in  certain  quantity  in  the  blood ;  but  it  soon  disappears  and  is 
either  destroyed  directly  in  the  circulatory  system  or  is  deposited  in  the  form 
of  adipose  tissue  to  supply  a  certain  quantity  of  this  substance  consumed. 
That  it  may  be  destroyed  directly,  is  proved  by  the  consumption  of  fat  in 
instances  where  the  quantity  of  adipose  matter  is  insignificant ;  and  that  the 
adipose  tissue  of  the  organism  may  be  consumed,  is  shown  by  its  rapid  dis- 
appearance in  starvation. 

Formation  and  Deposition  of  Fat. — The  question  of  the  formation  of  fat 
in  the  economy  is  one  of  great  importance.  Whatever  the  exact  nature  of 
the  changes  accompanying  the  destruction  of  non-nitrogenized  matters  may 
be,  it  is  certain  that  the  fat  stored  up  in  the  body  is  consumed,  when  there 
is  a  deficiency  in  any  of  the  constituents  of  food,  as  well  as  that  which  is 
taken  into  the  alimentary  canal.  It  is  rendered  probable,  indeed,  by  the  few 
experiments  that  have  been  made  upon  the  subject,  that  obesity  increases  the 
power  of  resistance  to  inanition.  At  all  events,  in  starvation,  the  fatty  con- 
stituents of  the  body  are  the  first  to  be  consumed,  and  they  almost  entirely 
disappear  before  death.  Sugar  is  never  deposited  in  any  part  of  the  organ- 
ism, and  it  is  merely  a  temporary  constituent  of  the  blood.  If  the  sugars 
and  fats  have,  in  certain  regards,  similar  relations  to  nutrition,  and  if,  in  addi- 
tion to  the  mechanical  uses  of  fat,  it  may  be  retained  in  the  organism  for  use 
under  extraordinary  conditions,  it  becomes  important  to  ascertain  the  mech- 
anism of  its  production  and  deposition. 

The  production  of  fatty  matter  by  certain  insects,  in  excess  of  the  fat 
supplied  with  the  food,  was  established  long  ago  by  the  researches  of  Huber ; 


NON-NITROGENIZED  CONSTITUENTS  OF  THE  BODY.        441 

and  analogous  observations  have  been  made  upon  birds  and  mammals,  by 
Boussingault,  Under  certain  conditions  more  fat  exists  in  the  bodies  of  ani- 
mals than  can  be  accounted  for  by  the  total  quantity  of  fat  taken  as  food 
added  to  the  fat  existing  at  birth.  In  experiments  with  reference  to  the  in- 
fluence of  different  kinds  of  food  upon  the  development  of  fat,  it  has  been 
ascertained  that  fat  can  be  produced  in  animals  upon  a  regimen  sufficiently 
nitrogenized  but  deprived  of  fatty  matters ;  but  the  fact  should  be  recognized 
that  "  the  nutriment  which  produces  the  most  rapid  and  pronounced  fatten- 
ing is  precisely  that  which  joins  to  the  proper  proportion  of  albuminoid  sub- 
stances the  greatest  proportion  of  fatty  matters  "  (Boussingault). 

There  can  be  no  doubt  with  regard  to  the  formation  of  fat  in  the  organ- 
ism from  albuminoid  matters.  Where  an  excess  of  such  matters  is  taken  as 
food,  it  is  probable  that  the  albuminoid  substance  is  decomposed,  and  that  a 
part  of  it  is  either  deposited  as  fat  or  is  oxidized  into  carbon  dioxide  and 
water,  and  a  part  is  discharged  from  the  body  in  the  form  of  urea. 

Theoretical  considerations  point  to  starch  and  sugar  as  the  constituents 
of  food  most  easily  convertible  into  fat,  as  they  contain  the  same  elements, 
though  in  different  proportions ;  and  it  is  more  than  probable  that  this  view 
is  correct.  It  is  said  that  in  sugar-growing  sections,  during  the  time  of 
grinding  the  cane,  the  laborers  become  excessively  fat,  from  eating  large 
quantities  of  saccharine  matter ;  and  although  there  are  no  exact  scientific 
observations  upon  this  point,  the  fact  is  generally  admitted  by  physiologists. 
Again,  it  has  been  frequently  a  matter  of  individual  experience  that  sugar 
and  starch  are  favorable  to  the  deposition  of  fat,  especially  when  there  is  a 
constitutional  tendency  to  obesity.  Carbohydrates  added  in  quantity  to  a 
nitrogenized  diet  favor  the  formation  of  fat.  The  fat  may  be  formed  from 
the  carbohydrates  either  directly  (Lawes  and  Gilbert)  or  indirectly.  If 
formed  indirectly,  it  is  probable  that  the  carbohydrates  are  oxidized  into  car- 
bon dioxide  and  water,  and  that  this  saves,  to  a  certain  extent,  destruction  of 
albuminoids.  The  albuminoids  are  split  up  into  fats,  which  are  deposited 
in  the  body,  and  into  urea. 

Fatty  degeneration  occurs  in  tissues  during  certain  retrograde  processes. 
The  muscular  fibres  of  the  uterus,  during  the  involution  of  this  organ  after 
parturition,  become  filled  with  fatty  granulations.  Long  disuse  of  any  part 
will  produce  such  changes  in  its  power  of  appropriating  nitrogenized  matter 
for  its  regeneration,  that  it  soon  becomes  atrophied  and  altered.  A  portion  of 
the  nitrogenized  constituents  of  the  tissue,  under  these  conditions,  is  changed 
into  fatty  matter.  The  fat  is  here  inert,  and  it  takes  the  place  of  the  sub- 
stance that  gives  to  the  part  its  characteristic  properties.  These  changes  are 
observed  in  muscles  and  nerves  that  have  been  long  disused  or  paralyzed. 
If  the  change  be  not  too  extensive,  the  fat  may  be  made  to  disappear  and 
the  part  will  return  to  its  normal  constitution,  under  appropriate  exercise ; 
but  frequently  the  alteration  has  proceeded  so  far  as  to  be  irremediable  and 
permanent. 

It  is  Difficult  to  explain  the  tendency  to  obesity  observed  in  some  indi- 
viduals, which  is  very  often  hereditary.  Such  persons  will  become  fat  upon 


442  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

a  comparatively  low  diet,  while  others  deposit  but  little  adipose  matter,  even 
when  the  regimen  is  abundant.  It  is  to  be  noted,  however,  that  the  former 
are  generally  addicted  to  the  use  of  starchy,  saccharine  and  fatty  articles  of 
food,  while  the  latter  consume  a  greater  proportion  "of  nitrogenized  matter. 
It  is  not  an  uncommon  remark  that  the  habit  of  taking  large  quantities  of 
liquids  favors  the  formation  of  fat ;  but  it  is  not  easy  to  find  any  scientific 
basis  for  such  an  opinion.  The  formation  of  fat  by  any  particular  organ  or 
organs  in  the  body  has  not  been  determined. 

Condition  under  which  Fat  exists  in  the  Organism. — It  is  said  that  fat, 
combined  with  phosphorus,  is  united  with  nitrogenized  matter  in  the  sub- 
stance of  the  nervous  tissue ;  but  its  condition  here  is  not  well  understood. 
A  small  quantity  of  fat  is  contained  in  the  blood-corpuscles  and  is  held  in 
solution  in  the  bile ;  but  with  these  exceptions,  fat  always  exists  in  the  body 
isolated  and  uncombined  with  nitrogenized  matter,  in  the  form  of  granules 
or  globules  and  of  adipose  tissue.  The  three  varieties  of  fat  (stearine,  palmi- 
tine  and  oleine)  are  here  combined  in  different  proportions,  which  is  the 
cause  of  the  differences  in  its  consistence  in  different  situations. 

Physiological  Anatomy  of  Adipose  Tissue. — Adipose  tissue  is  found  in 
abundance  in  the  interstices  of  the  subcutaneous  areolar  tissue,  where  it  is 
sometimes  known  as  the  panniculus  adiposus.  It  is  not,  however,  to  be  con: 
founded  with  the  so-called  cellular  or  areolar  tissue,  and  is  simply  associated 
with  it  without  being  one  of  its  essential  parts;  for  the  areolar  tissue  is 
abundant  in  certain  situations,  as  the  eyelids  and  scrotum,  where  there  is  no 
adipose  matter,  and  adipose  tissue  exists  sometimes,  as  in  the  marrow  of  the 
bones,  without  any  areolar  tissue. 

Adipose  tissue  is  widely  distributed  in  the  body  and  has  important  me- 
chanical uses.  Its  anatomical  element  is  a  rounded  or  ovoid  vesicle,  -^  to 
j-J-g-  of  an  inch  (30  to  80  //,)  in  diameter,  composed  of  a  delicate,  structureless 
membrane,  ^TOTTO  °^  an  incn  (1  /*)  thick,  enclosing  fluid  contents.  The 
membrane  sometimes  presents  a  small  nucleus  attached  to  its  inner  surface. 
The  contents  of  the  vesicles  are  a  minute  quantity  of  an  albuminoid  fluid 
moistening  the  internal  surface  of  the  membrane,  and  a  mixture  of  oleine, 
palmitine  and  stearine,  nearly  liquid  at  the  temperature  of  the  body  but 
becoming  harder  on  cooling.  Little  rosettes  of  acicular  crystals  of  palmitine 
are  frequently  observed  in  the  fat-vesicles  at  a  low  temperature.  The  quan- 
tity of  fat  in  a  man  of  ordinary  development  equals  about  one-twentieth  of 
the  weight  of  the  body  (Carpenter).  The  adipose  vesicles  are  collected  into 
little  lobules,  -^  to  £  of  an  inch  (1  to  G  mm.)  in  diameter,  which  are  sur- 
rounded by  a  rather  wide  net- work  of  capillary  blood-vessels.  Close  examina- 
tion of  these  vessels  shows  that  they  frequently  surround  individual  fat-cells, 
in  the  form  of  single  loops.  There  is  no  distribution  of  nerves  or  lymphatics 
to  the  elements  of  adipose  tissue. 

Conditions  which  influence  Nutrition. — Physiologists  know  more  con- 
cerning the  conditions  that  influence  the  general  process  of  nutrition  than 
about  the  nature  of  the  process  itself.  It  will  be  seen,  for  example,  in  studying 
the  nervous  system,  that  there  are  nerves  which  regulate,  to  a  certain  extent, 


CONDITIONS  WHICH  INFLUENCE  NUTRITION.  443 

the  nutritive  forces.  This  does  not  imply  that  nutrition  is  effected  through 
the  influence  of  the  nerves,  but  it  is  the  fact  that  certain  nerves,  by  regulat- 
ing the  supply  of  blood,  and  perhaps  by  other  influences,  are  capable  of 
modifying  the  nutrition  of  parts  to  a  very  considerable  extent. 

As  regards  the  influence  of  exercise  upon  the  development  of  parts,  it  has 
been  shown  that  this  is  not  only  desirable  but  indispensable ;  and  the  proper 
performance  of  the  offices  of  nearly  all  parts  involves  the  action  of  the  nerv- 
ous system.  It  is  true  that  the  separate  parts  of  the  organism  and  the  organ- 
ism as  a  whole  have  a  limited  existence ;  but  it  is  not  true  that  the  change 
of  nitrogenized  substances  into  effete  matters — a  process  that  is  increased  in 
activity  by  physiological  exercise — consumes,  so  to  speak,  a  definite  amount 
of  the  limited  life  of  the  parts.  Physiological  exercise  increases  disassimila- 
tion,  but  it  also  increases  the  activity  of  nutrition  and  favors  development. 
It  is  often  said  that  bodily  or  mental  effort  is  made  always  at  the  expense  of 
a  definite  amount  of  vitality  and  matter  consumed.  This  is  partly  true,  but 
mainly  false.  Work  involves  change  into  effete  matter ;  but  when  restricted 
within  physiological  limits,  it  engenders  a  corresponding  activity  of  nutri- 
tion, assuming,  of  course,  that  the  supply  from  without  be  sufficient.  Other 
things  being  equal,  a  man  would  live  longer  under  a  system  of  physiological 
exercise  of  every  part  than  if  he  made  the  least  effort  possible.  It  is,  indeed, 
only  by  such  use  of  parts,  that  they  can  undergo  proper  development  and 
become  the  seat  of  normal  nutrition.  Notwithstanding  all  these  facts,  life 
is  self-limited.  Organic  substances  are  constantly  undergoing  transforma- 
tion. In  the  living  body,  their  metabolism  is  unceasing ;  and  after  they  are 
removed  from  what  are  termed  vital  conditions,  they  change,  first  losing 
excitability,  and  afterward  decomposing  into  matters  which,  like  the  products 
of  their  disassimilation,  are  destined  to  be  appropriated  by  the  vegetable 
kingdom.  Nutrition  sufficient  to  supply  the  physiological  decay  of  parts 
can  not  continue  indefinitely.  The  forces  in  the  fecundated  ovum  lead  it 
through  a  process  of  development  that  requires,  in  the  human  subject,  more 
than  twenty  years  for  its  completion ;  and  when  development  ceases,  no  one 
can  say  why  it  becomes  arrested,  nor  can  any  sufficient  reason  be  given  why, 
with  an  adequate  and  appropriate  supply  of  material,  a  man  should  not  grow 
indefinitely.  When  the  being  is  fully  developed,  and  during  what  is  known 
as  adult  life,  the  supply  seems  to  be  about  equal  to  the  waste ;  but  after  this, 
nutrition  gradually  becomes  deficient,  and  the  deposition  of  new  matter  in 
progressive  old  age  becomes  more  and  more  inadequate  to  supply  the  place 
of  the  nitrogenized  substance.  There  may  be  at  this  time,  as  an  exception, 
a  considerable  deposition  of  fat ;  but  the  nitrogenized  matter  is  always  de- 
ficient, and  the  proportion  of  inorganic  matter  combined  with  it  is  increased. 

There  can  be  little  if  any  doubt  that  the  properties  which  involve  the 
regeneration  or  nutrition  of  parts  reside  in  the  organic  nitrogenized  sub- 
stance, the  inorganic  matter  being  passive,  or  having  purely  physical  uses. 
If,  therefore,  as  age  advances,  the  organic  matter  be  gradually  losing  the 
power  of  completely  regenerating  its  substance,  and  if  its  proportion  be  pro- 
gressively diminishing  while  the  inorganic  matter  is  increasing  in  quantity, 


444  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

a  time  will  come  when  some  of  the  organs  necessary  to  life  will  be  unable  to 
perform  their  office.  When  this  occurs,  there  is  death  from  old  age,  or  physio- 
logical dissolution.  This  may  be  a  gradual  failure  of  the  general  process  of 
nutrition  or  it  may  occur  in  some  one  organ  or  system  that  is  essential  to 
life. 

ANIMAL  HEAT  AND  FORCE. 

The  processes  of  nutrition  in  animals  are  always  attended  with  the  devel- 
opment and  maintenance  of  a  bodily  temperature  that  is  more  or  less  inde- 
pendent of  external  conditions.  This  is  true  in  the  lowest  as  well  as  the 
highest  animal  organizations ;  and  analogous  phenomena  have  been  observed 
in  plants.  In  cold-blooded  animals,  nutrition  may  be  suspended  by  a  dimin- 
ished external  temperature,  and  certain  of  the  functions  become  temporarily 
arrested,  to  be  resumed  when  the  animal  is  exposed  to  a  greater  heat.  This 
is  true,  to  some  extent,  in  certain  warm-blooded  animals  that  periodically 
pass  into  a  condition  of  stupor,  called  hibernation ;  but  in  man  and  most 
of  the  warm-blooded  animals,  the  general  temperature  of  the  body  can  un- 
dergo but  slight  variations.  The  animal  heat  is  nearly  the  same  in  cold  and 
in  hot  climates ;  and  if  from  any  cause  the  body  become  incapable  of  keep- 
ing up  its  temperature  when  exposed  to  cold,  or  of  moderating  it  when 
exposed  to  heat,  death  is  the  inevitable  result. 

Estimated  Quantity  of  Heat  produced  by  the  Body. — In  order  to  express 
quantities  of  heat,  it  is  necessary  to  fix  upon  some  definite  quantity  to  be 
taken  as  a  heat-unit.  In  what  is  to  follow,  a  heat-unit  is  to  be  understood 
as  the  heat  required  to  raise  the  temperature  of  one  pound  of  water  1°  Fahr. 
(pound-degree  Fahr.). 

It  has  been  calculated  that  one  heat-unit  is  equal  to  the  force  expended 
in  raising  one  pound  772  feet  or  772  pounds  one  foot  (Joule).  This  force 
is  called  a  foot-pound.  The  equivalent  of  heat  in  force  has  been  calculated 
by  estimating  the  heat  produced  by  a  certain  weight  falling  through  a  certain 
distance,  assuming  the  falling  force  to  be  precisely  equal  to  the  force  which 
has  been  used  in  raising  the  weight ;  but  physicists  have  not  actually  suc- 
ceeded in  so  completely  converting  heat  into  force  as  to  raise  one  pound  772 
feet  or  772  pounds  one  foot,  by  the  expenditure  of  one  heat-unit. 

The  heat-unit  and  its  equivalent  in  force  are,  of  course,  differently  ex- 
pressed according  to  the  metric  system.  When  heat-units  or  foot-pounds  are 
given  in  the  text,  the  equivalents,  according  to  the  metric  system,  are  given 
in  parantheses.  These  equivalents  are  as  follows : 

A  heat-unit,  according  to  the  metric  system,  or  the  heat  required  to  raise 
the  temperature  of  one  kilo,  of  water  one  degree  C.,  will  be  designated  as  a 
kilo.-degree  C. 

One  pound-degree  =  0-252  kilo.-degree  C.  One  kilo.-degree  C.  =  3-96 
(nearly  4)  pound-degrees.  A  kilogrammetre  represents  the  force  required  to 
raise  a  weight  of  one  kilogramme  one  metre.  One  foot-pound  =  O138  kilo- 
grammetre. One  kilogrammetre  =  7'24  foot-pounds.  One  pound-degree  = 
772  foot-pounds.  One  pound-degree  =  106'6  kilogrammetres.  One  kilo.- 


QUANTITY  OF  HEAT  PRODUCED  BY  THE  BODY.  445 

degree  C.  =  422*25    kilogrammetres.      One    kilo.-degree    C.  =  3,057    foot- 
pounds. 

Two  methods  have  been  employed  in  arriving  at  estimates  of  the  actual 
quantity  of  heat  produced  by  the  body  in  a  definite  time : 

1.  The  direct  method  consists  in  placing  an  animal  in  a  calorimeter  and 
measuring  the  heat  produced,  making  all  necessary  corrections.     This  has 
been  repeatedly  done,  but  the  results  obtained  have  been  very  variable  and 
not  entirely  satisfactory. 

The  observations  of  Senator  (1872)  seemed  to  fulfill  the  necessary  experi- 
mental conditions ;  and  as  an  average  of  five  observations  made  on  dogs  at 
rest  and  fasting,  he  found  a  production  of  about  4-21  heat-units  per  hour 
per  pound  weight  of  the  body  (2*34  kilo.-degree  C.  per  kilo.). 

J.  C.  Draper  (1872)  estimated  the  heat-production  in  his  own  person  by 
immersing  the  body  in  water.  In  this  observation,  many  errors  must  have 
escaped  correction ;  but  the  results  agreed  remarkably  with  those  obtained 
by  Senator.  Deducting  1°  Fahr.  of  heat  lost  by  the  body,  as  shown  by  a 
reduction  in  the  general  temperature,  and  imparted  to  the  water — a  correc- 
tion not  made  by  Draper — about  4  heat-units  were  produced  per  hour  per 
pound  weight  of  the  body  (2*22  kilo.-degrees  C.  per  kilo.).  According  to 
the  estimate  of  Draper,  a  man  weighing  140  pounds  (63*5  kilos.)  would  pro- 
duce 13,440  heat-units  (3-383  kilo.-degrees  C.)  in  twenty-four  hours  of  repose. 
This  would  be  equal  to  10,375,680  foot-pounds,  or  about  1,430,000  kilogram- 
metres. 

An  important  element  of  inaccuracy  in  all  direct  observations  and  one, 
indeed,  which  it  seems  impossible  to  correct  absolutely,  is  due  to  the  great 
variations  in  heat-production  with  digestion,  conditions  of  muscular  repose 
or  exercise,  external  temperature  etc.  Another  source  of  error  is  the  diffi- 
culty in  estimating  the  heat  lost  by  the  body  and  not  actually  produced  dur- 
ing the  time  of  the  observation.  These  possible  inaccuracies  are  so  impor- 
tant and  so  evident,  that  the  results  of  direct  observations  have  not  been 
generally  accepted  by  physiologists. 

2.  The  indirect  method  consists  in  estimating  the  heat  represented  by 
oxidation,  calculated  from  the  quantity  of  oxygen  consumed  in  the  various 
processes  which  result  in  the  production  and  discharge  of  carbon  dioxide, 
water,  urea  etc.     These  estimates  have  been  compared  with  the  calculated 
heat-value  of  the  food  consumed,  and  the  results  very  nearly  correspond. 

According  to  the  estimates  of  Helmholtz,  Ranke  and  others,  by  the  in- 
direct method,  the  heat-production  is  equal  to  about  2-5  heat-units  per  hour 
per  pound  weight  of  the  body  (T39  kilo.-degree  C.  per  kilo.)  In  a  man  weigh- 
ing 180-4  pounds  (82  kilos.)  the  heat-production  in  twenty-four  hours 
(Helmholtz)  was  10,818  heat-units  (2,732  kilo.-degrees  C.).  According  to 
this  estimate,  a  man  weighing  140  pounds  (63'5  kilos.)  would  produce  8,400 
heat-units  (2,118  kilo.-degrees  C.)  in  twenty-four  hours.  This  would  be 
equal  to  6,484,800  foot  pounds,  or  about  894,500  kilogrammetres. 

Comparing  the  results  of  direct  observations,  showing  a  production  of 
about  four  heat-units  per  pound  per  hour  (2*22  kilo.-degrees  C.  per  kilo.), 

30 


446  NUTKITION— ANIMAL  HEAT  AND  FORCE. 

with  those  obtained  by  the  indirect  methods,  2*5  heat-units  per  pound  per 
hour  (1-39  kilo.-degree  C.  per  kilo.),  it  is  seen  that  the  indirect  estimates 
give  about  37^  per  cent,  less  heat  produced  than  is  given  by  direct  estimates. 
It  is  on  account  of  this  great  difference,  that  writers  are  at  a  loss  to  give 
definite  estimates  of  the  actual  quantity  of  heat  produced  by  the  body. 

A  study  of  this  subject  and  of  the  details  of  observations  both  direct 
and  indirect  has  made  it  evident  that  the  experimental  difficulties  to  be 
overcome  and  the  unavoidable  elements  of  inaccuracy  are  greater  in  the 
direct  than  in  the  indirect  method.  In  comparing  the  estimates  of  heat 
actually  produced  with  the  heat  value  of  food — which,  of  course,  is  the  ulti- 
mate source  of  heat  and  force  in  the  body — the  correspondence  is  much 
closer  if  the  indirect  estimates  be  adopted.  It  therefore  seems  more  in  ac- 
cordance with  ascertained  facts  to  adopt  the  indirect  estimates,  although  this 
can  not  be  done  without  reserve.  The  heat  produced,  then,  is  probably 
equal  to  about  2-5  heat-units  (pound-degrees)  per  hour  per  pound  weight  of 
the  body  (nearly  1-4  kilo.-degree  C.  per  kilo.)  This  is  equal  to  about  8,400 
heat-units,  or  about  2,120  kilo.-degrees  C.,  in  twenty-four  hours ;  which  is 
equal  to  about  6,500,000  foot-pounds,  or  about  900,000  kilogrammetres. 

The  normal  variations  in  the  production  of  heat  are  not  absolutely  and 
definitely  represented  by  variations  in  the  actual  temperature  of  the  body 
and  by  the  consumption  of  oxygen.  Muscular  work  may  increase  the  pro- 
duction of  heat  60  per  cent.  (Him)  while  it  increases  the  consumption  of 
oxygen  about  4£  times,  a  large  part  of  the  oxidation  being  expended  in  the 
form  of  work.  The  production  of  heat  is  diminished  in  fasting  animals 
(dogs)  by  nearly  45  per  cent.  (Senator),  after  deprivation  of  food  for  two 
days.  In  old  age  and  in  infancy,  there  is  less  heat  produced  than  in  adult 
life.  The  production  of  heat  is  less  in  females  than  in  males  and  is  less  dur- 
ing the  night  than  during  the  day.  These  points  will  be  touched  upon  again 
in  connection  with  the  normal  variations  in  the  temperature  of  the  body. 

Limits  of  Variation  in  the  Normal  Temperature  in  Man. — One  of  the 
most  common  methods  of  taking  the  general  temperature  has  been  to  intro- 
duce a  registering  thermometer  into  the  axilla,  reading  off  the  degrees  after 
the  mercury  has  become  absolutely  stationary.  Nearly  all  observations  made 
in  this  way  agree  with  the  results  obtained  by  Gavarret,  who  estimated  that 
the  temperature  in  the  axilla,  in  a  perfectly  healthy  adult  man,  in  a  temper- 
ate climate,  ranges  between  97'7°  and  99-5°  Fahr.  (36-5°  and  37'5°  C.).  Davy, 
from  a  large  number  of  observations  upon  the  temperature  under  the  tongue, 
fixed  the  standard,  in  a  temperate  climate,  at  98°  Fahr.  (36-67°  C.)  The 
axilla  and  the  tongue,  however,  being  more  or  less  exposed  to  external  influ- 
ences, do  not  exactly  represent  the  general  heat  of  the  organism ;  but  these 
are  the  situations,  particularly  the  axilla,  in  which  the  temperature  is  most 
frequently  taken  in  pathological  examinations.  As  a  standard  for  compari- 
son, it  may  be  assumed  that  the  most  common  temperature  in  these  situa- 
tions is  98°  Fahr.  (36-67°  C.)  subject  to  variations,  within  the  limits  of 
health  of  about  0-5°  Fahr.  (0-27°  C.)  below  and  1-5°  (0-82°  Fahr.  C.)  above. 

Variations  with  External  Temperature. — The  general  temperature  of  the, 


VARIATIONS  IN  THE  HEAT  OF  THE  BODY.  447 

body  varies,  though  within  very  restricted  limits,  with  extreme  changes  in 
climate.  The  results  obtained  by  Davy,  in  a  large  number  of  observations  in 
temperate  and  hot  climates,  show  an  elevation  in  the  tropics  of  0'5°  to  3°  Fahr. 
(0'27°  to  1-65°  C.).  It  is  well  known,  also,  that  the  human  body,  the  surface 
being  properly  protected,  is  capable  of  enduring  for  some  minutes  a  heat 
greater  than  that  of  boiling  water.  Under  these  conditions,  the  animal 
temperature  is  raised  but  slightly,  as  compared  with  the  intense  heat  of  the 
surrounding  atmosphere.  In  the  observations  by  Dobson,  the  temperature  was 
raised  to  99-5°  Fahr.  (37'5°  C.)  in  one  instance,  101-5°  Fahr.  (38-6°  C.)  in 
another,  and  102°  Fahr.  (38-9°  C.)  in  a  third,  when  the  body  was  exposed  to 
a  heat  of  more  than  212°  Fahr.  (100°  C.).  Delaroche  and  Berger,  however, 
found  that  the  temperature  in  the  mouth  could  be  increased  by  3°  to  9° 
Fahr.  (1-65°  to  5-05°  C.)  after  sixteen  minutes  of  exposure  to  intense  heat. 
This  was  for  the  external  parts  only ;  and  it  is  not  probable  that  the  tem- 
perature of  the  internal  organs  ever  undergoes  such  wide  variations. 

It  is  difficult  to  estimate  the  temperature  in  persons  exposed  to  intense 
cold,  as  in  Arctic  explorations,  because  care  is  always  taken  to  protect  the 
surface  of  the  body  as  completely  as  possible ;  but  experiments  have  shown 
that  the  animal  heat  may  be  considerably  reduced,  as  a  temporary  condition, 
without  producing  death.  In  the  latter  part  of  the  last  century,  Currie 
caused  the  temperature  in  a  man  to  fall  15°  Fahr.  (8-25°  C.)  by  immersion 
in  a  cold  bath  ;  but  he  could  not  bring  it  below  83°  Fahr.  (28-33°  C.)  This 
extreme  depression,  however,  lasted  only  two  or  three  minutes,  and  the  tem- 
perature afterward  returned  to  within  a  few  degrees  of  the  normal  standard. 
The  results  of  experiments  show  that  while  the  normal  variations  in  the 
temperature  in  the  human  subject,  even  when  exposed  to  great  climatic 
changes,  are  very  slight,  generally  not  more  than  two  degrees  Fahr.  (1-1°  C.), 
the  body  may  be  exposed  for  a  time  to  excessive  heat  or  cold,  and  the  extreme 
limits,  consistent  with  the  preservation  of  life,  may  be  reached.  As  far  as 
has  been  ascertained  by  direct  experiment,  these  limits  are  about  83°  and 
107°  Fahr.  (28-33°  and  41-67°  C.). 

Variations  in  Different  Parts  of  the  Body. — The  blood  becomes  slightly 
lowered  in  its  temperature  in  passing  through  the  general  capillary  circula- 
tion, but  the  difference  is  ordinarily  not  more  than  a  fraction  of  a  degree. 
This  fact  is  not  opposed  to  the  proposition  that  animal  heat  is  produced  in 
greatest  part  in  the  general  capillary  system,  as  one  of  the  results  of  nutri- 
tive action ;  for  the  blood  circulates  with  such  rapidity  that  the  heat  ac- 
quired in  the  capillaries  of  the  internal  organs,  where  little  or  none  is  lost, 
is  but  slightly  diminished  before  the  fluid  passes  into  the  arteries,  even  in 
circulating  through  the  lungs ;  and  cutaneous  evaporation  simply  moderates 
the  heat  acquired  in  the  tissues  and  keeps  it  at  the  proper  standard. 

Bernard  ascertained  that  the  blood  is  usually  0-36°  to  1-8°  Fahr.  (0-2°  to 
1°  C.)  warmer  in  the  hepatic  veins  than  in  the  aorta.  The  temperature  in 
the  hepatic  veins  is  0-18°  to  1-44°  Fahr.  (0-1°  to  0-8°  C.)  higher  than  in  the 
portal  veins.  These  results  show  that  the  blood  coming  from  the  liver  is 
warmer  than  in  any  other  part  of  the  body.  In  a  series  of  experiments  by 


448  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

Breschet  and  Becquerel,  who  were  among  the  first  to  employ  thermo-electric 
apparatus  in  the  study  of  animal  heat,  it  was  found  that  the  cellular  tissue 
was  2'5°  to  3'3°  Fahr.  (1'37°  to  1'8C  C.)  cooler  than  the  muscles.  As  regards 
the  temperature  of  the  blood  in  the  two  sides  of  the  heart,  experiments  upon 
the  lower  animals  have  been  somewhat  contradictory ;  but  there  is  no  positive 
evidence  of  any  considerable  change  in  the  temperature  of  the  blood  in  pass- 
ing through  the  lungs  in  the  human  subject.  In  the  lower  animals,  there 
probably  exist  no  constant  differences  in  temperature  in  the  two  sides  of  the 
heart.  When  the  loss  of  heat  by  the  general  surface  is  active,  as  in  animals 
with  a  slight  covering  of  hair,  the  blood  generally  is  cooler  in  the  right  cavi- 
ties ;  but  in  animals  with  a  thick  covering,  that  probably  lose  considerable 
heat  by  the  pulmonary  surface,  the  blood  is  cooler  in  the  left  side  of  the 
heart. 

Variations  at  Different  Periods  of  Life. — The  most  important  variations 
in  the  temperature  of  the  body  at  different  periods  of  life  are  observed  in  in- 
fants just  after  birth.  The  body  of  the  infant  and  of  young  mammalia 
removed  from  the  mother  presents  a  diminution  in  temperature  of  1°  to 
4°  Fahr.  (0'55°  to  2'2°  C.).  In  infancy  the  ability  to  resist  cold  is  less  than 
in  later  years;  but  after  a  few  days  the  temperature  of  the  child  nearly 
reaches  the  standard  in  the  adult,  and  the  variations  produced  by  external 
conditions  are  not  so  great. 

W.  F.  Edwards  found  that  in  certain  animals,  particularly  dogs  and  cats, 
that  are  born  with  the  eyes  closed  and  in  which  the  foramen  ovale  remains 
open  for  a  few  days,  the  temperature  rapidly  diminished  when  they  were  re- 
moved from  the  body  of  the  mother,  and  that  they  then  become  reduced  to  a 
condition  approximating  that  of  cold-blooded  animals ;  but  after  about  fifteen 
days,  this  change  in  temperature  could  riot  be  effected.  In  dogs  just  born, 
the  temperature  fell,  after  three  or  four  hours'  separation  from  the  mother, 
to  a  point  but  a  few  degrees  above  that  of  the  surrounding  atmosphere.  The 
views  advanced  by  Edwards  are  illustrated  in  instances  of  premature  birth, 
when  the  animal  heat  is  much  more  variable  than  in  infants  at  term,  and  in 
cases  of  persistence  of  the  foramen  ovale. 

In  adult  life  there  does  not  appear  to  be  any  marked  and  constant  varia- 
tion in  the  normal  temperature ;  but  in  old  age,  while  the  actual  temperature 
of  the  body  is  not  notably  reduced,  the  power  of  resisting  refrigerating  in- 
fluences is  diminished  very  considerably.  There  are  no  observations  showing 
any  constant  differences  in  the  temperature  of  the  body  in  the  sexes ;  and  it 
may  be  assumed  that  in  the  female  the  animal  heat  is  modified  by  the  same 
influences  and  in  the  same  way  as  in  the  male. 

Variations  in  the  Heat  of  the  Body  at  different  Times  of  the  Day  etc. — 
Although  the  limits  of  variation  in  the  animal  temperature  are  not  very  wide, 
certain  fluctuations  are  observed,  depending  upon  muscular  repose  or  activity, 
digestion,  sleep  etc;  It  has  been  ascertained  that  there  are  two  well  marked 
periods  in  the  day  when  the  heat  is  at  its  maximum.  These  are  at  eleven 
A.  M.  and  four  p.  M.  ;  and  while  all  observations  agree  upon  this  point,  the 
observations  of  Lichtenfels  and  Frohlich  have  shown  that  these  periods  are 


VARIATIONS  IN  THE  HEAT  OF  THE  BODY.  449 

well  marked,  even  when  no  food  is  taken.  Barensprung  and  Ladame  have 
observed  that  the  fall  in  temperature  during  the  night  takes  place  sleeping 
or  waking ;  and  that  when  sleep  is  taken  during  the  day,  it  does  not  dis- 
turb the  period  of  the  maximum,  which  occurs  at  about  four  p.  M.  Accord- 
ing to  these  experiments,  at  eleven  in  the  morning,  the  animal  heat  is  at  one 
of  its  periods  of  maximum;  it  gradually  diminishes  for  two  or  three  hours 
and  is  raised  again  to  the  maximum  at  about  four  in  the  afternoon,  when 
it  again  undergoes  diminution  until  the  next  morning.  The  variations 
amount  to  between  1°  and  2-16°  Fahr.  (0-55°  and  1-19°  C.).  The  minimum 
is  always  during  the  night. 

The  influence  of  defective  nutrition  or  of  inanition  upon  the  heat  of  the 
body  is  very  marked.  In  pigeons  the  extreme  variation  in  temperature  during 
the  day,  under  normal  conditions,  was  found  by  Chossat  to  be  1-3°  Fahr. 
(0-7°  C.).  During  the  progress  of  inanition  this  variation  was  increased  to 
5-9°  Fahr.  (3-25°  C.).  with  a  slight  diminution  in  the  absolute  temperature, 
and  the  periods  of  minimum  temperature  were  unusually  prolonged.  Imme- 
diately preceding  death  from  starvation,  the  diminution  in  temperature 
became  very  rapid,  the  rate  being  7°  to  11°  Fahr.  (3*85°  to  6°  C.)  per  hour. 
Death  usually  occurred  when  the  diminution  had  amounted  to  about  30° 
Fahr.  (16-5°  C.). 

When  the  surrounding  conditions  call  for  the  development  of  an  unusual 
quantity  of  heat,  the  diet  is  always  modified,  both  as  regards  the  quantity 
and  kind  of  food ;  but  when  food  is  taken  in  sufficient  quantity  and  is  of  a 
kind  capable  of  maintaining  proper  nutrition,  its  composition  does  not  affect 
the  general  temperature.  The  temperature  of  the  body,  indeed,  seems  to  be 
uniform  in  the  same  climate,  even  in  persons  living  upon  entirely  different 
kinds  of  food  (Davy).  Nevertheless,  the  conditions  of  external  temperature 
have  a  remarkable  influence  upon  the  diet.  It  is  well  known  that  in  the 
heat  of  summer,  the  quantity  of  meats  and  fat  taken  is  relatively  small, 
and  of  the  succulent,  fresh  vegetables  and  fruits,  large,  as  compared  with  the 
diet  in  the  winter ;  but  although  the  proportion  of  carbohydrates  in  many 
of  the  fresh  vegetables  used  during  a  short  season  of  the  year  is  not  great, 
these  articles  are  also  deficient  in  nitrogenized  matters.  During  the  winter 
the  ordinary  diet,  composed  of  meat,  fat,  bread,  potatoes  etc.,  contains  a 
large  proportion  of  nitrogenized  substances  as  well  as  a  considerable  propor- 
tion of  carbohydrates ;  and  in  the  summer  the  proportion  of  both  of  these 
varieties  of  food  is  reduced,  the  more  succulent  articles  taking  their  place. 
This  is  farther  illustrated  by  a  comparison  of  the  diet  in  the  torrid  or  tem- 
perate and  in  the  frigid  zones.  It  is  stated  that  the  daily  ration  of  the  Es- 
quimaux is  twelve  to  fifteen  pounds  (5-433  to  6-804  kilos.)  of  meat,  about 
one-third  of  which  is  fat.  Hayes  noted  that  with  a  temperature  of  —  60° 
to  —  70°  Fahr.  (about  —  51°  to  —  57°  C.),  there  was  a  continual  craving  for 
a  strong,  animal  diet,  particularly  fatty  substances. 

The  influence  of  alcoholic  beverages  upon  the  animal  temperature  has 
been  studied  chiefly  with  reference  to  the  question  of  their  use  in  enabling 
the  system  to  resist  excessive  cold.  The  universal  testimony  of  scientific 


450  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

Arctic  explorers  is  that  the  use  of  -alcohol  does  not  enable  men  to  endure  a 
very  low  temperature  for  any  considerable  length  of  time. 

As  a  rule,  when  the  respiratory  activity  is  physiologically  increased — as  it 
is  by  exercise,  bodily  or  mental,  ingestion  of  food  or  diminished  external 
temperature — the  generation  of  heat  in  the  body  is  correspondingly  raised ; 
and  on  the  other  hand,  it  is  diminished  by  conditions  which  physiologically 
decrease  the  absorption  of  oxygen  and  the  exhalation  of  carbon  dioxide.  The 
relations  of  animal  heat  to  the  general  process  of  nutrition  are  most  intimate. 
Any  condition  that  increases  the  activity  of  nutrition  and  of  disassimilation, 
or  even  any  thing  that  increases  disassimilation  alone,  will  increase  the  pro- 
duction of  heat.  The  reverse  of  this  proposition  is  equally  true. 

Notwithstanding  the  fact  that  there  is  a  certain  correspondence  between 
the  activity  of  the  respiratory  processes  and  the  production  of  heat,  this  is 
far  from  being  absolute.  It  has  been  shown  by  Senator  that  digestion  in- 
creases heat-production  rather  more  than  it  increases  the  exhalation  of  carbon 
dioxide.  Muscular  exertion  has  been  found  to  increase  the  quantity  of  oxy- 
gen consumed  in  very  much  greater  proportion  than  it  increased  the  heat- 
production  (Hirn).  Even  adding  to  the  heat  produced,  the  work,  reduced  to 
heat-units,  the  heat-production  was  about  doubled,  while  the  quantity  of 
oxygen  consumed  was  increased  about  four  and  a  half  times. 

Influence  of  Exercise  etc.,  upon  the  Heat  of  the  Body. — The  most  com- 
plete repose  of  the  muscular  system  is  observed  during  sleep,  when  hardly 
any  of  the  muscles  are  brought  into  action,  except  those  concerned  in  tran- 
quil respiration.  There  is  always  a  notable  diminution  in  the  general  tem- 
perature at  this  time.  In  the  variations  in  the  heat  of  the  body,  the  mini- 
mum is  always  during  the  night ;  and  this  is  not  entirely  dependent  upon 
sleep,  for  a  depression  in  temperature  is  always  observed  at  that  time,  even 
when  sleep  is  avoided.  It  is  a  matter  of  common  observation,  that  one 
of  the  most  efficient  means  of  resisting  the  depressing  influence  of  cold  is 
to  constantly  exercise  the  muscles;  and  it  is  well  known  that  after  long 
exposure  to  intense  cold,  the  tendency  to  sleep,  which  becomes  almost  irre- 
sistible, if  yielded  to,  is  followed  by  a  very  rapid  loss  of  heat  and  almost  cer- 
tain death.  Muscular  exercise  increases  the  production  of  heat;  but  the 
variations  in  the  actual  temperature  of  the  body  in  man,  although  distinct, 
are  seldom  very  considerable,  for  the  reason  that  muscular  exertion  is  gener- 
ally attended  with  increased  action  of  the  skin,  which  keeps  the  heat  of  the 
body  within  restricted  limits.  In  very  violent  muscular  exertion,  as  in  fast 
running,  the  increased  production  of  heat  may  be  so  rapid  that  it  can  not 
be  entirely  compensated  by  evaporation  from  the  skin,  and  the  temperature 
may  rise  to  104°  Fahr.  (40°  C.).  In  about  an  hour  and  a  half  the  tempera- 
ture falls  to  the  normal  standard  (Billroth,  quoted  by  Landois). 

The  elevation  in  temperature  that  attends  muscular  action  is  produced 
dirgctly  in  the  substance  of  the  muscle  (Becquerel  and  Breschet).  Intro- 
ducing a  thermo-electric  needle  into  the  biceps  of  a  man  who  used  the  arm 
in  sawing  wood  for  five  minutes,  these  physiologists  noted  an  elevation  of 
temperature  of  nearly  two  degrees  Fahr.  (1°  C.).  The  production  of  heat 


VAEIATIONS  IN  THE  HEAT  OF  THE  BODY.  451 

in  the  muscular  tissue  has  been  observed  in  experiments  with  portions  of 
muscle  from  the  frog.  Not  only  was  there  an  absorption  of  oxygen  and 
exhalation  of  carbon  dioxide  after  the  muscle  had  been  removed  from  the 
body  of  the  animal,  but  an  elevation  in  temperature  of  about  one  degree 
Fahr.  (0-55°  C.)  was  noted  following  contractions  artificially  excited  (Mat- 
teucci).  Observations  upon  the  influence  of  mental  exertion  on  the  tempera- 
ture of  the  body  have  not  been  so  many,  but  they  are,  apparently,  no  less 
exact  in  their  results.  Davy  observed  a  slight  but  constant  elevation  during 
"  excited  and  sustained  attention."  Lombard  noted  an  elevation  of  tempera- 
ture in  the  head  during  mental  exertion  of  various  kinds,  but  it  was  slight, 
the  highest  rise  not  exceeding  0-05°  Fahr.  (0-027°  C.).  According  to  Bur- 
dach,  the  temperature  of  the  body  is  increased  by  the  emotions  of  hope,  joy, 
anger  and  all  exciting  passions,  while  it  is  diminished  by  fear,  fright  and 
mental  distress. 

It  is  evident  that  if  animal  heat  be  one  of  the  necessary,  attendant  phe- 
nomena of  nutrition,  it  must  be  greatly  influenced  by  conditions  of  the  circu- 
lation. It  has  been  a  question,  indeed,  whether  the  modifications  in  tem- 
perature, produced  by  operating  upon  the  vaso-motor  nerves,  be  not  due 
entirely  to  changes  in  the  supply  of  blood.  It  is  certain  that  whatever  deter- 
mines an  increased  supply  of  blood  to  any  part  raises  the  temperature ;  and 
whenever  the  quantity  of  blood  in  any  organ  or  part  is  considerably  dimin- 
ished, the  temperature  is  reduced.  This  fact  is  constantly  illustrated  in 
operations  for  the  deligation  of  large  arteries.  It  is  well  known  that  after 
tying  a  large  vessel,  the  utmost  care  is  necessary  to  keep  up  the  temperature 
of  the  part  to  which  its  branches  are  distributed,  until  the  anastomosing  ves- 
sels become  enlarged  sufficiently  to  supply  the  quantity  of  blood  necessary 
for  healthy  nutrition. 

Influence  of  the  Nervous  .System  upon  the  Production  of  Animal  Heat 
(Heat- Centres). — The  local  influences  of  the  vaso-motor  nerves  upon  calori- 
fication operate  mainly  if  not  entirely  through  changes  in  the  nutrition  of 
parts,  produced  by  variations  in  blood-supply.  These  influences  will  be  fully 
considered  in  connection  with  the  physiology  of  the  nervous  system. 

The  general  temperature  of  the  body  may  be  modified  through  the  nerv- 
ous system  by  reflex  action,  and  this  implies  the  existence  of  nerve-centres,  or 
of  a  nerve-centre,  capable  of  influencing  the  general  process  of  calorification. 
Experiments  have  been  made,  chiefly  on  parts  of  the  encephalon,  with  the 
view  of  determining  the  existence  and  location  of  heat-centres.  In  a  recent 
publication  by  Ott  (1887),  four  heat-centres  are  recognized,  irritation  of 
which  by  puncture  increases  the  temperature  of  the  body  in  rabbits  by  several 
degrees  (4°  to  6°  Fahr.,  or  2-2°  to  3-3°  C.).  These  four  centres  are  as  fol- 
lows :  1,  in  front  of  and  beneath  the  corpus  striatum  (Ott) ;  2,  the  median 
portion  of  the  corpora  striata  and  the  subjacent  parts  (Aronsohn  and  Sachs) ; 
3,  between  the  corpus  striatum  and  the  optic  thalarnus  (Ott) ;  4,  the  anterior 
inner  end  of  the  optic  thalamus  (Ott).  Puncture  of  these  parts  is  followed 
by  rise  in  temperature,  which  continues  for  a  variable  time,  two  to  four  days. 
A  similar  centre  has  been  described  as  existing  in  the  dog,  in  the  cortex  of 


452  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

the  anterior  portion  of  the  upper  surface  of  the  brain,  near  the  median  line 
(Eulenberg  and  Landois).  The  conductors  connected  Avith  these  centres 
decussate  and  pass  through  the  medulla  oblongata  and  the  spinal  cord.  The 
question  arises  as  to  whether  the  effects  of  puncture  or  stimulation  of  these 
parts  be  exciting  or  inhibitory ;  but  observations  regarding  the  mechanism 
of  their  action  have  not  been  sufficiently  definite  to  warrant  any  positive  con- 
clusions on  this  point. 

MECHANISM  OF  THE  PBODUCTION  OF  ANIMAL  HEAT. 

The  definite  ideas  of  physiologists  concerning  the  mechanism  of  the  pro- 
duction of  heat  by  animals  date  from  the  researches  of  Lavoisier  (1777  to 
1790).  As  a  general  result  of  these  observations,  Lavoisier  concluded  that 
animal  heat  was  produced  by  an  internal  combustion  resulting  in  carbon 
dioxide  and  water.  Even  now  there  is  little  to  be  said  beyond  this,  as  regards 
the  general  mechanism  of  animal  calorification,  although  modern  investiga- 
tions have  brought  to  light  many  important  details  in  the  heat-producing 
processes. 

In  man  and  in  the  warm-blooded  animals  generally,  the  maintenance  of 
the  temperature  of  the  organism  at  a  nearly  fixed  standard  is  a  necessity  of 
life ;  and  while  heat  is  generated  in  the  organism  with  an  activity  that  is 
constantly  varying,  it  is  counterbalanced  by  physiological  loss  of  heat  from 
the  cutaneous  and  respiratory  surfaces.  Variations  in  the  activity  of  calori- 
fication are  not  to  be  measured  by  corresponding  changes  in  the  tempera- 
ture of  the  body,  but  are  to  be  estimated  by  calculating  the  quantity  of  heat 
lost.  The  ability  of  the  human  race  to  live  in  all  climates  is  explained 
by  the  adaptability  of  man  to  different  conditions  of  diet  and  exercise,  and 
by  the  power  of  regulating  loss  of  heat  from  the  surface  by  appropriate 
clothing. 

Heat  is  produced  in  the  general  system  and  not  in  any  particular  organ 
or  in  the  blood  as  it  circulates.  The  experiments  of  Matteucci,  showing  an 
elevation  of  temperature  in  a  muscle  excited  to  contraction  after  it  had  been 
removed  from  the  body,  and  the  observations  of  Becquerel  and  Breschet, 
showing  increased  development  of  heat  by  muscular  contraction,  are  sufficient 
evidence  of  the  production  of  heat  in  the  muscular  system ;  and  inasmuch 
as  the  muscles  constitute  by  far  the  greatest  part  of  the  weight  of  the  body, 
they  are  a  most  important  source  of  animal  heat.  It  has  been  observed  that 
the  blood  becomes  notably  warmer  in  passing  through  the  abdominal  viscera 
(Bernard).  This  is  particularly  marked  in  the  liver,  and  it  shows  that  the 
large  and  highly  organized  viscera  are  also  important  sources  of  caloric. 

As  far  as  it  is  possible  to  determine  by  experiment,  not  only  is  there  no 
particular  part  or  organ  in  the  body  endowed  with  the  special  office  of  calori- 
fication, but  every  part  in  which  the  nutritive  forces  are  in  operation  pro- 
duces a  certain  quantity  of  heat ;  and  this  is  probably  true  of  the  blood-cor- 
puscles and  other  anatomical  elements  of  this  class.  The  production  of  heat 
in  the  body  is  general  and  is  one  of  the  necessary  consequences  of  the  process 
of  nutrition ;  but,  with  nutrition,  it  is  subject  to  local  variations,  as  is  illus- 


MECHANISM  OF  THE  PRODUCTION  OF  HEAT,  453 

trated  in  the  effects  of  operations  upon  the  vaso-motor  nerves  and  in  the  phe- 
nomena of  inflammation. 

Nutrition  and  disassimilation  involve  the  appropriation  of  matters  taken 
into  the  body  and  the  production  and  discharge  of  effete  substances.  In  its 
widest  signification,  this  includes  the  consumption  of  oxygen  and  the  elimina- 
tion of  carbon  dioxide ;  and  consequently,  respiration  may  be  regarded  as  a 
nutritive  act.  All  of  the  nutritive  processes  go  on  together,  and  they  all 
involve,  in  most  warm-blooded  aiiimals  at  least,  a  nearly  uniform  tempera- 
ture. During  the  first  periods  of  intrauterine  life,  the  heat  derived  from  the 
mother  is  undoubtedly  necessary  to  the  development  of  tissue  by  a  change 
of  substance,  analogous  to  nutrition  and  even  superior  to  it  in  activity.  Dur- 
ing adult  life,  animal  heat  and  the  nutritive  force  are  co-existent.  It  now 
becomes  an  important  question  to  determine  whether  there  be  any  class  of 
nutritive  matters  specially  concerned  in  calorification  or  any  nutritive  acts 
exclusively  or  specially  directed  to  the  maintenance  of  the  normal  tempera- 
ture of  the  body. 

It  is  evident  that  in  normal  nutrition  by  food,  the  heat  of  the  body  must 
be  maintained  by  changes  which  take  place,  either  directly  in  the  blood  or 
indirectly  in  the  tissues,  in  alimentary  matters,  and  that  these  changes  involve 
oxidation  to  a  very  considerable  extent.  Under  ordinary  conditions  of  nutri- 
tion, it  is  assumed  that  the  food  furnishes  all  the  material  for  maintaining 
the  heat  of  the  body  and  for  the  development  of  force  in  work,  such  as  the 
muscular  work  of  respiration  and  circulation  and  general  muscular  effort. 
If  no  food  be  taken  for  a  certain  time,  the  heat  of  the  body  must  be  main- 
tained, the  work  must  be  accomplished  at  the  expense  of  the  substance  of 
the  body  itself,  and  the  individual  loses  weight.  In  order  to  maintain  the 
equilibrium  of  the  body,  therefore,  food  should  be  taken  in  quantity  sufficient 
to  supply,  by  its  changes  in  oxidation  etc.,  the  heat  and  force  required.  In 
this  condition  of  equilibrium,  the  body  neither  gains  nor  loses  weight.  To 
furnish  a  positive  .scientific  basis  for  calculations  with  reference  to  these 
points,  physiologists  have  burned  various  articles  of  food  in  oxygen,  and 
have  estimated  their  heat-value  in  heat-units. 

In  1866,  Frankland  made  a  number  of  calculations  of  the  heat-units  and 
the  estimated  force-value  of  various  articles  of  food,  which  are  now  accepted 
and  used  by  most  writers  upon  subjects  connected  with  the  theories  of  ani- 
mal heat  and  the  source  of  muscular  power.  As  regards  the  heat  produced 
by  the  oxidation  of  these  substances  in  the  body,  if  it  be  assumed  that  the 
same  quantity  of  heat  is  produced  by  the  oxidation,  under  all  circumstances, 
of  a  definite  quantity  of  oxidizable  matter,  it  is  necessary  simply  to  deduct 
from  the  heat- value  of  articles  of  food  the  heat-value  remaining  in  certain 
parts  of  the  food  which  pass  out  of  the  body  in  an  unoxidized  state.  It  was 
in  this  way  that  Frankland  arrived  at  a  determination  of  the  heat- value  of 
articles  of  food  oxidized  in  the  body. 

The  following  selections  from  Frankland's  table  will  give  an  idea  of  the 
heat-value  of  different  articles  of  food  oxidized  in  the  body.  In  this  table 
the  heat-units  are  calculated  as  pound-degrees. 


454  NUTRITION— ANIMAL  HEAT  AND  FOECE. 

HEAT-VALUE   OF   TEN    GRAINS   OF   THE   MATERIAL    OXIDIZED    INTO    CARBON 
DIOXIDE,   WATER   AND    UREA    IN   THE    ANIMAL   BODY    (FRANKLAND). 


Articles  of  food.  Heat-units. 

Butter 18-68 

Beef-fat  (dry) 23-33 


Articles  of  food.  Heat-units. 

Potatoes 2-56 

Cabbage 1-08 


Lump-sugar 8'61  [  Milk 1-64 

Grape-sugar    8-42  |  Egg  (boiled) 5-86 

Wheat-flour 9-87  !  Cheese 11-20 

Bread-crumb 5'52    Lean  beef 3-66 

Arrowroot 10-06    Ham  (boiled) 4-30 

Ground  rice 9-52    Mackerel 4-14 

In  the  following,  selected  from  the  table  quoted  by  Chapman,  the  heat- 
units  are  calculated  as  kilo.-degrees  C. 

HEAT-VALUE   OF    ONE   GRAMME   OF   THE   MATERIAL  OXIDIZED  INTO  CARBON 
DIOXIDE,    WATER   AND    UREA    IN   THE   ANIMAL   BODY    (FRANKLAND). 

Articles  of  food.  Heat-units. 


Butter 7-264 

Beef-fat  (dry)    9-069 

Lump-sugar 3-348 

Grape-sugar 3-227 

Wheat-flour 3-840 

Bread-crumb 1-450 

Arrowroot 3-912 

Ground  rice    .  .  3-760 


Articles  of  food.  Heat-units. 

Potatoes 0-990 

Cabbage 0-420 

Milk 0-620 

Egg  (boiled) 2-280 

Cheese 4-360 

Lean  beef 1-420 

Ham  (boiled) 1-680 

Mackerel . .  .   1-610 


The  heat-value  of  one  gramme  of  alcohol — taken  from  a  table  compiled 
by  Landois — is  equal  to  8*958  heat-units  (kilo.-degrees  C.),  or  the  heat- value 
of  10  grains  of  alcohol  is  equal  to  23  heat- units  (pound-degrees  Fahr.). 

As  regards  the  processes  of  combustion  which  take  place  in  the  living 
organism,  the  oxidation  of  the  constituents  of  food  produces  carbon  dioxide 
and  water,  but  it  is  probable  that  the  quantity  of  heat  produced  bears  a  defi- 
nite relation  to  the  total  consumption  of  oxygen,  the  heat,  as  far  as  this  is 
concerned,  being  the  same  whether  the  oxygen  unite  with  carbon  or  with 
hydrogen  (Pfliiger).  This  relation  between  the  quantity  of  oxygen  consumed 
and  the  production  of  heat  seems  to  be  disturbed  by  muscular  exercise ;  but 
it  has  thus  far  been  found  impossible  to  estimate  accurately  the  quantity  of 
heat  represented  by  the  force  expended  in  muscular  work,  circulation,  respi- 
ration etc. 

The  heat-producing  processes  undoubtedly  are  represented  mainly  by  the 
exhalation  of  carbon  dioxide  and  water,  and  to  a  less  degree  by  the  discharge 
of  urea,  the  quantity  of  heat  produced  by  other  chemical  processes  being 
comparatively  small.  It  is  also  true  that  the  carbohydrates  and  fats  are 
more  important  factors  in  calorification  than  the  albuminoids ;  but  it  seems 
beyond  question  that  there  must  be  heat  evolved  in  the  body  by  oxidation  of 
nitrogenized  matters.  When  the  daily  quantity  of  food  is  largely  increased 
for  the  purpose  of  generating  the  immense  quantity  of  heat  required  in  ex- 
cessively cold  climates,  the  nitrogenized  matters  are  taken  in  greater  quan- 


MECHANISM  OF  THE  PRODUCTION  OF  HEAT.      455 

tity,  as  well  as  the  fats,  although  their  increase  is  not  in  the  same  proportion. 
From  these  facts,  and  from  other  considerations  that  have  already  been  fully 
discussed,  it  is  evident  that  the  physiological  metamorphoses  of  nitrogenized 
matters  bear  a  certain  share  in  the  production  of  animal  heat.  The  carbo- 
hydrates and  fats  are  not  concerned  in  the  building  up  of  tissues  and  organs, 
except  as  the  fats  are  deposited  in  the  form  of  adipose  tissue.  Their  addition 
to  the  food  saves  the  nitrogenized  tissues,  which  latter  must  be  used  in  heat- 
production  in  starvation  and  in  a  restricted  diet  deficient  in  non-nitrogenized 
matters.  If  the  non-nitrogeiiized  constituents  of  food  do  not  form  tissue, 
are  not  discharged  from  the  body,  and  are  consumed  in  some  of  the  processes 
of  nutrition,  it  would  seem  that  their  change  must  involve  the  production  of 
carbon  dioxide  and  water  and  the  evolution  of  heat. 

Although  it  may  be  assumed  that  the  non-nitrogenized  constituents  of 
food  are  particularly  important  in  the  production  of  animal  heat,  and  that 
they  are  not  concerned  in  the  repair  of  tissue,  it  must  be  remembered  that 
the  animal  temperature  may  be  kept  at  the  proper  standard  upon  a  nitrogen- 
ized diet ;  and  it  is  not  possible  to  connect  calorification  exclusively  with  the 
consumption  of  any  single  class  of  alimentary  matters  or  with  any  single 
one  of  the  acts  of  nutrition. 

The  exact  mechanism  of  the  oxidation-processes  in  the  body  is  not  under- 
stood. All  physiologists,  however,  are  agreed  that  the  quantity  of  heat  pro- 
duced by  oxidation  is  the  same,  whether  the  combustion  be  rapid  or  slow. 
The  fact  that  fats  are  never  discharged,  but  are  either  consumed  entirely  or 
are  deposited  in  the  body  as  fat,  leaves  their  oxidation  and  discharge  as  oxi- 
dation-products the  only  alternative.  The  oxidation  of  albuminoids  has 
already  been  considered.  As  regards  the  carbohydrates,  if  it  can  be  shown 
that  alcohol  normally  exists  in  the  blood,  even  in  very  small  quantity,  the 
idea  that  these  matters  are  slowly  passed  from  the  liver  as  sugar,  into  the 
general  circulation,  and  are  then  converted  into  alcohol  which  is  promptly 
oxidized,  is  worthy  of  serious  consideration.  Such  a  theory  would  explain 
the  destination  of  the  carbohydrates  and  their  relations  to  calorification. 
There  can  be  no  doubt  that  in  certain  cases  of  fever,  alcohol  administered  in 
large  quantity  may  be  oxidized  and  "  feed  "  the  fever,  thus  saving  consump- 
tion of  tissue. 

In  a  series  of  observations  made  in  1879  (Flint),  it  seemed  impossible  to 
account  for  the  heat  actually  produced  in  the  body  and  expended  as  force  in 
muscular  work  etc.,  by  the  heat-value  of  food  and  of  tissue  consumed.  The 
estimates  of  heat-production,  made  by  the  direct  method,  were  then  adopted; 
but  even  the  indirect  estimates,  which  were  much  less,  presented  difficulty, 
though  in  a  less  degree.  In  these  observations,  it  was  shown  that  water  was 
actually  produced  in  the  body  in  quantity  over  and  above  that  contained  in 
food  and  drink,  during  severe  and  prolonged  muscular  exertion.  It  was 
also  shown  that  water  was  produced  in  considerable  quantity  during  twenty- 
four  hours  of  abstinence  from  food.  It  has  been  shown  by  Pettenkofer  and 
Voit  that  "  the  elimination  of  water  is  very  much  increased  by  work,  and 
the  increase  continues  during  the  ensuing  hours  of  sleep."  As  regards  the 


456  NUTRITION— ANIMAL  HEAT  AND  FORCE. 

oxidation  of  hydrogen  in  this  formation  of  water,  it  is  probable  that  the 
hydrogen  of  the  tissues  is  used  and  that  the  matter  thus  consumed  is  sup- 
plied again  to  the  tissues  in  order  to  maintain  the  physiological  status  of  the 
organism.  Adding  the  heat-value  of  the  water  thus  produced  to  the  heat- 
value  of  food,  there  is  little  difficulty  in  accounting  for  the  heat  and  force 
actually  produced  and  expended. 

The  demonstration  that  water  is  actually  formed  within  the  organism, 
under  certain  conditions,  not  only  completes  the  oxidation-theory  of  the  pro- 
duction of  animal  heat,  but  it  affords  an  explanation  of  certain  physiological 
phenomena  that  have  been  heretofore  obscure.  It  is  well  known,  for  exam- 
ple, that  a  proper  system  of  physical  training  will  reduce  the  fat  of  the  body 
to  a  minimum  consistent  with  health  and  strength.  This  involves  a  diet  con- 
taining a  relatively  small  proportion  of  fat  and  liquids,  and  regular  muscular 
exercise  attended  with  profuse  sweating.  Muscular  work  increases  the  elimi- 
nation of  water,  Avhile  it  also  exaggerates  for  the  time  the  calorific  processes. 
Muscular  exercise  undoubtedly  favors  the  consumption  of  the  non-nitrogenized 
parts  of  the  body,  and  a  diminution  of  the  supply  of  fats,  carbohydrates  and 
water  in  the  food  prevents,  to  a  certain  extent,  the  new  formation  of  fat.  In 
excessive  muscular  exertion,  the  production  of  water  is  increased  and  the 
circulation  becomes  more  active.  The  volume  of  blood  then  circulating  in 
the  skin  and  passing  through  the  lungs  in  a  given  time  is  relatively  in- 
creased, and  there  is  an  increased  discharge  of  water  from  these  surfaces. 
The  same  condition  that  produces  an  increased  quantity  of  water  in  the 
body  and  has  a  tendency  to  exaggerate  the  process  of  calorification  seems  to 
produce  also  an  increased  evaporation  from  the  surface,  which  serves  to 
equalize  the  animal  temperature. 

Equalization  of  the  Animal  Temperature. — A  study  of  the  phenomena  of 
calorification  in  the  human  subject  has  shown  that  under  all  conditions  of 
climate  the  general  heat  of  the  body  is  equalized.  There  is  always  more  or 
less  loss  of  heat  by  evaporation  from  the  general  surface,  and  when  the  sur- 
rounding atmosphere  is  very  cold,  it  becomes  desirable  to  reduce  this  loss  to 
the  minimum.  This  is  done  by  appropriate  clothing,  which  must  certainly  be 
regarded  as  a  physiological  necessity.  Clothing  protects  from  excessive  heat 
as  well  as  from  cold.  Thin,  porous  articles  moderate  the  heat  of  the  sun, 
equalize  evaporation  and  afford  great  protection  in  hot  climates.  In  excessive 
cold,  clothing  moderates  the  loss  of  heat  from  the  surface.  When  the  body 
is  not  exposed  to  currents  of  air,  garments  are  useful  chiefly  as  non-conduct- 
ors, imprisoning  many  layers  of  air,  which  are  warmed  by  contact  with  the 
person.  It  is  also  important  to  protect  the  body  from  the  wind,  which  greatly 
increases  the  loss  of  heat  by  evaporation. 

When  from  any  cause  there  is  a  tendency  to  undue  elevation  of  the  heat 
of  the  body,  cutaneous  transpiration  is  increased,  and  the  temperature  is  kept 
at  the  proper  standard.  This  has  already  been  considered  in  treating  of 
the  action  of  the  skin,  and  facts  were  noted  showing  that  men  can  work 
when  exposed  to  a  heat  much  higher  than  that  of  the  body  itself.  The 
quantity  of  vapor  that  is  lost  under  these  conditions  is  sometimes  very  large. 


RELATIONS  OF  HEAT  TO  FORCE.  457 

Tillet  recorded  an  instance  of  a  young  girl  who  remained  in  an  oven  for  ten 
minutes  without  inconvenience,  at  a  temperature  of  324-5°  Fahr.  (162-5°  C.). 
Blagden,  in  his  noted  experiments  in  a  heated  room,  made  in  connection  with 
Banks,  Solander,  Fordyce,  and  others,  found  in  one  series  of  observations,  that 
a  temperature  of  211°  Fahr.  (99-5°  C.)  could  be  easily  borne;  and  at  another 
time  the  heat  was  raised  to  260°  Fahr.  (126-5°  C.).  Under  these  extraordi- 
nary external  conditions,  the  body  is  protected  from  the  radiated  heat  by 
clothing,  the  air  is  perfectly  dry,  and  the  animal  temperature  is  kept  down 
by  increased  evaporation  from  the  surface. 

It  is  a  curious  fact  that  after  exposure  of  th3  body  to  an  intens3,  dry  heat 
or  to  a  heated  vapor,  as  in  the  Turkish  or  Russian  baths,  when  the  general 
temperature  is  somewhat  raised  and  the  surface  is  bathed  in  perspiration,  a 
cold  plunge,  which  checks  the  action  of  the  skin  almost  immediately,  is  not 
injurious  and  is  decidedly  agreeable.  This  presents  a  striking  contrast  to  the 
effects  of  sudden  cold  upon  a  system  heated  and  exhausted  by  long-continued 
exertion.  In  the  latter  instance,  when  the  perspiration  is  suddenly  checked, 
serious  disorders  of  nutrition,  with  inflammation  etc.,  are  liable  to  occur.  The 
explanation  of  this  seems  to  be  the  following  :  When  the  skin  acts  to  keep 
down  the  temperature  of  the  body  in  simple  exposure  to  external  heat,  there 
is  no  modification  in  nutrition,  and  the  tendency  to  an  elevation  of  the  ani- 
mal temperature  comes  from  causes  entirely  external.  It  is  a  practical  ob- 
servation that  no  ill  effects  are  produced,  under  these  circumstances,  by  sud- 
denly changing  the  external  conditions ;  but  when  the  animal  temperature 
is  raised  by  a  modification  of  the  internal  nutritive  processes,  as  in  prolonged 
muscular  effort,  these  changes  should  not  be  suddenly  arrested ;  and  a  sup- 
pression of  the  compensative  action  of  the  skin  is  liable  to  produce  disturb- 
ances in  nutrition,-  often  resulting  in  inflammations. 

RELATIONS  OF  HEAT  TO  FORCE. 

Since  the  development  of  the  theory  of  the  conservation  of  forces,  which 
had  its  origin  in  an  essay  published  by  J.  R.  Mayer,  in  1842,  physiologists 
have  applied  the  laws  of  correlation  and  conservation  of  forces  to  operations 
involving  the  production  of  heat  and  the  development  and  expenditure  of 
force  in  animals.  This  theory,  if  applicable  to  what  were  formerly  called 
vital  operations,  certainly  affords,  in  its  definite  quantities  of  heat  and  force  as 
expressed  in  heat-units  and  foot-pounds,  a  basis  for  calculating  the  absolute 
value  of  material  changes  in  the  body.  Without  discussing  the  purely  physi- 
cal questions  involved,  the  laws  of  correlation  and  conservation  of  forces,  as 
they  are  applicable  to  human  physiology,  may  be  briefly  stated  as  follows : 

Potential  energy  is  something  either  residing  in  or  imparted  to  matter, 
which  is  capable  of  being  converted  directly  or  indirectly  into  heat.  The 
animal  body,  for  example,  is  a  store-house  of  potential  energy.  Its  tissues 
may  be  made  to  unite  with  oxygen  and  heat  is  produced.  Any  body  may 
have  potential  energy  imparted  to  it.  If  a  weight  be  raised  to  a  certain 
height,  when  the  force  which  has  accomplished  this  work  is  exhausted,  the 
potential  energy  imparted  to  the  weight  causes  it  to  fall,  and  in  this  fall,  heat 


4:58        NUTEITION— ANIMAL  HEAT  AND  FORCE. 

is  produced.  The  weight  may  be  supported  at  the  height  to  which  it  has 
been  raised,  for  an  indefinite  time ;  but  it  still  possesses  the  potential  energy 
which  has  been  imparted  to  it,  and  when  the  support  is  removed,  this  poten- 
tial energy  is  converted  into  force  which  may  be  converted  into  heat.  Poten- 
tial energy  may  be  converted  directly  into  heat,  as  when  a  body  is  oxidized. 
It  is  converted  indirectly  into  heat,  when  movement,  falling  or  other  force  is 
produced,  for  all  force  may  be  converted  into  heat.  This  conversion  into 
heat,  directly  or  indirectly,  affords  a  convenient  measure  of  potential  energy. 
Using  the  example  of  the  change  of  potential  energy  into  heat  by  oxida- 
tion, the  energy  stored  up  in  matter  is  measured  by  estimating  the  heat 
produced  by  oxidation,  as  so  many  heat-units.  Using  the  example  of  falling 
force  imparted  to  a  weight,  the  potential  energy  imparted  to  the  body  is  esti- 
mated by  calculating  the  heat  produced  by  the  body  falling. 

If  the  entire  body  of  an  animal  were  burned  in  a  calorimeter,  the  heat 
produced  would  be  an  exact  measure  of  the  potential  energy  of  the  tissues, 
converted  into  heat  by  oxidation.  If  one  can  imagine  an  animal  perfectly 
quiescent,  neither  losing  nor  gaining  weight,  nourished  by  food,  expending 
no  force  in  circulation  and  respiration,  but  supplied  with  oxygen,  the  poten- 
tial energy  of  the  food  could  be  measured  by  the  heat  produced.  In  animal 
organisms,  heat  is  produced  mainly  by  oxidation,  although  other  chemical 
processes  contribute  to  the  production  of  heat,  to  some  extent.  The  body 
contains  the  potential  energy  stored  up  in  its  tissues.  The  oxygen  taken  in 
by  respiration  changes  a  certain  part  of  this  potential  energy  into  heat.  If 
food  be  not  supplied  in  adequate  quantity,  the  body  loses  weight  by  this 
change  of  tissue  into  certain  matters,  such  as  carbon  dioxide,  water  and  urea, 
which  are  discharged.  Food  supplies  the  waste  of  tissue  and  is  the  ultimate 
source  of  the  potential  energy  of  the  body.  If  food  be  supplied  in  excess, 
that  which  is  not  in  some '  form  discharged  from  the  body  remains  and  adds 
to  the  total  potential  energy  stored  up  in  the  organism. 

Kinetic  energy  is  mechanical  force.  It  is  the  force  of  a  falling  body,  or 
as  regards  animal  mechanics,  it  is  muscular  force  used  in  respiration,  circu- 
lation or  any  kind  of  muscular  work.  In  physics,  kinetic  energy,  or  force, 
and  heat  are  regarded  as  mutually  convertible.  The  reasoning  by  which  this 
law  was  formulated  is  the  following : 

The  force  used  in  raising  a  weight  to  a  certain  height,  which  is  imparted 
to  the  weight  as  potential  energy,  is  precisely  equal  to  the  force  developed  by 
this  body  as  it  falls.  If  this  force  could  be  transmitted  to  another  body  of 
equal  weight,  without  any  expenditure  of  energy  in  friction,  it  would  raise 
the  second  weight  to  an  equal  height.  The  arbitrary  unit  of  this  force  is  a 
foot-pound  or  a  kilogrammetre,  terms  which  have  already  been  defined.  The 
falling  of  a  body  of  a  certain  weight  through  a  definite  distance  produces  a 
definite  quantity  of  heat  that  itself  is  capable  of  producing  force ;  and  it  is 
assumed  that  the  heat  produced  by  a  falling  body,  if  absolutely  and  entirely 
converted  into  force,  would  raise  that  body  to  the  height  from  which  it  had 
fallen,  or  would  exactly  equal  the  falling  force.  A  heat-unit  is  therefore  said 
to  be  equal  to  a  definite  number  of  foot-pounds  or  kilogrammetres.  Cal- 


RELATIONS  OF  HEAT  TO  FORCE.  459 

dilations  have  boen  made  showing  the  conversion  of  foot-pounds  or  kiio- 
grammetres  into  heat-units,  but  mechanical  difficulties  have  thus  far  pre- 
vented the  actual  conversion  of  heat-units  into  their  equivalents  in  foot-pounds 
or  kilogrammetres.  As  a  matter  of  reasoning,  however,  it  is  assumed  that  if 
a  certain  number  of  foot-pounds  or  kilogrammetres  be  equal  to  a  certain 
number  of  heat-units,  the  reverse  of  the  equation  is  true ;  but  in  the  applica- 
tion of  this  law  to  animal  physiology,  it  is  always  by  a  conversion  of  heat- 
units  into  foot-pounds  or  kilogrammetres.  The  experiments  on  which  the 
law  rests  have  been  made  by  converting  foot-pounds  or  kilogrammetres  into 
heat-units. 

In  work  by  machinery  a  very  large  proportion  of  the  force-value  of  fuel 
is  dissipated  in  the  form  of  heat.  This  is  well  illustrated  by  Landois.  If  a 
steam-engine  burning  a  certain  quantity  of  coal,  but  doing  no  work,  be 
placed  in  a  calorimeter,  the  heat  produced  can  be  measured.  If,  now,  the 
engine  be  made  to  do  a  certain  work,  as  in  raising  a  weight,  the  heat,  as 
measured  by  the  calorimeter,  will  be  less  and  the  work  done  is  found  to  be 
very  nearly  proportional  to  the  decrease  in  the  measured  heat  (Hirn).  It  is 
estimated  by  Landois,  that  of  the  heat  produced  by  the  body,  one-fifth  may 
be  used  as  work.  In  the  best  steam-engine,  it  is  possible  to  use  only  one- 
eighth  as  work,  seven-eighths  being  dissipated  as  heat. 

Many  elaborate  and  careful  estimates  have  been  made  of  the  mechanical 
work  produced  by  the  human  body.  The  basis  of  such  calculations  is  more 
or  less  indefinite,  and  the  reduction  of  the  work  to  foot-pounds  or  kilogram- 
metres  is  difficult  and  inexact.  Even  the  general  statement,  that  of  the 
heat-units  produced  by  the  body,  four-fifths  remain  as  heat  and  one-fifth  is 
converted  into  work,  must  be  regarded  as  merely  approximate. 

In  the  animal  organism,  a  part  of  the  potential  energy  of  the  tissues  may 
be  converted  into  force  by  voluntary  effort.  In  fevers,  an  abnormally  large 
proportion  of  the  potential  energy  of  the  organism  is  converted  into  heat, 
and  it  is  not  possible  to  use  much  of  this  energy  as  force.  These  and  other 
peculiarities  of  living  bodies,  as  regards  the  production  of  heat  and  force, 
are  difficult  of  explanation.  In  the  essential  fevers,  the  conditions  which 
involve  the  abnormal  production  of  heat  finally  consume  the  substance  of  the 
tissues.  They  involve  especially  an  increased  production  of  carbon  dioxide 
and  urea  and  not  to  any  great  extent  the  formation  of  water.  If  heat-pro- 
ducing alimentary  substances  and  alcohol  can  be  introduced  and  consumed, 
the  tissues  are  thereby  proportionally  saved  from  destruction  and  degenera- 
tions. 


4:60  MOVEMENTS— VOICE  AND  SPEECH. 

CHAPTER   XV. 

MOVEMENTS— VOICE  AND  SPEECH. 

Amorphous  contractile  substance  and  amoeboid  movements — Ciliary  movements— Movements  due  to  elas- 
ticity—Elastic tissue — Muscular  movements— Physiological  anatomy  of  the  involuntary  muscular  tissue 
— Contraction  of  the  involuntary  muscular  tissue— Physiological  anatomy  of  the  voluntary  muscular 
tissue— Connective  tissue— Connection  of  the  muscles  with  the  tendons— Chemical  composition  of  the 
muscles — Physiological  properties  of  the  muscles — Muscular  contractility,  or  excitability — Muscular 
contraction — Electric  phenomena  in  muscles — Muscular  effort — Passive  organs  of  locomotion — Physio- 
logical anatomy  of  the  bones — Physiological  anatomy  of  cartilage — Voice  and  speech — Sketch  of  the 
physiological  anatomy  of  the  vocal  organs — Mechanism  of  the  production  of  the  voice — Laryngeal 
mechanism  of  the  vocal  registers— Mechanism  of  speech — The  phonograph. 

THE  various  processes  connected  with  the  nutrition  of  animals  involve 
certain  movements;  and  almost  all  animals  possess  in  addition  the  power 
of  locomotion.  Many  of  these  movements  have  of  necessity  been  considered 
in  connection  with  the  different  functions ;  as  the  action  of  the  heart  and 
vessels  in  the  circulation,  the  uses  of  the  muscles  in  respiration,  the  ciliary 
movements  in  the  air-passages,  the  muscular  acts  in  deglutition,  the  peri- 
staltic movements  and  the  mechanism  of  defaecation  and  urination.  There 
remain,  however,  certain  general  facts  with  regard  to  various  kinds  of  move- 
ment and  the  mode  of  action  of  the  different  varieties  of  muscular  tissue, 
that  will  demand  more  or  less  extended  consideration.  As  regards  the  varied 
and  complex  acts  concerned  in  locomotion,  it  is  difficult  to  fix  a  limit  between 
anatomy  and  physiology.  A  full  comprehension  of  such  movements  should 
be  preceded  by  a  complete  descriptive  anatomical  account  of  the  passive  and 
active  organs  of  locomotion  ;  and  special  treatises  on  anatomy  give  the  uses 
and  actions  as  well  as  the  structure  and  relations  of  these  parts. 

Amorphous  Contractile  Substance  and  Amoeboid  Movements. — In  some  of 
the  lowest  forms  of  beings,  in  which  hardly  any  thing  but  amorphous  mat- 
ter and  a  few  granules  can  be  recog- 
nized by  the  microscope,  certain 
movements  of  elongation  and  retrac- 
tion of  their  amorphous  substance 
have  been  observed.  In  the  higher 
animals,  similar  movements  have 
been  noticed  in  certain  of  their  struct- 
ures, such  as  the  leucocytes,  the  con- 

FIQ.  142.—  Amoeba  diffluens,  changing  inform  and 

moving  in  the  direction  indicated  by  the  ar-      tents  of  the  OVUm,  epithelial  Cells  and 
row  (Longet).  '    * 

connective-tissue  cells.  1  hese  move- 
ments generally  are  simple  changes  in  the  form  of  the  cell,  nucleus,  or  what- 
ever it  may  be.  They  depend  upon  an  organic  principle  formerly  called  sar- 
code  and  now  known  as  protoplasm ;  but  it  is  not  known  that  such  move- 
ments are  characteristic  of  any  one  definite  constituent  of  the  body,  nor  is  it 
easy  to  determine  their  cause  and  their  physiological  importance.  In  the 
anatomical  elements  of  adult  animals  of  the  higher  classes,  these  movements 
usually  appear  slow  and  gradual,  even  when  viewed  with  high  magnifying 
powers;  but  in  some  of  the  very  lowest  forms  of  life,  these  movements 


CILIAEY  MOVEMENTS.  461 

serve  as  a  means  of  progression  and  are  more  rapid.  Such  movements  are 
called  amoeboid.  It  does  not  seem  possible  to  explain  the  nature  and  cause 
of  the  movements  of  homogeneous  contractile  substance ;  and  it  must  be  ex- 
cessively difficult,  if  not  impossible,  to  observe  directly  the  effects  of  differ- 
ent stimuli,  in  the  manner  in  which  the  movements  of  muscles  are  studied. 
They  seem  to  be  analogous  to  the  ciliary  movements,  the  cause  of  which  is 
equally  obscure. 

Ciliary  Movements. — The  epithelium  covering  certain  of  the  mucous 
membranes  is  provided  with  little,  hair-like  processes  upon  the  borders  of 
the  cells,  called  cilia.  These  are  in  constant  motion,  from  the  beginning  to 
the  end  of  life,  and  they  produce  currents  upon  the  surfaces  of  the  mem- 
branes to  which  they  are  attached,  the  direction  being  generally  from  within 
outward.  In  man  and  in  the  warm-blooded  animals  generally,  the  ciliated 
or  vibratile  epithelium  is  of  the  variety  called  columnar,  conoidal  or  pris- 
moidal.  The  cilia  are  attached  to  the  thick  ends  of  the  cells,  and  they  form 
on  the  surface  of  the  membrane  a  continuous  sheet  of  vibrating  processes. 
In  general  structure  the  ciliary  processes  are  entirely  homogeneous,  and  they 
gradually  taper  from  their  attachment  to  the  cell  to  an  extremity  of  excess- 
ive tenuity. 

The  presence  of  cilia  has  been  demonstrated  upon  the  following  surfaces : 
The  respiratory  passages,  including  the  nasal  fossas,  the  pituitary  membrane, 
the  summit  of  the  larynx,  the  bronchial  tubes,  the  superior  surface  of  the 
velum  palati  and  the  Eustachian  tubes ;  the  sinuses  about  the  head ;  the 
lachrymal  sac  and  the  internal  surface  of  the  eyelids ;  the  genital  passages  of 
the  female,  from  the  middle  of  the  neck  of  the  uterus  to  the  fimbriated 
extremities  of  the  Fallopian  tubes ;  the  ventricles  of  the  brain.  In  these 
situations,  on  each  cell  of  conoidal  epithelium  are 
six  to  twelve  prolongations, about  2g^00  of  an  inch 
(1  p.)  in  thickness  at  their  base,  and  -goVo  ^°  nrVo 
of  an  inch  (5  to  6  /u.)  in  length.  Between  the  cilia 
and  the  substance  of  the  cell,  there  is  usually  a 
thin,  transparent  disk.  The  appearance  of  the  cilia 
is  represented  in  Fig.  143.  When  seen  in  situ, 
they  appear  regularly  disposed  upon  the  surface, 
are  of  nearly  equal  length  and  are  generally  slight- 
ly inclined  in  the  direction  of  the  opening  of  the 
cavity  lined  by  the  membrane. 

When  the  ciliary  movements  are  seen  in  a  large  number  of  cells  in  situ, 
the  appearance  is  well  illustrated  by  the  comparison  by  Henle  to  the  undula- 
tions of  a  field  of  wheat  agitated  by  the  wind.  In  watching  this  movement, 
it  is  usually  seen  to  gradually  diminish  in  rapidity,  until  what  at  first  ap- 
peared simply  as  currents,  produced  by  movements  too  rapid  to  be  studied 
in  detail,  become  revealed  as  distinct  undulations,  in  which  the  action  of 
individual  cilia  can  be  readily  studied.  Several  kinds  of  movement  have 
been  described,  but  the  most  common  is  a  bending  of  the  cilia,  simultaneously 
or  in  regular  succession,  in  one  direction,  followed  by  an  undulating  return 

31 


4:62  MOVEMENTS— VOICE  AND  SPEECH. 

to  the  perpendicular.  The  other  movements,  such  as  the  infundibuliform, 
in  which  the  point  describes  a  circle  around  the  base,  the  pendulum-move- 
ment etc.,  are  not  common  and  are  unimportant. 

The  combined  action  of  the  cilia  upon  the  surface  of  a  mucous  mem- 
brane, moving  as  they  do  in  one  direction,  is  to  produce  currents  of  consid- 
erable power.  This  may  be  illustrated  under  the  microscope  by  covering  the 
surface  with  a  liquid  holding  little,  solid  particles  in  suspension ;  when  the 
granules  are  tossed  from  one  portion  of  the  field  to  another,  with  consid- 
erable force.  It  is  not  difficult,  indeed,  to  measure  in  this  way  the  rapidity 
of  the  ciliary  currents.  In  the  frog  it  has  been  estimated  at  ^\^  to  y^-g-  of  an 
inch  (100  to  140  ft)  per  second,  the  number  of  vibratile  movements  being 
seventy-five  to  one  hundred  and  fifty  per  minute.  In  the  fresh- water  polyp 
the  movements  are  more  rapid,  being  two  hundred  and  fifty  or  three  hundred 
per  minute.  There  is  no  reliable  estimate  of  the  rapidity  of  the  ciliary  cur- 
rents in  man,  but  they  are  probably  more  active  than  in  animals  low  in  the 
scale. 

The  movements  of  cilia,  like  those  observed  in  fully  developed  spermato- 
zoids,  seem  to  be  independent  of  nervous  influence,  and  they  are  affected  only 
by  local  conditions.  They  will  continue,  under  favorable  circumstances,  for 
more  than  twenty-four  hours  after  death,  and  they  can  be  seen  in  cells  entire- 
ly detached  from  the  body  when  they  are  moistened  with  proper  fluids.  When 
the  cells  are  moistened  with  pure  water,  the  activity  of  the  movement  is  at 
first  increased ;  but  it  soon  disappears  as  the  cells  become  swollen.  Acids 
arrest  the  movement,  but  it  may  be  excited  by  feebly  alkaline  solutions. 
There  seems  to  be  no  possibility  of  explaining  the  movement  except  by  a 
simple  statement  of  the  fact  that  the  cilia  have  the  property  of  moving  in  a 
certain  way  so  long  as  they  are  under  normal  conditions.  As  regards  the 
physiological  uses  of  these  movements,  it  is  sufficient  to  refer  to  the  physi- 
ology of  the  parts  in  which  cilia  are  found,  where  the  peculiarities  of  their 
action  are  considered  more  in  detail.  In  the  lungs  and  the  air-passages  gen- 
erally and  in  the  genital  passages  of  the  female,  the  currents  are  of  consid- 
erable importance ;  but  it  is  difficult  to  imagine  the  use  of  these  movements 
in  certain  other  situations,  as  the  ventricles  of  the  brain. 

Movements  due  to  Elasticity. — There  are  certain  important  movements 
in  the  body  that  are  due  simply  to  the  action  of  elastic  ligaments  or  mem- 
branes. These  are  distinct  from  muscular  movements,  and  are  not  even  to 
be  classed  with  the  movements  produced  by  the  resiliency  of  muscular  tissue, 
in  which  muscular  tonicity  is  more  or  less  involved.  Movements  of  this  kind 
consist  simply  in  the  return  of  movable  parts  to  a  certain  position  after  they 
have  been  displaced  by  muscular  action,  and  in  the  reaction  of  tubes  after 
forcible  distention,  as  in  the  walls  of  the  large  arteries. 

Elastic  Tissue. — Most  anatomists  adopt  the  division  of  the  elements 
of  elastic  tissue  into  three  varieties.  This  division  relates  to  the  size  of 
the  fibres ;  and  all  varieties  are  found  to  possess  essentially  the  same  chem- 
ical composition  and  general  properties.  On  account  of  the  yellow  color  of 
this  tissue,  presenting,  as  it  does,  a  strong  contrast  to  the  white,  glistening 


MOVEMENTS  DUE  TO   ELASTICITY. 


463 


um  •'  magnified  350  di- 
ameters  (Kolliker). 


FIG.  145.—  Larger  elastic  fibres 
(Robin). 


appearance  of  the  inelastic  fibres,  it  is  frequently  called  the  yellow,  elastic 
tissue. 

The  first  variety  of  elastic  tissue  is  composed  of  small  fibres,  generally  in- 
termingled with  fibres  of  the  ordinary  inelastic  tissue.     They  possess  all  the 
chemical  and  physical  charac- 
ters of  the  larger  fibres,  but  are 
very  fine,  measuring  ^-j^nr  to 

TroVo-  or  yoVo-  of  an  inch  (1  to  4 
or  5  /*)  in  diameter.  If  acetic 
acid  be  added  to  a  preparation 
of  ordinary  connective  tissue, 
the  inelastic  fibres  are  rendered 
semi-transparent,  but  the  elas- 
tic fibres  are  unaffected  and  be- 
come quite  distinct.  They  are 
then  seen  isolated,  that  is,  never 
arranged  in  bundles,  generally 
with  a  dark,  double  contour, 

h  ran  phi  no-      hrittlp      anrl     whpn    FlG-  144-—  Small  elastic  fi- 
Drancnmg,     I         ,16,    ant  bresfrom  the  per/tone- 

Ivrntpn    thpir  PvfrpTYiiHp<!  pnvlprl 
OKen,  tl 

and  presenting  a  sharp  fract- 
ure, like  a  piece  of  India-rubber.  These  fibres  pursue  a  wavy  course  between 
the  bundles  of  inelastic  fibres  in  the  areolar  tissue  and  in  most  of  the  ordinary 
fibrous  membranes.  They  are  found  in  greater  or  less  abundance  in  the 
situations  just  mentioned  ;  in  the  ligaments,  but  not  the  tendons  ;  in  the  lay- 
ers of  non-striated  muscular  tissue  ;  the  true  skin  ;  the  true  vocal  chords  ;  the 
trachea,  bronchial  tubes,  and  largely  in  the  parenchyma  of  the  lungs  ;  the 
external  layer  of  the  large  arteries  ;  and,  in  brief,  in  nearly  all  situations  in 
which  the  ordinary  connective  tissue  exists. 

The  second  variety  of  elastic  tissue  is  composed  of  fibres,  larger  than  the 
first,  ribbon-shaped,  with  well-defined  outlines,  anatomosing,  undulating  or 
curved  in  the  form  of  the  letter  S,  presenting  the  same 
curled  ends  and  sharp  fracture  as  the  smaller  fibres. 
These  measure  -g-gVrr  to  30*00  °f  an  ^ncn  (5  to  8  /*)  in  di- 
ameter. Their  type  is  found  in  the  ligamenta  subflava 
and  the  ligamentum  nuchae.  They  are  also  found  in 
some  of  the  ligaments  of  the  larynx,  the  stylo-hyoid  liga- 
ment and  the  suspensory  ligament  of  the  penis. 

The  third  variety  of  elastic  tissue  is  found  forming 
.—  Large  elastic  the  middle  coat  of  the  large  arteries,  and  it  has  already 
been  described  in  connection  with  the  vascular  system. 
°Lrse-  The  fibres  are  large  and  flat>  inosculating  freely  with 
diame~  each  other  by  short,  communicating  branches.  These 
anastomosing  fibres,  forming  the  so-called  fenestrated 
membranes,  are  arranged  in  layers,  and  the  structure  is  sometimes  called  the 
lamellar  elastic  tissue. 


"erf 


id  oathe 


464:  MOVEMENTS— VOICE  AND  SPEECH. 

The  great  resistance  which  the  elastic  tissue  presents  to  chemical  action 
serves  to  distinguish  it  from  nearly  every  other  structure  in  the  body.  It  is 
not  affected  by  acetic  acid  or  by  boiling  with  sodium  hydrate.  It  is  not  soft- 
ened by  prolonged  boiling  in  water,  but  it  is  slowly  dissolved,  without  decom- 
position, by  sulphuric,  nitric  or  hydrochloric  acid,  the  solution  not  being 
precipitable  by  potassium  hydrate.  Its  organic  constituent  is  a  nitrogenized 
substance  called  elastine,  containing  carbon,  hydrogen,  oxygen  and  nitrogen, 
without  sulphur.  This  is  supposed  to  be  identical  with  the  sarcolemma  of 
the  muscular  tissue. 

The  purely  physical  property  of  elasticity  plays  an  important  part  in 
many  of  the  animal  functions.  Examples  of  this  are  in  the  action  of  the 
large  arteries  in  the  circulation,  and  in  the  resiliency  of  the  parenchyma  of 
the  lungs.  The  ligamenta  subflava  and  the  ligamentum  nuchae  are  important 
in  aiding  to  maintain  the  erect  position  of  the  body  and  head  and  to  restore 
this  position  when  flexion  has  been  produced  by  muscular  action.  Still,  the 
contraction  of  muscles  also  is  necessary  to  keep  the  body  in  a  vertical  posi- 
tion. 

MUSCULAR  MOVEMENTS. 

The  muscular  movements  are  divided  into  voluntary  and  involuntary; 
and  generally  there  is  a  corresponding  division  of  the  muscles  as  regards 
their  minute  anatomy.  The  latter,  however,  is  not  absolute ;  for  there  are  cer- 
tain involuntary  actions,  like  the  contractions  of  the  heart  or  the  movements 
of  deglutition,  that  require  the  rapid,  vigorous  contraction  characteristic  of 
the  voluntary  muscular  tissue,  and  here  the  structure  resembles  that  of  the 
voluntary  muscles.  With  a  few  exceptions,  however,  the  anatomical  division 
of  the  muscular  tissue  into  voluntary  and  involuntary  is  sufficiently  distinct. 

Physiological  Anatomy  of  the  Involuntary  Muscular  Tissue. — The  invol- 
untary muscular  system  presents  a  striking  contrast  to  the  voluntary  muscles, 
not  only  in  its  minute  anatomy  and  mode  of  action,  but  in  the  arrangement 
of  its  fibres.  While  the  voluntary  muscles  are  almost  invariably  attached  by 
their  extremities  to  movable  parts,  the  involuntary  muscles  form  sheets  or 
membranes  in  the  walls  of  hollow  organs,  and  by  their  contraction,  they  sim- 
ply modify  the  capacity  of  the  cavities  which  they  surround.  On  account  of 
the  peculiar  structure  of  the  fibres,  they  have  been  called  muscular  fibre-cells, 
smooth  muscular  fibres,  pale  fibres,  non-striated  fibres,  fusiform  fibres  and  con- 
tractile cells.  The  distribution  of  these  fibres  to  parts  concerned  in  the  or- 
ganic functions,  as  the  alimentary  canal,  has  given  them  the  name  of  organic 
muscular  fibres,  or  fibres  of  organic  life.  In  their  natural  condition,  the 
involuntary  muscular  fibres  are  pale,  finely  granular,  flattened,  and  of  an 
elongated  spindle-shape,  with  a  very  long,  narrow,  almost  linear  nucleus  in 
the  centre.  The  nucleus  generally  has  no  distinct  nucleolus,  and  it  is  some- 
times curved  or  shaped  like  the  letter  S.  The  ordinary  length  of  these  fibres 
is  about -g^y  (50  /x,)  and  their  breadth,  about  ^Vo  °f  an  incn  (6  /*)•  I11  the 
gravid  uterus  they  undergo  remarkable  hypertrophy,  measuring  here  -g^  to-g1^ 
of  an  inch  (300  to  500  /*)  in  length,  and  2Q*00  of  an  inch  (12  /JL)  in  breadth. 


MUSCULAR  MOVEMENTS. 


465 


In  the  contractile  sheets  formed  of  involuntary  muscular  tissue,  the  fibres 
are  arranged  side  by  side,  are  closely  adherent,  and  their  extremities  are,  as 


FIG.  148. — Muscular  fibres 
from  the  aorta  of  the 
calf ;  magnified  200 
diameters  (Sappey). 

1, 1,  fibres  joined  with  each 
other ;  2,  2,  2,  isolated 
fibres. 


FIQ.  149.— Muscular  fibres  from  the  uterus  of 
a  woman  who  died  at  the  ninth  month  of 

utero-gestation  ;    magnified   350   diameters 
(Sappey). 

1,  1,2,  short,  wide  fibres  ;  3,  4,  5,  5.  longer  and 
narrower  fibres ;  6,  6,  two  fibres  united 
at  7  ;  8,  small  fibres  in  process  of  develop- 
ment. 


FIG.  147. — Muscular  fibre* 
from  the  urinary  blad- 
der of  thehuman  subject; 
magnified  200  diameters 
(Sappey). 

1,  1,  1,  nuclei  ;  2,  2,  2,  bor- 
ders of  some  of  the 
fibres  :  3,  3,  isolated 
fibres ;  4,  4,  two  fibres 
joined  together  at  5. 

it  were,  dove-tailed  into  each  other.  Generally  the  borders  of  the  fibres  are 
regular  and  their  extremities  are  simple ;  but  sometimes  the  ends  are  forked 
and  the  borders  present  one  or  more  little  projections.  The  fibres  seldom 
exist  in  a  single  layer  except  in  the  very  smallest  arterioles.  Usually  the  layers 
are  multiple,  being  superimposed  in  regular  order.  The  action  of  acetic  acid 
is  to  render  the  fibres  pale  so  that  their  outlines  become  almost  indistin- 
guishable, and  to  bring  the  nuclei  more  distinctly  into  view. 

Contraction  of  the  Involuntary  Muscular  Tissue. — The  mode  of  contrac- 
tion of  the  involuntary  muscles  is  peculiar.  It  does  not  take  place  immedi- 
ately upon  the  reception  of  a  stimulus,  applied  either  directly  or  through  the 
nerves,  but  it  is  gradual,  enduring  for  a  time  and  then  followed  by  slow  and 
gradual  relaxation.  A  description  of  the  peristaltic  movements  of  the  intes- 
tines gives  an  idea  of  the  mode  of  contraction  of  these  fibres,  with  the  grad- 
ual propagation  of  the  stimulus  along  the  alimentary  canal  as  the  food  makes 
its  impression  upon  the  mucous  membrane.  Another  illustration  is  afforded 
by  labor-pains.  These  are  due  to  the  muscular  contractions  of  the  uterus, 
and  they  last  for  a  few  seconds  or  one  or  two  minutes.  Their  gradual  access, 
continuation  for  a  certain  period,  and  gradual  disappearance  coincide  with 
the  history  of  the  contractions  of  the  involuntary  muscular  fibres. 

The  contraction  of  the  involuntary  muscular  tissue  is  slow,  and  the  fibres 
return  slowly  to  a  condition  of  repose.  The  movements  are  always  involun- 


466  MOVEMENTS— VOICE  AND  SPEECH. 

tary.  Peristaltic  action  is  the  rule,  and  the  contraction  takes  place  progress- 
ively and  without  oscillations.  Contractility  persists  for  a  long  time  after 
death.  Excitation  of  the  nerves  has  less  influence  upon  contraction  of  these 
fibres  than  direct  excitation  of  the  muscles.  The  involuntary  muscular  tis- 
sue is  regenerated  very  rapidly,  while  the  structure  of  the  voluntary  muscles 
is  restored  with  great  difficulty  after  destruction  or  division  (Legros  and  Oni- 
mus). 

Physiological  Anatomy  of  the  Voluntary  Muscular  Tissue. — A  voluntary 
muscle  contains,  in  addition  to  its  peculiar  contractile  substance,  fibres  of  in- 
elastic and  elastic  tissue,  adipose  tissue,  abundant  blood-vessels,  nerves  and 
lymphatics,  with  certain  nuclear  and  cellular  anatomical  elements.  The 
muscular  system  in  a  well  proportioned  man  is  equal  to  about  two-fifths  of  the 
weight  of  the  body  (Sappey).  Its  nutrition  consumes  a  large  proportion  of 
the  reparative  material  of  the  blood,  while  its  disassimilation  furnishes  a  cor- 
responding quantity  of  excrementitious  matter.  The  condition  of  the  mus- 
cular system,  indeed,  is  an  almost  unfailing  evidence  of  the  general  state  of 
the  body,  allowing,  of  course,  for  peculiarities  in  different  individuals. 
Among  the  characteristic  properties  of  the  muscles,  are  elasticity,  a  constant 
and  insensible  tendency  to  contraction,  called  tonicity,  the  power  of  contract- 
ing forcibly  on  the  reception  of  a  proper  stimulus,  and  a  peculiar  kind  of 
sensibility.  The  relations  of  particular  muscles,  as  taught  by  descriptive  anat- 
omy, involve  special  acts  ;  but  the  most  important  physiological  points  con- 
nected with  this  system  relate  to  the  general  properties  and  uses  of  the  mus- 
cles. 

The  voluntary  muscles  are  made  up  of  a  great  number  of  microscopic 
fibres,  known  as  the  primitive  muscular  fasciculi.  These  are  called  red,  stri- 
ated or  voluntary  fibres.  Their  structure  is  complex,  and  they  may  be  sub- 
divided longitudinally  into  fibrillae  and  transversely  into  disks.  In  very  short 
muscles,  some  of  the  primitive  fasciculi  may  run  the  entire  length  of  the 
muscle;  but  the  fasciculi  usually  are  1-2  to  1-6  inch  (30  to  40  mm.)  in 
length.  The  fasciculi,  however,  do  not  inosculate  with  each  other,  but  the 
end  of  one  fasciculus  is  united  longitudinally  with  the  end  of  another  by  a 
strongly  adhesive  substance,  the  line  of  union  being  oblique ;  so  that  the  fibres 
practically  run  the  entire  length  of  the  muscle.  Each  fasciculus  is  enclosed  in 
its  own  sheath,  without  branching  or  inosculation.  This  sheath  contains 
the  true  muscular  substance  only,  and  it  is  not  penetrated  by  blood-vessels, 
nerves  or  lymphatics.  In  a  thin,  transverse  section  of  a  muscle,  the  divided 
ends  of  the  fibres  present  an  irregularly  polygonal  form  with  rounded  cor- 
ners. They  seem  to  be  cylindrical,  however,  when  viewed  in  their  length  and 
isolated.  Their  color  by  transmitted  light  is  a  delicate  amber,  resembling 
the  color  of  the  blood-corpuscles. 

The  primitive  fasciculi  vary  very  much  in  size  in  different  individuals,  in 
the  same  individual  under  different  conditions,  and  in  different  muscles.  As 
a  rule  they  are  smaller  in  young  persons  and  in  females  than  in  adult  males. 
They  are  comparatively  small  in  persons  of  slight  muscular  development. 
In  persons  of  great  muscular  vigor,  or  when  the  general  muscular  system  or 


MUSCULAR  MOVEMENTS. 


467 


particular  muscles  have  been  increased  in  size  and  power  by  exercise,  the  fas- 
ciculi are  relatively  larger.  It  is  probable  that  the  physiological  increase  in 
the  size  of  a  muscle  from  exercise  is  due  to  an  increase  in  the  size  of  the  pre- 


FIG.  150.—  Striated  muscular  fibres  from  the  mouse ;  magnified  500  diameters  (from  a  photograph 

taken  at  the  United  States  Army  Medical  Museum). 
The  injected  capillaries  are  seen,  somewhat  out  of  focus. 

existing  fasciculi  and  not  to  the  formation  of  new  elements.  In  young  per- 
sons the  fasciculi  are  y^ViF  to  T^fro  °f  an  inch  (15  to  20  /*)  in  diameter.  In 
the  adult  they  measure  ^^  to  ^^  of  an  inch  (55  to  100  //,). 

The  appearance  of  the  primitive  muscular  fasciculi  under  the  microscope 
is  characteristic.  They  present  regular,  transverse  strise,  formed  of  alternat- 
ing dark  and  clear  bands  about  j^^nr  °f  an  in°h  (1  /".)  wide.  With  a  high 
magnifying  power,  a  very  fine  transverse  line  is  observed  running  through  the 
middle  of  each  one  of  the  clear  bands.  In  addition  they  present  longitudi- 
nal strise,  not  so  distinct,  and  difficult  to  follow  to  any  extent  in  the  length 
of  the  fasciculus,  but  tolerably  well  marked,  particularly  in  muscles  that 
are  habitually  exercised.  The  muscular  substance,  presenting  this  peculiar, 
striated  appearance,  is  enclosed  in  a  very  thin  but  elastic  and  resisting  tubu- 
lar membrane,  called  the  sarcolemma  or  myolemma.  This  envelope  can  not 
be  seen  in  ordinary  preparations  of  the  muscular  tissue ;  but  it  frequently 
happens  that  the  contractile  muscular  substance  is  broken,  leaving  the  sarco- 
lemma intact,  which  gives  a  good  view  of  the  membrane  and  conveys  an  idea 


468 


MOVEMENTS— VOICE  AND  SPEECH. 


magnified  250 


of  its  strength  and  elasticity.  Attached  to  the  inner  surface  of  the  sarco- 
lemma,  are  small,  elongated  nuclei  with  their  long  diameter  in  the  direction 
of  the  fasciculi.  These  are  usually  not  well  seen  in  the  unaltered  muscle,  but 
the  addition  of  acetic  acid  renders  the  muscular  substance  pale  and  destroys 
the  striae,  when  the  nuclei  become  distinct. 

Water  after  a  time  acts  upon  the  muscular  tissue,  rendering  the  fasciculi 

somewhat  paler  and  larger.  Acetic 
acid  and  alkaline  solutions  efface  the 
striae,  and  the  fibres  become  semi-trans- 
parent. In  fasciculi  that  are  slightly 
decomposed,  there  is  frequently  a  sepa- 
ration at  the  extremity  into  smaller 
fibres,  called  fibrilLne.  These,  when 
isolated,  present  the  same  striated  ap- 
pearance as  the  primitive  fasciculus ; 
viz.,  alternate  dark  and  light  portions. 
They  measure  about  -^^^  of  an  inch 
(1  /*)  in  diameter,  and  their  number, 
in  the  largest  primitive  fibres,  is  esti- 
mated at  about  two  thousand  (Kolli- 
ker).  The  interior  of  each  primitive 
fasciculus  is  penetrated  by  a  very  del- 

A,  transverse  striae  and  nuclei  of  a  primitive  f ascic-    i  Pa  f  P    m  pnl  hra  r,  P    pi  nsipl  v    <m  rrnn  n  i\  \  n  o- 
ulus:    B,  longitudinal  striae  _  and  flbrilte  of  a    l  'elJ   SUrrounamg 

the  fibrillae.  This  arrangement  may 
be  distinctly  seen  in  a  thin  section  of 
a  fibre  treated  with  a  solution  of  common  salt  in  water,  in  the  proportion  of 
five  parts  per  thousand  (Kolliker). 

Connective  Tissue. — In  the  muscles  there  is  a  membrane  surrounding  a 
number  of  the  primitive  fasciculi.  This  is  called  the  perimysium.  The 
fibrous  membranes  that  connect  together  the  sesecondary  bundles,  with  their 
contents,  are  enclosed  in 
a  sheath  enveloping  the 
whole  muscle,  sometimes 
called  the  external  peri- 
mysium. The  peculiari- 
ty of  these  membranes  as 
distinguished  from  the 
sarcolemma  is  that  they 
have  a  fibrous  structure 
and  are  connected  togeth- 
er throughout  the  muscle, 
while  the  tubes  forming 
the  sarcolemma  are  struct- 
ureless and  each 


FIG.  151. — Striated  muscular  fibres 
diameters  (Sappey). 


primitive  fasciculus  in  which  the  sarcolemma 
has  been  lacerated  at  one  point  by  pressure. 


FIG.  152.—  Fibres  of  tendon  of  the  human  subject  (Rollett). 


one  is 
distinct. 

The  name  now  most  generally  adopted  for  the  ordinary  fibrous  tissue  is 


CONNECTIVE  TISSUE. 


469 


connective  tissue.  It  has  been  called  cellular,  areolar  or  fibrous,  but  most 
of  these  names  were  given  to  it  without  a  clear  idea  of  its  structure.  Its  prin- 
cipal anatomical  element  is  a  fibre  of  excessive  tenuity,  wavy  and  with  a  sin- 
gle contour.  These  fibres  are  collected  into  bundles  of  variable  size  and 
are  held  together  by  an  adhesive  amorphous  substance.  The  wavy  lines  that 
mark  the  bundles  of  fibres  give  them  a  very  characteristic  appearance. 

The  direction  and  arrangement  of  the  fibres  in  the  various  tissues  present 
marked  differences.  In  the  loose  areolar  tissue  beneath  the  skin  and  between 
the  muscles,  and  in  the  loose  structure  surrounding  some  of  the  glands  and 
connecting  the  sheaths  of  blood-vessels  and  nerves  to  the  adjacent  parts,  the 
bundles  of  fibres  form  a  large  net-work  and  are  very  wavy  in  their  course. 
In  the  strong,  dense  membranes,  as  the  aponeuroses,  the  proper  coats  of  many 
glands,  the  periosteum  and  perichondrium  and  the  serous  membranes,  the 
waves  of  the  fibres  are  shorter,  and  the  fibres  themselves  interlace  much  more 
closely.  In  the  ligaments  and  tendons,  the  fibres  are  more  nearly  straight 
and  are  arranged  longitudinally. 

On  the  addition  of  acetic  acid  the  bundles  of  inelastic  fibres  swell  up, 
become  semi-transparent,  and  the  nuclei  and  elastic  fibres  are  brought  into 


FIG.  153.— Loose  net-work  of  connective  tissue  from  the  human  subject,  showing  the  fibres  and  cells 

(Rollett). 
a,  a,  a  capillary  blood-vessel. 

view.  The  proportion  of  elastic  fibres  differs  very  much  in  different  situa- 
tions, but  they  are  all  of  the  smallest  variety,  and  they  present  a  striking 
contrast  to  the  inelastic  fibres  in  their  form  and  size.  Although  they  are 
very  small,  they  always  present  a  double  contour. 

Certain  cellular  and  nuclear  elements  are  always  found  in  the  connective 
tissue.  The  cells  are  known  as  connective-tissue  cells.  They  are  very  irregu- 
lar in  size  and  form,  some  of  them  being  spindle-shaped  or  caudate,  and 


470  MOVEMENTS— VOICE  AND  SPEECH. 

others,  star-shaped.  They  possess  one,  and  sometimes  two  or  three  clear, 
ovoid  nuclei,  with  distinct  nucleoli.  On  the  addition  of  acetic  acid  the  cells 
disappear  but  the  nuclei  are  unaffected.  It  is  impossible  to  give  any  accu- 
rate measurements  of  the  cells,  on  account  of  their  great  variations  in  size. 
The  appearance  of  the  connective  tissue,  with  a  few  cells  and  nuclei,  is  repre- 
sented in  Fig.  153. 

Between  the  muscles,  and  in  the  substance  of  the  muscles,  between  the 
bundles  of  fibres,  there  always  exists  a  greater  or  less  quantity  of  adipose 
tissue  in  the  meshes  of  the  fibrous  structure. 

Blood-vessels  and  Lymphatics. — The  muscles  are  abundantly  supplied 
with  blood-vessels,  generally  by  a  number  of  small  arteries  with  two  satellite 
veins.  The  capillary  arrangement  in  this  tissue  is  peculiar.  From  the  small- 
est arterioles,  capillary  vessels  are  given  off,  arranged  in  a  net- work  with  tol- 
erably regular,  oblong,  rectangular  meshes,  their  long  diameter  following  the 
direction  of  the  fibres.  These  envelop  each  primitive  fasciculus,  enclosing 
it  completely,  the  artery  and  vein  being  upon  the  same  side.  The  capillaries 
are  smaller  than  in  any  other  part  of  the  vascular  system. 

The  arrangement  of  the  lymphatics  in  the  muscles  has  never  been  defi- 
nitely ascertained.  There  are  lymphatics  surrounding  the  large  vascular 
trunks  of  the  extremities  and  of  the  abdominal  and  thoracic  walls,  which,  it 
would  appear,  must  come  from  the  substance  of  the  muscles ;  but  they  have 
never  been  traced  to  their  origin.  Sappey  has  succeeded  in  injecting  lym- 
phatics upon  the  surface  of  some  of  the  larger  muscles,  but  he  has  not  been 
able  to  follow  them  into  the  muscular  substance. 

Connection  of  the  Muscles  with  the  Tendons. — The  primitive  muscular 
fasciculi  terminate  in  little,  conical  extremities,  which  are  received  into  corre- 
sponding depressions  in  the  bundles  of  fibres  composing  the  tendons ;  but 
this  union  is  so  close  that  the  muscle  or  the  tendon  may  be  ruptured  without 
a  separation  at  the  point  of  union.  In  the  penniform  muscles  this  arrange- 
ment is  quite  uniform.  In  other  muscles  it  is  essentially  the  same,  but  the 
perimysium  seems  to  be  continuous  with  the  loose  areolar  tissue  enveloping 
the  corresponding  tendinous  bundles. 

Chemical  Composition  of  the  Muscles. — The  most  important  nitrogenized 
constituent  of  the  muscles  is  myosine.  This  resembles  fibrin,  but  it  presents 
certain  points  of  difference  in  its  behavior  to  reagents,  by  which  it  may  be 
readily  distinguished.  One  of  its  peculiar  properties  is  that  it  is  dissolved 
at  an  ordinary  temperature  by  a  mixture  of  one  part  of  hydrochloric  acid 
and  ten  of  water.  The  muscular  substance  is  permeated  by  a  fluid,  called 
the  muscular  juice,  which  contains  certain  coagulable  albuminoid  substances. 
Combined  with  the  organic  constituents  of  the  muscular  substance  are  min- 
eral salts  in  great  variety,  which  can  not  be  separated  without  incineration. 
Certain  excrementitious  matters  have  also  been  found  in  the  muscles ;  and 
probably  nearly  all  of  those  eliminated  by  the  kidneys  exist  here,  although 
they  are  taken  up  by  the  blood  as  fast  as  they  are  produced  and  are  conse- 
quently detected  with  difficulty.  The  muscles  also  contain  inosite,  inosic 
acid,  lactic  acid  and  certain  volatile  acids  of  fatty  origin.  During  life  the 


ELASTICITY  AND  TONICITY  OF  MUSCLES.  471 

muscular  fluid  is  slightly  alkaline,  but  it  becomes  acid  soon  after  death.  The 
muscle  itself,  during  contraction,  has  an  acid  reaction.  The  muscular  juice 
is  alkaline  or  neutral  after  moderate  exercise  as  well  as  during  complete 
repose ;  but  when  a  muscle  is  made  to  undergo  excessive  exercise,  the  lactic 
and  other  acids  exist  in  greater  quantity  and  the  reaction  becomes  acid. 

PHYSIOLOGICAL  PROPERTIES  OF  THE  MUSCLES. 

The  important  general  properties  of  the  striated  muscles  are  the  following : 
1.  Elasticity ;  2.  Tonicity ;  3.  Sensibility  of  a  peculiar  kind ;  4.  Contractility, 
or  excitability.  These  are  all  necessary  to  the  physiological  action  of  the  mus- 
cles. Their  elasticity  is  brought  into  play  in  opposing  muscles  or  sets  of 
muscles ;  one  set  acting  to  move  a  part  and  to  extend  the  antagonistic  mus- 
cles, which,  by  virtue  of  their  elasticity,  retract  when  the  extending  force  is 
removed.  Their  tonicity  is  an  insensible  and  a  more  or  less  constant  con- 
traction, by  which  the  action  of  opposing  muscles  is  balanced  when  both  are 
in  the  condition  of  what  is  called  repose.  Their  sensibility  is  peculiar  and 
is  expressed  chiefly  in  the  sense  of  fatigue  and  in  the  appreciation  of  weight 
and  of  resistance  to  contraction.  Their  contractility  or  excitability  is  the 
property  which  enables  them  to  contract  under  stimulation.  All  of  these 
general  properties  strictly  belong  to  physiology,  as  do  some  special  acts  that 
are  not  necessarily  involved  in  the  study  of  ordinary  descriptive  anatomy. 

Elasticity  of  Muscles. — The  true  muscular  substance  contained  in  the 
sarcolemma  is  eminently  contractile ;  and  although  it  may  possess  a  certain 
degree  of  elasticity,  this  property  is  most  strongly  marked  in  the  accessory 
anatomical  elements.  The  interstitial  fibrous  tissue  is  loose  and  presents  a 
certain  number  of  elastic  fibres ;  and  the  sarcolemma  is  very  elastic.  It  is 
probably  the  sarcolemma  that  gives  to  the  muscles  their  retractile  power  after 
simple  extension. 

It  is  unnecessary  to  follow  out  in  detail  all  of  the  many  experiments  that 
have  been  made  upon  the  elasticity  of  muscles.  There  is  a  certain  limit,  of 
course,  to  their  perfect  elasticity — understanding  by  this  the  degree  of  exten- 
sion that  is  followed  by  complete  retraction — and  this  can  not  be  exceeded 
in  the  human  subject  without  dislocation  of  parts.  It  has  been  found  by 
Marey,  that  the  gastrocnemius  muscle  of  a  frog,  detached  from  the  body,  can 
be  extended  about  -fa  of  an  inch  (0-5  mm.)  by  a  weight  of  a  little  more  than 
300  grains  (20  grammes).  This  weight,  however,  did  not  extend  the  muscle 
beyond  the  limit  of  perfect  elasticity.  The  muscle  of  a  frog  of  ordinary  size 
was  extended  beyond  the  possibility  of  complete  restoration,  by  a  weight  of 
about  seven  hundred  and  fifty  grains  (48'6  grammes).  Marey  also  showed 
that  fatigue  of  the  muscles  increased  their  extensibility  and  diminished  their 
power  of  subsequent  retraction.  This  fact  has  an  application  to  the  physio- 
logical action  of  muscles ;  for  it  is  well  known  that  they  are  unusually  relaxed 
during  fatigue  after  excessive  exertion,  and  they  are  at  that  time  more  than 
ordinarily  extensible. 

Muscular  Tonicity. — The  muscles,  under  normal  conditions,  have  an 
insensible  and  a  constant  tendency  to  contract,  which  is  more  or  less  depend- 


472  MOVEMENTS— VOICE  AND  SPEECH. 

cnt  upon  the  action  of  the  motor  nerves.  If,  for  example,  a  muscle  be  cut 
across  in  a  surgical  operation,  the  divided  extremities  become  permanently 
retracted ;  or  if  the  muscles  of  one  side  of  the  face  be  paralyzed,  the  muscles 
upon  the  opposite  side  insensibly  distort  the  features.  It  is  difficult  to 
explain  these  phenomena  by  assuming  that  tonicity  is  due  to  reflex  action, 
for  there  is  no  evidence  that  the  contraction  takes  place  as  the  consequence 
of  a  stimulus.  All  that  can  be  said  is  that  a  muscle,  not  excessively  fatigued, 
and  with  its  nervous  connections  intact,  is  constantly  in  a  state  of  insensible 
contraction,  more  or  less  marked. 

Sensibility  of  the  Muscles. — The  muscles  possess  that  kind  of  sensibility 
which  gives  an  appreciation  of  the  power  of  resistance,  immobility,  and  elas- 
ticity of  substances  that  are  grasped,  or  which,  by  their  weight,  are  opposed 
to  the  exertion  of  muscular  power.  It  is  by  the  appreciation  of  weight  and 
resistance  that  the  force  required  to  accomplish  muscular  acts  is  regulated. 
These  properties  refer  chiefly  to  simple  muscular  efforts.  After  long-con- 
tinued exertion  there  is  a  sense  of  fatigue  that  is  peculiar  to  the  muscles. 
It  is  difficult  to  separate  this  entirely  from  the  sense  of  nervous  exhaustion, 
but  it  seems  to  be  to  a  certain  extent  distinct ;  for  when  suffering  from  the 
fatigue  that  follows  over-exertion,  it  seems  as  though  a  nervous  stimulus 
could  be  sent  to  the  muscles,  to  which  they  are  for  the  time  unable  to  respond. 

When  the  muscles  are  thrown  into  tetanic  contraction,  a  peculiar  sensa- 
tion is  produced,  which  is  entirely  different  from  painful  impressions  made 
upon  the  ordinary  sensory  nerves.  In  the  cramps  of  cholera,  tetanus,  or  the 
convulsions  from  strychnine,  these  distressing  sensations  are  very  marked. 

If  the  muscles  possess  any  general  sensibility,  it  is  very  slight.  A  muscle 
may  be  lacerated  or  irritated  without  producing  actual  pain,  although  con- 
traction produced  by  irritants  and  the  sense  of  tension  when  the  muscles  are 
drawn  upon  can  always  be  appreciated. 

Muscular  Contractility,  or  Excitability. — During  life  and  under  normal 
conditions,  the  muscles  will  always  contract  in  obedience  to  a  proper  stimulus 
applied  either  directly  or  through  the  nerves.  In  the  natural  action  of  the 
organism,  this  contraction  is  induced  by  nervous  influence  either  through  voli- 
tion or  reflex  action.  Still,  a  muscle  may  be  living  and  yet  have  lost  its  con- 
tractility. For  example,  after  a  muscle  has  been  for  a  long  time  paralyzed 
and  disused,  the  application  of  the  most  powerful  stimulus  will  fail  to  induce 
contraction ;  but  when  examined  with  the  microscope,  it  is  found  that  the 
nutrition  of  the  muscle  has  become  profoundly  affected,  and  that  the  con- 
tractile substance  has  disappeared.  Muscular  contractility  persists  for  a  cer- 
tain time  after  death  and  in  muscles  separated  from  the  body ;  and  this  fact 
has  been  taken  advantage  of  by  physiologists  in  the  study  of  the  properties 
of  the  muscular  tissue.  A  muscle  detached  from  the  living  body  continues 
for  a  time  to  respire,  and  it  undergoes  some  of  the  changes  of  disassimilation 
observed  in  the  organism.  So  long  as  these  changes  are  restricted  within 
the  limits  of  physical  and  chemical  integrity  of  the  fibre,  contractility  re- 
mains. As  these  processes  are  very  slow  in  the  cold-blooded  animals,  the 
excitability  of  all  the  parts  persists  for  a  considerable  time  after  death. 


MUSCULAR  CONTRACTILITY,   OR  EXCITABILITY. 


473 


In  the  human  subject  and  the  warm-blooded  animals,  the  muscles  cease 
to  respond  to  a  stimulus  a  few  hours  after  death,  although  the  time  of  dis- 
appearance of  excitability  is  very  variable.  Nysten,  in  a  number  of  experi- 
ments upon  the  disappearance  of  excitability  in  the  human  subject  after  de- 
capitation, found  that  different  parts  lost  their  contractility  at  different  peri- 
ods, but  that  generally  this  depended  upon  exposure  to  the  air.  With  the 
exception  of  the  right  auricle  of  the  heart,  the  striated  muscles  were  the  last 
to  lose  their  excitability.  In  one  instance,  certain  of  the  voluntary  muscles 
that  had  not  been  exposed  retained  their  contractility  seven  hours  and  fifty 
minutes  after  death.  Longet  and  Masson  found  that  an  electric  shock,  suf- 
ficiently powerful  to  produce  death  instantly,  destroyed  the  excitability  of 
the  muscular  tissue  and  of  the  motor  nerves. 

The  experiments  of  Longet  (1841)  presented  almost  conclusive  proof  of 
the  independence  of  muscular  excitability.  He  resected  the  facial  nerve  and 
found  that  it  ceased  to  respond  to  mechanical  and  electric  stimulus,  or  in 
other  words,  lost  its  excitability,  after  the  fourth  day.  Operating,  however, 
upon  the  muscles  supplied  exclusively  with  filaments  from  this  nerve,  he 
found  that  they  responded  promptly  to  me- 
chanical and  electric  stimulation,  and  that 
this  continued  for  more  than  twelve  weeks. 
In  other  experiments  it  was  shown  that  while 
the  contractility  of  the  muscles  could  be  seri- 
ously influenced  through  the  nervous  system, 
this  was  effected  only  by  modifications  in  their 
nutrition.  When  the  mixed  nerves  were  di- 
vided, the  nutrition  of  the  muscles  was  gener- 
ally disturbed  ;  and  although  muscular  con- 
tractility persisted  for  some  time  after  the 
nervous  excitability  had  disappeared,  it  be- 
came very  much  diminished  at  the  end  of  six 
weeks.  Some  varieties  of  curare  destroy  the 
excitability  of  the  motor  nerves,  leaving  the 
sensitory  filaments  intact.  If  a  frog  be  poi- 
soned by  introducing  a  little  of  this  agent 
under  the  skin,  stimulation,  electric  or  me- 
chanical, applied  to  an  exposed  nerve,  fails  to 

produce    muscular     Contraction  ;     but     if     the  FlG-  1M-—  Frog's  legs  prepared  so  as  to 

.                                     .                                   '  show  the  effects  of  curare  (Bernard). 

Stimulus   be   applied   directly   to    the    mUSCleS,  Faradization  of  the  nerves  in  this  ani- 

/i             -ii                           •                 i           T      ,-,  .                ,-,  mal.  which  has  been  poisoned  with 

they  Will  Contract  Vigorously.      In  this  Way  the  curare,  has  no  effect  ;   while   the 


contraction. 


nerves  are,  as  it  were,  dissected  out  from  the 

muscles  ;  and  the  discovery  of  an  agent  that 

will  paralyze  the  nerves  without   affecting  the   muscles  affords  conclusive 

proof  that  the  excitability  of  these  two  systems  is  distinct.     If  a  frog  be 

poisoned  with  potassium  sulphocyanide,  precisely  the  contrary  effect  is  ob- 

served ;  that  is,  the  muscles  will  become  insensible  to  excitation,  while  the 

nervous  system  is  unaffected.     This  fact  may  be  demonstrated  by  apply- 


474  MOVEMENTS— VOICE  AND  SPEECH. 

ing  a  tight  ligature  around  the  body  in  the  lumbar  region,  involving  all  the 
parts  except  the  lumbar  nerves.  If  the  poison  be  now  introduced  beneath 
the  skin  above  the  ligature,  only  the  anterior  parts  are  affected,  because  the 
vascular  communication  with  the  posterior  extremities  is  cut  off.  If  the 
exposed  nerves  be  now  stimulated,  the  muscles  of  the  legs  are  thrown  into 
contraction,  showing  that  the  nervous  excitability  remains.  Reflex  move- 
ments in  the  posterior  extremities  may  also  be  produced  by  irritation  of  the 
parts  above  the  ligature.  These  experiments  leave  no  doubt  of  the  existence 
of  an  inherent  and  independent  excitability  in  the  muscular  tissue  (Bernard). 
Contractions  of  muscles,  it  is  true,  are  normally  excited  through  the  nervous 
system,  and  artificial  stimulation  of  a  motor  nerve  is  the  most  efficient  method 
of  producing  the  simultaneous  action  of  all  the  fibres  of  a  muscle  or  of  a  set 
of  muscles ;  but  electric,  mechanical,  or  chemical  irritation  of  the  muscles 
themselves  will  produce  contraction,  after  the  nervous  excitability  has  been 
abolished.  The  conditions  under  which  muscular  contractility  exists  are 
simply  those  of  normal  nutrition  of  the  muscular  tissue.  When  the  muscles 
have  become  profoundly  affected  in  their  nutrition,  as  the  result  of  section 
of  the  mixed  nerves  or  after  prolonged  paralysis,  their  excitability  disappears 
and  can  not  be  restored. 

Experiments  have  been  made  with  regard  to  the  influence  of  the  cir- 
culation upon  muscular  excitability,  chiefly  with  reference  to  the  effects  of 
tying  large  vessels.  Longet  tied  the  abdominal  aorta  in  five  dogs  and  found 
that  voluntary  motion  ceased  in  about  a  quarter  of  an  hour,  and  that  the 
muscular  excitability  was  extinct  in  two  hours  and  a  quarter.  When  the 
circulation  was  restored,  after  three  or  four  hours,  by  removing  the  ligature, 
the  excitability,  and  finally  voluntary  movement,  returned.  These  experiments 
show  that  the  circulation  of  the  blood  is  necessary  to  the  contractility  of  the 
muscles.  Tying  the  vena  cava  did  not  affect  the  excitability  of  the  muscles. 
In  dogs  in  which  this  experiment  was  performed,  the  lower  extremities  pre- 
served their  contractility,  and  the  voluntary  movements  were  unaffected  up 
to  the  time  of  death,  which  took  place  in  twenty-six  hours. 

The  relations  of  muscular  excitability  to  the  circulation  have  been  farther 
illustrated  in  the  following  experiments  by  Brown-Sequard :  The  first  ob- 
servations were  made  upon  two  men  executed  by  decapitation.  Thirteen 
hours  and  ten  minutes  after  death,  when  the  muscular  excitability  had  disap- 
peared and  was  succeeded  by  cadaveric  rigidity,  a  quantity  of  fresh,  defibri- 
nated  venous  blood  from  the  human  subject  was  injected  into  the  arteries  of 
one  hand  and  was  returned  by  the  veins.  It  was  afterward  re-injected  sev- 
eral times  during  a  period  of  thirty-five  minutes.  The  whole  time  occupied 
in  the  different  injections  was  ten  to  fifteen  minutes.  Ten  minutes  after  the 
last  injection,  and  about  fourteen  hours  after  death,  the  excitability  was  found 
to  have  returned  in  a  marked  degree  in  twelve  muscles  of  the  hand.  There 
were  only  two  muscles  out  of  the  nineteen,  in  which  the  excitability  could  not 
be  demonstrated.  Three  hours  after,  the  excitability  still  existed,  but  it  disap- 
peared a  quarter  of  an  hour  later.  The  second  observation  was  essentially 
the  same,  except  that  defibrinated  blood  from  the  dog  was  used  and  the  ex- 


MUSCULAR  CONTRACTION.  475 

periments  were  made  upon  the  muscles  of  the  arm.  The  excitability  was  re- 
stored in  all  of  the  muscles,  and  it  persisted,  the  cadaveric  rigidity  having 
disappeared,  twenty  hours  after  decapitation. 

MUSCULAR  CONTRACTION. 

The  stimulus  of  the  will,  conveyed  through  the  conductors  of  motor  im- 
pulses from  the  brain  to  a  muscle  or  set  of  muscles,  excites  the  muscular 
fibres  and  causes  them  to  contract.  In  muscles  that  have  been  exercised 
and  educated,  this  action  is  regulated  with  great  nicety,  so  that  the  most 
delicate  and  rapid  as  well  as  powerful  contractions  may  be  produced.  Cer- 
tain movements,  not  under  the  control  of  the  will,  are  produced  as  the  result 
of  unconscious  reflection  from  a  nervous  centre,  along  the  motor  conductors, 
of  an  impression  made  upon  sensory  nerves.  During  this  action  certain 
important  phenomena  are  observed  in  the  muscles  themselves.  They  change 
in  form,  consistence,  and  to  a  certain  extent,  in  their  constitution ;  the  dif- 
ferent periods  of  their  stimulation,  contraction  and  relaxation  are  positive 
and  well  marked;  their  nutrition  is  for  the  time  modified;  they  develop 
galvanic  currents ;  and  in  short,  they  present  a  number  of  general  phenomena, 
distinct  from  the  results  of  their  action,  that  are  more  or  less  important. 

The  most  prominent  of  the  phenomena  accompanying  muscular  action  is 
shortening  and  hardening  of  the  fibres.  It  is  necessary  only  to  observe  the 
action  of  any  well  developed  muscle  to  appreciate  these  changes.  The  active 
shortening  is  shown  by  the  approximation  of  the  points  of  attachment,  and 
the  hardening  is  sufficiently  palpable.  The  latter  phenomenon  is  marked 
in  proportion  to  the  development  of  the  true  muscular  tissue  and  its  freedom 
from  inert  matter,  such  as  fat.  It  is  the  muscular  substance  alone  which  has 
the  property  of  contraction  ;  and  this  action  increases  the  consumption  of 
oxygen  and  probably  of  other  matters,  the  formation  of  carbon  dioxide  and 
some  other  excrementitious  products,  and  develops  heat. 

Notwithstanding  the  marked  and  constant  changes  in  the  form  and  con- 
sistence of  the  muscles  during  contraction,  their  actual  volume  undergoes 
modifications  so  slight  that  they  may  practically  be  disregarded.  The  ex- 
ceeding slight  change  which  has  been  observed  in  recent  experiments  (Valen- 
tin, Landois)  is  a  diminution  in  volume. 

Changes  in  the  Form  of  the  Muscular  Fibres  during  Contraction. — All 
physiologists  are  agreed  that  in  muscular  contraction  there  is  an  increase  in 
the  thickness  of  the  fibre,  nearly  compensating  its  diminution  in  length. 
This  has  been  repeatedly  observed  in  microscopical  examinations,  and  the 
only  points  now  to  determine  are  the  exact  mechanism  of  this  transverse  en- 
largement, its  duration,  the  means  by  which  it  may  be  excited,  and  its  physi- 
ological modifications.  These  questions  have  been  made  the  subjects  of  in- 
vestigation by  Helmholtz,  Du  Bois-Reymond,  Aeby,  Marey  and  others  ;  and 
although  it  is  hardly  necessary  to  follow  these  experimenters  through  nil  the 
details  of  their  observations,  many  important  points  have  been  developed, 
particularly  by  the  methods  of  registering  the  muscular  movements. 

One  essential  condition  in  the  study  of  the  mechanism  of  muscular  con- 


4TC  MOVEMENTS— VOICE  AND  SPEECH. 

traction  is  to  imitate,  in  a  muscle  or  a  part  of  a  muscle  that  can  be  subjected 
to  direct  observation,  the  force  that  naturally  excites  it  to  contraction.  The 
application  of  electricity  to  the  nerve  is  the  most  perfect  method  that  can 
be  employed  for  this  purpose.  In  this  way  a  single  contraction  may  be  pro- 
duced, or  by  employing  a  rapid  succession  of  impulses,  so-called  tetanic 
action  may  be  excited.  While  the  electric  current  is  not  identical  with  the 
nervous  force,  it  is  the  best  substitute  that  can  be  used  in  experiments 
upon  muscular  contractility,  and  it  has  the  advantage  of  affecting  but  little 
the  physical  and  chemical  integrity  of  the  nervous  and  muscular  tissues. 

There  are  two  classes  of  phenomena  that  may  be  produced  by  electric 
excitation  of  motor  nerves  :  1.  When  the  stimulus  is  applied  in  the  form  of 
a  single  discharge,  it  is  followed  by  a  single  muscular  contraction.  2.  Un- 
der a  rapid  succession  of  discharges,  the  muscle  is  thrown  into  a  state  of 
permanent,  or  tetanic  contraction.  It  will  facilitate  a  comprehension  of  the 
subject  to  study  these  phenomena  separately  and  successively. 

Mechanism  of  a  Single  Muscular  Contraction. — If  an  electric  discharge, 
even  very  feeble,  be  applied  to  a  motor  nerve  connected  with  a  fresh  muscle, 
it  is  followed  by  a  sudden  contraction,  which  is  succeeded  by  a  rapid  relaxa- 
tion. Under  this  stimulation,  the  muscle  shortens  by  about  three-tenths  of 
its  entire  length.  The  form  of  the  contraction,  as  registered  by  the  appa- 
ratus of  Helmholtz,  Marey  and  others  who  have  applied  the  graphic  method 
to  the  study  of  muscular  action,  presents  certain  peculiarities. 

According  to  Helmholtz,  the  whole  period  of  a  single  contraction  and 
relaxation  of  the  gastrocnemius  muscle  of  a  frog  is  a  little  less  than  one-third 
of  a  second.  The  muscles  of  mammals  and  birds  contract  more  rapidly, 
but  with  this  exception,  the  essential  characters  of  the  contraction  are  the 
same.  The  following  are  the  periods  occupied  by  these  different  phenomena 
in  the  gastrocnemius  of  a  frog  : 

Interval  between  stimulation  and  contraction  (latent  period) 0"'020 

Contraction 0"'180 

Relaxation..  .  0"-105 


0"'305 

The  latent  period  in  man  is  0*004  to  O'Ol  of  a  second,  the  contraction  oc- 
cupies 0*03  to  0'4  of  a  second,  and  the  period  of  relaxation  is  a  little  shorter 
than  the  period  of  contraction.  The  duration  of  the  electric  current  is  only 
0"'0008.  This  description  represents  the  contraction  of  an  entire  muscle, 
but  it  does  not  indicate  the  changes  in  form  of  the  individual  fibres,  a  point 
much  more  difficult  to  determine  satisfactorily.  It  is  well  established,  how- 
ever, that  a  single  fibre,  with  its  excitability  unimpaired,  becomes  contracted 
and  swollen  at  the  point  where  the  stimulation  is  applied.  The  question 
now  is  whether,  in  normal  contraction  of  the  fibres  in  obedience  to  the  nat- 
ural nervous  stimulus,  there  be  a  uniform  shortening  of  the  whole  fibre,  a 
shortening  of  those  portions  only  that  are  the  seat  of  the  terminations  of  the 
motor  nerves,  or  a  peristaltic  shortening  and  swelling,  rapidly  running  the 
length  of  the  fibre. 


MUSCULAR  CONTRACTION.  477 

The  experiments  of  Aeby,  which  have  been  repeated  and  extended  by 
Marey,  have  shown  that  when  one  extremity  of  a  muscle  is  excited,  a  con- 
traction occurs  at  that  point  and  is  propagated  along  the  muscle,  in  the  form 
of  a  wave.  The  estimated  rapidity  of  this  wave  is  33  to  43  feet  (10  to  13 
metres)  per  second  (Hermann).  Applying  this  principle  to  the  physio- 
logical action  of  muscles,  Aeby  proposed  the  theory  that  shortening  of  the 
fibres  takes  place  wherever  a  stimulus  is  received,  and  that  this  is  propagated 
in  the  form  of  a  wave,  which  meets  in  its  course  another  wave  starting  from 
a  different  point  of  stimulation.  Although  this  view  -of  the  physiological 
action  of  the  muscular  fibres  is  very  probable,  it  can  not  be  assumed  that  it 
has  been  absolutely  demonstrated  ;  but  it  is  certainly  more  satisfactory  and 
better  sustained  by  experimental  facts  than  any  other  theory  that  has  yet 
been  advanced. 

Mechanism  of  Tetanic  Muscular  Contraction. — By  a  voluntary  effort  a 
muscular  contraction  may  be  produced,  of  a  certain  duration  and  of  a  power, 
within  certain  limits,  proportionate  to  the  amount  of  force  required ;  but 
after  a  time  the  muscle  becomes  fatigued,  and  it  may  become  exhausted 
to  the  extent  that  it  will  no  longer  respond  to  the  normal  stimulus.  This 
normal  muscular  action  in  obedience  to  impulses  conveyed  by  motor  nerves 
may  be  closely  imitated  by  electric  stimulation.  When  a  single  electric  dis- 
charge is  applied  to  a  nerve,  there  is  a  single  muscular  contraction ;  but  a 
rapid  succession  of  discharges  produces  a  persistent  contraction,  which  is 
called  tetanic. 

During  the  passage  of  a  feeble  galvanic  current  through  a  nerve,  there  is 
no  contraction  in  the  muscles  to  which  the  nerve  is  attached ;  and  it  is  only 
when  the  circuit  is  closed  or  opened  that  any  action  is  observed.  The  inter- 
rupted galvanic  current,  the  induced  current,  or  a  succession  of  discharges  of 
statical  electricity,  when  they  do  not  follow  each  other  too  rapidly,  produces 
a  corresponding  succession  of  muscular  contractions.  As  the  rapidity  of 
these  electric  impulses  is  increased,  the  individual  contractions  become  less 
and  less  distinct,  until  finally  the  contraction  is  persistent.  Distinct  single 
contractions  occur  with  ten  excitations  per  second,  a  partial  fusion  of  the 
different  acts  takes  place  with  twenty  per  second,  and  a  complete  fusion,  or 
tetanus,  with  twenty-seven  per  second  (Marey).  When  the  contraction  be- 
comes continuous,  there  is  an  elevation  of  the  line  marked  on  a  registering 
apparatus,  showing  increased  power  as  the  excitations  are  more  and  more 
rapid.  This  is  artificial  tetanus ;  but  it  probably  is  the  kind  of  contrac- 
tion that  occurs  in  the  physiological  action  of  the  voluntary  muscles. 

It  is  probable  that  the  normal  nervous  stimulus  in  voluntary  muscular 
action  is  a  succession  of  impulses,  which  produce  a  power  of  muscular  con- 
traction that  is  proportionate  to  their  rapidity.  Vibrations,  which  are  more 
or  less  regular,  actually  occur  during  the  contraction  of  muscles  (Wollaston, 
Haughton,  Helmholtz).  Helmholtz,  indeed,  has  recognized  a  musical  note 
produced  by  contracting  muscles,  which  exactly  corresponds  to  the  number 
of  excitations  per  second  applied  to  the  nerve.  This  can  be  heard  in  the 
temporal  and  masseter  muscles  by  filling  the  ears  with  wax  and  causing  these 
32 


478  MOVEMENTS— VOICE  AND  SPEECH. 

muscles  to  contract.  The  number  of  vibrations  noted  by  Helmholtz  was  19f 
per  second ;  but  the  sound  heard  was  the  first  overtone,  or  the  octave,  the 
fundamental  tone  being  too  low  to  be  appreciated  by  the  ear. 

Some  physiologists  have  denied  the  supposed  identity  between  the  tetanic 
contraction  produced  by  a  rapid  succession  of  stimuli  applied  to  a  motor 
nerve  and  voluntary  muscular  contraction.  Complete  fusion  of  contraction 
occurs  with  twenty-seven  or  more  stimuli  per  second  applied  to  a  nerve ; 
but  it  is  stated  that  stimuli  applied  to  the  motor  cerebral  centres,  even  when 
very  rapid,  do  not  produce  more  than  eight  to  thirteen  muscular  contrac- 
tions, the  average  being  ten  per  second  (Horsley  and  Schafer,  1887).  The 
average  in  voluntary  muscular  contraction  is  about  the  same.  From  these 
observations  it  is  argued  that  the  rate  of  so-called  vibration  in  voluntary 
muscular  contraction  has  an  average  of  about  ten  per  second.  This  conclu- 
sion is  based  upon  actual  myographic  tracings.  It  is  difficult,  however,  to  rec- 
oncile these  results  with  those  obtained  by  Marey,  Helmholtz  and  others. 
It  is  a  fact,  also,  that  distinct  muscular  contractions  may  be  produced  very 
rapidly  by  an  effort  of  the  will.  It  is  not  difficult  for  any  one  to  make  five 
taps  of  the  finger  per  second  for  a  few  seconds,  and  skillful  performers  on 
musical  instruments  are  able,  by  using  the  same  muscle  or  set  of  muscles,  to 
make  movements  that  are  very  much  more  rapid,  each  movement  presumably 
requiring  a  distinct  nervous  impulse.  It  may  be  that  in  an  unweighted  mus- 
cle,' the  contractions  are  discontinuous,  and  that  the  average  number  of 
waves  is  about  ten  per  second ;  but  it  is  probable  that  the  estimate  of  Helm- 
holtz— 19£  waves  per  second — is  nearly  correct  for  muscles  in  a  condition  of 
powerful  contraction.  In  a  series  of  observations  by  Griffiths  (1888),  it  was 
found  that  voluntary  contraction  of  the  biceps  weighted  with  a  little  more 
than  eleven  pounds  (5,000  grammes),  for  one  hundred  seconds,  gave  an  aver- 
age of  eighteen  waves  per  second,  the  average  for  the  unweighted  muscle 
being  fourteen  waves  per  second  for  thirty-three  seconds. 

The  nerves  are  not  capable  of  conducting  an  artificial  stimulus  for  an  in- 
definite period,  nor  are  the  muscles  able  to  contract  for  more  than  a  limited 
time  upon  the  reception  of  such  an  excitation.  The  electric  current  may  be 
made  to  destroy  for  a  time  both  the  nervous  and  muscular  excitability ;  and 
these  properties  become  gradually  extinguished,  the  parts  becoming  fatigued 
before  they  are  completely  exhausted.  Precisely  the  same  phenomena  are 
observed  in  the  physiological  action  oi  muscles.  When  a  muscle  is  fatigued 
artificially,  a  tetanic  condition  is  excited  more  and  more  easily,  but  the  power 
of  the  contraction  is  proportionally  diminished.  Muscles  contracting  in 
obedience  to  an  effort  of  the  will  pass  through  the  same  stages  of  action.  It 
is  probable  that  constant  contraction  is  excited  more  and  more  easily  as  the 
muscles  become  fatigued,  because  the  nervous  force  gradually  diminishes  in  in- 
tensity ;  but  it  is  certain  that  the  vigor  of  contraction  at  the  same  time  pro- 
gressively diminishes. 

The  phenomena  of  muscular  contraction  thus  far  considered  are  those 
produced  by  voluntary  effort  or  by  stimulation  of  motor  nerves ;  but  many 
important  phenomena  have  been  observed  in  muscles  detached  from  the  body 


ELECTRIC  PHENOMENA  IN  MUSCLES. 


4-79 


and  stimulated  directly.  These  observations  have  generally  been  made  on 
the  gastrocnemius  of  the  frog,  the  phenomena  being  recorded  by  a  register- 
ing apparatus,  the  simplest  form 
of  which  is  the  myograph  of 
Helmholtz.  This  instrument  is 
used  in  recording  muscular  con- 
tractions by  causing  the  record- 
ing point  to  play  upon  a  smoked 
paper  moving  at  a  known  rate. 
If  the  muscle  of  the  frog,  slight- 
ly weighted,  be  stimulated  by  a 
single  induction-shock,  there  is 
first  a  latent  period,  when  there 
is  no  contraction,  then  a  con- 
traction followed  by  relaxation, 
and  finally  a  slight,  elastic  vibra- 
tion before  the  muscle  becomes 

rn,  ,  FIG.  155.—  Diagram  of  the  myograph  of  Helmholtz  (Lan- 

quiescent.      These    phenomena  dois). 

nrp  illna-rra+prl  in  thp  mirvp  o-ivpn     Mi  muscle  fixed  by  the  clamp  (K)  by  a  portion  of  the  fe- 
mur ;  F,  recording  point ;  P,  counterpoise  used  to  bal- 
in   Fig.  156   in   which     however  ance  the  lever  ;  W,  pan  for  weights  ;  S,  S,  supports  for 

the  latent  period  is  not  measured. 

In  a  muscle  prepared  in  this  way,  the  maximum  of  stimulation  and  the 
maximum  of  power  measured  by  a  weight  lifted  can  readily  be  ascertained, 
and  certain  phenomena  due  to  fatigue  of  the  muscle  have  been  observed.  In 
a  fatigued  muscle,  the  latent  period  is  lengthened  and  the  elevation  of  the 
curve  of  contraction  is  not  so  high,  showing  a  slower  and  longer  action. 
When  a  muscle  is  excited  to  tetanic  contraction  by  a  rapidly  interrupted 
current  of  considerable  strength,  the  elevation  produced  by  the  initial  con- 
traction is  nearly  vertical, 
and  is  followed  by  a  hori- 
zontal straight  line  which 
marks  the  tetanic  condi- 
tion. The  phenomena  in- 
duced by  direct  stimulation 
of  muscles  are  somewhat 

FIG.  m.-Curve  of  a  tingle  muscular  contraction  (Landois).         exaggerated  when  the  stim- 

ulus  is  applied  to  the  mo- 
tor nerve. 

Electric  Phenomena  in  Muscles. — It  was  ascertained  a  number  of  years 
ago,  by  Matteucci,  that  all  living  muscles  present  electric  currents.  The 
direction  of  these  currents  is  from  the  longitudinal  surface  to  the  transverse, 
or  cut  surface  of  the  muscle,  as  is  shown  in  Fig.  157.  A  simple  method 
of  demonstrating  the  muscular  current  is  to  prepare  the  leg  of  a  frog  with 
the  crural  nerve  attached,  and  to  apply  one  portion  of  the  nerve  to  the 
deep  parts  of  an  incised  muscle  and  the  other  to  the  surface.  As  soon  as 
the  connection  is  made,  a  contraction  of  the  leg  takes  place.  The  current 


A  F,  abscissa  ;  A  C,  ordinate  ;  A  B,  latent  period  ;  B  D,  period  of 
contraction ;  D  E,  period  of  relaxation ;  E  F,  elastic  vibra- 
tion. 


480 


MOVEMENTS— VOICE  AND  SPEECH. 


may  also  be  demonstrated  with  an  ordinary  galvanometer ;  but  the  evidence 

obtained  by  the  frog's  leg  is  sufficiently  conclusive. 

Matteucci  constructed  out  of  the  fresh  muscles  from  the  thigh  of  the  frog, 

what  is  sometimes   called  a   frog-battery;   which  is  made   by   taking   the 

muscles  of  the  lower  half 
of  the  thigh  from  several 
frogs,  removing  the  bones, 
and  arranging  them  in  a 
series,  each  with  its  coni- 
cal extremity  inserted  into 
the  central  cavity  of  the 
one  below.  In  this  way 
the  external  surface  of 
each  thigh  except  the  last 
is  in  contact  with  the  in- 
ternal surface  of  the  one 
below.  If  the  two  extrem- 
ities of  the  pile  be  con- 
nected with  a  galvanome- 
ter, quite  a  powerful  cur- 
rent from  the  internal  to 
the  external  surface  of  the 

FIG.  157.—  Muscular  current  in  the  frog  (Bernard).  muscle     may    be     demon- 

Fig.  1,  portion  of  the  thigh,  with  the  skin  removed  ;  a,  surface  of 
the  muscles  ;  6,  section  ;  the  direction  of  the  current  is  indi- 
cated by  the  arrow. 

Fig.  2,  the  nerve  of  a  frog's  leg  (the  leg  enclosed  in  a  glass  tube)  is 

applied  to  the  section  and  the  surface  of  the  muscle.     There  is     ji_   _-c  _   o-ilvinnrnp+pr 

no  contraction,  because  it  is  necessary  that  a  portion  of  the    L 

nerve  should  be  raised  up.  rlpvifltprl    30°  tn  4-0° 

Fig.  3,  a  portion  of  the  nerve  is  raised  with  a  glass  rod.    The  con-    ut!Vld'  «• 

traction  of  the  galvanoscopic  leg  occurs  at  the  making  of  the  TTlpn+vio     mir-ronta     avo 

circuit,  because  the  current  follows  the  course  of  the  nerve,  or 

Fig.*4,  the  contraction  here  occurs  at  the  breaking  of  the  circuit,  observed  in  all  living  niUS- 
because  the  direction  of  the  current  is  opposite  the  course  of  nloq  hut  thov  flrp  most 
the  nerve,  or  is  ascending.  J 

marked  in  the  mammalia 

and  warm-blooded  animals.  They  exist,  also,  for  a  certain  time  after  death. 
Artificial  tetanus  of  the  muscles,  however,  instead  of  intensifying  the  cur- 
rent, causes  the  galvanometer  to  recede.  If,  for  example,  the  needle  <5f  the 
instrument  show  a  deviation  of  30°  during  repose,  when  the  muscle  is  excited 
to  tetanic  contraction,  it  will  return  so  as  to  mark  only  10°  or  15°,  or  it  may 
even  return  to  zero.  This  phenomenon,  which  is  called  negative  variation  of 
the  muscular  current,  is  observed  only  during  a  continued  muscular  contrac- 
tion and  it  does  not  attend  a  single  contraction. 

Muscular  Effort. — The  mere  voluntary  movement  of  parts  of  the  body, 
when  there  is  no  obstacle  to  be  overcome  or  no  great  force  is  required,  is 
very  different  from  a  muscular  effort.  For  example,  in  ordinary  progression 
there  is  simply  a  movement  produced  by  the  action  of  the  proper  muscles, 
almost  without  consciousness,  and  this  is  unattended  with  any  considerable 
modification  in  the  circulation  or  respiration ;  but  in  attempting  to  lift  a 
heavy  weight,  to  jump,  to  strike  a  powerful  blow  or  to  make  any  vigorous 


T,,  „ 
in  a 

ten   elements,  the   nee- 


PHYSIOLOGICAL  ANATOMY  OF  THE  BONES.  481 

effort,  the  action  is  different.  In  the  latter  instance,  a  certain  preparation 
for  the  muscular  effort  is  made  by  inflating  the  lungs,  closing  the  glottis 
and  contracting  more  or  less  forcibly  the  expiratory  muscles  so  as  to  render 
the  thorax  rigid  and  unyielding ;  and  by  a  concentrated  effort  of  the  will,  the 
proper  muscles  are  then  brought  into  action.  This  action  of  the  muscles  of 
the  thorax  and  abdomen,  due  to  simple  effort  and  independent  of  the  partic- 
ular muscular  act  that  is  to  be  accomplished,  compresses  the  contents  of  the 
rectum  and  bladder  and  obstructs  very  materially  the  venous  circulation  in  the 
large  vessels.  It  is  well  known  that  hernia  frequently  is  produced  in  this 
way ;  the  veins  of  the  face  and  neck  become  turgid ;  the  conjunctiva  may  be- 
come ecchymosed ;  and  sometimes  aneurismal  sacs  are  ruptured.  An  effort 
of  this  kind  is  generally  of  short  duration,  and  it  can  not,  indeed,  be  pro- 
longed beyond  the  time  during  which  respiration  can  be  conveniently  arrested. 
There  are  degrees  of  effort  which  are  not  attended  with  this  powerful  ac- 
tion of  the  muscles  of  the  chest  and  abdomen,  and  in  which  the  glottis  Is 
not  completely  closed ;  and  an  opening  into  the  trachea  or  larynx,  rendering 
immobility  of  the  thorax  impossible,  does  not  interfere  with  certain  acts  that 
require  considerable  muscular  power.  If  the  glottis  be  exposed  in  a  dog, 
when  he  makes  violent  efforts  to  escape,  the  opening  is  firmly  closed.  This 
is  often  observed  in  vivisections ;  but  Longet  has  shown  that  dogs  with  an 
opening  into  the  trachea  are  frequently  able  to  run  and  leap  with  "  astonish- 
ing agility."  He  also  saw  a  horse,  with  a  large  canula  in  the  trachea,  that 
performed  severe  labor  and  drew  heavily  loaded  wagons  in  the  streets  of  Paris. 

PASSIVE  ORGANS  OF  LOCOMOTION. 

It  would  be  out  of  place  to  describe  fully  and  in  detail  all  of  the  varied 
and  complex  movements  produced  by  muscular  action.  Many  of  these,  such 
as  the  movements  of  deglutition  and  of  respiration,  are  necessarily  consid- 
ered in  connection  with  the  functions  of  which  they  form  a  part;  but 
others  are  purely  anatomical  questions.  Associated  and  antagonistic  move- 
ments, automatic  and  reflex  movements  etc.,  belong  to  the  history  of  the 
motor  nerves  and  will  be  fully  considered  in  connection  with  the  physiology 
of  the  nervous  system. 

The  study  of  locomotion  involves  a  knowledge  of  the  physiological  anat- 
omy of  certain  passive  organs,  such  as  the  bones,  cartilages  and  ligaments. 
Although  a  complete  history  of  the  structure  of  these  parts  trenches  some- 
what upon  the  domain  of  anatomy,  a  brief  description  of  their  histology  will 
practically  complete  the  account  of  the  tissues  of  the  body,  with  the  excep- 
tion of  the  nervous  system  and  the  organs  of  generation,  which  will  be 
taken  up  hereafter. 

Locomotion  is  effected  by  the  muscles  acting  upon  certain  passive,  mov- 
able parts.  These  are  the  bones,  cartilages,  ligaments,  aponeuroses  and  ten- 
dons. The  fibrous  structures  have  already  been  described,  and  it  only  remains 
to  study  the  structure  of  bones  and  cartilages. 

Physiological  Anatomy  of  the  Bones. — The  bones  are  composed  of  what  is 
called  the  fundamental  substance,  with  cavities  and  canals  of  peculiar  form. 


482 


MOVEMENTS— VOICE  AND  SPEECH. 


The  cavities  contain  corpuscular  bodies  called  bone-corpuscles.     The  canals 
of  larger  size  serve  for  the  passage  of  blood-vessels,  while  the  smaller  canals 

(canaliculi)  connect  the  cavities 
with  each  other  and  finally  with  the 
vascular  tubes.  Many  of  the  bones 
present  a  medullary  cavity,  filled 
with  a  peculiar  structure  called 
marrow.  In  almost  all  bones  there 
are  two  distinct  portions  ;  one, 
which  is  exceedingly  compact,  and 
the  other,  more  or  less  spongy  or 
cancellated.  The  bones  are  also 
invested  with  a  membrane,  con- 
taining vessels  and  nerves,  called 
the  periosteum. 

The  fundamental  substance  is 
composed  of  an  organic  matter, 
called  osseine,  combined  with  vari- 
ous inorganic  salts,  in  which  calci- 
um phosphate  largely  predomi- 
nates. In  addition  to  calcium  phos- 

canals  and  lacuna*,  seen  in  a  Ion-    Phate>    the    bones    Contain    Calcium 

the  humerus ;  magnified  200  carbonate,  calcium  fluoride,  mag- 

ct,  a,  a,  vascular  canals  ;  6,  6,  b,  lacunas  and  canaliculi    nesium    phosphate,    Sodium     pllOS- 
in  the  fundamental  substance.  . 

phate  and  sodium  chloride.     The 

relative  proportions  of  the  organic  and  inorganic  constituents  are  somewhat 
variable ;  but  the  average  is  about  one-third  of  the  former  to  two-thirds  of 
salts.  This  proportion  is  necessary  to 
the  proper  consistence  and  toughness 
of  the  bones. 

Anatomically,  the  fundamental 
substance  of  the  bones  is  arranged  in 
the  form  of  regular,  concentric  lam- 
ellae, about  30*0()  of  an  inch  (8  p.]  in 
thickness.  This  matter  is  of  an  in- 
definitely and  faintly  striated  appear- 
ance, but  it  can  not  be  reduced  to  dis- 
tinct fibres.  In  the  long  bones  the 
arrangement  of  the  lamellae  is  quite 
regular,  surrounding  the  Haversian 
canals  and  forming  what  are  some- 
times Called  the  Haversian  rods,  fol-  FIG.  IW.-LongitudtnaTTection  of  bone,  from  the 
lr.winrr  in  fnoiv  rlii-or.fi/vn  fho  lorxrfVi  shaft  of  the  human  femur  ;  magnified  ISO  di- 

lUVVing   1  ameters  (from  a  photograph  taken  at  the  Unit- 

Of     the    bone.       In    the    short,    thick  ed  States  Army  Medical  Museum). 

bones  the  lamellae  are  more  irregular,  frequently  radiating  from  the  central 
portion  toward  the  periphery. 


PHYSIOLOGICAL  ANATOMY  OF  THE  BONES. 


483 


The  Haversiaii  canals  exist  in  the  compact  bony  'structure.  They  are 
either  absent  or  are  very  few  in  the  spongy  and  reticulated  portions.  Their 
form  is  rounded  or  ovoid,  the  larger  canals  being  sometimes  quite  irregular. 
In  the  long  bones  their  direction  is  generally  longitudinal,  although  they 
anastomose  by  lateral  branches.  Each  one  of  these  canals  contains  a  blood- 
vessel, and  their  disposition  constitutes  the  vascular  arrangement  of  the 
bones.  They  are  all  connected  with  the  openings  on  the  surface  of  the 
bones,  by  which  the  arteries  penetrate  and  the  veins  emerge.  Their  size, 
of  course,  is  variable.  The  largest  are  about  ^  of  an  inch  (400  /A)  and  the 
smallest,  -^  of  an  inch  (30  /A)  in  diameter  (Sappey).  Their  average  size 
is  ^fg-  to  -%fa  of  an  inch  (100  to  125  /A).  In  a  transverse  section  of  a  long 
bone,  the  Haversian  canals  may  be  seen  cut  across  and  surrounded  by  twelve 
to  fifteen  lamellae. 

Lacuna. — The  fundamental  substance  is  everywhere  marked  by  irregular, 
microscopic  excavations,  of  a  peculiar  form,  called  lacunae.  They  are  con- 
nected with  little  canals,  giving  them  a  stellate  appearance.  These  canals 
are  most  abundant  at  the  sides  of  the  lacunae.  The  lacunae  measure  -^^  to 
•gfjj-  of  an  inch  (20  to  30  p)  in  their  long  diameter,  by  about  ^^F  of  an  inch 
(10  /A)  in  width. 

CanaUculi. — These  are  little,  wavy  canals,  connecting  the  lacunas  with 
each  other  and  presenting  a  communication  between  the  first  series  of  lacuna? 
and  the  Haversi- 
an canals.  Each 
lacuna  presents 
eighteen  to  twen- 
ty canaliculi  radi- 
ating from  its 
borders.  The 
length  of  the  can- 
aliculi is  -5^  to 
•g-^j-  of  an  inch 
(30  to  40  it),  and 
their  diameter  is 
about  2^0  oir  °^  an 
inch  (1  /*).  The 
arrangement  and 
relations  of  the 
Haversian  canals, 
lacunas  and  oana- 
liculi  are  shown 
in  Fig.  160. 

Bone-cells  or  Corpuscles. — These  structures  are  stellate,  granular,  with  a 
large  nucleus  and  several  nucleoli,  and  are  of  exactly  the  size  and  form  of 
the  lacunae.  They  send  out  prolongations  into  the  canaliculi,  but  it  has 
been  impossible  to  ascertain  positively  whether  or  not  they  form  membranes 
lining  the  canaliculi  throughout  their  entire  length. 


FIG.  160. — Vascular  canals  and  lacunas,  seen  in  a  transverse  section  of  the 
humerus  ;  magnified  200  diameters  (Sappey). 

1, 1,  1,  section  of  the  Haversian  canals  ;  2,  section  of  a  longitudinal  canal  di- 
vided at  the  point  of  its  anastomosis  with  a  transverse  canal.  Around  the 
canals,  cut  across  perpendicularly,  are  seen  the  lacunas  (with  their  canali- 
culi), forming  concentric  rings. 


484 


MOVEMENTS— VOICE  AND  SPEECH. 


section  of  bone,  from  the  shaft 
of  the  human  hutnerus  ;  magnified  180  diame- 


Marrow  of  the  Bones.  —  The  marrow  is  found  in  the  medullary  cavities  of 
the  long  bones,  filling  them  completely  and  moulded  to  all  the  irregularities 

of  their  walls.  It  is  also  found  filling 
the  cells  of  the  spongy  portion.  In 
other  words,  with  the  exception  of 
the  vascular  canals,  lacunae  and  cana- 
liculi,  the  marrow  fills  all  the  spaces 
in  the  fundamental  substance.  The 
cavities  of  the  bones  are  not  lined 
with  a  membrane  corresponding  to 
the  periosteum,  and  the  marrow  is 
applied  directly  to  the  bony  sub- 
stance. In  the  foetus  and  in  very 
young  children  the  marrow  is  red 
and  very  vascular.  In  the  adult  it  is 
yellow  in  some  bones  and  gray  or 
gelatiniform  in  others.  It  contains 

pprfoir,  r.ppnliar  ppll.  3T^  nnplpi    wifh 
ellfe  ana  "11(5161,  Wltn 

ters  (from  a  photograph  taken  at  the  United    arnnrrYhrm<5    matfpr     nrlinncp   vocinloc 
States  Army  Medical  Museum).  dmorpllOUS    matter,    adipose   VCSlCleS, 

connective  tissue,  blood-vessels  and 

nerves.  Eobin  has  described  little  bodies,  existing  both  in  the  form  of  cells 
and  free  nuclei,  called  medullocells.  These  are  found  in  greater  or  less  num- 
ber in  the  bones  at 
all  ages,  but  they  are 
more  abundant  in 
proportion  as  the 
amorphous  matter 
and  fat-cells  are  de- 
ficient. The  nuclei  are 
spherical,  sometimes 
with  irregular  bor- 
ders, generally  with- 
out nucleoli,  finely 
granular,  and  -^fa 

to  -joV?r  of  an  inch  (5 

to  8  /A)  in  diameter. 

They  are  insoluble  in 

acetic  acid.  The  cells, 

which  are  less  abun- 

dant than  the  free  nu- 

clei, are  spherical  or 

slightly     polyhedric, 

contain  a  few  pale  granulations,  are  rendered  pale  but  are  not  dissolved 

by  acetic  acid,  and  they  measure  about  t  fa  0  of  an  inch  (15  /*,)  in  diameter. 

Irregular,  nucleated  patches,  described  by  Eobin  under  the  name  of  myelo- 

plaxes,  more  abundant  in  the  spongy  portions  than  in  the  medullary  canals, 


FIG.  162.— Bone-corpuscles,  with  their  prolongations  (Rollett). 


PHYSIOLOGICAL  ANATOMY  OF   THE  BONES.  485 

are  found  applied  to  the  internal  surfaces  of  the  bones.  They  are  very  irreg- 
ular in  size  and  form  (measuring  y^r  to  -vfa  of  an  inch,  or  20  to  100  //,  in 
diameter),  are  finely  granular,  and  present  two  to  twenty  or  thirty  nuclei. 
The  nuclei  are  clear  and  ovoid  and  are  generally  provided  with  a  distinct 
nucleolus.  The  myeloplaxes  are  rendered  pale  by  acetic  acid,  and  the  nuclei 
are  then  brought  distinctly  into  view.  They  are  particularly  abundant  in 
the  red  marrow. 

In  addition  to  the  anatomical  elements  just  described,  the  marrow  con- 
tains a  few  very  delicate  bundles  of  connective  tissue,  most  of  which  accom- 
pany the  blood-vessels.  In  the  fetus  the  adipose  vesicles  are  few  or  may 
be  absent ;  but  in  the  adult  they  are  quite  abundant,  and  in  some  bones  they 
seem  to  constitute  the  whole  mass  of  the  marrow.  They  do  not  differ  ma- 
terially from  the  fat-cells  in  other  situations.  Holding  these  different  struct- 
ures together,  is  a  variable  quantity  of  semi-transparent,  amorphous  or  slightly 
granular  matter. 

The  nutrient  artery  of  the  bones  sends  branches  to  the  marrow,  generally 
two  in  number  for  the  long  bones,  which  are  distributed  between  the  various 
anatomical  elements  and  finally  surround  the  fatty  lobules  and  the  fat- vesicles 
with  a  delicate  capillary  plexus.  The  veins  correspond  to  the  arteries  in 
their  distribution.  The  nerves  follow  the  arteries  and  are  lost  when  these 
vessels  no  longer  present  a  muscular  coat.  Nothing  is  known  of  the  presence 
of  lymphatics  in  any  part  of  the  bones  or  in  the  periosteum. 

The  chief  physiological  interest  connected  with  the  marrow  of  the  bones 
is  in  its  relations  to  the  formation  of  blood-corpuscles.  This  question  has 
already  been  discussed  in  connection  with  the  development  of  the  corpuscular 
elements  of  the  blood. 

Periosteum. — In  most  of  the  bones  the  periosteum  presents  a  single  layer 
of  fibrous  tissue,  but  in  some  of  the  long  bones  two  or  three  layers  may  be 
demonstrated.  This  membrane  adheres  to  the  bone  but  can  generally  be 
separated  without  much  difficulty.  It  covers  the  bones  completely,  except 
at  the  articular  surfaces,  where  its  place  is  supplied  by  cartilaginous  incrusta- 
tion. It  is  composed  mainly  of  ordinary  fibrous  tissue  with  small  elastic 
fibres,  blood-vessels,  nerves  and  a  few  adipose  vesicles. 

The  arterial  branches  ramifying  in  the  periosteum  are  quite  abundant, 
forming  a  close,  anastomosing  plexus,  which  sends  small  branches  into  the 
bony  substance.  There  is  nothing  peculiar  in  the  arrangement  of  the  veins. 
The  distribution  of  the  veins  in  the  bony  substance  itself  has  been  very  little 
studied. 

The  nerves  of  the  periosteum  are  very  abundant  and  form  in  its  substance 
quite  a  close  plexus. 

The  adipose  tissue  is  very  variable  in  quantity.  In  some  parts  it  forms  a 
continuous  sheet,  and  "in  others  the  vesicles  are  scattered  here  and  there  in 
the  substance  of  the  membrane. 

The  importance  of  the  periosteum  to  the  nutrition  and  regeneration  of 
the  bones  is  very  great.  Instances  are  on  record  where  bones  have  been 
removed,  leaving  the  periosteum,  and  in  which  the  entire  bone  has  been 


486 


MOVEMENTS— VOICE  AND  SPEECH. 


, 

cells;  magnified  370  diameters  (from  a  photo- 
graph  taken  at  the  United  States  Army  Medical 


regenerated.  The  importance  of  the 
periosteum  has  been  still  farther  illus- 
trated by  the  experiments  of  Oilier 
and  others,  upon  transplantation  of 
this  membrane  in  the  different  tissues 
of  living  animals,  which  has  been  fol- 
lowed by  the  formation  of  bone  in 
these  situations. 

Physiological  Anatomy  of  Carti- 
lage. —  In  this  connection  the  structure 
of  the  articular  cartilages  presents  the 
chief  physiological  interest.  The  ar- 
ticular surfaces  of  all  the  bones  are 
FIG.  m.-section  of  cartilage  from  the  rib  of  the  encrusted  with  a  layer  of  cartilage, 

ox,  showing  the  homogeneous  fundamental    Vflrvin0-    in  thip]cnp<^  hpfwppn      1      nnH 
substance,    cartilage  -  cavities  and  cartilage-    Vdl7m6    l  1   To    ana 

1  ftf  arl  inpV.  ^0-^  nnH  1  mm  "I  T>IP 
27  C  m-)' 

cartilaginous  substance  is  white,  opal- 
ine, and  semi-transparent  when  examined  in  thin  sections.  It  is  not 
covered  with  a  membrane,  but  in  the 
non  -  articular  cartilages  it  has  an 
investment  analogous  to  the  perios- 
teum. 

Examined  in  thin  sections,  cartilage 
is  found  to  consist  of  a  homogeneous 
fundamental  substance,  marked  with 
excavations,  called  cartilage-cavities  or 
chondroplasts.  The  intervening  sub- 
stance has  a  peculiar  organic  constitu- 
ent, called  chondrine.  The  organic 
matter  is  united  with  a  certain  propor- 
tion of  inorganic  salts.  This  funda- 
mental substance  is  elastic  and  resist- 
ing. The  cartilages  are  closely  united 
to  the  subjacent  bony  tissue.  The 
free  articular  surface  has  already  been 
described  in  connection  with  the  syn- 
ovial  membranes. 

Cartilage-  Cavities.  —  These  cavities 
are  rounded  or  ovoid,  measuring  12igo 
to  -3-^  of  an  inch  (20  to  80  /A)  in  diam- 
eter. They  are  generally  smaller  in 
the  articular  cartilages  than  in  other  _ 

FIG.  1&4. 

situations,  as  in  the  costal  cartilages. 

mi  i  ,•  ,1 

Ihey    are    Simple    excavations    in    the 
»j  j.   i        t_  j  t.  T     • 

f  undamental  substance,  have  no  lining 
membrane,  and  they  contain  a  small 


Perpendicular  section  of  a  diarthrodial 

cartila 


1,  1,  osseous  tissue  ;  2,  2,  superficial  layer  of  osse- 
ous  tissue  treated  with  hydrochloric  acid;  3,3, 
cavities  and  cells  of  the  deep  layer  of  carti- 

\&%&  •  4,  4,  cavities  and  ceils  of  the  middle  lay- 
5>  cavities  and  cells  of  the 


PHYSIOLOGICAL  ANATOMY  OF  CARTILAGE. 


48  T 


quantity  of  a  viscid  liquid  with  one  or  more  cells.  They  are  analogous  to  the 
lacunas  of  the  bones. 

Cartilage- Cells. — Near  the  surface  of  the  articular  cartilages  the  cavities 
contain  each  a  single  cell ;  but  in  the  deeper  portions  the  cavities  are  long 
and  contain  two  to  twenty  cells  arranged  longitudinally.  The  cells  are  of 
about  the  size  of  the  smallest  cavities.  They  are  ovoid,  with  a  large,  granular 
nucleus.  They  often  contain  a  few  small  globules  of  oil.  In  the  costal  carti- 
lages the  cavities  are  not  abundant  but  are  rounded  and  quite  large.  The 
cells  contain  generally  a  certain  quantity  of  fatty  matter.  The  appearance 
of  the  ordinary  articular  cartilage  is  represented  in  Fig.  164. 

The  ordinary  cartilages  have  neither  blood-vessels,  lymphatics  nor  nerves, 
and  are  nourished  by  imbibition  from  the  surrounding  parts.  In  the  develop- 
ment of  the  body,  the  anatomy  of  the  cartilaginous  tissue  possesses  peculiar 
importance,  from  the  fact  that  the  deposition  of  cartilage,  with  a  few  excep- 
tions, precedes  the  formation  of  bone. 

Fibro-  Cartilage. — This  variety  of  cartilage  presents  certain  important 
peculiarities  in  the  structure  of  its  fundamental  substance.  It  exists  in  the 
synchondroses,  the  cartilages  of  the  ear  and  of  the  Eustachian  tubes,  the 
interarticular  disks,  the  intervertebral  cartilages,  the  cartilages  of  Santorini 
and  of  Wrisberg,  and  the  epiglottis. 

Fibro-cartilage  is  composed  of  true  fibrous  tissue  with  a  great  predomi- 
nance of  elastic  fibres,  fusiform,  nucleated  fibres,  a  certain  number  of  adipose 


FIG.  165.—  Section  of  the  cartilage  of  the  ear  of  the  human  subject  (Rollett). 
a,  flbro-cartilage  ;  6,  connective  tissue.    In  this  preparation,  the  cartilage  had  been  boiled  and  dried. 

vesicles,  cartilage-cells,  blood-vessels  and  nerves  (Sappey).  The  fibrous  ele- 
ments above  mentioned  take  the  place  of  the  homogeneous  fundamental  sub- 
stance of  the  true  cartilage.  The  most  important  peculiarity  in  the  structure 
of  this  tissue  is  that  it  is  abundantly  supplied  with  blood-vessels  and  nerves. 

The  reader  is  referred  to  works  upon  anatomy  for  a  history  of  the  action 
of  the  muscles.     In  some  works  upon  physiology,  will  be  found  descriptions 


488 


MOVEMENTS— VOICE  AND  SPEECH. 


of  the  acts  of  walking,  running,  leaping,  swimming  etc.  j  but  it  has  been 
thought  better  to  omit  these  subjects,  rather  than  to  enter  so  minutely  as 

would  be  necessary  into  anatomical  details 
and  to  give  elaborate  descriptions  of  move- 
ments that  are  simple  and  familiar. 

VOICE  AND  SPEECH. 

The  principal  organ  concerned  in  the  pro- 
duction of  the  voice  is  the  larynx.  The  ac- 
cessory organs  are  the  lungs,  trachea,  expi- 
ratory muscles,  the  mouth  and  the  resonant 
cavities  about  the  face.  The  lungs  furnish 
the  air  by  which  the  vocal  chords  are  thrown 
into  vibration,  and  the  mechanism  of  this 
action  is  merely  a  modification  of  expiration. 
By  the  action  of  the  expiratory  muscles  the 
intensity  of  vocal  sounds  is  regulated.  The 
trachea  not  only  conducts  the  air  to  the 
larynx,  but  it  may  assist,  by  resonance,  in 
modifying  the  quality  of  the  voice.  Most 
of  the  variations  in  the  tone  and  quality, 
however,  are  effected  by  the  action  of  the 
larynx  itself  and  of  the  parts  situated  above 
the  larynx. 

Sketch  of  the  Physiological  Anatomy  of 
the  Vocal  Organs. — The  vocal  chords  are 
stretched  across  the  superior  opening  of  the 
larynx  from  before  backward.  They  consist 
of  two  pairs.  The  superior,  called  the  false 
vocal  chords  or  the  ventricular  bands,  are  not 
concerned  in  the  production  of  the  voice. 
They  are  less  prominent  than  the  inferior 
chords,  although  they  have  nearly  the  same 
direction.  They  are  covered  by  a  thin  mu- 
cous membrane,  which  is  closely  adherent  to 
the  subjacent  tissue.  The  chords  themselves  are  composed  of  ordinary 
fibrous  tissue,  with  a  few  elastic  fibres. 

The  true  vocal  chords,  or  vocal  bands,  are  situated  just  below  the  superior 
chords.  Their  anterior  attachments  are  near  together,  at  the  middle  of  the 
thyroid  cartilage,  and  are  immovable.  Posteriorly  they  are  attached  to  the 
movable  arytenoid  cartilages ;  and  by  the  action  of  certain  muscles,  their 
tension  may  be  modified  and  the  chink  of  the  glottis  may  be  opened  or  closed. 
These  are  much  larger  than  the  false  vocal  chords,  and  they  contain  a  great 
number  of  elastic  fibres.  Like  the  superior  vocal  chords,  they  are  covered 
with  a  very  thin  and  closely  adherent  mucous  membrane.  The  mucous 
membrane  over  the  borders  of  the  chords  is  covered  with  flattened  epithelium 


FIG.  166.—  Longitudinal  section  of  the 
human  larynx,  showing  the  vocal 
chords  (Sappey). 

1,  ventricle  of  the  larynx ;  2,  superior 
vocal  chord ;  3,  inferior  vocal  cnord  ; 
4,  arytenoid  cartilage  ;  5,  section  of 
the  arytenoid  muscle  ;  6,  6,  inferior 
portion  of  the  cavity  of  the  larynx  ; 
7,  section  of  the  posterior  portion  of 
the  cricoid  cartilage  ;  8,  section  of 
the  anterior  portion  of  the  cricoid 
cartilage  ;  9,  superior  border  of  the 
cricoid  cartilage  ;  10,  section  of  the 
thyroid  cartilage  ;  11,  11,  superior 
portion  of  the  cavity  of  the  larynx  ; 
12,  13.  arytenoid  gland  ;  14,  16,  epi- 
glottis ;  15,  17,  adipose  tissue  ;  18, 
section  of  the  hyoid  bone  ;  19, 19, 20, 
trachea. 


MUSCLES  OF  THE  LARYNX. 


489 


without  cilia.  There  are  no  mucous  glands  in  the  membrane  covering  either 
the  superior  or  the  inferior  chords.  The  inferior  vocal  chords  alone  are  con- 
cerned in  the  production  of  the  voice. 

Muscles  of  the  Larynx.  —  The  muscles  of  the  larynx  are  classified  as  ex- 
trinsic and  intrinsic.  The  extrinsic  muscles  are  attached  to  the  outer  surface 
of  the  larynx  and  to  adjacent  organs,  such  as  the  hyoid  bone  and  the  sternum. 
They  are  concerned  chiefly  in  the  movements  of  elevation  and  depression  of 
the  larynx.  The  intrinsic  muscles  are  attached  to  the  different  parts  of  the 
larynx  itself,  and  by  their  action  upon  the  articulating  cartilages,  are  capable 
of  modifying  the  condition  of  the  vocal  chords. 

The  vocal  chords  can  be  rendered  tense  or  loose  by  muscular  action. 
Their  fixed  point  is  in  front,  where  their  extremities,  attached  to  the  thyroid 
cartilage,  are  nearly  or  quite  in  contact 
with  each  other.  The  arytenoid  cartilages, 
to  which  they  are  attached  posteriorly, 
present  a  movable  articulation  with  the 
cricoid  cartilage  ;  and  the  cricoid,  which 
is  narrow  in  front,  and  is  wide  behind, 
where  the  arytenoid  cartilages  are  attached, 
presents  a  movable  articulation  with  the 
thyroid  cartilage.  It  is  evident,  therefore, 
that  muscles  acting  upon  the  cricoid  car- 
tilage can  cause  it  to  swing  upon  its  two 
points  of  articulation  with  the  inferior 
cornua  of  the  thyroid,  raising  the  anterior 
portion  and  approximating  it  to  the  lower 
edge  of  the  thyroid  ;  and  as  a  consequence, 
the  posterior  portion,  which  carries  the 
arytenoid  cartilages  and  the  posterior  at- 
tachments of  the  vocal  chords,  is  depressed. 
This  action  would,  of  course,  increase  the  FIG.  i6?.—  Posterior 
distance  between  the  arytenoid  cartilages 
and  the  anterior  portion  of  the  thyroid, 
elongate  the  vocal  chords,  and  subject 
them  to  a  certain  degree  of  tension.  Experiments  have  shown  that  such  an 
effect  is  produced  by  the  contraction  of  the  crico-thyroid  muscles. 

The  articulations  of  the  different  parts  of  the  larynx  are  such  that  the 
arytenoid  cartilages  may  be  approximated  to  each  other  posteriorly,  thus 
diminishing  the  interval  between  the  posterior  attachments  of  the  vocal 
chords.  This  action  can  be  effected  by  contraction  of  the  single  muscle  of 
the  larynx  (the  aryteuoid)  and  also  by  the  lateral  crico-arytenoid  muscles. 
The  thyro-arytenoid  muscles,  the  most  complicated  of  all  the  intrinsic  mus- 
cles in  their  attachments  and  the  direction  of  their  fibres,  are  important  in 
regulating  the  tension  and  capacity  of  vibration  of  the  vocal  chords. 

The  posterior  crico-arytenoid  muscles,  arising  from  each  lateral  half  of 
the  posterior  surface  of  the  cricoid  cartilage  and  passing  upward  and  outward 


of  the  muscles  of 
2,3,4, 


490 


MOVEMENTS— VOICE  AND  SPEECH. 


to  be  inserted  into  the  outer  angle  of  the  inferior  portion  of  the  arytenoid 
cartilages,  rotate  these  cartilages  outward,  separate  them,  and  act  as  dilators  of 

the  chink  of  the  glottis.  These  muscles  are 
chiefly  concerned  in  the  respiratory  move- 
ments during  inspiration. 

12  / 1  \\TO  r^e  mnscles   mainly   concerned    in    the 

Py  \  modifications  of  the  voice  by  their  action 
upon  the  vocal  chords,  are  the  crico-thyroids, 
the  arytenoid,  the  lateral  crico-arytenoids  and 
the  thyro  -  arytenoids.  The  following  is  a 
sketch  of  their  attachments  and  mode  of  ac- 
tion: 

Crico-thyroid  Muscles.  —  These  muscles 
are  situated  on  the  outside  of  the  larynx,  at 
the  anterior  and  lateral  portions  of  the  cri- 
coid cartilage.  Each  muscle  is  of  a  triangu- 
lar f orni,  the  base  of  the  triangle  presenting 
posteriorly.  It  arises  from  the  anterior  and 
lateral  portions  of  the  cricoid  cartilage,  and 
its  fibres  diverge  to  be  inserted  into  the  in- 
to. 168.— Lateral  view  of  me  muscles  of  ferior  border  of  the  thyroid  cartilage,  extend- 

the  larynx  (Sappey).  .         .  ,  .,,.        .     ,  . 

body  of  the  hyoid  bone ;  2,  vertical  mg  *™m  the  middle  of   this  border  posterior- 
section  of  the  thyroid  cartilage  ;   3,  iv    QQ  for  hanV  a«   fhp    infprinr   nnrnnn        T  nn 
horizontal  section  of  the  thyroid  car-  iy,  as  iar  DaCK  as    me  COmua.       _LiOn- 

tilage,  turned  downward  to  show  the     ^^    affpr   riivirlino-   thp  nprvnnQ  filflmpnt<a  rli<5 

deep  attachment  of  the  crico-thy-   &et>  d1'  m&  r    '  nervous  niamenis  dis- 

tributed to  these  muscles,  noted  a  certain  de- 
gree of  hoarseness  of  the  voice  due  to  relaxa- 
tion of  the  vocal  chords;  and  by  imitating 
their  action  mechanically,  he  approximated 
the  cricoid  and  thyroid  cartilages  in  front, 
carried  back  the  arytenoid  cartilages  and  ren- 
dered the  chords  tense. 
Arytenoid  Muscle. — This  single  muscle  fills  up  the  space  between  the  two 
arytenoid  cartilages  and  is  attached  to  their  posterior  surface  and  borders. 
Its  action  evidently  is  to  approximate  the  posterior  extremities  of  the  chords 
and  to  constrict  the  glottis,  as  far  as  the  articulations  of  the  arytenoid  carti- 
lage with  the  cricoid  will  permit.  In  any  event,  this  muscle  is  important  in 
phonation,  as  it  serves  to  fix  the  posterior  attachments  of  the  vocal  chords 
and  to  increase  the  efficiency  of  certain  of  the  other  intrinsic  muscles. 

Lateral  Crico-arytenoid  Muscles. — These  muscles  are  situated  in  the  in- 
terior of  the  larynx.  They  arise  from  the  sides  and  superior  borders  of  the 
cricoid  cartilage,  pass  upward  and  backward,  and  are  attached  to  the  base  of 
the  arytenoid  cartilages.  By  dividing  all  the  filaments  of  the  recurrent  laryn- 
geal  nerves,  except  those  distributed  to  these  muscles,  and  then  stimulating 
the  nerves,  Longet  has  shown  that  they  act  to  approximate  the  vocal  chords, 
and  that  they  constrict  the  glottis,  particularly  in  its  interligamentous  por- 
tion. These  muscles,  with  the  arytenoid,  act  as  constrictors  of  the  larynx. 


enoid  muscle  ;  8,  lateral  crico-aryte- 
noid  muscle  ;  9,  thyro  -  arytenoid 
muscle  ;  10,  arytenoid  muscle  ;  11, 
aryteno  -  epiglottidean  muscle  ;  12, 
middle  thyro  -  hyoid  ligament  ;  13, 
lateral  thyro-hyoid  ligament. 


MOVEMENTS  OF  THE  GLOTTIS  DURING  PHONATION.      491 

Thyro-arytenoid  Muscles. — These  muscles  are  situated  within  the  larynx. 
They  are  broad  and  flat,  and  they  arise  in  front  from  the  upper  part  of  the 
crico-thyroid  membrane  and  the  lower  half  of  the  thyroid  cartilage.  From 
this  line  of  origin,  each  muscle  passes  backward  in  two  fasciculi,  both  of 
which  are  attached  to  the  anterior  surface  and  the  outer  borders  of  the  aryt- 
enoid  cartilages.  Stimulation  of  the  nervous  filaments  distributed  to  these 
muscles  renders  the  vocal  chords  tense.  The  great  variations  that  maybe 
produced  in  the  pitch  and  quality  of  the  voice  by  the  action  of  muscles  oper- 
ating directly  or  indirectly  upon  the  vocal  chords  render  the  problem  of  de- 
termining the  precise  mode  of  action  of  the  intrinsic  muscles  of  the  larynx 
complicated  and  difficult.  It  is  certain,  however,  that  in  these  muscular 
acts,  the  thyro-arytenoids  play  an  important  part.  Their  contraction  regu- 
lates the  thickness  of  the  vocal  chords,  while  at  the  same  time  it  modifies 
their  tension.  The  swelling  of  the  chords,  which  may  be  rendered  regular 
and  progressive  under  the  influence  of  the  will,  is  one  of  the  most  important 
elements  in  the  formation  of  the  timbre  of  the  voice. 

Mechanism  of  the  Production  of  the  Voice. — If  the  glottis  be  examined 
with  the  laryngoscope  during  ordinary  respiration,  the  wide  opening  of  the 
chink  during  forced  inspiration,  due  to  the  action  of  the  posterior  crico- 
arytenoid  muscles,  can  be  observed  without  difficulty.  This  action  is  effected 
by  a  separation  of  the  posterior  points  of  attachment  of  the  vocal  chords  to 
the  arytenoid  cartilages.  During  ordinary  expiration,  none  of  the  intrinsic 
muscles  seem  to  act  and  the  larynx  is  entirely  passive,  while  the  air  is  gently 
forced  out  by  the  elasticity  of  the  lungs  and  of  the  thoracic  walls ;  but  so 
soon  as  an  effort  is  made  to  produce  a  vocal  sound,  the  appearance  of  the 
glottis  undergoes  a  change,  and  it  becomes  modified  in  the  most  varied  man- 
ner with  the  different  changes  in  pitch  and  intensity  that  the  voice  can  be 
made  to  assume.  Although  sounds  may  be  produced,  and  even  words  may 
be  articulated,  with  the  act  of  inspiration,  true  and  normal  phonation  takes 
place  during  expiration  only.  It  is  evident,  also,  that  the  inferior  vocal 
chords  alone  are  concerned  in  this  act. 

Movements  of  the  Glottis  during  Phonation. — It  is  somewhat  difficult  to 
observe  with  the  laryngoscope  all  of  the  vocal  phenomena,  on  account  of  the 
epiglottis,  which  hides  a  considerable  portion  of  the  vocal  chords  anteriorly, 
especially  during  the  production  of  certain  notes ;  but  the  patience  and  skill 
of  Manuel  Garcia,  a  celebrated  teacher  of  singing,  enabled  him  to  overcome 
most  of  these  difficulties,  and  to  settle,  by  autolaryngoscopy,  certain  impor- 
tant questions  with  regard  to  the  action  of  the  larynx  in  singing.  It  is  for- 
tunate that  these  observations  were  made  by  one  versed  theoretically  and 
practically  in  music  and  possessed  of  great  control  over  the  vocal  organs. 

Garcia,  after  having  observed  the  respiratory  movements  of  the  larynx, 
as  they  have  just  been  briefly  described,  noted  that  as  soon  as  any  vocal  effort 
was  made,  the  arytenoid  cartilages  were  approximated,  so  that  the  glottis 
appeared  as  a  narrow  slit  formed  by  two  chords  of  equal  length,  firmly 
attached  posteriorly  as  well  as  anteriorly.  The  glottis  thus  undergoes  a 
marked  change.  A  nearly  passive  organ,  opening  for  the  passage  of  air 


492 


MOVEMENTS— VOICE  AND  SPEECH. 


into  the  lungs  but  entirely  inactive  in  expiration,  has  now  become  a  musi- 
cal instrument,  presenting  a  slit  with  borders  capable  of  accurate  vibra- 
tions. 

The  approximation  of  the  posterior  extremities  of  the  vocal  chords  and 
their  tension  by  the  action  of  certain  of  the  intrinsic  muscles  are  accom- 
plished just  before  the  vocal  effort  is  actually 
made.  The  glottis  being  thus  prepared  for  the 
emission  of  a  particular  sound,  the  expiratory 
muscles  force  air  through  the  larynx  with  the  re- 
quired power.  The  power  of  the  voice  is  due 
simply  to  the  force  of  the  expiratory  act,  which 
is  regulated  chiefly  by  the  antagonistic  relations 
of  the  diaphragm  and  the  abdominal  muscles. 
From  the  fact  that  the  diaphragm,  as  an  inspira- 
torv  muscle,  is  exactly  opposed  to  the  muscles 
which  have  a  tendency  to  push  the  abdominal 
Bon>-  organs,  with  the  diaphragm  over  them,  into  the 

1, 2,  base  of  the  tongue ;  3, 4,  epi-     . ,  .  .  , .      .     .  ,      , , 

glottis ;  5, 6,  pharynx ;  r.  aryte-   thoracic  cavity  and  thus  to  dimmish  the  pulmo- 

iK  lid  cartilages  ;  8,  opening  be-  • ,  •  -,   • 

tween  the  true  vocal  chords ;   nary  capacity,  the  expiratory  and  mspiratory  acts 

9,  aryteno-epiglottidean  folds ;  V     i~    i     "       j  •      i  xi  J.JT 

10,  cartilage  of  Santorini ;  ii,   may  be  balanced  so  nicely  that  the  most  delicate 

cuneiform  cartilage ;  12,  supe-  i       ••,        ,  •  i  j          -,        rni.          i    J.J.- 

rior  vocal  chords ;  is,  inferior  vocal  vibrations  can  be  produced.  The  glottis, 
thus  closed  as  a  preparation  to  a  vocal  act,  pre- 
sents a  certain  resistance  to  the  egress  of  air.  This  is  overcome  by  the  action 
of  the  expiratory  muscles,  and  with  the  passage  of  air  through  the  chink,  the 
edges  of  the  opening,  which  are  formed  by  the  true  vocal  chords,  are  thrown 
into  vibration.  Many  of  the  different  qualities  that  are  recognized  in  the 
human  voice  are  due  to  differences  in  the  length,  breadth  and  thickness  of 
the  vibrating  bands ;  but  aside  from  what  is  technically  known  as  quality, 
the  pitch  is  dependent  upon  the  length  of  the  opening  through  which  the  air 
is  made  to  pass  and  the  degree  of  tension  of  the  chords.  The  mechanism  of 
these  changes  in  the  pitch  of  vocal  sounds  is  illustrated  by  Garcia  in  the  fol- 
lowing, which  relates  to  what  is  known  as  the  chest-voice  : 

"If  we  emit  veiled  and  feeble  sounds,  the  larynx  opens  at  the  notes 
and  we  see  the  glottis  agitated  by  large  and  loose  vibra- 
tions throughout  its  entire  extent.  Its  lips  comprehended 


in  their  length  the  anterior  apophyses  of  the  arytenoid  cartilages  and  the 
vocal  chords ;  but,  I  repeat  it,  there  remains  no  triangular  space. 

"  As  the  sounds  ascend,  the  apophyses,  which  are  slightly  rounded  on 
their  internal  side,  by  a  gradual  apposition  commencing  at  the  back,  encroach 
on  the  length  of  the  glottis ;  and  as  soon  as  we  reach  the  sounds 
they  finish  by  touching  each  other  throughout  their  whole 
extent ;  but  their  summits  are  only  solidly  fixed  one  against 
the  other  at  the  notes  , — Q ,  In  some  organs  these  summits  are  a 


little  vacillating  when 
tis,  and  two  or  three 


they  form  the  posterior  end  of  the  glot- 
half-tones  which  are  formed  show  a  cer- 


tain want  of  purity  and  strength,  which  is  very  well  known  to  singers.    From 


MOVEMENTS  OF  THE  GLOTTIS  DURING-  PHONATION.      493 

the  vibrations,  having  become  rounder  and  purer,  are  accom- 
plished by  the  vocal  ligaments  alone,  up  to  the  end  of  the 
register. 

"  The  glottis  at  this  moment  presents  the  aspect  of  a  line  swelled  toward 
its  middle,  the  length  of  which  diminishes  still  more  as  the  voice  ascends. 
We  shall  also  see  that  the  cavity  of  the  larynx  has  become  very  small,  and 
that  the  superior  ligaments  have  contracted  the  extent  of  the  ellipse  to  less 
than  one-half." 

These  observations  have  been  in  the  main  confirmed  by  Battaille,  Emma 
Seiler  and  others  who  have  applied  the  laryngoscope  to  the  study  of  the 
voice  in  singing. 

In  childhood  the  general  characters  of  the  voice  are  essentially  the  same 
in  both  sexes.  The  larynx  is  smaller  than  in  the  adult,  and  the  vocal  mus- 
cles are  more  feeble ;  but  the  quality  of  the  vocal  sounds  at  this  period  of 
life  is  peculiarly  penetrating.  While  there  are  certain  characters  that  dis- 
tinguish the  voices  of  boys  before  the  age  of  puberty,  they  present,  as  in 
the  female,  the  different  qualities  of  the  soprano  and  contralto.  After  the 
age  of  puberty,  the  female  voice  does  not  commonly  undergo  any  very 
marked  change,  except  in  the  development  of  additional  strength  and  in- 
creased compass,  the  quality  remaining  the  same ;  but  in  the  male  there  is  a 
rapid  change  at  this  time  in  the  development  of  the  larynx,  and  the  voice 
assumes  an  entirely  different  quality.  This  change  does  not  usually  take 
place  if  castration  be  performed  in  early  life ;  and  this  operation  was  fre- 
quently resorted  to  in  the  seventeenth  century,  for  the  purpose  of  preserving 
the  qualities  of  the  male  soprano  and  contralto,  particularly  for  church- 
music.  It  is  only  of  late  years,  indeed,  that  this  practice  has  fallen  into 
disuse  in  Italy. 

The  ordinary  range  of  all  varieties  of  the  human  voice  is  equal  to  nearly 
four  octaves ;  but  it  is  rare  that  any  single  voice  has  a  compass  of  more  than 
two  and  a  half  octaves.  There  are  examples,  however,  in  which  singers  have 
acquired  a  compass  of  three  octaves.  In  music  the  notes  are  written  the 
same  for  the  male  as  for  the  female  voice,  but  the  actual  value  of  the  female 
notes,  as  reckoned  by  the  number  of  vibrations  in  a  second,  is  always  an 
octave  higher  than  the  male. 

In  both  sexes  there  are  differences,  both  in  the  range  and  the  quality  of 
the  voice,  which  it  is  impossible  for  a  cultivated  musical  ear  to  mistake.  The 
different  voices  in  the  male  are  the  bass,  the  tenor,  and  an  intermediate  voice 
called  the  barytone.  The  female  voices  are  the  contralto,  the  soprano,  and 
the  intermediate,  or  mezzo-soprano.  In  the  bass  and  barytone,  the  lower  and 
middle  notes  are  the  most  natural  and  perfect ;  and  while  the  higher  notes 
may  be  acquired  by  cultivation,  they  do  not  possess  the  same  quality  as  the 
corresponding  notes  of  the  tenor.  The  same  remarks  apply  to  the  contralto 
and  soprano. 

The  following  scale  (Landois)  gives  the  ordinary  ranges  of  the  different 
kinds  of  voice ;  but  it  must  be  remembered  that  there  are  individual  in- 
stances in  which  these  limits  are  exceeded  : 

*->*> 


MOVEMENTS— VOICE  AND  SPEECH. 

256  Soprano. 


1024 


171 


Contralto. 


E  F  G  A15        cde 

f  g  a  b 

c'd'e'Tg'a'b'      ^           t                   - 

Q 

r 

1                1 

/ 

* 

EE 

1 

SEE          i 

« 

1 

80 


c"  d"  e"  f"  g"  a"  b"  c'" 


Bass. 


342 


128 


Tenor, 


512 


The  accompanying  figures  indicate  the  number  of  vibrations  per  second  in  the  corresponding  tone.  It 
is  evident  that  from  c'  to  /'  is  common  to  all  voices  ;  nevertheless,  they  have  a  different  timbre. 
The  lowest  note  or  tone,  which,  however,  is  only  occasionally  sung  by  bass  singers,  is  the  contra-F, 
with  42  vibrations  ;  the  highest  note  of  the  soprano  voice  is  a'",  with  1,708  vibrations  (Landois  and 
Stirling). 

There  is  really  no  great  difference  in  the  mechanism  of  the  different  kinds 
of  voice,  and  the  differences  in  pitch  are  due  chiefly  to  the  greater  length  of 
the  vocal  chords  in  the  low-pitched  voices  and  to  their  shortness  in  the  higher 
voices.  The  differences  in  quality  are  due  to  peculiarities  in  the  conforma- 
tion of  the  larynx,  to  differences  in  its  size  and  to  variations  in  the  size  and 
form  of  the  auxiliary  resonant  cavities.  Great  changes  in  the  quality  of  the 
voice  may  be  effected  by  practice.  A  cultivated  note,  for  example,  has  an 
entirely  different  sound  from  a  harsh,  irregular  vibration ;  and  by  practice, 
a  tenor  may  imitate  the  quality  of  the  bass,  and  vice  versd,  although  the 
effort  is  unnatural.  It  is  not  at  all  unusual  to  hear  male  singers  imitate  very 
closely  the  notes  of  the  female,  and  the  contralto  will  sometimes  imitate  the 
voice  of  the  tenor  in  a  surprisingly  natural  manner. 

Action  of  the  Intrinsic  Muscles  of  the  Larynx  in  Phonation. — In  the 
production  of  low  chest-notes,  in  which  the  vocal  chords  are  elongated  and 
are  at  the  minimum  of  tension  that  will  allow  of  regular  vibrations,  the  crico- 
thyroid  muscles  are  undoubtedly  brought  into  action,  and  these  are  assisted 
by  the  arytenoid  and  the  lateral  crico-arytenoids,  which  combine  to  fix  the 
posterior  attachments  of  the  vibrating  ligaments.  It  will  be  remembered 
that  the  crico-thyroids,  by  approximating  the  cricoid  and  thyroid  cartilages 
in  front,  increase  the  distance  between  the  arytenoid  cartilages  and  the  an- 
terior attachment  of  the  vocal  chords. 

As  the  notes  produced  by  the  larynx  become  higher  in  pitch,  the  pos- 
terior attachments  of  the  chords  are  approximated,  and  at  this  time  the  lat- 
eral crico-arytenoids  are  probably  brought  into  vigorous  action. 

The  uses  of  the  thyro-arytenoids  are  more  complex ;  and  it  is  probably  in 
great  part  by  the  action  of  these  muscles  that  the  varied  and  delicate  modi- 
fications in  the  rigidity  of  the  vocal  chords  are  produced. 

The  differences  in  singers  as  regards  the  purity  of  their  notes  are  due  in 
part  to  the  accuracy  with  which  some  put  the  vocal  chords  upon  the  stretch ; 
while  in  those  in  whom  the  voice  is  of  inferior  quality,  the  action  of  the 
muscles  is  more  or  less  vacillating  and  the  tension  is  frequently  incorrect. 


ACTION  OF  ACCESSORY  VOCAL  ORGANS.  495 

The  fact  that  some  singers  can  make  the  voice  heard  above  the  combined 
sounds  from  a  large  chorus  and  orchestra  is  not  due  entirely  to  the  intensity 
of  the  sound,  but  in  a  great  measure  to  the  mathematical  equality  of  the 
sonorous  vibrations  and  the  comparative  absence  of  discordant  waves. 

Action  of  Accessory  Vocal  Organs. — A  correct  use  of  the  accessory  organs 
of  the  voice  is  of  great  importance  in  singing ;  but  the  action  of  these  parts 
is  simple  and  does  not  require  a  very  extended  description.  The  human 
vocal  organs,  indeed,  consist  of  a  vibrating  instrument,  the  larynx,  and  of 
certain  tubes  and  cavities  by  which  the  sound  is  re-enforced  and  modified. 

The  trachea  serves,  not  only  to  conduct  air  to  the  larynx,  but  to  re-enforce 
the  sound  to  a  certain  extent  by  the  vibrations  of  the  column  of  air  in  its 
interior.  When  a  powerful  vocal  effort  is  made,  it  is  easy  to  feel,  with  the 
finger  upon  the  trachea,  that  the  contained  air  is  thrown  into  vibration. 

The  capacity  of  the  cavity  of  the  larynx  is  capable  of  certain  variations. 
In  fact,  both  the  vertical  and  the  bilateral  diameters  are  diminished  in  high 
notes  and  are  increased  in  low  notes.  The  vertical  diameter  may  be  modified 
slightly  by  ascent  and  descent  of  the  true  vocal  chords,  and  the  lateral  di- 
ameter may  be  reduced  by  the  action  of  the  inferior  constrictors  of  the 
pharynx  upon  the  sides  of  the  thyroid  cartilage. 

The  epiglottis,  the  superior  vocal  chords  and  the  ventricles  are  by  no 
means  indispensable  to  the  production  of  vocal  sounds.  In  the  emission  of 
high  notes  the  epiglottis  is  somewhat  depressed,  and  the  superior  chords  are 
brought  nearer  together ;  but  this  affects  the  form  of  the  resonant  cavity  only 
above  the  glottis.  In  low  notes  the  superior  chords  are  separated.  It  was 
before  the  use  of  the  laryngoscope  in  the  study  of  vocal  phenomena  that  the 
epiglottis  and  the  ventricles  were  thought  to  be  so  important  in  phonation. 
Undoubtedly,  the  epiglottis  has  something  to  do  with  the  character  of  the 
voice ;  but  its  action  is  not  absolutely  necessary  or  even  very  important,  as 
has  been  shown  in  experiments  of  excising  the  part  in  living  animals. 

The  most  important  modifications  of  the  laryngeal  sounds  are  produced 
by  the  resonance  of  air  in  the  pharynx,  mouth  and  nasal  fossa?.  This  reso- 
nance is  indispensable  to  the  production  of  the  natural,  human  voice.  Under 
ordinary  conditions,  in  the  production  of  low  notes  the  velum  palati  is  fixed 
by  the  action  of  its  muscular  fibres,  so  that  there  is  a  reverberation  of  the 
bucco-pharyngeal  and  naso-pharyngeal  cavities ;  that  is,  the  velum  is  in  such 
a  position  that  neither  the  opening  into  the  nose  nor  the  opening  into  the 
mouth  is  closed,  and  all  of  the  cavities  resound.  As  the  notes  are  raised  in 
pitch,  the  isthmus  contracts,  the  part  immediately  above  the  glottis  is  also 
constricted,  the  resonant  cavity  of  the  pharynx  and  mouth  is  reduced  in 
size,  until  finally,  in  the  highest  notes  of  the  chest-register,  the  communica- 
tion between  the  pharynx  and  the  nasal  fossae  is  closed,  and  the  sound  is 
re-enforced  entirely  by  the  pharynx  and  mouth.  At  the  same  time  the 
tongue — a  very  important  organ  to  singers,  particularly  in  the  production 
of  high  notes — is  drawn  backward.  The  point  being  curved  downward,  its 
base  projects  upward  posteriorly  and  assists  in  diminishing  the  capacity  of 
the  bucco-pharyngeal  cavity.  In  the  changes  which  the  pharynx  thus  under- 


496  MOVEMENTS— VOICE  AND  SPEECH. 

goes  in  the  production  of  different  notes,  the  uvula  acts  with  the  velum  and 
assists  in  the  closure  of  the  different  openings.  In  singing  up  the  scale,  this 
is  the  mechanism,  as  far  as  the  chest-notes  extend.  When,  however,  a 
singer  changes  into  what  is  sometimes  called  the  head-voice  (falsetto),  the 
velum  palati  is  drawn  forward  instead  of  backward,  and  the  resonance  takes 
place  chiefly  in  the  naso-pharyngeal  cavity. 

Laryngeal  Mechanism  of  the  Vocal  Registers. — One  difficulty  at  the  very 
beginning  of  a  discussion  of  this  subject  is  in  fixing  upon  clear  definitions  of 
what  are  to  be  recognized  as  different  vocal  registers.  In  the  first  place  it 
must  be  understood  that  the  singing  voice  is  very  different  from  the  speaking 
voice.  Without  being  actually  so  far  discordant  as  to  offend  a  musical  ear,  the 
ordinary  voice  in  speaking  never  has  what  may  strictly  be  called  a  musical 
quality,  while  the  perfect  singing  voice  produces  true  musical  notes.  This  is 
probably  due  to  the  fact  that  the  inflections  of  the  voice  in  speaking  are  not 
in  the  form  of  distinct  musical  intervals,  that  the  vibrations  follow  each 
other  and  are  superimposed  in  an  irregular  manner,  and  that  no  special  effort 
is  made  to  put  the  vocal  chords  upon  any  definite  tension,  unless  to  meet  a 
more  powerful  expiratory  effort  when  the  voice  is  increased  in  force.  A 
shout  or  a  scream  is  entirely  different  from  a  powerful,  singing  note.  This 
difference  is  at  once  apparent  in  contrasting  recitative  with  ordinary  dialogue 
in  operatic  performances. 

The  divisions  of  the  voice  into  registers,  made  by  physiologists,  are  some- 
times based  upon  theories  with  regard  to  the  manner  of  their  production ; 
and  if  these  theories  be  not  correct,  the  division  into  registers  must  be  equally 
faulty.  Again,  there  are  such  marked  differences  between  male  and  female 
voices,  that  it  does  not  seem  possible  to  apply  the  same  divisions  to  both  sexes. 
There  is  no  difficulty,  however,  in  recognizing  the  qualities  of  voice,  called  bass, 
barytone  and  tenor,  in  the  male,  or  contralto,  mezzo  and  soprano,  in  the 
female.  A  division  of  the  voice  into  registers  should  be  one  easily  recog- 
nizable by  singers  and  singing  teachers ;  and  this  must  be  different  for  male 
and  female  voices.  If  a  division  were  made  such  as  would  be  universally 
recognized  by  the  ear,  irrespective  of  theories,  it  would  remain  only  to  as- 
certain as  nearly  as  possible  the  exact  vocal  mechanism  of  each  regis- 
ter. It  must  be  remembered  that  the  voice  of  a  perfect  singer  shows  no 
recognizable  break,  or  line  of  division  between  the  vocal  registers,  except 
when  a  difference  is  made  apparent  in  order  to  produce  certain  legitimate 
musical  effects.  One  great  end  sought  to  be  attained  in  training  the  voice 
in  singing  is  to  make  the  voice -as  nearly  as  possible  uniform  throughout  the 
extent  of  its  range ;  and  this  has  been  measurably  accomplished  in  certain 
singers. 

Judging  of  different  registers  entirely  by  the  effect  produced  upon  the  ear, 
both  by  cultivated  and  uncultivated  singers,  the  following  seem  to  be  the 
natural  divisions  of  the  male  voice : 

1.  The  chest-register.  This  is  the  register  commonly  used  in  speaking. 
Though  usually  called  the  chest-voice,  it  has,  of  course,  no  connection  with 
any  special  action  of  the  chest,  except,  perhaps,  with  reverberation  of  air  in 


MECHANISM  OF  THE  VOCAL  REGISTERS.  497 

the  trachea  and  the  larger  bronchial  tubes.    This  register  is  sensibly  the  same 
in  the  male  and  in  the  female. 

2.  The  head-register.    In  cultivated  male  voices,  a  quality  is  often  produced, 
probably  by  diminished  power  of  the  voice,  with  some  modification  in  the 
form  and  capacity  of  the  resonant  cavities,  which  is  recognized  as  a  "  head- 
voice,"  by  those  who  do  not  regard  the  head-register  as  equivalent  to  the 
falsetto. 

3.  The  falsetto-register.     By  the  use  of  this  register,  the  male  may  imitate 
the  voice  of  the  female.     Its  quality  is  different  from  that  of  the  chest-voice, 
and  the  transition  from  the  chest  to  falsetto  usually  is  abrupt  and  quite 
marked.     It  may  be  called  an  unnatural  voice  in  the  male ;  still,  by  very 
careful  cultivation,  the  transition  may  be  made  almost  imperceptibly.     The 
falsetto  never  has  the  power  and  resonance  of  the  full  chest-voice.     It 
resembles  the  head-voice,  but  every  good  singer  can  recognize  the  fact  that 
he  employs  a  different  mechanism  in  its  production. 

Applying  an  analogous  method  of  analysis  to  the  female  voice,  the 
natural  registers  seems  to  be  the  following : 

1.  The  chest-register.     This  register  is  the  same  in  the  female  as  in  the 
male. 

2.  The  lower  medium  register,  generally  called  the  medium.     This  is  the 
register  commonly  used  by  the  female  in  speaking. 

3.  The  upper  medium  register.     This  is  sometimes  called  the  head-regis- 
ter and  is  thought  by  some  to  be  produced  by  precisely  the  same  mechanism 
as  the  falsetto-register  in  the  male.     It  has,  however,  a  vibrant  quality,  is  full 
and  powerful,  and  is  not  an  unnatural  voice  like  the  male  falsetto. 

4.  The  true  head-register.     This  is  the  pure  tone,  without  vibrant  qual- 
ity, which  seems  analogous  to  the  male  falsetto. 

Vocal  Registers  in  the  Male. — According  to  the  division  and  definitions 
just  given  of  the  vocal  registers,  in  the  male  voice  there  is  but  one  register, 
extending  from  the  lowest  note  of  the  bass  to  the 
falsetto,  and  this  is  the  chest-register.  In  the  low 
notes,  the  vocal  chords  vibrate,  and  the  arytenoid 
cartilages  participate  in  this  vibration  to  a  greater 
or  less  extent.  In  the  low  notes,  also,  the  larynx 
is  open ;  that  is,  the  arytenoid  cartilages  do  not 
touch  each  other.  As  the  notes  are  raised  in  pitch, 
the  arytenoid  cartilages  are  approximated  more 
and  more  closely,  and  they  touch  each  other  in  the 

highest  notes,  the  vocal  chords  vibrating  alone.  O/M^^-TO^,  after  Mandi 
It  is  probable  that  the  degree  of  approximation 
of  the  arytenoid  cartilages  is  different  in  different  singers,  and  that  the  part 
of  the  musical  scale  at  which  they  actually  touch  is  not  invariable.  This 
appears  to  be  the  case  in  the  observations  made  by  Mills. 

AVhat  has  been  called,  in  this  classification,  the  head-register  of  the  male, 
is  not  a  full,  round  voice,  but  the  notes  are  more  or  less  sotto  voce.  This 
peculiar  quality  of  voice  does  not  seem  to  have  been  made  the  subject  of 


498 


MOVEMENTS— VOICE  AND  SPEECH. 


laryngoscopic  investigation.  It  has  a  vibrant  character,  which  is  undoubtedly 
modified  by  peculiar  action  of  the  resonant  cavities,  which  latter  has  not  been 
described.  It  is  not  probable  that  its  mechanism  differs  essentially,  as  re- 
gards the  action  of  the  glottis,  from  that  of  the  full  chest-register,  shown  in 
Fig.  170. 

The  falsetto-register  in  the  male  undoubtedly  involves  such  a  division  of 
the  length  of  the  vocal  chords  that  only  a  portion  is  thrown  into  vibration. 
There  is  always  an  approximation  of  the  chords  in  their  posterior  portion, 
and  sometimes  also  in  their  anterior  portion.  This  is  illustrated  in  Fig.  171. 

I  II  ill 


FIG.  171.— Appearances  of  fhe  vocal  chords  in  the  production  of  the  falsetto-voice  (Mills). 
I.  The  larynx  during  falsetto-production  ;  after  Mandl. 

II.  The  larynx  during  the  emission  of  falsetto-tones  ;  middle  range  ;  after  Holmes. 
III.  The  larynx  of  the  female  during  the  production  of  head-tones,  as  seen  by  the  author  (Mills). 

The  mechanism  by  which  the  vocal  chords  are  approximated  in  portions 
of  their  length  has  not  been  satisfactorily  explained ;  but  laryngoscopic  ex- 
aminations leave  no  doubt  of  the  fact  of  such  action.  The  extent  of  this 
shortening  of  the  chords  must  vary  in  different  persons  and  in  the  same  per- 
son, probably,  in  the  production  of  falsetto-notes  of  different  pitch.  Accord- 
ing to  Mrs.  Seiler,  the  shortening  is  due  to  the  action  of  a  muscular  bundle, 
called  the  internal  thyro-arytenoid,  upon  little  cartilages  extending  forward 
from  the  arytenoid  cartilage,  in  the  substance  of  the  vocal  chords,  as  far  as 
the  middle  of  the  glottis ;  but  dissections  made  by  Mills  failed  to  confirm 
this  view. 

Some  singers,  especially  tenors,  have  been  able  by  long  practice  to  pass 
from  the  chest  to  the  falsetto  so  skillfully  that  the  transition  is  scarcely  ap- 
parent, but  the  falsetto  is  devoid  of  what  is  called  vibrant  quality. 

Vocal  Registers  in  the  Female. — There  is  absolutely  no  difference  between 
the  vocal  mechanism  of  the  chest-voice  in  the  sexes.  In  the  best  methods  of 
teaching  singing,  one  important  object  is  to  smooth  the  transition  from  the 
chest-voice  to  the  lower  medium.  The  full  chest-notes,  especially  in  con- 
traltos, closely  resemble  the  corresponding  notes  of  the  tenor. 

According  to  the  laryngoscopic  observations  of  Mills,  the  mechanism  of 
the  lower  medium  and  upper  medium  in  females  does  not  radically  differ 
from  the  mechanism  of  the  chest-voice.  In  these  registers,  the  arytenoid 
cartilages  become  more  and  more  closely  approximated  to  each  other  as  the 
voice  ascends  in  the  scale  until,  in  the  higher  notes,  they  probably  are  firmly 


MECHANISM  OF  THE  VOCAL  REGISTERS.  499 

in  apposition.  It  is  probable  that  the  vocal  chords  alone  vibrate  in  the  lower 
and  upper  medium,  while  the  apophyses  of  the  arytenoid  cartilages  partici- 
pate in  the  vibrations  in  the  female  chest-voice. 

The  vocal  chords  are  much  shorter  in  the  female  than  in  the  male.  Ac- 
cording to  Sappey,  the  average  length  in  the  male  is  about  -J  of  an  inch  (22 
mm.)  and  in  the  female,  about  -f  of  an  inch  (17  mm.).  If  the  chords  alone 
vibrate,  without  the  apophyses  of  the  arytenoid  cartilages,  the  difference  in 
length  would  account  for  the  differences  in  pitch  of  the  voice  in  the  sexes. 
The  tenor  can  not  sing  above  the  chest-range  of  the  female  voice  without 
passing  into  the  falsetto,  to  produce  which  he  must  actually  shorten  his  vocal 
chords  so  that  they  are  as  short  or  shorter  than  the  vocal  chords  of  the  female. 
This  is  shown  by  the  scale  of  range  of  the  different  voices  compared  with 
the  length  of  the  vocal  chords ;  and  this  idea  is  sustained  still  farther  by  a 
comparison  of  "the  larynx  during  falsetto  production"  (Fig.  171,1).  In 
the  male  falsetto,  produced  by  this  shortening  of  the  vocal  chords,  the  more 
nearly  the  resonant  cavities  are  made  to  resemble,  in  form  and  capacity,  the 
corresponding  cavities  in  the  female,  the  more  closely  will  the  quality  of  the 
female  voice  be  imitated.  It  is  probable  that  the  vocal  bands  in  the  female 
present  a  thinner  and  narrower  vibrating  edge  than  the  chords  in  the  male, 
although  there  are  no  exact  anatomical  observations  on  this  point.  This 
would  account  for  the  clear  quality  of  the  upper  registers  of  the  female 
voice  as  compared  with  the  male  voice  or  with  the  female  chest-register. 
Analogous  differences  exist  in  reed-instruments,  such  as  the  clarinet  and  the 
bassoon.  This  comparison  of  the  female  upper  registers  with  the  male 
falsetto  does  not  necessarily  imply  a  similarity  in  the  mechanism  of  their 
production,  as  is  assumed  by  some  writers.  The  vocal  chords,  in  the  female 
lower  and  upper  medium,  vibrate  in  their  entire  length ;  in  the  male  falsetto, 
the  chords  are  artificially  shortened  so  that  they  are  approximated  in  length 
to  the  length  of  the  chords  in  the  female. 

To  reduce  to  brief  statements  the  views  just  expressed,  based  partly  upon 
laryngoscopic  examinations — that  are  far  from  complete — by  a  number  of 
competent  observers,  the  following  may  be  given  as  the  mechanism  of  the 
vocal  registers  in  the  female,  taking  no  account  of  the  changes  in  form  and 
capacity  of  the  resonant  cavities  : 

1.  The  chest-voice  is  produced  by  "  large  and  loose  vibrations  "  (Garcia) 
of  the  entire  length  of  the  vocal  chords,  in  which  the  apophyses  of  the  aryt- 
enoid cartilages  participate  to  a  greater  or  less  extent,  these  cartilages  not 
being  in  close  apposition. 

2.  In  passing  to  the  lower  medium,  the  arytenoid  cartilages  probably  are 
not  closely  approximated,  but  they  do  not  vibrate,  the  vocal  chords  alone 
acting. 

3.  In  passing  to  the  upper  medium,  the  arytenoid  cartilages  probably  are 
closely  approximated,  and  the  vocal  chords  alone  vibrate,  but  they  vibrate  in 
their  entire  length. 

4.  The  head-register,  which  may  be  called  the  female  falsetto,  bears  the 
same  relation  to  the  lower  registers  in  both  sexes.     The  notes  are  clear  but 


500  MOVEMENTS— VOICE  AND  SPEECH. 

deficient  in  vibrant  quality.  They  are  higher  in  the  female  than  in  the 
male  because  the  vocal  chords  are  shorter.  Laryngoscopic  observations  dem- 
onstrating this  fact  in  the  female  are  as  accurate  and  definite  as  in  the  male. 
(See  Fig.  171.) 

The  reasons  why  the  range  of  the  different  vocal  registers  is  limited  are 
the  following :  Within  the  limits  of  each  register,  the  tension  of  the  vocal 
chords  has  an  exact  relation  to  the  pitch  of  the  sound  produced.  This  tension 
is  of  course  restricted  by  the  limits  of  power  of  the  muscles  acting  upon  the 
vocal  chords,  for  high  notes,  and  by  the  limit  of  possible  regular  vibration  of 
chords  of  a  certain  length,  for  low  notes.  The  higher  the  tension  and  the 
greater  the  rigidity  of  the  chords,  the  greater  is  the  force  of  air  required  to 
throw  them  into  vibration ;  and  this,  also,  has,  of  course,  certain  limits.  It 
is  never  desirable  to  push  any  of  the  lower  registers  in  female  voices  to  their 
highest  limits.  All  competent  singing  teachers  recognize  this  fact.  The 
female  chest-register  may  be  made  to  meet  the  upper  medium,  particularly 
in  contraltos ;  but  the  singer  then  has  practically  two  voices,  a  condition 
which  is  musically  intolerable.  In  blending  the  different  registers  so  as  to 
make  a  perfectly  uniform,  single  voice,  the  arytenoid  vibrations  should  be 
rendered  progressively  and  evenly  less  and  less  prominent,  until  they  imper- 
ceptibly cease  when  the  lower  medium  is  fully  reached ;  the  arytenoid  car- 
tilages should  then  be  progressively  and  evenly  approximated  to  each  other, 
until  they  are  firmly  in  contact  and  the  upper  medium  is  fully  reached. 
The  female  vocal  apparatus  is  then  perfect.  While  single  notes  of  the 
chest,  lower  medium  and  upper  medium,  contrasted  with  each  other,  have 
different  qualities,  the  voice  is  even  throughout  its  entire  range,  and  the 
proper  shading  called  for  in  musical  compositions  can  be  made  in  any  part  of 
the  scale.  The  blending  of  the  male  chest-register  into  the  falsetto  and  of  the 
upper  medium  into  the  female  falsetto,  or  true  head-voice,  is  more  difficult, 
but  it  is  not  impossible.  Theoretically,  this  must  be  done  by  shortening  the 
vocal  chords  gradually  and  progressively  and  not  abruptly,  unless  the  latter 
be  required  to  produce  a  legitimate  effect  of  contrast. 

Even  in  singing  identical  notes,  there  are  distinctly  recognizable  differ- 
ences in  quality  between  the  bass,  barytone  and  tenor,  and  between  the  con- 
tralto, mezzo  and  soprano.  For  the  female,  these  may  be  compared  to  the 
differences  in  identical  notes  played  on  different  strings  of  the  violin.  For 
the  male,  they  may  be  compared  to  the  qualities  of  the  different  strings  of 
the  violoncello.  Falsetto-notes  may  be  compared  to  harmonics  produced  on 
these  instruments. 

These  ideas  with  regard  to  the  mechanism  of  the  different  vocal  registers 
have  resulted  from  a  study  of  these  registers,  first  from  an  aesthetic  point  of 
view ;  endeavoring  then  to  find  explanations  of  different  qualities  of  sound 
appreciated  by  the  ear,  in  laryngoscopic  and  other  scientific  observations,  and 
not  by  reasoning  from  scientific  observations,  as  to  what  effects  upon  the  ear 
should  be  produced  by  certain  acts  performed  by  the  vocal  organs.  It  may 
be  stated,  in  this  connection,  that  the  works  of  Bach,  Beethoven  and  other 
old  masters  were  composed,  exactly  in  accordance  with  purely  physical  laws, 


MECHANISM  OF  SPEECH.  501 

long  before  these  laws  were  ascertained  and  defined,  as  has  lately  been  done, 
particularly  by  Helmholtz. 

MECHAXISM  OF  SPEECH. 

Articulate  language  consists  in  a  conventional  series  of  sounds  made  for 
the  purpose  of  conveying  certain  ideas.  There  being  no  universal  language,  it 
will  be  necessary  to  confine  the  description  of  speech  to  the  language  in  which 
this  work  is  written.  Language,  as  it  is  naturally  acquired,  is  purely  imitative 
and  does  not  involve  of  necessity  the  construction  of  an  alphabet,  with  its 
combinations  into  syllables,  words  and  sentences  ;  but  as  civilization  has  ad- 
vanced, certain  differences  in  the  accuracy  and  elegance  with  which  ideas  are 
expressed  have  become  associated  with  the  degree  of  development  and  culti- 
vation of  the  intellectual  faculties.  Philologists  have  long  since  established 
a  certain  standard — varying,  to  some  extent,  it  is  true,  with  usage  and  the  ad- 
vance of  knowledge,  but  still  sufficiently  definite — by  which  the  correctness 
of  modes  of  expression  is  measured.  It  is  not  proposed  to  discuss  the  science 
of  language,  or  to  consider,  in  this  connection  at  least,  the  peculiar  mental 
operations  concerned  in  the  expression  of  ideas,  but  to  take  the  language  as 
it  exists,  and  to  describe  briefly  the  mechanism  of  the  production  of  the 
most  important  articulate  sounds. 

Almost  every  language  is  imperfect,  as  far  as  an  exact  correspondence  be- 
tween its  sounds  and  written  characters  is  concerned.  The  English  language 
is  full  of  incongruities  in  spelling,  such  as  silent  letters  and  arbitrary  and 
unmeaning  variations  in  pronunciation ;  but  these  do  not  belong  to  the  sub- 
ject of  physiology.  There  are,  however,  certain  natural  divisions  of  the  sounds 
as  expressed  by  the  letters  of  the  alphabet. 

Vowels. — Certain  articulate  sounds  are  called  vowel,  or  vocal,  from  the 
fact  that  they  are  produced  by  the  vocal  chords  and  are  but  slightly  modified 
as  they  pass  out  of  the  mouth.  The  true  vowels,  «,  0,  /,  0,  u,  can  all  be  sounded 
alone  and  may  be  prolonged  in  expiration.  These  are  the  sounds  chiefly  em- 
ployed in  singing.  The  differences  in  their  characters  are  produced  by  changes 
in  the  position  of  the  tongue,  mouth  and  lips.  The  vowel-sounds  are  neces- 
sary to  the  formation  of  a  syllable,  and  although  they  generally  are  modified 
in  speech  by  consonants,  each  one  may  of  itself  form  a  syllable  or  a  word. 
In  the  construction  of  syllables  and  words,  the  vowels  have  many  different 
qualities,  the  chief  differences  being  as  they  are  made  long  or  short.  In  addi- 
tion to  the  modifications  in  the  vowel-sounds  by  consonants,  two  or  three 
may  be  combined  so  as  to  be  pronounced  by  a  single  vocal  effort,  when  they 
are  called  respectively,  diphthongs  and  triphthongs.  In  the  proper  diph- 
thongs, as  0?',  in  voice,  the  two  vowels  are  sounded.  In  the  improper  diph- 
thongs, as  ea,  in  heat,  and  in  the  Latin  diphthongs,  as  ce,  in  Caesar,  one  of 
the  vowels  is  silent.  In  triphthongs,  as  eau,  in  beauty,  only  one  vowel  is 
sounded.  I7,  at  the  beginning  of  words,  is  usually  pronounced  as  a  conso- 
nant ;  but  in  other  positions  it  is  pronounced  as  e  or  i. 

An  important  question  relates  to  the  differences  in  the  quality  of  the  dif- 
ferent vowel-sounds  when  pronounced  with  equal  pitch  and  intensity.  The 


502  MOVEMENTS— VOICE  AND  SPEECH. 

cause  of  these  differences  was  studied  very  closely  in  the  latter  part  of  the 
last  century,  but  it  has  lately  been  rendered  clear  by  the  researches  of  Helm- 
holtz  and  of  Koenig.  In  this  connection  it  will  be  sufficient  to  indicate  the 
results  of  the  modern  investigations  very  briefly.  It  will  be  seen  in  studying 
the  physics  of  sound  in  connection  with  the  sense  of  hearing,  that  nearly  all 
sounds,  even  when  produced  by  a  single,  vibrating  body,  are  compound.  Helm- 
holtz,  by  means  of  his  resonators,  has  succeeded  in  analyzing  the  apparently 
simple  sounds  into  different  component  parts,  and  he  has  shown  that  the  qual- 
ity of  such  sounds  may  be  modified  by  re-enforcing  certain  of  the  overtones,  as 
they  are  called,  such  as  the  third,  fifth  or  octave.  For  those  who  are  famil- 
iar with  the  physics  of  sound,  the  explanation  of  the  mechanism  of  the  pro- 
duction of  vowel-sounds  will  be  readily  comprehensible.  The  reader  is  re- 
ferred, however,  to  the  remarks  upon  overtones  in  another  part  of  this  work, 
under  the  head  of  audition,  for  a  more  thorough  exposition  of  this  subject. 
The  different  vowel-sounds  may  be  emitted  with  the  same  pitch  and  intensity, 
but  the  sound  in  each  is  different  on  account  of  variations  in  the  resonant 
cavities  of  the  accessory  vocal  organs,  especially  the  mouth.  It  has  been  ascer- 
tained experimentally  that  the  overtones  in  each  instance  are  different,  as  they 
are  re-enforced  by  the  vibrations  of  air  in  the  accessory  vocal  organs,  in  some 
instances  the  third,  in  others,  the  fifth  etc.,  being  increased  in  intensity. 
This  can  hardly  be  better  illustrated  than  by  the  following  quotation  from 
Tyndall,  in  which  modern  researches  have  been  applied  to  the  vowel-sounds 
of  the  English  language  : 

"  For  the  production  of  the  sound  U  (oo  in  hoop),  I  must  push  my  lips 
forward  so  as  to  make  the  cavity  of  the  mouth  as  deep  as  possible,  at  the  same 
time  making  the  orifice  of  the  mouth  small.  This  arrangement  corresponds 
to  the  deepest  resonance  of  which  the  mouth  is  capable.  The  fundamental 
tone  of  the  vocal  chords  is  here  re-enforced,  while  the  higher  tones  are  thrown 
into  the  shade.  The  U  is  rendered  a  little  more  perfect  when  a  feeble  third 
tone  is  added  to  the  fundamental. 

"  The  vowel  0  is  pronounced  when  the  mouth  is  so  far  opened  that  the  fun- 
damental tone  is  accompanied  by  its  strong  higher  octave.  A  very  feeble 
accompaniment  of  the  third  and  fourth  is  advantageous,  but  not  necessary. 

"  The  vowel  A  derives  its  character  from  the  third  tone,  to  strengthen 
which  by  resonance  the  orifice  of  the  mouth  must  be  wider,  and  the  volume 
of  air  within  it  smaller  than  in  the  last  instance.  The  second  tone  ought  to 
be  added  in  moderate  strength,  whilst  weak  fourth  and  fifth  tones  may  also 
be  included  with  advantage. 

"  To  produce  E  the  fundamental  tone  must  be  weak,  the  second  tone  com- 
paratively strong,  the  third  very  feeble,  but  the  fourth,  which  is  characteris- 
tic of  this  vowel,  must  be  intense.  A  moderate  fifth  tone  may  be  added. 
No  essential  change,  however,  occurs  in  the  character  of  the  sound  when  the 
third  and  fifth  tones  are  omitted.  In  order  to  exalt  the  higher  tones  which 
characterize  the  vowel-sound  E,  the  resonant  cavity  of  the  mouth  must  be 
small. 

"  In  the  production  of  the  sound  all  !  the  higher  overtones  come  princi- 


MECHANISM  OF  SPEECH.  503 

pally  into  play ;  the  second  tone  may  be  entirely  neglected  ;  the  third  ren- 
dered very  feebly ;  the  higher  tones,  particularly  the  fifth  and  seventh,  being 
added  strongly. 

"  These  examples  sufficiently  illustrate  the  subject  of  vowel-sounds.  "We 
may  blend  in  various  ways  the  elementary  tints  of  the  solar  spectrum,  produc- 
ing innumerable  composite  colors  by  their  admixture.  Out  of  violet  and  red 
vie  produce  purple,  and  out  of  yellow  and  blue  we  produce  white.  Thus  also 
may  elementary  sounds  be  blended  so  as  to  produce  all  possible  varieties 
of  clang-tint.  After  having  resolved  the  human  voice  into  its  constituent 
tones,  Helmholtz  was  able  to  imitate  these  tones  by  tuning-forks,  and,  by  com- 
bining them  appropriately  together,  to  produce  the  clang-tints  of  all  the 
vowels. " 

Consonants. — Some  of  the  consonants  have  no  sound  in  themselves  and 
serve  merely  to  modify  vowel-sounds.  These  are  called  mutes.  They  are  #, 
(I,  k,  p,  t,  and  c  and  g  hard.  Their  office  in  the  formation  of  syllables  is  suf- 
ficiently apparent. 

The  consonants  known  as  semi-vowels  are  /,  Z,  w,  n,  r,  s,  and  c  and  g  soft. 
These  have  an  imperfect  sound  of  themselves,  approaching  in  character  the 
true  vowel-sounds.  Some  of  these,  ?,  m,  n  and  r,  from  the  facility  with 
which  they  flow  into  other  sounds,  are  called  liquids.  Orthoepists  have  far- 
ther divided  the  consonants  with  reference  to  the  mechanism  of  their  pronun- 
ciation :  d,j,  s,  t,  z,  and  g  soft,  being  pronounced  with  the  tongue  against  the 
teeth,  are  called  dentals ;  d,  g,  /,  &,  £,  w,  and  q  are  called  palatals ;  6,  p,  /,  v 
and  m  are  called  labials ;  m,  n  and  ng  are  called  nasals ;  and  k,  q,  and  c  and 
g  hard  are  called  gutturals.  After  the  description  already  given  of  the  voice, 
it  is  not  necessary  to  discuss  farther  the  mechanism  of  these  simple  acts  of 
articulation.  , 

For  the  easy  and  proper  production  of  articulate  sounds,  absolute  integrity 
of  the  mouth,  teeth,  lips,  tongue  and  palate  is  required.  All  are  acquainted 
with  the  modifications  in  articulation  in  persons  in  whom  the  nasal  cavi- 
ties resound  unnaturally  from  imperfection  of  the  palate ;  and  the  slight 
peculiarities  observed  after  loss  of  the  teeth  and  in  harelip  are  sufficiently 
familiar.  The  tongue  is  generally  regarded,  also,  as  an  important  organ  of 
speech,  and  this  is  the  fact  in  the  great  majority  of  cases ;  but  instances  are 
on  record  in  which  distinct  articulation  has  been  preserved  after  complete 
destruction  of  this  organ.  These  cases,  however,  are  unusual,  and  they  do 
not  invalidate  the  great  importance  of  the  tongue  in  ordinary  speech. 

It  is  thus  seen  that  speech  consists  essentially  in  a  modification  of  the 
vocal  sounds  by  the  accessory  organs,  or  by  parts  situated  above  the  larynx  ; 
the  latter  being  the  true  vocal  instrument.  While  the  peculiarities  of  pro- 
nunciation in  different  persons  and  the  difficulty  of  acquiring  foreign  lan- 
guages after  the  habits  of  speech  have  been  formed  show  that  the  organs  of 
articulation  must  perform  their  office  with  great  accuracy,  their  movements 
are  simple,  and  they  vary  with  the  peculiarities  of  different  languages. 

Whispering. — Articulate  sounds  may  be  produced  by  the  action  of  the  res- 
onant cavities,  the  lips,  teeth  and  tongue,  in  which  the  larynx  takes  no  part. 


504  MOVEMENTS— VOICE  AND  SPEECH. 

This  action  occurs  in  whispering  and  it  can  not  properly  be  called  vocal.  It 
is  difficult  to  make  any  considerable  variations  in  the  pitch  of  a  whisper,  and 
articulation  in  this  way  may  be  produced  in  inspiration  as  well  as  in  expira- 
tion, although  the  act  in  expiration  is  more  natural  and  easy.  The  character 
of  a  whisper  may  be  readily  distinguished  from  that  of  the  faintest  audible 
sound  involving  vibration  of  the  vocal  chords.  In  aphonia  from  simple  pa- 
ralysis of  the  vocal  muscles  of  the  larynx,  patients  can  articulate  distinctly  in 
whispering ;  but  in  cases  of  chronic  bulbar  paralysis  (glosso-labio-laryngeal 
paralysis),  speech  is  entirely  lost. 

The  Phonograph. — In  1877,  a  remarkable  invention  was  made  in  this 
country,  by  Mr.  Thomas  A.  Edison,  which  possesses  considerable  physiologi- 
cal importance.  Mr.  Edison  constructed  a  very  simple  instrument,  called  the 
phonograph,  which  will  repeat,  with  a  certain  degree  of  accuracy,  the  pecul- 
iar characters  of  the  human  voice  both  in  speaking  and  singing,  as  well  as  the 
pitch  and  quality  of  musical  instruments.  This  demonstrates  conclusively 
the  fact  that  the  qualities  of  vocal  sounds  depend  upon  the  form  of  the  sono- 
rous vibrations.  The  following  are  the  main  features  in  the  construction  of 
this  instrument :  It  consists  of  a  cylinder  of  iron  provided  with  very  fine, 
shallow  grooves  in  the  form  of  an  exceedingly  close  spiral.  Upon  the  cylin- 
der, a  sheet  of  tin-foil  is  accurately  fitted.  Bearing  upon  the  tin-foil,  is  a 
steel-point  connected  with  a  vibrating  plate  of  mica  or  of  thin  iron.  The  vi- 
brating plate  is  connected  with  a  mouth-piece  which  receives  the  vibrations  of 
the  voice  or  of  a  musical  instrument.  The  cylinder  is  turned  with  a  crank, 
and  at  the  same  time,  the  plate  is  thrown  into  vibration  by  speaking  into 
the  mouth-piece.  As  the  disk  vibrates  in  consonance  with  the  voice,  the  vi- 
brations are  marked  by  little  indentations  upon  the  tin-foil.  When  this  has 
been  done,  the  cylinder  is  moved  back  to  the  starting  point  and  is  turned 
again  at  the  same  rate  as  before.  As  the  steel-point  passes  over  the  indenta- 
tions in  the  tin-foil,  the  plate  is  thrown  into  vibration,  and  the  sound  of  the 
voice  is  actually  repeated,  although  much  diminished  in  intensity  and  dis- 
tinctness. The  improvements  that  have  lately  been  made  in  the  phonograph 
do  not  involve  any  modifications  in  the  principles  of  its  construction. 


DIVISIONS  AND  STRUCTURE  OF  THE  NERVOUS  TISSUE.   505 


CHAPTER  XVI. 

PHYSIOLOGICAL  DIVISIONS,  STRUCTURE  AND  GENERAL  PROPERTIES  OF 
THE  NERVOUS  SYSTEM. 

Divisions  and  structure  of  the  nervous  tissue — Medullated  nerve-fibres — Simple,  or  non-medullated  nerve- 
fibres — Gelatinous  nerve-fibres  (fibres  of  Reniak) — Accessory  anatomical  elements  of  the  nerves — 
Termination  of  the  nerves  in  the  muscular  tissue — Termination  of  the  nerves  in  glands — Modes  of 
termination  of  the  sensory  nerves— Corpuscles  of  Vater,  or  of  Pacini— Tactile  corpuscles— End-bulbs 
—Structure  of  the  nerve-centres— Nerve-cells— Connection  of  the  cells  with  the  fibres  and  with  each 
other — Accessory  anatomical  elements  of  the  nerve-centres— Composition  of  the  nervous  substance — 
Degeneration  and  regeneration  of  the  nerves— Motor  and  sensory  nerves— Mode  of  action  of  the  motor 
nerves— Associated  movements— Mode  of  action  of  the  sensory  nerves— Physiological  differences  be- 
tween motor  and  sensory  nerve-fibres— Nervous  excitability— Different  means  employed  for  exciting 
the  nerves — Rapidity  of  nervous  conduction— Personal  equation— Action  of  electricity  upon  the  nerves 
—Law  of  contraction— Induced  muscular  contraction— Electrotonus,  anelectrotonus  and  catelectrotonus 
— Negative  variation. 

THE  nervous  system  is  anatomically  and  physiologically  distinct  from  all 
other  systems  and  organs  in  the  body.  It  receives  impressions  made  upon 
the  terminal  branches  of  its  sensory  portion  and  it  conveys  stimulus  to  parts, 
determining  and  regulating  their  actions;  but  its  physiological  properties 
are  inherent,  and  it  gives  to  no  tissue  or  organ  its  special  excitability  or  the 
power  of  performing  its  particular  office  in  the  economy.  The  nervous  sys- 
tem connects  into  a  co-ordinated  organism  all  parts  of  the  body.  It  is  the 
medium  through  which  all  impressions  are  received.  It  animates  or  regu- 
lates all  movements,  voluntary  and  involuntary.  It  regulates  secretion, 
nutrition,  calorification  and  all  the  processes  of  organic  life. 

In  addition  to  its  action  as  a  medium  of  conduction  and  communication, 
the  nervous  system,  in  certain  of  its  parts,  is  capable  of  receiving  impressions 
and  of  generating  a  stimulating  influence,  or  force,  peculiar  to  itself.  As 
there  can  be  no  physiological  connection  or  co-ordination  of  different  parts 
of  the  organism  without  nerves,  there  can  be  no  unconscious  reception  of 
impressions  giving  rise  to  involuntary  movements,  no  appreciation  of  impres- 
sions, general,  as  in  ordinary  sensation,  or  special,  as  in  sight,  smell,  taste 
or  hearing,  no  instinct,  volition,  thought  or  even  knowledge  of  existence, 
without  nerve-centres. 

DIVISIONS  AND  STRUCTURE  OF  THE  NERVOUS  TISSUE. 

The  nervous  tissue  presents  two  great  divisions,  each  with  distinct  ana- 
tomical as  well  as  physiological  differences.  One  of  these  divisions  is  com- 
posed of  fibres  or  tubes.  This  kind  of  nervous  matter  is  incapable  of  gener- 
ating a  force  or  stimulus,  and  it  serves  only  as  a  conductor.  The  other 
division  is  composed  of  cells,  and  this  kind  of  nervous  matter,  while  it  may 
act  as  a  conductor,  is  capable  of  generating  the  so-called  nerve-force. 

The  nerve-fibres  and  cells  are  also  divided  into  two  great  systems,  as 
follows : 

1.  The  cerebro-spinal  system,  composed  of  the  brain  and  spinal  cord  with 
the  nerves  directly  connected  with  these  centres.  This  system  is  specially 
connected  with  the  functions  of  relation,  or  of  animal  life.  The  centres  pre- 


506  NERVOUS  SYSTEM. 

side  over  general  sensation,  the  special  senses,  voluntary  and  some  involun- 
tary movements,  intellection,  and,  in  short,  all  of  the  functions  that  charac- 
terize the  animal.  The  nerves  serve  as  the  conductors  of  impressions  known 
as  general  or  special  sensations  and  of  the  stimulus  that  gives  rise  to  volun- 
tary and  certain  involuntary  movements,  the  latter  being  the  automatic 
movements  connected  with  animal  life. 

2.  The  sympathetic,  or  organic  system.  This  system  is  specially  con- 
nected with  the  functions  relating  to  nutrition,  operations  which  have  their 
analogue  in  the  vegetable  kingdom  and  are  sometimes  called  the  functions 
of  vegetative  life.  Although  this  system  presides  over  functions  entirely 
distinct  from  those  characteristic  of  and  peculiar  to  animals,  the  centres  of 
this  system  all  have  an  anatomical  and  physiological  connection  with  the 
cerebro-spinal  nerves. 

The  cerebro-spinal  system  is  subdivided  into  centres  presiding  over  move- 
ments and  ordinary  sensation,  and  centres  capable  of  receiving  impressions 
connected  with  the  special  senses,  such  as  sight,  audition,  olfaction  and  gusta- 
tion. The  nerves  which  receive  these  special  impressions  and  convey  them 
to  the  appropriate  centres  are  more  or  less  insensible  to  ordinary  impressions. 
The  organs  to  which  these  special  nerves  are  distributed  are  generally  of  a 
complex  and  peculiar  structure,  and  they  present  accessory  parts  which  are 
important  and  essential  in  the  transmission  of  the  special  impressions  to  the 
terminal  branches  of  the  nerves. 

The  physiological  division  of  the  nervous  system  into  nerves  and  nerve- 
centres  is  carried  out  as  regards  the  anatomical  structure  of  these  parts.  The 
two  great  divisions  of  the  system,  anatomically  considered,  are  into  nerve- 
cells  and  nerve-fibres. 

The  cells  of  the  nerve-centres,  while  they  may  transmit  impressions  and 
impulses,  are  the  only  parts  capable,  under  any  circumstances,  of  generating 
the  nerve-force ;  and  as  a  rule,  they  do  not  receive  impressions  in  any  other 
way  than  through  the  nerve-fibres.  There  are,  however,  many  exceptions 
to  this  rule,  as  in  the  case  of  movements  following  direct  stimulation  of  the 
sympathetic  ganglia  and  certain  centres  in  the  brain  and  spinal  cord ;  but 
the  cells  of  many  of  the  ganglia  belonging  to  the  cerebro-spinal  axis  are 
insensible  to  direct  stimulation  and  can  receive  only  impressions  conducted 
to  them  by  the  nerves. 

The  nerve-fibres  act  only  as  conductors  and  are  incapable  of  generating 
nerve-force.  There  is  no  exception  to  this  rule,  but  there  are  differences  in 
the  properties  of  certain  fibres.  The  nerves  generally,  for  example,  receive 
direct  impressions,  the  motor  filaments  conducting  these  to  the  muscles  and 
the  sensory  filaments  conveying  the  impressions  to  the  centres.  These  fibres 
also  conduct  the  force  generated  by  the  nerve-centres ;  but  there  are  many 
fibres,  such  as  those  composing  the  white  matter  of  the  encephalon  and  the 
spinal  cord,  that  are  insensible  to  direct  irritation,  while  they  convey  to  the 
centres  impressions  conveyed  to  them  by  sensory  nerves  and  conduct  to  the 
motor  nerves  the  stimulus  generated  by  nerve-cells. 

In  the  most  natural  classification  of  the  nerve-fibres,  they  are  divided  into 


STRUCTURE  OF  THE  NERVOUS  TISSUE.  507 

two  groups ;  one  embracing  those  fibres  which  have  the  conducting  element 
alone,  and  the  other  presenting  this  anatomical  element  surrounded  by  cer- 
tain accessory  structures.  In  the  course  of  the  nerves,  the  simple  fibres 
are  the  exception,  and  the  other  variety  is  the  rule ;  but  as  the  nerves  are^ 
followed  to  their  terminations  in  muscles  or  sensitive  parts  or  are  traced  to 
their  origin  in  the  nerve-centres,  they  lose  one  or  another  of  their  coverings. 
These  two  varieties  are  designated  as  medullated  and  non-medullated  fibres. 

Medullated  Nerve-fibres. — These  fibres  are  so  called  because,  in  addition 
to  the  axis-cylinder,  or  conducting  element,  they  contain,  enclosed  in  a  tubu- 
lar sheath,  a  soft  substance  called  medulla.  This  substance  is  strongly  re- 
fractive and  gives  the  nerves  a  peculiar  appearance  under  the  microscope, 
from  which  they  are  sometimes  called  dark-bordered  nerve-fibres.  As  the 
whole  substance  of  the  fibre  is  enclosed  in  a  tubular  membrane,  these  are  fre- 
quently called  nerve-tubes. 

If  the  nerves  be  examined  while  perfectly  fresh  and  unchanged,  their  ana- 
tomical elements  appear  in  the  form  of  simple  fibres  with  strongly  accentu- 
ated borders.  The  diameter  of  these  fibres  is  ?^Vff  t°  TT^OTT  °*  an  incn  (10  to 
15  p.).  In  a  very  short  time  the  borders  become  darker  and  the  fibres  assume 
an  entirely  different  appearance.  By  the  use  of  certain  reagents,  it  can  be 
demonstrated  that  a  medullated  nerve-fibre  is  composed  of  three  distinct 
portions ;  viz.,  a  homogeneous  sheath,  a  semi-fluid  matter  contained  in  the 
sheath,  and  a  delicate,  central  band. 

The  tubular  sheath  of  the  nerve-fibres,  the  neurilemma,  is  a  somewhat 
elastic,  homogeneous  membrane,  never  striated  or  fibrillated,  and  generally 
presenting  oval  nuclei  with  their  long  diameter  in  the  direction  of  the  tube. 
This  is  sometimes  called  the  sheath  of  Schwann.  In  its  chemical  and  gen- 
eral properties  this  membrane  resembles  the  sarcolemma,  although  it  is  less 
elastic  and  resisting.  It  exists  in  all  the  medullated  nerve-fibres,  large  and 
small,  except  those  in  the  white  portions  of  the  encephalon  and  spinal  cord. 
It  is  not  certain  that  it  does  not  exist  in  the  small,  non-medullated  fibres, 
although  its  presence  here  has  never  been  satisfactorily  demonstrated. 

The  medullary  substance  fills  the  tube  and  surrounds  the  central  band. 
This  is  called  by  various  names,  as  myeline,  white  substance  of  Schwann, 
medullary  sheath,  nervous  medulla  etc.  It  does  not  exist  either  at  the  ori- 
gin of  the  nerves  in  the  gray  substance  of  the  nerve-centres  or  at  the  periph- 
eral termination  of  the  nerves,  and  it  is  probably  not  an  essential  conducting 
element.  When  the  nerves  are  perfectly  fresh,  this  substance  is  transparent, 
homogeneous,  and  strongly  refracting,  like  oil ;  but  as  the  nerves  become 
altered  by  desiccation,  the  action  of  water,  acetic  acid  and  various  other 
reagents,  it  coagulates  into  an  opaque,  granular  mass.  In  the  white  sub- 
stance of  the  encephalon  and  spinal  cord,  the  neurilemma  is  wanting  and 
the  fibres  present  only  the  axis-cylinder  surrounded  with  the  white  substance 
of  Schwann.  As  a  post-mortem  condition,  these  fibres  present,  under  the 
microscope,  varicosities  at  irregular  intervals,  which  give  them  a  peculiar 
and  characteristic  appearance. 

The  medullated  nerve-fibres  do  not  have  regular  outlines,  but  present  con- 


508 


NERVOUS  SYSTEM. 


strictions  at  various  points  in  their  length,  called  the  constrictions  or  nodes 
of  Ranvier.     At  these  nodes  the  medullary  substance  is  wanting  and  the 

neurilemma  is  in  contact  with  the  axis- 
cylinder.  It  is  at  these  points  that  the 
transverse  lines  of  Fromann,  produced  by 
the  action  of  silver  nitrate  upon  the  axis- 
cylinder,  are  particularly  prominent. 

When  a  medullated  nerve  -  fibre  is 
slightly  stretched,  a  number  of  oblique 
cuts  are  observed  running  across  the  fibre 
and  extending  to  the  axis-cylinder,  called 
incisures.  These  involve  the  medullary 
substance  only,  and  are  best  observed  when 
this  substance  has  been  stained  with  os- 
mic  acid.  It  is  not  known  that  they  pos- 
sess any  physiological  importance. 

The  axis-cylinder,  which  occupies  one- 
FIO.  m.-Nerve-fibres  from  the  human  sub-  fifth  to  one-fourth  of  the  diameter  of  the 

ject;  magnified^  diameters  (Keller).       nerve_tube,    is    probably    the    Conducting 
Four  small  fibres  of  which  two  are  vancose,  .  J 

one  medium-sized  fibre  with  borders  of  portion  of  the  nerve.     In  the  ordinary 

single  contour,  and  four  large  fibres.     Of    J  J 

the  latter,  two  have  a  double  contour,  and  medullated  fibres,  the  axis-cylinder  can 

two  contain  granular  matter. 

not  be  seen  in  the  natural  condition,  be- 
cause it  refracts  in  the  same  manner  as  the  medullary  substance;  and  it 
can  not  easily  be  demonstrated  afterward,  on  account  of  the  opacity  of  the 
coagulated  matter.  If  a  fresh  nerve,  however,  be  treated  with  strong  acetic 
acid,  the  divided  ends  of  the  fibres  retract,  leaving  the  axis-cylinder,  which 
latter  is  but  slightly  affected  by  reagents.  It  then  presents  itself  in  the 
form  of  a  pale,  slightly  flattened  band,  with  outlines  tolerably  regular, 
though  slightly  varicose  at  intervals.  It  is  somewhat  granular  and  very  finely 
striated  in  a  longitudinal  direction.  This  band  is  elastic  but  not  very  resist- 
ing. What  serves  to  distinguish  it  from  all  other  portions  of  the  nerve-fibre 
is  its  insolubility  in  most  of  the  reagents  employed  in  anatomical  investiga- 
tions. It  is  slightly  swollen  by  acetic  acid  but  is  dissolved  after  prolonged 
boiling.  If  nerve-tissue  be  treated  with  a  solution  of  carmine,  the  axis-cyl- 
inder only  is  colored.  It  has  been  observed  that  the  nerve-fibres  treated  with 
silver  nitrate  present  in  the  axis-cylinder  well  marked,  transverse  striations 
(Fromann) ;  and  some  anatomists  regard  both  the  nerve-cells  and  the  axes 
of  the  fibres  as  composed  of  two  substances,  the  limits  of  which  are  marked 
by  the  regular  striae  thus  developed.  This,  however,  is  a  point  of  purely 
anatomical  interest.  The  presence  of  regular  and  well  marked  strias  in  the 
axis-cylinder  after  the  addition  of  a  solution  of  silver  nitrate  and  the  action 
of  light  can  not  be  doubted ;  but  it  has  not  yet  been  determined  whether 
these  markings  be  entirely  artificial  or  whether  the  axis-cylinder  be  really 
composed  of  two  kinds  of  substance. 

For  some  time  it  has  been  known  that  the  axis-cylinders  in  the  organs  of 
special  sense,  in  the  final  distribution  of  sensory  nerves  and  in  some  other 


STRUCTURE  OF  THE  NERVOUS  TISSUE. 


509 


(Ranvier). 

A.  Intercostal  nerve  of  the  mouse,  treated  with  sil- 

ver nitrate. 

B.  Nerve-fibre  from  the  sciatic  nerve  of  a  full-grown 

rabbit.  A,  node  of  Ranvier  ;  M,  medullary  sub- 
stance rendered  transparent  by  the  action  of 
glycerine  ;  CY,  axis-cylinder  presenting  the  lines 
of  Fromann,  which  are  very  distinct  near  the 
node.  The  lines  are  less  marked  at  a  distance 
from  the  node. 


situations,  break  up  into  fibrillae.  A 
fibrillated  appearance,  indeed,  is  often 
observed  in  nerves  in  their  course,  and 
it  is  now  the  general  opinion  that  the 
axis-cylinders  are  composed  of  fibrilla3 
held  closely  together  by  connective 
substance.  This  fibrillated  structure 
of  the  nerves  is  quite  prominent  in 
some  of  the  lower  orders  of  animals. 

The  various  appearances  which 
the  nerve-fibres  present  under  differ- 
ent conditions  are  represented  in 
Figs.  172  and  173. 

Non-medullated  Nerve  -  Fibres. — 
These  fibres,  which  are  largely  dis- 
tributed in  the  nerVOUS  System,  ap-  FlG.  m.-Nodesof  Ranvier  and  lines  of  Fromann 

pear  to  be  simple  prolongations, 
without  alteration,  of  the  axis-cylin- 
ders of  the  medullated  fibres.  They 
are  found  chiefly  in  the  peripheral 
terminations  of  the  nerves  and  in  the 
filaments  of  origin  of  the  fibres  from 

_  the  nerve-cells.  Some  anatomists  think  that  they  have  a 
delicate  investing  membrane,  but  this  has  not  been  satis- 
factorily demonstrated. 

Gelatinous  Nerve -Fibres  (Fibres  of  Remak}. — There 
has  been  some  difference  of  opinion  with  regard  to  the 
physiology  of  the  so-called  gelatinous  nerve-fibres.     Some 
anatomists  have  regarded  them  simply  as  elements  of  con- 
nective tissue,  and  others  have  described  them  as  axis-cyl- 
inders surrounded  with  a  nucleated  sheath ;  but  the  fibres 
do  not  present  the  lines  of  Fromann  when  treated  with  sil- 
ver nitrate.     While  elements  of  connective  tissue  may  have 
been  mistaken  for  true  nerve-fibres,  there  are  in  the  nerves, 
particularly  in  those  belonging  to  the  sympathetic  system, 
fibres  resembling  the  nerve-fibres  of  the  embryon.     These 
are  the  true,  gelatinous  nerve-fibres,  or  fibres  of  Remak. 
All  the  nerves  have   this  structure  until  about  the  fifth 
month  of  intrauterine   life,   and  in  the  regeneration  of 
nerves  after  division  or  injury,  the  new  elements  usually 
assume  this  form  before  they  arrive  at  their  full  develop- 
Fro.  174.  —  Fibres  of 
Remak  ;  magnified 
300  diameters  (Rob- 
in). 

with  the  ^gelatinous  characters  :  They  are  flattened,  with  regular  and  sharp  bor- 

Mhe*™  ders,  grayish,  pale  and  always  fibrillated,  with  very  fine 

f-flbres!"'  granulations,  and  a  number  of  oval,  longitudinal  nuclei,  a 
34 


The  true,  gelatinous  nerve-fibres  present  the  following 


510  NERVOUS  SYSTEM. 

characteristic  which  has  given  them  the  name  of  nucleated  nerve-fibres. 
The  diameter  of  the  fibres  is  about  -g^^  of  an  inch  (3  /*).  The  nuclei  have 
nearly  the  same  diameter  as  the  fibres  and  are  about  YgVo  of  an  inch  (20  /*.) 
in  length.  They  are  finely  granular  and  present  no  nucleoli.  The  fibres  are 
rendered  pale  by  the  action  of  acetic  acid,  but  they  are  slightly  swollen  only, 
and  present,  in  this  regard,  a  marked  contrast  with  the  elements  of  connect- 
ive tissue.  They  are  found  chiefly  in  the  sympathetic  system  and  in  that 
particular  portion  of  this  system  connected  with  involuntary  movements. 
They  are  not  usually  found  in  the  white  filaments  of  the  sympathetic. 

Accessory  Anatomical  Elements  of  the  Nerves. — The  nerves  present,  in 
addition  to  the  different  varieties  of  true  nerve-fibres  just  described,  certain 
accessory  anatomical  elements  common  to  nearly  all  of  the  tissues  of  the 
organism,  such  as  connective  tissue,  blood-vessels  and  lymphatics. 

Like  the  muscular  tissue,  the  nerves  are  made  up  of  their  true  anatomical 
elements — the  nerve-fibres — held  together  into  primitive,  secondary  and  terti- 
ary bundles,  and  so  on,  in  proportion  to  the  size  of  the  nerve.  The  primitive 
fasciculi  are  surrounded  with  a  delicate  membrane,  described  by  Robin,  under 
the  name  of  perinevre,  but  which  had  been  already  noted  by  other  anatomists, 
under  different  names,  and  is  now  frequently  called  the  sheath  of  Henle. 
This  membrane  is  homogeneous  or  very  finely  granular,  sometimes  marked 
with  longitudinal  strige,  and  possessing  elongated,  granular  nuclei.  Accord- 
ing to  Ranvier,  there  are  three  kinds  of  nuclei  either  attached  to  or  situated 
near  the  sheath.  These  are  (1)  nuclei  attached  to  the  inner  surface  of  the 
;sheath;  (2)  nuclei  belonging  to  the  nerve-fibres  within  the  sheath;  and  (3) 
nuclei  of  connective-tissue  elements  near  the  sheath.  Treated  with  silver 
nitrate,  the  sheath  presents  the  borders  of  a  lining  endothelium.  The  sheath 
•of  Henle  begins  at  the  point  where  the  nerve-fibres  emerge  from  the  white 
•portion  of  the  nervous  centres,  and  it  extends  to  their  terminal  extremities, 
being  interrupted  by  the  ganglia  in  the  course  of  the  nerves.  This  mem- 
brane generally  envelops  a  primitive  fasciculus  of  fibres,  branching  as  the  bun- 
dles divide  and  pass  from  one  trunk  to  another,  and  is  sometimes  found 
surrounding  single  fibres.  It  usually  is  not  penetrated  by  blood-vessels,  the 
smallest  capillaries  of  the  nerves  ramifying  in  its  substance  but  seldom  pass- 
ing through  to  the  individual  nerve-fibres.  Within  the  sheath  of  Henle  are 
sometimes  found  elements  of  connective  tissue,  with  very  rarely  a  few  capil- 
lary blood-vessels  in  the  largest  fasciculi. 

The  quantity  of  fibrous  tissue  in  the  different  nerves  is  very  variable  and 
depends  upon  the  conditions  to  which  they  are  subjected.  In  the  nerves 
within  the  bony  cavities,  where  they  are  entirely  protected,  the  fibrous  tissue 
is  very  scanty ;  but  in  the  nerves  between  muscles,  there  is  a  tolerably  strong 
investing  membrane  or  sheath  surrounding  the  whole  nerve  and  sending  into 
its  interior  processes  which  envelop  smaller  bundles  of  fibres.  This  sheath 
is  formed  of  ordinary  fibrous  tissue,  with  small  elastic  fibres  and  nucleated 
connective-tissue  cells.  These  latter  may  be  distinguished  from  the  gelati- 
nous nerve-fibres  by  the  action  of  acetic  acid,  which  swells  and  finally  dissolves 
them,  while  the  nerve-fibres  are  but  slightly  affected. 


TERMINATIONS  OF  THE  MOTOR  NERVES. 


511 


The  greatest  part  of  the  fibrous  sheath  of  the  nerves  is  composed  of  bun- 
dles of  white  inelastic  tissue,  interlacing  in  every  direction ;  but  it  contains 
also  many  elastic  fibres,  adipose  tissue,  a  net- work  of  arteries  and  veins,  and 
"  nervi  nervorum,"  which  are  to  these  structures  what  the  vasa  vasorum  are 
to  the  blood-vessels.  The  adipose  tissue  is  constant,  being  found  even  in  ex- 
tremely emaciated  persons  (Sappey). 

.The  vascular  supply  to  most  of  the  nerves  is  rather  scanty.  The  arteries 
break  up  into  a  plexus  of  very  fine  capillaries,  arranged  in  oblong,  longi- 
tudinal meshes  surrounding  the  fasciculi  of  fibres ;  but  they  rarely  penetrate 
the  sheath  of  Henle,  and  they  do  not  usually  come  in  contact  with  the  ulti- 
mate nervous  elements.  The  veins  are  rather  more  voluminous  and  follow 
the  arrangement  of  the  arteries.  Lymph-spaces,  lined  by  delicate  endothe- 
lium,  are  found  in  the  connective-tissue  sheaths  of  the  bundles  of  fibres. 

Branching  and  Course  of  the  Nerves. — The  ultimate  nerve-fibres  in  the 
course  of  the  nerves  have  no  connection  with  each  other  by  branching  or  in- 
osculation. A  bundle  of  fibres  frequently  sends  branches  to  other  nerves  and 
receives  branches  in  the  same  way ;  but  this  is  simply  the  passage  of  fibres 
from  one  sheath  to  another,  the  ultimate  fibres  themselves  maintaining 
throughout  their  course  their  individual  physiological  properties.  The 
nerve-fibres  do  not  branch  or  inosculate  except  near  their  termination.  When 
there  is  branching  of  medullated  fibres,  it  is  always  at  the  site  of  one  of  the 
nodes  of  Ranvier.  The  branching 
and  inosculation  of  the  ultimate 
nerve-fibres  will  be  fully  described 
in  connection  with  their  final  dis- 
tribution to  muscles  and  sensitive 
parts. 

Termination  of  Nerves  in  Vol- 
untary Muscles. — The  mode  of 
termination  of  motor  nerves  in 
voluntary  muscles  was  indicated 
by  Doyere,  in  1840,  was  quite  fully 
described  by  Rouget,  in  1862,  and 
has  since  been  studied  by  anato-  FlG>  ™-Mode  °f  *"$%£$»  of  the  motor  nerves 

mists,  Who  have  extended  and  A'  Primitive  fasciculus  of  the  thyro-hyoid  muscle  of  the 

human  subject,  and  its  nerve-tube  :  1,  1,  primitive 

elaborated  these  researches.  It  is  muscular  fasciculus  ;  2,  nerve-tube  ;  3,  medullary 

.  .  .  substance  of  the  tube,  which  is  seen  extending  to  the 

the  general  Opinion  that  but  One  terminal  plate,  where  it  disappears  ;  4,  terminal 

...  .  .  plate  situated  beneath  the  sarcolemma,  that  is  to 

nerve-ending  exists  in  each  milS-  sa.V,  between  it  and  the  elementary  flbrillse  ;  5,  5, 

i  ,,,  .  ,,  ..  ,  „  sarcolemma. 

CUlar  Ilbre  in  the  mammalia,  While  B,  primitive  fasciculus  of  the  intercostal  muscle  of  the 

lizard,  in  which  a  nerve-tube  terminates  :  1 , 1.  sheath 
of  the  nerve-tube  ;  2,  nucleus  of  the  sheath  ;  3,  3, 
sarcolemma  becoming  continuous  with  the  sheath  ; 
4,  medullary  substance  of  the  nerve-tube,  ceasing 
abruptly  at  the  site  of  the  terminal  plate;  5,  5,  ter- 
minal plate  :  6,  6,  nuclei  of  the  plate  ;  7,  7,  granular 
substance  which  forms  the  principal  element  of  the 
terminal  plate  and  which  is  continuous  with  the  axis- 
cylinder  ;  8,  8,  undulations  of  the  sarcolemma  re- 
producing those  of  the  fibrillse  ;  9,  9,  nuclei  of  the 
sarcolemma. 


5  £^--'j- — i' 


several  exist  in  cold-blooded  ani- 
mals. In  man  and  in  the  warm- 
blooded animals  generally,  the 
medullated  nerve  -  fibres  divide 
dichotomously  near  their  endings 
in  the  muscular  fibres,  each  divis- 
ion always  taking  place  at  a  node  of  Ranvier. 


The  fibres  finally  resulting 


512 


NERVOUS  SYSTEM. 


from  these  divisions  pass  to  the  sarcolemma  and  terminate  in  a  rather  prom- 
inent mass  called  an  end-plate,  with  six  to  twelve  or  sometimes  sixteen  nuclei 
which  are  distinct  from  the  nuclei  of  the  muscular  fibre.  The  tubular  mem- 
brane of  the  nerve-fibre  here  fuses  with  the  sarcolemma  (Rouget)  and  the 
medullary  substance  is  lost.  By  the  action  of  gold  chloride,  it  has  been 
shown  that  fibrils  arise  from  the  under  surface  of  the  end-plates,  which  pass 
into  the  substance  of  the  muscular  fibres,  betAveen  the  muscular  fibrillge. 


Fio.  176. — Intrafibrillar  terminations  of  a  motor  nerve  in  striated  muscle,  stained  with  gold  chloride 

(Landois). 

These  fibrils  probably  are  connected  with  the  axis-cylinders,  but  their  exact 
mode  of  termination  in  the  muscular  substance  has  not  been  satisfactorily 
demonstrated. 

Although  the  sensibility  of  the  muscles  is  slight  as  compared  with  that 
of  the  skin  and  mucous  membranes,  they  are  not  insensible  and  they  possess 
nerve-fibres  other  than  those  exclusively  motor.  According  to  Kolliker, 
small  medullated  fibres  go  to  the  muscular  tissue  and  here  give  off  very  fine 
non-medullated  fibres,  which  terminate  in  fibres  of  the  same  appearance  but 

provided  with  nuclei.  These  form  a  plexus  on 
the  sarcolemma  and  surround  the  muscular  fibres. 
It  is  not  certain  that  they  penetrate  the  sarco- 
lemma and  terminate  in  the  muscular  substance, 
although  this  view  has  been  advanced. 

Termination  of  Nerves  in  the  Involuntary 
Muscular  Tissue. — According  to  the  observa- 
tions of  Frakenhaeuser  upon  the  nerves  of  the 
uterus,  the  nerve-fibres  form  a  plexus  in  the  con- 
nective tissue  surrounding  the  involuntary  mus- 
cles and  then  send  small  fibres  into  the  sheets  or 
layers  of  muscular-fibre  cells,  which  branch  and 
finally  go  into  the  nucleoli  of  these  structures. 
Arnold  has  confirmed  these  observations  and  has 
FIG.  irr  -Termination  of  nerves  in  shown  farther  that  in  many  instances,  the  fine, 

terminal  nerve-fibres  branch  and  go  into  the 

nuclei  of  the  muscular  fibres  and  afterward  pass  out  to  join  with  other  fibres 
and  form  a  plexus. 

Termination  of  the  Nerves  in  Glands. — The  researches  of  Pfliiger  upon 
the  salivary  glands  leave  no  doubt  of  the  fact  that  medullated  nerve-fibres 
pass  to  the  cells  of  these  organs  and  there  abruptly  terminate,  at  least  as 
dark-bordered  fibres.  This  author  believes,  however,  that  having  formed  a 


TERMINATIONS  OF  THE  SENSORY  NERVES.  513 

more  or  less  branching  plexus,  non-medullated  fibres  pass  directly  into  the 
glandular  cells  and  terminate  in  the  nucleoli.  The  same  observer  has  de- 
scribed and  figured  multipolar  cells,  mixed  with  the  glandular  cells,  in  which 
some  of  the  nerve-fibres  terminate.  These,  however,  are  not  found  in  the 
parotid.  These  nerve- 
fibres  are  regarded  as 
glandular  nerves,  and 
they  are  distinct  from 
the  vaso -motor  nerves. 
Modes  of  Termina- 
tion of  the  Sensory 
Nerves.  —  There  un- 
doubtedly are  several 
modes  of  termination 
of  the  sensory  nerves 
in  integument  and  in 
mucous  membranes, 
some  of  which  have 
been  quite  accurately 
described,  while  others 

are  Still  Somewhat  Un-      ^IG-  W8.— Termination  of  the  nerves  in  the  salivary  glands  (Pflttger). 

.  „      ,     I,  II,  branching  of  the  nerves  between  the  glandular  cefls  ;  III,  termina- 

Certaill.       Ill    the    first          tions  of  the  nerves  in  the  nuclei  of  the  cells  ;  IV,  multipolar  nerve- 
cell. 

place,  anatomists  now 

recognize  three  varieties  of  corpuscular  terminations,  differing  in  their 
structure,  probably,  according  to  the  different  properties  connected  with 
sensation,  with  which  the  parts  are  endowed.  In  addition  it  is  probable 
that  sensory  nerves  are  connected  with  the  hair-follicles,  which  are  so  largely 
distributed  throughout  the  cutaneous  surface.  There  are,  also,  terminal 
filaments  not  connected  with  any  special  organs,  some  of  them,  perhaps, 
ending  simply  in  free  extremities,  and  some  connected  with  epithelium. 
There  are  still  differences  of  opinion  concerning  these  various  modes  of 
termination  of  the  nerves,  but  with  regard  to  the  terminal  corpuscles,  these 
differences  relate  mainly  to  anatomical  points.  It  is  not  proposed,  therefore, 
to  enter  fully  into  the  discussions  upon  these  questions,  but  simply  to  pre- 
sent what  seem  to  be  the  most  reliable  anatomical  views. 

Corpuscles  of  Vater  or  of  Pacini. — These  bodies  were  called  corpuscles 
of  Pacini,  until  it  was  shown  that  they  had  been  seen  about  a  century  and 
a  half  ago  by  Vater.  In  man,  they  are  oval  or  egg-shaped  and  measure  ^ 
to  $  °f  an  incn  (1  to  4  mm.)  in  length.  They  are  always  found  in  the  sub- 
cutaneous layer  on  the  palms  of  the  hands  and  the  soles  of  the  feet,  and  are 
most  abundant  on  the  palmar  surfaces  of  the  fingers  and  toes,  particularly 
the  third  phalanges.  In  the  entire  hand  there  are  about  six  hundred,  and 
about  the  same  number  on  the  feet.  They  are  sometimes,  but  not  constantly, 
found  in  the  following  situations :  the  dorsal  surfaces  of  the  hands  and  feet, 
on  the  cutaneous  nerves  of  the  arm,  the  forearm  and  the  neck,  the  internal 
pudic  nerve,  the  intercostal  nerves,  all  of  the  articular  nerves  of  the  extremi- 


514  NERVOUS  SYSTEM. 

ties,  the  nerves  beneath  the  mammary  glands,  the  nerves  of  the  nipples,  and 
in  the  substance  of  the  muscles  of  the  hands  and  feet.  They  are  found  with- 
out exception  on  all  of  the  great  plexuses  of  the  sympathetic  system,  in  front 
of  and  by  the  sides  of  the  abdominal  aorta,  and  behind  the  peritoneum,  par- 
ticularly in  the  vicinity  of  the  pancreas.  They  some- 
times exist  in  the  mesentery  and  have  been  observed  near 
the  coccygeal  gland. 

The  corpuscles  consist  simply  of  several  layers  of 
connective  tissue  enclosing  one,  two  or  three  central 
bulbs  in  which  are  found  the  ends  of  the  nerve.  These 
bulbs  are  finely  granular  and  nucleated,  and  are  regarded 
by  most  anatomists  as  composed  of  connective  tissue. 
At  the  base  of  the  corpuscle,  is  a  pedicle  formed  of  con- 
nective tissue  surrounding  a  medullated  nerve  -  fibre 
which  penetrates  the  corpuscle.  Within  the  corpuscle 
the  medullary  substance  of  the  nerve-fibre  is  lost  and 
only  the  axis-cylinder  remains. 

The  situation  of  these  corpuscles,  beneath  the  true 
skin  instead  of  in  its  substance,  shows  that  they  can  not 
be  properly  considered  as  tactile  corpuscles,  a  name 
which  is  applied  to  other  structures  found  in  the  papillae 

Fio.   179.  —  Corpuscle    of  fr  .     . 

Vater  (Sappey).          of  the  corium  ;  and  it  is  impossible  to  assign  to  them  any 


special  use  connected  with  sensation,  such  as  the  appre- 
cjation  of  temperature,  pressure  or  weight.     All  that  can 
couscfef  r5atic!vity  be  said  with  regard  to  them  is  that  they  constitute  one  of 
ntrve?7Cne?veTwh:ich  tne  several  modes  of  termination  of  the  nerves  of  gen- 


has  lost  its  medullary   „_„] 

substance  and  sheath;    eral 


Tactile  Corpuscles.  —  The  name  tactile  corpuscles  im- 
piies  that  these  bodies  are  connected  with  the  sense  of 
touch  ;  and  this  view  is  sustained  by  the  fact  that  they 
are  found  almost  exclusively  in  parts  endowed  to  a  marked  degree  with 
tactile  sensibility.  They  are  sometimes  called  the  corpuscles  of  Meissner 
and  Wagner,  after  the  anatomists  by  whom  they  were  first  described.  The 
true,  tactile  corpuscles  are  found  in  greatest  number  on  the  palmar  sur- 
faces of  the  hands  and  fingers  and  the  plantar  surfaces  of  the  feet  and  toes. 
They  exist,  also,  in  the  skin  on  the  backs  of  the  hands  and  feet,  the  nipples, 
and  a  few  on  the  anterior  surface  of  the  forearm.  The  largest  papillae  of  the 
skin  are  found  on  the  hands,  feet  and  nipples,  precisely  where  the  tactile 
corpuscles  are  most  abundant.  Corpuscles  do  not  exist  in  all  papillae,  and 
they  are  found  chiefly  in  those  called  compound.  In  an  area  .a  little  more 
than  ^  of  an  inch  square  (2-2  mm.  square),  on  the  third  phalanx  of  the  in- 
dex-finger, Meissner  counted  four  hundred  papillae,  in  one  hundred  and  eight 
of  which  he  found  tactile  corpuscles,  or  about  one  in  four.  In  an  equal  area 
on  the  second  phalanx,  he  found  forty  corpuscles  ;  on  the  first  phalanx,  fif- 
teen ;  eight  on  the  skin  of  the  hypothenar  eminence  ;  thirty-four  on  the 
plantar  surface  of  the  ungual  phalanx  of  the  great-toe  ;  and  seven  or  eight  in 


TERMINATIONS  OF  THE  SENSORY  NERVES. 


515 


the  skin  on  the  middle  of  the  sole  of  the  foot.     In  the  skin  of  the  fore-arm 
the  corpuscles  are  very  rare.     According  to  Kolliker,  the  tactile  corpuscles 


FIG.  180.—Papillce  of  the  skin  of  the  palm  of  the  hand  (Sappey). 

1,  papilla  with  two  vascular  loops ;  2,  papilla  with  a  tactile  corpuscle  ;  3,  papilla  with  three  vascular 
loops  ;  4, 5,  large,  compound  papillae  ;  6, 6,  vascular  net-work  beneath  the  papillae  ;  7, 7, 7, 7,  vascular 
loops  in  the  papillae  ;  8,  8,  8,  8,  u'erves  beneath  the  papillae  ;  9,  9,  10,  11,  tactile  corpuscles. 

usually  occupy  special  papillge  which  are  not  provided  with  blood-vessels ;  so 
that  the  papillae  of  the  hand  may  be  properly  divided  into  vascular  and 
nervous. 

The  form  of  the  tactile  corpuscles  is  oblong,  with  their  long  diameter  in 
the  direction  of  the  papillae,  Their  length  is  -g-^  to  ^^  of  an  inch  (66  to 
100  p.}.  In  the  palm  of  the  hand  they  are  ^^  to  j^  of  an  inch  (100  to 
165  p.)  long,  and  -^  to  -^J-g-  of  an  inch  (45  to  50  p.)  in  thickness.  They  gen- 
erally are  situated  at  the  summits  of  the  secondary  eminences  of  the  com- 
pound papillas.  They  consist  of  a  central  bulb  of  homogeneous  or  slightly 
granular  connective-tissue  substance,  harder  than  the  central  bulb  of  the 
corpuscles  of  Vater,  and  a  covering.  The  covering  is  composed  of  connect- 
ive tissue  with  a  few  fine  elastic  fibres.  One,  two,  and  sometimes  three  or 
four  dark-bordered  nerve-fibres  pass  from  the  subcutaneous  nervous  plexus 
to  the  base  of  each  corpuscle.  These  surround  the  corpuscle  with  two  or 
three  spiral  turns,  and  they  terminate  by  pale  extremities  on  the  surface  of 
the  central  bulb. 

End-Bulbs. — Under  this  name,  a  variety  of  corpuscles  has  been  described 
by  Krause,  as  existing  in  the  conjunctiva  covering  the  eye  and  in  the  semi- 
lunar  fold,  in  the  floor  of  the  buccal  cavity,  the  tongue,  the  glans  penis  and 
the  clitoris.  They  bear  some  analogy  to  the  tactile  corpuscles,  but  they  are 
much  smaller  and  more  simple  in  their  structure.  They  form  rounded  or 
oblong  enlargements  at  the  ends  of  the  nerves,  which  are  composed  of  homo- 
geneous matter  with  a  delicate  investment  of  connective  tissue.  They  meas- 
ure  ToW  to  Tj^g-  of  an  inch  (25  to  100  /A)  in  diameter.  In  the  parts  provided 
with  papillae,  they  are  situated  at  the  summits  of  the  secondary  elevations. 
The  arrangement  of  the  nerve-fibres  in  these  corpuscles  is  very  simple.  One, 
two,  or  three  medullated  fibres  pass  from  the  submucous  plexus  to  the  cor- 
puscles. The  investing  sheath  of  the  fibres  is  here  continuous  with  the  con- 
nective-tissue covering  of  the  corpuscle,  and  the  nerve-fibres  pass  into  the 
corpuscle,  break  up  into  two  or  three  divisions,  and  terminate  in  convoluted 


516 


NEEVOUS  SYSTEM. 


or  knotted  coils.  The  nerve-fibres  are  medullated  for  a  certain,  distance, 
but  their  terminations  are  generally  pale.  The  above  is  one  form  of  these 
corpuscles.  Sometimes,  however,  the  terminal  bulbs 
are  oblong,  and  sometimes  but  a  single  nerve-fibre 
penetrates  the  bulb  and  terminates  in  a  simple,  pale 
filament.  The  principal  forms  of  the  terminal  bulbs 
are  shown  in  Fig.  181. 

General  Mode  of  Termination  of  the  Sensory 
Nerves. — The  actual  termination  of  the  sensory 
nerves  upon  the  general  surface  and  in  mucous 
membranes  is  still  a  question  of  -some  obscurity. 
Although  anatomists  have  arrived  at  a  pretty  definite 
knowledge  of  the  sensory  corpuscles,  it  must  be 
remembered  that  there  is  an  immense  cutaneous  and 
mucous  surface  in  which  no  corpuscles  have  as  yet 
been  demonstrated ;  and  it  is  in  these  parts,  endowed 
with  what  may  be  called  general  sensibility,  as  dis- 
tinguished from  the  sense  of  touch,  that  the  mode 
of  termination  of  the  nerves  remains  to  be  studied. 

According  to  Kolltker,  in  the  immense  majority 
of  instances  the  sensory  nerves  terminate  in  some 
way  in  the  hair-follicles.  If  this  be  true,  it  will 
account  for  the  termination  of  the  nerves  in  by  far 
the  greatest  portion  of  the  skin,  as  there  are  few 
parts  in  which  hair-follicles  do  not  exist ;  but  un- 
fortunately the  exact  mode  of  connection  of  the 
nerves  with  these  follicles  is  not  apparent.  The 
following  seems  to  be  all  that  is  positively  known 
of  the  terminations  of  the  nerves  on  the  general  sur- 

FIG.  \81.-End-bulbs,  or  corpus- 
cles of  Krause  (Ludden).  f  aC6  : 
A,  three  corpuscles  of  Krause  -»«•    -i    n    j.    t  .c-u  -e  i  •        it. 

from  the  conjunctiva  of         Medullated  nerve-fibres  form  a  plexus  m  the 

man.    treated   with   acetic     n  i  i»ii  i  •  TJ?  n  •        i 

acid ;  magnified  300  diam-  deeper  layers  of  the  true  skin,  and  from  this  plex- 
us, fibres,  some  pale  and  nucleated  and  others  me- 
dullated,   pass    to    the    hair-follicles,    divide    into 
ei  branches,  penetrate  into  their  interior  and  are  there 
^  lost.     A  certain  number  of  fibres  pass  to  the  non- 
striated  muscular  fibres  of  the  skin.      A   certain 


m  SXeeb™rpuscies,  the  number  pass  to  papillae  and  terminate  in  tactile  cor- 

2°iysedist1n^dSd  in  l  and  puscles,  and  others  pass  to  papillae  that  have  no  tac- 

B,  terminal  bulbs  from  the  con-  f  i]p  pnrrm«5plp<5 

junctiya9f  the  calf,  treated  T 

with  acetic  acid ;  magnified         jn  the  mucous  membranes  the  mode  of  termina- 

300  diameters  :  1,  extremity 

of  a  nerve  -  fibre  with  its  tion  is,  in  general  terms,  by  a  delicate  plexus  just 

bulb  ;  2,  double  bifurcation  J 

of  a  nerve-fibre,  with  two  beneath  the  epithelium,  coming  from  a  submucous 

terminal  bulbs  ;  n,  covering 

of  the  terminal  bulbs ;  6,  in-  plexus  analogous  to  the  deep  cutaneous  plexus.     In 

ternal  bulb ;  c,  pale  nerve-  x  .  .  , 

fibre.  certain  membranes   the   nerves   terminate   in  end- 
bulbs,  or  corpuscles  of  Krause.     In  the  cornea,  according  to  the  observations 


STRUCTURE  OF  THE  NERVE-CENTRES. 


517 


of  Hoyer,  Lipmann  and  others,  branching  nerve-fibres  pass  to  the  nucleoli 
of  the  corneal  corpuscles  and  to  the  nucleoli  of  the  cells  of  the  posterior 
layer  of  epithelium. 

Structure  of  the  Nerve-centres. — A  peculiar  pigmentary  matter  in  the 
nerve-cells  and  in  the  surrounding  granular  substance  gives  to  the  nerve- 
centres  a  grayish  color,  by  which  they  are  readily  distinguished  from  the 
white,  or  fibrous  division  of  the  nervous  system.  Wherever  this  gray  matter 
is  found,  the  anatomical  elements  of  the  tissue  are  cellular,  except  in  the 
nerves  formed  of  gray,  or  gelatinous  fibres.  Under  the  general  division  of 
nerve-centres,  are  included,  anatomically  at  least,  the  gray  matter  of  the 
cerebro-spinai  centres,  the  ganglia  of  the  roots  of  the  spinal  and  certain  of 
the  cranial  nerves,  and  the  ganglia  of  the  sympathetic  system.  In  these 
parts  are  found  cells,  which  constitute  the  essential  anatomical  element  of 
the  tissue,  granular  matter  resembling  the  contents  of  the  cells,  pale  fibres 
originating  in  prolongations  of  the  cells,  elements  of  connective  tissue,  deli- 
cate membranes  enveloping  some  of  the  cells,  with  blood-vessels  and  lym- 
phatics. The  most  important  of  these  structures, 
in  their  physiological  relations,  are  the  cells  and 
the  prolongations  by  which  they  are  connected  with 
the  nerves  and  with  each  other. 

Nerve-cells. — The  following  varieties  of  cells  ex- 
ist in  the  nerve-centres  and  constitute  their  essential 
anatomical  elements  ;  viz.,  unipolar,  bipolar  and 
multipolar  cells.  These  cells  present  great  differ- 
ences in  their  size  and  general  appearance,  and  some 
distinct  varieties  are  found  in  particular  portions  of 
the  nervous  system.  Unipolar  and  bipolar  cells  are 
found  in  the  ganglia  of  the  cranial  nerves  and  in 
the  ganglia  of  the  posterior  roots  of  the  spinal 
nerves.  Small  unipolar  cells  are  found  in  the  sym- 
pathetic ganglia.  Multipolar  cells  present  three  or 
more  prolongations.  Small  cells,  with  three  and 
rarely  four  prolongations,  are  found  in  the  posterior 
cornua  of  the  gray  matter  of  the  spinal  cord.  From 
their  situation  they  have  been  called  sensory  cells. 
They  are  found  in  greatest  number  in  parts  known 
to  be  endowed  exclusively  with  sensory  properties. 
Large,  irregularly  shaped  multipolar  cells,  with  a 
number  of  poles,  or  prolongations,  are  found  chiefly 
in  the  anterior  cornua  of  the  gray  matter  of  the 
spinal  cord,  and  these  have  been  called  motor  cells. 
They  sometimes  present  as  many  as  ten  or  twelve 
poles. 

Unipolar  cells,  such  as  exist  in  the  ganglia  of  FIG.  iss.— unipolar  ceil  from  tiie 

,.  -I  •     •  •  i  Gasserian  ganglion  (tich\\albv}. 

the  nerves  as  distinguished  from  the  ganglia  of  the  N,  N.  N,  nuciei  Of  the  sheath  ;  T, 
cerebro-spinai  axis,  have  but  a  single  prolongation,  |bre  branching  at  a  node  of 


518 


NERVOUS  SYSTEM. 


FIG.  183.—  Unipolar  nerve- 
cell  with  a  spiral  fibre 
(Landois). 


FIG.    184.  —  Bipolar 
nerve-cell  (Landois). 


which  is  continuous  with  a  nerve-fibre.  These  cells  frequently  have  a  con- 
nective-tissue envelope,  or  sheath,  which  is  prolonged  as  a  sheath  for  the 

nerve.  Unipolar  cells,  with  a  connect- 
ive-tissue sheath,  the  pole  being  sur- 
rounded by  a  spiral  fibre,  have  been 
observed  in  the  sympathetic  ganglia  of 
the  frog.  These  do  not  exist  in  the 
human  subject  or  in  the  mammalia  and 
nothing  is  known  of  the  uses  of  the 
spiral  fibres. 

Bipolar  cells  seem  to  be  nucleated 
enlargements  in  the  course  of  medul- 
lated  nerve-fibres.  Usually  the  medul- 
lary substance  does  not  extend  over 
the  cell,  although  this  sometimes  oc- 
curs. 

Multipolar  cells  have  a  number  of 
poles,  but  there  is  always  one  pole 
which  does  not  branch  and  which  becomes  continuous  with  the  axis-cylinder 
of  a  nerve-fibre.  This  is  called  the  axis-cylinder  prolongation.  Of  the 
other  poles,  some  are  continuous  with  poles  of  contiguous  cells,  connecting 
numbers  of  cells  into  groups,  and  others, 
which  are  sometimes  called  protoplasmic 
prolongations,  branch  freely  and  are  lost 
in  the  intercellular  substance. 

With  all  the  differences  in  the  size 
and  form  of  the  nerve-cells,  they  present 
tolerably  uniform  general  characters  as 
regards  their  structure  and  contents. 
With  the  exception  of  the  unipolar  and 
bipolar  cells,  they  are  irregular  in  shape, 
with  strongly  refracting,  granular  con- 
tents, frequently  a  considerable  number 
of  pigmentary  granules,  and  always  a  dis- 
tinct nucleus  and  nucleolus.  The  nucleus 
in  the  adult  is  almost  invariably  single, 
although,  in  rare  instances,  two  have  been  Fl°  1K-~ 

observed.       Cells  with    multiple  nuclei  are    z,  axis-cylinder  prolongation  ;   Y,  protoplas- 
,     .  •        i          rm  raic  branches. 

often  observed   in  young  animals,     ihe 

nucleoli  usually  are  single,  but  there  may  be  as  many  as  four  or  five.  The 
diameter  of  the  cells  is  variable.  They  usually  measure  y^-^  to  Tfg-  of  an 
inch  (20  to  50  //,)  ;  but  there  are  many  of  larger  size  and  some  are  smaller. 
The  nuclei  measure  ^^jVo  to  TsW  °^  an  incn  (12  to  20  /*).  The  nerve-cells 
are  soft,  have  no  true  cell-membrane  and  are  fibrillated,  the  fibrillation  ex- 
tending to  the  poles.  The  transverse  striae  in  the  axis-cylinder  treated  with 
silver  nitrate,  noted  by  Fromann  and  confirmed  by  Grandry  and  others, 


STRUCTURE  OF  THE  NERVE-CENTRES. 


519 


have  been  observed  by  Grandry  in,  the  substance  of  the  nerve-cells.  While 
this  fact,  perhaps,  shows  that  the  substance  contained  in  the  cells  and  their 
prolongations  is  like  the  substance  of  the  axis-cylinder,  it  is  possible  that  the 


FIG.  186. — Transverse  section  of  the  gray  substance  of  anterior  cornua  of  the  spinal  cord  of  the  ox, 
treated  with  silver  nitrate  (Grandry). 

markings  may  be  entirely  artificial,  and  that  they  do  not  indicate  the  exist- 
ence of  two  distinct  substances. 

Tracing  the  nerve-fibres  toward  their  origin,  they  are  seen  to  lose  their 
investing  membrane  as  they  pass  into  the  white  portion  of  the  centres,  being 
here  composed  only  of  medullary  substance  surrounding  the  axis-cylinders. 
They  then  penetrate  the  gray  substance,  in  the  form  of  axis-cylinders,  losing 
the  medullary  substance.  In  the  gray  substance,  it  is  impossible  to  make 
out  all  their  relations  distinctly,  and  it  can  not  be  stated,  as  a  matter  of 
positive  demonstration,  that  all  of  them  are  connected  with  the  poles  of 
nerve-cells.  Still,  it  has  been  shown  in  the  gray  matter  of  the  spinal  cord, 
that  many  of  the  fibres  are  actual  prolongations  of  the  cells,  others  probably 
passing  upward  to  be  connected  with  cells  in  the  encephalon. 

Tracing  the  prolongations  from  the  cells,  it  is  found  that  at  least  one  of 
the  poles  in  the  gray  substance  gives  origin  to  nerve-fibres,  but  that  these 
fibres  do  not  branch  after  they  pass  into  the  white  substance.  Other  poles 
connect  the  nerve-cells  with  each  other  by  commissural  fibres  of  greater  or 
less  length ;  and  it  is  probable  that  the  cells  are  thus  arranged  in  separate 
and  distinct  groups,  possibly  connected  with  sets  of  muscles. 

Accessory  Anatomical  Elements  of  the  Nerve-centres. — In  addition  to  the 
cells  of  the  gray  matter  and  the  axis-cylinder  of  the  nerves,  which  are  prob- 


520  NERVOUS  SYSTEM. 

ably  the  only  structures  directly  concerned  in  innervation,  are  the  following 
accessory  anatomical  elements :  1,  outer  coverings  surrounding  some  of  the 
cells;  2,  intercellular,  granular  matter;  3,  peculiar  corpuscles,  called  myelo- 
cytes ;  4,  connective-tissue  elements  ;  5,  blood-vessels  and  lymphatics. 

Certain  of  the  cells  in  the  spinal  ganglia  and  in  the  ganglia  of  the  sym- 
pathetic system  are  surrounded  with  a  covering,  removed  a  certain  distance 
from  the  cell  itself  so  as  to  be  nearly  twice  the  diameter  of  the  cell,  which  is 
continuous  with  the  sheath  of  the  dark-bordered  fibres.  This  membrane  is 
always  nucleated  and  is  composed  of  a  layer  of  very  delicate  endothelium. 
Its  physiological  significance  is  not  apparent. 

In  the  gray  matter  of  the  nerve-centres,  there  is  a  finely  granular  sub- 
stance between  the  cells,  which  closely  resembles  the  granular  contents  of 
the  cells  themselves.  In  addition  to  this  granular  matter,  Robin  has  de- 
scribed peculiar  anatomical  elements  which  he  called  myelocytes.  These  are 
found  in  the  cerebro-spinal  centres,  forming  a  layer  near  the  boundary  of 
the  white  substance,  and  they  are  particularly  abundant  in  the  cerebellum. 
They  exist  in  the  form  of  free  nuclei  and  nucleated  cells,  the  free  nuclei  be- 
ing by  far  the  more  abundant.  The  nuclei  are  rounded  or  ovoid,  with 
strongly  accentuated  borders,  are  unaffected  by  acetic  acid,  finely  granular 
and  generally  without  nucleoli.  The  cells  are  rounded  or  slightly  poly- 
hedric,  pale,  clear  or  very  slightly  granular,  and  contain  bodies  similar  to  the 
free  nuclei.  The  free  nuclei  are  -jnsVfr  t°  j-oVo"  °^  an  illcn  (5  to  6  /A)  in  diam- 
eter, and  the  cells  measure  ^-^  to  ^W'  an^  sometimes  y-yVfr  of  an  inch  (10, 
12  and  15  /u).  These  elements  also  exist  in  the  second  layer  of  the  retina. 

In  the  cerebro-spinal  centres  there  is  a  delicate  stroma  of  connective  tis- 
sue, chiefly  in  the  form  of  stellate,  branching  cells,  which  serves  in  a  meas- 
ure, to  support  the  nervous  elements.  This  tissue,  which  is  peculiar  to  the 
white  substance  of  the  encephalon  and  spinal  cord,  is  called  neuroglia. 

The  blood-vessels  of  the  nerve-centres  form  a  capillary  net- work  with 
large  meshes.  The  gray  substance  is  richer  in  capillaries  than  the  white. 

A  peculiarity  of  the  vascular  arrangement  in  the  cerebro-spinal  centres 
has  already  been  described  in  connection  with  the  anatomy  of  the  lymphatic 
system.  The  blood-vessels  here  are  surrounded  by  what  have  been  called 
perivascular  canals,  first  described  by  Robin  and  afterward  shown  by  His 
and  Robin  to  be  radicles  of  the  lymphatic  system. 

Composition  of  the  Nervous  Substance. — The  chemistry  of  the  nervous 
substance,  as  far  as  it  is  understood,  throws  little  light  on  its  physiology. 
Certain  albuminoids  have  been  extracted  which  do  not  possess  more  than  a 
purely  chemical  interest.  The  substance  called  cerebrine  is  composed  of 
carbon,  hydrogen,  oxygen  and  nitrogen,  without  either  sulphur  or  phosphorus. 
Protagon  is  a  nitrogenized  substance  containing  phosphorus  (Liebreich,  18G5). 
By  some  chemists  protagon  is  thought  to  be  a  mixture  of  cerebrine  and 
lecethine.  Lecethine  is  regarded  as  a  nitrogenous  fat.  Other  substances 
which  have  been  extracted — xanthine,  hypoxanthine,  inosite,  creatine  and 
various  volatile  fatty  acids — have  no  special  physiological  interest  connected 
with  the  nervous  system  and  are  found  in  many  other  situations.  Cholester- 


DEGENERATION  AND  REGENERATION  OF  NERVES.    521 

ine,  which  always  exists  in  considerable  quantity  in  the  nervous  tissue,  has 
been  considered  in  connection  with  the  physiology  of  excretion.  The  ordi- 
nary fats  are  in  combination  with  other  fats  or  with  peculiar  acid  substances. 
The  reaction  of  nerve-tissue  is  either  neutral  or  faintly  alkaline  under  normal 
conditions,  soon  becoming  acid  after  death. 

Degeneration  and  Regeneration  of  Nerves. — The  degenerations  observed 
in  nerves  separated  from  the  centres  to  which  they  are  normally  attached, 
first  studied  by  Waller,  in  1850,  are  now  used  in  following  out  certain 
nervous  connections  too  intricate  to  be  revealed  by  ordinary  dissection. 
This  is  known  as  the  Wallerian  method.  If  an  ordinary  mixed  nerve  be 
divided  in  its  course,  both  the  motor  and  sensory  fibres  of  the  peripheral 
portion  undergo  fatty  degeneration  and  lose  their  excitability.  As  regards 
the  spinal  nerves,  degeneration  occurs  in  the  motor  fibres  only,  when  the 
anterior  spinal  root  has  been  divided,  and  the  nerve  has  degenerated  fibres 
(motor)  mixed  with  the  sensory  fibres,  which  latter  retain  their  anatomical 
and  physiological  characters.  The  motor  fibres  of  the  spinal  nerves  are 
degenerated  when  separated  from  their  connections  with  the  anterior  cornua 
of  gray  matter  of  the  cord.  If  the  posterior  roots  of  the  spinal  nerves  be 
divided  beyond  the  ganglia,  the  peripheral  sensory  fibres  degenerate ;  but  if 
the  ganglia  be  exsected,  the  central  as  well  as  the  peripheral  portions  degen- 
erate. These  experiments  show  the  existence  of  centres  which  preside  over 
the  nutrition  of  the  nerves.  The  centres  for  the  motor  filaments  of  the 
spinal  nerves  are  in  the  anterior  cornua  of  gray  matter  of  the  cord.  The 
centres  for  the  sensory  fibres  are  the  ganglia  of  the  posterior  roots.  The 
centres  for  the  sensory  cranial  nerves  are  the  ganglia  on  their  roots ;  and 
the  centres  for  the  motor  cranial  nerves  are  probably  the  gray  nuclei  of 
origin  of  these  nerves.  The  Wallerian  method  has  been  found  useful  in 
studying  the  paths  of  conduction  in  the  encephalon  and  spinal  cord,  as  will 
be  seen  in  connection  with  the  physiology  of  these  parts. 

The  excitability  of  the  motor  nerves  disappears  in  about  four  days  after 
their  section.  Of  course,  in  experiments  upon  this  point,  it  is  necessary  to 
excise  a  portion  of  the  nerve  to  prevent  reunion  of  the  divided  extremities ; 
but  when  this  is  done,  after  about  the  fourth  day,  stimulation  of  the  nerve 
will  produce  no  contraction  in  the  muscles,  although  the  latter  retain  their 
contractility.  This  loss  of  excitability  is  gradual,  and  it  continues,  whether 
the  nerve  be  exposed  and  stimulated  from  time  to  time  or  be  left  to  itself, 
progressing  from  the  centres  to  the  periphery.  In  the  researches  of  Longet 
upon  this  subject,  it  was  found  that  the  lower  portion  of  the  peduncles  of  the 
brain  lost  their  excitability  first,  then  the  anterior  columns  of  the  cord,  then 
the  motor  roots  of  the  nerves,  and  last  of  all,  the  branches  of  the  nerves  near 
their  terminations  in  the  muscles. 

The  sensibility  of  the  sensory  nerves  disappears  from  the  periphery  to 
the  centres,  as  is  shown  in  dying  animals  and  in  experiments  with  anaesthet- 
ics. The  sensibility  is  lost,  first  in  the  terminal  branches  of  the  nerves,  next 
in  the  trunks  and  in  the  posterior  roots  of  the  spinal  nerves,  and  so  on  to  the 
centres 


522  NERVOUS  SYSTEM. 

Nerves  that  have  been  divided  may  be  regenerated  if  anatomical  union  of 
the  divided  ends  can  be  obtained ;  and  this  sometimes  takes  place  several 
months  after  injury  to  the  nerves,  the  regeneration  occurring  by  the  forma- 
tion of  new  fibres.  Mixed  nerves  are  regenerated  in  this  way,  and  conduction 
is  finally  restored  in  both  directions.  The  sensory  conduction  appears  first, 
and  next,  the  conduction  of  motor  impulses.  Tha  restoration  of  the  physio- 
logical properties  of  the  nerves  occupies  several  weeks.  The  central  end  of  a 
mixed  nerve  has  been  made  to  unite  with  the  peripheral  end  of  another 
mixed  nerve,  but  it  is  doubtful  whether  a  divided  end  of  a  motor  nerve  is 
ever  united  to  the  divided  end  of  a  sensory  nerve.  Experiments  upon  this 
latter  point  are  not  entirely  satisfactory. 

MOTOR  AND  SENSORY  NERVES. 

Aside  from  the  nerves  possessing  special  properties,  such  as  the  nerves  of 
sight,  hearing,  smell,  taste  and,  according  to  some  physiologists,  nerves  of 
touch,  temperature,  sense  of  weight  and  muscular  sense,  the  cerebro-spinal 
nerves  present  two  kinds  of  fibres.  These  are  (1)  centrifugal,  or  motor 
fibres,  and  (2)  centripetal,  or  sensory  fibres.  The  motor  fibres  conduct  im- 
pulses from  the  centres  to  the  muscles  and  excite  muscular  action.  The  sen- 
sory fibres  conduct  impressions  from  the  periphery  to  the  centres,  which  are 
appreciated  either  as  ordinary  sensation  or  as  pain.  As  regards  the  nerves 
arising  by  two  roots  from  the  spinal  cord,  the  exact  anatomical  and  physio- 
logical divisions  into  motor  and  sensory  were  first  made  by  Magendie,  in 
1822.  As  will  be  seen  farther  on,  this  division  is  distinct  for  the  cranial 
nerves,  so  that  it  is  universal  in  the  cerebro-spinal  system.  The  importance 
of  the  discovery  of  the  distinct  properties  of  the  two  roots  of  the  spinal 
nerves  is  such  that  it  merits  at  least  a  brief  historical  account,  particularly 
as  this  discovery  is  quite  generally  attributed  to  Charles-  Bell. 

The  first  definite  statement  with  regard  to  distinct  properties  of  the  two 
roots  of  the  spinal  nerves  was  made  by  Alexander  Walker,  in  1809,  who  said 
that  the  posterior  roots  were  for  motion  and  the  anterior  roots  for  sensation, 
the  exact  reverse  of  the  truth. 

In  a  pamphlet  privately  printed  by  Charles  Bell,  probably  in  1811,  and 
"  submitted  for  the  observations  of  his  friends,"  the  view  was  advanced  that 
the  anterior  roots  are  both  motor  and  sensory  and  that  the  posterior  preside 
over  "  the  secret  operations  of  the  bodily  frame,  or  the  connections  which 
unite  the  parts  of  the  body  into  a  system." 

In  1822,  Magendie,  as  the  result  of  experiments  upon  the  exposed  roots 
in  living  dogs,  stated  that  "  he  was  able  at  that  time  to  advance  as  positive, 
that  the  anterior  and  the  posterior  roots  of  the  nerves  which  arise  from  the 
spinal  cord  have  different  functions,  that  the  posterior  seem  more  particu- 
larly destined  to  sensibility,  while  the  anterior  seem  more  specially  con- 
nected with  motion." 

It  is  now  universally  admitted  that  the  mixed  nerves  arising  from  the 
spinal  cord  derive  their  motor  properties  from  the  anterior  roots  and  their 
sensory  properties  from  the  posterior  roots. 


MOTOR  AND  SENSORY  NERVES.  523 

The  anterior  roots  possess  a  certain  degree  of  sensibility  in  addition  to 
their  motor  properties  (Magendie).  This  sensibilitity,  which  is  slight,  is  de- 
rived from  fibres  from  the  posterior  roots,  which  turn  back  to  go  to  the  an- 
terior roots.  This  fact  has  been  positively  demonstrated  by  the  Wallerian 
method.  When  a  posterior  root  is  divided  beyond  the  ganglion,  the  sensi- 
bility of  the  corresponding  anterior  root  is  lost,  and  degenerated  fibres  appear, 
after  a  few  days,  in  the  anterior  roots  (Schiff).  This  sensibility  of  the  an- 
terior roots  is  called  recurrent  sensibility.  Similar  relations  are  observed 
between  certain  of  the  motor  and  sensory  cranial  nerves. 

Mode  of  Action  of  the  Motor  Nerves. — As  regards  the  normal  action  of 
the  motor  nerves,  a  force,  the  nature  of  which  is  unknown,  genereted  in  the 
centres,  is  conducted  from  the  centres  to  the  peripheral  distribution  of  the 
nerves  in  the  muscles,  and  is  here  manifested  by  contraction.  Their  mode 
of  action,  therefore,  is  centrifugal.  When  these  motor  filaments  are  divided, 
the  connection  between  the  parts  animated  by  them  and  the  centre  is  inter- 
rupted, and  motion  in  these  parts,  in  obedience  to  the  natural  stimulus,  be- 
comes impossible.  While,  however,  it  is  not  always  possible  to  induce  gen- 
eration of  nerve-force  in  the  centres  by  the  direct  application  of  any  agent  to 
them,  this  force  may  be  imitated  by  stimulation  applied  to  the  nerve  itself. 
A  nerve  that  will  thus  respond  to  direct  stimulation  is  said  to  be  excitable. 

If  a  motor  nerve  be  divided,  electric,  mechanical,  or  other  stimulus  ap- 
plied to  the  extremity  connected  with  the  centres  produces  no  effect ;  but  the 
same  stimulus  applied  to  the  extremity  connected  with  the  muscles  is  fol- 
lowed by  contraction.  The  phenomena  indicating  that  a  nerve  retains  its 
physiological  properties  are  always  manifested  at  its  peripheral  distribution, 
and  these  do  not  essentially  vary  when  the  nerve  is  stimulated  at  different 
points  in  its  course.  For  example,  stimulation  of  the  anterior  roots  near  the 
cord  produces  contraction  in  those  muscles  to  which  the  fibres  of  these  roots 
are  distributed ;  but  the  same  effect  follows  stimulation  of  the  nerve  going  to 
these  muscles,  in  any  part  of  its  course. 

As  far  as  their  physiological  action  is  concerned,  the  individual  nerve- 
fibres  are  entirely  independent ;  and  the  relations  which  they  bear  to  each 
other  in  nervous  fasciculi  and  in  the  so-called  anastomoses  of  nerves  involve 
simple  contiguity.  Comparing  the  nerve-force  to  galvanism,  each  individual 
fibre  seems  completely  insulated  ;  and  a  stimulus  conducted  by  it  to  muscles 
never  extends  to  the  adjacent  fibres.  That  it  is  the  axis-cylinder  which 
conducts  and  the  medullary  tube  which  insulates,  it  is  impossible  to  say  with 
positiveness  ;  but  it  is  more  than  probable  that  the  axis-cylinder  is  the  only 
conducting  element. 

The  generation  of  a  motor  impulse  may  be  induced  by  an  impression 
made  upon  sensory  nerves  and  conveyed  by  them  to  the  centres.  If,  for 
example,  a  certain  portion  of  the  central  nervous  system,  as  the  spinal  cord, 
be  isolated,  leaving  its  connections  with  the  motor  and  sensory  nerves 
intact,  these  phenomena  may  be  readily  observed.  An  impression  made 
upon  the  sensory  nerves  will  be  conveyed  to  the  gray  matter  of  the  cord 
and  will  induce  the  generation  of  a  motor  impulse  by  the  cells  of  this  part, 


524  NERVOUS  SYSTEM. 

which  will  be  conducted  to  the  muscles  and  give  rise  to  contraction.  As  the 
impulse,  in  such  observations,  seems  to  be  reflected  from  the  cord,  through 
the  motor  nerves,  to  the  muscles,  this  action  has  been  called  reflex.  These 
phenomena  constitute  an  important  division  of  the  physiology  of  the  nervous 
system  and  will  be  fully  considered  by  themselves. 

Associated  Movements. — It  is  well  known  that  the  action  of  certain  mus- 
cles is  with  difficulty  isolated  by  an  effort  of  the  will.  This  applies  to  sets  of 
muscles  upon  one  side  of  the  body  and  to  corresponding  muscles  upon  the 
two  sides.  For  example,  it  is  almost  impossible,  without  great  practice,  to 
move  some  of  the  fingers,  at  the  same  time  restraining  the  movements  of  the 
others ;  and  the  action  of  certain  sets  of  muscles  of  the  extremities  is  always 
simultaneous.  The  toes,  which  are  but  little  used  as  the  foot  is  confined  in  the 
ordinary  dress,  are  capable  of  very  little  independent  action.  It  is  difficult  to 
move  one  eye  without  the  other,  or  to  make  rapid  rotary  movements  of  one 
hand  while  an  entirely  different  order  of  movements  is  executed  by  the  other ; 
and  instances  of  this  kind  might  be  multiplied.  In  studying  these  associ- 
ated movements,  the  question  arises  as  to  how  far  they  are  due  to  the  ana- 
tomical relations  of  the  nerves  to  the  centres  and  their  connections  with 
muscles,  and  how  far  they  depend  upon  habit  and  exercise.  There  may  be 
certain  sets  of  nerve-cells  connected  with  each  other  by  commissural  fibres 
and  giving  origin  to  motor  nerves  distributed  to  sets  of  muscles,  an  anatomi- 
cal arrangement  that  might  render  a  separate  action  of  these  cells  impossi- 
ble. The  anatomy  of  the  nerve-centres  and  their  connection  with  fibres  are 
so  difficult  of  investigation,  that  demonstrative  proof  of  the  existence  of 
such  systems  is  impracticable ;  but  this  would  afford  a  ready  explanation  of 
the  fact  that  it  is  impossible,  as  a  rule,  by  an  effort  t>f  the  will,  to  cause  only  a 
portion  of  a  single  muscle  to  contract ;  yet  some  of  the  larger  muscles  receive 
a  considerable  number  of  motor  nerve-fibres  which  are  probably  connected 
with  gray  matter  composed  of  many  anastomosing  nerve-cells. 

Many  of  the  associated  movements  may  be  influenced  to  a  remarkable 
degree  by  education,  of  which  no  better  example  can  be  found  than  in  the 
case  of  skillful  performers  upon  certain  musical  instruments,  such  as  the 
piano,  harp,  violin  and  other  stringed  instruments.  In  the  technical  study 
of  such  instruments,  not  only  does  one  hand  become  almost  independent  of 
the  other,  but  very  complex  associated  movements  may  be  acquired.  An 
accomplished  pianist  or  violinist  executes  the  different  scales  automatically 
by  a  single  effort  of  the  will,  and  pianists  frequently  execute  at  the  same 
time  scales  with  both  hands,  the  action  being  entirely  opposed  to  the  natural 
association  of  movements. 

Looking  at  the  associated  movements  in  their  relations  to  the  mode  of 
action  of  the  motor  nerves,  it  seems  probable  that  as  a  rule,  the  anatomical 
relations  of  the  nerves  are  such  that  a  motor  impulse  or  an  effort  of  the 
will  can  not  be  conducted  to  a  portion  only  of  a  muscle,  but  must  act  upon 
the  whole  muscle,  and  the  same  is  true,  probably,  of  certain  restricted 
sets  of  muscles;  but  the  association  of  movements  of  corresponding  mus- 
cles upon  the  two  sides  of  the  body,  with  the  exception,  perhaps,  of  the  mus- 


MOTOR  AND  SENSORY  NERVES.  525 

cles  of  the  eyes,  is  due  mainly  to  habit  and  may  be  greatly  modified  by  edu- 
cation. 

Mode  of  Action  of  the  Sensory  Nerves. — The  sensory  nerve-fibres,  like 
the  fibres  of  the  motor  nerves,  are  entirely  independent  of  each  other  in 
their  action;  and  in  the  so-called  anastomoses  that  take  place  between 
sensory  nerves,  the  fibres  assume  no  new  relations,  except  as  regards  con- 
tiguity. 

As  motor  fibres  convey  to  their  peripheral  distribution  the  impulse  pro- 
duced by  a  stimulus  applied  in  any  portion  of  their  course,  so  an  impression 
made  upon  a  sensory  nerve  is  always  referred  to  the  periphery.  A  familiar 
example  of  this  is  afforded  by  the  very  common  accident  of  contusion  of  the 
ulnar  nerve  as  it  passes  between  the  olecranon  and  the  condyle  of  the  hu- 
merus.  This  is  attended  with  painful  tingling  of  the  ring  and  little  finger  and 
other  parts  to  which  the  filaments  of  this  nerve  are  distributed,  without, 
necessarily,  any  pain  at  the  point  of  injury.  More  striking  examples  are 
afforded  in  neuralgic  affections  dependent  upon  disease  of  or  pressure  upon 
the  trunk  of  a  sensory  nerve.  In  such  cases,  excision  of  the  nerve  is  often 
practised,  but  no  permanent  relief  follows  unless  the  section  be  made  be- 
tween the  affected  portion  of  the  nerve  and  the  nerve-centres ;  and  the  pain 
is  always  referred  to  the  termination  of  the  nerve,  even  after  it  has  been 
divided  between  the  seat  of  the  disease  and  the  periphery,  leaving  the  parts 
supplied  by  the  nerve  insensible  to  direct  irritation.  In  cases  of  disease  it 
is  not  unusual  to  note  great  pain  in  parts  of  the  skin  that  are  insensible  to 
direct  impressions.  The  explanation  of  this  is  that  the  nerves  are  paralyzed 
near  their  terminal  distribution,  so  that  an  impression  made  upon  the  skin 
can  not  be  conveyed  to  the  sensorium ;  but  the  trunks  of  the  nerves  still 
retain  their  conducting  power  and  are  the  seat  of  diseased  action,  producing 
pain  which  is  referred  by  the  patient  to  the  periphery.  In  the  very  common 
operation  of  restoring  the  nose  by  transplanting  skin  from  the  forehead, 
after  the  operation  has  been  completed,  the  skin  having  been  entirely  sepa- 
rated, and  united  in  its  new  relations,  the  patient  feels  that  the  forehead  is 
touched  when  the  finger  is  applied  to  the  artificial  nose.  After  a  time,  how- 
ever, the  sensorium  becomes  accustomed  to  the  new  arrangement  of  the 
parts,  and  this  deceptive  feeling  disappears. 

There  are  certain  curious  nervous  phenomena,  that  are  not  without  physi- 
ological interest,  presented  in  persons  who  have  suffered  amputations.  It 
has  long  been  observed  that  after  loss  of  a  limb,  the  sensation  of  the  part  re- 
mains ;  and  pain  is  frequently  experienced,  which  is  referred  to  the  ampu- 
tated member.  Thus  a  patient  will  feel  distinctly  the  fingers  or  toes  after 
an  arm  or  a  leg  has  been  removed,  and  irritation  of  the  ends  of  the  nerves  at 
the  stump  produces  sensations  referred  to  the  missing  member.  After  a 
time  the  sense  of  presence  of  the  lost  limb  becomes  blunted,  and  it  may  in 
some  cases  entirely  disappear.  This  may  take  place  a  few  months  after  the 
amputation  or  the  sensations  may  remain  for  years.  Examples  have  been 
reported  by  M tiller,  in  which  the  sense  was  undiminished  thirteen,  and  in 
one  case,  twenty  years  after  amputation.  In  a  certain  number  of  cases, 

35 


526  NERVOUS  SYSTEM. 

however,  the  sense  of  the  intermediate  part  is  lost,  the  feeling  in  the  hand  or 
foot,  as  the  case  may  be,  remaining  as  distinct  as  ever,  the  impression  being 
that  the  limb  is  gradually  becoming  shorter.  It  was  noted  by  Gueniot,  that 
the  sense  of  the  limb  becoming  shorter  exists  in  about  half  of  the  cases  of  am- 
putation in  which  cicatrization  goes  on  regularly ;  and  in  these  cases,  the  pa- 
tient finally  experiences  a  feeling  as  though  the  hand  or  foot  were  in  direct 
contact  with  the  stump. 

Physiological  Differences  between  Motor  and  Sensory  Nerve-Fibres. — It 
has  not  been  shown  that  there  is  any  essential  anatomical  difference  between 
the  conducting  elements  of  motor  and  sensory  nerve-fibres ;  but  the  physio- 
logical differences  are  sufficiently  distinct,  as  has  already  been  seen.  Under 
normal  conditions,  motor  fibres  conduct  motor  impulses  in  but  one  direction, 
and  these  fibres  are  insensible.  Sensory  fibres  conduct  impressions  always  in 
the  opposite  direction,  and  they  do  not  conduct  motor  impulses.  Certain 
experiments,  however,  have  led  some  physiologists  to  adopt  the  view  that  the 
conducting  properties  of  the  nerves  themselves,  both  motor  and  sensory,  are 
identical,  and  that  the  direction  of  conduction  depends  upon  the  kind  of 
centres  with  which  nerves  are  connected.  These  experiments  are  the  fol- 
lowing : 

It  is  said  that  the  peripheral  end  of  a  divided  motor  nerve,  the  sublin- 
gual,  can  be  made  to  unite  with  the  central  end  of  a  sensory  nerve,  the 
lingual  branch  of  the  fifth ;  and  that  after  a  time  motor  impulses  are  con- 
ducted by  the  sensory  fibres  and  sensory  impressions,  by  the  motor  fibres.  A 
careful  study  of  these  experiments,  however,  shows  that  the  results  are  far 
from  satisfactory. 

Another  experiment  is  grafting  the  end  of  the  tail  of  a  rat  into  the 
skin  of  the  back  (Bert).  When  the  union  has  become  complete,  the  tail  is 
divided  at  its  root  and  the  sensory  conduction,  after  five  or  six  months,  takes 
place  in  a  direction  opposite  to  the  normal.  While  this  experiment  may  be 
regarded  as  showing  that  sensory  fibres  may  be  made  to  assume  such  rela- 
tions with  other  sensory  fibres  as  to  change,  after  a  time,  the  direction  of 
conduction,  it  has  no  absolutely  direct  bearing  upon  the  question  of  the 
physiological  identity  of  motor  or  sensory  fibres. 

The  experiments  just  mentioned  seldom  succeed,  and  the  results  of 
union  of  motor  with  sensory  nerves  are  quite  indefinite;  but  the  divided 
ends  of  mixed  nerves  readily  reunite,  and  it  is  not  difficult  to  establish  a 
union  between  the  central  and  peripheral  ends  of  two  different  mixed 
nerves.  It  is  hardly  reasonable  to  assume  that  in  these  instances,  each  and 
every  divided  end  of  a  motor  fibre  selects  another  motor  fibre  with  which  it 
unites,  and  that  the  same  occurs  with  sensory  fibres ;  but  it  would  seem  that 
in  a  divided  mixed  nerve,  a  certain  number  of  fibres  of  each  kind  must 
unite  with  certain  fibres  that  have  similar  physiological  properties.  Com- 
plete physiological  regeneration  of  divided  nerves  is  always  slow,  and  fre- 
quently the  regeneration  never  becomes  complete.  The  fact,  also,  that 
curare  destroys  the  physiological  properties  of  motor  nerves,  leaving  the  sen- 
sory nerves  intact,  has  a  very  important  bearing  upon  the  question  under 


NERVOUS  EXCITABILITY.  527 

consideration ;  and  anaesthetics  temporarily  abolish  the  physiological  proper- 
ties of  the  sensory  nerves  without  necessarily  affecting  the  motor  nerves. 

Until  the  results  of  experiments  upon  the  artificial  union  of  motor 
and  sensory  nerves  become  much  more  positive  than  they  now  are,  it  must 
be  assumed  that  these  two  kinds  of  nerve-fibres  have  distinct  physiological 
properties,  both  as  regards  the  kind  of  impulse  or  impression  produced  by 
excitation  or  stimulation  and  the  direction  of  conduction.  It  is  possible, 
however,  that  these  properties  may  be  modified  by  altered  relations  for  a 
long  time  with  the  trophic  centres  that  influence  the  nutrition  of  the  differ- 
ent kinds  of  nerve-fibres. 

Nervous  Excitability. — Immediately  or  soon  after  death,  when  the  excit- 
ability of  the  nerves  is  at  its  maximum,  they  may  be  stimulated  by  mechani- 
cal, chemical  or  galvanic  irritation,  all  of  these  agents  producing  contraction 
of  the  muscles  to  which  the  motor  filaments  are  distributed.  Mechanical  irri- 
tation, simply  pinching  a  portion  of  the  nerve,  for  example,  produces  a  single 
muscular  contraction ;  but  if  the  injury  to  the  nerve  be  such  as  to  disorgan- 
ize its  fibres,  that  portion  of  the  nerve  will  no  longer  conduct  an  impulse. 
Among  the  irritants  of  this  kind,  are  extremes  of  heat  and  cold.  If  an  ex- 
posed nerve  be  cauterized,  a  vigorous  muscular  contraction  follows.  The 
same  effect,  though  less  marked,  may  be  produced  by  the  sudden  application 
of  intense  cold.  Among  chemical  reagents,  there  are  some  which  excite  the 
nerves  and  others  which  produce  no  effect ;  but  these  are  not  important  from 
a  physiological  point  of  view,  except  common  salt,  which  is  sometimes  used 
when  it  is  desired  to  produce  tetanic  action.  Mechanical  stimulation  and 
the  action  of  certain  chemicals  are  capable  of  exciting  the  nerves ;  but  when 
their  action  goes  so  far  as  to  disorganize  the  fibres,  the  conducting  power  of 
these  fibres  is  lost.  While,  however,  irritation  of  the  nerve  above  the  point 
of  such  injury  has  no  effect,  stimulation  between  this  point  and  the  muscles 
is  still  followed  by  contraction. 

The  most  convenient  method  of  exciting  the  nerves  in  physiological  ex- 
periments is  by  means  of  electricity.  This  may  be  employed  without  dis- 
organizing the  nerve-tissue,  and  it  consequently  admits  of  extended  and 
repeated  application.  The  action  of  electricity,  however,  with  the  methods 
of  preparing  the  nerves  and  muscles  for  experimentation,  will  be  considered 
under  a  separate  head. 

Rapidity  of  Nervous  Conduction. — The  first  accurate  estimates  of  the 
rapidity  of  nervous  conduction  were  made  by  Helmholtz,  in  1850,  and  were 
applied  to  the  motor  nerves  of  the  frog.  These  estimates  were  arrived  at  by 
an  application  of  the  graphic  method,  which  was  afterward  considerably  ex- 
tended and  improved  by  Marey.  The  process  employed  by  Marey,  which  is 
essentially  the  same  as  that  used  in  all  recent  investigations,  is  the  following : 

To  mark  small  fractions  of  a  second,  a  tuning-fork  vibrating  at  a  known 

"rate  (five  hundred  times  in  a  second)  is  so  arranged  that  a  point  connected 

with  one  of  its  arms  is  made  to  play  against  a  strip  of  blackened  paper.     As 

the  paper  remains  stationary,  the  point  makes  but  a  single  mark ;  but  when 

the  paper  moves,  as  the  point  vibrates  a  line  is  produced  with  regular  curves, 


528  NERVOUS  SYSTEM. 

each  curve  representing  -5-^-5-  of  a  second.  If  a  lever  be  attached  to  a  muscle 
and  be  so  arranged  as  to  indicate  upon  the  paper,  moving  at  the  same  rate, 
the  instant  when  contraction  takes  place,  it  is  evident  that  the  interval  be- 
tween two  contractions  produced  by  stimulating  the  nerve  at  different  points 
in  its  course  may  be  accurately  measured ;  and  if  the  length  of  the  nerve  be- 
tween the  two  points  of  stimulation  be  known,  the  difference  in  time  will 
represent  the  rate  of  nervous  conduction.  In  experiments  upon  frogs,  the 
leg  is  prepared  by  cutting  away  the  muscles  and  bone  of  the  thigh,  leaving 
the  nerve  attached.  The  lever  is  then  applied  to  the  muscles  of  the  leg,  and 
the  nerve  is  stimulated  successively  at  two  points,  the  distance  between  them 
being  measured. 

Employing  the  myograph  of  Marey,  Baxt,  in  the  laboratory  of  Helmholtz, 
succeeded  in  measuring  the  rate  of  nervous  conduction  in  the  human  sub- 
ject. In  these  experiments,  the  swelling  of  the  muscle  during  contraction 
was  limited  by  enclosing  the  arm  in  a  plaster-mould,  and  the  contraction 
was  observed  through  a  small  opening.  By  then  exciting  the  contraction  by 
stimulating  the  radial  nerve  successively  at  different  distances  from  the  mus- 
cle, the  estimate  was  made.  The  rate  in  the  human  subject  was  thus  esti- 
mated at  one  hundred  and  eleven  feet  (33*9  metres)  per  second. 

The  method  used  in  determining  the  rate  of  conduction  in  motor  nerves 
— an  estimation  of  the  difference  in  time  of  the  passage  of  a  stimulus  applied 
to  a  nerve  at  two  points  situated  at  a  known  distance  from  each  other — has 
been  applied  to  the  conduction  of  sensations.  Hirsch  made  the  first  attempt 
to  solve  this  question,  in  1861.  He  employed  the  delicate  chronometric  in- 
struments used  in  astronomy  and  noted  the  difference  in  time  between  the 
appreciation  of  an  impression  made  upon  a  part  of  the  body  far  removed 
from  the  brain,  as  the  toe,  and  an  impression  made  upon  the  cheek.  This 
process  admitted  of  a  rough  estimate  of  about  one  hundred  and  eleven  feet 
(33'9  metres)  per  second  as  the  rate  of  sensory  conduction. 

It  is  not  necessary  to  describe  fully  the  complicated  apparatus  by  means 
of  which  the  most  recent  estimates  of  the  rate  of  nervous  conduction  have 
been  made.  The  general  results  of  the  observations  of  Helmholtz,  Marey, 
Baxt,  Schleske  and  of  many  others  nearly  correspond  with  the  estimates  just 
given,  and  they  show  that  the  rate  is  about  the  same  for  motor  and  sensory 
nerves.  This  rate  is  modified  by  various  conditions.  It  is  diminished  in 
the  anelectrotonic  and  increased  in  the  catelectrotonic  condition  of  nerves. 
In  the  frog  Helmholtz  observed  that  the  rate  was  very  much  reduced  by 
cold,  at  32°  Fahr.  (0°  0.)  being  not  more  than  one-tenth  as  rapid  as  at  60° 
or  70°  Fahr.  (15-5°  or  21-11°  0.). 

The  rate  of  transmission  of  impulses  and  impressions  through  the  spinal 
cord  has  been  investigated  by  calculating  the  distances  between  nerves  as 
they  are  given  off  at  different  points  and  measuring  the  time  required  for 
the  appreciation  of  certain  impressions  and  the  beginning  of  certain  move- 
ments (Burkhardt).  While  these  observations  are  not  absolutely  exact,  their 
general  results  are  of  considerable  physiological  interest.  According  to  Burk- 
hardt, the  rate  of  motor  conduction  in  the  cord  is  about  one-third  of  the  nor- 


ACTION  OF  ELECTRICITY  UPON  THE  NERVES.  529 

mal  rate  in  the  motor  nerves.  As  compared  with  the  sensory  nerves,  the 
cord  conducts  tactile  impressions  a  little  faster  and  painful  impressions  less 
than  one  half  as  fast. 

Attempts  have  been  made  to  estimate  the  duration  of  acts  involving  the 
central  nervous  system,  such  as  the  reflex  phenomena  of  the  spinal  cord  or 
the  operations  of  the  cerebral  hemispheres.  These  have  been  partially  suc- 
cessful, or,  at  least,  they  have  shown  that  the  reflex  and  the  cerebral  acts 
require  a  distinctly  appreciable  period  of  time.  This  in  itself  is  an  impor- 
tant fact ;  although  the  duration  of  these  acts  has  not  been  measured  with 
absolute  accuracy.  As  the  general  result  of  experiments  upon  these  points, 
it  has  been  found  that  the  reflex  action  of  the  spinal  cord  occupies  more  than 
twelve  times  the  period  required  for  the  transmission  of  stimulus  or  impres- 
sions through  the  nerves.  Bonders  found,  in  experiments  upon  his  own 
person,  that  an  act  of  volition  required  -fa  of  a  second,  and  one  of  simple 
distinction  or  recognition  of  an  impression,  ^  of  a  second.  These  esti- 
mates, however,  are  merely  approximate,  and  until  they  attain  greater  cer- 
tainty, it  is  unnecessary  to  describe  in  detail  the  apparatus  employed. 

Personal  Equation. — In  recording  astronomical  observations,  it  has  been 
found  that  a  certain  time  elapsed  between  the  actual  observation  of  a  phe- 
nomenon and  the  moment  of  its  record.  This  error,  which  is  equal  to  the 
interval  of  time  between  the  impression  made  upon  the  retina  and  the  mus- 
cular act  by  which  a  record  is  made,  is  not  the  same  in  different  persons  or 
even  in  the  same  person  at  all  times.  It  may  amount  to  £  of  a  second  or 
even  more,  and  it  may  be  as  low  as  -fa  of  a  second.  If  this  difference  be  due 
to  different  rates  of  nervous  conduction,  and  not  entirely  to  variations  in  the 
rapidity  of  mental  operations,  it  is  evident  that  the  velocity  of  the  nerve-cur- 
rent must  vary  very  considerably  in  different  individuals. 

Action  of  Electricity  upon  the  Nerves. — So  long  as  the  nerves  retain  their 
excitability  and  anatomical  integrity,  they  will  respond  to  properly  regulated 
electric  stimulus.  Experiments  may  be  made  upon  the  exposed  nerves  in 
living  animals  or  in  animals  just  killed ;  and  of  all  classes,  the  cold-blooded 
animals  present  the  most  favorable  conditions,  on  account  of  the  persistence 
of  nervous  and  muscular  excitability  for  a  considerable  time  after  death. 
Experimenters  most  commonly  use  frogs,  on  account  of  the  long  persistence 
of  the  physiological  properties  of  their  tissues  and  the  facility  with  which 
certain  parts  of  the  nervous  system  can  be  exposed.  For  ordinary  experi- 
ments upon  nervous  conduction,  the  parts  are  prepared  by  detaching  the 
posterior  extremities,  removing  the  skin,  and  cutting  away  the  bone  and 
muscles  of  the  thigh,  so  as  to  leave  the  leg  with  the  sciatic  nerve  attached. 
A  frog's  leg  thus  isolated  presents  a  nervous  trunk  one  or  two  inches  (25  or 
50  mm.)  in  length,  attached  to  the  muscles,  which  will  respond  to  a  feeble 
electric  stimulus.  It  is  by  experiments  made  upon  frogs  prepared  in  this 
way  that  most  of  the  important  facts  with  regard  to  the  action  of  electricity 
upon  the  nervous  system  have  been  developed. 

In  physiological  experiments  it  is  sometimes  necessary  to  use  different 
forms  of  electrical  apparatus  in  order  to  study  different  properties  and 


530  NERVOUS  SYSTEM. 

phenomena  of  nerve  and  muscle.  A  full  description  of  the  apparatus  thus 
used  would  be  out  of  place  in  this  work,  and  it  will  be  necessary  only  to 
enumerate  and  describe  the  different  currents  used  and  the  manner  of  their 
application.  Many  of  the  phenomena,  also,  described  by  electro-physiolo- 
gists, although  curious  and  interesting,  have  little  apparent  application  to 
human  physiology  or  to  the  practice  of  medicine.  A  description  of  such 
phenomena  may  well  be  very  brief  in  a  work  for  the  use  of  students  and 
practitioners  of  medicine. 

In  studying  the  action  of  nerve  and  muscle,  observers  often  use  what  is 
called  a  single  Faradic,  or  induction  shock.  The  duration  of  this  stimulus 
is  about  y^-g-  (0-0008)  of  a  second  (Helmholtz).  The  excitation,  therefore, 
is  practically  instantaneous.  These  single  shocks  are  produced  by  Du  Bois- 
Reymond's  apparatus,  which  is  a  modification  of  the  Faradic,  or  induction 
battery.  It  will  be  seen  farther  on  that  somewhat  different  effects  are  pro- 
duced by  the  stimulus  due  to  closing  and  opening  the  circuit,  and  that  with 
a  feeble  current,  no  contractions  occur  at  any  other  time.  The  contractions 
thus  produced  are  known  respectively  as  opening  and  closing  contractions. 
By  the  use  of  Du  Bois-Reymond's  keys,  either  the  closing  or  the  opening  ex- 
citation may  be  diverted  from  the  nerve,  and  a  single  closing  or  opening 
shock  may  be  applied  at  will. 

What  is  commonly  known  as  an  interrupted  current  is  a  Faradic,  or  in- 
duced current,  in  which  the  closing  and  opening  excitations  follow  each 
other  with  greater  or  less  rapidity,  and  the  intervals  may  be  regulated  so 
that  they  occur  at  a  regular  rate.  A  rapid  succession  of  induction-shocks 
produces  a  more  or  less  prolonged  muscular  action,  called  tetanic  contrac- 
tion. The  number  of  successive  shocks  in  a  second,  required  to  produce  a 
tetanic  condition  of  a  muscle,  varies  in  different  animals  and  in  different 
muscles  in  the  same  animal.  The  minimum  seems  to  be  about  sixteen  per 
second,  with  a  very  considerable  range  of  variation.  Very  rapid  stimuli, 
even  more  than  24,000  per  second,  will  produce  tetanic  contraction. 

The  Faradic,  or  induced  current  is  different  in  its  effects,  under  certain 
conditions  of  the  nerves  and  muscles,  from  an  interrupted  galvanic,  or  pri- 
mary current.  This  question  is  important  in  practical  medicine,  in  deter- 
mining the  so-called  "  reaction  of  degeneration  "  of  nerve  and  muscle. 

The  constant  current,  under  certain  conditions,  has  no  effect  that  is  in- 
dicated by  muscular  phenomena,  contraction  occurring  only  on  closing  or 
opening  the  circuit.  This  is  known  as  the  galvanic,  or  primary  current. 
It  produces,  however,  a  peculiar  condition  of  nerves  and  muscles,  which  will 
be  described  under  the  head  of  electrotonus.  The  primary  current  is  de- 
rived directly  from  the  cells  of  a  galvanic  battery,  and  this  is  to  be  distin- 
guished from  the  Faradic,  or  induced  current.  The  Faradic  current  is 
induced  in  a  coil  of  small,  insulated  wire  brought  near  and  parallel  to  and 
partly  or  entirely  surrounding  a  coil  of  larger  wire  carrying  the  primary 
current.  When  the  circuit  of  the  primary  current  is  closed,  the  direction 
of  the  induced  current  is  the  reverse  of  that  of  the  primary  current. 
When  the  primary  circuit  is  opened,  the  induced  current  has  the  same 


ACTION  OF  ELECTEICITY  UPON  THE  NERVES.  531 

direction  as  the  primary  current.  The  direction  of  the  primary  current  is 
uniform,  but  the  direction  of  the  induced  current  alternates  with  every  in- 
terruption of  the  primary  current.  These  induced  currents  are  of  momen- 
tary duration,  being  produced  only  when  the  primary  current  is  closed  and 
opened.  A  rapid  interruption  of  the  primary  current  is  produced  by  what 
is  called  a  rheotome,  or  current-interrupter,  which  is  attached  to  all  induc- 
tion-batteries. 

The  points  or  surfaces  used  in  closing  a  circuit  in  which  a  portion  of 
nerve  or  muscle  is  included  are  called  electrodes.  They  are  usually  desig- 
nated as  the  copper,  or  positive  electrode  or  pole,  and  the  zinc,  or  negative 
electrode  or  pole.  The  positive  pole  is  also  called  the  anode,  and  the  nega- 
tive pole,  the  cathode.  The  direction  of  the  current,  when  the  circuit  is 
closed,  is  from  the  anode  to  the  cathode. 

When  a  galvanic  current  is  passed  through  a  liquid  or  a  moist,  animal 
tissue,  decomposition  occurs,  by  what  is  known  as  electrolysis  or  internal 
polarization.  The  results  of  this  decomposition,  called  ions,  are  of  course 
different  in  different  liquids  or  moist  tissues.  These  accumulate  at  the  poles 
and  after  a  time  disturb  the  currents  and  the  phenomena  produced.  In  ani- 
mal tissues,  acids  accumulate  at  the  anode,  and  alkalies,  at  the  cathode.  The 
ions  which  go  to  the  anode  are  called  anions,  and  those  which  accumulate  at 
the  cathode  are  called  cations.  In  physiological  experiments,  it  is  often  de- 
sirable to  eliminate  electrolysis,  or  internal  polarization,  and  this  is  done  by 
using  the  non-polarizable  electrodes  devised  by  Du  Bois-Eeymond.  These 
may  be  described  as  follows :  "  The  researches  of  Regnault,  Matteucci  and 
Du  Bois-Reymond  have  proved  that  such  electrodes  can  be  made  by  taking 
two  pieces  of  carefully  amalgamated  pure  zinc  wire,  and  dipping  these  in 
a  saturated  solution  of  zinc  sulphate  contained  in  tubes,  their  lower  ends 
being  closed  by  means  of  modeller's  clay,  moistened  with  a  0'6  per  cent, 
normal  saline  solution.  The  contact  of  the  tissues  with  these  electrodes 
does  not  give  rise  to  polarity."  (Landois  and  Stirling.) 

It  is  evident  that  the  galvanic  current  may  be  applied  to  a  nerve  so  that 
the  direction  may  in  the  one  case  follow  the  course  of  the  nerve,  that  is, 
from  the  centre  to  the  periphery,  and  in  the  other,  be  opposite  to  the  course 
of  the  nerve.  These  have  been  called  respectively  descending  and  ascending 
currents.  When  the  positive  pole  (copper)  is  placed  nearer  the  origin  of  the 
nerve,  and  the  negative  pole  (zinc),  below  this  point  in  the  course  of  the 
nerve,  the  galvanic  current  follows  the  normal  direction  of  the  motor  con- 
duction, and  this  is  called  the  descending  current.  When  the  poles  are  re- 
versed and  the  direction  is  from  the  periphery  toward  the  centre,  it  is  called 
the  ascending  current.  It  will  be  convenient  to  speak  of  these  two  currents 
respectively  as  descending  and  ascending,  in  detailing  experiments  upon  the 
action  of  electricity  upon  the  nerves. 

The  points  to  be  noted  with  regard  to  the  effects  of  the  application  of 
electricity  to  an  exposed  nerve  are  the  action  of  constant  currents,  the  phe- 
nomena observed  on  closing  and  opening  the  circuit,  and  the  effects  of  an 
interrupted  current. 


532  NEEVOUS  SYSTEM. 

During  the  passage  of  a  feeble  constant  current  through  a  nerve,  what- 
ever be  its  direction,  there  are  no  convulsive  movements  and  no  evidences  of 
pain.  This  fact  has  long  been  recognized  by  physiologists,  who  at  first  lim- 
ited the  effects  of  electricity  upon  the  nerves  to  two  periods,  one  at  the  clos- 
ing of  the  circuit  and  the  other  at  its  opening.  It  will  be  seen,  however,  that 
the  passage  of  electricity  through  a  portion  of  a  nervous  trunk  produces  a 
peculiar  condition  in  the  nerve,  which  has  been  described  under  the  name 
of  electrotonus ;  but  the  fact  remains  that  neither  motion  nor  sensation  is 
excited  in  a  mixed  nerve  during  the  actual  passage  of  a  feeble  constant  cur- 
rent. 

Law  of  Contraction. — All  who  have  experimented  upon  the'  action  of 
galvanism  upon  the  nerves  have,  noted  the  fact  alluded  to  above,  that  con- 
traction occurs  only  on  closing  or  on  opening  the'  circuit.  Take,  for  exam- 
ple, a  frog's  leg  prepared  with  the  nerve  attached :  Place  one  pole  of  a  gal- 
vanic apparatus  on  the  nerve  and  then  make  the  connection,  including  a 
portion  of  the  nerve  in  the  circuit.  With  the  feeblest  current,  contraction  oc- 
curs only  on  closing  the  circuit.  With  what  is  called  the  "  weak  "  current 
(Pfliiger),  contraction  occurs  only  on  closing  the  circuit,  for  currents  in 
either  direction.  With  the  "  moderate  "  current,  contraction  occurs  both  on 
closing  and  on  opening  the  circuit,  for  currents  in  either  direction.  With 
the  "  strong "  current,  contraction  occurs  only  on  closing  the  circuit,  with 
the  descending  current,  and  only  on  opening  the  circuit,  with  the  ascending 
current.  The  above  phenomena  constitute  what  is  called  Pfliiger's  "  law  of 
contraction."  The  explanations  of  this  law  are  the  following : 

The  stimulus  which  gives  rise  to  the  closing  contraction  occurs  at  the 
cathode,  when  the  electrotonus  produced  by  the  passage  of  the  current  be- 
gins. The  stimulus  which  produces  the  opening  contraction  occurs  at  the 
anode,  when  the  electrotonus  disappears.  The  impulse  is  always  stronger 
when  the  electrotonus  begins  than  when  it  disappears.  Therefore,  when  the 
current  is  so  feeble  that  but  one  contraction  is  produced,  this  contraction 
occurs  only  on  closing  the  circuit,  for  both  ascending  and  descending  currents. 

With  the  "  moderate  "  current,  the  strength  of  the  opening  impulse  is 
sufficient  to  produce  a  contraction ;  and  contractions  therefore  occur  both  on 
opening  and  closing  the  circuit,  for  both  ascending  and  descending  currents. 

Strong  currents  produce  closing  contraction  with  the  descending  current, 
for  the  reason  that  the  current  destroys  the  conducting  power  of  that  portion 
of  the  nerve  included  between  the  poles  of  the  battery,  and,  the  stimulus 
occurring  only  at  the  cathode  (see  above),  and  the  cathode  being  applied  to 
that  portion  of  the  nerve  nearest  the  muscle,  the  closing  impulse  only  is 
conveyed  to  the  muscle.  The  opening  impulse  (at  the  anode)  is  cut  off  from 
the  muscle  by  the  loss  of  conducting  power  in  the  intrapolar  portion  of  the 
nerve.  With  the  ascending  current,  the  opening  impulse,  occurring  at  the 
anode,  which  is  nearest  the  muscle,  produces  an  opening  contraction,  and 
the  closing  impulse,  which  is  at  the  cathode,  is  not  conducted  to  the  muscle. 

While  the  constant  current  does  not  usually  excite  contractions  during 
the  time  of  its  passage  through  a  nerve,  with  a  certain  strength  of  current, 


ACTION  OF  ELECTRICITY  UPON  THE  NERVES.  533 

the  muscle  is  thrown  into  a  tetanic  condition.  This  is  called  "  closing  teta- 
nus." When  a  constant  current,  not  of  sufficient  strength  to  produce  closing 
tetanus,  is  passed  for  several  minutes  through  a  long  extent  of  nerve,  a  very 
vigorous  contraction  occurs  on  opening  the  circuit,  which  is  followed  by  teta- 
nus lasting  for  several  seconds.  This  is  called  "  opening  tetanus."  After  a 
time,  this  varying  with  the  excitability  of  the  nerve  and  the  strength  of  the 
current,  the  descending  current  will  destroy  the  nervous  excitability,  but  it 
may  be  restored  by  repose,  or  more  quickly  by  the  passage  of  an  ascending 
current.  If  the  ascending  current  be  passed  first  for  a  few  seconds,  a  con- 
traction follows  the  opening  of  the  circuit ;  and  this  contraction,  within  cer- 
tain limits,  is  more  vigorous  the  longer  the  current  is  passed.  At  the  same 
time,  the  prolonged  passage  of  the  ascending  current  increases  the  excitabil- 
ity of  the  nerve  for  any  kind  of  stimulus. 

After  a  certain  time,  which  varies  in  different  animals,  the  nervous  excita- 
bility becomes  somewhat  enfeebled  by  exposure  of  the  parts.  The  phenom- 
ena then  observed  belong  to  the  conditions  involved  in  the  process  of  "  dying  " 
of  the  nerve.  In  the  later  stages  of  this  condition,  the  phenomena  may  be 
formulated  as  follows : 

If  the  sciatic  nerve  attached  to  the  leg  of  a  frog,  prepared  in  the  usual 
way  for  such  experiments,  be  subjected  to  a  feeble  galvanic  current,  there  is 
a  time  when  muscular  contraction  takes  place  only  at  the  instant  when  the 
circuit  is  closed,  no  contraction  occurring  when  the  circuit  is  opened ;  and 
this  occurs  only  with  the  descending  current.  With  the  ascending  current, 
contraction  of  the  muscles  occurs  only  when  the  circuit  is  opened  and  none 
takes  place  when  the  circuit  is  closed.  These  phenomena  are  distinct  after 
the  excitability  of  the  parts  has  become  somewhat  diminished  by  exposure  or 
by  electric  stimulation  of  the  nerve. 

If  a  sufficiently  powerful  constant  current  be  passed  through  a  nerve,  dis- 
organization of  its  tissue  takes  place,  and  the  nerve  finally  loses  its  excita- 
bility, as  it  does  when  bruised,  ligatured,  or  when  its  structure  is  destroyed 
in  any  other  way.  It  was  thought  by  Galvani,  and  the  idea  has  been  adopted 
by  Matteucci,  Guerard  and  Longet,  that  a  current  directed  exactly  across  a 
nerve,  so  as  to  pass  at  right  angles  to  its  fibres,  does  not  give  rise  to  muscular 
contraction.  This  view  is  generally  accepted  by  physiologists. 

The  muscular  contraction  produced  by  electric  stimulation  of  a  nerve  is 
more  vigorous  the  greater  the  extent  of  the  nerve  included  between  the  poles 
of  the  battery.  This  fact  has  long  been  observed,  and  its  accuracy  may  easily 
be  verified.  It  would  naturally  be  expected  that  the  greater  the  amount  of 
stimulation,  the  more  marked  would  be  the  muscular  action ;  and  the  stimu- 
lation seems  to  be  increased  in  proportion  to  the  extent  of  nerve  through 
which  the  current  is  made  to  pass. 

The  excitability  of  a  nerve,  it  is  well  known,  may  be  exhausted  by  the 
repeated  application  of  electricity,  whatever  be  the  direction  of  the  current, 
and  it  is  more  or  less  completely  restored  by  repose.  When  it  has  been  ex- 
hausted for  the  descending  current,  it  will  respond  to  the  ascending  current, 
and  vice  versa  ;  and  after  it  has  been  exhausted  by  the  descending  current, 


534 


NERVOUS  SYSTEM. 


it  is  restored  more  promptly  by  stimulation  with  the  ascending  current  than 
by  absolute  repose,  and  vice  versd.  This  phenomenon,  observed  by  Volta,  is 
known  as  "  voltaic  alternation." 

Many  of  the  phenomena  illustrating  the  law  of  contraction  may  be  ob- 
served without  the  use  of  complicated  apparatus.     A  form  of  battery,  very 

convenient  for  some  of  these  experiments, 
is  the  one  described  by  Bernard.  It  con- 
sists simpty  of  alternate  copper  and  zinc 
wires  wound  around  a  piece  of  wood  bent 
in  the  form  of  a  horseshoe  and  terminating 
in  two  platinum  points  representing  the 
positive  and  negative  poles.  This  forms  a 
sort  of  electric  forceps,  about  eight  inches 
(20  centimetres)  long,  which,  when  moist- 
ened with  water  slightly  acidulated  with 
acetic  acid,  will  give  a  constant  current  of 
about  the  required  strength. 

The  law  of  contraction  is  applicable  to 
inhibitory  nerves,  as  the  inhibitory  nerve  of 
the  heart,  the  difference  being  that  the 
stimulation  produces  inhibition  instead  of 


FIG.  187.— Electric  forceps  (Ld6geois). 
c,  copper ;  z,  zinc. 


FIG.  188.— Arrangement  of  frog's  legs  prepared  so  as  to 
show  induced  contraction  (Li6geois). 


contraction.     It  also  holds  good  for  sensory  nerves,  the  effects  being  observed 
by  noting  the  reflex  contractions  produced  (Pfliiger). 

A  peculiar  phenomenon,  discovered  by  Matteucci,  has  been  called  "  in- 
duced muscular  contraction."  If  the  nerve  of  a  galvanoscopic  frog's  leg  be 
placed  in  contact  with  the  muscles  of  another  leg  prepared  in  the  same  way, 
stimulation  of  the  nerve,  giving  rise  to  contraction  of  the  muscles  with  which 
the  nerve  of  the  first  leg  is  in  contact,  will  induce  contraction  in  the  muscles 
of  both.  This  experiment  may  be  extended,  arid  contractions  may  thus  be 
induced  in  a  series  of  legs,  the  nerve  of  one  being  in  contact  with  the  mus- 
cles of  another.  It  is  shown  that  "  induced  contraction  "  is  not  due  to  an 
actual  propagation  of  the  electric  current  but  to  a  stimulus  attending  the 


ELECTROTONUS.  535 

muscular  contraction  itself,  by  the  fact  that  the  same  phenomena  occur  when 
the  first  muscular  contraction  is  produced  by  mechanical  or  chemical  excita- 
tion of  the  nerve. 

Galvanic  Current  from  the  Exterior  to  the  Cut  Surface  of  a  Nerve. — Be- 
fore studying  certain  phenomena  presented  in  nerves  of  which  a  portion  is 
subjected  to  the  action  of  a  constant  galvanic  current,  it  is  important  to  note 
the  fact  that  there  exists  in  the  nerves,  as  in  the  muscles,  a  galvanic  current 
with  a  direction  from  the  exterior  to  the  cut  surface.  It  has  been  roughly 
estimated  that  the  nerve-current  has  one-eighth  to  one-tenth  the  intensity  of 
the  muscular  current  (Matteucci).  The  existence  of  the  nerve-current  has, 
as  far  as  is  known,  no  more  physiological  significance  than  the  analogous 
fact  observed  in  the  muscular  tissue.  Galvanic  currents  also  exist  in  the 
skin  and  in  mucous  membranes,  the  direction  being  from  the  outer  surface, 
which  is  positive,  to  the  inner  surface,  which  is  negative. 

Electrotonus,  Anelectrotonus  and  Catelectrotonus. — When  a  constant  gal- 
vanic current  is  passed  through  a  portion  of  a  freshly  prepared  nerve,  a  large 
part  of  the  entire  nerve  is  brought  into  a  peculiar  electric  condition  (Du 
Bois-Reymond).  While  in  this  state,  the  nerve  will  deflect  the  needle  of  a 
galvanometer,  and  its  excitability  is  modified.  The  deflection  of  the  needle 
in  this  instance  is  not  due  to  the  normal  nerve-current,  for  it  occurs  when 
the  galvanometer  is  applied  to  the  surface  of  the  nerve  only.  It  is  due  to 
an  electric  tension  of  the  entire  nerve,  induced  by  the  passage  of  a  current 
through  a  portion  of  its  extent.  This  condition  is  called  electrotonus.  There 
is  also  a  peculiar  condition  of  that  portion  of  the  nerve  near  the  anode, 
differing  from  the  condition  of  the  nerve  near  the  cathode.  Near  the  anode 
the  excitability  of  the  nerve  is  diminished,  and  this  condition  is  called  ane- 
electrotonus.  Near  the  cathode  the  excitability  is  increased,  and  this  condi- 
tion is  called  catelectrotonus  (Pfliiger).  These  phenomena  have  been  the 
subject  of  extended  investigation  by  electro-physiologists ;  and  although  the 
conditions  are  not  to  be  included  in  the  physiological  properties  of  the 
nerves,  they  have  considerable  pathological  and  therapeutical  importance. 
It  is  well  known,  for  example,  that  electricity  is  often  one  of  the  most  effi- 
cient agents  at  command  for  the  restoration  of  the  properties  of  nerves 
affected  with  disease ;  and  the  constant  current  has  been  extensively  and 
successfully  used  as  a  therapeutical  agent.  The  constant  current,  in  restoring 
the  normal  condition  of  nerves,  must  influence,  not  only  that  portion  included 
between  the  poles  of  the  battery,  but  the  entire  nerve ;  and  the  electrotonic 
condition,  with  its  modifications,  in  a  measure  explains  how  this  result  may 
be  obtained. 

The  electrotonic  condition  is  marked  in  proportion  to  the  excitability  of 
the  nerve,  and  it  is  either  entirely  absent  or  extremely  feeble  in  nerves  that 
are  dead  or  have  lost  their  excitability.  If  a  strong  ligature  be  applied  to  the 
extrapolar  portion  of  a  nerve,  or  if  the  nerve  be  divided  and  the  cut  ends  be 
brought  in  contact  with  each  other,  the  electrotonic  condition  is  either  not 
observed  or  is  very  feeble.  These  facts  show  that  the  phenomena  of  electrot- 
onus depend  upon  the  physiological  integrity  of  nerves.  A  dead  nerve  or 


536 


NERVOUS  SYSTEM. 


one  that  has  been  divided  or  ligated  may  present  these  phenomena  under 
the  stimulation  of  a  very  powerful  current — and  then  only  to  a  slight  degree — 
when  the  condition  depends  upon  the  purely  physical  properties  of  the  nerve 
as  a  conductor ;  but  these  phenomena  are  not  to  be  compared  with  those  ob- 
served in  nerves  that  retain  their  physiological  properties. 

As  stated  above,  the  electrotonic  condition  is  not  restricted  to  that  por- 
tion of  the  nerve  included  between  the  poles  of  the  battery.  The  condition 
of  the  portion  between  the  poles  is  called  intrapolar  electrotonus,  and  the 
condition  of  the  nerve  outside  of  the  poles  is  called  extrapolar  electrotonus. 

When  a  portion  of  a  nerve  is  subjected  to  a  moderately  strong  constant 
current,  the  conditions  of  the  extrapolar  portions  corresponding  to  the  two 
poles  of  the  battery  are  entirely  different.  Near  the  anode  the  excitability 
of  the  nerve  and  the  rate  of  nervous  conduction  are  diminished.  If,  how- 
ever, a  galvanometer  be  applied  to  this  portion  of  the  nerve,  its  electromo- 
tive power,  measured  by  the  deflection  of  the  galvanometric  needle,  is  in- 
creased. On  the  other  hand,  near  the  cathode  the  excitability  of  the  nerve 
is  increased,  as  well  as  the  rate  of  nervous  conduction,  but  the  electromo- 
tive power  is  diminished. 

The  anelectrotonic  condition,  on  the  one  hand,  and  the  catelectrotonic 
condition,  at  the  other  pole  of  the  battery,  are  marked  in  extrapolar  portions 
of  the  nerve  and  are  to  be  recognized,  as  well,  in  that  portion  through 
which  the  current  is  passing ;  but  between  the  the  poles,  there  is  a  point 
where  these  conditions  meet,  as  it  were,  and  where  the  excitability  is  un- 
changed. This  has  been  called  the  neutral  point.  When  the  galvanic  cur- 
rent is  of  moderate  strength,  the  neutral  point  is  about  half-way  between  the 
poles.  "  When  a  weak  current  is  used,  the  neutral  point  approaches  the 
positive  pole,  while  in  a  strong  current,  it  approaches 
the  negative  pole.  In  other  words,  in  a  weak  cur- 
rent the  negative  pole  rules  over  a  wider  territory 
than  the  positive  pole,  whereas  in  a  strong  current 
the  positive  pole  prevails  "  (Rutherford). 

The  conditions  of  extrapolar  excitability  vary 
with  the  direction  of  the  current  applied  to  the 
nerve.  A  convenient  stimulus  with  which  to  meas- 
ure this  excitability  is  a  solution  of  common  salt, 
which  excites  more  or  less  powerful  tetanic  contrac- 
tions of  the  muscles.  These  variations  are  illus- 
trated in  Fig.  189. 

In  Fig.  189,  A,  a  descending  constant  current  is 
applied  to  the  nerve.     When  the  circuit  is  open,  the 
FIG  189  -Method  of  testing  the  salt  applied  to  the  nerve  at  R  produces  contrac- 
Sndog^i"eZec*r°tonM8  tions  of  the  muscle.     If  the  circuit  be  closed,  the 
The  positive  poles  are  +  and  contractions  either  become  much  less  vigorous  or 

the  negative  poles  are  —  ; 

R,R,,R,R,,  points  excited  ceaSe,  on  account  of  the  diminished  excitability  near 

by  the  saline  solution. 

the  anode.     This  is  called  descending  extrapolar  an- 
electrotonus.     If  the  salt  be  applied  at  R15  the  contractions  are  increased  in 


ELECTROTONUS.  537 

vigor  by  closing  the  circuit,  on  account  of  the  increased  excitability  of  the 
nerve  near  the  cathode.  This  is  called  ascending  extrapolar  catelectronus. 

In  Fig.  189,  B,  the  conditions  are  reversed.  The  polarizing  current  here 
must  be  very  weak,  as  a  strong  current  may  destroy  the  conducting  power  of 
the  intrapolar  portion  of  the  nerve  and  thus  prevent  the  conduction  of  the 
stimulus  to  the  muscle  when  the  salt  is  applied  at  R.  On  closing  the  cir- 
cuit, there  is  ascending  extrapolar  catelectronus  at  R,  and  ascending  extra- 
polar  anelectronus  at  Rx. 

Within  certain  limits,  the  greater  the  strength  of  the  constant  current 
applied  to  the  nerve  and  the  greater  the  length  of  nerve  included  between 
the  poles  of  the  battery,  the  greater  is  the  deflection  of  the  galvanoscopic 
needle,  by  which  the  electrotonic  condition  is  measured. 

Electrotonic  conditions  in  sensory  nerves  are  measured  by  reflex  move- 
ments produced  by  the  action  of  a  stimulus  applied  to  these  nerves.  The 
variations  in  excitability  of  inhibitory  nerves,  produced  by  a  constant  current, 
are  indicated  by  increase  or  diminution  in  the  inhibitory  action.  The  phe- 
nomena in  sensory  and  inhibitory  nerves  are  analogous  to  those  observed  in 
motor  nerves.  The  influence  of  a  constant  current  upon  the  muscle  current 
is  distinct  though  feeble,  producing  a  kind  of  electrotonic  condition  of 
muscle. 

Negative  Variation. — When  a  rapidly  interrupted  current  is  applied  to  a 
nerve  so  as  to  produce  a  tetanic  condition  of  the  muscles  to  which  it  is  dis- 
tributed, the  normal  or  tranquil  nerve-current  is  overcome,  and  a  galvano- 
scopic needle  applied  to  the  nerve,  which  was  first  deviated  by  the  nerve- 
current,  will  be  observed  to  retrograde  and  will  finally  return  to  zero  (Du 
Bois-Reymond).  This  may  also  be  observed  to  a  slight  degree  under  the  in- 
fluence of  mechanical  or  chemical  stimulation  of  the  nerve,  the  proper  nerve- 
current  being  diminished,  but  generally  not  abolished.  The  variation  of  the 
needle  under  the  influence  of  the  tetanic  condition  has  been  called  negative 
variation.  It  is  not  known  that  this  has  any  important  physiological  or 
pathological  significance. 


0 
538  NERVOUS  SYSTEM. 

CHAPTER  XVII. 

SPINAL  AND   CRANIAL  NERVES. 

Spinal  nerves— Cranial  nerves— Anatomical  classification— Physiological  classification— Motor  oculi  cora- 
raunis  (third  nerve) — Physiological  anatomy — Properties  and  uses— Influence  upon  the  movements  of 
the  iris— Patheticus,  or  trochlearis  (fourth  nerve)— Physiological  anatomy— Properties  and  uses!— Motor 
oculi  externus,  or  abducens  (sixth  nerve)— Physiological  anatomy — Properties  and  uses— Nerve  of  mas- 
tication (the  small,  or  motor  root  of  the  fifth)— Physiological  anatomy— Properties  and  uses— Facial, 
or  nerve  of  expression  (seventh  nerve)— Physiological  Anatomy — Intermediary  nerve  of  Wrisberg— 
Alternate  paralysis— General  properties — Uses  of  the  chorda  tympani — Influence  of  various  branches 
of  the  facial  upon  the  movements  of  the  palate  and  uvula— Spinal  accessory  (eleventh  nerve)— Physio- 
logical anatomy — Uses  of  the  internal  branch  from  the  spinal  accessory  to  the  pneumogastric— Influ- 
ence of  the  spinal  accessory  upon  the  heart — Uses  of  the  external,  or  muscular  branch  of  the  spinal 
accessory— Sublingual,  or  hypoglossal  (twelfth  nerve)— Physiological  anatomy— Properties  and  uses 
— Trifacial,  or  trigeminal  (fifth  nerve)— Physiological  anatomy— Properties  and  uses— Pneumogastric 
(tenth  nerve) — Physiological  anatomy— Properties  and  uses— General  properties  of  the  roots — Prop- 
erties and  uses  of  the  auricular  nerves — Properties  and  uses  of  the  pharyngeal  nerves — Properties 
and  uses  of  the  superior  laryngeal  nerves — Properties  and  uses  of  the  inferior,  or  recurrent  laryngeal 
nerves — Properties  and  uses  of  the  cardiac  nerves — Depressor  nerve  of  the  circulation — Properties  and 
uses  of  the  pulmonary  nerves — Properties  and  uses  of  the  oesophageal  nerves — Properties  and  uses  of 
the  abdominal  nerves. 

WITH  a  knowledge  of  the  general  properties  of  the  nerves  belonging  to  the 
cerebro-spinal  system,  it  is  easy  to  understand  the  uses  of  most  of  the  special 
nerves,  simply  from  their  anatomical  relations.  This  is  especially  true  of 
the  spinal  nerves.  These,  in  general  terms,  are  distributed  to  the  muscles  of 
the  trunk  and  extremities,  to  the  sphincters  and  the  integument  covering  these 
parts,  the  posterior  segment  of  the  head,  and  to  certain  mucous  membranes. 
It  is  evident,  therefore,  that  an  account  of  the  exact  office  of  each  nervous 
branch  would  necessitate  a  full  description,  not  only  of  the  nerves,  but  of  the 
muscles  of  the  body,  which  is  manifestly  within  the  scope  only  of  treatises 
on  descriptive  anatomy. 

SPINAL  NERVES. 

There  are  thirty-one  pairs  of  spinal  nerves ;  eight  cervical,  twelve  dorsal, 
five  lumbar,  five  sacral  and  one  coccygeal.  Each  nerve  arises  from  the  spinal 
cord  by  an  anterior  (motor)  and  a  posterior  (sensory)  root,  the  posterior  roots 
being  the  larger  and  each  having  a  ganglion.  Immediately  beyond  the 
ganglion,  the  two  roots  unite  into  a  single  mixed  nerve,  which  passes  out  of 
the  spinal  canal  by  the  intervertebral  foramen.  The  nerve  thus  constituted 
\§  possessed  of  motor  and  sensory  properties.  It  divides  outside  of  the  spinal 
canal  into  two  branches,  anterior  and  posterior,  both  containing  motor  and 
sensory  filaments,  which  are  distributed  respectively  to  the  anterior  and  the  pos- 
terior parts  of  the  body.  The  anterior  branches  are  the  larger,  and  they  sup- 
ply the  limbs  and  all  parts  in  front  of  the  spinal  column. 

The  anterior  branches  of  the  upper  four  cervical  nerves  form  the  cervical 
plexus,  and  the  four  inferior  cervical  nerves,  with  the  first  dorsal,  form  the 
brachial  plexus.  The  anterior  branches  of  the  dorsal  nerves,  with  the  excep- 
tion of  the  first,  supply  the  walls  of  the  chest  and  abdomen.  These  nerves 
go  directly  to  their  distribution  and  do  not  first  form  a  plexus.  The  ante- 
rior branches  of  the  upper  four  lumbar  nerves  form  the  lumbar  plexus.  The 
anterior  branch  of  the  fifth  lumbar  nerve  and  a  branch  from  the  fourth 


CRANIAL  NERVES. 


539 


unite  with  the  anterior  branch  of  the  first  sacral,  forming  the  lumbo-sacral 
nerve,  and  enter  into  the  sacral  plexus.  The  upper  three  anterior  sa- 
cral nerves,  with  a  branch  from  the  fourth,  form  the  sacral  plexus.  The 
greatest  portion  of 
the  fourth  anterior 
sacral  is  distributed 
to  the  pelvic  viscera 
and  the  muscles  of 
the  anus.  The  fifth 
anterior  sacral  and 
the  coccygeal  are 
distributed  to  parts 
about  the  coccyx. 

The  posterior 
branches  of  the  spi- 
nal nerves  are  very 
simple  in  their  dis- 
tribution. With 
one  or  two  excep- 
tions, which  have 
no  great  physiolog- 
ical importance, 
these  nerves  pass 
backward  from  the 
main  trunk,  divide 
into  two  branches, 
external  and  inter- 
nal, and  their  fila- 
ments of  distribu- 
tion go  to  the  mus- 
cles and  to  integu- 
ment behind  the 
spinal  column. 

It  is  farther  im- 
portant to  note,  that  all  of  the  cerebro-spinal  nerves  anastomose  with  the 
sympathetic. 

CRANIAL  NERVES. 

Many  of  the  cranial  nerves  are  peculiar,  either  as  regards  their  general 
properties  or  in  their  distribution  to  parts  concerned  in  special  functions. 
In  some  of  these  nerves,  the  most  important  facts  concerning  their  distribu- 
tion have  been  ascertained  only  by  physiological  experimentation,  and  their 
anatomy  is  inseparably  connected  with  their  physiology.  It  would  be  desira- 
ble, if  it  were  possible,  to  classify  these  nerves  with  reference  strictly  to  their 
properties  and  uses ;  but  this  can  be  done  only  to  a  certain  extent.  The 
classification  of  the  cranial  nerves  adopted  by  most  anatomists  is  the  arrange- 


Fio.  190. — Cervical  por- 
tion of  the  spinal  cord 
(Hirschfeld). 


FIG.  191.— Dorsal  por- 
tion of  the  spinal 
cord  (Hirschfeld). 


FIG.  192.— Inferior  por- 
tion  of  the  spinal  cord, 
and  cauda  equina 
(Hirschfeld). 

1,  antero-inferior  wall  of  the  fourth  ventricle  :  2,  superior  peduncle  of  the 
cerebellum  ;  3,  middle  peduncle  of  the  cerebellum  :  4,  inferior  peduncle 
of  the  cerebellum  ;  5,  inferior  portion  of  the  posterior  median  columns 
of  the  cord  ;  6,  glosso-pharyngeal  nerve  ;  7.  pneumogastric  :  8,  spinal 
accessory  nerve  ;  9,  9,  9,  9,  dentated  ligament ;  10,  10,  10,  10,  posterior 
roots  of  the  spinal  nerves ;  11,  11,  11,  11,  posterior  lateral  groove  ;  12,  12, 
12,  12,  ganglia  of  the  posterior  roots  of  the  nerves  ;  13,  13,  anterior  roots 
of  the  nerves ;  14,  division  of  the  nerves  into  two  branches  ;  15,  lower  ex- 
tremity of  the  cord :  16,  16,  coccygeal  ligament ;  17, 17,  cauda  equina ; 
I-VTII,  cervical  nerves  ;  I,  II,  III,  IV-XII,  dorsal  nerves  ;  I,  II-V,  lumbar 
nerves ;  I-V,  sacral  nerves. 


540 


NERVOUS  SYSTEM. 


FIG.  193.— Roots  of  the  cranial  nerves  (Hirschfeld). 
I.  Olfactory. 
H.  Optic. 

III.  Motor  oculi  communis. 

IV.  Patheticus. 

V.  Nerve  of  mastication  and  trifacial. 
VI.  Motor  oculi  externus. 
VII.  Facial. 
Vin.  Auditory. 
IX.  Glosso-pharyngeal. 
X.  PneumoRastric. 
XI.  Spinal  accessory. 
XII.  Sublingual. 

The  numbers  1  to  15  refer  to  branches  which  will  be  de- 
scribed hereafter. 

Spinal  accessory.     (Eleventh  pair.) 
Sublingual.     (Twelfth  pair). 


ment  of  Sommerring,  in  which  the 
nerves  are  numbered  from  before 
backward,  in  the  order  in  which 
they  pass  out  of  the  skull,  making 
twelve  pairs. 

CLASSIFICATION  OF  THE  CKANI- 
AL  NERVES. 

Nerves  of  Special  Sense. 
Olfactory.     (First  pair.) 
Optic.     (Second  pair.) 
Auditory.     (Eighth  pair.) 
Gustatory,  comprising  a  part 
15  of  the  glosso  -  pharyngeal  (ninth 
pair)  and  a  small  filament  from 
the  facial  (seventh  pair)  to  the  lin- 
gual branch  of  the  fifth  pair. 

Nerves  of  Motion. 

Nerves  of  motion  of  the  eye- 
ball, comprising  the  motor  oculi 
communis  (third  pair),  the  pathet- 
icus  (fourth  pair),  and  the  motor 
oculi  externus  (sixth  pair). 

Nerve  of  mastication,  or  motor 
root  of  the  fifth  pair. 

Facial,  sometimes  called  the 
nerve  of  expression.  (Seventh 
pair.) 


Nerves  of  General  Sensibility. 

Trifacial,  or  large  root  of  the  fifth  pair. 

A  portion  of  the  glosso-pharyngeal.     (Ninth  pair.) 

Pneumogastric.     (Tenth  pair.) 

In  the  above  arrangement,  the  nerves  are  classified  according  to  their 
properties  at  their  roots.  In  their  course,  some  of  these  nerves  become 
mixed  and  their  branches  are  both  motor  and  sensory,  such  as  the  pneumo- 
gastric  and  the  inferior  maxillary  branch  of  the  trifacial. 

The  nerves  of  special  sense  have  little  or  no  general  sensibility ;  and  with 
the  exception  of  the  gustatory  nerves,  they  do  not  present  a  ganglion  on 
their  roots,  in  this,  also,  differing  from  the  ordinary  sensory  nerves.  They 
are  capable  of  conveying  to  the  nerve-centres  only  certain  peculiar  impres- 
sions, such  as  odors,  for  the  olfactory  nerves,  light,  for  the  optic  nerves,  and 


MOTOR  OCULI  COMMUNIS. 


541 


sound,  for  the  auditory  nerves.  The  proper  transmission  of  these  impres- 
sions, however,  involves  the  action  of  accessory  parts,  more  or  less  complex ; 
and  the  properties  of  these  nerves  will  be  fully  considered  in  connection  with 
the  physiology  of  the  special  senses. 

MOTOR  OCULI  COMMUNIS  (THIRD  NERVE). 

The  third  cranial  nerve  is  the  most  important  of  the  motor  nerves  dis- 
tributed to  the  muscles  of  the  eyeball.  Its  physiology  is  readily  understood 
in  connection  with  its  distribution,  the  only  point  at  all  obscure  being  its  re- 
lations to  the  movements  of  the  iris,  upon  which  the  results  of  experiments 
are  somewhat  contradictory. 

Physiological  Anatomy. — The  apparent  origin  of  the  third  nerve  is  from 
the  inner  edge  of  the  crus  cerebri,  directly  in  front  of  the  pons  Varolii,  mid- 
way between  the  pons  and  the  corpora  albicantia.  It  presents  here  eight  or 
ten  filaments,  of  nearly  equal  size,  which  soon  unite  into  a  single,  rounded 
trunk. 

The  deep  origin  of  the  nerve  has  been  studied  by  dissections  of  the  en- 
cephalon  fresh  and  hardened  by  different  liquids.  From  the  groove  by  which 
they  emerge  from  the  encephalon,  the 
fibres  spread  out  in  a  fan-shape,  the  mid- 
dle filaments  passing  inward,  the  anterior, 
inward  and  forward,  and  the  posterior, 
inward  and  backward.  It  is  probable 
that  the  middle  filaments  pass  to  the  me- 
dian line  and  decussate  with  correspond- 
ing fibres  from  the  opposite  side.  The 
anterior  filaments  pass  forward  and  are 
lost  in  the  optic  thalamus.  The  posterior 
filaments  on  either  side  pass  backward  to 
a  gray  nucleus  beneath  the  aqueduct  of 
Sylvius  and  here  decussate  with  fibres 
from  the  opposite  side,  This  decussation 
of  the  fibres  of  origin  of  the  third  nerves  ^^HHBP 

is  important  in  connection  with  the  har-  FIG.  194.— Distribution  of  the  motor  oculi 

communis  (Hirschfeld). 
mony  Of  action  O±    the    iriS    and    the   mUS-    lf  trunk  of  the  motor  oculi  communis ;  2,  su- 

P!P<?  of  thp  PVP«!  nnnn  thp  twn  sirlpsj  perior   branch;  3,  filaments  which  this 

i  eyes  upoi  ,es.  branch  sends  to  the  superior  rectus  and 

Thp  rlistrihntirm   nf    fhp  tliirrl  nprvp  i<5  the  levator  palpebri  superioris  ;  4,  branch 

OI    me  tilira  nerve  lb  to  the  internal  rectus  ;  5,  branch  to  the 

vprtT  airrmlp         A«  if   na««P«  infn  flip    nrhif  inferior  rectus;  6,  branch  to  the  inferior 

Very  Simple.       AS  It   passes  mtO  tlie       rDlt,  oblique  muscle;  7,  branch  to  the  lenticular 

V\v  -flip  anli  prim  rial    fiaanvp     if    rlivirlpa    infr>  ganglion  ;  8,  motor  oculi  externus  ;  9,  fila- 

oy  tne  spnenoi<  nssure,  it  divides  into  ^en^s  of  ^  motor  oculj  externus  anasto- 
two  branches.  The  superior,  which  is  the  Jj^ff with  the  sympathetic ;  10,  auary 
smaller,  passes  to  the  superior  rectus  mus- 
cle of  the  eye,  and  certain  of  its  filaments  are  continued  to  the  levator  palpe- 
bne  superioris.  The  inferior  division  breaks  up  into  three  branches.  The 
internal  branch  passes  to  the  internal  rectus  muscle ;  the  inferior  branch,  to 
the  inferior  rectus ;  the  external  branch,  the  largest  of  the  three,  is  distribu- 
ted to  the  inferior  oblique  muscle,  and  in  its  course,  it  sends  a  short  and 

36 


542  NERVOUS  SYSTEM. 

thick  filament  to  the  lenticular,  'or  ophthalmic  ganglion  of  the  sympathetic. 
It  is  this  branch  which  is  supposed,  through  the  short  ciliary  nerves  passing 
from  the  lenticular  ganglion,  to  furnish  the  motor  influence  to  the  iris.  In 
its  course  this  nerve  receives  a  few  very  delicate  filaments  from  the  cavernous 
plexus  of  the  sympathetic  and  a  branch  from  the  ophthalmic  division  of  the 
trifacial. 

Properties  and  Uses  of  the  Motor  Oculi  Communis. — Stimulation  of  the 
root  of  the  third  nerve  in  a  living  animal  produces  contraction  of  the  muscles 
to  which  it  is  distributed,  but  no  pain.  If  the  stimulus,  however,  be  applied  a 
little  farther  on  in  the  course  of  the  nerve,  there  are  evidences  of  sensibility ; 
and  this  is  readily  explained  by  its  communications  with  the  ophthalmic 
branch  of  the  trifacial.  At  its  root,  therefore,  this  nerve  is  exclusively  motor, 
and  its  office  is  connected  entirely  with  the  action  of  muscles. 

The  phenomena  which  are  observed  after  section  of  the  motor  oculi  com- 
munis  in  living  animals  are  the  following  : 

1.  Falling  of  the  upper  eyelid,  or  blepharoptosis. 

2.  External  strabismus,  immobility  of  the  eye  except  in  an  outward  di- 
rection, inability  to  rotate  the  eye  on  its  antero-posterior  axis  in  certain 
directions,  with  slight  protrusion  of  the  eyeball. 

3.  Dilatation  of  the  pupil,  with  a  certain  degree  of  interference  with  the 
movements  of  the  iris. 

The  falling  of  the  upper  eyelid  is  constantly  observed  after  division  of  the 
third  nerve  in  living  animals  and  always  follows  its  complete  paralysis  in  the 
human  subject.  An  animal  in  Avhich  the  nerve  has  been  divided  can  not 
raise  the  lid,  but  can  press  the  lids  together  by  a  voluntary  effort.  In  the 
human  subject  the  falling  of  the  lid  gives  to  the  face  a  peculiar  and  char- 
acteristic expression.  The  complete  loss  of  power  shows  that  the  levator 
palpebrae  superioris  muscle  depends  upon  the  third  nerve  entirely  for  its  mo- 
tor filaments.  In  pathology,  external  strabismus  is  frequently  observed  with- 
out falling  of  the  lid,  the  filaments  distributed  to  the  levator  muscle  not  be- 
ing affected. 

The  external  strabismus  and  the  immobility  of  the  eyeball  except  in  an 
outward  direction  are  due  to  paralysis  of  the  internal,  superior,  and  inferior 
recti  muscles,  the  external  rectus  acting  without  its  antagonist.  This  condi- 
tion requires  no  farther  explanation.  These  points  are  illustrated  by  the 
experiment  of  dividing  the  nerve  in  rabbits.  If  the  head  of  the  animal  be 
turned  inward,  exposing  the  eye  to  a  bright  light,  the  globe  will  turn  outward, 
by  the  action  of  the  external  rectus ;  but  if  the  head  be  turned  outward,  the 
globe  remains  motionless. 

It  is  somewhat  difficult  to  note  the  effects  of  paralysis  of  the  inferior 
oblique  muscle,  which  also  is  supplied  by  the  third  nerve.  This  muscle,  act- 
ing from  its  origin  at  the  inferior  and  internal  part  of  the  circumference  of 
the  base  of  the  orbit,  to  its  attachment  at  the  inferior  and  external  part  of  the 
posterior  hemisphere  of  the  eyeball,  gives  to  the  globe  a  movement  of  rotation 
on  an  oblique,  horizontal  axis,  downward  and  backward,  directing  the  pupil 
upward  and  outward.  When  this  muscle  is  paralyzed,  the  superior  oblique, 


MOTOE  OCULI  COMMUNIS.  543 

having  no  antagonist,  rotates  the  globe  upward  and  inward,  directing  the  pupil 
downward  and  outward.  The  action  of  the  oblique  muscles  is  observed 
when  the  head  is  moved  alternately  toward  one  shoulder  and  the  other.  In 
the  human  subject,  when  the  inferior  oblique  muscle  on  one  side  is  paralyzed, 
the  eye  can  not  move  in  a  direction  opposite  to  the  movements  of  the  head,  as 
it  does  upon  the  sound  side,  so  as  to  keep  the  pupil  fixed,  and  the  patient  has 
double  vision. 

When  all  the  muscles  of  the  eyeball,  except  the  external  rectus  and  supe- 
rior oblique,  are  paralyzed,  as  they  are  by  section  of  the  third  nerve,  the  globe 
is  slightly  protruded,  simply  by  the  relaxation  of  most  of  its  muscles.  An 
opposite  action  is  easily  observed  in  a  cat  with  the  facial  nerve  divided  so 
that  it  can  not  close  the  lids.  When  the  cornea  is  touched,  all  of  the  muscles, 
particularly  the  four  recti,  act  to  draw  the  globe  into  the  orbit,  which  allows 
the  lid  to  fall  slightly,  and  projects  the  little  membrane  which  serves  as  a 
third  eyelid  in  these  animals. 

The  third  nerve  sends  a  filament  to  the  ophthalmic  ganglion  of  the  sym- 
pathetic, and  from  this  ganglion,  the  short  ciliary  nerves  take  their  origin 
and  pass  to  the  iris.  While  it  is  undoubtedly  true  that  division  of  the  third 
nerve  affects  the  movements  of  the  iris,  it  becomes  a  question  whether  this 
be  a  direct  influence  or  an  influence  exerted  primarily  upon  the  ganglion,  not 
perhaps,  differing  from  the  general  effects  upon  the  sympathetic  ganglia  that 
follow  destruction  of  their  branches  of  communication  with  the  motor 
nerves. 

Herbert  Mayo  (1823)  made  experiments  on  thirty  pigeons,  living  or  just 
killed,  upon  the  action  of  the  optic,  the  third  and  the  fifth  nerves,  on  the 
iris.  When  the  third  nerves  were  divided  in  the  cranial  cavity  in  a  living 
pigeon,  the  pupils  became  fully  dilated  and  did  not  contract  on  the  admission 
of  intense  light ;  and  when  the  same  nerves  were  pinched  in  the  living  or 
dead  bird,  the  pupils  were  contracted  for  an  instant  on  each  stimulation  of 
the  nerves.  The  same  results  followed  division  or  stimulation  of  the  optic 
nerves,  under  similar  conditions ;  but  when  the  third  nerves  had  been 
divided,  no  change  in  the  pupil  ensued  upon  stimulating  the  entire  or 
divided  optic  nerves. 

The  third  nerves  animate  the  muscular  fibres  that  contract  the  pupil,  the 
contraction  produced  by  stimulation  of  the  optic  nerves  being  reflex  in  its 
character.  Longet  divided  the  motor  oculi  and  the  optic  nerve  upon  the  right 
side.  He  found  that  stimulation  of  the  central  end  of  the  divided  optic 
nerve  produced  no  movement  of  the  pupil  of  the  side  upon  which  the  motor 
oculi  had  been  divided,  but  caused  contraction  of  the  iris  upon  the  opposite 
side.  This,  taken  in  connection  with  the  fact  that  in  amaurosis  affecting  one 
eye,  the  iris  upon  the  affected  side  will  not  contract  under  the  stimulus  of 
light  applied  to  the  same  eye,  but  will  act  when. the  uninjured  eye  is  exposed 
to  the  light,  farther  illustrates  the  reflex  action  which  takes  place  through 
these  nerves. 

The  reflex  action  by  which  the  iris  is  contracted  is  not  instantaneous,  like 
most  of  the  analogous  phenomena  observed  in  the  cerebro-spinal  system,  and 


544  NERVOUS  SYSTEM. 

its  operations  are  rather  characteristic  of  the  action  of  the  sympathetic  sys- 
tem and  the  non-striated  muscular  tissue.  It  has  been  found,  also,  by  Ber- 
nard, in  experiments  upon  rabbits,  that  the  pupil  is  not  immediately  dilated 
after  division  of  the  third  nerve.  The  method  employed  by  Bernard,  intro- 
ducing a  hook  into  the  middle  temporal  fossa  through  the  orbit  and  tearing 
the  nerve,  can  hardly  be  accomplished  without  touching  the  ophthalmic 
branch  of  the  fifth,  which  produces  intense  pain  and  is  always  followed  by  a 
more  or  less  persistent  contraction  of  the  pupil.  Several  hours  after  the  op- 
eration, however,  the  pupil  is  generally  found  dilated,  and  it  may  slowly  con- 
tract when  the  eye  is  exposed  to  the  light.  In  one  experiment  this  occurred 
after  the  eye  had  been  exposed  for  an  hour.  Farther  experiments  have  shown 
that  although  the  pupil  contracts  feebly  and  slowly  under  the  stimulus  of 
light  after  division  of  the  motor  oculi,  it  will  dilate  under  the  influence  of 
belladonna  and  can  be  made  to  contract  by  operating  upon  other  nerves.  It 
is  well  known,  for  example,  that  division  or  stimulation  of  the  fifth  nerve 
produces  contraction  of  the  pupil.  This  takes  place  after  as  well  as  before  di- 
vision of  the  third  nerve.  Section  of  the  sympathetic  in  the  cervical  region 
also  contracts  the  pupil,  and  this  occurs  after  paralysis  of  the  motor  oculi. 
These  facts  show  that  the  third  nerve  is  not  the  only  one  capable  of  acting 
upon  the  iris  and  that  it  is  not  the  sole  avenue  for  the  transmission  of  reflex 
influences. 

Bernard  also  found  that  stimulation  of  the  motor  oculi  itself  did  not  pro- 
duce contraction  of  the  pupil,  but  this  result  followed  when  he  stimulated 
the  ciliary  nerves  coming  from  the  ophthalmic  ganglion.  Chauveau,  in  experi- 
ments upon  horses,  did  not  observe  contraction  of  the  pupil  following  stimula- 
tion of  the  motor  oculi,  although  it  was  sometimes  seen  in  rabbits.  At  all 
events,  contraction  is  by  no  means  constant ;  and  when  it  occurs,  it  probably 
depends  upon  stimulation  of  the  ciliary  nerves  themselves  or  irritation  of  the 
ophthalmic  branch  of  the  fifth,  and  not  upon  stimulation  of  the  trunks  of 
the  third  pair.  When  the  eye  is  turned  inward  by  a  voluntary  effort,  the  pu- 
pil is  contracted ;  and  when  the  axes  of  the  two  eyes  are  made  to  converge 
strongly,  as  in  looking  at  near  objects,  the  contraction  is  very  considerable 
(Miiller). 

The  third  nerve  contains  filaments  which  preside  over  voluntary  move- 
ments of  the  ciliary  muscle  in  the  accommodation  of  the  eye  to  vision  at  dif- 
ferent distances. 

The  following  case  illustrates,  in  the  human  subject,  nearly  all  of  the 
phenomena  following  paralysis  of  the  motor  oculi  communis  in  experiments 
upon  the  lower  animals : 

The  patient  was  a  girl,  nineteen  years  of  age,  with  complete  paralysis  of 
the  nerve  upon  the  left  side.  There  was  slight  protrusion  of  the  eyeball,  com- 
plete ptosis,  with  the  pupil  moderately  dilated  and  insensible  to  ordinary 
impressions  of  light.  The  sight  was  not  affected,  but  there  was  double  vision, 
except  when  objects  were  placed  before  the  eyes  so  that  the  axes  were  paral- 
lel, or  when  an  object  was  seen  with  but  one  eye.  The  axis  of  the  left  eye 
was  turned  outward,  but  it  was  not  possible  to  detect  any  deviation  upward 


PATHETICUS,  OR  TROCHLEARIS. 


545 


or  downward.  Upon  causing  the  patient  to  incline  the  head  alternately  to 
one  shoulder  and  the  other,  it  was  evident  that  the  affected  eye  did  not  rotate 
in  the  orbit  but  moved  with  the  head.  This  seemed  to  be  a  case  of  complete 
and  uncomplicated  paralysis  of  the  third  nerve. 

PATHETICUS,  OR  TROCHLEARIS  (FOURTH  NERVE). 

The  physiology  of  the  patheticus  is  very  simple  and  resolves  itself  into 
the  action  of  a  single  muscle,  the  superior  oblique. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  patheticus  is  from 
the  superior  peduncles  of  the  cerebellum  ;  but  it  may  be  easily  followed  to  the 
valve  of  Vieussens.  The  deep  roots  can  be  traced,  passing  from  without  in- 
ward, to  the  following  parts  :  One  filament  is  lost  in  the  substance  of  the 
peduncles  ;  other  filaments  pass  from  before  backward  into  the  valve  of  Vieus- 
sens and  are  lost,  and  a  few  pass  into  the  f  renulum  ;  a  few  filaments  pass 
backward  and  are  lost  in  the  corpora  quadrigemina  ;  but  the  greatest  number 
pass  to  the  median  line  a"nd  decussate  with  corresponding  filaments  from  the 
opposite  side.  The  fibres  can  be  traced  to  a  nucleus  in  the  floor  of  the  aque- 
duct of  Sylvius,  beneath  the  nucleus  of  the  third  nerve.  The  decussation  of 
the  fibres  of  origin  of  the  fourth  nerve  has  the  same  physiological  signifi- 
cance as  the  decussation  of  the  roots  of  the  third.  From  this  origin,  the 
patheticus  passes  into  the  orbit,  by  the  sphenoidal  fissure,  and  is  distributed  to 
the  superior  oblique  muscle  of  the  eyeball.  In  the  cavernous  sinus  it  receives 
branches  of  communication  from  the  ophthalmic  branch  of  the  fifth,  but 
these  are  not  closely  united  with  the 
nerve.  A  small  branch  passes  into  the 
tentorium,  and  one  joins  the  lachrymal 
nerve,  these,  however,  being  exclusively 
sensory  and  coming  from  the  ophthal- 
mic branch  of  the  fifth.  It  also  re- 
ceives a  few  filaments  from  the  sympa- 
thetic. 

Properties  and  Uses  of  the  Pathet- 
icus. —  Direct  observations  upon  the  pa- 
theticus in  living  animals  have  shown 
that  it  is  motor,  and  its  stimulation  ex- 
cites contraction  of  the  superior  oblique 
muscle  only.  This  muscle  arises  just 
above  the  inner  margin  of  the  optic  fo- 

ramen, passes  forward,  along   the  upper    FIG.  195.—  IXstribution  of  the  patheticus  (Hirsch- 

wall  of  the  orbit  at  its  inner  angle,  to  a  Ii0lfact?ry  nerve  .  .n'e^c  nerves;  m.  motor 
little,  cartilaginous  ring  which  serves  as 

a  pulley.       From  its  Origin  to  this  point 

*          •* 

it    is    muscular.         Its     tendon    becomes 

rounded  just  before  it  passes  through 

the  pulley,  where  it  makes  a  sharp  curve,  passes  outward  and  slightly  back- 

ward, and  becomes  spread  out  to  be  attached  to  the  globe,  at  the  superior  and 


passing  to  the  superior  oblique  muscle  ;  VI, 
motor  ocuh  externus  ;  1  ,  ganglion  of  Gasser  ; 
2  3,  4,  5,  6,  7,  8,  9,  10,  ophthalmic  division  of 
the  fifth  nerve,  with  its  branches. 


546 


NERVOUS  SYSTEM. 


external  part  of  its  posterior  hemisphere.  It  acts  upon  the  eyeball  from  the 
pulley  at  the  upper  and  inner  portion  of  the  orbit  as  the  fixed  point  and  ro- 
tates the  eye  upon  an  oblique,  horizontal  axis,  from  below  upward,  from 
without  inward  and  from  behind  forward.  By  its  action,  the  pupil  is  di- 
rected downward  and  outward.  It  is  the  antagonist  of  the  inferior  oblique, 
the  action  of  which  has  been  described  in  connection  with  the  motor  oculi 
communis.  When  the  patheticus  is  paralyzed,  the  eyeball  is  immovable,  as 
far  as  rotation  is  concerned.  When  the  head  is  moved  toward  the  shoulder, 
the  eye  does  not  rotate  to  maintain  the  globe  in  the  same  relative  position,  and 
there  is  double  vision. 

MOTOR  OCULI  EXTERNUS,  OR  ABDUCENS  (SIXTH  NERVE). 

Like  the  patheticus,  the  motor  oculi  externus  is  distributed  to  but  a  single' 
muscle.  Its  uses,  therefore,  are  apparent  from  a  study  of  its  distribution  and 
properties. 

Physiological  Anatomy.  —  The  apparent  origin  of  the  sixth  nerve  is  from 
the  groove  separating  the  anterior  corpus  pyramidale  of  the  medulla  oblon- 

gata  from  the  pons  Varolii,  from  the  up- 
per portion  of  the  medulla  and  from  the 
lower  portion  of  the  pons,  next  the  groove. 
Its  origin  at  this  point  is  by  two  roots  : 
an  inferior,  which  is  the  larger  and  comes 
from  the  corpus  pyramidale  ;  and  a  supe- 
rior root,  sometimes  wanting,  which  seems 
to  come  from  the  lower  portion  of  the 
pons.  All  anatomists  are  agreed  that  the 
deep  fibres  of  origin  of  this  nerve  pass  to 
the  gray  matter  in  the  floor  'of  the  fourth 
ventricle.  Vulpian  followed  these  fibres 
to  within  about  two-fifths  of  an  inch  (10 
mm.)  of  the  median  line,  but  they  could 
not  be  traced  beyond  this  point.  It  is 

FIG.  m^ 

i,  trunk  of  the  motor  oculi  communis,  with  decussate.     From  this  origin  the  nerve 

its  branches  (2,  3,  4,  5,  6,  7)  ;  8,  motor  oculi 

externus,  passing  to  the  external  rectus    paSSCS    into    the    Ol'blt    by    the    Sphenoidal 

muscle  ;  9,  filaments  of  the  motor  oculi  ex-    *  ,.,.        .,  -  . 

ternus,  anastomosing  with  the  sympathet-    IlSSUre  and  IS  distributed  exclusively  to  the 

ic  ;  10,  ciliary  nerves.  , 

external  rectus  muscle  of  the  eyeball.    In 

the  cavernous  sinus  it  anastomoses  with  the  sympathetic  through  the  carotid 
plexus  and  receives  a  filament  from  Meckel's  ganglion.  It  also  receives 
sensory  filaments  from  the  ophthalmic  branch  of  the  fifth.  It  is  thought  by 
some  anatomists  that  this  nerve  occasionally  sends  a  small  filament  to  the 
ophthalmic  ganglion  ;  and  it  was  stated  by  Longet  that  this  branch,  which 
is  exceptional,  exists  in  those  cases  in  which  paralysis  of  the  motor  oculi 
communis,  which  usually  furnishes  all  the  motor  filaments  to  this  ganglion, 
is  not  attended  with  immobility  of  the  iris. 

Properties  and  Uses  of  the  Motor  Oculi  Externus.  —  Direct  experiments 


NEEVE  OF  MASTICATION.  547 

have  shown  that  the  motor  oculi  externus  is  entirely  insensible  at  its  origin,  its 
stimulation  producing  contraction  of  the  external  rectus  muscle  and  no  pain. 
The  same  experiments  illustrate  the  action  of  the  nerve,  inasmuch  as  its 
stimulation  is  followed  by  contraction  of  the  muscle  and  deviation  of  the  eye 
outward.  Division  of  the  nerve  in  the  lower  animals  or  its  paralysis  in  the 
human  subject  is  attended  with  internal,  or  converging  strabismus,  due  to  the 
unopposed  action  of  the  internal  rectus  muscle. 

With  regard  to  the  associated  movements  of  the  eyeball,  it  is  important  to 
note  that  all  of  the  muscles  of  the  eye  which  have  a  tendency  to  direct  the 
pupil  inward  or  to  produce  the  simple  movements  upward  and  downward 
(the  internal,  inferior,  and  superior  recti)  are  animated  by  a  single  nerve,  the 
motor  oculi  communis,  this  nerve  also  supplying  the  inferior  oblique ;  and 
that  each  of  the  two  muscles  that  move  the  globe  so  as  to  direct  the  pupil 
outward,  except  the  inferior  oblique  (the  superior  oblique  and  the  external 
rectus),  is  supplied  by  a  special  nerve.  The  movements  of  the  eyeball  will 
be  described  more  minutely  in  connection  with  the  physiology  of  vision. 

NERVE  OF  MASTICATION  (THE  SMALL,  OR  MOTOR  KOOT  OF  THE  FIFTH 

NERVE). 

The  motor  root  of  the  fifth  nerve  is  entirely  distinct  from  its  sensory 
portion,  until  it  emerges  from  the  cranial  cavity,  by  the  foramen  ovale.  It  is 
then  closely  united  with  the  inferior  maxillary  branch  of  the  large  root ;  but 
at  its  origin  it  has  been  shown  to  be  motor,  and  its  section  in  the  cranial  cav- 
ity has  demonstrated  its  distribution  to  a  particular  set  of  muscles. 

Physiological  Anatomy. — The  apparent  origin  of  the  fifth  nerve  is  from 
the  lateral  portion  of  the  pons  Varolii.  The  small,  or  motor  root  arises  from 
a  point  a  little  higher  and  nearer  the  median  line  than  the  large  root,  from 
which  it  is  separated  by  a  few  fibres  of  the  white  substance  of  the  pons.  At 
the  point  of  apparent  origin,  the  small  root  presents  six  to  eight  rounded  fila- 
ments. If  a  thin  layer  of  the  pons  covering  these  filaments  be  removed,  the 
roots  will  be  found  penetrating  its  substance,  becoming  flattened,  passing 
under  the  superior  peduncles  of  the  cerebellum  and  going  to  a  gray  nucleus, 
with  large  multipolar  cells,  in  the  anterior  wall  of  the  fourth  ventricle,  near 
the  median  line.  At  this  point,  the  fibres  change  their  direction,  passing  from 
without  inward  and  from  behind  forward  toward  the  median  line,  the  fibres 
diverging  rapidly.  The  posterior  fibres  pass  to  the  median  line,  and  cer- 
tain of  them  decussate  with  fibres  from  the  opposite  side.  The  anterior 
fibres  pass  toward  the  aqueduct  of  Sylvius  and  are  lost.  The  fibres  become 
changed  in  their  character  when  they  are  followed  inward  beyond  the  ante- 
rior wall  of  the  fourth  ventricle.  Here  they  lose  their  white  color,  become 
gray  and  present  a  number  of  globules  of  gray  substance  between  their  fila- 
ments. 

From  the  origin  above  described,  the  small  root  passes  beneath  the  gan- 
glion of  Gasser — from  which  it  sometimes,  though  not  constantly,  receives  a 
filament  of  communication — lies  behind  the  inferior  maxillary  branch  of  the 
large  root,  and  passes  out  of  the  cranial  cavity,  by  the  foramen  ovale.  With- 


54-8 


NERVOUS  SYSTEM. 


in  the  cranium  the  two  roots  are  distinct ;  but  after  the  small  root  passes 
through  the  foramen,  it  is  united  by  a  mutual  interlacement  of  fibres  with 
the  sensory  branch. 

The  inferior  maxillary  nerve,  made  up  of  the  motor  root  and  the  inferior 
maxillary  branch  of  the  sensory  root,  just  after  it  passes  out  by  the  foramen 
ovale,  divides  into  two  branches,  anterior  and  posterior.  The  anterior  branch, 

which  is  the  smaller, 
is  composed  almost 
entirely  of  motor 
filaments  and  is  dis- 
tributed to  the  mus- 
cles of  mastication. 
It  gives  off  five 
branches.  The  first 
of  these  passes  to 
be  distributed  to 
the  masseter  mus- 
cle, in  its  course  oc- 
casionally giving  off 
a  small  branch  to 
the  temporal  mus- 
cle and  a  filament 
to  the  articulation 
of  the  inferior  max- 
illa with  the  tem- 
poral bone.  The 
two  deep  temporal 
branches  are  dis- 
tributed to  the  tem- 
poral muscle.  The 
buccal  branch  sends 
filaments  to  the 
external  pterygoid 
and  the  temporal 
muscles,  and  a  small 
branch  is  distribu- 
ted to  the  internal 

pterygoid  muscle.  From  the  posterior  branch,  which  is  chiefly  sensory  but 
contains  some  motor  filaments,  branches  are  sent  to  the  mylo-hyoid  muscle 
and  to  the  anterior  belly  of  the  digastric.  In  addition  the  motor  branch  of 
the  fifth  sends  filaments  to  the  tensor  muscles  of  the  velum  palati. 

The  above  description  gives  in  general  terms  the  distribution  of  the 
nerve  of  mastication,  without  taking  into  consideration  its  various  anastomo- 
ses, the  most  important  of  which  are  with  the  facial.  Experiments  have 
shown  that  the  buccinator  muscle  receives  no  motor  filaments  from  the  fifth 
but  is  supplied  entirely  by  the  facial.  The  buccal  branch  of  the  fifth  sends 


FIG.  197.— Distribution  of  the  small  root  of  the  fifth  nerve  (Hirschfeld). 
1,  branch  to  the  masseter  muscle  ;  2,  filament  of  this  branch  to  the  temporal 
muscle ;  3,  buccal  branch!  4,  branches  anastomosing  with  the  facial 
nerve  ;  5,  filament  from  the  buccal  branch  to  the  temporal  muscle  ;  6, 
branches  to  the  external  pterygoid  muscle ;  7,  middle  deep  temporal 
branch ;  8.  auriculo-temporal  nerve  ;  9,  temporal  branches  ;  10,  auricu- 
lar branches  ;  11,  anastomosis  with  the  facial  nerve  ;  12,  lingual  branch  ; 
13,  branch  of  the  small  root  to  the  mylo-hyoid  muscle  ;  14,  inferior  den- 
tal nerve,  with  its  branches  (15, 15) ;  16,  mental  branch  ;  17,  anastomosis 
of  this  branch  with  the  facial  nerve. 


NERVE  OF  MASTICATION. 


549 


motor  filaments  only,  to  the  external  pterygoid  and  the  temporal,  its  final 
branches  of  distribution  being  sensory  and  going  to  integument  and  to 
mucous  membrane. 

In  treating  of  the  physiology  of  digestion,  a  table  has  been  given  of  the 
muscles  of  mastication,  with  a  description  of  their  action.  It  will  be  seen  by 
reference  to  this  table  that  the  following  muscles  depress  the  lower  jaw  ;  viz., 
the  anterior  belly  of  the  digastric,  the  mylo-hyoid,  the  genio-hyoid  and  the 
platysma  myoides.  Of  these  the  digastric  and  the  mylo-hyoid  are  animated 
by  the  motor  root  of  the  fifth  ;  the  genio-hyoid  is  supplied  by  filaments  from 
the  sublingual  ;  and  the  platysma  myoides,  by  branches  from  the  facial  and 
from  the  cervical  plexus.  All  of  the  muscles  which  elevate  the  lower  jaw 
and  move  it  laterally  and  antero-posteriorly  ;  viz.,  the  temporal,  masseter,  and 
the  internal  and  external  pterygoids—  the  muscles  most  actively  concerned  in 
mastication  —  are  animated  by  the  motor  root  of  the  fifth. 

Properties  and  Uses  of  the  Nerve  of  Mastication.  —  The  anatomical  dis- 
tribution of  the  small  root  of  the  fifth  nerve  points  at  once  to  its  uses. 
Charles  Bell,  whose  ideas  of  the  nerves  were  derived  almost  entirely  from 
their  anatomy,  called  it  the  nerve  of  mastication,  in  1821,  although  he  did 
not  state  that  any  experiments  were  made  with  regard  to  its  action.  All  ana- 
tomical and  physiological  writers  since  that  time  have  adopted  this  view.  It 
would  be  difficult  if  not  impossible  to  stimulate  the  root  in  the  cranial  cav- 
ity in  a  living  animal  ;  but  its  Faradization  in  animals  just  killed  determines 
very  marked  movements  of  the  lower  jaw.  Experiments  have  demonstrated 
the  physiological  properties  of  the  small  root,  which  is  without  doubt  solely 
a  nerve  of  motion. 

The  observations  upon  section  of  the  fifth  pair  in  the  cranial  cavity 
are  most  important  in  connection  with  the  uses  of  its  sensory  branches  and 
will  be  referred  to  in  detail  in  treating  of 
the  properties  of  the  large  root.  In  addi- 
tion to  the  loss  of  sensibility  following  sec- 
tion of  the  entire  nerve,  Bernard  noted 
the  effects  of  division  of  the  small  root, 
which  can  not  be  avoided  in  the  operation. 
In  rabbits  the  paralysis  of  the  muscles  of 
mastication  upon  one  side,  and  the  con- 
sequent action  of  the  muscles  upon  the 
unaffected  side  only,  produce,  a  few  days 
after  the  operation,  a  remarkable  change 
in  the  appearance  of  the  incisor  teeth.  . 

As  the    teeth    in    these    animals  are  2Tadu-    B'  incisors,  seven  days  after  section  of  the 

nerve  on  one  side. 

ally  worn  away  in  mastication  and  repro- 

duced, the  lower  jaw  being  deviated  by  the  action  of  the  muscles  of  the 
sound  side,  the  upper  incisor  of  one  side  and  the  lower  incisor  of  the  other 
touch  each  other  but  slightly  and  the  teeth  are  worn  unevenly.  This  makes 
the  line  of  contact  between  the  four  incisors,  when  the  jaws  are  closed,  ob- 
lique instead  of  horizontal. 


ormal  condition. 


550  NERVOUS  SYSTEM. 

There  is  little  left  to  say  with  regard  to  the  uses  of  the  motor  root  of  the 
fifth  nerve,  in  addition  to  the  description  of  the  action  of  the  muscles  of  mas- 
tication, contained  in  the  chapters  on  digestion,  except  as  regards  the  action 
of  the  filaments  sent  to  the  muscles  of  the  velum  palati.  In  deglutition  the 
muscles  of  mastication  are  indirectly  involved.  This  act  can  not  be  well 
performed  unless  the  mouth  be  closed  by  these  muscles.  When  the  food  is 
brought  in  contact  with  the  velum  palati,  muscles  are  brought  into  action 
which  render  this  membrane  tense,  so  that  the  opening  is  adapted  to  the 
size  of  the  alimentary  bolus.  These  muscles  are  animated  by  the  motor  root 
of  the  fifth.  This  nerve,  then,  is  not  only  the  nerve  of  mastication,  animat- 
ing all  of  the  muscles  concerned  in  this  act,  except  two  of  the  most  unimpor- 
tant depressors  of  the  lower  jaw  (the  genio-hyoid  and  the  platysma  myoides), 
but  it  is  concerned  indirectly  in  deglutition. 

FACIAL,  OK  NERVE  OF  EXPRESSION  (SEVENTH  NERVE). 

The  anatomical  relations  of  the  facial  nerve  are  quite  intricate  and  it 
communicates  freely  with  other  nerves.  As  far  as  can  be  determined  by  exper- 
iments upon  living  animals,  this  nerve  is  exclusively  motor  at  its  origin ;  but 
in  its  course  it  presents  anastomoses  with  the  sympathetic,  with  branches  of 
the  fifth  and  with  the  cervical  nerves,  undoubtedly  receiving  sensory  filaments. 

Physiological  Anatomy. — The  facial  nerve  has  its  apparent  origin  from 
the  lateral  portion  of  the  medulla  oblongata,  in  the  groove  between  the  oli- 
vary and  restiform  bodies,  just  below  the  border  of  the  pons  Varolii,  its 
trunk  being  internal  to  the  trunk  of  the  auditory  nerve.  It  is  separated  from 
the  auditory  by  the  two  filaments  constituting  what  is  known  as  the  interme- 
diary nerve  of  Wrisberg,  or  the  portio  inter  duram  et  mollem.  As  this  little 
nerve  joins  the  facial,  it  is  usually  included  in  its  root. 

Many  anatomists  have  endeavored  to  trace  the  fibres  of  the  facial  from 
their  point  of  emergence  from  the  encephalon  to  their  true  origin,  but  with 
results  not  entirely  satisfactory.  Its  fibres  pass  inward,  with  one  or  two  de- 
viations from  a  straight  course,  to  the  floor  of  the  fourth  ventricle,  where 
they  spread  out  and  become  fan-shaped.  In  the  floor  of  the  fourth  ventricle 
certain  of  the  fibres  have  been  thought  to  terminate  in  the  cells  of  the  gray 
substance,  and  others  have  been  traced  to  the  median  line,  where  they  decus- 
sate ;  the  course  of  most  of  the  fibres,  however,  has  not  been  satisfactorily 
established.  The  fibres  of  origin  of  the  intermediary  nerve  of  Wrisberg  have 
been  traced  to  the  nucleus  of  the  glosso-pharyngeal. 

It  is  evident  from  physiological  experiments,  that  the  decussation  of  the 
fibres  in  the  floor  of  the  fourth  ventricle  itself  is  not  very  important.  Vul- 
pian  made,  in  dogs  and  rabbits,  a  longitudinal  section  in  the  middle  line  of 
the  ventricle,  which  would  necessarily  have  divided  the  fibres  passing  from 
one  side  to  the  other,  without  producing  notable  paralysis  of  the  facial  nerves 
upon  either  side.  This  single  fact  is  sufficient  to  show  that  the  main  decus- 
sation of  the  fibres  animating  the  muscles  of  the  face  takes  place,  if  at  all,  at 
some  other  point. 

The  pathological  facts  bearing  upon  the  question  of  decussation  of  the 


FACIAL  NERVE. 


551 


filaments  of  origin  of  the  facial  have  long  been  recognized.  They  are  in 
brief  as  follows :  When  there  is  a  lesion  of  the  brain-substance  anterior  to 
the  pons  Varolii,  the  phenomena  due  to  paralysis  of  the  facial  are  observed 
upon  the  same  side  as  the  hemiplegia,  opposite  the  side  of  injury  to  the  brain. 
When  the  lesion  is  either  in  the  pons  or  below  it,  the  face  is  affected  upon 
the  same  side,  and 
not  upon  the  side 
of  the  hemiplegia. 
This  is  called  alter- 
nate paralysis.  In 
view  of  these  facts, 
the  phenomenon  of 
hemiplegia  upon 
one  side  and  facial 
paralysis  upon  the « 
other  is  regarded 
as  indicating,  with 
tolerable  certainty, 
that  the  injury  to 
the  brain  has  oc- 
curred upon  the 
same  side  as  the 
facial  paralysis, 
either  within  or 
posterior  to  the 
pons  Varolii. 

As  already  stat- 
ed, the  fibres  of  or- 
igin of  the  facial 
have  been  traced  to 
the  floor  of  the 
fourth  ventricle, 
where  a  few  decus- 
sate but  most  of 
them  are  lost.  The 
question  now  is, 
whether  or  not  the 

fibres  pass  up  through  the  pons  and  decussate  above,  as  the  pathological  facts 
just  noted  would  seem  to  indicate.  Anatomical  researches  upon  this  point 
are  not  satisfactory,  and  the  existence  of  such  a  decussation  has  never  been 
clearly  demonstrated.  The  pathological  observations,  nevertheless,  remain ; 
and  however  indefinite  anatomical  researches  may  have  been,  there  can  be 
no  doubt  that  lesions  in  one  lateral  half  of  the  pons  affect  the  facial  upon 
the  same  side,  while  lesions  above  have  a  crossed  action.  The  most  that  can 
be  said  upon  this  point  is  that  it  is  a  reasonable  inference  from  pathological 
facts  that  the  nerves  decussate  anterior  to  the  pons. 


FIG.  199.— Superficial  branches  of  the  facial  and  the  fifth  (Hirschfeld). 
I,  trunk  of  the  facial ;  2,  posterior  auricular  nerve  ;  3,  branch  which  it  re- 
ceives from  the  cervical  plexus  ;  4,  occipital  branch  ;  5,  6,  branches  to  the 
muscles  of  the  ear ;  7,  digastric  branches ;  8,  branch  to  the  stylo-hyoid 
muscle  ;  9,  superior  terminal  branch  ;  10,  temporal  branches  ;  11,  frontal 
branches  ;  12,  branches  to  the  orbicularis  palpebrarum  ;  13,  nasal,  or  sub- 
orbital  branches  ;  14,  buccal  branches  ;  15,  inferior  terminal  branch  ;  16, 
mental  branches  ;  17,  cervical  branches  ;  18,  superficial  temporal  nerve 
(branch  of  the  fifth) ;  19,  20,  frontal  nerves  (branches  of  the  fifth) ;  21,  23, 
23,  24, 25, 26,  27,  branches  of  the  fifth  ;  28,  29,  30,  31,  32,  branches  of  the  cer- 
vical nerves. 


552  NERVOUS  SYSTEM. 

The  main  root  of  the  facial,  the  auditory  nerve  and  the  intermediary 
nerve  of  Wrisberg  pass  together  into  the  internal  auditory  meatus.  At  the 
bottom  of  the  meatus,  the  facial  and  the  nerve  of  Wrisberg  enter  the  aquae- 
ductus  Fallopii,  following  its  course  through  the  petrous  portion  of  the  tem- 
poral bone.  In  the  aqueduct  the  nerve  of  Wrisberg  presents  a  little,  ganglio- 
form  enlargement  (geniculate  ganglion)  of  a  reddish  color,  which  has  been 
shown  to  contain  nerve-cells.  The  main  root  and  the  intermediary  nerve 
then  unite  and  form  the  common  trunk  of  the  facial,  which  emerges  from 
the  cranial  cavity,  by  the  stylo-mastoid  foramen. 

In  the  aquaeductus  Fallopii  the  facial  gives  off  the  following  branches: 

1.  The  large  petrosal  branch  is  given  off  at  the  ganglioform  enlargement 
and  goes  to  Meckel's  ganglion. 

2.  The  small  petrosal  branch  is  given  off  at  the  ganglioform  enlargement 
or  a  very  short  distance  beyond  it  and  passes  to  the  otic  ganglion. 

3.  A  small  branch,  the  tympanic,  is  distributed  to  the  stapedius  muscle. 

4.  The  chorda  tympani  passes  through  the  cavity  of  the  tympanum  and 
joins  the  lingual  branch  of  the  inferior  maxillary  division  of  the  fifth,  as  it 
passes  between  the  two  pterygoid  muscles,  with  which  nerve  it  becomes 
closely  united. 

5.  Opposite  to  the  point  of  origin  of  the  chorda  tympani,  a  communicat- 
ing branch  passes  between  the  facial  and  the  pneumogastric,  connecting  these 
nerves  by  a  double  inosculation. 

The  five  branches  above  described  are  given  off  in  the  aquaaductus  Fal- 
lopii. The  following  branches  are  given  off  after  the  nerve  has  emerged 
from  the  cranial  cavity : 

1.  Just  after  the  facial  has  passed  out  at  the  stylo-mastoid  foramen,  it 
sends  a  small,  communicating  branch  to  the  glosso-pharyngeal  nerve.     This 
branch  is  sometimes  wanting. 

2.  The  posterior  auricular  nerve  is  given  off  by  the  facial,  a  little  below 
the  stylo-mastoid  foramen.     Its  superior  branch  is  distributed  to  the  re- 
trahens  aurem  and  the  attollens  aurem,     In  its  course  this  nerve  receives  a 
communicating  branch  of  considerable  size  from  the  cervical  plexus,  by  the 
auricularis  magnus.     It  sends  some  filaments  to  the  integument.     The  in- 
ferior, or  occipital  branch,  the  larger  of  the  two,  is  distributed  to  the  occipi- 
tal portion  of  the  occipito-frontalis  muscle  and  to  the  integument. 

3.  The  digastric  branch  is  given  off  near  the  root  of  the  posterior  auricu- 
lar.    It  is  distributed  to  the  posterior  belly  of  the  digastric  muscle.     In  its 
course  it  anastomoses  with  filaments   from  the   glosso-pharyngeal  nerve. 
From  the  plexus  formed  by  this  anastomosis,  filaments  are  given  off  to  the 
digastric  and  to  the  stylo-hyoid  muscle. 

4.  Near  the  stylo-mastoid  foramen,  a  small  branch  is  given  off,  which  is 
distributed  exclusively  to  the  stylo-hyoid  muscle. 

5.  Near  the  stylo-mastoid  foramen,  or  sometimes  a  little  above  it,  a  long, 
delicate  branch  is  given  off,  which  is  not  noticed  in  many  works  on  anatomy. 
It  is  described,  however,  by  Hirschfeld,  under  the  name  of  the  lingual  branch. 
It  passes  behind  the  stylo-pharyngeal  muscle,  and  then  by  the  sides  of  the 


FACIAL  NERVE.  553 

pharynx  to  the  base  of  the  tongue.  In  its  course  it  receives  one  or  two 
branches  from  the  glosso-pharyngeal  nerve,  which  are  nearly  as  large  as  the 
original  branch  from  the  facial.  As  it  passes  to  the  base  of  the  tongue,  it 
anastomoses  again  by  a  number  of  filaments  with  the  glosso-pharyngeal.  It 
then  sends  filaments  of  distribution  to  the  mucous  membrane  and  finally 
passes  to  the  stylo-glossus  and  palato-glossus  muscles. 

Having  given  off  these  branches,  the  trunk  of  the  facial  passes  through 
the  parotid  gland,  dividing  into  its  two  great  terminal  branches : 

1.  The  temporo-facial  branch,  the  larger,  passes  upward  and  forward  to 
be  distributed  to  the  superficial  muscles  of  the  upper  part  of  the  face ;  viz., 
the  attrahens  aurem,  the  frontal  portion  of  the  occipito-frontalis,  the  orbicu- 
laris  palpebrarum,  corrugator  supercilii,  pyramidalis  nasi,  levator  labii  supe- 
rioris,  levator  labii  superioris  alaeque  nasi,  the  dilators  and  compressors  of  the 
nose,  part  of  the  buccinator,  the  levator  anguli  oris  and  the  zygomatic  mus- 
cles.    In  its  course  it  receives  branches  of  communication  from  the  auriculo- 
temporal  branch  of  the  inferior  maxillary  nerve.     It  joins  also  with  the  tem- 
poral branch  of  the  superior  maxillary  and  with  branches  of  the  ophthalmic. 
It  thus  becomes  a  mixed  nerve  and  is  distributed  in  part  to  integument. 

2.  The  cervico-facial  nerve  passes  downward  and  forward  to  supply  the 
buccinator,  orbicularis  oris,  risorius,  levator  labii  inferioris,  depressor  labii 
inferioris,  depressor  anguli  oris  and  platysma. 

General  Properties  of  the  Facial  Nerve. — It  has  long  been  recognized 
that  the  facial  is  the  motor  nerve  of  the  superficial  muscles  of  the  face  and 
that  its  division  produces  paralysis  of  motion  and  no  marked  effects  upon 
sensation.  It  is  evident,  also,  from  the  communications  of  the  facial  with 
the  fifth,  that  it  probably  contains  in  its  course  sensory  fibres.  Indeed,  all 
who  have  operated  upon  this  nerve  have  found  that  it  is  slightly  sensory 
after  it  has  emerged  from  the  cranial  cavity.  It  is  a  question,  however,  of 
great  importance  to  determine  whether  -or  not  the  facial  be  endowed  with 
sensibility  by  virtue  of  its  own  fibres  of  origin.  The  main  root  is  evidently 
from  the  motor  tract,  resembles  the  anterior  roots  of  the  spinal  nerves,  and 
is  distributed  to  muscles ;  but  this  root  is  joined  by  the  intermediary  nerve 
of  Wrisberg,  which  presents  a  small,  ganglionic  enlargement,  that  is  analo- 
gous to  the  ganglia  upon  the  posterior  roots  of  the  spinal  nerves.  The  testi- 
mony of  direct  experimentation  is  in  favor  of  the  insensibility  of  the  facial 
at  its  origin.  It  is  true  that  the  intermediary  nerve  of  Wrisberg  has  a  cer- 
tain anatomical  resemblance  to  the  sensory  nerves,  chiefly  by  reason  of  its 
ganglioform  enlargement ;  but  direct  experiments  are  wanting  to  show  that 
it  is  sensory. 

Uses  of  the  Branches  of  the  Facial  given  off  within  the  Aqueduct  of  Fal- 
lopius. — The  first  branch,  the  large  petrosal,  is  the  motor  root  of  Meckel's 
ganglion.  This  will  be  referred  to  again,  in  connection  with  the  sympathetic 
system.  The  second  branch,  the  small  petrosal,  is  one  of  the  motor  roots  of 
the  otic  ganglion  of  the  sympathetic.  The  third  branch,  the  tympanic,  is 
distributed  exclusively  to  the  stapedius  muscle.  The  second  and  third 
branches  will  be  again  considered,  in  connection  with  the  physiology  of  the 


554: 


NERVOUS  SYSTEM. 


internal  ear.  The  fourth  branch,  the  chorda  tympani,  is  so"  important  that 
it  demands  special  consideration.  The  fifth  branch  is  given  off  opposite  the 
origin  of  the  chorda  tympani  and  passes  to  the  pneumogastric,  to  which  nerve 
it  probably  supplies  motor  filaments.  In  this  branch,  sensory  filaments  pass 
from  the  pneumogastric  and  constitute  a  part  of  the  sensory  connections  of 
the  facial. 

Uses  of  the  Chorda  Tympani. — This  nerve  passes  between  the  bones  of 
the  ear  and  through  the  tympanic  cavity,  to  the  lingual  branch  of  the  infe- 
rior maxillary  division  of  the  fifth^ 
which  it  joins  at  an  acute  angle,  be- 
tween the  pterygoid  muscles.  As 
regards  the  portion  of  the  facial 
which  furnishes  the  filaments  of  the 
chorda  tympani,  it  is  nearly  certain 
that  these  come  from  the  intermedi- 
ary nerve  of  Wrisberg. 

There  can  be  no  doubt  with  re- 
gard to  the  influence  of  the  chorda 
tympani  upon  the  sense  of  taste  in 
the  anterior  two  -  thirds  of  the 
tongue.  In  cases  of  disease  or  in- 
jury in  which  the  root  of  the  facial 
is  involved  so  that  the  chorda  tym- 


FIG.  MO.-Chorda-tympani  nerve  (Hirschfeld). 


Pani  is  Paralyzed,  in  addition  to  the 
ordinary  phenomena  of  paralysis  of 
the  superficial  muscles  of  the  face, 
there  is  loss  of  taste  in  the  anterior  two-thirds  of  the  tongue,  upon  the  side 
corresponding  to  the  lesion.  The  action  of  the  chorda  tympani  will  be  con- 
sidered again,  in  connection  with  the  physiology  of  gustation. 

Influence  of  Various  Branches  of  the  Facial  upon  the  Movements  of  the 
Palate  and  Uvula.  —  There  can  be  little  doubt  that  filaments  from  the  facial 
animate  certain  of  the  movements  of  the  velum  palati  and  uvula.  It  has 
been  observed  that  in  certain  cases  of  facial  paralysis  the  palate  upon  one 
side  is  flaccid  and  the  uvula  is  drawn  to  the  opposite  side  ;  but  these  phe- 
nomena do  not  occur  unless  the  nerve  be  affected  at  its  root  or  within  the 
aquaeductus  Fallopii.  It  is  true  that  the  uvula  frequently  is  drawn  to  one 
side  or  the  other  in  persons  unaffected  with  facial  paralysis,  but  it  is  none 
the  less  certain  that  it  is  deviated  as  a  consequence  of  paralysis  of  the  facial 
in  some  instances.  The  filaments  of  the  facial  which  influence  the  levator 
palati  and  azygos  uvulae  muscles  are  derived  from  the  large  petrosal  branch 
of  the  nerve,  passing  to  the  muscles  through  Meckel's  ganglion,  the  filaments 
to  the  palato-glossus  and  the  palato-pharyngeus  being  given  off  from  the 
glosso-pharyngeal,  but  originally  coming  from  an  anastomosing  branch  of 
the  facial  (Longet).  As  regards  the  branches  of  communication  from  the 
glosso-pharyngeal,  Longet  has  mentioned  a  preparation  by  Richet,  in  the 
museum  of  the  Ecole  de  medecine,  of  Paris,  in  which  branches  of  the  facial 


FACIAL  NERVE.  555 

upon  one  side  pass  directly  to  the  palato-glossus  and  the  palato-pharyngeus, 
without  any  connection  with  the  glosso-pharyngeal  nerve.  In  the  anatomical 
description  of  the  branches  of  the  facial,  it  has  already  been  noted  that  a 
filament,  described  by  Hirschfeld,  passes  to  the  stylo-glossus  and  the  palato- 
glossus  muscles.  This  is  the  filament  affected  when  there  is  deviation  of  the 
point  of  the  tongue. 

In  view  of  the  examples  of  paralysis  of  the  palate  and  uvula  in  certain 
cases  of  facial  palsy,  the  frequent  occurrence  of  contractions  of  the  muscles 
of  these  parts  upon  stimulation  of  the  facial  and  the  reflex  action  through 
the  glosso-pharyngeal  and  the  facial,  there  can  be  little  doubt  that  the  mus- 
cles of  the  palate  and  uvula  are  animated  by  filaments  derived  from  the  sev- 
enth nerve.  The  effects  of  paralysis  of  these  muscles  are  manifested  by  more 
or  less  trouble  in  deglutition  and  in  the  pronunciation  or  certain  words,  with 
great  difficulty  in  the  expulsion  of  mucus  collected  in  the  back  part  of  the 
mouth  and  the  pharynx. 

Uses  of  the  External  Branches  of  the  Facial. — The  general  action  of  the 
branches  of  the  facial  going  to  the  superficial  muscles  of  the  face  is  suffi- 
ciently evident,  in  view  of  what  is  known  of  the  distribution  of  these  branches 
and  the  general  properties  of  the  nerve.  Throughout  the  writings  of  Charles 
Bell,  the  facial  is  spoken  of  as  the  "  respiratory  nerve  of  the  face."  It  is 
now  recognized  as  the  nerve  which  presides  over  the  movements  of  the  su- 
perficial muscles  of  the  face,  not  including  those  directly  concerned  in  the  act 
of  mastication.  This  being  its  general  action,  it  is  easy  to  assign  to  each  of 
the  external  branches  of  the  facial  its  particular  office. 

Just  after  the  facial  nerve  has  passed  out  at  the  stylo-mastoid  foramen,  it 
sends  to  the  glosso-pharyngeal  the  communicating  branch,  the  action  of  which 
has  just  been  mentioned  in  connection  with  the  movements  of  the  palate. 

The  posterior  auricular  branch,  becoming  partly  sensory  by  the  addition 
of  filaments  from  the  cervical  plexus,  gives  sensibility  to  the  integument  on 
the  back  part  of  the  ear  and  over  the  occipital  portion  of  the  occipito-fron- 
tulis  muscle.  It  animates  the  retrahens  and  the  attollens  aurem,  muscles  that 
are  little  developed  in  man  but  are  very  important  in  certain  of  the  inferior 
animals.  It  also  animates  the  posterior  portion  of  the  occipito-frontalis 
muscle. 

The  branches  distributed  to  the  posterior  belly  of  the  digastric  and  to 
the  stylo-hyoid  muscle  simply  animate  these  muscles,  one  of  the  uses  of 
which  is  to  assist  in  deglutition.  The  same  may  be  said  of  the  filaments 
that  go  to  the  stylo-glossus. 

The  two  great  branches  distributed  upon  the  face,  after  the  trunk  of  the 
nerve  has  passed  through  the  parotid  gland,  have  the  most  prominent  action. 
Both  of  these  branches  are  slightly  sensory,  from  their  connections  with 
other  nerves,  and  are  distributed  in  small  part  to  integument. 

The  temporo-facial  branch  animates  all  of  the  muscles  of  the  upper  part 
of  the  face.  In  complete  paralysis  of  this  branch,  the  eye  is  constantly  open, 
even  during  sleep,  on  account  of  paralysis  of  the  orbicularis  muscle.  In 
cases  of  long  standing,  the  globe  of  the  eye  may  become  inflamed  from  con- 


556 


NERVOUS  SYSTEM. 


stant  exposure,  from  abolition  of  the  movements  of  winking  by  which  the 
tears  are  distributed  over  its  surface  and  little  foreign  particles  are  removed, 
and,  in  short,  from  absence  of  the  protective  action  of  the  lids.  In  these 
cases  the  lower  lid  may  become  slightly  everted.  The  frontal  portion  of  the 
occipito-frontalis,  the  attrahens  aurem,  and  the  corrugator  supercilii  muscles, 
are  also  paralyzed.  The  most  prominent  symptom  of  paralysis  of  these  mus- 
cles is  inability  to  corrugate  the  brow  upon  one  side. 

Paralysis  of  the  muscles  that  dilate  the  nostrils  has  been  shown  to  have 
an  important  influence  upon  respiration  through  the  nose.  It  was  the  syn- 
chronism between  the  acts  of  dilatation  of  the  nostrils  and  the  movements  of 
inspiration  which  first  led  Charles  Bell  to  regard  the  facial  as  a  respiratory 
nerve.  In  instances  of  complete  paralysis  of  the  nostril  of  one  side,  there  is 
frequently  some  difficulty  in  inspiration,  even  in  the  human  subject. 

Charles  Bell  and  others  have  also  noted  an  interference  with  olfaction, 
due  to  the  inability  to  inhale  with  one  nostril,  in  cases  of  facial  paralysis. 


FIG.  204.  FIG.  205.  FIG.  206. 

Expressions  of  the  face  produced  by  contraction  of  the  muscles  under  electrical  excitation  (Le  Bon, 

after  Duchenne). 

Fig.  201,  front  view  of  the  face  in  repose. 
Fig.  202,  profile  view. 

Fig.  203,  expression  of  laughter  upon  one  side,  produced  by  contraction  of  the  zygomaticus  major. 
Fig.  204,  expression  of  lear,  produced  by  contraction  of  the  frontal  muscle  and  the  depressors  of  the 

lower  jaw. 

Fig.  205,  expression  of  fear,  profile  view. 
Fig.  206,  expression  of  fear  and  great  pain,  produced  by  contraction  of  the  corrugator  supercilii  and 

the  depressors  of  the  lower  jaw. 

The  influence  of  the  nerve  in  the  act  of  conveying  odorous  emanations  to  the 
olfactory  membrane  is  sufficiently  evident,  after  what  has  been  said  con- 
cerning the  action  of  the  facial  in  respiration. 

The  effects  of  paralysis  of  the  other  superficial  muscles  of  the  face  are 
manifested  in  the  distortion  of  the  features,  on  account  of  the  unopposed 
action  of  the  muscles  upon  the  sound  side,  a  phenomenon  which  is  suf- 


SPINAL  ACCESSORY  NERVE.  557 

ficiently  familiar.  When  facial  palsy  affects  one  side  and  is  complete,  the 
angle  of  the  mouth  is  drawn  to  the  opposite  side,  the  eye  upon  the  affected 
side  is  widely  and  permanently  opened,  even  during  sleep,  and  the  face  has 
upon  that  side  a  peculiarly  expressionless  appearance.  When  a  patient 
affected  in  this  way  smiles  or  attempts  to  grimace,  the  distortion  is  much 
increased.  The  lips  are  paralyzed  upon  one  side,  which  sometimes  causes  a 
flow  of  saliva  from  the  corner  of  the  mouth.  In  the  lower  animals  that  use 
the  lips  in  prehension,  paralysis  of  these  parts  interferes  considerably  with 
the  taking  of  food.  The  flaccidity  of  the  paralyzed  lips  and  cheek  in  the 
human  subject  sometimes  causes  a  puffing  movement  with  each  act  of  expi- 
ration, as  if  the  patient  were  smoking  a  pipe. 

The  buccinator  is  not  supplied  by  filaments  from  the  nerve  of  mas- 
tication but  is  animated  solely  by  the  facial.  Paralysis  of  this  muscle  inter- 
feres materially  with  mastication,  from  a  tendency  to  accumulation  of  the 
food  between  the  teeth  and  the  cheek.  Patients  complain  of  this  difficulty, 
and  they  sometimes  keep  the  food  between  the  teeth  by  pressure  with  the 
hand.  In  the  rare  instances  in  which  both  facial  nerves  are  paralyzed,  there 
is  very  great  difficulty  in  mastication,  from  the  cause  just  mentioned. 

The  action  of  the  external  branches  of  the  facial  is  thus  sufficiently  sim- 
ple ;  and  it  is  only  as  its  deep  branches  affect  the  sense  of  taste,  the  move- 
ments of  deglutition,  etc.,  that  it  is  difficult  to  ascertain  their  exact  office. 
As  this  is  the  nerve  of  expression  of  the  face,  it  is  in  the  human  subject  that 
the  phenomena  attending  its  paralysis  are  most  prominent.  When  both 
sides  are  affected,  the  aspect  is  remarkable,  the  face  being  absolutely  expres- 
sionless and  looking  as  if  it  were  covered  with  a  mask. 

SPINAL  ACCESSORY  (ELEVENTH  NERVE). 

The  spinal  accessory  nerve,  from  the  great  extent  of  its  origin,  its  impor- 
tant anastomoses  with  other  nerves  and  its  peculiar  course  and  distribution, 
has  long  engaged  the  attention  of  anatomists  and  physiologists,  who  have 
advanced  many  theories  with  regard  to  its  office.  Its  physiological  history, 
however,  begins  with  comparatively  recent  experiments,  which  alone  have 
given  a  positive  knowledge  of  its  properties  and  uses. 

Physiological  Anatomy — The  origin  of  this  nerve  is  very  extensive.  A 
certain  portion  arises  from  the  lower  half  of  the  medulla  oblongata,  and  the 
rest  takes  its  origin  below,  from  the  upper  two-thirds  of  the  cervical  portion 
of  the  spinal  cord.  That  portion  of  the  root  which  arises  from  the  medulla 
oblongata  is  called  the  bulbar  portion,  the  roots  from  the  cord  constituting 
the  spinal  portion.  Inasmuch  as  there  is  a  marked  difference  between  the 
uses  of  these  two  portions,  the  anatomical  distinction  just  mentioned  is  im- 
portant. 

The  superior  roots  arise  by  four  or  five  filaments,  from  the  lower  half  of 
the  medulla  oblongata,  below  the  origin  of  the  pneumogastrics.  These  fila- 
ments of  origin  pass  to  a  gray  nucleus  in  the  medulla,  below  the  origin  of 
the  pneumogastric. 

The  spinal  portion  of  the  nerve  arises  from  the  upper  part  of  the  spinal 
37 


NERVOUS  SYSTEM. 


cord,  between  the  anterior  and  posterior  roots  of  the  upper  four  or  five  cervi- 
cal nerves.  The  filaments  of  origin  are  six  to  eight  in  number.  The  most 
inferior  of  these  is  generally  single,  the  other  filaments  frequently  being 
arranged  in  pairs.  These  take  their  origin  from  the  lateral  portion  of  the 
cord  and  are  connected  with  the  anterior  cornua  of  gray  matter. 

Following  the  nerve  from  its  most  inferior  filament  of  origin  upward,  it 
gradually  increases  in  size  by  union  with  its  other  roots,  enters  the  cranial  cav- 
ity by  the  foramen  magnum,  and  passes  to  the  jugular  foramen,  by  which  it 
emerges,  with  the  glosso-pharyngeal,  the  pneumogastric  and  the  internal 
jugular  vein. 

In  its  course  the  spinal  accessory  anastomoses  witli  several  nerves.  Just 
as  it  enters  the  cranial  cavity,  it  receives  filaments  of  communication  from 

the  posterior  roots  of  the  upper  two 
cervical  nerves.  These  filaments,  how- 
ever, are  not  constant.  It  frequently 
though  not  constantly  sends  a  few  fila- 
ments to  the  superior  ganglion,  or  the 
ganglion  of  the  root  of  the  pneumogas- 
tric. After  it  has  emerged  by  the  jug- 
ular foramen  it  sends  a  branch  of  con- 
siderable size  to  the  pneumogastric,  from 
which  nerve  it  also  receives  a  few  fila- 
ments of  communication.  In  its  course 
it  also  receives  filaments  of  communica- 
tion from  the  anterior  branches  of  the 
second,  third,  and  fourth  cervical 
nerves. 

In  its  distribution  the  spinal  acces- 
sory presents  two  branches.  The  inter- 
nal, or  anastomotic  branch,  passes  to 
the  pneumogastric  just  below  the  plexi- 
form  enlargement  which  is  sometimes 
called  the  ganglion  of  the  trunk  of  the 
pneumogastric.  This  branch  is  com- 
posed principally  if  not  entirely  of  the 

filaments    that    take    their    Origin    from 

»•••,! 

,    ,  As  it  lOinS  the 

of  the  spinal  accessory;  5,  sublingual  nerve;  .  . 

6.  superior  cervical  ganglion  ;   7.  7,  anasto-     pneumogastric    it    Subdivides    into    two 
mosis  of  the  first  two  cervical  nerves  ;  8,  ca-  ,,  ,  m,         „  „    ,, 

rotid  branch  of  the  sympathetic;  9,  10,  ii,  12,   smaller  branches.      The  first  01  these 

13,  branches  of  the  glosso-pharyngeal:  14,  15,      „  .  „      ,,  ,  , 

branches  of  the  facial:  16,  otic  ganglion;  17,    forms    a    portion    of    the    pharyngcal 

branch  of  the  pneumogastric.     The  sec- 
The   ond  becomes  intimately  united  with  the 
pneumogastric,   lying    at   its   posterior 

nerves  ;  21,  pharyngenl  plexus  ;  22,  superior    „-._<.:„„     nriri  fiirr,ichp(j    filnmpnfq   tn    tho 
laryngeal    nerve  ;    23,    external    laryngeal    portion,  ana  lUmiSneS    niameniS   1 

nerve  ;  24,  middle  cervical  ganglion.  inferior,  or  recurrent  laryngeal  branch, 

which  is  distributed  to  all  of  the  muscles  of  the  larynx  except  the  crico- 


FIG.  Sm.-Spinal  accessory  nerve  (Hirschfeld). 
1,  trunk  of  the  facial  nerve  ;  2,  2,  glosso-pharyn- 

geal  nerve  ;  3,  3,  pneumogastric  ;  4,  4,  4,  trunk    the  medulla  ODlongata. 


nl'rves 


SPINAL  ACCESSOEY  NERVE.  559 

thyroid.  The  passage  of  the  filaments  from  the  spinal  accessory  to  the  pharyn- 
geal  branch  of  the  pneumogastric  is  easily  observed ;  but  the  fact  that  fila- 
ments from  this  nerve  pass  to  the  larynx  by  the  recurrent  laryngeal  has  been 
ascertained  by  physiological  experiments. 

The  external,  or  large  branch  of  the  spinal  accessory,  called  the  muscular 
branch,  penetrates  and  passes  through  the  posterior  portion  of  the  upper 
third  of  the  sterno-cleido-mastoid  muscle,  and  goes  to  the  anterior  surface  of 
the  trapezius,  which  muscle  receives  its  ultimate  branches  of  distribution. 
In  its  passage  through  the  sterno-cleido-mastoid,  it  joins  with  branches  from 
the  second  and  third  cervical  nerves  and  sends  filaments  of  distribution  to 
the  muscle.  Although  the  two  muscles  just  mentioned  receive  motor  fila- 
ments from  the  spinal  accessory,  they  are  also  supplied  from  the  cervical 
nerves;  and  consequently  they  are  not  entirely  paralyzed  when  the  spinal 
accessory  is  divided. 

Properties  and  Uses  of  the  Spinal  Accessory, — Notwithstanding  the  great 
difficulty  in  exposing  and  operating  upon  the  roots  of  the  spinal  accessory, 
it  has  been  demonstrated  that  their  stimulation  produces  convulsive  move- 
ments in  certain  muscles.  By  stimulating  the  filaments  that  arise  from  the 
medulla  oblongata,  contractions  of  the  muscles  of  the  pharynx  and  larynx 
are  produced,  but  no  movements  of  the  sterno-mastoid  and  trapezius.  Stim- 
ulation of  the  roots  arising  from  the  spinal  cord  produces  movements  of  the 
two  muscles  just  mentioned  and  absolutely  no  movements  in  the  larynx  (Ber- 
nard). In  view  of  these  experiments,  it  is  evident  that  the  true  filaments  of 
origin  of  the  spinal  accessory  are  motor ;  and  it  is  farther  evident  that  the 
filaments  from  the  medulla  oblongata  are  distributed  to  the  muscles  of  the 
pharynx  and  larynx,  while  the  filaments  from  the  spinal  cord  go  to  the  ster- 
no-cleido-mastoid and  trapezius. 

The  trunk  of  the  spinal  accessory,  after  the  nerve  has  passed  out  of  the 
cranial  cavity,  has  a  certain  degree  of  sensibility.  If  the  nerve  be  divided, 
the  peripheral  extremity  manifests  recurrent  sensibility,  but  the  central  end 
is  also  sensible,  probably  from  direct  filaments  of  communication  from  the 
cervical  nerves  and  the  pneumogastric. 

Uses  of  the  Internal  Branch  from  the  Spinal  Accessory  to  the  Pneumo- 
gastric.— Bischoff  attempted  to  ascertain  the  uses  of  this  branch  by  dividing 
the  roots  of  the  spinal  accessory  upon  both  sides  in  a  living  animal.  The 
results  of  his  experiments  may  be  stated  in  a  very  few  words :  He  attempted 
to  divide  all  of  the  roots  of  the  nerves  upon  both  sides  by  dissecting  down  to 
the  occipito-atloid  space  and  penetrating  into  the  cavity  of  the  spinal  canal. 
In  the  first  three  experiments  upon  dogs,  the  animals  died  so  soon  after  sec- 
tion of  the  nerves,  that  no  satisfactory  results  were  obtained.  In  two  suc- 
ceeding experiments  upon  dogs,  the  animals  recovered.  After  division  of 
the  nerves  the  voice  became  hoarse,  but  a  few  weeks  later  it  became  normal. 
On  killing  the  animals,  an  examination  of  the  parts  showed  that  some  of  the 
filaments  of  origin  had  not  been  divided.  An  experiment  was  then  made 
upon  a  goat,  but  this  was  unsatisfactory,  as  the  roots  were  not  completely 
divided.  Finally  another  experiment  was  made  upon  a  goat.  In  this  the 


560  NERVOUS  SYSTEM. 

results  were  more  satisfactory.  After  division  of  the  nerve  upon  one  side, 
the  voice  became  hoarse.  As  the  filaments  were  divided  upon  the  opposite 
side,  the  voice  was  enfeebled,  until  finally  it  became  extinct.  The  sound 
emitted  afterward  was  one  which  could  in  nowise  be  called  voice  ("  qui  neuti- 
quam  vox  appellari  potuit").  This  experiment  was  made  in  the  presence  of 
Tiedemann  and  Seubertus  and  was  not  repeated. 

Bernard,  who  determined  exactly  the  influence  of  the  spinal  accessory 
over  the  vocal  movements  of  the  larynx,  first  repeated  the  experiments  of 
Bischoff ;  but  the  animals  operated  upon  died  so  soon,  from  haemorrhage  or 
other  causes,  that  his  observations  were  not  satisfactory.  After  many  unsuc- 
cessful trials,  he  succeeded  in  overcoming  all  difficulties,  by  following  the 
trunk  of  the  nerve  back  to  the  jugular  foramen,  seizing  it  here  with  a  strong 
forceps  and  drawing  it  out  by  the  roots.  The  operation  is  generally  most 
successful  in  cats,  although  Bernard  succeeded  frequently  in  other  animals. 

When  one  spinal  accessory  is  extirpated,  the  vocal  sounds  are  hoarse  and 
unnatural.  When  both  nerves  are  torn  out,  in  addition  to  the  disturbance 
of  deglutition  and  the  partial  paralysis  of  the  sterno-mastoid  and  trapezius 
muscles,  the  voice  becomes  extinct.  Animals  operated  upon  in  this  way 
move  the  jaws  and  make  evident  efforts  to  cry,  but  no  vocal  sound  is  emitted. 
Bernard  kept  animals,  with  both  nerves  extirpated,  for  several  months  and 
did  not  observe  any  return  of  the  voice.  His  observations,  which  have  been 
fully  confirmed,  show  that  the  internal  branch  of  the  spinal  accessory  is  the 
nerve  of  phonation.  The  filaments  which  preside  over  the  vocal  movements 
of  the  larynx  pass  in  greatest  part  through  the  recurrent  laryngeal  branches 
of  the  pneumogastrics ;  but  the  recurrent  laryngeals  also  contain  motor  fila- 
ments from  other  sources,  which  latter  are  concerned  in  the  respiratory  move- 
ments of  the  glottis. 

Influence  of  the  Internal  Branch  of  the  Spinal  Accessory  upon  Degluti- 
tion.— There  are  two  ways  in  which  deglutition  is  affected  through  this 
nerve :  1.  When  the  larynx  is  paralyzed  as  a  consequence  of  extirpation  of 
both  nerves,  the  glottis  can  not  be  completely  closed  to  prevent  the  entrance 
of  foreign  bodies  into  the  air-passages.  In  rabbits  particularly,  it  has  been 
noted  that  particles  of  food  penetrate  the  trachea  and  find  their  way  into  the 
lungs.  2.  The  spinal  accessory  furnishes  filaments  to  the  pharyngeal  branch 
of  the  pneumogastric,  and  through  this  nerve,  it  directly  affects  the  muscles 
of  deglutition ;  but  the  muscles  animated  in  this  way  by  the  spinal  accessory 
have  a  tendency  to  draw  the  lips  of  the  glottis  together,  while  they  assist  in 
passing  the  alimentary  bolus  into  the  oesophagus.  When  these  important 
acts  are  wanting,  there  is  some  difficulty  in  the  process  of  deglutition  itself, 
as  well  as  danger  of  the  passage  of  foreign  particles  into  the  larynx. 

Influence  of  the  Spinal  Accessory  upon  the*Heart. — The  spinal  accessory 
furnishes  to  the  pneumogastric  the  inhibitory  fibres  which  influence  the 
action  of  the  heart.  A  sufficiently  powerful  Faradic  current,  passed  through 
one  pneumogastric  only,  will  in  some  animals  arrest  the  cardiac  movements. 
Waller  found  that  if  he  extirpated  the  spinal  accessory  upon  one  side,  after 
four  or  five  days  the  action  of  the  heart  could  not  be  arrested  by  stimulating 


SPINAL  ACCESSORY  NERVE.  561 

the  pneumogastric  upon  the  same  side ;  but  inhibition  followed  stimulation 
of  the  pneumogastric  upon  the  opposite  side,  on  which  the  connections  with 
the  spinal  accessory  were  intact.  In  these  observations,  it  seemed  necessary 
that  a  sufficient  time  should  elapse  after  extirpation  of  the  spinal  accessory 
for  the  excitability  of  the  filaments  that  join  the  pneumogastric  to  become 
extinct ;  but  the  experiments  are  sufficient  to  show  the  direct  inhibitory  in- 
fluence of  the  spinal  accessory  upon  the  heart.  After  extirpation  of  the  spi- 
nal accessory,  degenerated  fibres  are  found  in  the  trunk  of  the  pneumogastric. 
The  mechanism  of  inhibition  of  the  heart  has  already  been  considered  in 
connection  with  the  physiology  of  the  circulation. 

Uses  of  the  External,  or  Muscular  Branch  of  the  Spinal  Accessory. — 
Observations  have  shown  that  the  internal  branch  of  the  spinal  accessory, 
and  the  internal  branch  only,  is  directly  concerned  in  the  vocal  movements 
of  the  larynx,  and  to  a  great  extent,  in  the  closure  of  the  glottis  during 
deglutition.  It  has  been  noted,  in  addition,  that  animals  in  which  both 
branches  have  been  extirpated  present  irregularity  of  the  movements  of  the 
anterior  extremities  and  suffer  from  shortness  of  breath  after  violent  muscu- 
lar exertion.  The  use  of  the  corresponding  extremities  in  the  human  subject 
is  so  different,  that  it  is  not  easy  to  make  a  direct  application  of  these  experi- 
ments ;  still,  certain  inferences  may  be  drawn  from  them  with  regard  to  the 
action  of  the  external  branch  in  man. 

In  prolonged  vocal  efforts,  the  vocal  chords  are  put  upon  the  stretch,  and 
the  act  of  expiration  is  different  from  that  in  tranquil  breathing.  In  sing- 
ing, for  example,  the  shoulders  frequently  are  fixed ;  and  this  is  done  to  some 
extent  by  the  action  of  the  sterno-cleido-mastoid  and  the  trapezius.  It  is 
probable,  then,  that  the  action  of  the  branch  of  the  spinal  accessory  which  goes 
to  these  muscles  has  a  certain  synchronism  with  the  action  of  the  branch  going 
to  the  larynx  and  the  pharynx ;  the  one  fixing  the  upper  part  of  the  chest  so 
that  the  expulsion  of  the  air  through  the  glottis  may  be  more  nicely  regu- 
lated by  the  expiratory  muscles,  and  the  other  acting  upon  the  vocal  chords. 

In  what  is  known  as  muscular  effort,  the  glottis  is  closed,  the  thorax  is 
fixed  after  a  full  inspiration,  and  respiration  is  arrested  so  long  as  the  effort, 
if  it  be  not  too  prolonged,  is  continued.  The  same  synchronism,  therefore, 
obtains  in  this  as  in  prolonged  vocal  efforts.  In  experiments  in  which  the 
muscular  branch  only  has  been  divided,  shortness  of  breath,  after  violent 
muscular  effort,  is  observed ;  and  this  is  probably  due  to  the  want  of  syn- 
chronous action  of  the  sterno-cleido-mastoid  and  trapezius.  The  irregularity 
in  the  movements  of  progression  in  animals  in  which  either  both  branches 
or  the  muscular  branches  alone  have  been  divided  is  due  to  anatomical  pecul- 
iarities. Bernard  has  observed  these  irregularities  in  the  dog  and  the  horse, 
but  they  are  not  so  well  marked  in  the  cat.  There  have  been  no  opportuni- 
ties for  illustrating  these  points  in  the  human  subject. 

SUBLINGUAL   (TWELFTH   NERVE). 

The  last  of  the  motor  cranial  nerves  is  the  sublingual ;  and  its  action  is 
intimately  connected  with  the  physiology  of  the  tongue  in  deglutition  and 


562  NERVOUS  SYSTEM. 

articulation,  although  the  sublingual  is  also  distributed  to  certain  of  the 
muscles  of  the  neck. 

Physiological  Anatomy. — The  apparent  origin  of  the  sublingual  is  from 
the  medulla  oblongata,  in  the  groove  between  the  olivary  body  and  the 
anterior  pyramid,  on  the  line  of  the  anterior  roots  of  the  spinal  nerves.  At 
this  point,  its  root  is  formed  of  ten  to  twelve  filaments,  which  extend  from 
the  inferior  portion  of  the  olivary  body  to  about  the  junction  of  the  upper 
with  the  middle  third  of  the  medulla.  These  filaments  of  origin  are  sepa- 
rated into  two  groups,  superior  and  inferior.  From  this  apparent  origin,  the 
filaments  have  been  traced  into  the  gray  matter  of  the  floor  of  the  fourth 
ventricle,  between  the  deep  origin  of  the  pneumogastric  and  the  glosso- 
pharyngeal.  Although  there  is  much  difference  of  opinion  upon  this  point, 
it  is  probable  that  some  of  the  filaments  of  origin  of  these  nerves  decussate 
in  the  floor  of  the  fourth  ventricle.  The  superior  and  inferior  filaments  of 
origin  of  the  nerve  unite  to  form  two  bundles,  which  pass  through  distinct 
perforations  in  the  dura  mater.  These  two  bundles  then  pass  into  the  ante- 
rior condyloid  foramen  and  unite  into  a  single  trunk  as  they  emerge  from 
the  cranial  cavity. 

After  the  sublingual  has  passed  out  of  the  cranial  cavity,  it  anastomoses 
with  several  nerves.  It  sends  a  filament  of  communication  to  the  sympa- 
thetic as  it  branches  from  the  superior  cervical  ganglion.  Soon  after  it  has 
passed  through  the  foramen,  it  sends  a  branch  to  the  pneumogastric.  It 
anastomoses  by  two  or  three  branches  with  the  upper  two  cervical  nerves, 
the  filaments  passing  in  both  directions  between  the  nerves.  It  anastomoses 
with  the  lingual  branch  of  the  fifth,  by  two  or  three  filaments  passing  in  both 
directions. 

In  its  distribution  the  sublingual  presents  several  peculiarities : 

Its  first  branch,  the  descendens  noni,  passes  down  the  neck  to  the  sterno- 
hyoid,  sterno-thyroid  and  omo-hyoid  muscles. 

The  thyro-hyoid  branch  is  distributed  to  the  thyro-hyoid  muscle. 

The  other  branches  are  distributed  to  the  stylo-glossus,  hyo-glossus,  genio- 
hyoid  and  genio-hyo-glossus  muscles,  their  terminal  filaments  going  to  the 
intrinsic  muscles  of  the  tongue. 

It  is  thus  seen  that  the  sublingual  nerve  is  distributed  to  all  of  the  mus- 
cles in  the  infra-hyoid  region,  the  action  of  which  is  to  depress  the  larynx 
and  the  hyoid  bone  after  the  passage  of  the  alimentary  bolus  through  the 
pharynx ;  to  one  of  the  muscles  in  the  supra-hyoid  region,  the  genio-hyoid ; 
to  most  of  the  muscles  which  move  the  tongue ;  and  to  the  muscular  fibres 
of  the  tongue  itself.  The  action  of  these  muscles  and  of  the  tongue  itself  in 
deglutition  has  already  been  fully  discussed. 

Properties  and  Uses  of  the  Sublingual. — The  fact  that  the  sublingual 
nerve  arises  from  a  continuation  of  the  motor  tract  of  the  spinal  cord  and 
has  no  ganglion  upon  its  main  root  would  lead  to  the  supposition  that  it  is 
an  exclusively  motor  nerve.  In  operating  upon  the  roots  of  the  spinal  acces- 
sory— when  the  origin  of  the  sublingual  is  necessarily  exposed — Longet  has 
irritated  the  roots  in  the  dog,  without  any  evidence  of  pain  on  the  part  of 


SUBLINGUAL  NERVE. 


5G3 


the  animal.     Such  experiments,  taken  in  connection  with  the  anatomical 
characters  of  the  nerve,  render  it  almost  certain  that  its  root  is  devoid  of 


FIG.  208.— Distribution  of  the  sublingual  nerve  (Sappey). 

1,  root  of  the  fifth  nerve  ;  2,  ganglion  of  Gasser  ;  3,  4,  5,  6,  7,  9,  10,  12,  branches  and  anastomoses  of  the 
fifth  nerve  ;  11,  submaxillary  ganglion  ;  13,  anterior  belly  of  the  digastric  muscle  ;  14,  section  of  the 
mylo-hyoid  muscle  ;  15,  glosso-pharyngeal  nerve  ;  16,  ganglion  of  Andersen  ;  17,  18,  branches  of  the 
glosso-pharyngeal  nerve  ;  19,  19,  pneumogastric  ;  20,  21,  ganglia  of  the  pneumogastric  ;  22,  22,  su- 
perior laryngeal  branch  of  the  pneumogastric  ;  23,  spinal  accessory  nerve  ;  24,  sublingual  nerve  ; 
25,  descendens  noni ;  26.  thyro-hyoid  branch ;  27,  terminal  branches ;  28,  two  branches,  one  to  the 
genio-hyo-glossus  and  the  other  to  the  genio-hyoid  muscle. 

sensibility  at  its  origin.  All  modern  experimenters  have  confirmed  the 
observations  of  Mayo  and  of  Magendie,  with  regard  to  the  sensibility  of  the 
sublingual  after  it  has  passed  out  of  the  cranial  cavity.  The  anastomoses  of 
this  nerve  with  the  upper  two  cervical  nerves,  with  the  pneumogastric,  and 
with  the  lingual  branch  of  the  fifth,  afford  a  ready  explanation  of  this  fact. 

The  sublingual  may  be  easily  exposed  in  the  dog  by  making  an  incision 
just  below  the  border  of  the  lower  jaw,  dissecting  down  to  the  carotid  artery 
and  following  the  vessel  upward  until  the  nerve  is  seen  as  it  crosses  its  course. 
On  applying  a  feeble  Faradic  current  at  this  point,  there  are  evidences  of 
sensibility,  and  the  tongue  is  moved  at  each  stimulation. 

The  phenomena  following  section  of  both  sublingual  nerves  point  directly 
to  their  uses.  The  most  notable  fact  observed  after  this  operation  is  that 
the  movements  of  the  tongue  are  entirely  lost,  while  general  sensibility  and 
the  sense  of  taste  are  not  affected.  The  phenomena  which  follow  division  of 
these  nerves  consist  simply  in  loss  of  power  over  the  tongue,  with  considera- 
ble difficulty  in  deglutition. 


564 


NERVOUS  SYSTEM. 


In  the  human  subject  the  sublingual  is  usually  more  or  less  affected  in 
hemiplegia.  In  these  cases,  as  the  patient  protrudes  the  tongue  the  point  is 
deviated.  This  is  due  to  the  unopposed  action  of  the  genio-hyo-glossus  upon 
the  sound  side,  which,  as  it  protrudes  the  tongue,  directs  the  point  toward 
the  side  affected  with  paralysis. 

A  disease  of  rather  rare  occurrence  has  been  described  under  the  name 
of  glosso-labio-laryngeal  paralysis,  characterized  by  paralysis  of  the  muscles 
of  the  lips,  tongue,  soft  palate,  pharynx,  and  frequently  the  intrinsic  muscles 
of  the  larynx.  The  phenomena  referable  to  the  loss  of  power  over  the  tongue 
correspond  to  those  observed  in  animals  after  section  of  the  sublingual  nerves. 
Patients  affected  in  this  way  experience  difficulty  in  deglutition,  and  in  addi- 
tion there  is  some  interference  with  articulation,  which  can  not  be  observed 
in  experiments  upon  animals. 

TRIFACIAL  (LARGE  ROOT  OF  THE  FIFTH  NERVE). 

A  single  nerve,  the  large  root  of  the  fifth  pair,  called  the  trifacial  or  the 

trigeminal,  gives  general  sensibility  to 
the  face  and  to  the  head  as  far  back 
as  the  vertex.  This  nerve  is  impor- 
tant, not  only  as  the  great  sensitive 
nerve  of  the  face,  but  from  its  con- 
nections with  other  nerves  and  its  re- 
lations to  the  organs  of  special  sense. 
Physiological  Anatomy. — The  ap- 
parent origin  of  the  large  root  of  the 
fifth  is  from  the  lateral  portion  of  the 
pons  Varolii,  posterior  and  inferior  to 
the  origin  of  the  small  root,  from 
which  it  is  separated  by  a  few  trans- 
verse fibres  of  white  substance.  The 
deep  origin  is  far  removed  from  its 
point  of  emergence  from  the  encepha- 
lon.  The  roots  pass  entirely  through 
the  substance  of  the  pons,  from  with- 
out inward  and  from  before  back- 
ward, without  any  connection  with 
the  fibres  of  the  pons  itself.  By  this 
course  the  fibres  reach  the  medulla 
oblongata,  where  the  roots  divide  into 
three  bundles.  The  anterior  bundle 
passes  from  behind  forward,  between 
the  anterior  fibres  of  the  pons  and  the 
cerebellar  portion  of  the  restiform 
bodies,  to  anastomose  with  the  fibres 
of  the  auditory  nerve.  The  other 
bundles,  which  are  posterior,  pass,  the 


FIG.  209. — Principal  branches  of  the  large  root  of 
the  fifth  nerve  (Robin). 

a,  ganglion  of  Gasser ;  a-w.  ophthalmic  division 
of  the  fifth  ;  6,  ^ophthalmic  ganglion  ;  c, 
branch  from  the  ophthalmic  division  of  the 
fifth  to  the  ophthalmic  ganglion  ;  d,  motor 
oculi  communis  ;  e,  carotid  ;  /,  ciliary  nerves  : 
g,  cornea  and  iris  ;  a-h,  superior  maxillary  di- 
vision of  the  fifth  ;  i,  two  branches  from  the 
superior  maxillary  division  of  the  fifth  to  the 
'  spheno-palatine  ganglion  ;  j,  deep  petrosal 
nerve  ;  fc,  filaments  from  the  motor  root  of  the 
fifth  to  the  internal  muscle  of  the  malleus  :  I, 
naso-palatine  ganglion  ;  TO.  otic  ganglion  :  n, 
small  superficial  petrosal  nerve  ;  o,  branches 
of  the  fifth  to  the  submaxillary  ganglion  ;  p. 
branches  to  the  sublingual  aland  ;  g,  facial 
nerve  ;  r,  sympathetic  ganglion  :  s,  nerve  of 
mastication  :  t,  chorda  tympa-ni,  .joining  the 
lingual  branch  of  the  fifth  ;  u,  Vidian  nerve  : 
v,  branch  from  the  motor  root,  to  the  internal 
pterygoid  muscle  ;  w,  branch  of  the  fifth  to 
the  lachrymal  gland  ',  x.  bend  of  the  facial 
nerve  ;  ?/,  middle  meningeal  artery  ;  z,  fila- 
ment from  the  carotid  plexus,  to  the  ophthal- 
mic ganglion  ;  (1  and  2  are  not  in  the  figure)  3, 
external  spheno-palatine  filaments  ;  4,  spheno- 
palatine  ga.nglion  ;  5,  naso-palatine  nerve  ;  (i, 
anterior  palatine  nerve  ;  7,  inferior  maxillary 
division  of  the  fifth  ;  8,  nerve  of  Jacobson. 


TRIFACIAL  NEEVE. 


565 


one  in  the  anterior  wall  of  the  fourth  ventricle  to  the  lateral  tract  of  the 
medulla  oblongata,  and  the  other,  becoming  grayish  in  color,  to  the  restiform 
bodies,  from  which  they  may  be 
followed  as  far  as  the  point  of  the 
calamus  scriptorius,  A  few  fibres 
from  the  two  sides  decussate  at 
the  median  line,  in  the  anterior  3. 
wall  of  the  fourth  ventricle.  From 
this  origin,  the  large  root  of  the  £ 
fifth  passes  obliquely  upward  and  a. 
forward  to  the  ganglion  of  Gasser,  '- 
which  is  situated  in  a  depression  3 
in  the  petrous  portion  of  the  tem- 
poral bone,  on  the  internal  portion 
of  its  anterior  face. 

The  Gasserian  ganglion  is  semi- 
lunar  in  form,  with  its  concavity 
looking  upward  and  inward.  At 
the  ganglion  the  nerve  receives 
filaments  of  communication  from 
the  carotid  plexus  of  the  sym- 
pathetic. This  anatomical  point 
is  of  importance  in  view  of 
some  of  the  remote  effects  which 
follow  division  of  the  fifth  nerve 
through  the  ganglion  in  living 
animals. 

At    the    ganglion    of    Gasser, 
from  its  anterior  and  external  por- 
tion, are  given  off  a  few  small  and  unimportant  branches  to  the  dura  mater 
and  the  tentorium. 

From  the  convex  border  of  the  ganglion  the  three  great  divisions,  or 
branches  arise,  which  have  given  to  the  nerve  the  name  of  trifacial  or  tri- 
geminal.  These  are :  1,  the  ophthalmic ;  2,  the  superior  maxillary ;  3,  the 
inferior  maxillary.  The  ophthalmic  and  superior  maxillary  branches  are 
derived  entirely  from  the  sensory  root.  The  inferior  maxillary  branch  joins 
with  the  motor  root  and  forms  a  mixed  nerve. 

The  ophthalmic  branch,  the  first  division  of  the  fifth,  is  the  smallest  of 
the  three.  Before  it  enters  the  orbit  it  receives  filaments  of  communication 
from  the  sympathetic,  sends  small  branches  to  all  of  the  motor  nerves  of  the 
eyeball  and  gives  off  a  small  recurrent  branch  which  passes  between  the 
layers  of  the  tentorium. 

Just  before  the  ophthalmic  branch  enters  the  orbit  by  the  sphenoidal  fis- 
sure it  divides  into  three  branches,  the  lachrymal,  frontal  and  nasal. 

The  lachrymal,  the  smallest  of  the  three,  sends  a  branch  to  the  orbital 
branch  of  the  superior  maxillary  nerve,  passes  through  the  lachrymal  gland, 


FIG.  210.— Ophthalmic  division  of  the  fifth  (Hirschfeld). 

1,  ganglion  of  Gasser ;  2,  ophthalmic  division  of  the 
fifth  ;  3,  lachrymal  branch  ;  4,  frontal  branch  ;  5, 
external  frontal ;  6,  internal  frontal ;  7,  supratro- 
chlear ;  8,  nasal  branch  ;  9,  extei-nal  nasal ;  10,  in- 
ternal nasal ;  11,  anterior  deep  temporal  nerve  ; 
12,  middle  deep  temporal  nerve  ;  13,  posterior  deep 
temporal  nerve;  14,  origin  of  the  superficial  tempo- 
ral nerve;  15,  great  superficial  petrous  nerve. 

I  to  XII,  roots  of  the  cranial  nerves. 


566 


NERVOUS  SYSTEM. 


to  which  certain  of  its  filaments  are  distributed,  and  its  terminal  filaments 
go  to  the  conjunctiva  and  to  the  integument  of  the  upper  eyelid. 

The  frontal  branch,  the  largest  of  the  three,  divides  into  the  supratroch- 
lear  and  supraorbital  nerves.     The  supratroachlear  passes  out  of  the  orbit 

between  the  supraorbital 
foramen  and  the  pulley  of 
the  superior  oblique  mus- 
cle. It  sends  in  its  course 
a  long,  delicate  filament  to 
the  nasal  branch  and  is 
finally  lost  in  the  integu- 
ment of  the  forehead. 
The  supraorbital  passes 
through  the  supraorbital 
foramen,  sends  a  few  fila- 
ments to  the  upper  eye- 
lid, and  supplies  the  fore- 
head, the  anterior  and  the 
median  portions  of  the 

FIG.  211.—  Superior  maxillary  division  of  the  fifth  (Hirschfeld).  ,         ,  ,*~ 

1,  ganglion  of  Gasser;  2,  lachrymal  branch  of  the  ophthalmic  di-  SCalp,    the    HIUCOUS    mem- 

vision  ;  3,  superior  maxillary  division  of  the  fifth;  4,  orbital  V.rarlp  of  +1,  p  frfmtql  cirm« 

branch  ;  5,  lachrymo-palpebral  filament  ;  6,  malar  branch  ;  7,  ul  d11  ufe> 

temporal  branch;  8,   spheno-  palatine   ganglion;  9,   Vidian  Qnrl    +V>a  -rkovinT-aninm  r>r\ir 

nerve  ;  10,  great  superficial  petrosal  nerve  ;  11,  facial  nerve  ;  • 


orinrr  -Hio  frnr<fil  anrl  nor-i 
e   ln&  tj 


12,  branch  of  the  Vidian  nerve  ;  13,  anterior  and  two  posterior 
dental  branches  ;  14,  branch  to  the  mucous  membrane  of  the 
alveolar  processes  ;  15,  terminal  branches  of  the  superior  max- 
illary  division  ;  16,  branch  of  the  facial. 

The  nasal  branch,  be- 

fore it  penetrates  the  orbit,  gives  off  a  long,  delicate  filament  to  the  ophthal- 
mic ganglion.  It  then  gives  off  the  long  ciliary  nerves,  which  pass  to  the 
ciliary  muscle  and  iris.  Its  trunk  finally  divides  into  the  external  nasal,  or 
infratrochlearis,  and  the  internal  nasal,  or  ethmoidal.  The  infratrochlearis 
is  distributed  to  the  integument  of  the  forehead  and  nose,  to  the  internal 
surface  of  the  lower  eyelid,  the  lachrymal  sac  and  the  caruncula.  The  inter- 
nal nasal  is  distributed  to  the  mucous  membrane  and  also  in  part  to  the  in- 
tegument of  the  nose. 

The  superior  maxillary  branch  of  the  fifth  passes  out  of  the  cranial  cav- 
ity by  the  foramen  rotundum,  traverses  the  infraorbital  canal,  and  emerges 
upon  the  face  by  the  infraorbital  foramen.  Branches  from  this  nerve  are 
given  off  in  a  spheno-maxillary  fossa  and  the  infraorbital  canal,  before  it 
emerges  upon  the  face.  In  the  spheno-maxillary  fossa,  the  first  branch  is 
the  orbital,  which  passes  into  the  orbit,  giving  off  one  branch,  the  temporal, 
which  passes  through  the  temporal  fossa  by  a  foramen  in  the  malar  bone  and 
is  distributed  to  the  integument  on  the  temple  and  the  side  of  the  forehead. 
Another  branch,  the  malar,  which  likewise  emerges  by  a  foramen  in  the 
malar  bone,  is  distributed  to  the  integument  over  this  bone.  In  the  spheno- 
maxillary  fossa,  are  also  given  off  two  branches,  which  pass  to  the  spheno- 
palatine,  or  Meckel's  ganglion.  From  this  portion  of  the  nerve,  branches 
are  given  off,  the  two  posterior  dental  nerves,  which  are  distributed  to  the 


TRIFACIAL  NERVE. 


567 


molar  and  bicuspid  teeth,  the  mucous  membrane  of  the  corresponding  alve- 
olar processes  and  to  the  antrum. 

In  the  infraorbital  canal,  a  large  branch,  the  anterior  dental,  is  given  off 
to  the  teeth  and  mucous  membrane  of  the  alveolar  processes  not  supplied 
by  the  posterior  den- 
tal branches.     This 
branch  anastomoses 
with   the    posterior 
dental. 

The  terminal 
branches  upon  the 
face  are  distributed 
to  the  lower  eye- 
lid (the  palpebral 
branches),  to  the 
side  of  the  nose 
(the  nasal  branch- 
es), anastomosing 
with  the  nasal 
branch  of  the  oph- 
thalmic, and  to  the 
integument  and  the 
mucous  membrane 
of  the  upper  lip  (the 
labial  branches). 

The  inferior 
maxillary  is  a  mixed 
nerve,  composed  of 
the  inferior  division 
of  the  large  root 
and  the  entire  small 
root.  The  distribu- 
tion of  the  motor 
filaments  has  al- 
ready been  described.  This  nerve  passes  out  of  the  cranial  cavity  by  the  for- 
amen ovale,  and  then  separates  into  the  anterior  division,  containing  nearly 
all  of  the  motor  filaments,  and  the  posterior  division,  which  is  chiefly  sensory. 
The  sensory  portion  breaks  up  into  the  following  branches : 

1.  The  auriculo-temporal  nerve  supplies  the  integument  in  the  temporal 
region,  the  auditory  meatus,  the  integument  of  the  ear,  the  temporo-maxillary 
articulation  and  the  parotid  gland.     It  also  sends  branches  of  communica- 
tion to  the  facial. 

2.  The  lingual  branch  is  distributed  to  the  mucous  membrane  of  the 
tongue  as  far  as  the  point,  the  mucous  membrane  of  the  mouth,  the  gums, 
and  to  the  sublingual  gland.     This  nerve  receives  a  branch  from  the  facial 
(the  chorda  tympani)  which  has  already  been  described.     From  this  nerve, 


Fro.  212.— Inferior  maxillary  division  of  the  fifth  (Hirschfeld). 
1,  branch  from  the  motor  root  to  the  masseter  muscle  ;  2,  filaments  from 
this  branch  to  the  temporal  muscle  ;  3,  buccal  branch  ;  5,  6,  7,  branches 
to  the  muscles  ;  8,  auriculo-temporal  nerve  ;  9,  temporal  branches  ;  10, 
auricular  branches  ;  11,  anastomosis  with  the  faded  nerve  ;  12,  lingual 
branch;  13,  branch  of  the  motor  root  to  the  mylo-hyoid  muscle  ;  14,  15, 
15,  inferior  dental  nerve,  ivith  its  branches ;  16,  mental  branch ;  17, 
anastomosis  of  this  branch  with  the  facial  nerve. 


568 


NERVOUS  SYSTEM. 


also,  are  given  off  two  or  three  branches  which  pass  to  the  submaxillary 

ganglion. 

3.  The  inferior  dental  nerve,  the  largest  of  the  three,  passes  in  the  sub- 

stance of  the  inferior  maxillary  bone,  beneath  the  teeth,  to  the  mental  fora- 

men, where  it  emerges  upon  the  face.  The  most 
important  sensory  branches  are  those  which  sup- 
ply the  pulps  of  the  teeth  and  the  branches  upon 
the  face.  The  nerve,  emerging  upon  the  face 
by  the  mental  foramen,  called  the  mental  nerve, 
supplies  the  integument  of  the  chin  and  the 
lower  part  of  the  face  arid  the  lower  lip.  It  also 
sends  certain  filaments  to  the  mucous  membrane 
of  the  mouth. 

Properties  and  Uses  of  the  Trifacial.  —  The 
trifacial  is  the  great  sensory  nerve  of  the  face 
and  of  the  mucous  membranes  lining  the  cavi- 
ties about  the  head.  It  is  impossible  to  stimu- 
late this  nerve  at  its  origin  without  seriously  in- 

Fio.213.—  Limits  of  cutaneous  distri-  volving  other  parts,  but  all  observations  with 

button  of  sensory  nerves  to  the  -,     .        .-,  .  .  <•    11       i 

face,  head  and  neck  (Beciard).      regard  to  the  properties  of  the  large  root  go  to 

1,  cutaneous  distribution  of  the  oph-    5,],,-.,.,  +V,of  if  ia   ori    <3vr>lnaivplv  otmanrv  norvo  onrl 

thaimic  division  of  the  fifth  ;  2,  snow  tnat  it  is  an  exclusively  sensory  nerve  ana 
vbdi^nio0nf  •  t  *SffibSS£  that  its  sensibility  is  very  acute  as  compared  with 

nerves.  It  was  divided  in  the  cranial  cav- 
MaJ°  (1822-^3),  Fodera  (1823)  and  Ma- 

cafnerrvesbranches  °f  the  cervi"  gendie  (1824).  Magendie  divided  the  nerve  at 

its  root  by  introducing  a  small,  cutting  stylet 

through  the  skull.  He  succeeded  in  keeping  the  animals  alive  for  several 
days  or  weeks  and  noted  in  his  experiments  immediate  loss  of  sensibility  in 
the  face  on  the  side  on  which  the  nerve  was  divided.  The  operative  proced- 
ure employed  by  Magendie  has  been  followed  by  other  physiologists,  particu- 
larly Bernard,  who  made  a  number  of  important  observations  on  the  immedi- 
ate and  remote  effects  of  section  of  the  nerve.  The  section  is  usually  made 
through  the  ganglion  of  Gasser.  The  operation  is  difficult  on  account  of 
the  danger  of  wounding  large  blood-vessels.  AVhen  this  operation  is  per- 
formed without  accident,  the  cornea  and  the  integument  and  mucous  mem- 
brane upon  that  side  of  the  head  are  instantaneously  deprived  of  sensibility 
and  may  be  pricked,  lacerated  or  burned,  without  the  slightest  evidence  of 
pain  on  the  part  of  the  animal.  Almost  always  the  small  root  of  the  fifth 
is  divided  as  well  as  the  large  root,  and  the  muscles  of  mastication  are  para- 
lyzed upon  one  side  ;  but  with  this  exception,  there  is  no  paralysis  of  motion, 
sensation  alone  being  destroyed  upon  one  side. 

Immediate  Effects  of  Division  of  the  Trifacial,  —  This  nerve  has  never 
been  exposed  in  the  cranial  cavity  in  living  animals  ;  but  its  branches  upon 
the  face  and  the  lingual  branch  of  the  inferior  maxillary  division  have  been 
operated  upon  and  found  to  be  exquisitely  sensitive.  Physiologists  have  ex- 
posed the  roots  in  animals  immediately  after  death,  and  have  found  that 


ion;  4 


TEIFACIAL  NERVE.  569 

stimulation  of  the  large  root  carefully  insulated  produces  no  muscular  con- 
traction. All  who  have  divided  this  root  in  living  animals  must  have  recog- 
nized, not  only  that  it  is  sensitive,  but  that  its  sensibility  is  far  more  acute 
than  that  of  any  other  nervous  trunk  in  the  body. 

As  far  as  audition  and  olfaction  are  concerned,  there  are  no  special  effects 
immediately  following  section  of  the  trifacial ;  but  there  are  certain  impor- 
tant phenomena  observed  in  connection  with  the  eye  and  the  organs  of 
taste. 

At  the  instant  of  division  of  the  fifth,  the  eyeball  is  protruded  and  the 
pupil  becomes  strongly  contracted.  This  occurs  in  rabbits,  and  the  contrac- 
tion of  the  pupil  was  observed  in  the  first  operations  of  Magendie.  The 
pupil,  however,  usually  is  restored  to  the  normal  condition  in  a  few  hours. 
After  division  of  the  nerve  the  lachrymal  secretion  becomes  very  much  less 
in  quantity ;  but  this  is  not  the  cause  of  the  subsequent  inflammation,  for 
the  eyes  are  not  inflamed,  even  after  extirpation  of  both  lachrymal  glands 
(Magendie).  The  movements  of  the  eyeball  are  not  affected  by  division  of 
the  fifth. 

Another  of  the  immediate  effects  of  complete  division  of  the  fifth  nerve 
is  loss  of  general  sensibility  in  the  tongue.  Most  experiments  upon  the  influ- 
ence of  this  nerve  over  the  general  sensibility  and  the  sense  of  taste  in  the 
tongue  have  been  made  by  dividing  the  lingual  branch  of  the  inferior  maxil- 
lary division.  When  this  branch  is  irritated,  there  are  evidences  of  intense 
pain.  When  it  is  divided,  the  general  sensibility  and  the  sense  of  taste  are 
destroyed  in  the  anterior  portion  of  the  tongue.  It  will  be  remembered, 
however,  that  the  chorda  tympani  joins  the  lingual  branch  of  the  fifth  as  it 
passes  between  the  pterygoid  muscles,  and  that  section  of  this  branch  of  the 
facial  abolishes  the  sense  of  taste  in  the  anterior  two-thirds  of  the  tongue. 
If  the  gustatory  properties  of  the  lingual  branch  of  the  fifth  be  derived  from 
the  chorda  tympani,  lesions  of  the  fifth  not  involving  this  nerve  would  be 
followed  by  loss  of  general  sensibility,  but  the  taste  would  be  unaffected. 
This  has  been  shown  to  be  the  fact,  by  cases  of  paralysis  of  general  sensibility 
of  the  tongue  without  loss  of  taste  in  the  human  subject,  which  will  be  dis- 
cussed more  fully  in  connection  with  the  physiology  of  gustation. 

Among  the  immediate  effects  of  section  of  the  fifth,  is  an  interference 
with  the  reflex  phenomena  of  deglutition.  In  a  series  of  observations  upon 
the  action  of  the  sensory  nerves  in  deglutition,  by  Waller  and  Prevost,  it 
was  found  that  after  section  of  the  fifth  upon  both  sides,  it  was  impossible 
to  excite  movements  of  deglutition  by  stimulating  the  mucous  membrane  of 
the  velum  palati.  After  section  of  the  superior  laryngeal  branches  of  the 
pneumogastrics,  no  movements  of  deglutition  followed  stimulation  of  the 
mucous  membrane  of  the  top  of  the  larynx.  In  these  experiments,  when  the 
fifth  Avas  divided  upon  one  side,  stimulation  of  the  velum  upon  the  corre- 
sponding side  had  no  effect,  while  movements  of  deglutition  were  produced 
by  irritating  the  velum  upon  the  sound  side.  These  experiments  show  that 
the  fifth  nerve  is  important  in  the  reflex  phenomena  of  deglutition,  as  a  sen- 
sory nerve,  conveying  the  impression  from  the  velum  palati  to  the  nerve-cen- 


570  NERVOUS  SYSTEM. 

tres.  This  action  probably  takes  place  through  filaments  which,  pass  from 
the  fifth  to  the  mucous  membrane,  through  Meckel's  ganglion. 

Remote  Effects  of  Division  of  the  Trifacial. — After  section  of  the  fifth 
nerve  in  the  cranial  cavity,  the  immediate  loss  of  sensibility  of  the  integu- 
ment and  mucous  membranes  of  the  face  and  head  is  usually  supplemented 
by  serious  disturbances  in  the  nutrition  of  the  eye,  the  ear  and  the  mucous 
membranes  of  the  nose  and  mouth.  After  a  period  varying  between  a  few 
hours  and  one  or  two  days  after  the  operation,  the  eye  upon  the  affected  side 
becomes  the  seat  of  purulent  inflammation,  the  cornea  becomes  opaque  and 
ulcerates,  the  humors  are  discharged  and  the  organ  is  destroyed.  Conges- 
tion of  the  parts  is  usually  very  prominent  a  few  hours  after  division  of  the 
nerve.  At  the  same  time  there  is  an  increased  discharge  from  the  mucous 
membranes  of  the  nose  and  mouth  upon  the  affected  side,  and  ulcers  appear 
upon  the  tongue  and  lips.  It  is  probable,  also,  that  disorders  in  the  nutrition 
of  the  auditory  apparatus  follow  the  operation,  although  these  are  not  so 
prominent.  Animals  affected  in  this  way  usually  die  in  fifteen  to  twenty 
days. 

In  the  early  experiments  of  Magendie,  it  was  noted  that  "  the  alterations 
in  nutrition  are  much  less  marked  "  when  the  division  is  effected  behind  the 
ganglion  of  Gasser  than  when  it  is  done  in  the  ordinary  way  through  the 
ganglion.  It  is  difficult  enough  to  divide  the  nerve  completely,  within  the 
cranium,  and  is  almost  impossible  to  make  the  operation  at  will  through  or 
behind  the  ganglion ;  and  the  phenomena  of  inflammation  are  absent  only 
in  exceptional  and  accidental  instances.  Magendie  offered  no  satisfactory 
explanation  of  the  differences  in  the  consecutive  phenomena  coincident  with 
the  place  of  section  of  the  nerve.  The  facts,  however,  have  been  repeatedly 
verified.  In  a  number  of  experiments  in  which  the  nerve  was  divided  in  the 
cranial  cavity  (Flint),  the  consecutive  inflammatory  effects  were  almost  always 
observed;  but  in  an  experiment  made  in  1808,  the  nerve  was  completely 
divided  on  the  left  side,  as  was  shown  by  total  loss  of  sensibility  of  the  parts 
to  which  it  is  distributed,  and  the  animal  (a  rabbit)  lived  nearly  four  months. 
Four  days  after  the  operation  the  loss  of  sensibility  was  still  complete.  There 
was  very  little  redness  of  the  conjunctiva  of  the  left  eye,  and  a  very  slight 
streak  of  opacity,  so  slight  that  it  was  distinguished  with  difficulty.  Twelve 
days  after  the  operation  the  sensibility  of  the  left  eye  was  distinct  but  slight. 
There  was  no  redness  of  the  conjunctiva,  and  the  opacity  of  the  cornea  had 
disappeared.  The  animal  was  in  good  condition,  and  the  line  of  contact  of 
the  upper  with  the  lower  incisors,  when  the  jaws  were  closed,  was  very  oblique. 
The  animal  was  kept  alive  by  careful  feeding  with  bread  and  milk  for  one 
hundred  and  seven  days  after  the  operation,  and  there  was  no  inflammation 
of  the  organs  of  special  sense.  It  died  at  that  time  of  inanition,  having 
become  extremely  emaciated.  The  animal  never  recovered  power  over  the 
muscles  of  the  left  side,  and  the  incisors  grew  to  a  great  length,  interfering 
very  mucli  with  mastication. 

Longet,  in  1842,  gave  an  explanation  of  the  absence  of  inflammation  in 
certain  cases  of  division  of  the  fifth.  He  attributed  the  consecutive  inflaru- 


TEIFACIAL  NERVE.  571 

mation  in  most  experiments  to  lesion  of  the  ganglion  of  Gasser  and  of  the 
sympathetic  connections,  which  are  very  abundant  at  this  point.  Theso 
sympathetic  filaments  are  avoided  when  the  section  is  made  behind  the  gan- 
glion. 

The  explanation  of  the  phenomena  of  disordered  nutrition  in  the  organs 
of  special  sense,  particularly  the  eye,  following  division  of  the  fifth,  is  not 
afforded  by  the  section  of  this  nerve  alone ;  for  when  the  loss  of  sensibility 
is  complete  after  division  of  the  nerve  behind  the  Gasserian  ganglion,  these 
results  may  not  follow.  They  are  not  explained  by  deficiency  in  the  lachry- 
mal secretion,  for  they  are  not  observed  when  both  lachrymal  glands  have 
been  extirpated.  They  are  not  due  to  exposure  of  the  eyeball,  for  they  do 
not  follow  section  of  the  facial.  They  are  not  due  simply  to  an  enfee- 
bled general  condition,  for  in  the  experiment  just  detailed,  the  animal  died 
of  inanition  after  section  of  the  nerve,  without  any  evidences  of  inflam- 
mation. In  view  of  the  fact  that  section  of  the  sympathetic  filaments  is 
well  known  to  modify  nutrition  of  parts  to  which  they  are  distributed, 
producing  congestion,  increase  in  temperature  and  other  phenomena,  it  is 
rational  to  infer  that  the  modifications  in  nutrition  which  follow  section  of 
the  fifth  after  it  receives  filaments  from  the  sympathetic  system,  not  occur- 
ring when  these  sympathetic  filaments  escape  division,  are  to  be  attributed  to 
lesion  of  the  sympathetic  and  not  to  the  division  of  the  sensory  nerve  itself. 

A  farther  explanation  is  demanded  for  the  inflammatory  results  which 
follow  division  of  the  sympathetic  filaments  joining  the  fifth,  inasmuch  as 
division  of  the  sympathetic  alone  in  the  neck  simply  produces  exaggeration 
of  the  nutritive  processes,  as  evidenced  chiefly  by  local  increase  in  the  animal 
temperature,  and  not  the  well-known  phenomena  of  inflammation. 

It  was  remarked  by  Bernard  that  the  "  alterations  in  nutrition  appear 
more  promptly  in  animals  that  are  enfeebled."  Section  of  the  small  root  of 
the  fifth,  which  is  unavoidable  when  the  nerve  is  divided  within  the  cranial 
cavity,  generally  interferes  so  much  with  mastication  as  to  influence  seriously 
the  general  nutrition ;  and  this  might  modify  the  nutritive  processes  in  deli- 
cate organs,  like  the  eye,  so  as  to  induce  those  changes  which  are  called 
inflammatory.  The  following  observation  (W.  H.  Mason)  has  an  important 
bearing  on  this  question  : 

The  fifth  pair  of  nerves  was  divided  in  a  cat  in  the  ordinary  way.  By 
feeding  the  animal  carefully  with  milk  and  finely  chopped  meat,  the  nutri- 
tion was  maintained  at  a  high  standard,  and  no  inflammation  of  the  eye 
occurred  for  about  four  weeks.  The  supply  of  food  was  then  diminished  to 
about  the  quantity  it  would  be  able  to  take  without  any  special  care,  when 
the  eye  became  inflamed,  and  perforation  of  the  cornea  and  destruction  of 
the  organ  followed.  The  animal  was  kept  for  about  five  months ;  at  the  end 
of  which  time,  sensation  upon  the  affected  side,  which  had  been  gradually 
improving,  was  completely  restored. 

The  following  explains,  in  a  measure  at  least,  the  consecutive  inflamma- 
tory effects  of  section  of  the  fifth  with  its  communicating  sympathetic  fila- 
ments :  By  dividing  the  sympathetic,  the  eye  and  the  mucous  membranes  of 


572  NERVOUS  SYSTEM. 

the  noss,  mouth  and  ear  are  rendered  hyperasmic,  the  temperature  probably 
is  raised,  and  the  processes  of  nutrition  are  exaggerated.  This  condition 
of  the  parts  would  seem  to  require  a  full  supply  of  nutritive  material  from 
the  blood,  in  order  to  maintain  the  condition  of  exaggerated  nutrition ;  but 
when  the  blood  is  impoverished — probably  as  the  result  of  deficiency  in  the 
introduction  of  nutritive  matter,  from  paralysis  of  the  muscles  of  mastication 
upon  one  side — the  nutritive  processes  in  these  delicate  parts  are  seriously 
modified,  so  as  to  constitute  inflammation.  The  observation  just  detailed  is 
an  argument  in  favor  of  this  view ;  for  here  the  inflammation  was  arrested 
when  the  action  of  the  paralyzed  muscles  was  supplied  by  careful  feeding. 
With  this  view,  the  disorders  of  nutrition  observed  after  division  of  the  fifth 
may  properly  be  referred  to  the  sympathetic  system. 

Pathological  facts  in  confirmation  of  experiments  upon  the  fifth  pair  in 
the  lower  animals  are  not  wanting ;  but  it  must  be  remembered  that  in  cases 
of  paralysis  of  the  nerve  in  the  human  subject,  it  is  not  always  possible  to 
locate  exactly  the  seat  of  the  lesion  and  to  appreciate  fully  its  extent,  as  can 
be  done  when  the  nerve  is  divided  by  an  operation.  In  studying  these  cases, 
it  sometimes  occurs  that  the  phenomena,  particularly  those  of  modified  nutri- 
tion, are  more  or  less  contradictory. 

In  nearly  all  works  upon  physiology,  are  references  to  cases  of  paralysis 
of  the  fifth  in  the  human  subject.  Two  cases  have  been  reported  by  Noyes, 
in  both  of  which  there  was  inflammation  of  the  eye.  In  one  case  the  tongue 
was  entirely  insensible  upon  one  side,  but  there  was  no  impairment  of  the 
sense  of  taste.  A  notable  feature  in  one  of  the  cases  was  the  fact  that  an 
operation  upon  the  eyelid  of  the  affected  side  was  performed  without  the 
slightest  evidence  of  pain  on  the  part  of  the  patient. 

Cases  of  paralysis  of  the  fifth  in  the  human  subject  in  the  main  confirm 
the  results  of  experiments  upon  the  inferior  animals.  In  cases  in  which  the 
fifth  nerve  alone  is  involved  in  the  disease,  without  the  facial,  there  is  simply 
loss  of  sensibility  upon  one  side,  the  movements  of  the  superficial  muscles 
of  the  face  being  unaffected.  When  the  small  root  is  involved,  the  muscles 
of  mastication  upon  one  side  are  paralyzed ;  but  in  certain  reported  cases  in 
which  this  root  escaped,  there  was  no  muscular  paralysis.  The  senses  of 
sight,  hearing  and  smell,  except  as  they  were  affected  by  consecutive  inflam- 
mation, are  little  if  at  all  disturbed  in  uncomplicated  cases.  The  sense  of 
taste  in  the  anterior  portion  of  the  tongue  is  perfect,  except  in  those  cases  in 
which  the  facial,  the  chorda  tympani  or  the  lingual  branch  of  the  fifth  after 
it  had  been  joined  by  the  chorda  tympani  is  involved  in  the  disease.  In 
some  cases  there  is  no  alteration  in  the  nutrition  of  the  organs  of  special 
sense ;  but  in  this  respect  the  facts  with  regard  to  the  seat  of  the  lesion  are 
not  so  satisfactory  as  in  experiments  upon  the  lower  animals,  it  being  diffi- 
cult, in  most  of  them,  to  exactly  limit  the  boundaries  of  the  lesion. 

PNEUMOGASTRIC  (TENTH  NERVE). 

Of  all  the  nerves  emerging  from  the  cranial  cavity,  the  pneumogastric 
presents  the  greatest  number  of  anastomoses,  the  most  remarkable  course  and 


PNEUMOGASTRIC  NERVE.  573 

the  most  varied  uses.  Arising  from  the  medulla  oblongata  by  a  purely  senso- 
ry root,  it  communicates  with  at  least  five  motor  nerves,  and  it  is  distributed 
largely  to  muscular  tissue,  both  of  the  voluntary  and  the  involuntary  variety. 

Physiological  Anatomy. — The  apparent  origin  of  the  pneumogastric  is 
from  the  lateral  portion  of  the  medulla  oblongata,  just  behind  the  olivary 
body,  between  the  roots  of  the  glosso-pharyngeal  and  the  spinal  accessory. 
The  deep  origin  is  mainly  from  what  is  called  the  nucleus  of  the  pneumogas- 
tric, in  the  inferior  portion  of  the  gray  substance  in  the  floor  of  the  fourth 
ventricle.  The  course  of  the  fibres,  traced  from  without  inward,  is  somewhat 
intricate. 

The  deep  origins  of  the  pneumogastric  and  glosso-pharyngeal  nerves  ap- 
pear to  be  in  the  main  identical.  Tracing  the  filaments  from  without  in- 
ward, they  may  be  followed  in  four  directions:  (1)  The  anterior  filaments 
pass  from  without  inward,  first  very  superficially,  in  the  direction  of  the 
olivary  body ;  but  they  then  turn  and  pass  deeply  into  the  substance  of  the 
restiform  body,  in  which  they  are  lost.  (2)  The  posterior  filaments  are 
superficial,  and  they  pass,  with  the  fibres  of  the  restiform  body,  toward  the 
cerebellum.  (3)  Of  the  intermediate  filaments,  the  anterior  pass  through 
the  restiform  body,  the  greatest  number  extending  to  the  median  line,  in 
the  floor  of  the  fourth  ventricle.  A  few  fibres  are  lost  in  the  middle  fascic- 
uli of  the  medulla  and  a  few  pass  toward  the  brain.  (4)  The  posterior 
intermediate  filaments  traverse  the  restiform  body,  to  the  floor  of  the  fourth 
ventricle,  when  some  pass  to  the  median  line,  and  others  descend  in  the  sub- 
stance of  the  medulla.  It  is  difficult  to  follow  the  fibres  of  origin  of  the 
pneumogastrics  beyond  the  median  line ;  but  recent  observations  leave  no 
doubt  of  the  fact  that  many  of  these  fibres  decussate  in  the  floor  of  the 
fourth  ventricle. 

There  are  two  ganglionic  enlargements  belonging  to  the  pneumogastric. 
In  the  jugular  foramen,  is  a  well  marked,  grayish,  ovoid  enlargement,  one- 
sixth  to  one-fourth  of  an  inch  (4'2  to  G'4  mm.)  in  length,  called  the  jugular 
ganglion,  or  the  ganglion  of  the  root.  This  is  united  by  two  or  three  fila- 
ments with  the  ganglion  of  the  glosso-pharyngeal.  It  is  a  true  ganglion, 
containing  nerve-cells.  After  the  nerve  has  emerged  from  the  cranial  cav- 
ity, it  presents  on  its  trunk  another  grayish  enlargement,  half  an  inch  to  an 
inch  (12  to  25  mm.)  in  length,  called  the  ganglion  of  the  trunk.  This  has 
a  plexiform  structure,  the  white  fibres  being  mixed  with  grayish  fibres  and 
nerve-cells.  The  exit  of  the  nerve  from  the  cranial  cavity  is  by  the  jugular 
foramen,  or  posterior  foramen  lacerum,  in  company  with  the  spinal  acces- 
sory, the' glosso-pharyngeal  nerve  and  the  internal  jugular  vein. 

Anastomoses. — There  are  occasional  filaments  of  communication  which 
pass  from  the  spinal  accessory  to  the  ganglion  of  the  root  of  the  pneumogas- 
tric, but  these  are  not  constant.  After  both  nerves  have  emerged  from  the 
cranial  cavity,  an  important  branch  of  considerable  size  passes  from  the  spi- 
nal accessory  to  the  pneumogastric,  with  which  it  becomes  closely  united. 
Experiments  have  shown  that  these  filaments  from  the  spinal  accessory  pass 
in  great  part  to  the  larynx,  by  the  inferior  laryngeal  nerves. 

38 


574 


NERVOUS  SYSTEM. 


In  the  aquaeductus  Fallopii,  the  facial  nerve  gives  off  a  filament  of  com- 
munication to  the  pneumogastric,  at  the  ganglion  of  the  root.  This  filament, 

joined  at  the  ganglion  by  sensory  fila- 
ments from  the  pneumogastric  and 
some  filaments  from  the  glosso-pha- 
ryngeal,  is  called  the  auricular  branch 
of  Arnold.  By  some  anatomists  it  is 
regarded  as  a  branch  from  the  facial, 
and  by  others  it  is  described  with  the 
pneumogastric. 

Two  or  three  small  filaments  of 
communication  pass  from  the  sublin- 
gual  to  the  ganglion  of  the  trunk  of 
the  pneumogastric. 

At  the  ganglion  of  the  trunk,  the 
pneumogastric  generally  receives  fila- 
ments of  communication  from  the  ar- 
cade formed  by  the  anterior  branches 
of  the  first  two  cervical  nerves.  These, 
however,  are  not  constant. 

The  pneumogastric  is  connected 
with  the  sympathetic  system  by  a  num- 
ber of  filaments  of  communication  from 
the  superior  cervical  ganglion,  passing 
in  part  upward  toward  the  ganglion 
of  the  root  of  the  pneumogastric,  and 
in  part  transversely  and  downward. 
These  filaments  frequently  are  short, 
and  they  bind  the  sympathetic  gan- 
glion to  the  trunk  of  the  nerve.  The 
main  trunk  of  the  pneumogastric  and 
its  branches  receive  a  few  filaments 
of  communication  from  the  middle 
and  inferior  cervical  and  the  upper  dorsal  ganglia  of  the  sympathetic. 

The  pneumogastric  frequently  sends  a  slender  filament  to  the  glosso- 
pharyngeal  nerve,  at  or  near  the  ganglion  of  Andersch.  Branches  from  the 
pneumogastric  join  branches  from  the  glosso-pharyngeal,  the  spinal  accessory 
and  the  sympathetic,  to  form  the  pharyngeal  plexus. 

Distribution. — Although  the  pneumogastric  nerves  upon  the  two  sides  do 
not  present  any  important  differences  in  the  destination  of  their  filaments, 
as  far  down  as  the  diaphragm,  the  distribution  of  the  abdominal  branches  is 
not  the  same.  The  most  important  branches  are  the  following : 


FIG.  214.—  Anastomoses  of  the  pneumogastric 

(Hirschfeld). 

1,  facial  nerve ;  2,  glosso-pharyngeal  nerve  :  2', 
anastomoses  of  the  glosso-pharyngeal  with 
the  facial ;  3,  3,  pneumogastric,  with  its  two 
ganglia  ;  4,  4,  spinal  accessory  ;  5,  sublingual 
nerve  :  6,  superior  cervical  ganglion  of  the 
sympathetic  ;  7,  anastomotic  arcade  of  the 
first  two  cervical  nerves ;  8,  carotid  branch 
of  the  superior  cervical  ganglion  of  the  sym- 
pathetic :  9,  nerve  of  Jacobson  :  10,  branches 
of  this  nerve  to  the  sympathetic  ;  11,  branch 
to  the  Eustachian  tube  ;  12,  branch  to  the 
fenestra  ovalis  ;  13,  branch  to  the  fenestra 
rotunda  ;  14,  external  deep  petrous  nerve  ; 
15,  internal  deep  petrous  nerve  ;  16,  otic  gan- 
glion ;  17,  auricular  branch  of  the  pneumo- 
gastric ',  18,  anastomosis  of  the  pneumogas- 
tric with  the  spinal  accessory ;  19,  anastomo- 
sis of  the  pneumogastric  with  the  sublingual ; 
20.  anastomosis  of  the  spinal  accessory  with 
the  second  pair  of  cervical  nerves ;  21,  pha- 
ryngeal plexus  ;  22,  superior  laryngeal  nerve. 


1.  Auricular. 

2.  Pharyngeal. 

3.  Superior  laryngeal. 

4.  Inferior,  or  recurrent  laryngeal. 


5.  Cardiac,  cervical  and  thoracic. 

6.  Pulmonary,  anterior  and  posterior. 

7.  (Esophageal. 

8.  Abdominal. 


PNEUMOGASTRIC  NEEVE. 


575 


The  auricular  nerves  are  sometimes  described  in  connection  with  the 
facial.  They  are  given  off  from  the  ganglion  of  the  trunk  of  the  pneumo- 
gastric  and  are  com- 
posed of  filaments 
of  communication 
from  the  facial  and 
from  the  glosso- 
pharyngeal,  as  well 
as  of  filaments  from 
the  pneumogastric 
itself.  The  nerves 
thus  constituted  are 
distributed  to  the 
integument  of  the 
upper  portion  of  the 
external  auditory 
meatus,  and  a  small 
filament  is  sent  to 
the  membrana  tym- 
pani. 

The  pharyngeal 
nerves  are  given  off 
from  the  superior 
portion  of  the  gan- 
glion of  the  trunk, 
and  they  contain  a 
large  number  of  the 
filaments  of  com- 
munication which 
the  pneumogastric 
receives  from  the 
spinal  accessory.  In 
their  course  by  the 
sides  of  the  superior 
constrictor  muscles 
of  the  pharynx,  these 
nerves  anastomose 
with  filaments  from 


FIG.  215.— Distribution  of  the  pneumogastric  (Hirschfeld). 
1,  trunk  of  the  left  pneumogastric  ;  2,  ganglion  of  the  trunk ;  3,  anastomo- 
sis ivith  the  spinal  accessory  ;  4,  anastomosis  with  the  sublingual ;  5, 
plmryngeal  branch  (the  auricular  branch  is  not  shown  in  the  figure) ;  6, 
superior  laryngeal  branch ;  7,  external  laryngeal  nerve  ;  8,  laryngeal 
plexus  ;  9,  9,  inferior  laryngeal  branch  ;  10,  cervical  cardiac  branch  ; 
11,  thoracic  cardiac  branch;  12,  13,  pulmonary  branches;  14,  lingual 
branch  of  the  fifth  ;  15,  lower  portion  of  the  sublingual ;  16,  glosso- 
pharyngeal ;  17,  spinal  accessory  ;  18,  19,  20.  spinal  nerves  ;  21,  phrenic 
nerve  ;  22,  23,  spinal  nerves  ;  24,  25,  26,  27, 28,  29,  30,  sympathetic  ganglia. 


the  glosso-pharyngeal  and  the  superior  cervical  ganglion  of  the  sympathetic, 
to  form  what  is  known  as  the  pharyngeal  plexus.  The  ultimate  filaments  of 
distribution  pass  to  the  muscles  and  the  mucous  membrane  of  the  pharynx. 
Physiological  experiments  have  shown  that  the  motor  influence  transmitted 
to  the  pharyngeal  muscles  through  the  pharyngeal  branches  of  the  pneumo- 
gastric is  derived  from  the  spinal  accessory. 

The  superior  laryngeal  nerves  are  given  off  from  the  lower  part  of  the 
ganglion  of  the  trunk.     Their  filaments  come  from  the  side  opposite  to  the 


576  NERVOUS  SYSTEM. 

point  of  junction  of  the  pnenmogastric  with  the  communicating  branch 
from  the  spinal  accessory,  so  that  probably  the  superior  laryngeals  contain 
few  if  any  motor  fibres  from  the  eleventh  nerve.  The  superior  laryngeal 
gives  off  the  external  laryngeal,  a  long,  delicate  branch,  which  sends  a  few 
filaments  to  the  inferior  constrictor  of  the  pharynx  and  is  distributed  to  the 
crico-thyroid  muscle  and  the  mucous  membrane  of  the  ventricle  of  the 
larynx.  The  external  laryngeal  branch  anastomoses  with  the  inferior  laryn- 
geal nerve  and  with  the  sympathetic.  The  internal  branch  is  distributed  to 
the  mucous  membrane  of  the  epiglottis,  the  base  of  the  tongue,  the  aryteno- 
epiglottidean  fold  and  the  mucous  membrane  of  the  larynx  as  far  down  as 
the  true  vocal  chords.  A  branch  from  this  nerve,  in  its  course  to  the  larynx, 
penetrates  the  arytenoid  muscle,  to  which  it  sends  a  few  filaments,  but  these 
are  all  sensory.  This  branch  also  supplies  the  crico-thyroid  muscle.  It 
anastomoses  with  the  inferior  laryngeal  nerve.  An  important  branch,  de- 
scribed by  Cyon  and  Ludwig,  in  the  rabbit,  under  the  name  of  the  depressor 
nerve,  arises  by  two  roots,  one  from  the  superior  laryngeal  and  the  other 
from  the  trunk  of  the  pneumogastric.  It  passes  down  the  neck  by  the  sitle 
of  the  sympathetic,  and  in  the  chest,  it  joins  filaments  from  the  thoracic 
sympathetic,  to  pass  to  the  heart,  between  the  aorta  and  the  pulmonary 
artery.  This  nerve  is  not  isolated  in  the  human  subject,  but  it  is  probable 
that  analagous  fibres  exist  in  man  in  the  trunk  of  the  pneumogastric. 

It  is  important  from  a  physiological  point  of  view  to  note  that  the  supe- 
rior laryngeal  nerve  is  the  nerve  of  sensibility  of  the  upper  part  of  the  larynx, 
as  well  as  of  the  supralaryngeal  mucous  membranes,  and  that  it  animates  a 
single  muscle  of  the  larynx  (the  crico-thyroid)  and  the  inferior  constrictor 
of  the  pharynx. 

The  inferior,  or  recurrent  laryngeal  nerves  present  some  slight  differences 
in  their  anatomy  upon  the  two  sides.  Upon  the  left  side  the  nerve  is  the 
larger  and  is  given  off  at  the  arch  of  the  aorta.  Passing  beneath  this  vessel, 
it  ascends  in  the  groove  between  the  trachea  and  the  oesophagus.  In  its  up- 
ward course  it  gives  off  certain  filaments  which  join  the  cardiac  branches, 
filaments  to  the  muscular  tissue  and  mucous  membrane  of  the  upper  part  of 
the  oesophagus,  filaments  to  the  mucous  membrane  and  the  intercartilaginous 
muscular  tissue  of  the  trachea,  one  or  two  filaments  to  the  inferior  constric- 
tor of  the  pharynx  and  a  branch  which  joins  the  superior  laryngeal.  Its 
terminal  branches  penetrate  the  larynx,  behind  the  posterior  articulation  of 
the  thyroid  with  the  cricoid  cartilage,  and  are  distributed  to  all  of  the  in- 
trinsic muscles  of  the  larynx,  except  the  crico-thyroids,  which  are  supplied 
by  the  superior  laryngeal.  Upon  the  right  side  the  nerve  winds  from  before 
backward  around  the  subclavian  artery,  and  it  has  essentially  the  same  course 
and  distribution  as  upon  the  left  side,  except  that  it  is  smaller  and  has  fewer 
filaments  of  distribution. 

The  important  physiological  point  connected  with  the  anatomy  of  the  re- 
current laryngeals  is-  that  they  animate  all  of  the  intrinsic  muscles  of  the 
larynx,  except  the  crico-thyroid.  Experiments  have  shown  that  these  nerves 
contain  a  large  number  of  motor  filaments  derived  from  the  spinal  accessory. 


PNEUMOGASTRIC  NERVE.  577 

The  cervical  cardiac  branches,  two  or  three  in  number,  arise  from  the 
pneumogastrics  at  different  points  in  the  cervical  portion,  and  pass  to  the 
cardiac  plexus,  which  is  formed  in  great  part  of  filaments  from  the  sympa- 
thetic. The  thoracic  cardiac  branches  are  given  off  from  the  pneumogas- 
trics, below  the  origin  of  the  inferior  laryngeals,  and  join  the  cardiac  plexus. 

The  anterior  pulmonary  branches  are  few  and  delicate  as  compared  with 
the  posterior  branches.  They  are  given  off  below  the  origin  of  the  thoracic  car- 
diac branches,  send  a  few  filaments  to  the  trachea,  and  then  form  a  plexus 
which  surrounds  the  bronchial  tubes  and  follows  the  bronchial  tree  to  its  ter- 
minations in  the  air-cells.  The  posterior  pulmonary  branches  are  larger  and 
more  abundant  than  the  anterior.  They  communicate  freely  with  sympa- 
thetic filaments  from  the  upper  three  or  four  thoracic  ganglia  and  then  form 
the  great  posterior  pulmonary  plexus.  From  this  plexus  a  few  filaments  go 
to  the  inferior  and  posterior  portion  of  the 'trachea,  a  few  pass  to  the  mus- 
cular tissue  and  mucous  membrane  of  the  middle  portion  of  the  oesophagus, 
and  a  few  are  sent  to  the  posterior  and  superior  portion  of  the  pericardium. 
The  plexus  then  surrounds  the  bronchial  tree  and  passes  with  its  ramifications 
to  the  pulmonary  •  tissue,  like  the  corresponding  filaments  of  the  anterior 
branches.  The  pulmonary  branches  are  distributed  to  the  mucous  mem- 
brane, and  not  to  the  walls  of  the  blood-vessels. 

The  oasophageal  branches  take  their  origin  from  the  pneumogastrics, 
above  and  below  the  pulmonary  branches.  These  branches  from  the  two 
sides  join  to  form  the  ossophageal  plexus,  their  filaments  of  distribution 
going  to  the  muscular  tissue  and  the  mucous  membrane  of  the  lower  third  of 
the  oesophagus. 

The  abdominal  branches  are  quite  different  in  their  distribution  upon 
the  two  sides. 

Upon  the  left  side  the  nerve,  which  is  here  anterior  to  the  cardiac 
opening  of  the  stomach,  immediately  after  its  passage  by  the  side  of  the 
O3sophagus  into  the  abdomen,  divides  into  a  number  of  branches,  which  are 
distributed  to  the  muscular  walls  and  the  mucous  membrane  of  the  stomach. 
As  the  branches  pass  from  the  lesser  curvature,  they  take  a  downward  direc- 
tion and  go  to  the  liver,  and  with  another  branch  running  between  the  folds 
of  the  gastro-hepatic  omentum,  they  follow  the  course  of  the  portal  vein  in  the 
hepatic  substance.  The  branches  of  this  nerve  anastomose  with  the  nerve  of 
the  right  side  and  with  the  sympathetic. 

The  right  pneumogastric,  situated  posteriorly,  at  the  oesophageal  open- 
ing of  the  diaphragm,  sends  a  few  filaments  to  the  muscular  coat  and  the 
mucous  membrane  of  the  stomach,  passes  backward  and  is  distributed  to  the 
liver,  spleen,  kidneys,  suprarenal  capsules  and  finally  to  the  whole  of  the 
small  intestine  (Kollmann).  The  anatomical  researches  by  Kollmann  (1860) 
have  been  fully  confirmed  by  physiological  experiments.  Before  the  nerves 
pass  to  the  intestines,  there  is  a  free  anastomosis  and  interchange  of  fila- 
ments between  the  right  and  the  left  pneumogastric. 

General  Properties  of  the  Roots  of  Origin  of  the  Pneumogastrics. — The 
sensibility  of  the  pneumogastrics  in  the  neck,  while  it  is  dull  as  compared 


578  NERVOUS  SYSTEM. 

with  the  properties  of  other  sensory  nerves,  is  nevertheless  distinct.  It  is 
impossible,  however,  to  expose  the  roots  of  the  nerves  in  living  animals,  be- 
fore they  have  received  communicating  motor  filaments,  without  such  muti- 
lation as  would  interfere  with  accurate  observations ;  but  in  animals  just 
killed,  if  the  roots  be  exposed  and  divided,  so  as  to  avoid  reflex  movements, 
and  if  care  be  taken  to  avoid  stimulation  of  motor  filaments  from  adjacent 
nerves,  it  is  found  that  the  application  of  electricity  to  the  peripheral  end  of 
the  root,  from  its  origin  to  the  ganglion,  gives  rise  to  no  movements.  It  may 
therefore  be  assumed  that  the  true  filaments  of  origin  of  the  pneumogastrics 
are  exclusively  sensory  or  at  least  that  they  have  no  motor  properties. 

Properties  and  Uses  of  the  Auricular  Nerves. — There  is  very  little  to  be 
said  with  regard  to  the  auricular  nerves  after  a  description  of  their  anatomy. 
They  are  sometimes  described  with  the  facial  and  sometimes  with  the  pneu- 
mogastric.  They  contain  filaments  from  the  facial,  the  pneumogastric  and 
the  glosso-pharyngeal.  The  sensory  filaments  of  these  nerves  give  sensibility 
to  the  upper  part  of  the  external  auditory  meatus  and  the  membrana  tym- 
pani. 

Properties  and  Uses  of  the  Pharyngeal  Nerves. — The  pharyngeal  branches 
of  the  pneumogastric  are  mixed  nerves,  their  motor  filaments  being  derived 
from  the  spinal  accessory ;  and  their  direct  action  upon  the  muscles  of  deglu- 
tition belongs  to  the  physiological  history  of  the  last-named  nerve.  As 
already  stated  in  treating  of  the  spinal  accessory,  the  filaments  of  communica- 
tion that  go  to  the  pharyngeal  branches  of  the  pneumogastric  are  distributed 
to  the  pharyngeal  muscles. 

It  is  impossible  to  divide  all  of  the  pharyngeal  filaments  in  living  animals 
and  observe  directly  how  far  the  general  sensibility  of  the  pharynx  and  the 
reflex  phenomena  of  deglutition  are  influenced  by  this  section.  As  far  as 
one  can  judge  from  the  distribution  of  the  filaments  to  the  mucous  membrane, 
it  would  seem  that  they  combine  with  the  pharyngeal  filaments  of  the  fifth, 
and  possibly  with  sensory  filaments  from  the  glosso-pharyngeal,  in  giving 
general  sensibility  to  these  parts. 

In  the  experiments  of  Waller  and  Prevost,  upon  the  reflex  phenomena  of 
deglutition,  it  is  shown  that  the  action  of  the  pharyngeal  muscles  can  not  be 
excited  by  stimulation  of  the  mucous  membrane  of  the  supralaryngeal  region 
and  the  pharynx,  after  section  of  the  fifth  and  of  the  superior  laryngeal 
branches  of  the  pneumogastrics.  This  would  seem  to  show  that  the  pharyu- 
geal  branches  of  the  pneumogastrics  are  of  little  importance  in  these  reflex 
phenomena. 

Properties  and  Uses  of  the  Superior  Laryngeal  Nerves. — The  stimulation 
of  these  nerves  produces  intense  pain  and  contraction  of  the  crico-thyroids ; 
but  it  has  been  shown  by  experiment  that  the  arytenoid  muscles,  through 
which  the  nerves  pass,  receive  no  motor  filaments.  The  influence  of  the 
nerves  upon  the  muscles  resolves  itself  into  the  action  of  the  crico-thyroids, 
which  has  been  treated  of  fully  under  the  head  of  phonation.  AVhen  these 
muscles  are  paralyzed,  the  voice  becomes  hoarse.  The  filaments  to  the  in- 
ferior muscles  of  the  pharynx  are  few  and  comparatively  unimportant.  The 


PNEUMOGASTRIC  NERVE.  579 

superior  laryngeals  do  not  receive  their  motor  filaments  from  the  spinal  acces- 
sory. 

The  sensory  filaments  of  the  superior  laryngeals  have  important  uses  con- 
nected with  the  protection  of  the  air-passages  from  the  entrance  of  foreign 
matters,  particularly  in  deglutition,  and  they  are  also  concerned  in  the  reflex 
action  of  the  constrictors  of  the  pharynx.  When  both  superior  laryngeals 
have  been  divided  in  living  animals,  liquids  often  pass  in  small  quantity  into 
the  larynx,  owing  to  the  absence  of  the  reflex  closure  of  the  glottis  when 
foreign  matters  are  brought  in  contact  with  its  superior  surface  and  the  occa- 
sional occurrence  of  inspiration  during  deglutition. 

Aside  from  the  protection  of  the  air-passages,  the  superior  laryngeal  is 
one  of  the  sensory  nerves  through  which  the  reflex  acts  in  deglutition  operate. 
There  are  certain  parts  which  depend  for  their  sensibility  entirely  upon  this 
nerve ;  viz.,  the  mucous  membrane  of  the  epiglottis,  of  the  aryteno-epiglot- 
tidean  fold  and  of  the  larynx  as  far  down  as  the  true  vocal  chords.  When 
an  impression  is  made  upon  these  "parts,  as  when  they  are  touched  with  a 
piece  of  meat,  regular  and  natural  movements  of  deglutition  ensue. 

If  the  superior  laryngeal  nerves  be  divided  and  a  stimulus  be  applied  to 
their  central  ends,  movements  of  deglutition  are  observed,  and  there  is  also 
arrest  of  the  action  of  the  diaphragm.  From  these  experiments,  it  would 
seem  that  the  impression  which  gives  rise  to  the  movements  of  deglutition 
aids  in  protecting  the  air-passages  from  the  entrance  of  foreign  matters,  by 
temporarily  arresting  the  inspiratory  act. 

Properties  and  Uses  of  the  Inferior,  or  Recurrent  Laryngeal  Nerves. — 
The  anatomical  distribution  of  these  nerves  shows  that  their  most  important 
action  is  connected  with  the  muscles  of  the  larynx.  The  few  filaments  which 
are  given  off  in  the  neck,  to  join  the  cardiac  branches,  are  probably  not  very 
important.  It  is  proper  to  note,  however,  that  the  inferior  laryngeal  nerves 
supply  the  muscular  tissue  and  mucous  membrane  of  the  upper  part  of  the 
oesophagus  and  trachea,  and  one  or  two  branches  are  sent  to  the  inferior 
constrictor  of  the  pharynx.  The  action  of  these  filaments  is  sufficiently 
evident. 

The  inferior  laryngeals  contain  chiefly  motor  filaments,  as  is  evident 
from  their  distribution  as  well  as  from  the  effects  of  direct  stimulation.  All 
who  have  experimented  upon  these  nerves  have  noted  little  or  no  evidence 
of  pain  when  they  are  irritated  or  divided. 

One  of  the  most  important  uses  of  the  recurrents  relates  to  the  production 
of  vocal  sounds.  In  connection  with  the  physiology  of  the  internal,  or  com- 
municating branch  from  the  spinal  accessory  to  the  pneumogastric,  it  has 
been  shown  that  this  branch  of  the  spinal  accessory  is  the  true  nerve  of 
phonation.  Before  the  uses  of  the  spinal  accessory  were  fully  understood, 
the  experiments  upon  the  inferior  laryngeals  led  to  the  opinion  that  these 
were  the  nerves  of  phonation,  as  loss  of  voice  follows  their  division  in  living 
animals.  It  is  true  that  these  nerves  contain  the  filaments  which  preside 
over  the  vocal  movements  of  the  larynx ;  but  it  is  also  the  fact  that  these 
vocal  filaments  are  derived  exclusively  from  the  spinal  accessory,  and  that  the 


580  NERVOUS  SYSTEM. 

recurrents  contain  as  well  motor  filaments  which  preside  over  movements  of 
the  larynx  not  concerned  in  the  production  of  vocal  sounds. 

The  muscles  of  the  larynx  concerned  in  phonation  are  the  crico-thyroids, 
animated  by  the  superior  laryngeals,  and  the  arytenoid,  the  lateral  crico- 
arytenoids  and  the  thyro-arytenoids,  animated  by  the  inferior  laryngeals.  The 
posterior  crico-arytenoids  are  respiratory  muscles,  and  these  are  not  affected 
by  extirpation  of  the  spinal  accessories,  but  the  glottis  is  still  capable  of  dilata- 
tion, so  that  inspiration  is  not  impeded.  If,  however,  the  spinal  accessories 
be  extirpated  and  the  larynx  be  then  exposed  in  a  living  animal,  the  glottis 
still  remains  dilated,  but  will  not  close  when  irritated.  If  the  inferior  laryn- 
geals be  then  divided,  the  glottis  is  mechanically  closed  with  the  inspiratory 
act,  and  the  animals  often  die  of  suffocation.  In  view  of  the  varied  sources 
from  which  the  pneumogastrics  receive  their  motor  filaments,  it  is  easy  to 
understand  how  certain  of  these  may  preside  over  the  vocal  movements,  and 
others,  from  a  different  source,  may  animate  the  respiratory  movements. 

The  impediment  to  the  entrance  of  air  into  the  lungs  is  a  sufficient 
explanation  of  the  increase  in  the  number  of  the  respiratory  acts  after  divis- 
ion of  both  recurrents.  The  acceleration  of  respiration  is  much  greater  in 
young  than  in  adult  animals.  This  does  not  apply  to  very  young  animals,  in 
which  section  of  the  recurrents  produces  almost  instant  death. 

Feeble  stimulation  of  the  central  ends  of  the  inferior  laryngeals,  after 
their  division,  produces  rhythmical  movements  of  deglutition,  generally  coin- 
cident with  arrest  of  the  action  of  the  diaphragm.  These  phenomena  are 
generally  observed  in  rabbits,  but  they  are  not  constant.  The  reflex  action 
of  these  nerves  in  deglutition  probably  is  dependent  upon  the  communicating 
filaments  which  they  send  to  the  superior  laryngeal  nerves. 

Properties  and  Uses  of  the  Cardiac  Nerves. — The  chief  uses  of  the  cardiac 
branches  relate  to  the  influence  of  the  pneumogastrics  on  the  action  of  the 
heart.  This  has  already  been  considered  in  connection  with  the  physiology  of 
the  circulation.  The  effect  of  dividing  the  pneumogastrics  in  the  neck  is  to 
remove  the  heart  from  the  influence  of  its  inhibitory  nerves ;  but  at  the  same 
time,  the  operation  profoundly  affects  the  respiratory  movements,  and  this 
latter  effect  must  be  eliminated  as  far  as  possible  in  studying  the  influence 
of  the  pneumogastrics  on  the  circulation.  The  same  remark  applies  to  the 
experiment  of  Faradization  of  the  pneumogastrics  in  the  neck.  The  cardiac 
branches  are  operated  upon  with  difficulty,  and  most  experiments  have  been 
made  upon  the  cervical  portion  of  the  pneumogastric  itself. 

Faradization  of  the  pneumogastrics  in  the  neck  arrests  the  action  of  the 
heart  in  diastole  (the  brothers  Weber,  1846).  This  is  a  direct  action  and  is 
due  to  the  excitation  of  the  inhibitory  fibres,  which  are  derived  from  the 
spinal  accessory  nerves.  The  phenomena  following  stimulation  of  these 
nerves  have  already  been  described  in  connection  with  the  physiology  of  the 
circulation  and  the  properties  and  uses  of  the  spinal  accessories. 

Depressor  Nerve. — While  this  nerve,  which  has  been  described  in  the 
rabbit  (Cyon  and  Ludwig,  1867),  is  not  isolated  in  the  human  subject,  it  is 
probable  that  fibres,  the  action  of  which  is  analogous  to  the  action  observed 


PNEUMOGASTRIC  NERVE.  581 

in  animals  in  which  the  nerve  is  anatomically  distinct,  exist  in  the  trunk  of 
the  pneumogastric.  The  action  of  the  depressor  nerves,  which  is  reflex,  has 
already  been  described  in  connection  with  the  physiology  of  the  circulation. 

Properties  and  Uses  of  the  Pulmonary  Nerves. — The  trachea,  bronchia 
and  the  pulmonary  structure  are  supplied  with  motor  and  sensory  filaments 
by  branches  of  the  pneumogastrics.  The  recurrent  laryngeals  supply  the 
upper  part,  and  the  pulmonary  branches,  the  lower  part  of  the  trachea,  the 
lungs  themselves  being  supplied  by  the  pulmonary  branches  alone.  The 
sensibility  of  the  mucous  membrane  of  the  trachea  and  bronchia  is  due  to  the 
pneumogastrics,  for  these  parts  are  insensible  to  irritation  when  the  nerves 
have  been  divided  in  the  neck.  Longet  has  shown  that  while  an  animal 
coughed  and  showed  signs  of  pain  when  the  mucous  membrane  of  the  respira- 
tory passages  was  irritated,  after  division  of  the  pneumogastrics  there  was 
no  evidence  of  sensibility,  even  when  the  tracheal  mucous  membrane  was 
treated  with  strong  acid  or  cauterized.  He  also  saw  the  muscular  fibres  of 
the  small  bronchial  tubes  contract  when  an  electric  stimulus  was  applied  to 
the  branches  of  the  pneumogastrics. 

Effects  of  Division  of  the  Pneumogastrics  upon  Respiration. — Section  of 
both  pneumogastrics  in  the  neck,  in  mammals  and  birds,  is  usually  followed 
by  death,  in  two  to  five  days.  In  very  young  animals,  death  may  occur 
almost  instantly  from  paralysis  of  the  respiratory  movements  of  the  glottis. 
It  has  been  found  by  all  experimenters  that  animals  survived  and  presented 
no  very  distinct  abnormal  phenomena  after  section  of  one  nerve.  Accord- 
ing to  Longet,  animals  operated  upon  in  this  way  present  hoarseness  of  the 
voice  and  a  slight  increase  in  the  number  of  respiratory  acts.  Some  observ- 
ers have  found  the  corresponding  lung  partly  emphysematous  and  partly  en- 
gorged with  blood,  and  others  have  not  noted  any  change  in  the  pulmonary 
structure. 

When  both  nerves  are  divided  in  full-grown  dogs,  the  effect  upon  the 
respiratory  movements  is  very  marked.  For  a  few  seconds  the  number  of 
respiratory  acts  may  be  increased ;  but  so  soon  as  the  animal  becomes  tran- 
quil, the  number  is  very  much  diminished  and  the  movements  change  their 
character.  The  inspiratory  acts  become  unusually  profound  and  are  at- 
tended with  excessive  dilatation  of  the  thorax.  The  animal  generally  is  quiet 
and  indisposed  to  move.  Under  these  conditions  the  number  of  respirations 
may  fall  from  sixteen  or  eighteen  to  four  per  minute. 

In  most  animals  that  die  from  section  of  both  pneumogastrics,  the  lungs 
are  found  engorged  with  blood,  and,  as  it  were,  carnified,  so  that  they  sink  in 
water.  This  condition  is  not  the  result  of  inflammation  of  the  pulmonary 
parenchyma,  although  this  was  the  view  formerly  entertained  and  is  even  now 
held  by  some  physiologists.  Bernard  found  that  the  pulmonary  lesion  did 
not  exist  in  birds,  although  section  of  both  nerves  was  fatal.  It  had  previ- 
ously been  ascertained  that  in  some  animals  death  takes  place  with  no  altera- 
tion of  the  lungs.  When  the  entrance  of  the  secretions  into  the  air  passages 
was  prevented  by  the  introduction  of  a  canula  into  the  trachea,  the  solidifica- 
tion of  the  lungs  was  nevertheless  observed.  Without  detailing  all  of  the 


582  NERVOUS  SYSTEM. 

experiments  upon  which  the  explanation  offered  by  Bernard  is  based,  it  is 
sufficient  to  state  that  he  observed  a  traumatic  emphysema  as  a  consequence 
of  the  excessively  labored  and  profound  inspirations.  Indeed,  this  can  be  actu- 
ally seen  when  the  pleura  is  exposed  in  living  animals.  As  a  result  of  this 
excessive  distention  of  the  air-cells,  the  pulmonary  capillaries  are  ruptured  in 
different  parts,  the  blood  becomes  coagulated  and  the  lungs  are  finally  solidi- 
fied. This  can  not  occur  in  birds,  because  the  lungs  are  fixed,  and  their  rela- 
tions are  such  that  they  are  not  exposed  to  excessive  distention  in  inspiration. 

The  pneumogastrics  sometimes  reunite  after  division.  The  following 
observation  (Flint,  1874)  illustrates  this  fact,  which  has  frequently  been 
noted :  Both  pneumogastrics  were  divided  in  the  neck  in  a  medium-sized 
dog.  The  pulse  was  immediately  increased  from  one  hundred  and  twenty 
to  two  hundred  and  forty  in  the  minute,  and  the  number  of  respirations  fell 
from  twenty-four  to  four  or  six.  In  ten  days  the  pulse  and  respirations  had 
become  normal.  The  dog  was  then  killed  by  section  of  the  medulla  oblon- 
gata,  and  the  reunion  of  the  divided  ends  of  the  nerves  was  found  to  be 
nearly  complete. 

The  relations  of  the  pneumogastrics  to  the  respiratory  nervous  centre 
have  been  fully  considered  in  connection  with  the  physiology  of  respiration. 

Effects  of  Faradization  of  the  Pneumogastrics  upon  Respiration. — Fara- 
dization of  the  pneumogastrics  in  the  neck,  if  the  current  be  sufficiently 
powerful,  arrests  respiration.  This  arrest  may  be  produced  at  any  time  with 
reference  to  the  respiratory  act,  either  in  expiration  or  inspiration,  although 
it  is  more  readily  effected  in  expiration.  During  the  passage  of  the  current 
the  general  movements  of  the  animal  are  also  arrested.  Although  respira- 
tion may  always  be  arrested  in  this  way,  quite  a  powerful  current  is  required. 
During  the  passage  of  a  very  feeble  current,  the  respirations  are  accelerated. 
They  are  then  retarded  as  the  current  is  made  stronger,  until  they  finally 
cease  (Bert). 

The  following  are  the  phenomena,  observed  by  Bert,  during  the  passage 
of  a  powerful  Faradic  current : 

"  If  an  excitation  be  employed  sufficiently  powerful  to  arrest  respiration 
in  inspiration,  all  respiratory  movements  may  be  made  to  cease  at  the  very 
moment  when  the  excitation  is  applied  (inspiration,  half-inspiration,  expira- 
tion), either  by  operating  upon  the  pneumogastric,  or  operating  upon  the 
laryngeal.  .  .  . 

"  Any  feeble  excitation  of  centripetal  nerves  increases  the  number  of  the 
respiratory  movements ;  any  powerful  excitation  diminishes  them.  A  pow- 
erful excitation  of  the  pneumogastrics,  of  the  superior  laryngeal,  of  the  nasal 
branch  of  the  infraorbital,  may  arrest  them  completely ;  if  the  excitation  be 
sufficiently  energetic,  the  arrest  takes  place  at  the  very  moment  it  is  applied. 
Finally,  sudden  death  of  the  animal  may  follow  a  too  powerful  impression 
thus  transmitted  to  the  respiratory  centre :  all  this  bsing  true  for  certain 
mammalia,  birds  and  reptiles." 

The  above  expresses  the  most  important  experimental  facts  at  present 
known  with  regard  to  the  influence  of  stimulation  of  the  pneumogastrics 


PNEUMOGASTKIC  NEKVE.  583 

upon  respiration.  The  pulmonary  branches  themselves  are  so  deeply  situated 
that  they  have  not  as  yet  been  made  the  subject  of  direct  experiment,  with 
any  positive  and  satisfactory  results. 

Properties  and  Uses  of  the  (Esophageal  Nerves. — The  muscular  walls  and 
the  mucous  membrane  of  the  oesophagus  are  supplied  entirely  by  branches 
from  the  pneumogastrics.  The  upper  portion  is  supplied  by  filaments  from 
the  inferior  laryngeal  branches,  the  middle  portion,  by  filaments  from  the 
posterior  pulmonary  branches,  and  the  inferior  portion  receives  the  oesopha- 
geal  branches.  These  branches  are  both  sensory  and  motor ;  but  probably 
the  motor  filaments  largely  predominate,  for  the  mucous  membrane,  although 
it  is  sensible  to  the  extremes  of  heat  and  cold,  the  feeling  of  distention,  and 
a  burning  sensation  upon  the  application  of  strong  irritants,  is  by  no  means 
acutely  sensitive. 

That  the  movements  of  the  oesophagus  are  animated  by  branches  from 
the  pneumogastrics,  has  been  clearly  shown  by  experiments.  In  the  first 
place,  except  in  animals  in  which  the  anatomical  distribution  of  the  nerves 
is  different  from  the  arrangement  in  the  human  subject,  the  entire  oesopha- 
gus is  paralyzed  by  dividing  the  nerves  in  the  neck.  When  the  pneumogas- 
trics are  divided  in  the  cervical  region  in  dogs,  if  the  animals  attempt  to 
swallow  a  considerable  quantity  of  food,  the  upper  part  of  the  oesophagus  is 
found  enormously  distended.  Bernard  noted  in  a  dog  in  which  a  gastric 
fistula  had  been  established,  that  articles  of  food  given  to  the  animal  did  not 
pass  into  the  stomach,  although  he  made  great  efforts  to  swallow.  An  in- 
stant after  the  attempt,  the  matters  were  regurgitated,  mixed  with  mucus, 
but  of  course  did  not  come  from  the  stomach. 

Direct  experiments  upon  the  roots  of  the  pneumogastrics  have  shown  that 
these  nerves  influence  the  movements  of  the  oesophagus,  and  that  the  motor 
filaments  involved  do  not  come  from  the  spinal  accessory  ;  but  it  is  not  known 
from  what  nerves  these  motor  filaments  are  derived. 

Properties  and  Uses  of  the  Abdominal  Nerves. — In  view  of  the  exten- 
sive distribution  of  the  terminal  branches  of  the  pneumogastrics  to  the  ab- 
dominal organs,  it  is  evident  that  the  action  of  these  nerves  must  be  very 
important,  particularly  since  it  has  been  shown  that  the  right  nerve  is  dis- 
tributed to  the  whole  of  the  small  intestine. 

Influence  of  the  Pneumogastrics  upon  the  Liver. — There  is  very  little 
known  with  regard  to  the  influence  of  the  pneumogastrics  upon  the  se- 
cretion of  bile ;  and  the  most  important  experiments  upon  the  innervation 
of  the  liver  relate  to  the  production  of  glycogen.  If  both  pneumogastrics  be 
divided  in  the  neck,  and  if  the  animal  be  killed  at  a  time  varying  between  a 
few  hours  and  one  or  two  days  after,  the  liver  contains  no  sugar,  under  the 
conditions  in  which  it  is  generally  found  ;  viz.,  a  certain  time  after  death. 
From  experiments  of  this  kind,  Bernard  concluded  that  the  glycogenic  pro- 
cesses are  suspended  when  the  nerves  are  divided.  The  experiments,  how- 
ever, made  by  irritating  the  pneumogastrics,  were  more  satisfactory,  as  in 
these  he  looked  for  sugar  in  the  blood  and  in  the  urine  and  did  not  confine 
his  examinations  for  sugar  to  the  substance  of  the  liver. 


584  NERVOUS  SYSTEM. 

After  division  of  pneumogastrics  in  the  neck,  if  the  peripheral  ends  be 
stimulated  there  is  no  effect  upon  the  liver ;  but  if  the  stimulus  be  applied 
to  the  central  ends,  the  glycogenic  processes  become  exaggerated,  and  sugar 
makes  its  appearance  in  the  blood  and  in  the  urine.  Bernard  made  a  num- 
ber of  experiments  illustrating  this  point,  upon  dogs  and  rabbits.  The  cur- 
rent employed  was  generally  feeble,  and  it  was  continued  for  five  or  ten  min- 
utes, two  or  three  times  in  an  hour.  In  some  instances  the  stimulation  was 
kept  up  for  thirty  minutes.  From  these  experiments,  it  is  assumed  that  the 
physiological  production  of  glycogen  by  the  liver  is  reflex  and  is  due  to  an 
impression  conveyed  to  the  nerve-centres  through  the  pneumogastrics.  The 
inhalation  of  irritating  vapors  and  of  anaesthetics  produces  an  increased  gly- 
cogenic action  in  the  liver. 

The  effects  of  irritating  the  floor  of  the  fourth  ventricle,  by  which  tem- 
porary diabetes  is  produced,  have  been  considered  in  connection  with  the 
glycogenic  action  of  the  liver.  This  effect  is  not  due  to  a  direct  transmis- 
sion of  the  irritation  to  the  liver  through  the  pneumogastrics,  for  the  phe- 
nomena are  observed  in  animals  upon  which  this  operation  has  been  per- 
formed after  section  of  both  pneumogastrics  in  the  neck.  It  is  probable, 
indeed,  that  the  impression  is  conveyed  to  the  liver  through  the  sympathetic 
system ;  for  it  has  been  shown  that  animals  do  not  become  diabetic  after 
irritation  of  the  floor  of  the  fourth  ventricle  when  the  branches  of  the  sympa- 
thetic going  to  the  solar  plexus  have  been  divided.  The  operation,  however, 
of  dividing  the  sympathetic  nerves  in  this  situation  is  so  serious,  that  it  may 
interfere  with  the  experiment  in  some  other  way  than  by  the  direct  influence 
of  the  nerves  upon  the  liver. 

Influence  of  the  Pneumogastrics  upon  the  Stomach  and  Intestines. — Lit- 
tle or  nothing  is  known  with  regard  to  the  action  of  the  pneumogastrics  on 
the  spleen,  kidneys  and  suprarenal  capsules.  The  influence  of  these  nerves 
upon  the  stomach  and  intestine  will  be  considered  under  the  following  heads  : 

1.  The  effects  of  Faradization  of  the  nerves. 

2.  The  effects  of  section  of  the  nerves  upon  the  movements  of  the  stom- 
ach in  digestion. 

3.  The  influence  of  the  nerves  upon  the  small  intestine. 

Effects  of  Faradization. — The  stomach  contracts  under  stimulation  of 
the  pneumogastrics  in  the  neck,  not  instantly,  but  after  the  lapse  of  five  or 
six  seconds  (Longet).  Longet  explained  some  of  the  contradictory  results 
obtained  by  other  observers  by  the  fact  that  these  contractions  are  very 
marked  during  stomach-digestion,  while  they  are  wanting  "  when  the  stom- 
ach is  entirely  empty,  retracted  on  itself  and  in  a  measure  in  repose."  Stim- 
ulation of  the  splanchnic  nerves,  while  it  produces  movements  of  the  intes- 
tines, does  not  affect  the  stomach.  Judging  from  the  tardy  contraction  of 
the  stomach  and  the  analogy  between  the  action  of  the  pneumogastrics  upon 
this  organ  and  the  action  of  the  sympathetic  nerves  upon  the  non-striated 
muscular  tissue,  Longet  assumed  that  the  motor  action  of  the  pneumogas- 
trics is  due,  not  to  the  proper  filaments  of  these  nerves,  but  to  filaments  de- 
rived from  the  sympathetic. 


PNEUMOGASTRIC  NERVE.  585 

Effects  of  Section  of  the  Pneumogastrics  upon  the  Movements  of  the 
Stomach. — If  the  pneumogastrics  be  divided  in  the  neck  in  a  dog  in  full 
digestion,  in  which  a  gastric  fistula  has  been  established  so  that  the  interior 
of  the  organ  can  be  explored,  the  following  phenomena  are  observed : 

In  the  first  place,  before  division  of  the  nerves,  the  mucous  membrane  of 
the  stomach  is  turgid,  its  reaction  is  intensely  acid,  and  if  the  finger  be  intro- 
duced through  the  fistula,  it  will  be  firmly  grasped  by  the  contractions  of  the 
muscular  walls.  When  the  pneumogastrics  are  divided,  the  contractions  of 
the  muscular  walls  instantly  cease,  the  mucous  membrane  becomes  pale,  the 
secretion  of  gastric  juice  is  apparently  arrested  and  the  sensibility  of  the 
organ  is  abolished  (Bernard). 

Notwithstanding  the  apparent  arrest  of  the  movements  of  the  stomach  in 
digestion,  by  section  of  the  pneumogastrics,  it  has  been  shown  that  substances 
may  be  very  slowly  passed  to  the  pylorus,  and  that  the  movements,  although 
they  are  greatly  diminished  in  activity,  are  not  entirely  abolished.  This  fact 
has  been  established  by  the  experiments  of  Schiff,  who  attributed  the  move- 
ments occurring  after  section  of  the  nerves  to  local  irritation  of  the  intra- 
muscular terminal  nervous  filaments. 

The  influence  of  the  pneumogastrics  upon  the  general  processes  of  diges- 
tion, the  sensations  of  hunger  and  thirst  and  upon  absorption  from  the  ali- 
mentary canal  have  already  been  considered  in  connection  with  the  physiol- 
ogy of  digestion  and  absorption. 

Influence  of  the  Pneumogastrics  upon  the  Small  Intestine. — Physiologists 
have  given  but  little  attention  to  the  influence  of  the  pueumagastrics  upon 
the  intestinal  canal,  for  the  reason  that  the  distribution  of  the  abdominal 
branches  to  the  small  intestine,  notwithstanding  the  researches  of  Kollmann, 
in  1860,  does  not  appear  to  have  been  generally  recognized.  The  right,  or 
posterior  abdominal  branch  was  formerly  supposed  to  be  lost  in  the  semi- 
lunar  ganglion  and  the  solar  plexus,  after  sending  a  few  filaments  to  the 
stomach ;  but  since  it  has  been  shown  that  this  nerve  is  supplied  to  the 
whole  of  the  small  intestine,  its  physiology,  in  connection  with  intestinal 
secretion,  has  assumed  considerable  importance. 

The  experiments  of  Wood  have  shown  that  the  pneumogastrics  influence 
intestinal  as  well  as  gastric  secretion.  After  section  of  the  nerves  in  the 
cervical  region,  the  most  powerful  cathartics  (croton-oil,  calomel,  podophyl- 
lin,  jalap,  arsenic  etc.),  fail  to  produce  purgation,  even  in  doses  sufficient  to 
cause  death.  The  articles  used  were  either  given  by  the  mouth,  just  before 
dividing  the  nerves,  or  were  injected  under  the  skin. 

Although  the  observations  of  Wood  are  not  entirely  new,  they  are  by  far 
the  most  extended  and  satisfactory,  and  were  made  with  a  knowledge  of  the 
fact  of  the  distribution  of  the  nerves  to  the  small  intestine.  Brodie  failed 
to  produce  purging  in  dogs,  when  both  pneumogastrics  had  been  divided  in 
the  neck,  after  the  administration  of  arsenic  by  the  mouth  and  after  inject- 
ing it  under  the  skin.  Eeid  made  five  experiments,  and  in  all  but  one,  it  is 
stated  that  diarrheas  existed  after  division  of  the  nerves.  In  twenty  experi- 
ments by  Wood,  there  was  no  purgation  after  division  of  the  nerves,  in  one 


586  NERVOUS  SYSTEM. 

there  was  free  purgation,  and  in  one  there  was  "  some  slight  muco-faBcal  dis- 
charge." From  these,  Wood  concluded  that  while  section  of  the  cervical 
pneumogastrics,  in  the  great  majority  of  instances,  arrests  gastro-intestinal 
secretion  and  prevents  the  action  of  purgatives  upon  the  intestinal  canal,  a 
few  exceptional  cases  occur  in  which  these  effects  are  not  observed. 

It  would  be  interesting  to  determine  whether  the  pneumogastrics  influ- 
ence the  intestinal  secretions  through  their  own  fibres  or  through  filaments 
received  from  the  sympathetic  system ;  but  there  are  no  experimental  facts 
sufficiently  definite  to  admit  of  a  positive  answer  to  this  question.  If  the 
action  take  place  through  the  sympathetic  system,  as  in  the  case  of  the  stom- 
ach, the  filaments  of  communication  join  the  pneumogastrics  high  up  in  the 
neck. 

The  cranial  nerves  that  have  been  considered  in  this  chapter  are  the 
third,  fourth,  fifth,  sixth,  seventh,  tenth,  eleventh  and  twelfth.  The  ana- 
tomical and  physiological  history  of  the  olfactory  (first),  optic  (second), 
auditory  (eighth),  gustatory  (branch  of  the  seventh  and  a  part  of  the  ninth) 
and  of  the  general  sensory  nerves,  as  far  as  they  are  concerned  in  the  sense 
of  touch,  belongs  properly  to  the  chapters  on  the  special  senses. 


CHAPTER  XVIII. 

THE  SPINAL   CORD. 

Genera]  arrangement  of  the  cerebro-spinal  axis— Membranes  of  the  encephalon  and  spinal  cord— Cephalo- 
rachidian  fluid— Physiological  anatomy  of  the  spinal  cord— Columns  of  the  Cord— Direction  of  the 
nerve-fibres  in  the  cord— General  properties  of  the  spinal  cord— Motor  paths  in  the  cord— Sensory  paths 
in  the  cord— Relations  of  the  posterior  white  columns  of  the  cord  to  muscular  co-ordination— Nerve-centres 
in  the  spinal  cord— Reflex  action  of  the  spinal  cord— Exaggeration  of  reflex  excitability  by  decapitation, 
poisoning  with  strychnine  etc.— Reflex  phenomena  observed  in  the  human  subject. 

THE  nervous  matter  contained  in  the  cavity  of  the  cranium  and  in  the 
spinal  canal,  exclusive  of  the  roots  of  the  cranial  and  spinal  nerves,  is  known 
as  the  cerebro-spinal  axis.  This  portion  of  the  nervous  system  is  composed 
of  white  and  gray  matter.  The  fibres  of  the  white  matter  act  solely  as  con- 
ductors. The  gray  matter  constitutes  a  chain  of  ganglia,  which  act  as  nerve- 
centres,  receiving  impressions  and  generating  the  so-called  nerve-force.  Cer- 
tain parts  of  the  gray  matter  also  serve  as  conductors. 

The  cerebro-spinal  axis  is  enveloped  in  membranes,  which  are  for  its  pro- 
tection and  for  the  support  of  its  nutrient  vessels.  It  is  surrounded  to  a  cer- 
tain extent  with  liquid,  and  it  presents  cavities,  as  the  ventricles  of  the  brain 
and  the  central  canal  of  the  cord,  which  contain  liquid.  The  gray  matter 
is  distinct  from  the  white,  even  to  the  naked  eye.  In  the  spinal  cord  the 
white  substance  is  external  and  the  gray  is  internal.  The  surface  of  the 
brain  presents  an  external  layer  of  gray  matter,  the  white  substance  being 


SPINAL  CORD.  587 

internal.  In  the  white  substance  of  the  brain,  also,  are  collections  of  gray 
matter.  The  white  matter  of  the  cerebro-spinal  axis  is  composed  largely  of 
fibres.  The  gray  substance  is  composed  chiefly  of  cells. 

The  encephalon  is  contained  in  the  cranial  cavity  and  consists  of  the 
cerebrum,  cerebellum,  pons  Varolii  and  medulla  oblongata.  In  the  human 
subject  and  in  many  of  the  higher  animals,  its  surface  is  marked  by  convo- 
lutions, by  which  the  extent  of  its  gray  substance  is  much  increased.  The 
cerebrum,  the  cerebellum  and  most  of  the  encephalic  ganglia  are  connected 
with  the  white  substance  of  the  encephalon  and  with  the  spinal  cord.  All 
of  the  cerebro-spinal  nerves  are  connected  with  the  encephalon  and  the  cord. 
The  cerebro-spinal  axis  acts  as  a  conductor,  and  its  different  collections  of 
gray  matter,  or  ganglia,  receive  impressions  conveyed  by  the  sensory  conduct- 
ing fibres,  and  generate  motor  impulses  which  are  transmitted  to  the  proper 
organs  by  the  motor  fibres. 

Membranes  of  the  Encephalon  and  Spinal  Cord. — The  membranes  of  the 
brain  and  spinal  cord  are  the  dura  mater,  the  arachnoid  and  the  pia  mater. 

The  dura  mater  of  the  encephalon  is  a  dense  membrane,  in  two  layers, 
composed  chiefly  of  ordinary  fibrous  tissue,  which  lines  the  cranial  cavity 
and  is  adherent  to  the  bones.  In  certain  situations  its  two  layers  are  sepa- 
rated and  form  what  are  known  as  the  venous  sinuses.  The  dura  mater 
also  sends  off  folds  or  processes  of  its  internal  layer.  One  of  these  passes  in- 
to the  longitudinal  fissure  and  is  called  the  falx  cerebri ;  another  lies  between 
the  cerebrum  and  the  cerebellum  and  is  called  the  tentorium ;  another  is  sit- 
uated between  the  lateral  halves  of  the  cerebellum  and  is  called  the  falx  cere- 
belli.  The  dura  mater  is  closely  attached  to  the  bone  at  the  border  of  the 
foramen  magnum.  From  this  point  it  passes  into  the  spinal  canal  and  forms 
a  loose  covering  for  the  cord.  In  the  spinal  canal,  this  membrane  is  not  ad- 
herent to  the  bones,  which  have,  like  most  other  bones  in  the  body,  a  special 
periosteum.  At  the  foramina  of  exit  of  the  cranial  and  the  spinal  nerves,  the 
dura  mater  sends  out  processes  which  envelop  the  nerves,  with  the  fibrous 
sheaths  of  which  they  soon  become  continuous. 

The  arachnoid  is  a  delicate  membrane,  resembling  the  serous  membranes, 
with  the  exception  that  it  presents  but  one  layer.  Its  inner  surface  is  cov- 
ered with  a  layer  of  tesselated  endothelium.  There  is  a  considerable  quantity 
of  liquid  between  the  arachnoid  and  the  pia  mater,  surrounding  the  cerebro- 
spinal  axis,  in  what  is  called  the  subarachnoid  space.  This  is  called  the  cer- 
ebro-spinal, or  cephalo-rachidiaii  fluid.  The  arachnoid  does  not  follow  the 
convolutions  and  fissures  of  the  encephalon  or  the  fissures  of  the  cord,  but  it 
simply  covers  their  surfaces.  Magendie  described  a  longitudinal,  incom- 
plete, cribriform,  fibrous  septum  in  the  cord,  passing  from  the  inner  layer  of 
the  arachnoid  to  the  pia  mater.  A  similar  arrangement  is  found  in  certain 
situations  at  the  base  of  the  skull. 

The  pia  mater  of  the  encephalon  is  a  delicate,  fibrous  structure,  very  vas- 
cular, seeming  to  present,  indeed,  only  a  skeleton  net-work  of  fibres  for 
the  support  of  the  vessels  going  to  the  nervous  substance.  This  membrane 
covers  the  surface  of  the  encephalon  immediately,  follows  the  sulci  and  fis- 


588  NERVOUS  SYSTEM. 

sures,  and  is  prolonged  into  the  ventricles,  where  it  forms  the  choroid  plexus 
and  the  velum  interpositum.  From  its  internal  surface  small  vessels  are 
given  off  which  pass  into  the  nervous  substance. 

The  pia  mater  of  the  encephalon  is  continuous  with  the  corresponding 
membrane  of  the  cord  ;  but  in  the  spinal  canal  the  membrane  is  thicker, 
stronger,  more  closely  adherent  to  the  subjacent  parts,  and  its  blood-vessels 
are  not  so  abundant.  In  this  situation  many  of  the  fibres  are  arranged  in 
longitudinal  bands.  This  membrane  lines  the  anterior  fissure  and  a  portion 
of  the  posterior  fissure  of  the  cord.  At  the  foramina  of  exit  of  the  cranial 
and  the  spinal  nerves,  the  fibrous  structure  of  the  pia  mater  becomes  contin- 
uous with  the  nerve-sheaths. 

Between  the  anterior  and  posterior  roots  of  the  spinal  nerves,  on  either 
side  of  the  cord,  is  a  narrow,  ligamentous  band,  the  ligamentum  denticulatum, 
which  assists  in  holding  the  cord  in  place.  This  extends  from  the  foramen 
magnum  to  the  terminal  filament  of  the  cord,  and  is  attached,  internally,  to 
the  pia  mater,  and  external!}',  to  the  dura  mater. 

It  is  not  necessary  to  enter  into  a  detailed  description  of  the  arrangement 
of  the  blood-vessels,  nerves  and  lymphatics  of  the  membranes  of  the  brain  and 
spinal  cord,  or  of  the  vascular  arrangement  in  the  substance  of  the  cerebro- 
spinal  axis,  as  these  points  are  chiefly  of  anatomical  interest.  The  circula- 
tion in  these  parts  presents  certain  peculiarities.  In  the  first  place,  the  en- 
cephalon being  contained  in  an  air-tight  case  of  invariable  capacity,  it  has  been 
a  question  whether  or  not  the  vessels  be  capable  of  contraction  and  dilatation, 
or  whether  the  quantity  of  blood  in  the  brain  be  subject  to  modifications  in 
health  or  disease.  These  questions  may  certainly  be  answered  in  the  affirm- 
ative. In  infancy  and  in  the  adult,  when  an  opening  has  been  made  in  the 
skull,  the  volume  of  the  encephalon  is  evidently  increased  during  expiration 
and  is  diminished  in  inspiration.  Under  normal  conditions,  in  the  adult,  it 
is  probable  that  the  quantity  of  blood  is  increased  in  expiration  and  dimin- 
ished in  inspiration ;  but  it  is  not  probable  that  the  cerebro-spinal  axis  under- 
goes any  considerable  movements.  The  important  peculiarities  in  the  cere- 
bral circulation  have  already  been  fully  considered  in  connection  with  the 
physiology  of  the  circulation.  It  has  been  shown  that  the  encephalic  capilla- 
ries are  surrounded  or  nearly  surrounded  by  canals  (peri vascular  canal-sys- 
tem), which  are  connected  with  lymphatic  trunks  or  reservoirs  situated  under 
the  pia  mater.  The  system  of  canals  may,  by  variations  in  its  contents,  serve 
to  equalize  the  quantity  of  liquid  in  the  brain,  as  the  blood-vessels  are  dis- 
tended or  contracted. 

Ceplialo-Racliidian  Fluid. — The  greatest  part  of  the  fluid  in  the  cranium 
and  in  the  spinal  canal  is  contained  in  the  subarachnoid  space.  The  ventri- 
cles of  the  encephalon  are  in  communication  with  the  central  canal  of  the 
cord,  and  are  also  connected  with  the  general  subarachnoid  space,  by  a  narrow, 
triangular  orifice  situated  at  the  inferior  angle  of  the  fourth  ventricle.  By 
this  arrangement  the  liquid  in  the  ventricles  of  the  encephalon  and  in  the 
central  canal  of  the  cord  communicates  with  the  liquid  surrounding  the  cer- 
ebro-spinal axis,  and  the  pressure  upon  these  parts  is  equalized. 


PHYSIOLOGICAL  ANATOMY  OF  THE  SPINAL  CORD.        589 

As  far  as  is  known,  the  office  of  the  cephalo-rachidian  fluid  is  simply 
mechanical,  and  its  properties  and  composition  have  no  very  definite  physio- 
logical significance.  Its  quantity  was  estimated  by  Magendie,  in  the  human 
subject,  at  about  two  fluidounces  (60  c.  c.) ;  but  this  was  the  smallest  quan- 
tity obtained  by  placing  the  subject  upright,  making  an  opening  in  the  lum- 
bar region  and  a  counter-opening  in  the  head  to  admit  the  pressure  of  the 
atmosphere.  The  exact  quantity  in  the  living  subject  could  hardly  be  esti- 
mated in  this  way ;  and  it  is  difficult,  indeed,  to  see  how  any  thing  more  than 
a  roughly  approximate  idea  could  be  obtained.  The  quantity  obtained  by 
Magendie  probably  does  not  represent  all  the  liquid  contained  in  the  ventri- 
cles and  in  the  subarachnoid  space,  but  it  is  the  most  definite  estimate  that 
has  been  given. 

The  general  properties  and  composition  of  the  cephalo-rachidian  fluid 
are  in  brief  the  following  :  It  is  transparent  and  colorless,  free  from  viscid- 
ity, of  a  distinctly  saline  taste,  an  alkaline  reaction,  and  it  resists  putrefaction 
for  a  long  time.  It  is  not  affected  by  heat  or  acids.  It  contains  a  large  pro- 
portion of  water  (981  to  985  parts  per  thousand),  a  considerable  quantity  of 
sodium  chloride,  a  trace  of  potassium  chloride,  sulphates,  carbonates  and  alka- 
line and  earthy  phosphates.  In  addition  it  contains  traces  of  urea,  glucose, 
sodium  lactate,  fatty  matter,  cholesterine  and  albumen. 

As  a  summary  of  the  office  of  the  cephalo-rachidian  fluid,  it  may  be 
stated  in  general  terms  that  it  serves  to  protect  the  cerebro-spinal  axis, 
chiefly  by  equalization  of  the  pressure  in  the  varying  condition  of  the  blood- 
vessels, filling  the  space  between  the  centres  and  the  bony  cavities  in  which 
they  are  contained.  That  the  blood-vessels  of  the  cerebro-spinal  axis  are  sub- 
ject to  variations  in  tension,  is  readily  shown  by  introducing  a  canula  into 
the  subarachnoid  space,  when  the  jet  of  fluid  discharged  will  be  increased 
with  every  violent  muscular  effort.  The  pressure  of  the  fluid,  in  this  in- 
stance, could  be  affected  only  through  the  blood-vessels. 

PHYSIOLOGICAL  ANATOMY  OF  THE  SPINAL  CORD. 

The  spinal  cord,  with  its  membranes,  the  roots  of  the  spinal  nerves  and 
the  surrounding  liquid,  occupies  the  spinal  canal  and  is  continuous  with  the 
encephalon.  Its  length  is  fifteen  to  eighteen  inches  (38*1  to  45'7  centi- 
metres) and  its  weight  is  about  an  ounce  and  a  half  (42*5  grammes).  Its 
general  form  is  cylindrical,  but  it  is  slightly  flattened  in  certain  portions. 
It  extends  from  the  foramen  magnum  to  the  lower  border  of  the  body  of  the 
first  lumbar  vertebra.  It  presents,  at  the  origin  of  the  brachial  nerves,  an 
elongated  ovoid  enlargement  flattened  antero  posteriorly,  and  a  correspond- 
ing enlargement  at  the  origin  of  the  nerves  which  supply  the  lower  extremi- 
ties. It  terminates  below  in  a  slender,  gray  filament,  called  the  filum  termi- 
nale.  The  sacral  and  coccygeal  nerves,  after  their  origin  from  the  lower 
portion  of  the  cord,  pass  downward  to  emerge  by  the  sacral  foramina,  and 
they  form  what  is  known  as  the  cauda  equina.  The  substance  of  the  cord 
is  composed  of  white  and  gray  matter,  the  white  matter  being  external. 
The  inferior,  pointed  termination  of  the  cord  consists  entirely  of  gray  matter. 
39 


590 


NERVOUS  SYSTEM. 


The  cord  is  marked  by  an  anterior  and  a  posterior  median  fissure,  and 
by  imperfect  and  somewhat  indistinct  anterior  and  posterior  lateral  grooves, 


FIG.  216.— Transverse  section  of  the  spinal  cord  of  a  child  six  months  old,  at  the  middle  of  the  lumbar 
enlargement,  treated  with  potassium-auric  chloride  and  uranium  nitrate  ;  magnified  20  diame- 
ters. By  means  of  these  reagents,  the  direction  of  the  fibres  in  the  gray  substance  is  rendered  un- 
usually distinct  (Gerlach). 

a,  anterior  columns  ;  6,  posterior  columns  ;  c,  lateral  columns  :  d,  anterior  roots  ;  e,  posterior  roots  ;  /, 
anterior  white  commissure,  in  communication  with  the  fasciculi  of  the  anterior  cornua  and  the  an- 
terior columns  ;  g,  central  canal  with  its  epithelium  ;  ft,  surrounding  connective  substance  of  the 
central  canal  ;  i,  transverse  fasciculi  of  the  gray  commissure  in  front  of  the  central  canal :  fc,  trans- 
verse fasciculi  of  the  gray  commissure  behind  the  central  canal ;  I,  transverse  section  of  the  two 
central  veins  ;  m,  anterior  cornua  ;  n,  great,  lateral  cellular  layer  of  the  anterior  cornua  ;  o,  lesser, 
anterior  cellular  layer  ;  p,  smallest,  median  cellular  layer  ;  q,  posterior  cornua  ;  r,  ascending  fas- 
ciculi in  the  posterior  cornua  ;  «,  substantia  gelatinosa. 

from  which  latter  arise  the  anterior  and  the  posterior  roots  of  the  spinal 
nerves.  The  posterior  lateral  groove  is  tolerably  well  marked,  but  there  is 
no  distinct  line  at  the  origin  of  the  anterior  roots.  The  anterior  median  fis- 
sure is  perfectly  distinct.  It  penetrates  the  anterior  portion  of  the  cord,  in 
the  median  line,  for  about  one-third  of  its  thickness  and  receives  a  highly  vas- 
cular fold  of  the  pia  mater.  It  extends  to  the  anterior  white  commissure. 
The  posterior  fissure  is  not  so  distinct  as  the  anterior,  and  it  is  not  lined 
throughout  by  a  fold  of  the  pia  mater,  but  is  filled  with  connective  tissue 
and  blood-vessels,  which  form  a  septum  posteriorly,  between  the  lateral 
halves  of  the  cord.  The  posterior  median  fissure  extends  nearly  to  the  cen- 
tre of  the  cord,  as  far  as  the  posterior  gray  commissure. 

The  arrangement  of  the  white  and  the  gray  matter  in  the  cord  is  seen  in  a 
transverse  section.  The  gray  substance  is  in  the  form  of  a  letter  H,  present- 
ing two  anterior  and  two  posterior  cornua  connected  by  what  is  called  the 
gray  commissure.  The  anterior  cornua  are  short  and  broad,  and  they  do  not 


PHYSIOLOGICAL  ANATOMY  OF  THE  SPINAL  CORD.        591 

reach  to  the  surface  of  the  cord.  The  posterior  cornua  are  larger  and  nar- 
rower, and  they  extend  nearly  to  the  surface,  at  the  point  of  origin  of  the 
posterior  roots  of  the  spinal  nerves.  In  the  centre  of  the  gray  commissure,  is 
a  narrow  canal,  lined  by  cells  of  ciliated  epithelium,  called  the  central  canal. 
This  is  in  communication  above  with  the  fourth  ventricle,  and  it  extends  be- 
low to  the  filum  terminale.  That  portion  of  the  gray  commissure  situated  in 
front  of  this  canal  is  sometimes  called  the  anterior  gray  commissure,  the 
posterior  portion  being  known  as  the  posterior  gray  commissure.  The  cen- 
tral canal  is  immediately  surrounded  by  connective  tissue.  In  front  of  the 
gray  commissure,  is  the  anterior  white  commissure. 

The  proportion  of  the  white  to  the  gray  substance  is  variable  in  different 
portions  of  the  cord.  In  the  cervical  region,  the  white  substance  is  most 
abundant,  and  in  fact  it  progressively  increases  in  quantity  from  below  up- 
ward throughout  the  whole  extent  of  the  cord.  -In  the  dorsal  region,  the 
gray  matter  is  least  abundant,  and  it  exists  in  greatest  quantity  in  the  lumbar 
enlargement. 

The  white  substance  of  the  cord  is  composed  of  nerve-fibres,  connective- 
tissue  elements  (neuroglia)  and  blood-vessels,  the  latter  arranged  in  a  very 
wide  and  delicate  plexus.  The  nerve-fibres  are  variable  in  size  and  are  com- 
posed of  the  axis-cylinder  and  the  medullary  substance,  without  the  tubular 
membrane. 

The  anterior  cornua  of  gray  matter  contain  blood-vessels,  connective-tis- 
sue elements  (neuroglia),  very  fine  nerve-fibres,  and  large  multipolar  nerve- 
cells,  which  are  sometimes  called  motor  cells.  The  posterior  cornua  are  com- 
posed of  the  same  elements,  the  cells  being  much  smaller,  and  the  fibres  ex- 
ceedingly small,  presenting  very  fine  plexuses.  The  cells  in  this  situation 
are  sometimes  called  sensory  cells.  Near  the  posterior  portion  of  each  poste- 
rior cornu,  is  an  enlargement,  of  a  gelatiniform  appearance,  containing 
small  cells  and  fibres,  called  the  substantia  gelatinosa.  The  connections 
between  the  nerve-cells  and  the  nerve-fibres  have  already  been  described  in 
connection  with  the  general  structure  of  t^e  nervous  system.  The  multi- 
polar  nerve-cells  are  supposed  to  present  ce  ain  prolongations  which  do  not 
branch  and  are  directly  connected  with  the  meduliated  nerve-fibres.  These 
are  called  axis-cylinder  prolongations.  In  addition,  fine,  branching  poles  are 
described  under  the  name  of  protoplasmic  prolongations.  In  both  the  white 
and  the  gray  substance  of  the  cord,  is  a  ground-work  of  delicate  connective- 
tissue  fibres  and  cells,  called  neuroglia.  This  supports  the  nerve-cells,  nerve- 
fibres,  vessels  etc.  The  neuroglia  is  particularly  abundant  in  that  part  of  the 
posterior  cornua  of  gray  matter,  called  the  substantia  gelatinosa. 

The  division  of  the  spinal  cord  into  columns  has  a  physiological  as  well 
as  an  anatomical  basis.  Anatomists  usually  recognize,  on  either  side  of  the 
cord,  an  anterior  column,  bounded  by  the  anterior  median  fissure  and  the 
line  of  origin  of  the  anterior  roots  of  the  spinal  nerves,  a  lateral  column, 
bounded  by  the  lines  of  origin  of  the  anterior  and  of  the  posterior  roots  of 
the  nerves,  and  a  posterior  column,  bounded  by  the  line  of  the  posterior  roots 
of  the  spinal  nerves  and  the  posterior  median  fissure.  As  the  anterior  or 


592  NERVOUS  SYSTEM. 

posterior  columns  include  either  the  white  or  the  gray  matter,  they  are  called 
respectively  the  anterior  or  posterior  white  and  gray  columns.  Physiological 
and  pathological  researches,  however,  have  shown  that  the  cord  may  prop- 
erly be  farther  divided  as  follows  : 

1.  Columns  of  Tiirck. — By  the  sides  of  the  anterior  median  fissure,  are 
two  narrow  columns  of  white  matter,  one  on  either  side,  extending  to  the 
white  commissure  (A,  in  Fig.  217),  called  the  columns  of  Tiirck,  the  direct, 
or  the  uncrossed  pyramidal  tracts.     The  fibres  of  these   columns  descend, 
probably  decussate  in  the  cervical  region  of  the  cord,  and  the  columns  are 
lost  in  the  lower  dorsal  region.     Destruction  of  certain  motor  parts  in  the 
brain  is  followed  by  descending  secondary  degeneration  of  the  fibres  of  these 
columns. 

2.  Crossed  Pyramidal  Tracts. — These  are  situated,  one  on  either  side,  in 
the  posterior  portion  of  the  lateral  columns  (G,  G,  in  Fig.  217),  and  are 
bounded  internally  by  the  posterior  cornua  of  gray  matter  and  externally  by 
a  narrow  band  called  the  direct  cerebellar  tract.     In  following  the  columns 
upward,  it  is  found  that  they  pass  forward  in  the  upper  part  of  the  cervical 
region  and  decussate  in  the  lower  portion  of  the  anterior  pyramids  of  the 
medulla  oblongata.     These  are  descending  tracts,  and  their  fibres  undergo 
descending  secondary  degeneration  as  the  result  of  destruction  of  certain 
motor  parts  in  the  brain. 

3.  Anterior  Fundamental  Fasciculi. — These  fasciculi  (B,  in  Fig.  217), 
are  bounded  internally  by  the  columns  of  Tiirck  and  externally  by  the  ante- 
rior cornua  of  gray  matter  and  the  anterior  roots  of  the  spinal  nerves.    Their 
fibres  are  supposed  to  connect  the  gray  matter  of  the  anterior  cornua  of  the 
cord  with  the  gray  matter  of  the  medulla  oblongata. 

4.  Anterior  Radicular  Zones. — These  columns  (E,  E,  in  Fig.  217)  are  in 
the  anterior  portion  of  the  lateral  columns.     Their  fibres  are  supposed  to 
connect  the  gray  matter  of  the  cord  with  the  gray  matter  of  the  medulla 
oblongata. 

5.  Mixed  Lateral  Columns. — These  columns  (F,  F,  in  Fig.  217)  are  in 
the  lateral  columns  of  the  cord,  next  the  gray  matter.     AVith  the  anterior 
fundamental  fasciculi  and  the  anterior  radicular  zones,  they  probably  connect 
the  gray  matter  of  the  cord  with  the  gray  matter  of  the  medulla  oblongata. 

The  fibres  of  the  anterior  fundamental  fasciculi,  the  anterior  radicular 
zones  and  the  mixed  lateral  columns  do  not  degenerate  in  either  direction  as 
the  result  of  section  of  the  cord.  Their  fibres  seem  to  connect  nerve-cells  with 
each  other,  and  their  trophic  cells  exist  at  both  extremities,  which  accounts 
for  the  absence  of  degeneration,  just  mentioned. 

6.  Direct  Cerebellar  Fasciculi. — These  fasciculi  (H,  H,  in  Fig.  217)  are 
situated  at  the  outer  and  posterior  portion  of  the  lateral  columns.     Their 
fibres  pass  to  the  funiculi  graciles,  or  posterior  pyramids  of  the  medulla 
oblongata,  and  thence  to  the  cerebellum,  by  the  inferior  peduncles.     They 
connect  the  cells  of  the  posterior  cornua  of  gray  matter  with  the  cerebellum. 
These  columns  make  their  appearance  first  in  the  lumbar  region  of  the  cord, 
and  they  increase  in  size  from  below  upward.     After  section  of  the  spinal 


PHYSIOLOGICAL  ANATOMY  OF  THE  SPINAL  CORD.        593 


B 

A. 


cord,  the  fibres  of  the  direct  cerebellar  fasciculi  show  ascending  secondary 
degeneration.  Their  trophic  centres  probably  are  the  cells  of  the  posterior 
cornua  of  gray  matter  of  the  cord. 

7.  Columns  of  Burdacli. — These  columns  (D,  in  Fig.  217)  are  in  the  pos- 
terior columns  of  *the  cord,  between  the  columns  of  Goll  and  the  posterior 
cornua  of  gray  matter.     Their  fibres  connect  some  of  the  cells  of  the  gray 
matter  of   the  posterior  cornua  with  the 

cerebellum ;  or  at  least  the  fibres  pass  up- 
ward and  are  connected  with  the  restiform 
bodies,  going  to  the  cerebellum  through 
the  inferior  peduncles.  The  fibres  also 
connect  nerve-cells  of  different  portions  of 
the  cord  with  each  other.  No  secondary 
degenerations  have  been  noted  in  these 
columns. 

8.  Columns   of  Goll — These  delicate 
columns  (C,  in  Fig.  217)  are  situated  on 
either  side  of  the  posterior  median  fissure. 
They  are  lost  in  the  lower  dorsal  or  upper 
lumbar  region.     Their  fibres  pass  upward 
and  are  lost  in  the  funiculi  graciles  of  the 
medulla  oblongata.     After  section  of  the 
cord,  ascending  secondary  degeneration  is 
observed  in  the  fibres  of  these  columns. 

Directions  of  Nerve  -  Fibres  in  the 
Cord. — Many  of  the  points  in  the  descrip- 
tion of  the  course  and  connections  of  the 
fibres  in  the  cord  are  given  as  probable. 
Anatomical  observations  have  been  some- 
what contradictory,  but  these  have  been 
corrected  or  verified  by  following  the  paths 
of  degeneration.  What  is  called  secondary  degeneration  is  the  anatomical 
change  in  the  nerve-fibres  which  follows  separation  of  the  fibres  from  the 
cells  which  act  as  their  trophic  centres,  or  the  centres  presiding  over  their 
nutrition,  these  changes  being  secondary  to  the  destruction  or  degeneration 
of  the  centres. 

The  fibres  of  the  anterior  roots  of  the  spinal  nerves,  following  these  fibres 
inward  and  upward,  pass  directly  to  the  large,  multipolar  motor  cells  of  the 
anterior  cornua  of  gray  matter  and  have  no  direct  connection  with  the  white 
columns.  Their  direction  through  the  white  columns  of  the  cord  is  oblique 
and  slightly  upward.  They  are  continuous  with  the  axis-cylinder  prolonga- 
tions of  the  cells.  From  the  nerve-cells,  prolongations  are  given  off,  by 
branching  processes,  in  two  bundles,  median  and  lateral.  The  fibres  of  the 
median  bundle  pass  to  the  anterior  white  commissure,  in  which  they  decus- 
sate. They  then  go  each  one  to  the  column  of  Tiirck  on  the  opposite  side 
and  pass  upward  in  the  so-called  direct  pyramidal  tracts.  The  fibres  of  the 


FIG.  217.— Diagram  of  the  columns  and  con- 
ducting paths  in  the  spinal  cord  in  the 
upper  dorsal  region  (enlarged  and  modi- 
fied from  Landols). 

AR,  AR,  anterior  roots  of  the  spinal  nerves  ; 
PR,  PR,  posterior  roots  ;  A,  columns  of 
Tflrck  ;  B,  anterior  fundamental  fascicu- 
li ;  C,  columns  of  Goll ;  D,  columns  of 
Burdach  ;  E.  E,  anterior  radicular  zones  ; 
F,  F,  mixed  lateral  columns  ;  G,  G, 
crossed  pyramidal  tracts ;  H,  H,  direct 
cerebellar  fasciculi.  The  pray  matter  of 
the  cord  is  in  black.  The  figure  also 
shows  the  anterior  and  posterior  median 
fissures,  the  white  and  gray  commissures 
and  the  central  canal. 


594  NERVOUS  SYSTEM. 

lateral  bundle  go  to  the  crossed  pyramidal  tract  in  the  lateral  column  of  the 
same  side  and  pass  upward  to  decussate  at  the  medulla  oblongata. 

The  fibres  of  the  columns  of  Tiirck  and  the  crossed  pyramidal  tracts  are 
the  only  fibres  of  the  cord  which  are  known  to  convey  motor  impulses  from 
the  brain.  Destruction  of  certain  parts  of  the  brain  produces  descending 
secondary  degeneration  of  these  fibres. 

It  is  probable  that  fibres  arise  from  the  cells  of  the  gray  matter  of  the 
cord,  which  connect  these  cells  with  each  other  and  are  concerned  in  cer- 
tain reflex  phenomena  involving  the  action  of  the  cord  alone.  These  fibres 
are  in  the  anterior  fundamental  fasciculi,  the  anterior  radicular  zones  and 
the  mixed  lateral  columns.  They  present  no  secondary  degeneration. 

The  fibres  of  the  posterior  roots  of  the  spinal  nerves  pass  to  the  small, 
sensory  cells  of  the  posterior  cornua  of  gray  matter  of  the  cord  and  are  con- 
nected by  branching  processes  with  branching  prolongations  of  these  cells. 
Processes  from  these  cells  pass  to  the  gray  commissure  and  decussate  around 
the  central  canal,  conducting  sensory  impressions  to  the  brain,  in  the  gray 
matter  of  the  opposite  side  of  the  cord.  The  sensory  conductors  therefore 
decussate  all  along  the  cord.  Some  of  the  fibres  go  to  the  columns  of  Goll 
and  pass  upward  to  and  are  continuous  with  the  funiculi  graciles  of  the 
medulla  oblongata.  Fibres  also  pass  to  the  direct  cerebellar  fasciculi  and  a 
few,  perhaps,  to  the  columns  of  Burdach,  to  go  upward  to  the  cerebellum. 
Section  of  the  cord  produces  ascending  secondary  degenerations  in  the  col- 
umns of  Goll  and  the  direct  cerebellar  fasciculi.  Fibres  originating  in  the 
nerve-cells  of  the  posterior  cornua  pass  in  and  out,  along  the  cord,  and  con- 
nect the  cells  with  each  other.  These  may  properly  be  called  longitudinal 
commissural  fibres.  They  probably  constitute  the  greater  part  of  the  col- 
,umns  of  Burdach  and  they  present  no  secondary  degeneration. 

GENERAL  PROPERTIES  OF  THE  SPINAL  CORD. 

As  regards  the  general  properties  of  the  cord,  as  shown  by  the  effects  of 
stimulus  applied  to  its  exterior  or  to  its  cut  surface,  the  term  excitability  will 
be  used  to  express  a  property  indicated  by  direct  muscular  contraction  follow- 
ing stimulation  of  the  cord,  and  sensibility,  a  property  which  enables  it  to 
receive  impressions  which  produce  pain.  In  exciting  different  parts  of  the 
cord  with  electricity,  it  is  necessary  to  carefully  guard  against  an  extension 
of  the  current  beyond  the  points  which  it  is  intended  to  stimulate.  Some 
physiologists  regard  the  cord  as  absolutely  inexcitable  and  insensible,  both  on 
its  surface  and  in  its  deeper  portions.  AVith  this  view,  it  is  supposed  that 
parts  of  the  cord  will  conduct  motor  impulses  received  from  the  centres 
situated  above,  but  are  not  excited  by  a  stimulus  applied  directly.  In  the 
same  way,  it  is  thought,  parts  of  the  cord  will  convey  sensory  impressions 
received  through  the  nerves,  but  are  insensible  to  direct  irritation. 

The  results  of  the  observations  of  Van  Deen,  Brown-Sequard,  Schiff  and 
others,  were  simply  negative ;  but  the  positive  results  obtained  by  Longet, 
Fick,  Vulpian  and  those  who  regard  parts  of  the  cord  as  excitable  and  sen- 
sible, show  that  certain  of  the  columns  react  under  direct  stimulation. 


PATHS  OF  CONDUCTION  IN  THE  CORD.  595 

In  some  experiments  made  in  1863  (Flint)  upon  a  living  dog,  the  cord 
having  been  exposed  in  the  lumbar  region  and  stimulated  mechanically  and 
with  an  electric  current  two  hours  after  the  operation,  certain  positive  results 
were  obtained,  which  led  to  the  following  conclusions : 

The  gray  substance  is  probably  inexcitable  and  insensible  under  direct 
stimulation. 

The  antero-lateral  columns  are  insensible,  but  are  excitable  both  on  the 
surface  and  in  their  substance ;  and  direct  stimulation  of  these  columns  pro- 
duces convulsive  movements  in  certain  muscles,  which  movements  are  not 
reflex  and  are  not  attended  with  pain.  The  lateral  columns  are  less  excitable 
than  the  anterior  columns. 

The  surface,  at  least,  of  the  posterior  columns  is  very  sensitive,  especially 
near  the  posterior  roots  of  the  nerves.  The  deep  portions  of  the  posterior 
columns  are  probably  insensible,  except  very  near  the  origin  of  the  nerves. 

The  above  conclusions  refer  only  to  the  general  properties  of  different 
portions  of  the  cord,  as  shown  by  direct  stimulation,  in  the  same  way  that 
the  general  properties  of  the  nerves  in  their  course  are  demonstrated. 

Motor  Paths  in  the  Cord. — What  has  been  said  regarding  the  direction 
of  the  fibres  in  the  cord  and  the  situation  and  course  of  the  degenerations 
following  destruction  of  motor  cerebral  centres  conveys  a  definite  idea  of  the 
motor  paths  in  the  cord.  This  idea  is  sustained  by  experiments  in  which 
different  columns  of  the  cord  have  been  divided  in  living  animals. 

The  motor  paths  are  in  the  direct  pyramidal  tracts  (columns  of  Tiirck) 
and  in  the  crossed  pyramidal  tracts  of  the  lateral  columns.  The  motor  im- 
pulses are  conveyed  by  the  fibres  of  these  tracts  to  the  multipolar  cells  in  the 
anterior  cornua  of  gray  matter  and  are  thence  transmitted  if)  the  anterior 
roots  of  certain  spinal  nerves.  In  the  lower  dorsal  region  the  conduction 
is  confined  to  the  crossed  pyramidal  tracts  in  the  lateral  columns,  while 
above,  the  direct  pyramidal  tracts  participate  in  this  action. 

The  motor  fibres  decussate  in  the  anterior  pyramids  of  the  medulla  oblon- 
gata  (crossed  pyramidal  tracts),  and  in  the  cervical  region,  to  a  comparatively 
slight  extent,  before  the  direct  pyramidal  tracts  (columns  of  Tiirck)  pass  to 
the  encephalon.  In  the  cervical  region  the  decussation  takes  place  probably 
in  the  anterior  white  commissure.  The  fact  of  this  decussation  of  motor 
conductors  is  sustained  by  pathology — paralysis  of  motion  following  brain- 
lesions,  occurring  on  the  opposite  side  of  the  body — and  by  experiments  in 
which  the  fibres  as  they  cross  are  divided  by  a  longitudinal  median  section 
in  the  medulla  and  in  the  cervical  region  of  the  cord. 

Vaso-motor  nerve-fibres  exist  in  the  lateral  columns  of  the  cord  and 
probably  are  connected  with  the  cells  of  the  gray  matter.  They  pass  out  in 
the  anterior  roots  of  the  spinal  nerves  and  go  to  the  blood-vessels  either 
from  the  branches  of  the  spinal  nerves  directly  or  through  filaments  sent  to 
the  sympathetic. 

Sensory  Paths  in  the  Cord. — The  gray  matter  of  the  cord  is  the  part 
concerned  in  the  conduction  of  sensory  impressions  (Bellingeri,  1823).  This 
fact  has  been  verified  by  recent  experiments ;  but  it  is  thought  that  some  of 


596  NEKVOUS  SYSTEM. 

the  sensory  conductors  run  in  the  columns  of  Goll  (Flechsig).  The  columns 
of  Goll,  however,  exist  only  in  the  cervical  and  dorsal  regions. 

The  sensory  conductors  do  not  decussate  at  any  particular  point  as  do  the 
motor  conductors  in  the  crossed  pyramidal  tracts.  The  fibres  from  the  pos- 
terior roots  of  the  spinal  nerves  pass  to  the  sensory  cells  of  the  posterior  cor- 
nua  and  decussate  throughout  the  entire  length  of  the  cord  (Brown-Sequard). 
If  the  cord  be  divided  longitudinally  in  the  median  line,  there  is  complete 
paralysis  of  sensation  on  both  sides  in  all  parts  below  the  section  (Fodera, 
1822,  and  Brown-Sequard).  In  this  section,  the  only  fibres  that  are  divided 
are  those  passing  from  one  side  of  the  cord  to  the  other.  This  decussation 
is  by  fibres  prolonged  from  the  cells  of  the  posterior  cornua,  which  cross  in 
the  gray  commissure,  around  the  central  canal. 

When  one  lateral  half  of  the  cord  is  divided  in  a  living  animal,  sensibil- 
ity is  impaired  or  lost  on  the  opposite  side  of  the  body,  below  the  section, 
but  there  is  hyperaesthesia  on  the  side  corresponding  to  the  section.  The 
exaggeration  of  sensibility  has  not  been  satisfactorily  explained. 

Relations  of  the  Posterior  White  Columns  of  the  Cord  to  Muscular  Co- 
ordination.— It  was  noticed  by  Todd,  many  years  ago  (1839-1847),  in  cases 
of  that  peculiar  form  of  muscular  inco-ordination  now  known  as  locomotor 
ataxia,  that  the  posterior  white  columns  of  the  cord  were  diseased.  Reason- 
ing from  this  fact,  Todd  made  the  following  statement  with  regard  to  the 
office  of  these  columns  : 

"  I  have  long  been  impressed  with  the  opinion,  that  the  office  of  the  pos- 
terior columns  of  the  spinal  cord  is  very  different  from  any  yet  assigned  to 
them.  They  may  be  in  part  commissural  between  the  several  segments  of 
the  cord,  serving  to  unite  them  and  harmonize  them  in  their  various  actions, 
and  in  part  subservient  to  the  function  of  the  cerebellum  in  regulating  and 
co-ordinating  the  movements  necessary  for  perfect  locomotion." 

The  view  thus  early  advanced  by  Todd  has  been  sustained  by  the  results 
of  experiments  on  living  animals.  If  the  posterior  columns  be  completely 
divided,  by  two  or  three  sections  made  at  intervals  of  about  three-fourths  of 
an  inch  to  an  inch  and  a  quarter  (20  to  30  mm.),  the  most  prominent  effect 
is  a  remarkable  trouble  in  locomotion,  consisting  in  a  want  of  proper  co-ordi- 
nation of  movements  (Vulpian).  Experiments  upon  the  different  columns 
of  the  cord  in  living  animals,  however,  are  so  difficult  that  physiologists  have 
preferred  to  take  the  observations  in  cases  of  disease  in  the  human  subject  as 
the  basis  of  their  ideas  with  regard  to  the  office  of  the  posterior  white  col- 
umns. 

The  characteristic  phenomenon  of  locomotor  ataxia  is  inability  to  co-ordi- 
nate muscular  movements,  particularly  those  of  the  extremities.  There  is 
not  of  necessity  any  impairment  of  actual  muscular  power ;  and  although 
pain  and  more  or  less  disturbance  of  sensibility  are  usual,  these  conditions 
are  not  absolutely  invariable  and  they  are  always  coincident  with  disease  of 
sensory  conductors.  The  characteristic  pathological  condition  is  disease  of 
the  posterior  white  columns  (columns  of  Burdach).  This  is  usually  followed 
by  or  is  co-existent  with  disease  of  the  posterior  roots  of  the  spinal  nerves 


NERVE-CENTRES  IN  THE  SPINAL  CORD.  597 

and  disease  of  the  cells  of  the  posterior  gray  matter  of  the  cord.  As  the 
cells  are  affected,  there  follows  ascending  secondary  degeneration  of  the  col- 
umns of  Goll.  It  is  fair  to  assume  that  the  disease  of  the  cells  of  the  gray 
matter  of  the  cord  and  of  the  posterior  roots  of  the  spinal  nerves  is  con- 
nected with  the  disorders  of  general  sensibility.  The  disease  of  the  columns 
of  Burdach  produces  the  disorder  in  movements. 

Eeasoning  from  the  characteristic  phenomena  and  the  essential  patholog- 
ical conditions  of  the  cord  in  typical  cases  of  locomotor  ataxia,  the  posterior 
white  columns  of  the  cord,  connecting  cells  of  the  gray  matter  in  different 
planes  with  each  other,  assist  in  regulating  and  co-ordinating  the  voluntary 
movements.  The  fibres  of  these  columns  also  connect  the  cord  with  the 
cerebellum,  which  has  an  important  office  in  muscular  co-ordination.  It  is 
probable  that  the  appreciation  of  the  muscular  sense  and  the  sense  of  press- 
ure, if  these  can  be  separated  from  what  is  known  as  general  sensibility, 
are  connected  with  the  action  of  the  fibres  of  the  posterior  white  columns. 

NERVE-CEXTRES  isr  THE  SPINAL  CORD. 

It  has  long  been  known  that  decapitation  of  animals  does  not  arrest  mus- 
cular action ;  and  the  movements  observed  after  this  mutilation  present  a 
certain  degree  of  regularity  and  have  been  shown  to  be  in  accordance  with 
well  defined  laws.  Under  these  conditions,  the  regulation  of  such  move- 
ments is  effected  through  the  spinal  cord  and  the  spinal  nerves.  If  an  ani- 
mal be  decapitated,  leaving  only  the  cord  and  its  nerves,  there  is  no  sensa- 
tion, foi  the  parts  capable  of  appreciating  sensation  are  absent ;  nor  are 
there  any  true  voluntary  movements,  as  the  organ  of  the  will  is  destroyed. 
Still,  in  decapitated  animals,  the  sensory  nerves  are  for  a  time  capable  of 
conducting  impressions,  and  the  motor  nerves  can  transmit  a  stimulus  to  the 
muscles ;  but  the  only  part  capable  of  receiving  an  impression  or  of  generat- 
ing a  motor  impulse  is  the  gray  matter  of  the  cord.  If  in  addition  to  the 
removal  of  all  of  the  encephalic  ganglia,  the  cord  itself  be  destroyed,  all  mus- 
cular movements  are  abolished,  except  as  they  may  be  produced  by  direct 
stimulation  of  the  muscular  tissue  or  of  individual  motor  nerves. 

The  gray  matter  of  the  brain  and  spinal  cord  is  a  connected  chain  of 
ganglia,  capable  of  receiving  impressions  through  the  sensory  nerves  and  of 
generating  motor  impulses.  The  cerebro-spinal  axis,  taken  as  a  whole,  has 
this  general  office ;  but  some  parts  have  separate  and  distinct  properties  and 
can  act  independently  of  the  others.  The  cord,  acting  as  a  conductor,  con- 
nects the  brain  with  the  parts  to  which  the  spinal  nerves  are  distributed.  If 
the  cord  be  separated  from  the  brain  in  a  living  animal,  it  may  act  as  a  cen- 
tre, independently  of  the  brain  •  but  the  encephalon  has  no  communication 
with  the  parts  supplied  with  nerves  from  the  cord,  and  it  can  act  only  upon 
the  parts  which  receive  nerves  from  the  brain  itself. 

When  the  cord  is  separated  from  the  encephalon,  an  impression  made 
upon  the  general  sensory  nerves  is  conveyed  to  its  gray  substance,  and  this 
gives  rise  to  a  stimulus,  which  is  transmitted  to  the  voluntary  muscles,  pro- 
ducing certain  movements,  independently  of  sensation  and  volition.  This 


598  NERVOUS  SYSTEM. 

impression  is  said  to  be  reflected  back  from  the  cord  through  the  motor 
nerves ;  and  the  movements  occurring  under  these  conditions  are  called 
reflex.  As  they  are  movements  excited  by  stimulation  of  sensory  nerves, 
they  are  sometimes  called  excito-motor. 

The  term  reflex,  as  it  is  now  generally  understood  by  physiologists,  may 
properly  be  applied  to  any  generation  of  nerve-force  which  occurs  as  a  con- 
sequence of  an  impression  received  by  a  nerve-centre ;  and  it  is  evident  that 
reflex  phenomena  are  by  no  means  confined  to  the  action  of  the  spinal  cord. 
The  movements  of  the  iris  are  reflex,  and  yet  they  take  place  in  many  in- 
stances without  the  intervention  of  the  cord.  Movements  of  the  intestines 
and  of  the  involuntary  muscles  generally  are  reflex,  and  they  involve  the 
action  of  the  sympathetic  system  of  nerves.  Impressions  made  upon  the 
nerves  of  special  sense,  as  those  of  smell,  sight,  hearing  etc.,  give  rise  to  cer- 
tain trains  of  thought.  These  involve  the  action  of  the  brain,  but  still  they 
are  reflex.  In  this  last  example  of  reflex  action,  it  is  sometimes  difficult  to 
connect  the  operations  of  the  mind  with  external  impressions  as  an  exciting 
cause ;  but  it  is  evident,  from  a  little  reflection,  that  this  is  often  the  case. 

Reflex  Action  of  the  Spinal  Cord. — Simple  reflex  action  involves  the 
existence  of  an  afferent  (sensory)  nerve,  a  collection  of  nerve-cells,  and  an 
efferent  (motor)  nerve,  the  nerves  being  connected  with  the  nerve-cells.  In 
a  decapitated  animal,  not  only  are  the  movements  independent  of  sensation 
and  volition,  but  no  movements  occur  if  the  sensory  nerves  be  protected 
from  any  kind  of  impression  or  stimulation  (Marshall  Hall,  1832  and  1833). 
If  the  cord  be  destroyed,  however,  no  movements  follow  stimulation  of  the 
surface;  and  if  either  the  afferent  and  the  efferent  nerves  be  divided,  no 
reflex  movements  can  take  place.  Experiments  upon  decapitated  animals 
are  in  accord  with  the  results  of  observations  upon  acephalous  foetuses  and 
in  cases  of  complete  paraplegia  from  injury  to  the  cord. 

In  the  simplest  form  of  a  reflex  movement,  the  muscular  contraction  is 
confined  to  the  muscle  or  muscles  which  correspond,  in  their  nervous  supply, 
to  the  afferent  nerve  stimulated ;  but  when  the  stimulus  is  sufficiently  power- 
ful or  when  the  cord  is  in  a  condition  of  exalted  excitability,  the  impression 
is  disseminated  throughout  the  gray  matter,  and  the  entire  muscular  system 
may  be  thrown  into  action.  With  feebler  stimulation,  one  side  only  of  the 
muscular  system  may  respond.  When  the  reaction  extends  to  the  opposite 
side,  it  is  called  crossed  reflex.  The  extension  of  a  stimulus  conveyed  by  a 
single  afferent  nerve  throughout  the  cord  is  called  irradiation. 

When  a  feeble  stimulus  applied  to  an  afferent  nerve  is  repeated  frequently 
and  at  short  intervals,  general  muscular  movements  are  produced.  This  fol- 
lows stimuli  applied  three  times  in  a  second,  and  the  effect  is  increased  up 
to  sixteen  shocks  in  a  second,  but  not  beyond  this  number  (Rosenthal). 

In  studying  the  paths  of  conduction  in  the  cord  it  has  been  seen  that 
sensory  conduction  takes  place  through  the  gray  matter  and  possibly  through 
the  columns  of  Goll,  that  motor  impulses  are  conducted  by  the  direct  and 
the  crossed  pyramidal  tracts,  and  that  the  columns  of  Burdach  are  connected 
with  muscular  co-ordination.  The  fibres  of  the  cord  that  are  specially  con- 


REFLEX  ACTION  OF  THE  SPINAL  CORD. 


599 


nected  with  reflex  action  are  probably  in  the  anterior  fundamental  fasciculi, 
the  anterior  radicular  zones  and  the  mixed  lateral  columns. 

It  is  well  known  that  the  reflex  excitability  of  the  cord  is  exaggerated  by 
removal  of  the  encephalon.  According  to  Setschenow  (1863),  certain  parts 
in  the  encephalon,  particularly  the  optic  lobes  in  frogs,  exert  an  inhibitory 
influence  over  the  reflex  acts  of  the  cord,  and  as  a  consequence,  the  reflex 
phenomena  are  more  marked  when  this  influence  is  suppressed. 

Various  poisons,  especially  strychnine,  have  a  remarkable  influence  over 
reflex  excitability.  In  a  frog  decapitated  and  poisoned  with  strychnine,  no 
reflex  movements  occur  unless  an  impression  be  made  on 
the  sensory  nerves ;  but  the  slightest  irritation,  such  as  a 
breath  of  air,  throws  the  entire  muscular  system  into  a 
condition  of  violent  tetanic  spasm.  The  same  phenome- 
na are  observed  in  cases  of  poisoning  by  strychnine  or 
of  tetanus  in  the  human  subject. 

The  inhalation  of  anaesthetic  agents  may  abolish  all 
of  the  ordinary  reflex  phenomena.  Whether  this  be  due 
to  an  action  upon  the  cord  itself  or  to  a  paralysis  of  the 
sensory  nerves,  it  is  difficult  to  determine.  Ordinarily, 
in  animals  rendered  insensible  by  anaesthetics,  the  move- 
ments of  respiration  continue ;  but  these  also  may  be 
arrested,  as  has  been  observed  by  all  who  have  experi- 
mented with  anaesthetics,  especially  with  chloroform.  A 
common  way  of  determining  that  an  animal  is  complete- 
ly under  the  influence  of  an  anaesthetic  is  by  noting  an 
absence  of  the  reflex  act  of  closing  the  eyelids  when  the 
cornea  is  touched. 

It  is  only  necessary,  after  what  has  gone  before,  to  in- 
dicate in  a  general  way  certain  phenomena  observed  in 
the  human  subject  which  illustrate  the  reflex  action  of 
the  cord.  It  is  a  common  observation,  in  cases  of  para- 
plegia in  which  the  lower  portion  of  the  cord  is  intact, 
that  movements  of  the  limbs  follow  titillation  of  the  soles 
of  the  feet,  these  movements  taking  place  independently 
of  the  consciousness  or  the  will  of  the  subject  experi- 

...  ,     FIG.  218.— Frog  poisoned 

mented  upon.  Acephalous  iretuses  will  present  general  with  strychnine  (La6- 
reflex  movements  and  movements  of  respiration,  and  will 
even  suck  when  the  finger  is  introduced  into  the  mouth.  Observations  of 
this  kind  are  so  familiar  that  they  need  not  be  cited  in  detail.  Experiments 
have  also  been  made  upon  criminals  after  decapitation ;  and  although  the  re- 
flex phenomena  are  not  so  well  marked  and  can  not  be  excited  so  long  after 
death  as  in  cold-blooded  animals,  they  are  sufficiently  distinct. 

General  muscular  spasms  following  stimulation  of  sensory  nerves  are 
pathological  and  take  place  only  when  the  reflex  excitability  of  the  cord  is 
much  exaggerated.  Examples  of  this  action  are  the  spasms  observed  in  teta- 
nus or  in  poisoning  by  strychnine.  In  experiments  on  the  lower  animals, 


600  NERVOUS  SYSTEM. 

particularly  frogs,  co-ordinate  reflex  movements  are  often  observed,  such  as 
the  movements  of  jumping  or  swimming.  This  is  sometimes  called  purposive 
reflex  action,  as  the  movements  seem  to  have  a  definite  purpose  or  object.  The 
following  well  known  experiment  illustrates  a  co-ordinate,  or  purposive  reflex  : 
g^Pfliiger  (1853)  removed  the  entire  encephalon  from  a  frog,  leaving  only 
the  spinal  cord.  He  then  touched  the  surface  of  the  thigh,  over  the  inner 
condyle,  with  acetic  acid.  The  animal  thereupon  rubbed  the  irritated  sur- 
face with  the  foot  of  the  same  side,  apparently  appreciating  the  seat  of  the 
irritation,  and  endeavoring,  by  a  voluntary  effort,  to  remove  it.  The  foot  of 
this  side  was  then  amputated,  and  the  irritation  was  renewed  in  the  same 
place.  The  animal  made  an  ineffectual  effort  to  reach  the  spot  with  the 
amputated  member,  and  failing  in  this,  after  some  general  movements  of 
the  limbs,  rubbed  the  spot  with  the  foot  of  the  opposite  side. 

It  has  been  thought  that  this  experiment  shows  a  persistence  of  sensa- 
tion and  the  power  of  voluntary  movements  after  removal  of  the  entire  en- 
cephalon ;  but  it  must  be  remembered  that  the  cord  contains  cells  connected 
together  by  fibres  probably  into  groups  which  correspond  to  sets  of  muscles 
concerned  in  co-ordinate  movements,  and  that  many  movements  set  in  action 
by  an  effort  of  the  will  continue  in  an  automatic  manner,  as  the  ordinary 
movements  of  progression.  It  is  more  reasonable  to  suppose  that  a  persist- 
ent stimulation  of  the  surface,  such  as  is  produced  by  the  action  of  acetic 
acid  upon  the  skin  of  a  frog,  can  give  rise  to  co-ordinate  movements  of  a 
purely  reflex  character  than  to  assume  that  the  movements  in  Pfliiger's  ex- 
periment are  voluntary  efforts  to  remove  a  painful  impression.  It  is  certain 
that  in  the  higher  classes  of  animals  after  removal  of  the  encephalon,  in  ex- 
periments on  decapitated  criminals  and  in  patients  suffering  from  paraplegia, 
there  is  no  evidence  of  true  sensation  or  volition  in  the  spinal  cord.  In  man 
and  the  higher  animals,  all  muscular  movements  which  depend  solely  upon 
the  reflex  action  of  the  cord  must  be  regarded  as  automatic  and  entirely  in- 
dependent of  consciousness  and  of  the  will. 

Certain  reflex  movements  may  be  restrained  by  an  effort  of  the  will,  as  is 
well  known ;  provided,  always,  that  these  be  movements  that  can  be  exe- 
cuted by  voluntary  effort.  Nevertheless,  if  the  sensory  impression  be  suffi- 
ciently powerful  or  be  very  frequently  repeated,  it  is  often  impossible  to  con- 
trol such  movements  by  the  will.  Movements  that  are  never  in  themselves 
voluntary,  such  as  the  ejaculation  of  semen,  when  excited  by  reflex  action 
can  not  be  restrained  by  a  voluntary  effort ;  while  the  reflex  act  of  coughing, 
for  example,  may  be  measurably  controlled.  It  is  hardly  proper  to  speak  of 
inhibition  of  the  reflexes,  in  the  sense  in  which  the  term  inhibition  is  gener- 
ally used  in  physiology,  for  the  reason  that  there  are  probably  no  special  in- 
hibitory nerves  for  these  movements. 

Various  reflexes  are  made  use  of  in  pathology  as  means  of  diagnosis. 
The  superficial  reflexes  are  those  produced  by  tickling  the  soles  of  the  feet 
or  by  exciting  other  parts  of  the  skin.  The  most  prominent  of  the  deep  re- 
flexes is  the  patellar  reflex,  or  the  knee-jerk,  produced  by  percussion  of  the 
ligamentum  patellae. 


PHYSIOLOGICAL  DIVISIONS  OF  THE  ENCEPHALON.        601 

The  gray  matter  of  the  cord  is  not  a  single  centre,  but  consists  of  a  num- 
ber of  centres  connected  with  each  other  and  with  the  brain.  Some  of  these 
have  already  been  described  in  connection  with  the  history  of  various  physi- 
ological processes,  and  others  will  be  considered  hereafter  under  appropriate 
heads.  In  addition  to  those  already  described,  are  centres  for  defaecation,  at 
the  fifth  lumbar  vertebra  in  dogs  (Budge),  the  erection-centre,  in  the  lumbar 
region  (Eckhard),  and  the  parturition-centre  (Korner),  at  the  first  and  sec- 
ond lumbar  vertebrae.  All  of  the  spinal  centres  act  in  accordance  with  the 
general  laws  of  reflex  phenomena. 


CHAPTER  XIX. 

THE  ENCEPHALIC  GANGLIA. 

Physiological  divisions  of  the  encephalon— Weights  of  the  encephalon  and  of  certain  of  its  parts — The 
cerebral  hemispheres — Cerebral  Convolutions— Basal  ganglia— Corpora  striata,  optic  thalami  and  inter- 
nal capsule — Tubercular  quadrigemina— Pons  Varolii — Directions  of  the  fibres  in  the  cerebrum— Cere- 
bral localization— General  uses  of  the  cerebrum— Extirpation  of  the  cerebrum— Facial  angle— Pathologi- 
cal' observations— Reaction-time— Centre  for  the  expression  of  ideas  in  language— The  cerebellum- 
Physiological  anatomy— Extirpation  of  the  cerebellum— Pathological  observations — Connection  of  the 
cerebellum  with  the  generative  function— Medulla  oblongata  (Bulb)— Physiological  anatomy— Uses  of 
the  medulla  oblongata — Respiratory  nerve-centre — Cardiac  centres— Vital  point  (so  called)— Rolling  and 
turning  movements  following  injury  of  certain  parts  of  the  encephalon. 

THE  encephalic  ganglia  are  collections  of  gray  matter  found  in  the  en- 
cephalon, or  what  is  commonly  known  as  the  brain.  This  part  of  the  cerebro- 
spinal  axis  is  situated  in  the  cranial  cavity.  It  is  provided  with  membranes, 
which  are  similar  to  the  membranes  of  the  spinal  cord  and  have  been  de- 
scribed in  connection  with  the  cord  and  the  general  arrangement  of  the  cere- 
bro-spinal  axis.  The  gross  anatomical  divisions  of  the  encephalon  are  the 
cerebrum,  cerebellum,  pons  Varolii  and  medulla  oblongata.  As  regards  their 
physiological  uses,  the  cerebellum,  pons  and  medulla  are  to  a  certain  extent 
subordinate  to  the  cerebrum.  In  treating  of  the  physiology  of  these  parts, 
it  will  be  convenient  to  take  up  first  the  cerebrum,  or  the  cerebral  hemi- 
spheres, with  their  anatomical  and  physiological  connections  and  their  rela- 
tions to  the  other  parts  of  the  encephalon. 

All  parts  of  the  encephalon  which  act  as  nerve-centres  are  more  or  less 
intimately  connected  with  each  other  anatomically,  and  are  finally  connected, 
through  the  medulla  oblongata,  with  the  spinal  cord.  The  exceptions  to  this 
rule  are  the  centres  of  olfaction,  vision,  audition  and  gustation,  which  will 
be  considered  fully  in  connection  with  the  physiology  of  the  special  senses. 
The  spinal  cord,  as  has  been  seen,  is  capable  of  independent  action  as  a 
nerve-centre  or  collection  of  nerve-centres,  also  serving  as  a  means  of  connec- 
tion between  the  brain  and  the  parts,  through  the  spinal  nerves.  The  motor 
and  sensory  cranial  nerves  are  directly  connected  with  the  encephalon. 

A  detailed  anatomical  description  of  the  brain  would  be  out  of  place  in 


602 


NERVOUS  SYSTEM. 


this  work,  as  there  are  many  anatomical  parts,  the  exact  physiological  rela- 
tions of  which  are  not  understood ;  still,  there  are  certain  parts  which  will 
be  referred  to  by  name,  a  general  knowledge  of  the  arrangement  of  which 
is  necessary.  The  general  relations  of  these  parts  are  shown  in  Fig.  219, 
slightly  reduced  and  modified,  from  Harrison  Allen,  which  represents  a  ver- 
tical longitudinal  section  of  the  brain,  in  the  median  line. 

As  bearing  upon  certain  points  in  the  physiology  of  the  brain,  it  is  im- 
portant to  note  the  weight  of  the  entire  encephalon  and  of  its  great  divisions. 


ANTERIOR  CRUS 
OF  FORNIX 


A  N  T  E  R 1 0  FT^^mHIBI^ 
COMMISSURE  2°NERVE 

INFUNDIBULUM 


PITUITARY  BODY. 

FORAMEN  OFMO 
MIDDLE  COMMISSURE 


OPTIC  THALAMUS 

3P  NERVE 
AQUEDUCTOFSYLVIUS 

PINEAL  GLAND.' 
CORPORA  OUADRIGEMINA1 


4T"  VENTRICLE 


FIG.  219.— View  of  the  structures  displayed  upon  the  right  side  of  a  median  longitudinal  section  of  the 

brain — semi-diagrammatic. 
\ 

Weights  of  the  Encephalon  and  of  Certain  of  its  Parts. — Most  of  the 
tables  of  weights  of  the  healthy  adult  brain  of  the  Caucasian,  given  by  differ- 
ent observers,  give  essentially  the  same  figures,  the  differences  amounting 
to  only  one  or  two  ounces  (28*3  or  56*7  grammes)  for  the  entire  encepha- 
lon. The  average  weight  given  by  Quain,  combining  the  tables  of  Sims, 
Clendinning,  and  Reid,  is  49£  ounces  (1,408-3  grammes)  for  the  male,  and  44 
ounces  (1,247-4  grammes)  for  the  female.  The  number  of  male  brains 
weighed  was  278,  and  of  female  brains,  191.  In  males  the  minimum  weight 
was  34  ounces  (963'9  grammes),  and  the  maximum,  Go  ounces  (1,842*7 
grammes).  In  170  cases  out  of  the  278,  the  weights  ranged  between  46  and 
53  ounces  (1,304-1  and  1,502-5  grammes),  which  may  be  taken  as  the  average 
limits.  In  females  the  minimum  was  31  ounces  (878*8  grammes),  and 
the  maximum,  56  ounces  (1,587*6  grammes).  In  125  cases  out  of  the  191, 
the  weights  ranged  between  41  and  47  ounces  (1,162-3  and  1,332-4  grammes). 

Quain  assumed,  from  various  researches,  that  in  new-born  infants,  the 


THE  CEREBRAL  HEMISPHERES. 


603 


brain  weighs  11-65  ounces  (327-8  grammes),  for  the  male,  and  10  ounces 
(283-5  grammes),  for  the  female.  In  both  sexes,  "  the  weight  of  the  brain 
generally  increases  rapidly  up  to  the  seventh  year,  then  more  slowly  to  be- 
tween sixteen  and  twenty,  and  again  more  slowly  to  between  thirty-one  and 
forty,  at  which  time  it  reaches  its  maximum  point.  Beyond  that  period, 
there  appears  a  slow  but  progressive  diminution  in  weight  of  about  one 
ounce  (28-3  grammes)  during  each  subsequent  decennial  period ;  thus  con- 
firming the  opinion,  that  the  brain  diminishes  in  advanced  life." 

The  comparative  weights  of  the  several  parts  of  the  encephalon,  calcu- 
lated by  Reid  from  observations  upon  the  brains  of  fifty-three  males  and 
thirty-four  females  between  the  ages  of  twenty-five  and  fifty-five,  are  as  fol- 
lows : 


Divisions  of  the  encephalon. 

Males. 

Females. 

Average  weight  of  the  cerebrum 
Average  weight   of    the    cere- 
bellum               

43-98  oz.  (1,247-3  grammes). 
5-25  "       (148-8  grammes). 

38-75  oz.  (1,098-6  grammes). 
4-76  "       (134-9  grammes). 

Average  weight  of  the  pons  and 
medulla  obloncrata  

0-98  "        (28-2  grammes). 

1-01  "         (28-6  grammes). 

. 

Average  weight  of  the  en- 
tire encephalon  

50-21  oz.  (1,423-5  grammes). 

44-52  oz.  (1,262-1  grammes). 

The  proportionate  weight  of  the  cerebellum  to  that  of  the  cerebrum,  in 
the  male,  is  as  1  to  8-^-,  and  in  the  female,  as  1  to  8£  (Quain). 

The  specific  gravity  of  the  whole  encephalon  is  about  1036,  that  of  the 
gray  matter  being  1034,  and  of  the  white,  1040  (Quain). 

THE  CEEEBRAL  HEMISPHERES. 

Cortical  Substance. — The  surface  of  the  cerebral  hemispheres  is  marked 
by  fissures  and  convolutions,  which  serve  to  increase  the  extent  of  the  gray 
substance.  The  sulci  between  the  convolutions  vary  in  depth  in  different 
parts,  the  average  depth  being  about  an  inch  (25-4  mm.).  The  gray  mat- 
ter, which  is  external  and  follows  the  convolutions,  is  fa  to  £  of  an  inch 
(2-1  to  3-2  mm.)  in  thickness.  Anatomists  have  described  this  substance  as 
existing  in  several  layers,  but  this  division  is  mainly  artificial.  In  certain 
parts,  however,  particularly  in  the  posterior  portion  of  the  cerebrum,  the 
gray  substance  is  quite  distinctly  divided  into  two  layers,  by  a  very  delicate, 
intermediate  layer  of  a  whitish  color. 

There  is  a  marked  difference  in  the  appearance  of  the  cells  in  the  most 
superficial  and  in  the  deepest  portions  of  the  gray  substance.  The  super- 
ficial cells  are  small  and  present  a  net-work  of  delicate,  anastomosing  fibres. 
The  deepest  cells  are  much  larger.  Between  these  two  extremes,  in  the 
intermediate  layers,  there  is  a  gradual  transition  in  the  size  of  the  cells. 
Fig.  220  shows  the  layers  of  cells  in  a  vertical  section  of  a  cerebral  convolu- 
tion. The  most  superficial  layer  is  very  thin.  It  contains  much  neuroglia 
and  a  fine  net-work  of  fibrils,  with  a  few  small  nerve-cells.  The  second  layer 
presents  a  large  number  of  small,  so-called  pyramidal  cells.  The  third  layer 


604 


NERVOUS  SYSTEM. 


Iw^MM 

h/l;VM»W<W/tt 


Fio.  220.— Vertical  section  of  the  third  cerebral 
convolution  in  man  (Meynert). 

1,  superficial  layer  ;  2,  layer  of  small  pyramidal 
cells  ;  3.  laye'r  of  large  pyramidal  cells  ;  4,  lay- 
er of  small  irregular  cells  ;  5,  layer  of  spindle- 
shaped  cells  ;  M,  white  substance. 


is  the  thickest  of  all  and  contains 
large,  pyramidal  cells,  which  become 
larger  in  its  deeper  portions.  The 
fourth  layer  contains  a  large  number 
of  smaller  cells,  irregular  in  form  and 
with  branching  prolongations.  The 
fifth  layer  presents  spindle  -  shaped 
cells  with  branching  poles  and  this 
layer  is  just  above  the  white  sub- 
stance. The  pyramidal  cells  present 
a  long  process  above,  which  passes  to- 
ward the  surface,  lateral  branches, 
which  form  a  plexus  of  fine  fibrils, 
and  an  unbranched  prolongation  be- 
low, which  passes  to  the  white  sub- 
stance, in  the  form  of  an  axis-cylin- 
der. The  cells  vary  somewhat  in  their 
appearances  in  different  parts  of  the 
brain.  The  largest  pyramidal  cells 
are  found  in  the  anterior  central  con- 
volution, in  the  upper  part  of  the  pos- 
terior central  convolution  and  the  par- 
acentral  lobule.  Large  cells  with  few 
prolongations  are  found  in  the  poste- 
rior part  of  the  occipital  lobes.  The 
cells  in  this  part  are  connected  to- 
gether by  communicating  poles.  The 
mode  of  connection  of  the  cells  with 
each  other  and  with  the  fibres  of  the 
white  substance  has  already  been  de- 
scribed and  does  not  demand  farther 
mention. 

Cerebral  Convolutions. — The  cere- 
brum presents  a  great  longitudinal 
median  fissure  by  which  it  is  partially 
divided  into  two  lateral  halves.  Fig. 
221,  which  is  based  on  the  well  known 
diagram  of  the  brain,  by  Ecker,  shows 
three  great  fissures,  the  fissure  of  Syl- 
vius, the  fissure  of  Rolando  and  the 
parieto-occipital  fissure.  The  lobes  of 
the  cerebrum  are  (1)  the  frontal  lobe, 
lying  in  front  of  and  above  the  fissure 
of  Sylvius  and  in  front  of  the  fissure 
of  Rolando,  (2)  the  parietal  lobe,  be- 
hind the  frontal  lobe  and  in  front  of 


CEREBRAL  CONVOLUTIONS. 


605 


and  above  the  occipital  lobe,  (3)  the  occipital  lobe,  and  (4)  the  temporo- 
sphenoidal  lobe.     The  parietal  lobe  is  bounded  in  front  by  the  fissure  of 


FIG.  221.— Diagram  of  the  external  surface  of  the  left  cerebral  hemisphere  (modified  from  Ecker). 

Rolando  and  below  by  the  fissure  of  Sylvius  and  the  parieto-occipital  fissure 
(shown  in  Fig.  222).     The  occipital  lobe  lies  below  the  parieto-occipital  fis- 


FIG.  222.—  Diagram  of  the  internal  surface  of  the  right  cerebral  hemisphere,  shown  in  a  longitudinal 

section  in  the  median  line  (modified  from  Ecker). 
40 

\ 


606  NERVOUS  SYSTEM. 

sure.  The  temporo-sphenoidal  lobe  is  situated  below  the  fissure  of  Sylvius 
and  in  front  of  the  occipital  lobe. 

While  the  convolutions  are  not  exactly  the  same  in  all  human  brains,  or 
even  in  both  sides  of  the  brain,  their  arrangement  and  relations  may  be 
described  in  a  general  way  with  sufficient  accuracy  to  enable  one  to  recognize 
easily  the  most  important  physiological  points  in  the  descriptive  anatomy  of 
the  cerebral  surface.  The  diagrammatic  Figs.  221  and  222  give  a  general 
view  of  the  fissures  and  of  the  most  important  convolutions. 

The  first  frontal  convolution  is  bounded  internally  by  the  great  longi- 
tudinal fissure  and  externally  by  a  shallow  fissure  nearly  parallel  to  the  longi- 
tudinal fissure.  The  second  frontal  convolution  lies  next  the  first  frontal 
convolution,  and  is  bounded  externally  by  two  shallow  fissures  lying  in  front 
of  the  fissure  of  Sylvius.  The  third  frontal  convolution  curves  around  the 
short  branch  of  the  fissure  of  Sylvius.  On  either  side  of  the  fissure  of  Ro- 
lando, are  the  anterior  central  convolution  and  the  posterior  central  convolu- 
tion. Curving  around  the  posterior  extremity  of  the  fissure  of  Sylvius,  is 
the  supramarginal  convolution,  which  is  continuous  with  the  first  temporal 
convolution,  the  latter  lying  behind  and  parallel  with  the  fissure  of  Sylvius. 
Internal  to  the  posterior  portion  of  the  parieto-occipital  fissure,  is  the  angular 
convolution,  which  is  continuous  with  the  second  temporal  convolution.  At 
the  inferior  border  of  the  temporo-sphenoidal  lobe,  below  the  first  and  second 
temporal  convolutions,  is  the  third  temporal  convolution.  The  superior  pari- 
etal convolution  lies  by  the  side  of  the  median  fissure  and  is  the  posterior 
continuation  of  the  first  frontal  convolution.  The  situation  of  the  occipital 
convolutions  is  indicated  in  Fig.  221.  ,  In  addition  to  these  convolutions 
upon  the  general  surface  of  the  cerebrum,  there  are  convolutions  on  the  sur- 
face of  the  base  of  the  brain  and  in  the  gray  matter  of  the  sides  of  the  great 
longitudinal  fissure.  In  the  fissure  of  Sylvius,  near  its  ascending  branch, 
between  the  anterior  and  the  posterior  lobes  of  the  brain  and  beneath  the 
third  frontal  convolution,  is  a  group  of  convolutions  constituting  the  island 
of  Eeil. 

Fig.  222  shows  the  most  important  parts  observed  on  the  inner  surface 
of  the  right  hemisphere.  These  parts  do  not  demand  any  explanation  beyond 
that  given  in  the  diagram  itself. 

Basal  Ganglia. — The  ganglia  at  the  base  of  the  brain  are  the  olfactory 
ganglia,  the  corpora  striata,  optic  thalami,  tubercula  quadrigemina  and  the 
gray  matter  of  the  pons  varolii.  The  olfactory  ganglia  will  be  described  in 
connection  with  the  physiology  of  the  sense  of  smell.  The  corpora  striata 
and  the  optic  thalami  are  important  in  their  relations  to  the  internal  capsule 
and  the  paths  of  motor  and  sensory  conduction. 

Corpora  Striata,  Optic  Thalami  and  Internal  Capsule. — The  corpora 
striata  are  pear-shaped  bodies,  situated  at  the  base  of  the  brain,  with  their 
rounded  bases  directed  forward,  and  the  narrower  ends,  backward  and  out- 
ward. Their  external  surface  is  gray,  and  they  present,  on  section,  alternate 
striae  of  white  and  gray  matter.  Between  the  posterior  and  narrow  extremi- 
ties of  these  bodies,  are  the  optic  thalami.  The  corpora  striata  have  what  is 


BASAL  GANGLIA  OF  THE  ENCEPHALON. 


607 


called  an  intraventricular  portion,  projecting  into  the  anterior  part  of  the 
lateral  ventricles,  and  an  extraventricular  portion,  which  is  embedded  in  the 
white  substance  at  the  base  of  the  brain. 

The  optic  thalami  are  oblong  bodies  situated  between  the  posterior  ex- 
tremities of  the  corpora  striata  and  resting  upon  the  crura  cerebri  on  the  two 
sides.  These  are  white  externally,  and  in  their  interior  they  present  a  mixt- 
ure of  white  and  gray  matter. 

If  a  horizontal  section  be  made  through  the  brain,  involving  the  corpora 
striata  and  the  optic  thalami,  the  corpora  striata  present  a  division  into  two 
nuclei.  These  are  the 

caudate  nucleus,  which  1 

is  internal,  and  the 
lenticular  nucleus, 
which  is  external  to 
and  behind  the  cau- 
date nucleus.  Exter- 
nal to  the  lenticular 
nucleus,  is  a  band  of 
white  substance,  called 
the  external  capsule,  in 
which  there  is  a  band 
of  gray  matter,  called 
the  claustrum.  Exter-  K 
nal  to  the  external  cap- 
sule, at  its  anterior 
portion,  is  the  insula, 
or  island  of  Reil. 

Between  the  cau- 
date nucleus  and  the 
lenticular  nucleus  in 
front,  is  a  broad  band 
of  white  fibres,  which 
is  continuous  with  a 
band  of  white  fibres 
lying  posteriorly,  be- 
tween the  lenticular 
nucleus  and  the  optic 
thalamus  on  either 
side.  This  band  is  the 
internal  capsule.  The 
portion  of  the  internal 
capsule  which  lies  between  the  caudate  nucleus  and  the  lenticular  nucleus  is 
called  its  anterior  division.  The  portion  of  the  internal  capsule  situated 
between  the  lenticular  nucleus  and  the  optic  thalamus  is  its  posterior  divis- 
ion. The  bend  where  the  posterior  division  of  the  internal  capsule  joins  the 
anterior  division  is  called  the  knee  of  the  capsule. 


FIG.  223.— Horizontal  section  of  the  hemispheres,  at  the  level  of  the  cere- 
bral ganglia  (Dalton). 

1,  great  longitudinal  fissure  between  the  frontal  lobes  ;  2,  great  longi- 
tudinal fissure  between  the  occipital  lobes  ;  3,  anterior  part  of  the 
corpus  callosum  :  4,  fissure  of  Sylvius  ;  5,  convolutions  of  the  insu- 
la ;  6,  caudate  nucleus  of  the  corpus  striatum  ;  7,  lenticular  nucleus 
of  the  corpus  striatum  ;  8.  optic  thalamus  ;  9,  internal  capsule  ;  10, 
external  capsule  ;  11,  claustruni. 


608 


NERVOUS  SYSTEM. 


The  directions  of  the  fibres  of  the  internal  capsule  are  in  general  terms  the 
following :  Fibres  from  the  crura  cerebri  go  directly  into  the  corpora  striata 

in  front  and  into  the 
optic  thalami  behind. 
This  is  the  course  of 
greater  part   of 
fibres,  but  some 


the 
the 

fibres  go  directly 
through  the  internal 
capsule,  and  thence 
to  the  gray  matter  of 
the  cerebral  convolu- 
tions. Most  of  the 
fibres,  however,  which 
form  the  internal  cap- 
sule, come  from  the 
gray  matter  of  the 
corpora  striata  and 
optic  thalami  and 

FIG.  224.— Diagram  of  the  human  brain  in  a  transverse  vertical  section    curve     Outward      and 
(Dalton). 

1,  pons  Varolii ;  2,  2,  crura  cerebri ;  3,  3,  internal  capsule  ;  4,  4,  corona    Upward   to   gO  to   the 
radiata ;  5,  optic  thalamus ;  6,  lenticular  nucleus ;  7,  corpus  cal-    „„„ y    matter    of      the 

hemispheres.  As  they 

pass  from  the  internal  capsule  to  the  internal  surface  of  the  cerebral  convo- 
lutions, they  form  the  corona  radiata. 

In  the  human  subject,  lesions  affecting  the  anterior  two-thirds  of  the  pos- 
terior division  of  the  internal  capsule  produce  paralysis  of  motion  only,  and 
are  followed  by  descending  degenerations.  The  fibres  in  this  part  are  con- 
nected with  the  corpora  striata.  Lesions  affecting  both  the  anterior  two- 
thirds  and  the  posterior  third  of  the  posterior  division  of  the  internal  capsule 
produce  paralysis  of  motion  and  sensation.  The  fibres'  in  the  posterior  third 
are  connected  with  the  optic  thalami.  Ascending  degenerations  have  not 
been  observed  in  the  fibres  of  the  cerebrum. 

Tubercula  Quadriyemina.  —  These  little  bodies,  sometimes  called  the 
optic  lobes,  are  rounded  eminences,  two  upon  either  side,  situated  just  below 
the  third  ventricle.  The  anterior,  called  the  nates,  are  the  larger.  These 
are  oblong,  and  of  a  grayish  color  externally.  The  posterior,  called  the  testes, 
are  situated  just  behind  the  anterior.  They  are  rounded  and  are  rather 
lighter  in  color  than  the  anterior.  Both  contain  gray  nervous  matter  in 
their  interior.  They  are  the  main  points  of  apparent  origin  of  the  optic 
nerves  and  are  connected  by  commissural  fibres  with  the  optic  thalami.  In 
birds  the  tubercles  are  two  in  number,  instead  of  four,  and  are  called  tuber - 
cula  bigemina.  The  anatomical  and  physiological  relations  of  these  bodies 
will  be  fully  described  in  connection  with  the  sense  of  sight. 

Crura  Cerebri. — The  crura  are  short,  thick,  rounded  bands  which  pass 
from  the  cerebral  hemispheres  to  the  upper  border  of  the  pons  Varolii. 


BASAL  GANGLIA  OF  THE  ENCEPHALON.  609 

They  are  rather  broader  above  than  below  and  are  about  three-quarters  of  an 
inch  (19  mm.)  in  length.  They  are  composed  of  longitudinal  white  fibres 
connecting  various  parts  with  the  cerebrum.  Each  crus  is  divided  into  a 
superficial  and  a  deep  band,  by  a  layer  of  gray  substance  called  the  locus 
niger.  The  locus  niger  contains  small,  multipolar  nerve-cells  and  abundant 
pigmentary  granules.  The  lower,  or  superficial  band  of  the  crus  is  called 
the  crusta.  The  deep  band  is  called  the  tegmentum.  The  crusta  consists 
of  white  fibres  only.  In  the  tegmentum  the  fibres  are  mixed  with  masses 
of  gray  matter. 

Pons  Varolii. — The  pons  Varolii,  called  the  tuber  annulare  or  the  meso- 
cephalon,  is  situated  at  the  base  of  the  brain,  just  above  the  medulla  oblon- 
gata.  It  is  white  externally  and  contains  in  its  interior  a  large  admixture 
of  gray  matter.  It  presents  both  transverse  and  longitudinal  white  fibres. 
Its  transverse  fibres  connect  the  two  halves  of  the  cerebellum.  Its  longi- 
tudinal fibres  are  connected  below  with  the  anterior  pyramidal  bodies  and 
the  olivary  bodies  of  the  medulla  oblongata,  the  lateral  columns  of  the 
cord  and  a  certain  portion  of  the  posterior  columns.  The  fibres  are  con- 
nected above  with  the  crura  cerebri  and  pass  to  the  brain.  The  super- 
ficial transverse  fibres  are  wanting  in  animals  in  which  the  cerebellum  has 
no  lateral  lobes. 

If  the  cerebral  hemispheres,  the  olfactory  ganglia,  the  optic  lobes,  the 
corpora  striata  and  the  optic  thalami  be  removed,  the  animal  loses  the  spe- 
cial senses  of  smell  and  sight  and  the  intellectual  faculties,  there  is  a  certain 
degree  of  enfeeblement  of  the  muscular  system,  but  voluntary  motion  and 
general  sensibility  are  retained.  As  far  as  voluntary  motion  is  concerned, 
an  animal  operated  upon  in  this  way  is  in  nearly  the  same  condition  as  one 
simply  deprived  of  the  cerebral  hemispheres.  There  are  no  voluntary  move- 
ments which  show  any  degree  of  intelligence,  but  the  animal  can  stand,  and 
various  consecutive  movements  are  executed,  which  are  different  from  the 
simple  reflex  acts  depending  exclusively  upon  the  spinal  cord.  The  co-ordi- 
nation of  movements  is  perfect,  unless  the  cerebellum  be  removed.  As  re- 
gards general  sensibility,  an  animal  deprived  of  all  the  encephalic  ganglia, 
except  the  pons  Varolii  and  the  medulla  oblongata,  undoubtedly  feels  pain. 
This  has  been  demonstrated  by  Longet,  Vulpian  and  others.  In  rabbits,  rats 
and  other  animals,  after  removal  of  the  cerebrum,  corpora  striata  and  optic 
thalami,  pinching  of  the  ear  or  foot  is  immediately  followed  by  prolonged 
and  plaintive  cries.  Both  Longet  and  Vulpian  have  insisted  upon  the  char- 
acter of  these  cries  as  indicating  the  actual  perception  of  painful  impressions, 
and  as  very  different  from  cries  that  are  purely  reflex,  according  to  the  ordi- 
nary acceptation  of  this  term.  Longet  alluded  to  the  voluntary  movements 
and  the  cries  observed  in  persons  subjected  to  painful  surgical  operations, 
when  incompletely  under  the  influence  of  an  anesthetic,  concerning  the 
character  of  which  there  can  be  no  doubt.  He  regarded  the  movements  as 
voluntary,  and  the  cries  as  evidence  of  the  acute  perception  of  pain  ;  but  it 
is  well  known  that  such  patients  have  no  recollection  of  any  painful  impres- 
sion, although  they  have  apparently  experienced  great  suffering.  As  far  as 


610  NERVOUS  SYSTEM. 

can  be  judged  from  what  is  positively  known  of  the  action  of  the  encephalic 
centres,  the  pain  under  these  conditions  is  perceived  by  some  nerve-centre, 
probably  in  the  pons  Varolii,  but  the  impression  is  not  conveyed  to  the 
cerebrum  and  is  not  recorded  by  the  memory. 

Taking  all  the  experimental  facts  into  consideration,  the  following  seems 
to  be  the  most  reasonable  view  with  regard  to  the  action  of  the  pons  Varolii 
as  a  nerve-centre : 

It  is  an  organ  capable  of  originating  impulses  giving  rise  to  voluntary 
movements,  when  the  cerebrum,  corpora  striata  and  the  optic  thalami  have 
been  removed,  and  it  probably  regulates  the  automatic  voluntary  movements 
of  station  and  progression.  Many  voluntary  movements,  the  result  of  intel- 
lectual effort,  are  made  in  obedience  to  a  stimulus  transmitted  from  the  cere- 
brum, through  conducting  fibres  in  the  pons  Varolii,  to  the  motor  conduc- 
tors of  the  cord  and  the  general  motor  nerves. 

The  gray  matter  of  the  pons  Varolii  is  also  capable  of  perceiving  painful 
impressions,  which,  when  all  of  the  encephalic  ganglia  are  preserved,  are 
conducted  to  and  are  perceived  by  the  cerebrum,  and  are  remembered ;  but 
there  are  distinct  evidences  of  the  perception  of  pain,  even  when  the  cere- 
brum has  been  removed. 

Directions  of  the  Fibres  in  the  Cerebrum. — Fibres  pass  from  the  cerebral 
hemispheres  to  the  cerebellum.  Commissural  fibres  connect  the  cerebrum 
and  certain  of  the  basal  ganglia  on  the  two  sides.  Fibres  connect  the  gray 
matter  of  the  cerebral  convolutions  on  the  same  side  with  each  other.  Fibres 
pass  from  the  inner  surface  of  the  gray  matter  of  the  cerebrum  to  the  inter- 
nal capsule,  corpora  striata,  optic  thalami  and  pons  Varolii,  to  the  medulla  ob- 
longata  and  thence  to  the  spinal  cord.  The  directions  of  these  four  sets  of 
fibres  have  been  quite  accurately  described. 

1.  Fibres  connecting  the  Cerebrum  with  the  Cerebellum. — (A)  Fibres  from 
the  gray  matter  of  the  frontal  lobe,  in  front  of  the  anterior  central  convolution, 
pass  through  the  anterior  division  of  the  internal  capsule  and  thence  through 
the  inner  portion  of  the  outer  layer  of  the  crus  cerebri  (crusta)  to  the  pons 
Varolii,  where  they  seem  to  go  to  the  cells  of  the  gray  matter.     From  the 
pons,  fibres  go  to  the  lateral  and  posterior  regions  of  the  cerebellum  on  the 
opposite  side.     This  connection,  therefore,  is  crossed.     (B)  Fibres  from  the 
occipital  and  temporo-sphenoidal  lobes  of  the  cerebrum  pass  in  the  outer  por- 
tion of  the  crusta  and  go  to  the  upper  portion  of  the  cerebellum,  near  the 
middle  lobe.     This  connection  is  probably  crossed.     (C)  Above  the  pyramidal 
tract  of  the  crusta,  is  a  small  tract  of  fibres  which  connect  the  caudate  nu- 
cleus of  the  corpus  striatum  with  the  cerebellum  (Gowers). 

2.  Fibres  connecting  the  Two  Sides  of  the  Brain. — (A)  Fibres  coming  from 
the  inner  surface  of  the  gray  matter  of  the  cerebral  convolutions  pass  from 
one  side  to  the  other,  through  the  corpus  callosum,  and  connect  the  two  cere- 
bral hemispheres  with  each  other.     These  are  the  transverse  fibres  of  the 
corpus  callosum.     (B)  Fibres  from  the  gray  matter  of  the  temporo-sphenoidal 
lobe  on  either  side  pass  through  the  corpora  striata  to  the  anterior  com- 
missure.    These  fibres  connect  the  temporo-sphenoidal  lobes,  and  probably 


DIRECTION  OF  THE  FIBRES  IN  THE  CEREBRUM.  611 

also  the  corpora  striata,  on  the  two  sides.  (C)  Fibres  from  the  deeper  portion 
of  the  cms  cerebri  (tegmentnm)  pass  to  the  optic  thalamus  on  either  side  and 
thence  to  the  temporo-sphenoidal  lobes.  These  fibres  form  the  posterior  com- 
missure and  connect  the  temporo-sphenoidal  lobes  and  the  optic  thalami  of 
the  two  sides. 

3.  Fibres  connecting  Different  Cerebral  Convolutions  on  the  same  Side. — 
(A)  The  so-called  arcuate  fibres,  passing  in  a  curved  direction  from  one  con- 
volution to  another,  connect  adjacent  convolutions.     (B)  Other  fibres,  called 
longitudinal  or  collateral  fibres,  connect  distant  convolutions  with  each  other. 
The  fibres  of  the  fornix  connect  the  optic  thalamus  with  the  hippocampus 
major  and  the  ufaic&te  gyrus.     Fibres  in  the  corpus  callosum  connect  the  an- 
terior and  posterior  extremities  of  the  gyrus  f  ornicatus.     These  are  the  longi- 
tudinal fibres  of  the  corpus  callosum.     Other  longitudinal  fibres,  connecting 
parts  more  or  less  distant  from  each  other,  are  found  in  the  taenia  semicircu- 
laris,  the  uftioale  fasciculus,  the  fillet  of  the  gyrus  fornicatus  and  the  inferior 
longitudinal   fasciculus.     The  last-mentioned  fasciculus  connects  the  gray 
matter  of  the  temporo-sphenoidal  and  occipital  lobes. 

4.  Fibres  connecting  the  Brain  with  the  Spinal  Cord. — If  these  fibres  be 
followed  from  the  cortex  of  the  brain  downward,  they  are  called  converg- 
ing, and  if  they  be  followed  from  below  upward,  they  are  called  radiating 
fibres. 

Arising  from  the  internal,  concave  surface  of  the  cortical  substance  of  the 
cerebrum,  the  converging  fibres,  at  first  running  side  by  side  with  the  curved, 
commissure!  fibres,  separate  from  the  latter  as  they  curve  backward  to  pass 
again  to  the  cortical  substance,  and  are  directed  toward  the  corpora  striata 
and  the  optic  thalami.  The  limits  of  the  irregular  planes  of  separation  of 
the  commissural  and  the  converging  fibres  contribute  to-  form  the  boundaries 
of  the  ventricular  cavities  of  the  brain.  In  studying  the  course  of  the  con- 
verging fibres  arising  from  all  points  in  the  concave  surface  of  the  cerebral 
gray  matter,  it  is  found  that  they  take  various  directions.  The  fibres  from 
the  anterior  region  of  the  cerebrum  pass  backward  and  form  distinct  fascic- 
uli which  converge  to  the  gray  substance  of  the  corpora  striata.  The  fibres 
from  the  middle  portion  converge  regularly  to  the  middle  region  of  the  ex- 
ternal portions  of  the  optic  thalami.  The  fibres  from  the  posterior  portion 
pass  from  behind  forward  and  are  distributed  in  the  posterior  portion  of  the 
optic  thalami.  The  fibres  from  the  convolutions  of  the  hippocampi  and  the 
fascia  dentata  are  lost  in  the  gray  substance  lining  the  internal  borders  of 
the  optic  thalami  In  the  course  of  most  of  these  fibres  toward  the  corpora 
striata  and  the  optic  thalami,  they  pass  through  the  internal  capsule. 

The  fibres  from  the  anterior  and  middle  portions  of  the  cerebrum,  espe- 
cially the  middle  portion,  contribute  largely  to  the  formation  of  the  anterior 
two-thirds  of  the  posterior  division  of  the  internal  capsule.  The  fibres  from 
the  posterior  portion  of  the  cerebrum  are  found  in  the  posterior  third  of  the 
posterior  division  of  the  internal  capsule.  The  posterior  fibres  are  probably 
sensory.  The  middle  and  anterior  fibres  are  motor.  The  latter  undergo  de- 
scending degenerations  following  lesions  of  the  anterior  and  posterior  central 


G12 


NERVOUS  SYSTEM. 


convolutions  (Charcot).  A  few  of  the  converging  fibres  from  the  hemispheres 
pass  directly  through  the  internal  capsule  and  have  no  connection  with  the 
corpora  striata  and  optic  thalami. 

From  the  internal  capsule,  the  fibres  pass  in  the  crus  cerebri  to  the  upper 
border  of  the  pons  Varolii.     The  motor  fibres  pass  through  the  pons  as  lon- 


FIG.  225.— Diagrammatic  representation  of  the  direction  of  some  of  the  fibres  in  the  cerebrum  (Le  Bon). 

gitudinal  fibres,  go  to  the  anterior  pyramids  of  the  medulla  oblongata,  where 
most  of  them  decussate,  and  thence  to  the  pyramidal  tracts  of  the  spinal 
cord.  The  sensory  fibres  go  to  the  posterior  part  of  the  cord.  The  converg- 
ing cerebral  fibres  are  re-enforced,  in  their  downward  course,  by  fibres  from 
the  tubercular  quadrigemina  and  the  gray  matter  of  the  pons  Varolii.  Cer- 
tain fibres  go  to  the  olivary  bodies  in  the  medulla  oblongata.  A  more  extend- 
ed description  of  these  fibres  will  be  given  in  connection  with  the  physiologi- 
cal anatomy  of  the  medulla. 

Cerebral  Localization. — The  observations  of  Flourens  (1822  and  1823)  and 
his  immediate  followers,  which  seemed  to  show  that  the  cerebrum  was  neither 
excitable  nor  sensible  to  direct  stimulation,  have  been  so  completely  contra- 
dicted by  the  experiments  of  Fritsch  and  Hitzig  (1870),  Ferrier,  Munk,  Hors- 
ley  and  many  others,  that  the  question  of  the  existence  of  motor  and  sensory 
centres — especially  motor  centres — hardly  admits  of  discussion.  The  negative 
results  obtained  by  Floureus  were  probably  due  to  severe  haemorrhage,  which, 


CEREBRAL  LOCALIZATION. 


613 


according  to  Ferrier,  rapidly  destroys  the  excitability  of  the  motor  cortical 
areas.  Some  of  the  experiments  of  Goltz,  by  which  it  has  been  attempted  to 
prove  that  circumscribed  and  invariable  motor  areas  do  not  exist,  are  an- 
swered by  observations  showing  descending  secondary  degenerations  following 
injury  of  certain  parts  of  the  cerebral  cortex.  The  earlier  observations  on  cere- 
bral localization  were  made  on  dogs.  Later,  experiments  have  been  made 
on  monkeys,  and  the  results  of  these  have  been  to  a  certain  extent  confirmed 
by  pathological  observations  on  the  human  subject.  Beginning  with  the  ob- 
servations in  which  descending  degenerations  have  been  noted  as  a  consequence 
of  destruction  of  parts  of  the  cerebral  cortex,  it  may  be  assumed  that  a  distinct 
area  exists  which  presides  over  certain  localized  muscular  movements. 

Motor  Cortical  Zone. — The  motor  cortical  zone  is  on  either  side  of  the 
fissure  of  Rolando.     It  is  usually  described  as  including  the  anterior  and  pos- 


FIG.  226.— Motor  cortical  zone,  on  the  outer  surface  of  the  cerebrum  (Exner). 

terior  central  convolutions  (see  Fig.  221)  and  the  paracentral  lobule  (see  Fig. 
222).  Faradization  of  parts  in  this  zone  is  followed  by  localized  muscular 
movements.  In  fact,  the  motor  areas  seem  to  be  subject  to  nearly  the 
same  laws,  as  regards  their  reactions  to  Faradic  stimulation,  as  are  the 
motor  nerves.  Forty  Faradic  shocks  per  second  produce  a  corresponding 
number  of  single  muscular  contractions.  Forty-six  shocks  per  second  pro- 
duce a  tetanic  contraction  (Franck  and  Pitres).  Destruction  of  motor  areas 
is  followed  by  partial  loss  of  power  in  certain  sets  of  muscles,  and  by  descend- 
ing secondary  degeneration  of  nerve-fibres,  extending  through  the  corona 
radiata,  the  internal  capsule,  the  crura  cerebri,  the  anterior  pyramids  of  the 
medulla  oblongata  and  finally  the  pyramidal  tracts  of  the  spinal  cord. 


614 


NERVOUS  SYSTEM. 


It  remains  now  to  locate  the  distinct  motor  areas.     This  has  been  done 
on  the  brain  of  the  monkey,  by  Ferrier,  who  has  applied  his  observations  as 


FIG.  227.— Paracentral  lobule,  on  the  inner  surface  of  the  cerebrum  (Exner). 
The  shaded  area  in  the  diagram  is  the  paracentral  lobule. 

nearly  as  possible  to  the  human  brain.     While  the  divisions  made  by  Ferrier 
can  not  be  taken  as  absolute,  experiments  on  monkeys  have  been  followed  by 


FIG.  288.— Lateral  view  of  the  human  brain,  with  certain  motor  cortical  areas  (modified  from  Ferrier). 


CEREBRAL  LOCALIZATION.  615 

results  so  nearly  constant,  that  the  localizations  may  be  accepted  as  nearly  cor- 
rect. In  the  diagram  (Fig.  228)  and  descriptions,  the  centres  for  the  special 
senses  have  been  omitted,  to  be  taken  np  in  connection  with  the  physiology 
of  olfaction,  vision,  audition  and  gustation. 

In  the  following  description,  the  numbers  and  letters  refer  to  Fig.  22({ 
(I).  This,  which  is  on  the  precuneus  (compare  Fig.  222),  indicates  the 
position  of  the  centres  for  movements  of  the  opposite  leg  and  foot,  such  as 
are  concerned  in  locomotion. 

(2),  (3),  (4).  These  numbers,  which  are  over  the  convolutions  bounding 
the  upper  extremity  of  the  fissure  of  Eolando  (including  the  paracentral 
lobule — compare  Fig  222),  include  centres  for  various  complex  movements 
of  the  arms  and  legs,  such  as  are  concerned  in  climbing,  swimming,  etc. ' 

(5)  Situated  at  the  posterior  extremity  of  the  first  frontal  convolution,  at 
its  junction  with  the  anterior  central  convolution,  is  the  centre  for  the  ex- 
tension forward  of  the  arm  and  hand,  as  in  putting  forth  the  hand  to  touch 
something  in  front. 

(6)  Situated  on  the  anterior  central  convolution,  just  behind  the  upper 
end  of  the  posterior  extremity  of  the  second  frontal  convolution,  is  the  cen- 
tre for  the  movements  of  the  hand  and  forearm,  in  which  the  biceps  is  par- 
ticularly engaged ;  viz.,  supination  of  the  hand  and  flexion  of  the  forearm. 

(7),  (8).  Just  below  (6),  on  the  anterior  central  convolution,  are  centres 
respectively  for  the  elevators  and  depressors  of  the  mouth. 

(9),  (10).  These  numbers  taken  together,  on  the  third  frontal  convolu- 
tion, mark  the  centre  for  the  movements  of  the  lips  and  tongue,  as  in  articu- 
lation. "  This  is  the  region,  disease  of  which  causes  aphasia,  and  is  gener- 
ally known  as  Broca's  convolution." 

(11).  This,  which  is  on  the  lower  end  of  the  posterior  central  convolution, 
marks  "  the  centre  of  the  platysma,  retraction  of  the  angle  of  the  mouth." 

(12)  This,  which  is  on  the  posterior  part  of  the  first  and  second  frontal 
convolution,  marks  "  a  centre  for  lateral  movements  of  the  head  and  eyes, 
with  elevation  of  the  eyelids  and  dilatation  of  pupil." 

(«),  (#),  (c),  (d).  These  letters,  on  nearly  the  whole  of  the  posterior  cen- 
tral convolution,  "  indicate  the  centres  of  movement  of  the  hand  and  wrist." 

The  above  description  is  quoted  from  Ferrier,  with  certain  changes  in 
the  nomenclature  of  the  convolutions.  Schafer  and  Horsley  in  the  main 
have  confirmed  and  have  somewhat  extended  the  researches  of  Ferrier. 
These  observers  have  shown  that  the  centres  on  the  outer  surface  of  the 
cerebrum,  near  the  great  longitudinal  fissure,  extend  to  the  inner  surface.  In 
the  first  frontal  convolution,  in  front  of  the  paracentral  lobule,  is  a  centre 
for  movements  of  the  trunk  (Tr.,  Fig.  229),  and  in  front  of  this,  is  a  centre 
for  the  movements  of  the  arm  and  shoulder.  Other  parts  of  the  inner  cere- 
bral surface,  except  the  paracentral  lobule,  are  inexcitable. 

In  man  lesions  of  parts  of  the  motor-cortical  zone  produce  localized  paral- 
ysis, or  what  is  called  monoplegia,  the  action  being  crossed.  "  The  following 
forms  of  monoplegia  have  been  observed  to  attend  localized  cortical  lesions : 
1,  oculo-motor  monoplegia  (isolated  ptosis) ;  2,  facial  monoplegia,  sometimes 


616 


NERVOUS  SYSTEM. 


FIG.  229.— Inner  surface  of  the  right  cerebral  hem- 
isphere (Schafer  and  Horsley). 
A 


combined  with  paralysis  of  the  hypoglossal  nerve ;  3,  brachial  monoplegia, 
or  paralysis  of  the  opposite  arm;  4,  crural  monoplegia,  or  paralysis  of  the 

opposite  leg ;  5,  brachio-facial  mono- 
plegia, or  paralysis  of  the  arm  and 
face "  (Flint's  "  Practice  of  Medi- 
cine "). 

It  is  possible  that  there  may  be 
sensory  centres  in  the  cerebral  cortex, 
but  they  have  not  been  satisfactorily 
localized,  although  attempts  have  been 
made  to  limit  such  areas  by  studying 
reflex  phenomena  following  stimula- 
tion of  certain  parts.  It  may  be  stated 

.  S.,  area  governing  the  movements  of  the  arm    ^  o-pnpral  tprmq  thnr  fhp  oppinitfll  and 
and  shoulder  ;  Tr.,  area  for  movements  of  the    m  &elj 

lobule)  area  for  temporo -  sphenoidal  lobes,  the  fibres 
from  which  pass  through  the  posterior 
third  of  the  posterior  division  of  the  internal  capsule,  are  specially  connected 
with  sensation. 

One  of  the  most  important  of  the  cerebral  centres  is  the  centre  for 
speech,  which  will  be  fully  described  after  the  consideration  of  the  general 
uses  of  the  cerebral  hemispheres. 

GENERAL  USES  OF  THE  CEREBRUM. 

The  cortical  gray  substance  of  the  cerebral  hemispheres  not  only  is  capable 
of  generating  motor  impulses  of  the  kind  known  as  voluntary,  and  of  receiv- 
ing sensory  impressions,  including  those  connected  with  the  special  senses, 
but  its  anatomical  and  physiological  integrity,  and  its  connections,  especially 
with  sensory  conductors,  are  essential  to  what  are  known  as  mental  opera- 
tions. The  existence  of  the  mind  and  the  possibility  of  normal  operations 
of  the  intelligence  depend  upon  the  existence  of  the  gray  matter  of  the  cere- 
bral cortex  and  its  normal  physiological  condition  and  relations.  This  prop- 
osition does  not  imply  that  the  mind  is  a  force  which  operates  through  the 
brain,  or  even,  strictly  speaking,  that  the  brain  is  the  seat  of  the  intellectual 
faculties.  Mental  operations  involve  a  slight  elevation  of  temperature  and 
slightly  increase  some  of  the  excretions.  It  is  probable,  therefore,  that  they 
involve  changes  of  matter  ;  and  these  changes,  if  they  occur,  can  be  effected 
only  by  the  cells  of  the  brain.  Without  defining  or  analyzing  the  intellec- 
tual faculties  or  attempting  to  locate  different  faculties  in  special  parts,  it  is 
sufficient  to  state  that  certain  of  these  faculties  reside  probably  in  that  por- 
tion of  the  brain  which  is  anterior  to  the  motor  cortical  zone ;  that  is,  in  the 
frontal  lobes.  These  lobes,  as  far  as  is  known,  do  not  present  motor  or  sen- 
sory areas. 

The  brain  and  the  intellectual  power  of  man  are  so  far  superior  in  their 
development  to  this  organ  and  its  properties  in  the  lower  animals,  that  some 
philosophers  have  regarded  the  human  intelligence  as  distinct  in  nature  as 
well  as  in  degree.  Although  physiologists  do  not  generally  accept  this  prop- 


GENERAL  USES  OF  THE  CEREBRUM.  617 

osition,  regarding  the  intelligence  of  man  as  simply  superior  in  degree  to 
that  of  the  lower  animals,  it  is  evident  that  this  difference  in  the  degree  of 
development  is  so  great  as  to  render  the  human  mind  hardly  comparable 
with  the  intellectual  attributes  of  animals  low  in  the  scale.  Still,  there  can 
be  no  doubt  with  regard  to  the  identity  of  the  nature  of  the  faculties  of  the 
brain  in  man  and  in  some  of  the  lower  animals,  however  much  these  facul- 
ties may  differ  in  their  degree  of  development.  If  this  proposition  be  true, 
it  is  reasonable  to  apply  experiments  on  the  brain  in  the  lower  animals  to  the 
physiology  of  corresponding  parts  in  the  human  subject. 

Extirpation  of  the  Cerebrum. — Experiments  upon  different  classes  of 
animals  show  clearly  that  the  brain  is  less  important,  as  regards  the  ordinary 
manifestations  of  animal  life,  in  proportion  as  its  relative  development  is 
smaller.  For  example,  if  the  cerebral  hemispheres  be  removed  from  fishes 
or  reptiles,  the  movements  which  are  called  voluntary  may  be  but  little 
affected ;  while  if  the  same  mutilation  be  performed  in  birds  or  some  of  the 
mammalia,  the  diminished  power  of  voluntary  motion  is  much  more  marked. 
It  would  be  plainly  unphilosophical  to  assume,  because  a  fish  or  a  frog  will 
swim  in  water  and  execute  movements  after  removal  of  the  hemispheres 
very  like  those  of  the  uninjured  animal,  that  the  feeble  intelligence  possessed 
by  these  animals  is  not  destroyed  by  the  operation.  It  is  not  only  possible 
but  probable  that  in  the  very  lowest  of  the  vertebrates,  the  operations  of  the 
nervous  centres  are  not  the  same  as  in  higher  animals.  There  is,  for  exam- 
ple, a  fish  (the  lancet-fish,  Amphioxus  lanceolatus),  that  has  no  brain,  all  of 
the  functions  of  animal  life  being  regulated  by  the  gray  substance  of  the 
spinal  cord.  It  is  essential,  therefore,  in  endeavoring  to  apply  the  results  of 
experiments  upon  the  brain  in  the  lower  animals  to  human  physiology,  to 
isolate,  as  far  as  possible,  the  distinct  manifestations  of  intelligence  from 
automatic  movements. 

Flourens  (1822  and  1823)  made  a  series  of  important  observations  upon 
the  different  parts  of  the  encephalon.  As  regards  the  cerebral  hemispheres, 
he  found  that  the  complete  removal  of  these  parts  in  living  animals  (frogs, 
pigeons,  fowls,  mice,  moles,  cats  and  dogs),  was  invariably  followed  by 
stupor,  apparent  loss  of  intelligence  and  absence  of  even  the  ordinary  in- 
stinctive acts.  Animals  thus  mutilated  retained  general  sensibility  and  the 
power  of  voluntary  movements,  but  were  thought  to  be  deprived  of  the  spe- 
cial senses  of  sight,  hearing,  smell  and  taste.  As  regards  general  sensibility 
and  voluntary  movements,  Flourens  was  of  the  opinion  that  animals  de- 
prived of  their  cerebral  lobes  possessed  sensation,  but  had  lost  the  power  of 
perception,  and  that  they  could  execute  voluntary  movements  when  an 
irritation  was  applied  to  any  part,  but  had  lost  the  power  of  making  such 
movements  in  obedience  to  an  effort  of  the  will.  One  of  the  most  remark- 
able phenomena  observed  was  entire  loss  of  memory  and  of  the  power  of 
connecting  ideas.  The  voluntary  muscular  system  was  enfeebled  but  not 
paralyzed.  Removal  of  one  hemisphere  produced,  in  the  higher  classes  of 
animals  experimented  upon,  enfeeblement  of  the  muscles  upon  the  opposite 
side,  but  the  intellectual  faculties  were  in  part  or  entirely  retained. 


618  NERVOUS  SYSTEM. 

The  observations  of  Flourens  have  been  repeated  by  many  physiologists, 
and  were  in  the  main  confirmed,  except  as  regards  the  special  senses.  Bouil- 
laud  (1826)  made  a  large  number  of  observations  upon  pigeons,  fowls,  rab- 
bits and  other  animals,  in  which,  after  removal  of  the  hemispheres,  he  noted 
the  persistence  of  the  senses  of  sight  and  hearing.  Longet  finally  demon- 
strated the  fact  that  both  sight  and  hearing  are  retained  after  extirpation  of 
the  hemispheres,  even  more  clearly  than  Bouillaud,  by  the  following  experi- 
ments :  He  removed  the  hemispheres  from  a  pigeon,  the  animal  surviving 
the  operation  eighteen  days.  When  this  animal  was  placed  in  a  dark  room 
and  a  light  was  suddenly  brought  near  the  eyes,  the  iris  contracted  and  the 
animal  winked ;  "  but  it  was  remarkable,  that  when  a  lighted  candle  was 
moved  in  a  circle,  and  at  a  sufficient  distance,  so  that  there  should  be  no 
sensation  of  heat,  the  pigeon  executed  an  analogous  movement  of  the  head." 
An  examination  after  death  showed  that  the  removal  of  the  cerebrum  had 
been  complete.  An  animal  deprived  of  the  hemispheres  also  opened  the  eyes 
at  the  report  of  a  pistol  and  gave  other  evidence  that  the  sense  of  hearing 
was  retained. 

With  regard  to  the  senses  of  smell  and  taste,  it  is  more  difficult  to  deter- 
mine their  presence  than  to  ascertain  that  the  senses  of  sight  and  hearing  are 
retained.  It  is  probable,  however,  that  the  sense  of  smell  is  not  abolished, 
if  the  hemispheres  be  carefully  removed,  leaving  the  olfactory  ganglia  intact ; 
and  there  is  no  direct  evidence  that  extirpation  of  the  cerebrum  affects  the 
sense  of  taste ;  indeed,  in  young  cats  and  dogs,  Longet  has  noted  evidences 
of  a  disagreeable  impression  following  the  introduction  of  a  concentrated 
solution  of  colocynth  into  the  mouth,  as  distinctly  as  in  the  same  animals 
under  normal  conditions. 

Comparative  Development  of  the  Cerebrum  in  tlie  Lower  Animals. — It  is 
only  necessary  to  refer  very  briefly  to  the  development  of  the  cerebrum  in 
the  lower  animals  as  compared  with  the  human  subject,  to  show  the  connec- 
tion of  the  hemispheres  with  intelligence.  In  man  the  cerebrum  presents  a 
large  preponderance  in  weight  over  other  portions  of  the  encephalon ;  and 
in  some  of  the  lower  animals  the  cerebrum  is  even  less  in  weight  than  tho 
cerebellum.  In  man,  also,  not  only  the  relative  but  the  absolute  weight  of 
the  brain  is  greater  than  in  lower  animals,  with  but  two  exceptions.  Todd 
has  cited  a  number  of  observations  made  upon  the  brains  of  elephants,  in 
Avhich  the  weights  ranged  between  nine  and  ten  pounds  (about  4,000  and 
4,500  grammes).  Rudolphi  gave  the  weight  of  the  encephalon  of  a  whale, 
seventy-five  feet  long  (about  23  metres),  as  considerably  over  five  pounds 
(about  2,300  grammes).  With  the  exception  of  these  animals,  man  possesses 
the  largest  brain  in  the  zoological  scale. 

Another  interesting  point  in  this  connection  is  the  development  of  cere- 
bral convolutions  in  certain  animals,  by  which  the  relative  quantity  of  gray 
matter  is  increased.  In  fishes,  reptiles  arid  birds,  the  surface  of  the  hemi- 
spheres is  smooth ;  but  in  many  mammalia,  especially  in  those  remarkable  for 
intelligence,  the  cerebrum  presents  a  greater  or  less  number  of  convolutions, 
as  it  does  in  the  human  subject. 


GENERAL  USES  OF  THE  CEREBRUM.  619 

Development  of  the  Cerebrum  in  Different  Races  of  Men  and  in  Different 
Individuals. — It  may  be  stated  as  a  general  proposition,  that  in  the  different 
races  of  men,  the  cerebrum  is  developed  in  proportion  to  their  intellectual 
power ;  and  in  different  individuals  of  the  same  race,  the  same  general  rule 
obtains.  Still,  this  law  presents  marked  exceptions.  Certain  brains  in  an 
inferior  race  may  be  larger  than  the  average  in  the  superior  race ;  and  it  is 
frequently  observed  that  unusual  intellectual  vigor  is  co-existent  with  a  small 
brain,  and  the  reverse.  These  exceptions,  however,  do  not  take  away  from 
the  force  of  the  original  proposition.  As  regards  races,  the  rule  is  found  to 
be  invariable,  when  a  sufficient  number  of  observations  are  analyzed,  and  the 
same  holds  true  in  comparing  a  large  number  of  individuals  of  the  same  race. 
Average  men  have  an  advantage  over  average  women  of  about  six  ounces 
(170  grammes)  of  cerebral  substance ;  and  while  many  women  are  far  superior 
in  intellect  to  many  men,  such  instances  are  not  sufficiently  frequent  to 
invalidate  the  general  law,  that  the  greatest  intellectual  capacity  and  mental 
vigor  is  coincident  with  the  greatest  quantity  of  cerebral  substance.  If  the 
view,  which  is  in  every  way  reasonable,  be  accepted,  that  the  gray  substance 
alone  of  the  cerebral  hemispheres  is  directly  connected  with  the  mind,  it 
would  be  necessary,  in  comparing  different  individuals  with  the  view  of 
establishing  a  definite  relation  between  brain-substance  and  intelligence,  to 
estimate  the  quantity  of  gray  matter ;  but  it  is  not  easy  to  see  how  this  can 
be  done  with  any  degree  of  accuracy. 

It  is  undoubtedly  true  that  proper  training  and  exercise  develop  and 
increase  the  vigor  of  the  intellectual  faculties,  and  that  thereby  the  brain  is 
increased  in  power,  as  are  the  muscles  under  analogous  conditions.  This  will 
perhaps  explain  some  of  the  exceptions  above  indicated ;  but  an  additional 
explanation  may  be  found  in  differences  in  the  quality  of  brain-substance  in 
different  individuals,  irrespective  of  the  size  of  the  cerebral  hemispheres. 
One  evidence  that  these  differences  in  the  quality  of  intellectual  working 
matter  exist,  is  that  some  small  brains  actually  accomplish  more  and  better 
work  than  some  large  brains.  This  fact  may  be  due  to  differences  in  train- 
ing, to  the  extraordinary  development,  in  some  individuals,  of  certain  quali- 
ties, to  intensity  and  pertinacity  of  purpose,  capacity  for  persistent  labor  in 
certain  directions,  a  fortunate  direction  of  the  mental  efforts,  opportunity  and 
circumstances,  etc. ;  but  aside  from  these  considerations,  it  is  exceedingly 
probable  that  there  are  important  individual  differences  in  the  quality  of 
nervous  matter. 

facial  Angle. — It  is  not  necessary  to  enter  into  an  extended  discussion 
of  the  relations  of  the  facial  angle  to  intelligence.  It  was  proposed  by 
Camper  to  take  the  angle  made  at  the  junction  of  two  lines,  one  drawn  from 
the  most  projecting  part  of  the  forehead  to  the  alveolae  of  the  teeth  of  the 
upper  jaw,  and  another  passing  horizontally  backward  from  the  lower  ex- 
tremity of  the  first  line,  as  the  facial  angle.  This  angle  is  to  a  certain  extent 
a  measure  of  the  projection  of  the  anterior  lobes  of  the  brain.  A  number  of 
observations  upon  the  facial  angle  in  different  races  has  been  made  by  Camper 
and  by  other  physiologists  and  ethnologists.  These  show,  in  general  terms, 


620  NERVOUS  SYSTEM. 

that  the  angle  is  larger  in  man  than  in  any  of  the  inferior  animals  and  is 
largest  in  those  races  that  possess  the  greatest  intellectual  development. 

Pathological  Observations. — It  is  a  fact  now  generally  admitted  in  pathol- 
ogy, that  loss  of  cerebral  substance  from  repeated  haemorrhage  is  sooner  or 
later  followed  by  impairment  of  the  intellectual  faculties.  This  point  is 
frequently  difficult  to  determine  in  an  individual  instance,  but  an  analysis  of 
a  sufficient  number  of  cases  shows  impaired  memory,  tardy,  inaccurate  and 
feeble  connection  of  ideas,  abnormal  irritability  of  temper  with  a  childish 
susceptibility  to  petty  or  imaginary  annoyances,  easily  excited  emotional 
manifestations  and  a  variety  of  phenomena  denoting  abnormally  feeble  intel- 
lectual power,  following  any  considerable  disorganization  of  cerebral  sub- 
stance. In  short,  pathological  conditions  of  the  brain  all  go  to  show  that 
the  intellectual  faculties  are  directly  connected  with  the  cerebral  hemispheres. 

In  idiots  the  brain  usually  is  of  small  size,  although  there  are  exceptions 
to  this  rule.  In  two  cases  of  adult  idiots,  reported  by  Tiedemann,  the  brain 
was  about  one-half  of  the  normal  weight.  The  brain  of  an  idiotic  woman, 
forty-two  years  of  age,  reported  by  Gore,  weighed  ten  ounces  and  five  grains 
(about  284  grammes).  It  has  been  observed,  also,  that  the  cerebellum  is 
not  proportionally  diminished  in  size  in  idiots  (Bradley).  In  one  instance 
reported,  the  proportion  of  the  cerebellum  to  the  cerebrum  was  as  1  to  5-5. 
In  the  healthy  adult  male  of  ordinary  weight,  the  proportion  is  as  1  to  8^. 
The  statements  just  made  with  regard  to  the  brains  of  idiots  refer  to  cases 
characterized  by  complete  absence  of  intelligence,  and  f arthermore,  probably, 
by  very  small  development  of  the  body.  On  the  other  hand,  there  are 
instances  of  idiocy,  the  body  being  of  ordinary  size,  in  which  the  weight  of 
the  encephalon  is  little  if  any  below  the  average.  Lelut  has  reported  several 
cases  of  this  kind.  In  one  of  these,  a  deaf-mute  idiot,  forty-three  years  of 
age,  a  little  above  the  ordinary  stature,  presenting  "idiocy  of  the  lowest 
degree ;  almost  no  sign  of  intelligence ;  no  care  of  cleanliness,"  the  encepha- 
lon weighed  48*32  oz.  (1,369'8  grammes).  Other  cases  of  idiots  of  medium 
stature  are  given,  in  which  the  brain  weighed  but  little  less  than  the  normal 
average.  In  the  West  Riding  Lunatic  Asylum  Reports^  London,  1876,  is 
a  report  of  the  case  of  a  congenital  imbecile,  aged  thirty  years,  height  five 
feet  and  eight  inches  (172*7  centimetres),  died  of  phthisis,  whose  brain 
weighed  70£  oz.  (2,000  grammes).  This  is  heavier  than  the  heaviest  normal 
brain  on  record.  The  normal  brain-weight  is  49|-  oz.  (1,408'3  grammes). 

Reaction-Time. — The  time  which  elapses  between  the  application  of  a 
stimulus  and  its  appreciation  by  the  individual  experimented  upon  is  known 
as  reaction-time.  In  experiments  with  reference  to  this  point,  the  person 
observed  makes  an  electric  signal  when  the  sensation  is  perceived.  The  reac- 
tion-time is  0*12  of  a  second  for  a  shock  on  the  hand,  0*13  for  the  forehead, 
0-17  for  the  toe  and  0-13  for  a  sudden  noise  (Exner).  The  duration  is  about 
0-16  of  a  second  for  impressions  made  on  the  nerves  of  special  sense.  This  is 
the  time  of  conduction  of  the  impression  to  the  brain,  its  appreciation  by  the 
individual,  the  generation  of  the  voluntary  impulse  and  the  conduction  of 
this  impulse  to  the  muscles  concerned  in  making  the  signal.  It  is  probably 


CENTRE  FOR  SPEECH.  621 

subject  to  variations  analogous  to  those  observed  in  the  "personal  equa- 
tion." 

Centre  for  the  Expression  of  Ideas  in  Language. — The  location  of  this 
centre  depends  entirely  upon  the  study  of  cases  of  disease  in  the  human  sub- 
ject. It  is  evident  that  there  must  be  a  comprehension  of  the  significance  of 
words,  the  formation  of  an  idea  more  or  less  complex,  and  a  co-ordinate  action 
of  the  muscles  concerned  in  speech,  as  conditions  essential  to  expression  in 
spoken  words.  One  or  more  of  these  conditions  may  be  absent  in  cases  of 
disease ;  and  the  general  absence  of  the  power  of  verbal  expression,  when 
this  depends  on  cerebral  lesion,  is  known  as  aphasia.  This  is  quite  different 
.from  aphonia,  which  is  simply  loss  of  voice.  If  the  comprehension  of  the 
meaning  of  words  be  absent,  the  individual  is  incapable  of  receiving  ideas 
expressed  in  language.  In  cases  of  aphasia  it  often  is  difficult  to  determine 
this  point.  In  certain  cases  it  is  possible  that  the  individual  may  under- 
stand what  is  said  and  may  form  ideas  to  which  he  is  unable  to  give  verbal 
expression.  In  such  instances  he  can  neither  speak  nor  write.  There  are 
certain  cases  in  which  the  written  or  printed  words  convey  no  idea,  while 
spoken  words  are  understood,  but  there  is  no  loss  of  intelligence  and  words 
are  spoken  without  difficulty.  This  condition  is  called  word-blindness.  If 
there  be  simple  want  of  co-ordination  of  the  muscles  concerned  in  speech, 
words  are  spoken  which  may  have  no  connection  with  the  idea  to  be  con- 
veyed, but  the  individual  may  be  able  to  express  himself  in  writing.  This 
condition  is  known  as  ataxic  aphasia.  The  inability  to  express  ideas  in  writ- 
ing is  called  agraphia,  and  this  is  usually  an  indication  of  the  condition 
known  as  amnesic  aphasia,  in  which  it  is  impossible  to  put  ideas  into  words 
in  any  way.  Persons  affected  with  purely  ataxic  aphasia  may  understand 
and  write  perfectly,  but  they  can  not  read  aloud  or  repeat  words  or  sentences 
spoken  to  them.  In  cases  of  simple  amnesic  aphasia,  patients  can  sometimes 
repeat  dictated  words.  In  cases  in  which  hemiplegia  is  marked,  the  aphasia 
usually  is  ataxic.  In  cases  in  which  there  is  no  hemiplegia,  the  aphasia  usu- 
ally is  amnesic.  The  ataxic  and  amnesic  forms  of  aphasia  may  be  combined. 
A  full  description,  however,  of  the  many  and  varied  forms  of  aphasia  would 
be  out  of  place  in  this  work. 

In  1766,  Pourfour  du  Petit  reported  a  case  of  aphasia,  with  lesion  of  the 
left  frontal  lobe  of  the  cerebrum,  in  which  the  patient  could  pronounce 
nothing  but  "  non." 

Marc  Dax  (1836)  indicated  loss  or  impairment  of  speech  in  one  hundred 
and  forty  cases  of  right  hemiplegia.  These  observations  attracted  little  at- 
tention, until  1861,  when  the  subject  was  studied  by  Broca.  Since  then, 
many  cases  of  aphasia  with  lesion  of  the  left  frontal  lobe  have  been  reported 
by  various  writers.  In  1863,  M.  G.  Dax,  a  son  of  Marc  Dax,  limited  the 
lesion  to  the  middle  portion  of  the  left  frontal  lobe.  It  was  farther  stated, 
by  Broca  and  Hughlings  Jackson,  to  be  that  portion  of  the  brain  nourished 
by  the  left  middle  cerebral  artery  (the  inferior  frontal  branch).  According 
to  recent  observers,  the  most  frequent  lesion  is  in  the  parts  supplied  by  the 
left  middle  cerebral  artery,  particularly  the  lobe  of  the  insula,  or  the  island 

41 


622  NERVOUS  SYSTEM. 

of  Ilcil ;  iind  it  is  a  curious  fact  that  this  part  is  found  only  in  man  and 
monkeys,  being  in  the  latter  very  slightly  developed. 

While  (lie  cerebral  lesion  in  aphasia  involves  the  left  frontal  lobe  in  tho 
great  majority  of  cases,  there  are  instances  in  which  the  right  lobe  alone  is 
affected,  and  these  occur  in  left-handed  persons.  Aside  from  the  anatomi- 
cal arrangement  of  the  arteries,  which  seem  to  furnish  a  greater  quantity  of 
blood  to  the  left  hemisphere,  it  is  evident  that  as  far  as  voluntary  move- 
ments are  concerned,  the  right  hand,  foot,  eye  etc.,  are  used  in  preference 
to  the  left,  and  that  the  motor  operations  of  the  left  hemisphere  are  superior 
in  activity  to  those  of  the  right.  Batcman  has  quoted  two  cases  of  aphasia 
dependent,  upon  lesion  of  the  right  side  of  the  brain,  and  consequent  left 
hemiplegia,  in  which  the  persons  were  left-handed ;  and  these,  few  as  they 
are,  are  important,  as  showing  that  a  person  may  use  the  right  side  of  the 
brain  in  speech,  as  in  the  other  motor  acts.  Although  most  anatomists  have 
failed  to  find  any  considerable  difference  in  the  weight  of  the  two  cerebral 
hemispheres,  Boyd  has  shown  by  an  "  examination  of  nearly  two  hundred 
cases  at  St.  Marylebone,  in  which  the  hemispheres  were  weighed  separately, 
that  almost  invariably  the  weight  of  the  left  exceeded  that  of  the  right  by 
at  least  the  eighth  of  an  ounce  (4-5  grammes)." 

Broadbent  has  reported  an  examination  of  the  encephalon  of  a  deaf  and 
dumb  woman.  In  this  case  the  brain  was  found  to  be  of  about  the  usual 
weight,  but  tho  loft  third  frontal  convolution  was  of  "  comparatively  small 
size  and  simple  character." 

Taking  into  consideration  all  of  the  pathological  facts  bearing  upon  the 
question,  it  seems  certain  that  in  the  great  majority  of  persons,  the  organ  or 
part  presiding  over  the  faculty  of  language  is  situated  on  the  left  side,  at  or 
near  tho  third  frontal  convolution  and  the  island  of  Roil,  mainly  in  the  parts 
supplied  by  tho  middle  cerebral  artery.  In  some  few  instances  the  organ 
seems  to  be  in  the  corresponding  part  upon  the  right  side.  It  is  possible 
that  originally  both  sides  preside  over  speech,  and  the  superiority  of  the  left 
side  of  the  brain  over  the  right  and  its  more  constant  use  by  preference  in 
right-handed  persons  may  lead  to  a  gradual  abolition  of  the  action  of  tho 
right  side  of  tho  brain,  in  connection  with  speech,  simply  from  disuse.  This 
view,  however,  is  purely  hypothetical.  In  some  cases  of  aphasia  from  lesion 
of  the  speech-centre  in  the  left  hemisphere,  recovery  takes  place,  and  occa- 
sionally "  speech  has  been  again  lost  when  a  fresh  lesion  occurred  in  this 
part  of  the  right  hemisphere  "  (Gowers).  In  the  ataxic  form  of  aphasia,  the 
idea  and  memory  of  words  remain,  and  there  is  loss  of  speech  simply  from 
inability  to  co-ordinate  the  muscles  concerned  in  articulate  language.  Pa- 
tients affected  in  this  way  can  not  speak  but  can  write  with  ease  and  correct- 
ness. In  the  amiu-sie  form  of  the  disease,  the  idea  and  memory  of  language 
are  lost ;  patients  can  not  speak,  and  are  affected  with  agraphia,  or  inability 
to  write.  The  motor  tracts  from  the  centre  for  speech  pass  to  the  anterior 
portion  of  tho  posterior  division  of  the  internal  capsule  and  thence  through 
tho  left  cms,  into  tho  pons  Varolii,  where  they  decussate  and  go  to  the  right 
side  of  the  medulla  oblongata. 


THE  CEREBELLUM. 


623 


THE  CEREBELLUM. 

It  is  not  necessary  in  order  to  comprehend  the  uses  of  the  cerebel- 
lum, as  far  as  these  are  known,  to  enter  into  a  full  description  of  its 
anatomical  characters.  The  points,  in  this  connection,  that  are  most  im- 
portant are  the  following :  the  division  of  the  substance  of  the  cerebellum 
into  gray  and  white  matter;  the  connection  between  the  cells  and  the 
fibres ;  the  connection  of  the  fibres  with  the  cerebrum  and  with  the  prolon- 
gations of  the  columns  of  the  spinal  cord  ;  the  passage  of  fibres  between  the 
two  lateral  lobes.  These  are  the  only  anatomical  points  that  will  be  con- 
sidered. 

Physiological  Anatomy. — The  cerebellum,  situated  beneath  the  posterior 
lobes  of  the  cerebrum,  weighs  about  5*25  ounces  (148*8  grammes)  in  the  male, 
and  4*7  ounces  (135  grammes)  in  the  female.  The  proportionate  weight  to 
that  of  the  cerebrum  is  as  1  to  8$  in  the  male,  and  as  1  to  8£  in  the  female. 
The  cerebellum  is  separated  from  the  cerebrum  by  a  strong  process  of  the 
dura  mater,  called  the  tentorium.  Like  the  cerebrum,  the  cerebellum  pre- 
sents an  external  layer  of  gray  matter,  the  interior  being  formed  of  white,  or 
fibrous  nerve-tissue.  The  extent  of  the  gray  substance  is  much  increased 
by  abundant,  fine  convolutions  and  is  farther  extended  by  the  penetration, 
from  the  surface,  of  arborescent  processes  of  gray  matter.  Near  the  centre 
of  each  lateral  lobe,  embedded  in  the  white  substance,  is  an  irregularly  den- 
tated  mass  of  gray 

matter,  called   the  <t 

corpus  dentatum. 
The  convolutions 
are  finer  and  more 
abundant  and  the 
gray  substance  is 
deeper  in  the  cere- 
bellum than  in  the 
cerebrum.  These 
convolutions,  also, 
are  present  in  many 
of  the  inferior  ani- 
mals in  which  the 
surface  of  the  cere- 
brum is  smooth. 

The  cerebellum 
consists  of  two  lat- 
eral hemispheres, 

more  largely  developed  in  man  than  in  the  inferior  animals,  and  a  median 
lobe.  The  hemispheres  are  subdivided  into  smaller  lobes,  which  it  is  unne- 
cessary to  describe.  Beneath  the  cerebellum,  bounded  in  front  and  below  by 
the  medulla  oblongata  and  pons  Varolii,  laterally,  by  the  superior  peduncles, 
and  above,  by  the  cerebellum  itself,  is  a  lozenge-shaped  cavity,  called  the 


FIG.  230.— Cerebellum  and  medulla  oblongata  (Hirschfeld). 
1, 1,  corpus  dentatum  ;  2,  pons  Varolii ;  3,  section  of  the  middle  peduncle  ; 
4,  4,  4,  4,  4,  4,  laminae  forming  the  arbor  vitas  ;  5,  5,  olivary  body  of  the 
medulla  oblongata  ;  6,  anterior  pyramid  of  the  medulla  oblongata  ;  7, 
upper  extremity  of  the  spinal  cord. 


624  NERVOUS  SYSTEM. 

fourth  ventricle.  The  crura,  or  peduncles,  will  be  described  in  connection 
with  the  direction  of  the  fibres. 

The  gray  substance  of  the  convolutions  is  divided  quite  distinctly  into  an 
internal  and  an  external  layer.  The  internal  layer  presents  an  exceedingly 
delicate  net-work  of  fine  nerve-fibres  which  pass  to  the  cells  of  the  external 
layer.  The  external  layer  is  somewhat  like  the  external  layer  of  gray  sub- 
stance of  the  posterior  lobes  of  the  cerebrum  and  is  more  or  less  sharply  di- 
vided into  two  or  more  secondary  layers.  The  most  external  portion  of  this 
layer  contains  a  few  small  nerve-cells  and  fine  filaments  of  connective  tissue. 
The  rest  of  the  layer  contains  a  great  number  of  large  cells,  rounded  or  ovoid, 
with  two  or  three  and  sometimes  four  prolongations.  The  mode  of  connec- 
tion between  the  nerve-cells  and  the  fibres  has  already  been  described  under 
the  head  of  the  general  structure  of  the  nervous  system. 

Directions  of  the  Fibres  in  the  Cerebellum. — Fibres  from  the  gray  sub- 
stance of  the  convolutions  and  their  prolongations,  and  from  the  corpus  denta- 
tum,  converge  to  form  the  three  cerebellar  peduncles  on  either  side.  The 
superior  peduncles  pass  forward  and  upward  to  the  crura  cerebri  and  the 
optic  thalami.  These  connect  the  cerebellum  with  the  cerebrum.  Beneath 
the  tubercular  quadrigemina,  some  of  these  fibres  decussate  with  the  corre- 
sponding fibres  from  the  opposite  side ;  so  that  certain  of  the  fibres  of  the 
superior  peduncles  pass  to  the  corresponding  side  of  the  cerebrum  and  others 
pass  to  the  cerebral  hemisphere  of  the  opposite  side.  The  connections 
between  the  cerebrum  and  the  cerebellum,  through  the  pons  Varolii,  have 
already  been  described  (see  page  610). 

The  middle  peduncles  arise  from  the  lateral  hemispheres  of  the  cerebel- 
lum, pass  to  the  pons  Varolii,  where  they  cross,  connecting  the  two  sides  of 
the  cerebellum. 

The  inferior  peduncles  pass  to  the  medulla  oblongata  and  are  continuous 
with  the  restiform  bodies,  which,  in  turn,  are  continuations  chiefly  of  the 
posterior  columns  of  the  spinal  cord. 

From  the  above  sketch,  the  physiological  significance  of  the  direction  of 
the  fibres  is  sufficiently  evident.  By  the  superior  peduncles,  the  cerebellum 
is  connected,  as  are  all  of  the  encephalic  ganglia,  with  the  cerebrum ;  by  the 
middle  peduncles,  the  two  lateral  halves  of  the  cerebellum  are  intimately  con- 
nected with  each  other ;  and  by  the  inferior  peduncles,  the  cerebellum  is 
connected  with  the  posterior  columns  of  the  spinal  cord. 

Extirpation  of  the  Cerebellum. — AVhen  the  greatest  part  or  the  whole  of 
the  cerebellum  is  removed  from  a  bird  or  a  mammal,  the  animal  being,  before 
the  operation,  in  a  perfectly  normal  condition  and  no  other  parts  being 
injured,  there  are  no  phenomena  constantly  and  invariably  observed  except 
certain  modifications  of  the  voluntary  movements  (Flourens).  The  intelli- 
gence, general  and  special  sensibility,  the  involuntary  movements  and  the 
simple  faculty  of  voluntary  motion  remain.  The  movements  are  always 
exceedingly  irregular  and  inco-ordinate ;  the  animal  can  not  maintain  its 
equilibrium ;  and  on  account  of  the  impossibility  of  making  regular  move- 
ments, it  can  not  feed.  This  want  of  equilibrium  and  of  the  power  of  co-or- 


THE  CEREBELLUM.  625 

dinating  the  muscles  of  the  general  voluntary  system  causes  the  animal  to 
assume  the  most  absurd  and  remarkable  postures,  which,  to  one  accustomed 
to  these  experiments,  are  entirely  characteristic.  Calling  this  want  of  equi- 
libration, of  co-ordination,  of  "  muscular  sense,"  an  indication  of  vertigo,  or 
by  any  other  name,  the  fact  remains,  that  regular  and  co-ordinate  muscular 
action  in  standing,  walking  or  flying,  is  impossible,  although  voluntary  power 
is  retained.  It  is  well  known  that  many  muscular  acts  are  more  or  less  auto- 
matic, as  in  standing,  and  to  a  certain  extent,  in  walking.  These  acts,  as 
well  as  nearly  all  voluntary  movements,  require  a  certain  co-ordination  of  the 
muscles,  and  this,  and  this  alone,  is  affected  by  extirpation  of  the  cerebellum. 
It  is  true  that  destruction  of  the  semicircular  canals  of  the  internal  ear  pro- 
duces analogous  disorders  of  movement,  but  this  is  the  only  mutilation,  except 
division  of  the  posterior  white  columns  of  the  spinal  cord,  which  produces 
anything  resembling  the  results  of  cerebellar  injury. 

When  a  portion  only  of  the  cerebellum  is  removed,  there  is  slight  disturb- 
ance of  co-ordination,  and  the  disordered  movements  are  marked  in  propor- 
tion to  the  extent  of  the  injury.  After  extirpation  of  even  one-half  or  two- 
thirds  of  the  cerebellum,  the  disturbances  in  co-ordination  immediately  fol- 
lowing the  operation  may  disappear,  and  the  animal  may  entirely  recover, 
without  any  regeneration  of  the  extirpated  nerve-substance.  This  important 
fact  enables  one  to  understand  how,  in  certain  cases  of  disease  of  the  cere- 
bellum in  the  human  subject,  when  the  disorganization  of  the  nerve-tissue 
is  slow  and  gradual,  there  may  never  be  any  disorder  in  the  movements. 

If  there  be  a  distinct  nerve-centre  which  presides  over  the  co-ordination 
of  the  general  voluntary  movements,  experiments  upon  the  higher  classes  of 
animals  show  that  this  centre  is  situated  in  the  cerebellum.  If  the  cerebellum 
preside  over  co-ordination,  as  a  physiological  necessity,  the  centre  must  be 
connected  by  nerves  with  the  general  muscular  system.  If  this  connection 
exist,  a  complete  interruption  of  the  avenue  of  communication  between  the 
cerebellum  and  the  muscles  would  be  followed  by  loss  of  co-ordinating  power. 
From  the  anatomical  connections  of  the  cerebellum,  it  appears  that  the  main 
communication  between-  this  organ  and  the  general  system  is  through  the 
posterior  white  columns  of  the  spinal  cord.  These  columns  are  not  for  the 
transmission  of  the  general  sensory  impressions,  and  there  is  no  satisfactory 
evidence  that  they  convey  to  the  encephalon  the  so-called  muscular  sense. 
When  the  posterior  white  columns  are  divided  at  several  points,  there  is 
want  of  co-ordination  of  the  general  muscular  system.  When  the  posterior 
white  columns  are  disorganized  in  the  human  subject,  there  is  loss  or  impair- 
ment of  co-ordinating  power,  even  though  the  general  sensibility  be  not  af- 
fected, as  in  the  disease  called  locomotor  ataxia. 

Pathological  Observations. — Records  of  cases  of  lesion  of  the  cerebellum 
in  the  human  subject  have  accumulated  until  the  number  is  very  large.  A 
study  of  cases  in  which  the  phenomena  referable  to  cerebellar  injury  are  not 
complicated  by  paralysis,  coma  or  convulsions,  shows  that  serious  lesion  of 
the  middle  lobe  is  almost  always  attended  with  marked  muscular  inco-ordina- 
tion.  Cases  in  which  only  a  portion  of  one  or  of  both  hemispheres  is  involved 


626  NERVOUS  SYSTEM. 

may  not  present  any  disorder  in  the  muscular  movements.  These  facts  are 
in  accord  with  the  results  of  experiments  upon  the  lower  animals. 

The  phenomena  observed  in  the  few  cases  of  cerebellar  inco-ordination 
which  have  been  carefully  observed  are  notably  different  from  those  presented 
in  simple  locomotor  ataxia.  In  cerebellar  disease,  the  gait  is  staggering, 
much  as  it  is  in  alcoholic  intoxication.  The  chief  difficulty  seems  to  be  in 
maintaining  the  equilibrium  in  progression,  even  with  the  greatest  care  and 
closest  attention  on  the  part  of  the  patient.  With  the  idea  in  mind  that 
there  is  a  co-ordinating  centre  for  the  muscles  of  progression,  and  that  this 
centre  acts  imperfectly,  it  seems  as  though  an  efficient  effort  at  co-ordination 
were  impossible.  In  locomotor  ataxia,  patients  seem  to  make  co-ordinating 
efforts,  but  the  paths  by  which  these  efforts  find  their  way  to  the  muscles  are 
disturbed  and  the  co-ordinating  process,  which  is  more  or  less  automatic  in 
health,  requires  peculiar  care  and  attention.  By  the  aid  of  the  sense  of  sight 
and  by  artificial  supports,  progression  may  be  safely  though  irregularly  accom- 
plished. The  movements  are  jerky,  and  each  step  seems  to  require  a  distinct 
act  of  volition.  It  is  possible  to  imagine  that  in  disorganization  of  the  paths 
of  co-ordination  in  the  spinal  cord,  the  co-ordinating  centre  may  act  in  some 
degree  through  the  motor  paths  in  the  direct  and  crossed  pyramidal  tracts 
of  the  cord.  It  is  certain  that  the  want  of  normal  co-ordinating  power  is 
supplemented  by  ordinary  voluntary  acts  and  by  the  sense  of  sight. 

Vertigo  is  not  a  necessary  accompaniment  of  cerebellar  ataxia.  Disease 
of  the  semicircular  canals  of  the  internal  ear  (Meniere's  disease)  is  attended 
with  vertigo,  and  this  is  the  main  cause  of  the  disturbances  of  equilibrium. 

Connection  of  the  Cerebellum  with  the  Generative  Function. — The  fact 
that  the  cerebellum  is  the  centre  for  equilibration  and  the  co-ordination  of 
certain  muscular  movements  does  not  necessarily  imply  that  it  has  no  other 
office.  The  idea  of  Gall,  that  "  the  cerebellum  is  the  organ  of  the  instinct 
of  generation,"  is  sufficiently  familiar;  and  there  are  facts  in  pathology 
which  show  a  certain  relation  between  this  nerve-centre  and  the  organs  of 
generation,  although  the  view  that  it  presides  over  the  generative  function  is 
not  sustained  by  the  results  of  experiments  upon  animals  or  by  facts  in  com- 
parative anatomy. 

In  experiments  upon  animals  in  which  the  cerebellum  has  been  removed, 
there  is  nothing  pointing  directly  to  this  part  as  the  organ  of  the  generative 
instinct.  Flourens  removed  a  great  part  of  the  cerebellum  in  a  cock.  The 
animal  survived  for  eight  months.  It  was  put  several  times  with  hens  and 
always  attempted  to  mount  them,  but  without  success,  on  account  of  want  of 
equilibrium.  In  this  animal  the  testicles  were  enormous.  This  observation 
has  been  repeatedly  confirmed,  and  there  are  no  instances  in  which  the  cere- 
bellum has  been  removed  with  apparent  destruction  of  sexual  instinct.  In 
a  comparison  of  the  relative  weights  of  the  cerebellum  in  stallions,  mares 
and  geldings,  Leuret  found  that,  far  from  being  atrophied,  the  cerebellum  in 
geldings  was  even  larger  than  in  either  stallions  or  mares. 

In  certain  cases  of  disease  or  injury  of  the  cerebellum,  irritation  of  this 
part  has  been  followed  by  persistent  erection  and  manifest  exaggeration  of 


MEDULLA  OBLONGATA.  62T 

the  sexual  appetite,  and  in  others,  its  extensive  degeneration  or  destruction 
has  apparently  produced  atrophy  of  the  generative  organs  and  total  loss  of 
sexual  desire.  Serres  reported  several  cases  in  which  irritation  of  the  cere- 
bellum was  followed  by  satyriasis  or  nymphomania,  but  in  other  cases  there 
were  no  symptoms  referable  to  the  generative  organs.  In  the  well  known 
case  reported  by  Combette,  the  patient  had  the  habit  of  masturbation. 
Fisher,  of  Boston,  reported  (1838)  two  cases  of  diseased  or  atrophied  cere- 
bellum, with  absence  of  sexual  desire,  and  one  case  of  irritation,  with  saty- 
riasis. Similar  instances  have  been  given  by  other  writers.  The  observa- 
tions of  Budge,  in  which  mechanical  irritation  of  the  cerebellum  was  followed 
by  movements  of  the  uterus,  testicles  etc.,  have  not  been  satisfactorily  ex- 
plained. 

Although  there  are  many  facts  in  pathology  which  are  opposed  to  the 
view  that  the  cerebellum  presides  over  the  generative  function,  there  are 
cases  which  show  a  certain  connection  between  this  portion  of  the  central 
nervous  system  and  the  organs  of  generation  in  the  human  subject ;  but  this 
is  all  that  can  be  said  upon  this  point.  It  is  certain  that  the  facts  are  not 
sufficiently  definite  and  invariable  to  sustain  the  notion  that  the  cerebellum 
is  the  seat  of  the  sexual  instinct. 

It  is  not  necessary  to  discuss  the  vague  theories  with  regard  to  the  uses 
of  the  cerebellum  advanced  by  writers  anterior  to  the  publication  of  the  ob- 
servations of  Flourens.  There  is  no  evidence  that  the  cerebellum  is  the 
organ  presiding  over  memory,  the  involuntary  movements,  general  sensibility 
or  the  general  voluntary  movements.  The  only  view  that  has  any  positive 
experimental  or  pathological  basis  is  that  it  presides  over  equilibration  and  the 
co-ordination  of  certain  muscular  movements,  and  is,  perhaps,  in  some  way 
connected  with  the  generative  function. 

MEDULLA  OBLONGATA  (BULB). 

The  medulla  oblongata,  or  bulb,  connects  the  spinal  cord  with  the 
encephalic  ganglia.  It  is  composed  of  white  and  gray  matter  and  presents, 
in  its  substance,  a  number  of  important  nerve-centres.  It  is  not  necessary 
to  give  anything  like  a  complete  anatomical  description  of  the  medulla.  Its 
most  important  conducting  parts  are  those  which  are  continuous  with  the 
columns  of  the  cord  and  which  pass  to  the  cerebrum  and  cerebellum.  The 
nuclei  of  origin  of  certain  of  the  cranial  nerves  in  the  floor  of  the  fourth  ven- 
tricle have  already  been  mentioned. 

Physiological  A  natomy. — The  medulla  oblongata  is  pyramidal  in  form, 
with  its  broad  extremity  above,  and  rests  in  the  basilar  groove  of  the  occipital 
bone,  extending  from  the  lower  border  of  the  pons  Varolii  to  the  atlas.  It 
is  about  an  inch  and  a  quarter  (3T8  mm.)  in  length,  three-quarters  of  an 
inch  (19-1  mm.)  broad  at  its  widest  portion  and  half  an  inch  (12'7  mm.) 
thick.  It  is  flattened  antero-posteriorly.  Like  the  cord,  it  has  an  anterior 
and  a  posterior  median  fissure. 

Apparently  continuous  with  the  anterior  columns  of  the  cord,  are  the 


628 


NERVOUS  SYSTEM. 


18 


two  anterior  pyramids,  one  on  either  side.  Viewed  superficially,  the  inner- 
most fibres  of  these  pyramids  are  seen  to  decussate  in  the  median  line ;  but 
if  the  fibres  be  traced  from  the  cord,  it  is  found  that  they  come  from  the 
crossed  pyramidal  tracts  of  the  lateral  columns  and  that  none  of  them  are 
derived  from  the  anterior  columns.  The  fibres  of  the  external  portion  of 
the  anterior  pyramids  come  from  the  direct  pyramidal  tracts  of  the  cord. 
At  the  site  of  the  decussation,  the  pyramids  are  composed  entirely  of  white 

matter ;  but  as  the  fibres  spread  out  to  pass  to 
the  encephalon  above,  they  present  nodules  of 
gray  matter  between  the  fasciculi. 

External  to  the  anterior  pyramids,  are  the 
corpora  olivaria.  These  are  oval  and  are  sur- 
rounded by  a  distinct  groove.  They  are  white 
externally  and  contain  a  gray  nucleus  called 
the  corpus  dentatum. 

External  to  the  corpora  olivaria,  are  the 
6  restiform  bodies,  formed  chiefly  of  white  mat- 
ter and  constituting  the  postero-lateral  portion 
of  the  medulla.  They  are  continuous  with 
the  posterior  white  columns  of  the  cord.  The 
restiform  bodies  spread  out  as  they  ascend, 
and  pass  to  the  cerebellum,  forming  a  great 
portion  of  the  inferior  peduncles.  Some  fibres 
from  the  restiform  bodies  pass  to  the  cere- 
brum. 

Beneath   the  olivary  bodies  and  between 
the  anterior  pyramids  and  the  restiform  bod- 
ies, are  the  lateral  tracts  of  the  medulla,  some- 
times called  the  intermediary  or  lateral  fascic- 
uli, or  the  funiculi  of  Rolando.      These  are 
composed  of  an  intimate  mixture  of  white  and 
gray  matter  and  have  a  yellowish-gray  color. 
They  receive  all  that  portion  of  the  antero- 
lateral  columns  of   the  cord  which  does  not 
enter  into  the   composition  of   the    anterior 
il  14    pyramids.     They  are  usually  described  as  parts 
ihl5'  optic   °^  ^ie  restiform  bodies,  but  they  are  peculiarly 
:°m.mu.ui|);   important,  from  the  fact  that  they  contain 
motor  ocuii  externus ;  21,  facial   the   grav  centre   presiding   over   respiration ; 

nerve  ;  22,  auditory  nerve  ;  23,  nerve 

of  wrisberg ;  24,  giosso-pharyngeai   and  for  that  reason  they  are  here  described  as 

nerve  ;   25,  pneumogastric  ;   26,  26,  . 

spinal    accessory  ;    27,   sublingual    distinct  faSClCllll. 

nerve  ;  28,  29,  30,  cervical  nerves.  . 

ihe  posterior  pyramids  (funiculi  graciles) 

are  the  smallest  of  all.  They  pass  upward  to  the  cerebellum,  without  decus- 
sating, joining  the  restiform  bodies  above.  They  are  composed  chiefly  of 
white  matter.  As  they  pass  upward  in  the  medulla,  they  diverge,  leaving  a 
space  at  the  fourth  ventricle. 


FIG.  231. — Anterior  view  of  the  medulla 

oblongata  (Sappey). 
1,  infundibulum  ;   2,  tuber  cinereum  ; 


of  the  middle  peduncle  of  the  cere- 
bellum ;  7,  anterior  pyramids  of 
the  medulla  oblongata  ;  8,  decussa- 
tion of  the  anterior  pyramids  ;  9, 


THE  MEDULLA   OBLONGATA. 


629 


The  fourth  ventricle  is  the  cavity  between  the  pons  Varolii,  the  medulla 
oblongata  and  cerebellum.  It  is  lozenge-shaped,  the  acute  angles  being 
above  and  below.  The  upper  angle  extends  to  the  upper  border  of  the 
pons,  and  the  lower  angle,  to  the  lower  border  of  the  olivary  bodies.  The 
triangles  which  form  this  lozenge  are  of  nearly  equal  size.  The  superior 
triangle  is  bounded  laterally  by  the  superior  peduncles  of  the  cerebellum,  as 
they  converge  to  meet  at  the  corpora  quadrigemina.  The  inferior  triangle 
is  bounded  laterally  by  the  funiculi  graciles  and  the  restiform  bodies  of 
the  medulla,  which  diverge  at  its  lower  angle.  The  arched  roof  of  the  ven- 
tricle is  formed  by  the  valve  of  Vieussens,  which  is  stretched  between  the 
superior  peduncles  of  the  cerebellum  and  covers  the  anterior  triangle, 
and  the  cerebellum,  which  covers  the  posterior  triangle.  Beneath  the 
cerebellum,  is  a  reflection  of  the  pia  mater.  The  fourth  ventricle  com- 
municates above  with  the  third  ventricle,  by  the  aqueduct  of  Sylvius,  below 
with  the  subarachnoid  space,  by  the  foramen  of  Magendie,  and  by  a  small 
opening  below  with  the  central  canal  of  the  cord.  The  floor  of  the  ventri- 
cle is  formed  by  the  posterior  surface  of  the  pons  above  and  the  medulla 
below.  It  presents  a  fissure  in  the  median  line,  which  terminates  below 
in  the  calamus  scriptorius.  By  the  sides  of  the  median  fissure,  are  the 
fasciculi  teretes,  which  correspond  to  the  intermediary  fasciculi  of  the  me- 
dulla. Little  eminences  in  the  floor  indicate  the  situation  of  nuclei  of 
origin  of  cranial  nerves.  The  floor  is  composed  mainly  of  a  layer  of  gray 
matter,  continuous  with  the 
gray  commissure  of  the  cord. 
The  lower  portion  of  the  floor 
is  marked  by  transverse  lines 
of  white  matter  emerging  from 
the  median  fissure. 

The  two  lateral  halves  of 
the  posterior  portion  of  the 
medulla  are  connected  together 
by  fibres  arising  from  the  gray 
matter  of  the  lateral  tracts,  or 
intermediary  fasciculi,  passing 
obliquely,  in  a  curved  direction 
from  behind  forward,  to  the 
raphe  in  the  median  line.  There 
are  also  fibres  passing  from  be- 
fore backward,  to  form  a  pos- 
terior commissure,  and  fibres 
arising  from  the  cells  of  the 
olivary  bodies,  which  connect 
the  gray  substance  of  the  lateral  halves.  Commissural  fibres  also  connect  the 
gray  matter  of  the  lateral  tracts  with  the  corpora  dentata  of  the  olivary  bod- 
ies, and  the  olivary  bodies  with  the  cerebellum,  their  fibres  forming  part  of 
the  inferior  peduncles  of  the  cerebellum.  In  addition  it  is  probable  that 


Fio.  232.—  Floor  of  the  fourth  ventricle  (Hirschfeld). 
1,  median  fissure,  between  the  fasciculi  teretes  ;  2,  trans- 
verse, white  strige  ;  3.  inferior  peduncle  of  the  cerebel- 
lum ;  4,  posterior  pyramid  (funiculus  gracilis)  ;  5,  5,  su- 
perior peduncles  (divided)  of  the  cerebellum  ;  6,  6,  bands 
to  the  side  of  the  crura  cerebri  :  7,  7,  lateral  grooves  of 
the  crura  cerebri ;  8,  corpora  quadrigemina. 


630  NERVOUS  SYSTEM. 

fibres,  taking  their  origin  from  all  of  the  gray  nodules  of  the  medulla,  pass 
to  the  parts  of  the  encephalon  situated  above. 

The  uncrossed  pyramidal  tracts  of  the  spinal  cord  (columns  of  Tiirck) 
pass  to  the  encephalon,  by  direct  fibres  situated  at  the  outer  border  of  the 
anterior  pyramids  of  the  medulla. 

The  crossed  pyramidal  tracts  of  the  cord  decussate  in  the  lower  portion 
of  the  medulla  and  constitute  the  greatest  part  of  the  anterior  pyramids. 

Fibres  from  the  anterior  fundamental  fasciculi,  the  anterior  radicular 
zone  and  from  the  mixed  lateral  columns  of  the  cord,  probably  pass  to  the 
gray  matter  of  the  medulla. 

The  direct  cerebellar  fasciculi  of  the  cord  are  continuous  with  the  funic- 
uli  graciles  of  the  medulla. 

The  columns  of  Burdach  are  continuous  with  the  restiform  bodies  of 
the  medulla. 

The  columns  of  Goll  pass  to  the  medulla  and  are  lost  in  the  fasciculi 
graciles. 

As  far  as  the  fibres  of  origin  of  the  cranial  nerves  are  concerned,  it  may 
be  stated  in  general  terms  that  a  number  of  the  motor  roots  arise  from 
the  gray  matter  of  the  floor  of  the  fourth  ventricle,  the  roots  of  the  sen- 
sory nerves  arising  from  gray  matter  in  the  posterior  portions. 

USES  OF  THE  MEDULLA  OBLONGATA. 

It  is  hardly  necessary  to  discuss  the  action  of  the  medulla  oblongata  as  a 
conductor  of  sensory  impressions  and  of  motor  stimulus  to  and  from  the 
brain.  It  is  evident  that  there  is  conduction  of  this  kind  from  the  spinal 
cord  to  the  ganglia  of  the  encephalon,  and  this  must  take  place  through  the 
medulla ;  a  fact  which  is  inevitable,  from  its  anatomical  relations,  and  which 
is  demonstrated  by  its  section  in  living  animals.  Nor  is  it  necessary  to 
dwell  upon  the  general  properties  of  the  medulla,  in  which  it  resembles  the 
spinal  cord,  at  least  as  far  as  has  been  demonstrated  by  experiments  upon 
living  animals  or  upon  animals  just  killed.  It  is  difficult  to  expose  this  part 
in  the  higher  classes  of  animals,  but  experiments  show  that  it  is  sensitive 
on  its  posterior  surface  and  insensible  in  front.  The  difficulty  of  observing 
the  phenomena  which  follow  its  stimulation  in  living  animals  has  rendered 
it  impossible  to  determine  the  limits  of  its  excitability  and  sensibility  as 
exactly  as  has  been  done  for  the  different  portions  of  the  cord. 

It  is  also  somewhat  difficult  to  determine  whether  the  action  of  the  me- 
dulla itself,  in  its  relations  to  motion  and  sensation,  be  crossed  or  direct.  As 
regards  conduction  from  the  brain,  the  direction  is  sufficiently  well  shown 
by  cases  of  cerebral  disease,  in  which  the  paralysis,  in  simple  lesions,  is  on 
the  opposite  side  of  the  body. 

The  action  of  the  medulla  as  a  reflex  nerve-centre  depends  upon  its  gray 
matter.  When  this  gray  substance  is  destroyed,  certain  important  reflex 
phenomena  are  instantly  abolished.  From  its  connection  with  various  of 
the  cranial  nerves,  one  would  expect  it  to  play  an  important  part  in  the 
movements  of  the  face,  in  deglutition,  in  the  action  of  the  heart  and  of  vari- 


RESPIRATORY  NERVE-CENTRE.  631 

ous  glands  etc.,  important  points  which  are  fully  considered  in  their  appro- 
priate place.  The  various  reflex  centres  in  the  medulla  have  been  located 
chiefly  by  a  study  of  the  relations  of  the  gray  matter  to  the  deep  fibres  of 
origin  of  certain  of  the  cranial  nerves.  The  centre  for  the  orbicularis  oculi 
muscle  is  related  to  the  origin  of  the  large  root  of  the  fifth  nerve  and  the 
origin  of  the  facial ;  and  the  integrity  of  these  two  nerves  is  necessary  to  the 
reflex  act  of  closure  of  the  eyelids.  The  impression  which  produces  the  act 
of  sneezing  is  conveyed  to  the  medulla  through  the  nasal  branch  of  the 
fifth — possibly  sometimes  through  the  olfactory  nerves — and  excites  certain 
of  the  expiratory  muscles.  Impressions  conveyed  to  the  medulla  by  certain 
sensory  branches  of  the  pneumogastrics  give  rise  to  the  reflex  acts  of  cough- 
ing. The  reflex  acts  of  swallowing  and  vomiting  also  depend  upon  centres 
in  the  medulla  oblongata.  There  are  centres,  also,  which  influence  the 
glycogenic  action  of  the  liver,  the  secretion  of  saliva  and  the  secretion  of 
sweat.  The  vaso-motor  centres  will  be  considered  in  connection  with  the 
physiology  of  the  vaso-motor  nerves.  The  centres  connected  with  respira- 
tion are  so  important  that  they  demand  special  description. 

Respiratory  Nerve-Centre. — In  1809,  Legallois  made  a  number  of  ex- 
periments upon  rabbits,  cats  and  other  •  animals,  in  which  he  showed  that 
respiration  depends  upon  the  medulla  oblongata  and  not  upon  the  brain; 
and  he  farther  located  the  part  which  presides  over  the  respiratory  move- 
ments, at  the  site  of  origin  of  the  pneumogastric  nerves.  Flourens,  in  his 
elaborate  experiments  upon  the  nerve-centres,  extended  the  observations  of 
Legallois,  and  limited  the  respiratory  centre  in  the  rabbit,  between  the  upper 
border  of  the  roots  of  the  pneumogastrics  and  a  plane  situated  about  a  quar- 
ter of  an  inch  (6 -4  rnm.)  below  the  lowest  point  of  origin  of  these  nerves; 
these  limits,  of  course,  varying  with  the  size  of  the  animal.  Following  these 
experiments,  Longet  has  shown  that  the  respiratory  centre  does  not  occupy 
the  whole  of  the  medulla  included  between  the  two  planes  first  indicated  by 
Flourens,  but  that  it  is  confined  to  the  gray  matter  of  the  lateral  tracts,  or 
the  intermediary  fasciculi.  This  was  demonstrated  by  the  fact  that  respi- 
ration persists  in  animals  after  division  of  the  anterior  pyramids  and  the 
restiform  bodies.  Subsequently,  Flourens  restricted  the  limits  of  the  respir- 
atory centre  and  fully  confirmed  the  observations  of  Longet. 

The  portion  of  the  medulla  oblongata  above  indicated  presides  over  the 
movements  of  respiration  and  is  the  true  respiratory  nerve-centre.  Nearly  all 
who  have  repeated  the  experiments  of  Flourens  have  found  that  the  spinal 
cord  may  be  divided  below  the  medulla  oblongata,  and  that  all  of  the  en- 
cephalic ganglia  above  may  be  removed,  respiratory  movements  still  persist- 
ing. It  is  a  very  common  thing  in  vivisections  to  kill  an  animal  by  break- 
ing up  the  medulla.  When  this  is  done  there  are  no  struggles  and  no  mani- 
festations of  the  distress  of  asphyxia.  The  respiratory  muscles  simply  cease 
their  action,  and  the  animal  loses  instantly  the  sense  of  want  of  air.  A 
striking  contrast  to  this  is  presented  when  the  trachea  is  tied  or  when  all 
of  the  respiratory  muscles  are  paralyzed  without  touching  the  medulla. 

The  relations  of  the  respiratory  centre  have  already  been  fully  considered 


632  NERVOUS  SYSTEM. 

in  connection  with  the  physiology  of  respiration.  Under  normal  condi- 
tions, the  centres  on  the  two  sides  probably  operate  through  the  pneumogas- 
tric  nerves  and  the  respiratory  movements  on  the  two  sides  are  synchronous. 
That  there  is  a  respiratory  centre  on  either  side,  is  shown  by  the  experiment 
of  dividing  the  medulla  longitudinally  in  the  median  line,  the  respiratory 
movements  afterward  continuing  with  regularity.  If,  now,  the  pneumogas- 
tric  be  divided  on  one  side,  the  respiratory  movements  on  that  side  become 
slower  and  are  no  longer  synchronous  with  the  movements  on  the  opposite 
side.  This  shows  that  while  the  respiratory  centres  on  the  two  sides  nor- 
mally act  together,  being  undoubtedly  connected  with  each  other  by  com- 
missural  fibres,  each  one  has  independent  connections  with  the  pneu mo- 
gastric  on  the  corresponding  side  of  the  body. 

Cardiac  Centres. — There  can  be  scarcely  any  doubt  with  regard  to  the 
existence  of  cardiac  centres  in  the  medulla — perhaps  an  inhibitory  centre 
and  an  acceleratory  centre — but  the  situation  of  these  centres  has  not  been 
exactly  determined.  The  influence  of  the  nerves  and  nerve-centres  over  the 
movements  of  the  heart  has  been  fully  considered  in  connection  with  the 
physiology  of  the  circulation. 

Vital  Point  (so  called). — Since  it  has  been  definitely  ascertained  that 
destruction  of  a  restricted  portion  of  the  gray  substance  of  the  medulla 
produces  instantaneous  and  permanent  arrest  of  the  respiratory  movements, 
Flourens  and  others  have  called  this  centre  the  vital  knot,  destruction  of 
which  is  immediately  followed  by  death.  With  the  existing  knowledge  of  the 
properties  and  uses  of  the  different  tissues  and  organs  of  which  the  body  is 
composed,  it  is  almost  unnecessary  to  present  any  arguments  to  show  the  un- 
philosophical  character  of  such  a  proposition.  One  can  hardly  imagine  such 
a  thing  as  instantaneous  death  of  the  entire  organism  ;  and  still  less  can  it  be 
assumed  that  any  restricted  portion  of  the  nervous  system  is  the  one,  essential 
vital  point.  Probably,  a  very  powerful  electric  discharge  passed  through  the 
entire  cerebro-spinal  axis  produces  the  nearest  approach  to  instantaneous 
death  ;  but  even  then  it  is  by  no  means  certain  that  some  parts  do  not  for  a 
time  retain  their  physiological  properties.  In  apparent  death,  the  nerves 
and  the  heart  may  be  shown  to  retain  their  characteristic  properties ;  the 
muscles  will  contract  under  stimulus,  and  will  appropriate  oxygen  and  give 
off  carbon  dioxide,  or  respire  ;  the  glands  may  be  made  to  secrete,  etc. ;  and 
no  one  can  assume  that  under  these  conditions,  the  entire  organism  is  dead. 
There  seems  to  be  no  such  thing  as  death,  except  as  the  various  tissues  and 
organs  which  go  to  make  up  the  entire  body  become  so  altered  as  to  lose 
their  physiological  properties  beyond  the  possibility  of  restoration ;  and  this 
never  occurs  for  all  parts  of  the  organism  in  an  instant.  A  person  drowned 
may  be  to  all  appearances  dead,  and  would  certainly  die  without  measures 
for  restoration  ;  yet  in  such  instances,  restoration  may  be  accomplished,  the 
period  of  apparent  death  being  simply  a  blank,  as  far  as  the  recollection  of 
the  individual  is  concerned.  It  is  as  utterly  impossible  to  determine  the  ex- 
act instant  when  the  vital  principle,  or  whatever  it  may  be  called,  leaves  the 
body  in  death,  as  to  indicate  the  time  when  the  organism  becomes  a  living 


EOLLING  AND  TURNING  MOVEMENTS.  633 

being.  Death  is  nothing  more  than  a  permanent  destruction  of  so-called 
vital  physiological  properties ;  and  this  occurs  successively,  and  at  different 
times,  for  different  tissues  and  organs. 

When  it  is  seen  that  frogs  will  live  for  weeks,  and  sometimes  for  months, 
after  destruction  of  the  medulla  oblongata,  and  that  in  mammals,  by  keep- 
ing up  artificial  respiration,  many  of  the  most  important  physiological  acts, 
such  as  the  movements  of  the  heart,  may  be  prolonged  for  hours  after  de- 
capitation, one  can  understand  the  physiological  absurdity  of  the  proposition 
that  there  is  any  such  thing  as  a  vital  point,  in  the  medulla  or  in  any  part  of 
the  nervous  system. 

There  is  little  to  be  said  concerning  certain  ganglia  and  other  parts  of 
the  brain  that  have  not  yet  been  considered.  The  olfactory  ganglia  preside 
over  olf action  and  will  be  treated  of  fully  in  connection  with  the  special 
senses.  The  pineal  gland  and  the  pituary  body,  in  their  structure,  present  a 
certain  resemblance  to  the  ductless  glands,  and  their  anatomy  has  been  con- 
sidered in  another  chapter.  Passing  over  the  purely  theoretical  views  of  the 
older  writers,  who  had  very  indefinite  ideas  of  the  action  of  any  of  the  en- 
cephalic ganglia,  it  can  only  be  said  that  the  uses  of  the  pineal  gland  and 
pituitary  body  in  the  economy  are  entirely  unknown.  The  same  remark 
applies  to  the  corpus  callosum,  the  septum  lucidum,  the  ventricles,  hippo- 
campi and  various  other  parts  that  are  necessarily  described  in  anatomical 
works.  It  is  useless  to  discuss  the  early  or  even  the  recent  speculations  with 
regard  to  the  uses  of  these  parts,  which  are  entirely  unsupported  by  experi- 
mental or  pathological  facts  and  which  have  not  advanced  positive  knowledge. 

ROLLING  AND  TURNING  MOVEMENTS  FOLLOWING  INJURY  OF  CERTAIN 
PARTS  OF  THE  ENCEPHALON. 

The  remarkable  movements  of  rolling  and  turning,  produced  by  section 
or  injury  of  certain  of  the  commissural  fibres  of  the  encephalon,  are  not  very 
important  in  their  bearing  upon  the  uses  of  the  brain,  and  they  are  rather  to 
be  classed  among  the  curiosities  of  experimental  physiology.  These  move- 
ments follow  unilateral  lesions  and  are  dependent,  to  a  certain  extent,  upon 
a  consequent  inequality  in  the  power  of  the  muscles  on  one  side,  without 
actual  paralysis.  Vulpian  has  enumerated  the  following  parts,  injury  of 
which,  upon  one  side,  in  living  animals,  may  determine  movements  of 
rotation : 

"  1.  Cerebral  hemispheres ; 

"  2.  Corpora  striata ; 

"3.  Optic  thalami  (Flourens,  Longet,  Schiff); 

"  4.  Cerebral  peduncles  (Longet) ; 

"  5.  Pons  Varolii ; 

"  6.  Tubercula  quadrigemina,  or  bigemina  (Flourens) ; 

"  7.  Peduncles  of  the  cerebellum,  especially  the  middle,  and  the  lateral  por- 
tions of  the  cerebellum  (Magendie) ; 

"  8.  Olivary  bodies,  restiform  bodies  (Magendie) ; 


634  NERVOUS  SYSTEM. 

"  9.  External  part  of  the  anterior  pyramids  (Magendie) ; 

"  10.  Portion  of  the  medulla  from  which  the  facial  nerve  arises  (Brown- 
Sequard)  ; 

"  11.  Optic  nerves; 

"12.  Semicircular  canals  (Flourens) ;  auditory  nerve  (Brown-Sequard)." 

To  the  parts  above  enumerated,  Vulpian  added  the  upper  part  of  the 
cervical  portion  of  the  spinal  cord. 

The  movements  which  follow  unilateral  injury  of  the  parts  mentioned 
above  are  of  two  kinds ;  viz.,  rolling  of  the  entire  body  on  its  longitudinal 
axis,  and  turning,  always  in  one  direction,  in  a  small  circle,  called  by  the 
French  the  movement  of  manege.  A  capital  point  to  determine  in  these 
phenomena  is  whether  the  movements  be  due  to  paralysis  or  enfeeblement 
of  certain  muscles  upon  one  side  of  the  body,  to  a  direct  or  reflex  irritation 
of  the  parts  of  the  nervous  system  involved  or  to  both  of  these  causes  com- 
bined. The  experiments  of  Brown-Sequard  and  others  show  that  the  move- 
ments may  be  due  to  irritation  alone,  for  they  occur  when  parts  of  the  en- 
cephalon  and  the  upper  portions  of  the  cord  are  simply  pricked,  without 
section  of  fibres.  When  there  is  extensive  division  of  fibres,  it  is  probable 
that  the  effects  of  the  enfeeblement  of  certain  muscles  are  added  to  the  phe- 
nomena produced  by  simple  irritation.  The  most  satisfactory  explanation 
of  these  movements  is  the  one  proposed  by  Brown-Sequard,  who  attributed 
them  to  a  more  or  less  convulsive  action  of  muscles  on  one  side  of  the  body, 
produced  by  irritation  of  the.  nerve-centres.  He  regarded  the  rolling  as 
simply  an  exaggeration  of  the  turning  movements,  and  places  both  in  the 
same  category. 

It  is  not  necessary  to  enter  into  an  extended  discussion  of  the  above  ex- 
periments. In  some  of  them,  the  movements  have  been  observed  toward 
the  side  operated  upon,  and  in  others,  toward  the  sound  side.  These  differ- 
ences probably  depend  upon  the  fact  that  in  certain  experiments,  the  fibres 
are  involved  before  their  decussation,  and  in  others,  after  they  have  crossed 
in  the  median  line.  In  some  instances,  the  movements  may  be  due  to  a  reflex 
action,  from  stimulation  of  afferent  fibres,  and  in  others,  the  action  of  the 
irritation  may  be  direct.  Judging  from  the  fact  that  most  of  the  encephalic 
commissural  fibres  are  apparently  insensible  and  inexcitable  under  direct 
stimulation,  it  is  probable  that  the  action  generally  is  reflex. 


GENERAL  ARRANGEMENT  OF  THE  SYMPATHETIC  SYSTEM.  635 


CHAPTEE    XX. 

SYMPATHETIC  NERVOUS  SYSTEM— SLEEP. 

General  arrangement  of  the  sympathetic  system— General  properties  of  the  sympathetic  ganglia  and  nerves 
—Direct  experiments  on  the  sympathetic— Vaso-motor  centres  and  nerves— Reflex  vaso-motor  phenom- 
ena—Vaso-inhibitory  nerves— Trophic  centres  and  nerves  (so-called)— Sleep— Condition  of  the  brain 
and  nervous  system  during  sleep— Anaesthesia  and  sleep  produced  by  pressure  upon  the  carotid  arteries 
— Differences  between  natural  sleep  and  stupor  or  coma— Regeneration  of  the  brain-substance  during 
sleep — Condition  of  the  organism  during  sleep. 

LIKE  the  cerebro-spinal  system,  the  sympathetic  is  composed  of  centres, 
or  ganglia,  and  nerves,  at  least  as  far  as  can  be  seen  from  its  anatomy.  The 
ganglia  contain  nerve-cells,  most  of  which  differ  but  little  from  the  cells  of 
the  encephalon  and  spinal  cord.  The  nerves  are  composed  of  fibres,  some 
of  which  are  nearly  identical  in  structure  with  the  ordinary  motor  and  sen- 
sory fibres,  while  many  are  the  so-called  gelatinous  fibres.  The  fibres  are 
connected  with  the  nerve-cells  in  the  ganglia,  and  the  ganglia  are  connected 
with  each  other  by  commissural  fibres.  These  ganglia  constitute  a  continu- 
ous chain  on  either  side  of  the  body,  beginning  above,  by  the  ophthalmic  gan- 
glia, and  terminating  below  in  the  ganglion  impar.  It  is  important  to  note, 
however,  that  the  chain  of  sympathetic  ganglia  is  not  independent,  but  that 
each  ganglion  receives  motor  and  sensory  filaments  from  the  cerebro-spinal 
nerves,  and  that  filaments  pass  from  the  sympathetic  to  the  cerebro-spinal 
system.  The  general  distribution  of  the  sympathetic  filaments  is  to  mucous 
membranes — and  possibly  to  integument — to  non-striated  muscular  fibres, 
and  particularly  to  the  muscular  coat  of  the  arteries.  As  far  as  has  been 
shown  by  anatomical  investigations,  there  are  no  fibres  derived  exclusively 
from  the  sympathetic  which  are  distributed  to  striated  muscles,  except  those 
which  pass  to  the  muscular  tissue  of  the  heart.  Near  the  terminal  filaments 
of  the  sympathetic,  in  most  of  the  parts  to  which  these  fibres  are  distributed, 
there  exist  large  numbers  of  ganglionic  cells. 

The  general  arrangement  of  the  sympathetic  ganglia  and  the  distribution 
of  the  nerves  may  be  stated  very  briefly ;  but  a  knowledge  of  certain  anatom- 
ical points  is  indispensable  as  an  introduction  to  an  intelligent  study  of  the 
physiology  of  this  system. 

In  the  cranium,  are  the  four  cranial  ganglia ;  the  ophthalmic,  the  spheno- 
palatiue,  the  otic  and  the  submaxillary.  In  the  neck,  are  the  three  cervical 
ganglia ;  the  superior,  middle  and  inferior.  In  the  chest,  are  the  twelve  tho- 
racic ganglia,  corresponding  to  the  twelve  ribs.  The  great  semilunar  ganglia, 
the  largest  of  all  and  sometimes  called  the  abdominal  brain,  are  in  the  abdo- 
men, by  the  side  of  the  coeliac  axis.  In  the  lumbar  region,  in  front  of 
the  spinal  column,  are  the  four  lumbar  ganglia.  In  front  of  the  sacrum,  are 
the  four  or  five  sacral,  or  pelvic  ganglia ;  and  finally,  in  front  of  the  coccyx, 
is  a  small,  single  ganglion,  the  last  of  the  sympathetic  chain,  called  the  gan- 
glion impar.  Thus,  the  sympathetic  cord,  as  it  is  sometimes  called,  consists 
of  twenty-eight  to  thirty  ganglia  on  either  side,  terminating  below  in  a 
single  ganglion. 


636 


NERVOUS  SYSTEM. 


FIG.  233.— Cervical  and  thoracic  portion  of  the  sympathetic  (Sappey). 

1, 1, 1,  right  pneumogastric  ;  2.  glosso-pharyngeal ;  3,  spinal  accessory  ;  4,  sublingual ;  5,  5,  5,  chain  of 
ganglia  of  the  sympathetic  ;  6,  superior  cervical  ganglion  ;  7,  branches  to  the  carotid  ;  8,  nerve  of 
Jacobson  ;  9,  filaments  from  the  facial,  to  the  spheno-palatine  and  to  the  otic  ganglion  ;  10,  motor 
oculi  externus  :  11,  ophthalmic  ganglion  ;  12,  spheno-palatine  ganglion  ;  13,  otic  ganglion  ;  14,  lin- 
gual branch  of  the  fifth  nerve  ;  15,  submaxillary  ganglion  ;  16,  17,  superior  laryngeal  nerve  :  18.  ex- 
ternal laryngeal  nerve  ;  19,  20,  recurrent  laryngeal  nerve  ;  21,  22,  23,  anterior  branches  of  the  upper 
four  cervical  nerves  ;  24,  anterior  branches  of  the  fifth  and  sixth  cervical  nerves  :  25,  26.  anterior 
branches  of  the  seventh  and  eighth  cervical  and  the  first  dorsal  nerves  ;  27,  middle  cervical  gangli- 
on ,'  28,  cord  connecting  the  two  ganglia  ;  29,  inferior  cervical  ganglion  ;  30,  31.  filaments  connect- 


splanchnic  nerve  ;  43,  43,  solar  plexus  ;  44,  left  pneumogastric  ;  45,  right  pneumogastric  ;  46,  phrenic 
nerve  ;  47,  right  bronchus  ;  48,  aorta  ;  49,  right  auricle  ;  50,  right  ventricle  ;  51,52,  pulmonary  artery  ; 
53,  stomach  ;  54,  diaphragm. 


GENERAL  ARRANGEMENT  OF  THE  SYMPATHETIC  SYSTEM.  637 


27 


FIG.  234.—  Lumbar  and  sacral  portions  of  the  sympathetic  (Sappey). 

I,  section  of  the  diaphragm ;  2,  lower  end  of  the  oesophagus  ;  3,  left  half  of  the  stomach  ;  4,  small 
intestine  ;  5,  sigmoid  flexure  of  the  colon  ;  6,  rectum  ;  7,  bladder  ;  8,  prostate  ;  9,  lower  end  of  the 
left  pneumogastric  ;  10,  lower  end  of  the  right  pneumogastric  ;  11,  solar  plexus  ;  12,  lower  end  of 
the  great  splanchnic  nerve  ;  '13,  lower  end  of  the  lesser  splanchnic  nerve  ;  14,  14,  last  two  tho- 
racic ganglia  ;  15,  15,  the  four  lumbar  ganglia  ;  16, 16, 17, 17,  branches  from  the  lumbar  ganglia  ;  18, 
superior  mesenteric  plexus  ;  19,  21.  22,  23,  aortic  lumbar  plexus;  20.  inferior  mesenteric  plexus  ; 
24.  24,  sacral  portion  of  the  sympathetic ;  25,  25,  26,  26,  27.  27,  hypogastric  plexus  ;  28,  29,  30,  tenth, 
eleventh  and  twelfth  dorsal  nerves  ;  31,  32,  33,  34,  35,  36,  37,  38,  39,  lumbar  and  sacral  nerves. 

Cranial  Ganr/lia. — The  ophthalmic,  lenticular,  or  ciliary  ganglion  is  sit- 
uated deeply  in  the  orbit,  is  of  a  reddish  color  and  about  the  size  of  a  phi's- 
head.  It  receives  a  motor  branch  from  the  third  pair  and  sensory  filaments 
from  the  nasal  branch  of  the  ophthalmic  division  of  the  fifth.  It  is  also 
connected  with  the  cavernous  plexus  and  with  MeckePs  ganglion.  Its  so- 
called  motor  and  sensory  roots  from  the  third  and  the  fifth  pair  have  already 
42 


638  NERVOUS  SYSTEM. 

been  described  in  connection  with  these  nerves.  Its  filaments  of  distribution 
are  the  ten  or  twelve  short  ciliary  nerves,  which  pass  to  the  ciliary  muscle  and 
the  iris.  A  very  delicate  filament  from  this  ganglion  passes  to  the  eye,  with 
the  central  artery  of  the  retina,  in  the  canal  in  the  centre  of  the  optic  nerve. 

The  uses  of  the  ophthalmic  ganglion  are  related  mainly  to  the  action  of 
the  ciliary  muscle  and  iris ;  and  it  is  only  necessary  here  to  indicate  its  ana- 
tomical relations,  leaving  its  physiology  to  be  taken  up  in  connection  with 
the  physiology  of  the  sense  of  sight. 

The  spheno-palatine,  or  Meckel's  ganglion,  is  the  largest  of  the  cranial 
ganglia.  It  is  triangular  in  shape,  reddish  in  color,  and  is  situated  in  the 
spheno-maxillary  fossa,  near  the  spheno-palatine  foramen.  It  receives  a  mo- 
tor root  from  the  facial,  by  the  Vidian  nerve.  Its  sensory  roots  are  the  two 
spheno-palatine  branches  from  the  superior  maxillary  division  of  the  fifth. 
It  has  a  large  number  of  branches  of  distribution.  Two  or  three  delicate 
filaments  enter  the  orbit  and  go  to  its  periosteum.  Its  other  branches,  which 
it  is  unnecessary  to  describe  fully  in  detail,  are  distributed  to  the  gums,  the 
membrane  covering  the  hard  palate,  the  soft  palate,  the  uvula,  the  roof  of  the 
mouth,  the  tonsils,  the  mucous  membrane  of  the  nose,  the  middle  auditory 
meatus,  a  portion  of  the  pharyngeal  mucous  membrane,  and  the  levator  palati 
and  azygos  uvulae  muscles.  It  is  probable  that  the  filaments  sent  to  these 
two  striated  muscles  are  derived  from  the  facial  nerve  and  do  not  properly 
belong  to  the  sympathetic  system.  The  ganglion  also  sends  a  short  branch, 
of  a  reddish-gray  color,  to  the  carotid  plexus. 

The  otic  ganglion,  sometimes  called  Arnold's  ganglion,  is  a  small,  oval, 
reddish-gray  mass,  situated  just  below  the  foramen  ovale.  It  receives  a  mo- 
tor filament  from  the  facial  and  sensory  filaments  from  branches  of  the  fifth 
and  the  glosso-pharyngeal.  Its  filaments  of  distribution  go  to  the  mucous 
membrane  of  the  tympanic  cavity  and  Eustachian  tube  and  to  the  tensor  tym- 
pani  and  tensor  palati  muscles.  Reasoning  from  the  general  mode  of  distribu- 
tion of  the  sympathetic  filaments,  those  going  to  the  striated  muscles  are  de- 
rived from  the  facial.  It  also  sends  branches  to  the  carotid  plexus. 

The  submaxillary  ganglion,  situated  on  the  submaxillary  gland,  is  small, 
rounded,  and  reddish-gray  in  color.  It  receives  motor  filaments  from  the 
chorda  tympani  and  sensory  filaments  from  the  lingual  branch  of  the  fifth. 
Its  filaments  of  distribution  go  to  Wharton's  duct,  to  the  mucous  membrane 
of  the  mouth  and  to  the  submaxillary  gland. 

Cervical  Ganglia. — The  three  cervical  ganglia  are  situated  opposite  the 
third,  fifth  and  seventh  cervical  vertebras  respectively.  The  middle  ganglion 
is  sometimes  wanting,  and  the  inferior  ganglion  is  occasionally  fused  with 
the  first  thoracic  ganglion.  These  ganglia  are  connected  together  by  the  so- 
called  sympathetic  cord.  They  have  a  number  of  filaments  of  communica- 
tion above,  with  the  cranial  and  the  cervical  nerves  of  the  cerebro-spinal  sys- 
tem. Branches  from  the  superior  ganglion  go  to  the  internal  carotid,  to 
form  the  carotid  and  the  cavernous  plexus,  following  the  vessels  as  they 
branch  to  their  distribution.  Branches  from  this  ganglion  pass  to  the  cra- 
nial ganglia.  There  are  also  branches  which  unite  with  filaments  from  the 


GENERAL  ARRANGEMENT  OF  THE  SYMPATHETIC  SYSTEM.  639 

pnenmogastric  and  the  glosso-pharyngeal  to  form  the  pharyngeal  plexus,  and 
branches  which  form  a  plexus  on  the  external  carotid,  the  vertebral  and  the 
thyroid  arteries,  following  the  ramifications  of  these  vessels. 

From  the  cervical  portion  of  the  sympathetic  the  three  cardiac  nerves 
arise  and  pass  to  the  heart,  entering  into  the  formation  of  the  cardiac  plexus. 
The  superior  cardiac  nerve  arises  from  the  superior  ganglion ;  the  middle 
nerve,  the  largest  of  the  three,  arises  from  the  middle  ganglion  or  from  the 
sympathetic  cord,  when  this  ganglion  is  wanting;  and  the  inferior  nerve 
arises  from  the  inferior  cervical  ganglion  or  the  first  thoracic.  These  nerves 
present  frequent  communications  with  various  of  the  adjacent  cerebro-spinal 
nerves,  penetrate  the  thorax,  and  form  the  deep  and  superficial  cardiac  plex- 
uses and  the  posterior  and  the  anterior  coronary  plexuses.  In  these  various 
plexuses,  there  are  found  ganglioform  enlargements ;  and  upon  the  surface 
and  in  the  substance  of  the  heart,  are  collections  of  nerve-cells  connected 
with  the  fibres. 

Thoracic  Ganglia. — The  thoracic  ganglia  are  situated  in  the.  chest,  be- 
neath the  pleura,  and  rest  on  the  heads  of  the  ribs.  They  are  usually  twelve 
in  number,  but  occasionally  two  are  fused  into  one.  They  are  connected  to- 
gether by  the  sympathetic  cord.  They  each  communicate  by  two  filaments 
with  the  cerebro-spinal  nerves.  One  of  these  is  white,  like  the  spinal  nerves, 
and  probably  passes  to  the  sympathetic,  and  the  other,  of  a  grayish  color,  is 
thought  to  contain  the  true  sympathetic  filaments.  From  the  upper  six  gan- 
glia filaments  pass  to  the  aorta  and  its  branches.  The  branches  which  form 
the  posterior  pulmonary  plexus  arise  from  the  third  and  fourth  ganglia. 
The  great  splanchnic  nerve  arises  mainly  from  the  seventh,  eighth  and  ninth 
ganglia,  receiving  a  few  filaments  from  the  upper  six  ganglia.  This  is  a  large, 
white,  rounded  cord,  which  penetrates  the  diaphragm  and  passes  to  the  semi- 
lunar  ganglion,  sending  a  few  filaments  to  the  renal  plexus  and  the  suprare- 
nal capsules.  The  lesser  splanchnic  nerve  arises  from  the  tenth  and  eleventh 
ganglia,  passes  into  the  abdomen  and  joins  the  coeliac  plexus.  The  renal 
splanchnic  nerve  arises  from  the  last  thoracic  ganglion  and  passes  to  the  re- 
nal plexus.  The  three  splanchnic  nerves  present  frequent  anastomoses  with 
each  other. 

Ganglia  in  the  Abdominal  and  the  Pelvic  Cavity. — The  semilunar  gan- 
glia on  the  two  sides  send  off  radiating  branches  to  form  the  solar  plexus. 
They  are  situated  by  the  side  of  the  cceliac  axis  and  near  the  suprarenal  capsules. 
These  are  the  largest  of  the  sympathetic  ganglia.  From  these  arise  plexuses 
distributed  to  various  parts  in  the  abdomen,  as  follows :  The  phrenic  plexus 
follows  the  phrenic  artery  and  its  branches  to  the  diaphragm.  The  eceliac 
plexus  subdivides  into  the  gastric,  hepatic  and  splenic  plexuses,  which  are 
distributed  to  organs,  as  their  names  indicate.  From  the  solar  plexus  differ- 
ent plexuses  are  given  off,  which  pass  to  the  kidneys,  the  suprarenal  capsules, 
the  testes  in  the  male  and  the  ovaries  in  the  female,  the  intestines  (by  the 
superior  and  inferior  mesenteric  plexuses),  the  upper  part  of  the  rectum,  the 
abdominal  aorta  and  the  vena  cava.  The  filaments  follow  the  distribution  of 
the  blood-vessels  in  the  solid  viscera. 


640  NERVOUS  SYSTEM. 

The  lumbar  ganglia,  four  in  number,  are  situated  in  the  lumbar  region, 
upon  the  bodies  of  the  vertebrae.  They  are  connected  with  the  ganglia  above 
and  below  and  with  each  other  by  the  sympathetic  cord,  receiving,  like  the 
other  ganglia,  filaments  from  the  spinal  nerves.  Their  branches  of  distribu- 
tion form  the  aortic  lumbar  plexus  and  the  hypogastric  plexus  and  follow  the 
course  of  the  blood-vessels. 

The  four  or  five  sacral  ganglia  and  the  ganglion  impar  are  situated  by 
the  inner  side  of  the  sacral  foramina  and  in  front  of  the  coccyx.  These  are 
connected  with  the  ganglia  above  and  with  each  other,  and  they  receive  fila- 
ments from  the  sacral  nerves,  there  being  generally  two  branches  of  commu- 
nication for  each  ganglion.  The  filaments  of  distribution  go  to  all  of  the 
pelvic  viscera  and  blood-vessels.  The  inferior  hypogastric,  or  pelvic  plex- 
us is  a  continuation  of  the  hypogastric  plexus  above,  and  receives  a  few  fila- 
ments from  the  sacral  ganglia.  The  uterine  nerves  go  to  the  uterus  and  the 
Fallopian  tubes.  In  the  substance  of  the  uterus  the  nerves  are  connected 
with  small  collections  of  ganglionic  cells.  The  sympathetic  filaments  are 
prolonged  into  the  upper  and  lower  extremities,  following  the  course  of  the 
blood-vessels  and  terminating  in  their  muscular  coat. 

The  filaments  of  the  sympathetic,  at  or  near  their  terminations,  are  con- 
nected with  ganglionic  cells,  not  only  in  the  heart  and  the  uterus,  but  in  the 
blood-vessels,  lymphatics,  the  coccygeal  gland,  the  submucous  and  the  mus- 
cular layer  of  the  entire  alimentary  canal,  the  salivary  glands,  pancreas, 
excretory  ducts  of  the  liver  and  pancreas,  the  larynx,  trachea,  pulmonary 
tissue,  bladder,  ureters,  the  entire  generative  apparatus,  suprarenal  capsules, 
thymus,  lachrymal  canals,  ciliary  muscle  and  the  iris.  In  these  situations 
nerve-cells  have  been  demonstrated  by  various  observers,  and  it  is  probable 
that  they  exist  everywhere  in  connection  with  the  terminal  filaments  of  this 
system  of  nerves. 

General  Properties  of  the  Sympathetic  Ganglia  and  Nerves. — The  sym- 
pathetic ganglia  and  nerves  possess  a  dull  sensibility,  which  is  particularly 
marked  in  the  ganglia.  That  the  nerves  contain  afferent  fibres,  is  shown  by 
certain  reflex  phenomena. 

Stimulation  of  the  sympathetic  produces  muscular  movements,  but  these 
are  confined  generally  to  non-striated  muscular  fibres,  to  which  these  nerves 
are  largely  distributed.  The  muscular  movements  do  not  immediately  follow 
stimulation  of  the  nerves,  but  there  is  a  long,  latent  period.  The  muscular 
contraction,  also,  persists  for  a  time  and  the  subsequent  relaxation  is  slow. 
The  induced  current  applied  to  the  splanchnic  nerves  does  not  produce 
movements  of  the  intestines,  but  these  movements  are  excited  by  the  con- 
stant current  (Legros  and  Onimus).  The  properties  of  the  vaso-motor 
nerves  will  be  considered  separately. 

The  sympathetic  ganglia  are  connected  with  the  motor  and  sensory 
divisions  of  the  cerebro-spinal  system.  Some  of  the  ganglia  and  nerve- 
plexuses  are  directly  dependent  for  their  action  upon  the  cerebro-spinal 
system,  while  others  are  capable,  at  least  for  a  time,  of  independent  action. 
Among  the  latter,  are  the  ganglia  of  the  heart,  the  intestinal  plexuses,  the 


DIEECT  EXPERIMENTS  ON  THE  SYMPATHETIC.  641 

plexuses  of  the  uterus  and  Fallopian  tubes,  of  the  ureters  and  of  the  blood- 
vessels. 

Direct  Experiments  on  the  Sympathetic. — The  experiments  of  Pourfour 
du  Petit  (1712-1725)  were  the  first  to  give  any  positive  information  regard- 
ing the  action  of  the  sympathetic  system ;  and  these  observations  may  be 
taken  as  the  starting-point  of  a  definite  knowledge  of  the  physiology  of  the 
sympathetic,  although  they  showed  only  the  influence  of  the  cervical  portion 
upon  the  eye.  In  1816,  Dupuy  removed  the  superior  cervical  ganglia  in 
horses,  with  the  effect  of  producing  injection  of  the  conjunctiva,  increase  of 
temperature  in  the  ear  and  an  abundant  secretion  of  sweat  upon  one  side  of 
the  head  and  neck.  These  experiments  showed  that  the  sympathetic  has  an 
important  influence  upon  nutrition,  calorification  and  secretion.  In  1851, 
Bernard  divided  the  sympathetic  in  the  neck  on  one  side  in  rabbits,  and 
noted  on  the  corresponding  side  of  the  head  and  the  ear,  increased  vascularity 
and  an  elevation  in  temperature  of  7°  to  11°  Fahr.  (4°  to  6°  C.).  This  con- 
dition of  increased  heat  and  vascularity  continues  for  several  months  after 
division  of  the  nerve.  In  1852,  Brown-Sequard  repeated  these  experiments 
and  attributed  the  elevation  of  temperature  directly  to  an  increase  in  the 
supply  of  blood  to  the  parts  affected.  He  made  an  important  advance  in 
the  history  of  the  sympathetic,  by  demonstrating  that  its  section  paralyzed 
the  muscular  coat  of  the  arteries,  and  farther,  that  Faradization  of  the  nerve 
in  the  neck  caused  the  vessels  to  contract.  This  was  the  discovery  of 
the  vaso-motor  nerves,  and  it  belongs  without  question  to  Brown-Sequard, 
who  published  his  observations  in  August,  1852.  A  few  months  later  in  the 
same  year,  Bernard  made  analogous  experiments  and  presented  the  same  ex- 
planation of  the  phenomena  observed. 

The  important  points  developed  by  the  first  experiments  of  Bernard  and 
of  Brown-Sequard  were  that  the  sympathetic  system  influences  the  general 
process  of  nutrition,  and  that  many  of  its  filaments  are  distributed  to  the 
muscular  coat  of  the  blood-vessels.  Before  these  experiments,  it  had  been 
shown  that  filaments  from  this  system  influenced  the  contractions  of  the  mus- 
cular coats  of  the  alimentary  canal. 

When  the  sympathetic  is  divided  in  the  neck,  the  local  increase  in  tem- 
perature is  always  attended  with  a  very  great  increase  in  the  supply  of  blood 
to  the  side  of  the  head  corresponding  to  the  section.  The  increased  tem- 
perature is  due  to  a  local  exaggeration  of  the  nutritive  processes,  apparently 
dependent  directly  upon  the  hyperaemia.  There  are  many  instances  in 
pathology,  of  local  increase  in  temperature  attending  increased  supply  of 
blood  to  restricted  parts.  In  an  experiment  by  Bidder,  after  excising  about 
half  an  inch  (12*7  mm.)  of  the  cervical  sympathetic  in  a  half -grown  rabbit, 
the  ear  on  that  side,  in  the  course  of  about  two  weeks,  became  distinctly 
longer  and  broader  than  the  other. 

It  is  easy  to  observe  the  effects  of  dividing  the  sympathetic  in  the  neck, 
but  analogous  phenomena  have  been  noted  in  other  parts.  Among  the 
most  striking  of  these  experiments  are  those  reported  by  Samuel,  who  de- 
scribed an  intense  hypsrsemia  of  the  mucous  membrane  of  the  stomach  and 


* 
642  NERVOUS  SYSTEM. 

intestines,  following  extirpation  of  the  coeliac  plexus.  By  comparative  ex- 
periments it  was  shown  that  this  did  not  result  from  the  peritonitis  pro- 
duced by  the  operation. 

As  regards  secretion,  the  influence  of  the  sympathetic  is  very  marked. 
When  the  sympathetic  filaments  distributed  to  a  gland  are  divided,  the  sup- 
ply of  blood  is  much  increased  and  an  abundant  flow  of  the  secretion  follows 
(Bernard).  Peyrani  has  shown  that  the  sympathetic  has  an  influence  upon 
the  secretion  of  urine.  When  the  nerves  in  the  neck  are  stimulated,  the 
quantity  of  urine  and  of  urea  is  increased,  and  this  increase  is  greater  with 
the  induced  than  with  the  constant  current.  When  the  sympathetic  is 
divided,  the  quantity  of  urine  and  of  urea  sinks  to  the  minimum. 

Moreau  published  in  1870  a  series  of  observations  on  the  influence  of  the 
sympathetic  nerves  upon  the  secretion  of  liquid  by  the  intestinal  canal,  which 
are  important  as  affording  a  possible  explanation  of  the  sudden  occurrence 
of  watery  diarrhoea.  In  these  experiments,  the  abdomen  was  opened  in  a 
fasting  animal,  and  three  loops  of  intestine,  each  loop  four  to  eight  inches 
(100  to  200  mm.)  long,  were  isolated  by  ligatures.  All  of  the  nerves  passing 
to  the  middle  loop  were  divided,  taking  care  to  avoid  the  blood-vessels. 
The  intestine  was  then  replaced,  and  the  wound  in  the  abdomen  was  closed 
with  sutures.  The  next  day  the  animal  was  killed.  The  two  loops  with 
the  nerves  intact  were  found  empty,  as  is  normal  in  fasting  animals,  and 
the  mucous  membrane  was  dry ;  but  the  loop  with  the  nerves  divided  was 
found  filled  with  a  clear,  alkaline  liquid,  colorless  or  slightly  opaline,  which 
precipitated  a  few  flocculi  of  organic  matter  on  boiling. 

Vaso-Motor  Centres  and  Nerves. — The  principal  or  dominating  vaso- 
motor  centres  are  situated  in  the  medulla  oblongata,  one  on  either  side, 
about  one-tenth  of  an  inch  (2*5  mm.)  from  the  median  line.  Each  centre,  in 
the  rabbit,  is  about  one-eighth  of  an  inch  (3  mm.)  long  and  about  one-six- 
teenth of  an  inch  (1-5  mm.)  wide.  Its  lower  border  is  about  one-fifth  of  an 
inch  (5  mm.)  above  the  calamus  scriptorius.  Each  side  of  the  body  has  its 
special  vaso-motor  centre,  and  very  few  if  any  of  the  vaso-motor  fibres  decus- 
sate. The  situation  of  the  vaso-motor  centres  in  the  medulla  has  been  de- 
termined by  successive  removal  of  the  nerve-centres  above.  If  the  central 
end  of  a  large  cerebro-spinal  nerve  be  stimulated  in  an  animal  poisoned  with 
curare,  the  vaso-motor  nerves  produce  contraction  of  the  blood-vessels,  by 
reflex  action,  and  there  is  a  rise  in  the  blood -pressure.  The  action  is  not 
interfered  with  by  removal  of  the  encephalic  ganglia  from  above  downward, 
until  the  part  of  the  medulla  containing  the  vaso-motor  centres  is  reached. 
When  these  centres  are  removed,  the  reflex  vaso-motor  action  is  permanently 
arrested. 

Subordinate  vaso-motor  centres  exist  in  the  spinal  cord.  When  the 
vaso-motor  centre  in  the  medulla  is  destroyed,  there  is  a  fall  in  the  blood- 
pressure  ;  but  if  the  circulation  be  continued,  after  a  time  the  blood-vessels 
regain  their  "  tone  "  and  the  pressure  may  then  be  affected  by  reflex  action. 
It  is  probable  that  these  spinal  centres  exist  throughout  the  dorsal  region 
and  in  the  upper  part  of  the  lumbar  region  of  the  cord. 


VASO-MOTOR  CENTRES  AND  NERVES.  643 

All  the  vase-motor  nerves  are  derived  from  the  medulla  oblongata  and 
the  spinal  cord.  Some  of  the  vaso-motor  fibres  to  the  head  pass  in  the 
trunks  of  the  motor  cranial  nerves,  but  most  of  them  come  from  the  ante- 
rior roots  of  some  of  the  spinal  nerves  and  pass  to  the  head  by  the  filaments 
of  distribution  of  the  cervical  sympathetic.  The  vaso-motor  fibres  pass  in 
the  lateral  columns  of  the  cord,  and  from  the  cord,  in  the  anterior  roots  of 
the  spinal  nerves,  in  the  dog,  as  far  down  as  the  second  pair  of  lumbar 
nerves.  These  fibres  are  medullated  but  are  of  small  size.  They  pass  to 
the  blood-vessels  either  through  branches  from  the  sympathetic  ganglia  or 
through  the  ordinary  cerebro-spinal  nerves.  They  are  therefore  not  confined 
to  branches  of  the  sympathetic,  as  Bernard  has  shown  by  the  following  ex- 
periment :  He  divided  the  fourth,  fifth,  sixth,  seventh  and  eighth  pairs  of 
lumbar  nerves  on  one  side  in  a  dog,  at  the  spinal  column,  and  paralyzed  mo- 
tion and  sensation  in  the  leg  of  that  side,  but  the  temperature  of  the  two 
sides  remained  the  same.  He  afterward  exposed  and  divided  the  sciatic 
nerve  on  that  side,  and  then  noted  decided  increase  in  temperature.  This 
experiment,  which  is  only  one  of  a  large  number,  shows  that  the  ordinary 
mixed  nerves  contain  vaso-motor  fibres,  which  are  entirely  independent  of 
the  nerves  of  motion  and  sensation,  a  fact  which  is  now  well  known  to  physi- 
ologists and  has  frequently  been  illustrated  in  cases  of  disease  in  the  human 
subject. 

The  vaso-motor  nerves  are  capable  of  influencing  local  circulations, 
probably  through  distinct  centres  for  different  parts.  Direct  stimulation  of 
the  principal  vaso-motor  centre  (10  to  12  or  more  single  induction  shocks 
per  second  for  strong  currents  or  20  to  25  for  moderate  currents)  increases 
the  blood-pressure  to  the  maximum. 

The  contractile  coats  of  the  veins  and  lymphatics  probably  are  influenced 
by  vaso-motor  nerves,  but  there  is  little  known  of  the  mechanism  of  this  action. 

Reflex  Vaso- Motor  Phenomena. — The  most  important  physiological  acts 
connected  with  the  vaso-motor  nerves  are  reflex.  It  is  evident  from  experi- 
ments on  the  inferior  animals  and  observations  on  the  human  subject  that 
there  are  afferent  as  well  as  efferent  nerves.  The  reflex  acts  connected  with 
secretion  have  already  been  considered  ;  but  there  are  other  phenomena  that 
demand  a  brief  description. 

As  regards  animal  heat,  the  phenomena  of  which  are  intimately  con- 
nected with  the  supply  of  blood  to  the  parts,  it  is  important  to  note  the  ob- 
servations of  Brown-Sequard  and  Lombard,  who  found  that  pinching  of  the 
skin  on  one  side  was  attended  with  a  diminution  in  the  temperature  in  the 
corresponding  member  of  the  opposite  side,  and  that  sometimes,  when  the 
irritation  was  applied  to  the  upper  extremities,  changes  were  produced  in 
the  temperature  of  the  lower  limbs.  Tholozan  and  Brown-Sequard  found, 
also,  that  lowering  the  temperature  of  one  hand  produced  a  considerable  de- 
pression in  the  heat  of  the  other  hand,  without  any  notable  diminution  in 
the  general  heat  of  the  body.  Brown-Sequard  showed  that  by  immersing 
one  foot  in  water  at  41°  Fahr.  (5°  C.)  the  temperature  of  the  other  foot 
was  diminished  by  about  7°  Fahr.  (4°  C.)  in  the  course  of  eight  minutes. 


G44:  NERVOUS  SYSTEM. 

These  experiments  show  that  certain  impressions  made  upon  the  sensory 
nerves  affect  the  animal  heat,  by  reflex  action.  As  section  of  the  sympa- 
thetic filaments  increases  the  heat  in  particular  parts,  with  an  increase 
in  the  supply  of  blood,  and  their  Faradization  reduces  the  quantity  of  blood 
and  diminishes  the  temperature,  it  is  reasonable  to  infer  that  the  reflex 
action  takes  place  through  the  vaso-motor  nerves.  If  it  be  assumed  that 
the  impression  is  conveyed  to  the  centres  by  the  nerves  of  general  sensibility, 
and  that  the  vessels  are  modified  in  their  caliber  and  the  heat  is  affected 
through  the  sympathetic  fibres,  it  remains  only  to  determine  the  situation  of 
the  centres  which  receive  the  impression  and  generate  the  stimulus.  These 
centres  are  situated  in  the  cerebro-spinal  axis. 

The  existence  of  vaso-motor  nerves  and  their  connection  with  centres  in 
the  cerebro-spinal  axis  are  now  sufficiently  well  established.  It  is  certain, 
also,  that  centres  presiding  over  particular  acts  may  be  distinctly  located,  as 
the  genito-spinal  centre,  in  the  spinal  cord  opposite  the  fourth  lumbar  verte- 
bra, and  the  cilio-spinal  centre,  in  the  cervical  region  of  the  cord.  An  im- 
pulse generated  in  these  centres,  sometimes  as  the  result  of  impressions  re- 
ceived through  the  nerves  of  general  sensibility,  produces  contraction  of  the 
non-striated  muscular  fibres  of  the  iris,  vasa  deferentia  etc.,  including  the 
muscular  walls  of  the  blood-vessels.  The  contraction  of  the  muscular  walls 
of  the  vessels  is  tonic ;  and  when  their  nerves  are  divided,  relaxation  takes 
place  and  the  vessels  are  dilated  by  the  pressure  of  blood.  By  this  action 
the  local  circulations  are  regulated  in  accordance  with  impressions  made 
upon  sensory  nerves,  the  physiological  requirements  of  certain  parts,  mental 
emotions  etc.  Secretion,  the  peristaltic  movements  of  the  alimentary  canal, 
the  movements  of  the  iris  etc.,  are  influenced  in  this  way.  This  action  is 
also  illustrated  in  cases  of  reflex  paralysis,  in  inflammations  as  the  result  of 
"  taking  cold,"  and  in  many  other  pathological  conditions. 

It  remains  only  to  show  that  the  phenomena  following  section  of  the 
sympathetic  in  animals  are  illustrated  in  certain  cases  of  disease  or  injury  in 
the  human  subject.  It  is  rare  to  observe  traumatic  injury  confined  to  the 
sympathetic  in  the  neck.  A  single  case,  however,  apparently  of  this  kind, 
has  been  reported  by  Mitchell.  A  man  received  a  gunshot-wound  in  the 
neck.  Among  the  phenomena  observed  a  few  weeks  after,  were  contraction 
of  the  pupil  on  the  side  of  the  injury,  and  after  exercise,  flushing  of  the  face 
upon  that  side.  There  was  no  difference  in  the  temperature  upon  the  two 
sides  during  repose,  but  no  thermometric  observations  were  made  when  half 
of  the  face  was  flushed  by  exercise.  Bartholow  has  reported  several  cases  of 
unilateral  sweating  of  the  head  (two  observed  by  himself),  in  several  of 
which  there  probably  was  compression  of  the  sympathetic,  from  aneurism. 
In  those  cases  in  which  the  condition  of  the  eye  was  observed,  the  pupil  was 
found  contracted  in  some  and  dilated  in  others.  In  none  of  these  cases 
were  there  any  accurate  thermometric  observations.  In  a  series  of  obser- 
vations by  Wagner,  upon  the  head  of  a  woman,  eighteen  minutes  after 
decapitation,  powerful  stimulation  of  the  sympathetic  produced  great  en- 
largement of  the  pupil.  In  such  a  case  as  this,  it  would  not  be  possible  to 


TROPHIC  CENTRES  AND  NERVES.  645 

make  any  observations  on  the  influence  of  the  sympathetic  upon  the  tem- 
perature. 

Vaso- Inhibitory  Nerves. — There  are  certain  nerves,  the  direct  action  of 
which  under  Faradic  stimulation  is  to  dilate  certain  blood-vessels.  These 
nerves  may  also  be  excited  by  reflex  action  through  the  sensory  nerves.  In 
many  nerves,  as  the  chorda  tympani,  the  nervi  erigentes  etc.,  the  existence 
of  inhibitory  fibres  has  been  demonstrated  (Dastre  and  Morat,  Eckhard, 
Laffont,  Vulpian  and  others).  For  example,  division  of  the  nervi  erigentes 
has  no  immediate  effect  on  the  penis,  but  Faradization  of  the  peripheral 
ends  of  the  nerves  dilates  the  blood-vessels  and  produces  erection.  Fibres 
possessing  this  property  undoubtedly  exist  throughout  the  body,  in  the  sym- 
pathetic and  in  the  motor  and  mixed  nerves ;  and  it  is  possible  that  there  are 
vaso-motor  inhibitory  centres,  although  such  centres  have  not  been  located. 
The  mode  of  action  of  these  nerves  is  analogous  to  that  of  the  inhibitory 
nerve  of  the  heart,  restraining  and  regulating  the  action  of  the  vaso-motor 
nerves  and  allowing  the  pressure  of  blood  to  dilate  the  vessels.  It  does 
not,  however  seem  proper  to  call  them  "  vaso-dilator  "  nerves,  any  more  than 
it  would  be  correct  to  call  the  inhibitory  nerve  of  the  heart  the  cardiac  dilator 
nerve. 

Trophic  Centres  and  Nerves  (so-called}. — Collections  of  nerve-cells  act  as 
centres  presiding  over  the  nutrition  of  the  nerve-fibres  with  which  they  are 
connected  ;  but  it  has  been  found  that  the  nutrition  of  certain  parts  may  be 
profoundly  affected  through  the  nervous  system.  Many  pathologists,  relying 
upon  the  presence  of  certain  lesions  of  cells  in  the  cord,  in  connection  with 
cases  of  progressive  muscular  atrophy,  admit  the  existence  of  trophic  cells 
and  nerves.  These  views,  however,  rest  almost  entirely  upon  pathological 
observations.  Direct  experiments  upon  the  sympathetic  in  animals  do  not 
positively  show  any  influence  upon  nutrition,  except  as  this  system  of  nerves 
affects  the  supply  of  blood  to  the  parts.  "When  a  sympathetic  nerve  is 
divided,  there  is  an  apparent  exaggeration  of  the  nutritive  processes  in  par- 
ticular parts,  and  there  may  be  inflammatory  phenomena,  but  atrophy  of 
muscles  is  not  observed.  Atrophy  of  muscles,  indeed,  follows  division  of 
cerebro-spinal  nerves  only,  or  as  cases  of  disease  have  shown,  disorganization 
of  cells  belonging  to  what  are  recognized  as  motor  centres.  As  regards  the 
latter  condition,  there  can  be  no  doubt  of  the  fact  that  progressive  muscular 
atrophy  is  attended  with  disorganization  of  certain  of  the  motor  cells  of  the 
spinal  cord. 

Without  fully  discussing  this  subject,  which  belongs  to  pathology,  the 
facts  may  be  briefly  stated  as  follows  :  There  may  be  progressive  atrophy  of 
certain  muscles,  uncomplicated  with  paralysis  except  in  so  far  as  there  is 
weakness  of  these  muscles  due  to  partial  and  progressive  destruction  of  their 
contractile  elements.  The  only  constant  pathological  condition  in  these  cases, 
aside  from  the  changes  in  the  muscular  tissue,  is  destruction  of  certain  cells  in 
the  antero-lateral  portions  of  the  cord,  with  more  or  less  atrophy  of  the  corre- 
sponding anterior  roots  of  the  nerves.  It  has  never  been  assumed  that  there 
are  cells  in  the  cord,  presenting  anatomical  peculiarities  by  which  they  may  be 


64:6  NERVOUS  SYSTEM. 

distinguished  from  the  ordinary  motor  or  sensory  elements ;  but  the  fact  of 
the  degeneration  of  certain  cells,  others  remaining  normal,  has  led  to  the  dis- 
tinction by  certain  writers,  of  trophic  cells,  and,  of  course,  these  must  be 
connected  with  the  parts  by  trophic  nerves. 

There  can  be  no  doubt  of  the  fact  that  the  cells  of  the  antero-lateral 
columns  of  the  spinal  cord  are  connected  with  motion;  and  that  impulses 
generated  in  these  cells  are  conveyed  to  the  muscles  by  the  anterior  roots  of 
the  spinal  nerves.  It  also  is  a  fact,  no  less  definite,  that  when  a  muscle  or  a 
part  of  a  muscle  is  for  a  long  time  deprived  of  the  motor  influence  by  which 
it  is  brought  into  action,  its  fibres  undergo  atrophy,  become  altered  in  struct- 
ure and  lose  their  contractility.  Starting  with  these  two  propositions,  and 
assuming  that  certain  of  the  ordinary  motor  cells  of  the  cord  are  destroyed, 
it  is  easy  to  predict  the  phenomena  to  be  expected  as  a  consequence  of  such 
a  lesion. 

The  destruction  of  certain  motor  nerve-cells  connected  with  the  anterior 
roots  of  the  spinal  nerves  would  certainly  produce  degeneration  of  the  nerve- 
fibres  to  which  they  give  origin.  This  occurs  when  any  motor  nerves  are 
separated  from  their  cells  of  origin,  and  it  involves  no  necessity  of  assuming 
the  existence  of  special  trophic  cells  or  nerves. 

If  a  few  of  the  motor  cells  be  affected  with  disease,  and  if  the  degenera- 
tion be  gradual  and  progressive,  there  would  necessarily  be  progressive  and 
partial  paralysis  of  the  muscles  to  which  their  nerves  are  distributed.  This 
paralysis,  confined  to  a  limited  number  of  fibres  of  particular  muscles  or 
sets  of  muscles,  would  give  the  idea  of  progressive  weakening  of  the  muscles, 
and  the  phenomena  would  not  be  those  observed  in  complete  paralysis  pro- 
duced by  section  of  the  motor  nerves.  These  are  the  phenomena  observed 
in  progressive  muscular  atrophy,  preceding  the  paralysis  which  is  the  final 
result  of  the  disease  ;  and  these  do  not  of  necessity  involve  the  action  of  any 
special  centres  or  nerves. 

As  regards  the  muscular  atrophy  itself,  if  the  nervous  stimulus  be  grad- 
ually destroyed,  the  muscular  tissue  will  necessarily  undergo  progressive  de- 
generation and  atrophy. 

With  the  above  considerations,  the  question  of  the  trophic  cells  and 
nerves  may  be  left  to  the  pathologist ;  and  the  existence  of  centres  and 
nerves  specially  and  directly  influencing  the  nutrition  of  the  muscular  sys- 
tem can  be  admitted  only  when  it  has  been  demonstrated  that  there  are 
lesions  of  particular  structures  in  the  nervous  system,  which  produce  phe- 
nomena that  can  not  be  explained  by  the  action  of  ordinary  motor  and  sen- 
sory nerves  and  of  the  vaso-motor  system.  In  thus  dismissing  the  question, 
however,  it  is  not  intended  to  assume  that  the  existence  of  trophic  centres 
and  nerves  is  impossible.  There  are  certain  peculiar  changes  in  tissue  in 
progressive  muscular  atrophy,  and  section  of  nerves  produces  degenerations 
of  glandular  and  other  structures  that  are  not  muscular.  Future  observations 
may  show  that  there  are  special  parts  of  the  nervous  system  presiding  over 
nutrition  ;  but  at  present,  such  parts  have  not  been  accurately  described  and 
isolated,  either  anatomically  or  physiologically. 


SLEEP.  647 

SLEEP. 

When  it  is  remembered  that  about  one-third  of  each  day  is  passed  in 
sleep,  and  that  at  this  time,  voluntary  motion,  sensation,  the  special  senses 
and  various  of  the-  functions  of  the  organism  are  greatly  modified,  the  im- 
portance of  a  physiological  study  of  this  condition  is  sufficiently  apparent. 
The  subject  of  sleep  is  most  appropriately  considered  in  connection  with  the 
nervous  system,  for  the  reason  that  the  most  important  modifications  in 
function  are  observed  in  the  cerebro-spinal  axis  and  nerves.  Repose  is  as 
necessary  to  the  nutrition  of  the  muscular  system  as  proper  exercise ;  but  re- 
pose of  the  muscles  relieves  the  fatigue  due  to  exercise,  without  sleep.  It 
is  true  that  after  violent  and  prolonged  exertion,  there  is  frequently  a  desire 
for  sleep,  but  simple  repose  will  often  restore  the  muscular  power.  After  the 
most  violent  effort,  a  renewal  of  muscular  vigor  is  most  easily  and  completely 
effected  by  rest  without  sleep,  a  fact  familiar  to  all  who  are  accustomed  to 
athletic  exercises.  After  prolonged  and  severe  mental  exertion,  however,  or 
after  long-continued  muscular  effort  which  involves  an  excessive  expenditure 
of  the  so-called  nerve-force,  sleep  becomes  an  imperative  necessity.  If  the 
nervous  system  be  not  abnormally  excited  by  effort,  sleep  follows  moderate 
exertion  as  a  natural  consequence,  and  it  is  the  only  physiological  means  of 
complete  restoration ;  but  the  two  most  important  muscular  acts,  viz.,  those 
concerned  in  circulation  and  respiration,  are  never  completely  arrested,  sleep- 
ing or  waking,  although  they  undergo  certain  modifications. 

In  infancy  and  youth,  when  the  organism  is  in  process  of  development, 
sleep  is  more  important  than  in  adult  life  or  old  age.  The  infant  does  little 
but  sleep,  eat  and  digest.  In  adult  life,  under  perfectly  physiological  condi- 
tions, a  person  requires  about  eight  hours  of  sleep ;  some  need  less,  but  few 
require  more.  In  old  age,  unless  after  extraordinary  exertion,  less  sleep  is 
required  than  in  adult  life.  Each  individual  learns  by  experience  how  much 
sleep  is  necessary  for  perfect  health  ;  and  there  is  nothing  which  more  com- 
pletely incapacitates  one  for  mental  or  muscular  effort,  especially  the  former, 
than  loss  of  natural  rest. 

Sleeplessness  is  one  of  the  most  important  of  the  predisposing  causes  of 
certain  forms  of  brain-disease,  a  fact  which  is  well  recognized  by  practical 
physicians.  One  of  the  most  severe  methods  of  torture  is  long-continued 
deprivation  of  sleep ;  and  persons  have  been  known  to  sleep  when  subjected 
to  acutely  painful  impressions.  Severe  muscular  effort,  even,  may  be  con- 
tinued during  sleep.  In  forced  marches,  regiments  have  been  known  to 
sleep  while  walking  ;  men  have  slept  soundly  in  the  saddle ;  persons  will 
sometimes  sleep  during  the  din  of  battle ;  and  other  instances  illustrating 
the  imperative  demand  for  sleep  after  prolonged  vigilance  might  be  cited. 
It  is  remarkable,  also,  how  noises  to  which  one  has  become  accustomed  may 
fail  to  disturb  natural  rest.  Those  who  have  been  long  habituated  to  the 
noise  of  a  crowded  city  frequently  find  difficulty  in  sleeping  in  the  stillness 
of  the  country.  Prolonged  exposure  to  intense  cold  induces  excessive  som- 
nolence, and  if  this  be  not  resisted,  the  sleep  passes  into  stupor,  the  power 


648  NERVOUS  SYSTEM. 

of  resistance  to  cold  becomes  rapidly  diminished,  and  death  is  the  result. 
Intense  heat  often  produces  drowsiness,  but,  as  is  well  known,  is  not  favor- 
able to  natural  sleep. 

Sleep  is  preceded  by  a  feeling  of  drowsiness,  an  indisposition  to  mental  or 
physical  exertion,  and  a  general  relaxation  of  the  muscular  system.  It  then 
requires  a  decided  effort  to  keep  awake.  In  sleep  the  voluntary  muscles 
are  inactive,  the  lids  are  closed,  the  ordinary  impressions  of  sound  are  not 
appreciated,  and  sometimes  there  is  a  dreamless  condition,  in  which  all 
knowledge  of  existence  is  lost. 

There  may  be,  during  sleep,  mental  operations  of  which  there  is  no  con- 
sciousness or  recollection,  unconscious  cerebration,  as  it  was  called  by  Car- 
penter. It  is  well  known  that  dreams  are  vividly  remembered  immediately 
on  awakening,  but  that  the  recollection  of  them  rapidly  fades  away,  unless 
they  be  brought  to  mind  by  an  effort  to  recall  and  relate  them.  Whatever 
be  the  condition  of  the  mind  in  sleep,  if  the  sleep  be  normal,  there  is  repose 
of  the  cerebro-spinal  system  and  an  absence  of  voluntary  effort,  which  re- 
store the  capacity  for  mental  and  physical  exertion. 

The  impressionability  and  the  activity  of  the  human  mind  are  so  great, 
most  of  the  animal  functions  are  so  subordinate  to  its  influence,  and  the 
organism  is  so  subject  to  unusual  mental  conditions,  that  it  is  difficult  to 
determine  with  exactness  the  phenomena  of  sleep  that  are  absolutely  physio- 
logical and  to  separate  those  that  are  slightly  abnormal.  It  can  not  be  as- 
sumed, for  example,  that  a  dreamless  sleep,  in  which  existence,  is  as  it  were 
a  blank,  is  the  only  normal  condition  of  repose  of  the  system  ;  nor  is  it  pos- 
sible to  determine  what  dreams  are  due  to  previous  trains  of  thought,  to 
impressions  from  the  external  world  received  during  sleep,  and  are  purely 
physiological,  and  what  are  due  to  abnormal  nervous  influences,  disordered 
digestion,  etc.  It  may  be  assumed,  however,  that  an  entirely  refreshing  sleep 
is  normal. 

That  reflex  ideas  originate  during  sleep,  as  the  result  of  external  im- 
pressions, there  can  be  no  doubt ;  and  many  remarkable  experiments  upon 
the  production  of  dreams  of  a  definite  character,  by  subjecting  a  person  dur- 
ing sleep  to  peculiar  influences,  have  been  recorded.  The  hallucinations 
produced  in  this  way  are  called  hypnagogic,  and  they  occur  usually  when 
the  subject  is  not  in  a  condition  favorable  to  sound  sleep. 

As  regards  dreams  due  to  external  impressions,  it  is  a  curious  fact,  which 
has  been  noted  by  many  observers  and  is  one  which  accords  with  the  per- 
sonal experience  of  all  who  have  reflected  upon  the  subject,  that  trains  of 
thought  and  imaginary  events,  which  seem  to  pass  over  a  long  period  of 
time  in  dreams,  actually  occur  in  the  brain  within  a  few  seconds.  A  person 
is  awakened  by  a  certain  impression,  which  undoubtedly  has  given  rise  to 
a  dream  that  seemed  to  occupy  hours  or  days,  and  yet  the  period  of  time  be- 
tween the  impression  and  the  awakening  was  hardly  more  than  a  few  seconds ; 
and  persons  will  drop  asleep  for  a  very  few  minutes,  and  yet  have  dreams  with 
the  most  elaborate  details  and  apparently  of  great  length.  It  is  unnecessary 
to  cite  the  accounts  of  literary  compositions  of  merit,  the  working  out  of 


CONDITION  OF  THE  BRAIN  DURING  SLEEP.  649 

difficult  mathematical  problems  in  dreams,  etc.,  some  of  which  are  undoubt- 
edly accurate.  If  it  be  true  that  the  mind  is  capable  of  forming  consecu- 
tive ideas  during  sleep — which  can  hardly  be  doubted — there  is  no  good  rea- 
son why  these  phenomena  should  not  occur  and  the  thoughts  should  not  be 
remembered  and  noted  immediately  on  awakening.  In  most  dreams,  how- 
ever, the  mind  is  hardly  in  a  normal  condition,  and  the  brain  generally  loses 
the  power  of  concentration  and  of  accurate  reasoning. 

Condition  of  the  Brain  and  Nervous  System  during  Sleep. — During 
sleep  the  brain  may  be  in  a  condition  of  absolute  repose — at  least,  as  far  as 
there  is  any  subjective  knowledge  of  mental  operations — or  there  may  be 
more  or  less  connected  trains  of  thought.  There  is,  also,  as  a  rule,  absence 
of  voluntary  effort,  although  movements  may  be  made  to  relieve  discom- 
fort from  position  or  external  irritation,  without  awakening.  The  sensory 
nerves  retain  their  properties,  although  the  general  sensibility  is  somewhat 
blunted;  and  the  same  may  be  said  of  the  special  senses  of  hearing, 
smell,  and  probably  of  taste.  There  is  every  reason  to  believe  that  the 
action  of  the  sympathetic  system  is  not  disturbed  or  affected  by  sleep,  if 
the  influence  of  the  vaso-motor  nerves  upon  the  circulation  in  the  brain  be 
excepted. 

Two  opposite  theories  have  long  been  in  vogue  with  regard  to  the  imme- 
diate cause  of  sleep.  In  one,  this  condition  is  attributed  to  venous  conges- 
tion and  increased  pressure  of  blood  in  the  brain,  and.  this  view  probably 
had  its  origin  in  the  fact  that  cerebral  congestion  induces  stupor  or  coma. 
Stupor  and  coma,  however,  are  entirely  distinct  from  natural  sleep ;  for  in 
the  former  the  action  of  the  brain  is  entirely  suspended,  there  is  no  con- 
sciousness, no  dreaming,  and  the  condition  is  manifestly  abnormal.  In  ani- 
mals rendered  comatose  by  opium,  the  brain  when  exposed  is  found  deeply 
congested  with  venous  blood.  The  same  condition  often  obtains  in  pro- 
found anaesthesia  by  chloroform,  but  a  state  of  the  brain  very  nearly  resem- 
bling normal  sleep  is  observed  in  anaesthesia  by  ether.  These  facts  have  been 
demonstrated  by  experiments  upon  living  animals,  and  have  been  observed 
in  the  human  subject  in  cases  of  injury  of  the  head.  When  opium  is 
administered  in  large  doses,  the  brain  is  congested  during  the  condition  of 
stupor  or  coma,  but  this  congestion  is  relieved  when  the  animal  passes,  as 
sometimes  happens,  from  the  effects  of  the  agent  into  a  natural  sleep.  In 
view  of  these  facts  and  others  which  will  be  stated  hereafter,  it  is  unneces- 
sary to  discuss  the  theory  that  sleep  is  attended  with  or  is  produced  by  con- 
gestion of  the  cerebral  vessels. 

The  idea  that  the  circulation  in  the  brain  is  diminished  during  sleep  has 
long  been  entertained  by  some  physiologists ;  but  until  within  a  few  years, 
it  has  rested  chiefly  upon  theoretical  considerations.  The  experiments  of 
Durham  (1860)  seem  to  demonstrate  that  the  supply  of  blood  to  the  brain  is 
always  greatly  diminished  during  sleep.  These  experiments  were  made 
upon  dogs.  A  piece  of  the  skull  was  removed  with  a  trephine,  and  a  watch- 
glass  was  accurately  fitted  to  the  opening  and  cemented  at  the  edges  with 
Canada  balsam.  When  the  animals  operated  upon  were  awake,  the  vessels 


650  NERVOUS  SYSTEM. 

of  the  pia  mater  were  seen  moderately  distended  and  the  circulation  was 
active;  but  during  perfectly  natural  sleep,  the  brain  retracted  and  became 
pale.  "  The  contrast  between  the  appearance  of  the  brain  during  its  period 
of  functional  activity  and  during  its  state  of  repose  or  sleep  was  most  re- 
markable." There  can  be  hardly  any  doubt,  after  these  experiments,  that 
the  cerebral  circulation  is  considerably  diminished  in  activity  during  sleep. 

The  influence  of  diminished  supply  of  blood  to  the  brain  has  been  illus- 
trated by  compression  of  both  carotid  arteries.  In  an  experiment  performed 
upon  his  own  person,  Fleming  produced  immediate  and  profound  sleep  in 
this  way,  and  this  result  invariably  followed  in  subsequent  trials  upon  him- 
self and  others.  Waller  produced  anaesthesia  in  patients  by  pressure  upon 
both  pneumogastric  nerves ;  but  the  nerves  are  so  near  the  carotid  arteries 
that  they  could  hardly  be  compressed,  in  the  human  subject,  without  inter- 
fering with  the  current  of  blood,  and  such  experiments  do  not  positively 
show  whether  the  loss  of  sensibility  be  due  to  pressure  upon  the  nerves  or 
upon  the  vessels.  In  some  rare  instances  in  which  both  carotid  arteries  have 
been  tied  in  the  human  subject,  it  has  been  stated  that  there  is  an  unusual 
drowsiness  following  the  necessary  diminution  in  the  activity  of  the  cerebral 
circulation ;  but  this  result  is  by  no  means  constant,  and  the  morbid  condi- 
tions involving  so  serious  an  operation  are  usually  such  as  to  interfere  with 
their  value  as  facts  bearing  upon  the  question  under  consideration.  As  far 
as  the  human  subject  is  concerned,  the  most  important  facts  are  the  results 
of  compression  of  both  carotids  in  healthy  persons.  These,  as  well  as  experi- 
ments on  animals,  all  go  to  show  that  the  supply  of  blood  to  the  brain  is 
diminished  during  natural  sleep,  and  that  sleep  may  be  induced  by  retarding 
the  cerebral  circulation  by  compressing  the  vessels  of  supply.  When  the  cir- 
culation is  interfered  with  by  compressing  the  veins,  congestion  is  the  result, 
and  there  is  stupor  or  coma. 

If  diminished  flow  of  blood  through  the  cerebral  vessels  be  the  cause  of 
natural  sleep,  it  becomes  important  to  inquire  how  this  condition  of  physio- 
logical anaemia  is  brought  about.  It  must  be  that  when  the  system  requires 
sleep,  the  vessels  of  the  brain  contract  in  obedience  to  a  stimulus  received 
through  the  sympathetic  system  of  nerves,  diminishing  the  supply  of  blood, 
here,  as  in  other  parts  under  varied  physiological  conditions.  The  vessels  of 
the  brain  are  provided  with  vaso-mofcor  nerves,  and  it  is  sufficient  to  have 
noted  that  the  arteries  are  contracted  during  sleep,  the  mechanism  of  this 
action  being  well  established  by  observations  upon  other  parts  of  the  circu- 
latory system. 

Little  is  known  of  the  intimate  nature  of  the  processes  of  nutrition  of 
the  brain  during  its  activity  and  in  repose ;  but  there  can  be  no  doubt  of  the 
fact  that  there  is  more  or  less  cerebral  action  at  all  times  when  one  is  awake. 
Although  the  mental  processes  are  much  less  active  during  sleep,  even  at  this 
time,  the  operations  of  the  brain  are  not  always  suspended.  It  is  equally 
well  established  that  exercise  of  the  brain  is  attended  with  physiological 
wear  of  nervous  tissue,  and  like  other  parts  of  the  organism,  its  tissue  re- 
quires periodic  repose  for  regeneration  of  the  substance  consumed.  Analo- 


CONDITION  OF  THE  BRAIN  DURING  SLEEP.  651 

gies  to  this  are  to  be  found  in  parts  that  are  more  easily  subjected  to  direct 
observation.  The  muscles  require  repose  after  exertion,  and  the  glands,  when 
not  actively  engaged  in  discharging  their  secretions,  present  intervals  of  rest. 
As  regards  the  glands,  during  the  intervals  of  repose  the  supply  of  blood  to 
their  tissue  is  much  diminished.  It  is  probable,  also,  that  the  muscles  in 
action  receive  more  blood  than  during  rest ;  but  it  is  mainly  when  these  parts 
are  not  active,  and  when  the  supply  of  blood  is  smallest,  that  the  processes 
of  regeneration  of  tissue  seem  to  be  most  efficient.  As  a  rule  the  activity  of 
parts,  while  it  is  attended  with  an  increased  supply  of  blood,  is  a  condition 
more  or  less  opposed  to  the  processes  of  repair,  the  hyperfemia  being,  appar- 
ently, a  necessity  for  the  marked  and  powerful  manifestations  of  their  pecul- 
iar action.  When  the  parts  are  active,  the  blood  seems  to  be  required  to  keep 
at  the  proper  standard  the  so-called  irritability  of  the  tissues  and  to  increase 
their  power  of  action  under  proper  stimulus.  Exercise  increases  the  power 
of  regeneration  and  favors  full  development  in  the  repose  which  follows ;  but 
during  rest,  the  tissues  have  time  to  appropriate  new  matter,  and  this  does 
not  seem  to  involve  a  large  supply  of  blood.  A  muscle  is  exhausted  by  pro- 
longed exertion ;  and  the  large  quantity  of  blood  passing  through  the  tissue 
carries  away  carbon  dioxide  and  other  products  of  disassimilation,  which  are 
increased  in  quantity,  until  it  gradually  uses  up  its  capacity  for  work.  Then 
follows  repose;  the  supply  of  blood  is  reduced,  but  under  normal  condi- 
tions, the  tissue  repairs  the  waste  which  has  been  excited  by  action,  the  blood 
furnishing  nutritive  matter  and  carrying  away  a  comparatively  small  quan- 
tity of  effete  products. 

It  may  safely  be  assumed  that  processes  analogous  to  those  just  described 
take  place  in  the  brain.  By  absence  of  voluntary  effort,  the  muscles  have 
time  for  rest  and  for  the  repair  of  physiological  waste,  and  their  action  is  for 
the  time  suspended.  As  the  activity  of  the  brain  involves  consciousness, 
volition,  the  generation  of  thought,  and,  in  short,  the  mental  condition  ob- 
served while  awake,  complete  repose  of  the  brain  is  characterized  by  the 
opposite  conditions.  It  is  true  that  the  brain  may  be  rested  without  sleep, 
by  abstaining  from  mental  effort,  by  the  gratification  of  certain  of  the  senses, 
and  by  mental  distraction  of  various  kinds,  and  that  the  mind  may  work 
to  some  extent  during  sleep ;  but  during  the  period  of  complete  repose — that 
condition  which  is  so  necessary  to  perfect  health  and  full  mental  vigor — con- 
sciousness and  volition  are  lost,  there  is  no  thought,  and  the  brain,  which 
does  not  receive  blood  enough  to  stimulate  it  to  action,  is  simply  occupied  in 
the  insensible  repair  of  its  substance  and  is  preparing  itself  for  renewed  work. 
The  exhaustion  of  the  muscles  produces  a  sense  of  fatigue  of  the  muscular 
system,  indisposition  to  muscular  exertion,  and  a  desire  for  rest,  not  neces- 
sarily involving  drowsiness.  Fatigue  of  the  brain  is  manifested  by  indisposi- 
tion to  mental  exertion,  dullness  of  the  special  senses  and  a  desire  for  sleep. 
Simple  repose  will  relieve  physiological  fatigue  of  muscles ;  and  when  a  par- 
ticular set  of  muscles  has  been  used,  the  fatigue  often  disappears  when  these 
muscles  alone  are  at  rest,  though  others  be  brought  into  action.  Sleep,  and 
sleep  alone,  relieves  fatigue  of  the  brain. 


652  SPECIAL  SENSES. 

During  sleep  nearly  all  of  the  physiological  processes,  except  those  di- 
rectly under  the  control  of  the  sympathetic  nervous  system,  are  diminished 
in  activity.  The  circulation  is  slower,  and  the  pulsations  of  the  heart  are 
less  frequent,  as  well  as  the  respiratory  movements.  These  points  have 
already  been  considered  in  connection  with  the  physiology  of  circulation  and 
respiration.  Physiologists  have  but  little  positive  information  with  regard 
to  the  relative  activity  of  the  processes  of  digestion,  absorption  and  secretion, 
during  sleep.  The  drowsiness  which  many  persons  experience  after  a  full 
meal  is  probably  due  to  a  determination  of  blood  to  the  alimentary  canal  and 
a  consequent  diminution  in  the  supply  to  the  brain. 


CHAPTER  XXL 

SPECIAL  SENSES— TOUCH,    OLF ACTION  AND   GUSTATION. 

General  characters  of  the  special  senses— Muscular  sense  (so  called)— Sense  of  touch— Variations  in  tactile 
sensibility  in  different  parts  (sense  of  locality  of  impressions) — Table  of  variations  measured  by  the 
sesthesiometer— Appreciation  of  temperature— Tactile  centre— Olfaction — Nasal  fossje— Schneidermn 
and  olfactory  membranes— Olfactory  (first  nerve)— Physiological  anatomy — Olfactory  bulbs— Olfactory 
cells  and  terminations  of  the  olfactory  nerve-fibres — Properties  and  uses  of  the  olfactory  nerves — Mechan- 
ism of  olf action — Relations  of  olf action  to  the  sense  of  taste — Reflex  acts  through  the  olfactory  nerves 
— Olfactory  centre— Gustation— Savors— Nerves  of  taste— Chorda  tympani— Glosso-pharyngeal  (ninth 
nerve)— Physiological  anatomy— General  properties  of  the  glosso-pharyngeal— Relations  of  the  glosso- 
pharyngeal  nerves  to  gustation— Mechanism  of  gustation— Physiological  anatomy  of  the  organ  of  taste 
—Papillae  of  the  tongue — Taste-beakers— Connections  of  the  nerves  with  the  organs  of  taste— Taste- 
centre. 

THE  description  of  the  nerves  thus  far  has  included  motion  and  what  is 
known  as  general  sensibility ;  and  knowledge  of  these  properties  of  the  nerv- 
ous system  has  been  derived  mainly  from  experiments  upon  the  inferior  ani- 
mals. As  regards  sensation,  the  experiments  have  referred  to  impressions 
recognized  as  painful ;  and  these  are  conveyed  to  the  centres  by  nerve-fila- 
ments, anatomically  as  well  as  physiologically  distinct  from  those  which  con- 
vey to  the  contractile  parts  the  impulses  that  give  rise  to  motion.  In  regard 
to  the  sensory  nerves,  simple  impressions  only  have  been  described ;  but  it 
is  evident  that  the  filaments  of  peripheral  distribution  of  these  nerves  are 
capable  of  receiving  a  variety  of  impressions,  by  which,  to  a  certain  extent, 
the  form,  size,  character  of  surface,  density  and  temperature  of  objects  are 
recognized.  There  is  also  a  general  appreciation  of  heat  and  cold ;  a  sense 
of  resistance,  which  gives  an  idea  of  weight ;  and  finally,  there  are  nerves  of 
peculiar  properties,  terminating  in  organs  adapted  to  receive  the  impressions 
of  smell,  taste,  sight  and  hearing. 

The  senses  of  olfaction,  gustation,  vision  and  audition  belong  to  peculiar 
organs,  provided  with  nerves  which  have  special  properties  and  usually  are 
not  endowed  with  general  sensibility.  These  nerves  have  been  omitted  in 


GENERAL  CHAEACTERS  OF  THE  SPECIAL  SENSES.         653 

the  general  description  of  the  nervous  system,  as  well  as  the  accessory  organs 
to  which  they  are  distributed. 

The  senses  of  touch,  temperature  and  pain  are  all  conveyed  to  the  nerve- 
centres  by  what  have  been  described  as  sensory  nerves,  the  touch  being  per- 
fected in  certain  parts  by  peculiar  arrangements  of  the  terminal  nerve-fibres. 
Although  it  is  possible  that  each  one  of  these  impressions  is  transmitted  by 
special  and  distinct  fibres,  this  is  not  yet  a  matter  of  positive  demonstration. 
The  so-called  muscular  sense,  by  which  weight,  resistance  etc.,  are  appreci- 
ated, undoubtedly  depends  to  a  great  extent  upon  the  muscular  nerves.  What 
are  generally  recognized  as  sensory  impressions  have  been  thus  subdivided. 
These  subdivisions  are  sufficiently  distinct,  as  far  as  the  character  of  the 
sensations  themselves  are  concerned,  but  as  regards  their  paths  of  conduc- 
tion, as  before  intimated,  exact  and  positive  data  are  wanting.  It  is  impossi- 
ble to  study  with  advantage  the  different  varieties  of  ordinary  sensation  in 
the  lower  animals,  for  evident  reasons ;  and  physiologists  rely  mainly  upon 
observations  on  the  human  subject,  in  the  form  of  experiments  and  of  patho- 
logical phenomena. 

There  are  two  ways  of  regarding  the  different  varieties  of  general  sensa- 
tion :  One  is  to  look  at  each  as  a  peculiar  impression  conveyed  by  special 
nerve-fibres,  and  the  other  is  to  regard  the  nerves  of  general  sensibility  as 
capable  of  conducting  impressions  of  different  kinds.  It  has  never  been 
assumed  that  special  fibres  for  each  variety  of  sensation  have  been  demon- 
strated, and  it  is  possible  only  to  reason  as  to  this  from  what  is  actually 
known  of  the  general  properties  of  sensory  nerves. 

The  general  sensory  nerves  are  sufficiently  distinct  in  their  properties 
from  the  true  nerves  of  special  sense.  The  latter  convey  peculiar  impressions 
only,  such  as  those  of  sight,  hearing,  smell  and  taste.  The  former,  when 
strongly  stimulated  or  irritated,  always  convey  impressions  of  pain.  Separat- 
ing, then,  all  other  senses,  except  the  venereal  sense,  from  the  true  special 
senses,  it  is  proper  to  inquire  whether  it  be  reasonable  or  necessary  to  assume 
that  any  of  the  varieties  of  general  sensation  require  special  nerves  for  their 
conduction. 

It  is  well  known  that  a  relatively  powerful  stimulation  of  a  sensory  nerve 
or  of  sensitive  parts  is  necessary  to  the  production  of  a  painful  impression ; 
and  it  is  also  well  known  that  very  painful  impressions  overpower  impressions 
of  touch,  weight,  pressure,  temperature  and  the  so-called  muscular  sense.  In 
cases  of  disease,  it  is  sometimes  observed  that  tactile  sensibility  is  retained  in 
parts  that  are  insensible  as  regards  pain.  It  is  possible  that  sensory  nerve- 
fibres  may  become  so  altered  in  their  properties  as  to  be  incapable  of  con- 
ducting painful  impressions,  while  they  still  conduct  sensations  that  are 
appreciated  only  as  impressions  of  contact.  This  is  observed  in  certain  cases 
of  artificial  anaesthesia.  In  hyperaesthesia,  or  exaggerated  sensibility  to  pain- 
ful impressions,  the  tactile  sense  is  necessarily  overpowered  in  a  greater  or 
less  degree.  Impressions  made  on  a  sensory  nerve  in  its  course  are  always 
appreciated  as  painful,  and  the  pain  is  referred  to  the  terminal  distribution 
of  the  nerve,  this  being  a  law  of  sensory  perception.  There  is  no  sense  of 
43 


654  SPECIAL  SENSES. 

contact  at  the  ends  of  the  nerve,  and  there  is  no  contact.  The  impression, 
in  order  to  be  perceived  at  all,  must  be  painful.  These  facts  may  be  in  a 
measure  applied  to  local  impressions  produced  by  extremes  of  heat  and  cold 
or  by  chemical  or  electric  stimulation  of  sensitive  parts. 

The  internal  organs  have  as  a  rule  110  tactile  sensibility,  although  they 
may  be  sensitive ;  and  feeble  impressions  may  not  be  appreciated,  while 
stronger  impressions  are  painful. 

Titillation  is  the  result  of  unusual,  feeble  impressions  or  of  slight  impres- 
sions frequently  repeated  in  the  peripheral  ends  of  certain  sensory  nerves. 
These  impressions  are  not  precisely  tactile  nor  are  they  painful.  They  pro- 
duce peculiar  sensations,  and  they  frequently  give  rise  to  violent  reflex  move- 
ments, by  what  is  known  as  a  summation  of  sensory  stimulations. 

Muscular  Sense  (so  called}. — It  is  difficult  to  define  exactly  what  is  meant 
by  the  term  muscular  sense,  as  it  is  used  by  some  physiologists.  In  all  proba- 
bility, the  sense  which  enables  one  to  appreciate  the  resistance,  immobility 
and  elasticity  of  substances  that  are  grasped  or  stood  upon  or  which  are  in 
any  way  opposed  to  the  exertion  of  muscular  power,  may  be  greatly  modified 
by  education  and  habit.  It  is  undoubtedly  true,  however,  that  general  sensi- 
bility regulates  the  action  of  muscles  to  a  considerable  extent.  If,  for  exam- 
ple, the  lower  extremities  be  paralyzed  as  regards  sensation,  the  muscular 
power  remaining  intact,  frequently  the  person  so  affected  can  not  walk  unless 
he  be  able  to  see  the  ground.  This  difficulty  occurs  for  the  reason  that  the 
limbs  have  lost  the  sense  of  contact.  Many  curious  examples  of  this  kind 
are  to  be  found  in  works  upon  diseases  of  the  nervous  system.  One  of  the 
most  striking  is  a  case  communicated  to  Charles  Bell  by  Dr.  Ley.  The 
patient  was  affected  with  partial  loss  of  sensibility  upon  one  side  of  the  body, 
"  without,  however,  any  corresponding  diminution  of  power  in  the  muscles 
of  volition,  so  that  she  could  hold  her  child  in  the  arm  of  that  side  so  long 
as  her  attention  was  directed  to  it ;  but  if  surrounding  objects  withdrew  her 
from  the  notice  of  the  state  of  her  arm,  the  flexors  gradually  relaxed,  and  the 
child  was  in  hazard  of  falling."  This  is  like  certain  of  the  phenomena 
observed  in  cases  of  locomotor  ataxia.  In  this  disorder  there  is  disease  of 
the  posterior  white  columns  of  the  spinal  cord,  involving,  sometimes,  the 
posterior  roots  of  the  spinal  nerves,  with  more  or  less  impairment  of  general 
sensibility,  the  muscular  power  in  some  instances  being  intact.  Patients 
affected  in  this  way  frequently  are  unable  to  walk  or  stand  without  the  aid 
of  the  sight.  One  of  the  most  characteristic  phenomena  is  inability  to  stand 
when  blindfolded ;  although,  with  the  aid  of  the  sight,  the  muscles  can  be 
made  by  the  will  to  act  with  considerable  power.  Habit  and  education  enable 
some  persons  to  appreciate  with  great  nicety  slight  differences  in  weight ;  but 
this  is  due  chiefly  to  the  sense  of  resistance  to  muscular  effort  and  has  little 
dependence  upon  the  sense  of  touch. 

In  general  those  parts  which  are  most  sensitive  to  the  impressions  of 
touch,  as  the  fingers,  enable  one  to  appreciate  differences  in  pressure  and 
weight  with  greatest  accuracy.  The  sense  of  simple  pressure,  unaided  by 
the  estimation  of  weight  by  muscular  effort,  generally  is  more  acute  upon 


SENSE  OF  TOUCH.  655 

the  left  side.  Differences  in  weight  can  be  accurately  distinguished  when 
they  amount  to  only  one-sixteenth,  by  employing  muscular  effort  in  lifting 
as  well  as  the  sense  of  pressure ;  but  the  sense  of  pressure  alone  enables  most 
persons  to  appreciate  a  difference  of  not  less  than  one-eighth.  When  weights 
are  tested  by  lifting  with  the  hand,  the  appreciation  of  slight  differences  is 
more  delicate  if  the  weights  be  successively  tested  with  the  same  hand  than 
when  two  weights  are  placed,  one  on  either  hand.  When  the  interval  be- 
tween the  two  trials  is  more  than  forty  seconds,  slight  differences  in  weight 
—the  difference  between  fourteen  and  a  half  and  fifteen  ounces  (411  and 
425  grammes),  for  example — can  not  be  accurately  appreciated.  In  such 
trials,  it  is  necessary  to  have  the  metals  used  of  the  same  temperature,  for 
cold  metals  seem  heavier  than  warm. 

SENSE  OF  TOUCH. 

The  different  modes  of  termination  of  the  sensory  nerves  have  already 
been  described ;  and  in  many  instances  it  is  possible  to  explain,  by  the 
anatomical  characters  of  the  nerves,  the  great  differences  that  have  been 
observed  in  the  delicacy  of  the  tactile  sensibility  in  different  parts — differ- 
ences which  are  very  important  pathologically  as  well  as  physiologically, 
and  which  have  been  studied  by  Weber,  Valentin  and  others,  with  great 
minuteness. 

Variations  in  the  Tactile  Sensibility  in  Different  Parts  (Sense  of  Local- 
ity of  Impressions). — In  certain  parts  of  the  cutaneous  surface  the  general 
sensibility  is  much  more  acute  'than  in  others.  For  example,  a  sharp  blow 
upon  the  face  is  more  painful  than  a  similar  injury  to  other  parts ;  and  the 
eye,  as  is  well  known,  is  peculiarly  sensitive.  The  appreciation  of  tempera- 
ture varies  in  different  parts,  this  probably  depending  to  a  great  extent  upon 
habitual  exposure.  Some  parts,  as  the  soles  of  the  feet  or  the  axilla,  are 
peculiarly  sensitive  to  titillation.  The  sense  of  touch,  also,  by  which  the  size, 
form,  character  of  the  surface,  consistence  etc.,  of  objects  are  appreciated, 
is  developed  to  a  greater  degree  in  some  parts  than  in  others.  The  tips  of 
the  fingers  generally  are  used  to  ascertain  those  properties  of  objects  revealed 
by  the  sense  of  touch.  This  sense  is  capable  of  education  and  is  almost 
always  extraordinarily  developed  in  persons  who  are  deprived  of  some  other 
special  sense,  as  sight  or  hearing.  The  blind  learn  to  recognize  individuals 
by  feeling  of  the  face.  A  remarkable  instance  of  this  is  quoted  in  works  on 
physiology,  of  the  blind  sculptor,  Giovanni  Gonelli,  who  was  said  to  model 
excellent  likenesses,  being  guided  entirely  by  the  sense  of  touch.  Other 
instances  of  this  kind  are  on  record.  The  blind  have  been  known  to  become 
proficients  in  conchology  and  botany,  guided  entirely  by  the  touch.  It  is 
related  of  a  blind  botanist,  that  he  was  able  to  distinguish  ordinary  plants 
by  the  fingers  and  by  the  tip  of  the  tongue.  It  is  well  known  that  the  blind 
learn  to  read  with  facility  by  passing  the  fingers  over  raised  letters  but  little 
larger  than  the  letters  in  an  ordinary  folio  Bible. 

An  easy  method  of  determining  the  relative  delicacy  of  the  tactile  sen- 
sibility of  different  portions  of  the  cutaneous  surface  was  devised  a  num- 


656 


SPECIAL  SENSES. 


ber  of  years  ago  (1829)  by  E.  H.  Weber.  This  method  consists  in  the 
application  to  the  skin,  of  two  fine  points,  separated  from  each  other  by  a 
known  distance.  The  individual  experimented  upon  should  be  blindfolded, 
and  the  points  applied  to  the  skin  simultaneously.  By  carefully  adjusting 
the  distance  between  the  points,  a  limit  will  be  readied  where  the  two  im- 
pressions upon  the  surface  are  appreciated  as  one ;  {.  #.,  by  gradually  approx- 
imating them,  the  subject  will  suddenly  feel  both  points  as  one,  when  an 
instant  before,  with  the  points  a  little  farther  removed  from  each  other, 
he  distinctly  felt  two  impressions.  This  gives  a  measure  of  the  delicacy  of 
the  tactile  sensibility  of  different  parts.  Of  course  the  instrument  used 
may  be  very  simple — a  pair  of  ordinary  dividers  will  answer — but  it  is  con- 
venient to  have  some  ready  means  of  ascertaining  the  distances  between  the 
points.  An  instrument,  consisting  simply  of  a  pair  of  dividers  with  a  grad- 
uated bar  giving  a  measure  of  the  separation  of  the  points,  is  the  best,  as  it 
combines  simplicity,  convenience  of  use  and  portability.  This  instrument  is 
called  an  gethesiometer.  The  experiments  of  Weber  were  made  upon  his  own 
person.  They  showed  some  slight  variations  with  the  direction  of  the  line 
of  the  two  points,  but  these  are  not  very  important.  The  table  which  follows 
is  made  of  selections  from  the  observations  of  Weber,  taking  those  that  are 
most  likely  to  be  useful  as  a  guide  in  pathological  investigations.  The  ex- 
periments of  Valentin  and  others  on  different  persons  do  not  vary  much  in 
their  results  from  the  figures  given  in  the  table. 

TABLE   OF  VARIATIONS   IN   THE   TACTILE    SENSIBILITY   OF    DIFFERENT    POR- 
TIONS  OF   THE   SKIN    (WEBER). 

The  tactile  sensibility  is  measured  by  the  greatest  distance  between  two  points  at  which  they  convey  a 
single  impression  when  applied  simultaneously.  The  measurements  are  given  in  lines  (^5  of  au 
inch,  or  a  little  more  than  2  mm.). 


PART  OF  SURFACE. 

Lines. 

Mm. 

Tip  of  tongue  

0-50 

1-05 

Palmar  surface  of  third  phalanx  of  forefinger  

1-00 

2-10 

Red  surface  of  under  lip  

2-00 

4-20 

Palmar  surface  of  second  phalanges  of  fingers  

2-00 

4-20 

Dorsal  surface  of  third  phalanges  of  fingers  

3-00 

6-30 

Tip  of  nose  

3-00 

6-30 

Palmar  surface  of  metacarpus  

3-00 

6-30 

End  of  great  toe  

5-00 

10-50 

Palm  of  hand  

5-00 

10-50 

Skin  of  cheek,  over  buccinator  

5-00 

10-50 

Skin  of  cheek,  over  anterior  part  of  malar  bone  

7-00 

14-70 

Dorsal  surface  of  first  phalanges  of  fingers  

7-00 

14-70 

Lower  part  of  forehead  •  

10-00 

21-00 

Back  of  hand  

14-00 

29-40 

Patella  and  surrounding  part  of  thigh  

16-00 

33-60 

Dorsum  of  foot  near  toes  

18-00 

37-80 

Upper  and  lower  extremities  of  forearm  

18-00 

37-80 

Upper  and  lower  extremities  of  leg  

18-00 

37-80 

18-00 

37-80 

Acromion  and  upper  part  of  arm  

18'00 

37-80 

Gluteal  region  and  neighboring  part  of  thigh  

18-00 

37-80 

Middle  of  forearm  where  its  circumference  is  greatest  

30-00 

63-00 

Middle  of  thigh  where  its  circumference  is  greatest  

30-00 

63-00 

APPRECIATION  OF  TEMPERATURE.  657 

By  comparing  the  distribution  of  the  tactile  corpuscles  with  the  results 
given  in  the  table,  it  will  be  seen  that  the  sense  of  touch  is  most  acute  in 
those  situations  in  which  the  corpuscles  are  most  abundant.  In  the  space  of 
a  little  more  than  ^  of  an  inch  (2-2  mm.)  square,  on  the  palmar  surface  of 
the  third  phalanx  of  the  index-finger,  Meissner  counted  the  greatest  num- 
ber of  corpuscles ;  viz.,  one  hundred  and  eight.  In  this  situation  the  tactile 
sensibility  is  more  acute  than  in  any  other  part  of  the  skin,  the  mean  dis- 
tance indicated  by  the  sesthesiometer  being  0'603  of  a  line,  or  1'27  mm. 
(Valentin).  In  the  same  space  on  the  second  phalanx,  forty  corpuscles  were 
counted,  the  sesthesiometer  marking  1-558  line,  or  3*27  mm.  (Valentin),  this 
part  ranking  next  in  tactile  sensibility  after  the  red  surface  of  the  lips. 
One  can  readily  understand  how  the  tactile  corpuscles,  embedded  in  the 
amorphous  substance  of  the  cutaneous  papillae,  might  increase  the  delicacy  of 
appreciation  of  slight  impressions,  by  presenting  hard  surfaces  against 
which  the  nerve-filaments  can  be  pressed. 

As  regards  those  portions  of  the  general  cutaneous  surface  in  which  no 
tactile  corpuscles  have  been  demonstrated,  it  is  not  easy  to  connect  the  varia- 
tions in  the  tactile  sensibility  with  the  nervous  distribution,  as  little  is 
known  of  the  comparative  richness  of  the  terminal  nervous  filaments  in 
these  situations. 

Appreciation  of  Temperature. — It  is  not  known  that  the  sense  of  tem- 
perature, either  of  the  surrounding  medium  or  of  bodies  applied  to  different 
parts  of  the  skin,  is  appreciated  through  any  nerves  other  than  those  of  gen- 
eral sensibility  or  that  there  is  any  special  arrangement  of  the  terminations 
of  certain  of  the  nerves  connected  with  this  sense.  As  regards  the  general 
temperature,  the  sense  is  relative  and  is  much  modified  by  habit.  This  state- 
ment needs  no  explanation.  As  is  well  known,  what  is  cold  for  an  inhabitant 
of  the  torrid  zone  would  be  warm  for  one  accustomed  to  an  excessively  cold 
climate.  Habitual  exposure  also  modifies  the  sense  of  temperature.  Many 
persons  not  in  the  habit  of  dressing  warmly  suffer  but  little  in  extremely  cold 
weather.  Those  who  habitually  expose  the  hands  or  even  the  feet  to  cold, 
render  these  parts  comparatively  insensible  to  temperature  ;  and  the  same  is 
true  of  those  who  often  expose  the  hands,  face  or  other  parts  to  heat.  The 
variations  in  the  sensibility  of  different  parts  of  the  surface  to  temperature 
depend,  also,  upon  special  properties  of  the  parts  themselves.  The  differ- 
ences, however,  are  not  so  marked  as  to  be  of  any  great  importance,  and  the 
experiments  made  upon  this  point  are  simply  curious. 

The  experiments  of  Weber  and  others  show  that  the  skin  is  the  chief 
organ  for  the  appreciation  of  temperature,  if  the  mouth,  palate,  vagina  and 
rectum,  by  which  the  differences  between  warm  and  cold  substances  is 
readily  distinguished,  be  excepted.  In  several  instances  in  which  larger  por- 
tions of  the  skin  were  destroyed  by  burns  and  other  injuries,  experiments 
have  been  made  by  applying  spatulas  of  different  temperatures.  In  one  of 
these,  a  spatula  plunged  in  water  at  48°  to  55°  Fahr.  (9°  to  12°  C.)  was 
applied  to  a  denuded  surface,  and  again,  a  spatula  at  113°  to  122°  Fahr.  (45° 
to  50°  C.).  When  the  patient  was  requested  to  tell  which  was  the  warmer, 


658  SPECIAL  SENSES. 

the  answers  were  as  frequently  incorrect  as  they  were  correct;  but  the  dis- 
crimination was  easy  and  certain  when  the  applications  were  made  to  the 
surrounding  healthy  skin.  When  applications  at  a  higher  temperature  were 
made  to  the  denuded  part,  the  patient  suffered  only  pain. 

The  venereal  sense  is  unlike  any  other  sensation,  and  is  general  as  well 
as  referable  to  the  organs  of  generation.  In  this  connection,  however,  it  is 
important  to  note  that  the  tactile  sensibility  of  the  palmar  surface  of  the 
third  phalanx  of  the  fingers,  measured  by  the  aesthesiometer,  compared  with 
the  sensibility  of  the  penis,  is  as  0*802  to  0'034,  or  between  twenty-three  and 
twenty-four  times  greater. 

Ferrier  has  described  a  diffused  tactile  centre  in  the  "  hippocampal  re- 
gion," the  action  of  which  is  crossed ;  but  the  observations  to  determine  the 
loss  of  the  sense  of  touch  after  destruction  of  this  part,  which  were  made 
on  monkeys,  are  by  no  means  satisfactory.  It  must  be  very  difficult  to  study 
tactile  sensibility  in  the  inferior  animals. 

OLFACTION. 

The  nerves  directly  connected  with  the  senses  of  olfaction,  vision  and 
audition,  have  little  or  no  general  sensibility.  As  regards  the  olfactory 
nerves,  the  parts  to  which  they  are  distributed  are  so  largely  supplied  with 
branches  from  the  fifth,  that  it  is  difficult  to  determine  the  fact  of  their  sen- 
sibility or  insensibility  to  ordinary  impressions.  The  olfactory  nerves,  how- 
ever, are  distributed  to  the  mucous  membrane  of  that  portion  only  of  the 
nasal  cavity,  endowed  with  the  special  sense  of  smell. 

Nasal  Fossce.—The  two  irregularly  shaped  cavities  in  the  middle  of  the 
face,  opening  in  front  by  the  anterior  nares  and  connected  with  the  pharynx 
by  the  posterior  nares,  are  called  the  nasal  fossae.  The  membrane  lining 
these  cavities  is  generally  called  the  Schneiderian  mucous  membrane,  and 
sometimes,  the  pituitary  membrane.  This  membrane  is  closely  adherent  to 
the  fibrous  coverings  of  the  bones  and  cartilages  by  which  the  nasal  fossae 
are  bounded,  and  it  is  thickest  over  the  turbinated  bones.  It  is  continuous 
with  the  membrane  lining  the  pharynx,  the  nasal  duct  and  lachrymal  canals, 
the  Eustachian  tube,  the  frontal,  ethmoidal  and  sphenoidal  sinuses  arid  the 
antrum.  There  are  openings  leading  from  the  nasal  fossae  to  all  of  these 
cavities. 

The  essential  organ  of  olfaction  is  the  mucous  membrane  lining  the  upper 
half  of  the  nasal  fossae.  Not  only  has  it  been  shown  anatomically  that  this 
part  alone  receives  the  terminal  filaments  of  the  olfactory  nerves,  but  physio- 
logical experiments  have  demonstrated  that  it  is  the  only  part  capable  of  ap- 
preciating odorous  impressions.  If  a  tube  be  introduced  into  the  nostril, 
placed  horizontally  over  an  odorous  substance  so  that  the  emanations  can  not 
penetrate  its  caliber,  no  odor  is  perceived,  though  the  membrane  below  the 
end  of  the  tube  might  receive  the  emanations ;  but  if  the  tube  be  directed 
toward  the  odorous  substance,  so  that  the  emanations  can  penetrate  to  the 
upper  portion  of  the  nares,  the  odor  is  immediately  appreciated. 

That  portion  of  the  lining  of  the  nasal  fossae,  properly  called  the  olfactory 


OLFACTORY  NERVES. 


659 


membrane,  extends  from  the  cribiform  plate  of  tbe  ethmoid  bone  downward 
a  little  less  than  an  inch  (25  mm.).  It  is  soft  and  friable,  very  vascular, 
thicker  than  the  rest  of  the  Schneiderian  membrane,  and  in  man,  it  has  rather 
a  yellowish  color.  It  is  covered  by  long,  delicate,  columnar  cells,  nucleated, 
and  each  one  provided  with  three  to  eight  ciliary  processes,  the  movements  of 
which  are  from  before  backward.  The  olfactory  membrane  is  provided  with 
a  large  number  of  long,  racemose,  mucous  glands,  which  secrete  a  fluid  that 
keeps  the  surface  moist,  a  condition  essential  to  the  accurate  perception  of 
odorous  impressions. 

OLFACTORY  (FIRST  NERVE). 

The  apparent  origin  of  the  olfactory  nerve  is  by  three  roots,  from  the 
inferior  and  internal  portion  of  the  frontal  lobe  of  the  cerebrum,  in  front  of 
the  anterior  perforated 
space.  The  three  roots 
are  an  external  and  an 
internal  white  root,  and 
a  middle  root  composed 
of  gray  matter.  The 
external  white  root  is 
long  and  delicate,  pass- 
ing outward,  across  the 
fissure  of  Sylvius,  to 
the  temporo-sphenoidal 
lobe.  The  internal  white 
root  is  thicker  and  short- 
er than  the  external  root, 
and  it  arises  from  the 
most  posterior  portion 
of  the  frontal  lobe.  The 
middle,  or  gray  root 
arises  from  a  little  em- 
inence of  gray  matter 
situated  on  the  posterior  and  inner  portion  of  the  inferior  surface  of  the 
frontal  lobs. 

The  deep  origin  of  these  three  roots  of  the  olfactory  nerves  is  still  a  matter 
of  discussion.  The  external  root  passes  through  the  gray  substance  of  the 
island  of  Reil,  to  a  gray  nucleus  in  the  temporo-sphenoidal  lobe,  in  front  of 
the  pes  hippocampi.  The  fibres  of  the  middle  root  have  not  been  traced 
farther  than  the  gray  eminence  from  which  it  arises.  The  fibres  of  the  inter- 
nal root  probably  are  connected  with  the  fibres  of  the  gyrus  fornicatus.  The 
three  roots  converge  to  form  a  single  cord  at  the  inner  boundary  of  the  fissure 
of  Sylvius.  This  cord  passes  forward  and  slightly  inward,  in  a  deep  groove  be- 
tween two  convolutions  on  the  under  surface  of  the  frontal  lobe,  covered  by 
the  arachnoid  membrane,  to  the  ethmoid  bone.  This  portion  of  the  nerve  is 
soft  and  friable.  It  is  composed  of  both  white  and  gray  matter,  the  propor- 


FIG.  235.— Olfactory  ganglion  and  nerves  (Hirschfeld). 
olfactory  ganglion  and  nerves  :  2,  branch  of  the  nasal  nerve  ;  3, 
spheno-palatine  ganglion  ;  4,  7,  branches  of  the  great  palatine 
nerve  ;  5,  posterior  palatine  nerve  ;  6,  middle  palatine  nerve  ;  8, 9, 
branches  from  the  spheno-palatine  ganglion  ;  10,  11,  12,  Vidian 
nerve  and  its  branches  ;  13,  external  carotid  branch,  from  the  su- 
perior cervical  ganglion. 


060 


SPECIAL  SENSES. 


tions  being  about  two-thirds  of  the  former  to  one-third  of  the  latter.  The 
gray  substance,  derived  from  the  gray  root,  is  situated  at  the  upper  portion  of 
the  nerve,  the  white  substance  occupying  the  inferior  and  the  lateral  portions. 
By  the  side  of  the  crista  galli  of  the  ethmoid  bone,  the  nerve-trunk 
expands  into  an  oblong  ganglion  called  the  olfactory  bulb.  This  is  grayish 
in  color,  excessively  soft,  and  contains  the  ordinary  ganglionic  elements. 
From  the  olfactory  bulb,  fifteen  to  eighteen  nervous  filaments  are  given  off, 
which  pass  through  the  foramina  in  the  cribriform  plate  of  the  ethmoid  bone. 
These  filaments  are  composed  entirely  of  nerve-fibres,  and  are  quite  resisting, 
owing  to  fibrous  elements  prolonged  from  the  dura  mater.  It  is  strictly 

proper,  perhaps,  to  regard  these  as  the  true  olfac- 
tory nerves,  the  cord  leading  from  the  olfactory 
bulb  to  the  cerebrum  being  properly  a  commis- 
sure. Having  passed  through  the  cribriform 
plate,  the  olfactory  nerves  are  distributed  to  tho 
olfactory  membrane,  in  three  groups :  an  inner 
group,  distributed  to  the  mucous  membrane  of 
the  upper  third  of  the  septum ;  a  middle  group, 
to  the  upper  portion  of  the  nasal  fossae ;  and  an 
outer  group,  to  the  mucous  membrane  covering 
the  superior  and  middle  turbiuated  bones  and  a 
portion  of  the  ethmoid. 

The   mode  of  termination  of    the   olfactory 
FIG.  236.— Terminal  filaments  of  the  nerves  differs  from  that  of  the  ordinary  sensory 

olfactory  nerves ;  magnified  30  ,.  ,.  ,,  .      .  ... 

diameters  (Koiiiker).  nerves,  and  is  peculiar  and  characteristic,  as  it  is 

lf  ^^SS^^b^  in  the  other  organs  of  special  sense.     The  olfac- 

tory  cell ;  2,  small  branch  of  the    fnrv  rnnpoiis  mpmbranp  pnn  tains  fprminul    npr\Tp- 
olfactory  nerve  of  the  frog,  sep-     l 

ofava?fcose0flbrfrsd  jfotoSy  cells'  called  the  olfactory  cells,  which  are  situated 
ceil  of  the  sheep.  between  the  cells  of  epithelium.     These  are  long, 

delicate,  spindle-shaped,  varicose  structures,  each  one  containing  a  clear, 
round  nucleus.  In  the  frog  there  is  a  fine,  hair-like  process  projecting  from 
each  cell,  beyond  the  mucous  membrane,  which  has  not  been  observed  in 
man  or  the  mammalia.  The  delicacy  of  the  structures  entering  into  the 
composition  of  the  olfactory  membrane  renders  the  investigation  of  the  ter- 
mination of  its  nervous  filaments  exceedingly  difficult. 

Properties  and  Uses  of  the  Olfactory  Nerves. — It  is  almost  certain  that 
the  olfactory  nerves  possess  none  of  the  general  properties  of  the  ordinary 
nerves  belonging  to  the  cerebro-spinal  system,  and  are  endowed  with  the 
special  sense  of  smell  alone.  The  filaments  coming  from  the  olfactory  bulbs 
and  distributed  to  the  pituitary  membrane  have  not  been  exposed  and  stimu- 
lated in  living  animals;  but  experiments  upon  the  nerves  behind  the  olfac- 
tory bulbs  show  that  they  are  insensible  to  ordinary  impressions.  Attempts 
have  been  made  to  demonstrate,  in  the  human  subject,  the  special  properties 
of  these  nerves,  by  passing  an  electric  current  through  the  nostrils ;  but  the 
situation  of  the  nerves  is  such  that  these  observations  are  of  necessity  indefi- 
nite and  unsatisfactory. 


MECHANISM  OF  OLF ACTION.  661 

Among  the  experiments  upon  the  higher  orders  of  animals,  in  which  the 
olfactory  nerves  have  been  divided,  may  be  cited,  as  open  to  no  objections, 
those  of  Vulpian  and  Philipaux,  upon  dogs.  It  is  well  known  that  the  sense 
of  smell  usually  is  very  acute  in  these  animals.  Upon  dividing  or  extirpating 
the  olfactory  bulbs,  "  after  the  animal  had  completely  recovered,  it  was  de- 
prived of  food  for  thirty-six  or  forty-eight  hours ;  then,  in  its  absence,  a  piece 
of  cooked  meat  was  concealed  in  a  corner  of  the  laboratory.  Animals,  suc- 
cessfully operated  upon,  then  taken  into  the  laboratory,  never  found  the  bait ; 
and  nevertheless,  care  had  been  taken  to  select  hunting-dogs."  This  experi- 
ment is  conclusive ;  more  so  than  those  in  which  animals  deprived  of  the 
olfactory  bulbs  were  shown  to  eat  fgeces  without  disgust,  for  this  sometimes 
occurs  in  dogs  that  have  not  been  multilated. 

Comparative  anatomy  shows  that  the  olfactory  bulbs  generally  are  devel- 
oped in  proportion  to  the  acuteness  of  the  sense  of  smell.  Pathological  facts 
show,  in  the  human  subject,  that  impairment  or  loss  of  the  olfactory  sense  is 
coincident  with  injury  or  destruction  of  these  ganglia.  Cases  have  been 
reported  in  which  the  sense  of  smell  was  lost  or  impaired  from  injury  to  the 
olfactory  nerves.  In  nearly  all  of  the  cases  on  record,  the  general  sensibility 
of  the  nostrils  was  not  affected. 

Mechanism  of  Olfaction. — Substances  that  have  odorous  properties  give 
off  material  emanations,  which  must  come  in  contact  with  the  olfactory  mem- 
brane before  their  peculiar  odor  is  appreciated.  This  membrane  is  situated 
high  up  in  the  nostrils,  is  peculiarly  soft,  is  abundantly  provided  with  glands, 
by  the  secretions  of  which  its  surface  is  kept  in  proper  condition,  and  it  pre- 
sents the  peculiar  nerve-terminations  of  the  olfactory  filaments. 

In  experimenting  upon  the  sense  of  smell  it  has  been  found  difficult  to 
draw  an  exact  line  of  distinction  between  impressions  of  general  sensibility 
and  those  which  attack  the  special  sense,  or  in  other  words,  between  irritating 
and  odorous  emanations ;  and  the  vapors  of  ammonia,  acetic  acid,  nitric  acid 
etc.,  undoubtedly  possess  irritating  properties  which  overpower  their  odorous 
qualities.  It  is  unnecessary  in  this  connection  to  discuss  the  different  varie- 
ties of  odors  recognized  by  some  of  the  earlier  writers,  as  the  fragrant,  aro- 
matic, fetid,  nauseous  etc.,  distinctions  sufficiently  evident  from  their  mere 
enumeration ;  and  it  is  plain  enough  that  there  are  emanations,  like  those 
from  delicately  scented  flowers,  which  are  easily  recognizable  by  the  sense  of 
smell,  while  they  make  no  impression  upon  the  ordinary  sensory  nerves.  The 
very  marked  individual  differences  in  the  delicacy  of  the  olfactory  organs  in 
the  human  subject  and  in  different  animals  are  evidence  of  this  fact.  Hunt- 
ing-dogs recognize  odors  to  which  most  persons  are  absolutely  insensible ; 
and  certain  races  of  men  are  said  to  possess  a  remarkable  delicacy  of  the  sense 
of  smell.  Like  the  other  special  senses,  olfaction  may  be  cultivated  by  atten- 
tion and  practice,  as  is  exemplified  in  the  delicate  discrimination  of  wines, 
qualities  of  drugs  etc.,  by  experts. 

After  what  has  been  said  concerning  the  situation  of  the  true  olfactory 
membrane  in  the  upper  part  of  the  nasal  fossae  and  the  necessity  of  particles 
impinging  upon  this  membrane  in  order  that  their  odorous  properties  may 


662  SPECIAL  SENSES. 

be  appreciated,  it  is  almost  unnecessary  to  state  that  the  passage  of  odorous 
emanations  to  this  membrane  by  inspiring  through  the  nostrils  is  essential 
to  olfaction,  so  that  animals  or  men,  after  division  of  the  trachea,  being 
unable  to  pass  the  air  through  the  nostrils,  are  deprived  of  the  sense  of  smell. 
The  act  of  inhalation  through  the  nose  is  an  illustration  of  the  mechanism 
by  which  the  odorous  particles  may  be  brought  at  will  in  contact  with  the ' 
olfactory  membrane. 

It  is  a  curious  point  to  determine  whether  the  sense  of  smell  be  affected 
by  odors  passing  from  within  outward  through  the  nasal  fossae.  Persons  who 
have  offensive  emanations  from  the  respiratory  organs  usually  are  not  aware, 
from  their  own  sensations,  of  any  disagreeable  odor.  This  fact  is  explained 
by  Longet  on  the  supposition  that  the  olfactory  membrane  becomes  gradually 
accustomed  to  the  odorous  impression,  and  therefore  it  is  not  appreciated. 
This  is  an  apparently  satisfactory  explanation,  for  it  could  hardly  be  supposed 
that  the  direction  of  the  emanations,  provided  they  came  in  contact  with  the 
membrane,  could  modify  their  effects.  Longet  has  cited  a  case  of  cancer  of 
the  stomach,  in  which  the  vomited  matters  were  exceedingly  fetid.  At  first, 
the  patient,  when  he  expired  the  gases  from  the  stomach  through  the  nostrils, 
perceived  a  disagreeable  odor  at  each  expiration  ;  but  little  by  little  this  im- 
pression disappeared. 

Relations  of  Olfaction  to  the  Sense  of  Taste. — The  relations  of  the  sense 
of  smell  to  gustation  are  very  intimate.  In  the  appreciation  of  delicate 
shades  of  flavor,  it  is  well  known  that  the  sense  of  olfaction  plays  so  im- 
portant a  part,  that  it  can  hardly  be  separated  from  gustation.  The 
common  practice  of  holding  the  nose  when  disagreeable  remedies  are  swal- 
lowed is  an  illustration  of  the  connection  between  the  two  senses.  In 
most  cases  of  anosmia  there  is  inability  to  distinguish  delicate  flavors ;  and 
patients  can  distinguish  by  the  taste,  only  sweet,  saline,  acid  and  bitter  im- 
pressions. 

It  is  undoubtedly  true  that  the  delicacy  of  the  sense  of  taste  is  lost  when 
the  sense  of  smell  is  abolished.  The  experiment  of  tasting  wines  blind- 
folded and  with  the  nostrils  plugged,  and  the  partial  loss  of  taste  during  a 
severe  coryza,  are  sufficiently  familiar  illustrations  of  this  fact.  In  the  great 
majority  of  cases,  when  there  is  complete  anosmia,  the  taste  is  sensibly  im- 
paired ;  and  in  cases  in  which  this  does  not  occur,  it  is  probable  that  the 
savory  emanations  pass  from  the  mouth  to  the  posterior  portion  of  the  nasal 
fossae,  and  that  here  the  mucous  membrane  is  not  entirely  insensible  to  spe- 
cial impressions. 

It  is  unnecessary,  in  this  connection,  to  describe  fully  the  reflex  phenom- 
ena which  follow  impressions  made  upon  the  olfactory  membrane.  The 
odor  of  certain  sapid  substances,  under  favorable  conditions,  will  produce  an 
abundant  secretion  of  saliva  and  even  of  gastric  juice,  as  has  been  shown  by 
experiments  upon  animals.  Other  examples  of  the  effects  of  odorous  im- 
pressions of  various  kinds  are  sufficiently  familiar. 

According  to  Ferrier,  the  olfactory  centre  is  on  the  inner  surface  of 
the  anterior  extremity  of  the  unicate  gyrus ;  but  this  location  of  the  centre 


GUSTATION.  603 

is  not  regarded  as  definitely  determined.  Stimulation  of  this  part  in  mon- 
keys simply  produces  peculiar  movements  of  the  nostril  and  lip  of  the  same 
side. 

GUSTATIOX. 

The  special  sense  of  taste  gives  the  appreciation  of  what  is  known  as  the 
savor  of  certain  substances  introduced  into  the  mouth ;  and  this  sense  exists, 
in  general  terms,  in  parts  supplied  by  filaments  from  the  lingual  branch  of 
the  fifth  and  the  glosso-pharyngeal  nerves. 

It  is  assumed  by  some  physiologists,  that  the  true  tastes  are  quite  simple, 
presenting  the  qualities  which  are  recognized  as  sweet,  acid,  saline  and  bit- 
ter ;  while  the  more  delicate  shades  of  what  are  called  flavors  nearly  always 
involve  olfactory  impressions,  which  it  is  difficult  to  separate  entirely  from 
gustation.  Applying  the  term  savor  exclusively  to  the  quality  which  makes  an 
impression  upon  the  sense  of  taste,  it  is  evident  that  the  sensation  is  special  in 
its  character  and  different  from  the  tactile  sensibility  of  the  parts  involved  and 
from  the  sensation  of  temperature.  The  terminal  filaments  of  the  gustatory 
nerves  are  impressed  by  the  actual  contact  of  savory  substances,  which  must 
of  necessity  be  soluble.  To  a  certain  extent  there  is  a  natural  classification 
of  savors,  some  of  which  are  agreeable,  and  others,  disagreeable ;  but  even 
this  distinction  is  modified  by  habit,  education  and  various  other  circum- 
stances. Articles  that  are  unpleasant  in  early  life  often  become  agreeable  in 
later  years.  Inasmuch  as  the  taste  is  to  some  extent  an  expression  of  the 
nutritive  demands  of  the  system,  it  is  found  to  vary  under  different  condi- 
tions. Chlorotic  females,  for  example,  frequently  crave  the  most  unnatural 
articles,  and  their  morbid  tastes  may  disappear  under  appropriate  treatment. 
Inhabitants  of  the  frigid  zones  crave  fatty  articles  of  food  and  will  even 
drink  rancid  oils  with  avidity.  Patients  often  become  accustomed  to  the 
most  disagreeable  remedies  and  take  them  without  repugnance.  Again,  the 
most  savory  dishes  may  even  excite  disgust,  when  the  sense  of  taste  has  be- 
come cloyed,  while  abstinence  sometimes  lends  a  delicious  flavor  to  the  sim- 
plest articles  of  food.  The  taste  for  certain  articles  certainly  is  acquired, 
and  this  is  almost  always  true  of  tobacco,  now  so  largely  used  in  civilized 
countries. 

Any  thing  more  than  the  simplest  classification  of  savors  is  difficult  if 
not  impossible.  It  is  easy  to  recognize  that  certain  articles  are  bitter  or 
sweet,  empyreumatic  or  insipid,  acid  or  alkaline,  etc.,  but  beyond  these  sim- 
ple distinctions,  the  shades  of  difference  are  closely  connected  with  olfac- 
tion  and  are  too  delicate  and  too  many  for  detailed  description.  Some  per- 
sons are  comparatively  insensible  to  nice  distinctions  of  taste,  while  others 
recognize  with  facility  the  most  delicate  differences.  Strong  impressions 
may  remove  for  a  time  the  appreciation  of  less  powerful  and  decided 
flavors.  The  tempting  of  the  appetite  by  a  proper  gradation  of  gustatory 
and  odorous  impressions  is  illustrated  in  the  modem  cuisine,  which  aims 
at  an  artistic  combination  and  succession  of  dishes  and  wines,  so  that  the 
agreeable  sensations  are  prolonged  to  the  utmost  limit.  This  may  often  be 


664  SPECIAL  SENSES. 

regarded  as  a  violation  of  strictly  hygienic  principles,  but  it  none  the  less 
exemplifies  the  cultivation  of  the  sense  of  taste. 

Nerves  of  Taste. — Two  nerves,  the  chorda  tympani  and  the  gloss-pharyn- 
geal,  are  endowed  with  the  sense  of  taste.  These  nerves  are  distributed  to 
distinct  portions  of  the  gustatory  organ.  The  chorda  tympani  has  already 
been  referred  to  as  one  of  the  branches  of  the  facial ;  the  glosso-pharyngeal 
has  not  yet  been  described. 

Chorda  Tympani. — In  the  description  already  given  of  the  facial,  the 
chorda  tympani  is  spoken  of  as  the  fourth  branch.  It  passes  through  the 
tympanum,  between  the  ossicles  of  the  ear,  and  joins  the  inferior  maxillary 
division  of  the  fifth,  at  an  acute  angle,  between  the  two  pterygoid  muscles, 
becoming  so  closely  united  with  it  that  it  can  not  be  followed  farther  by  dis- 
section. The  filaments  of  this  branch  probably  originate  from  the  interme- 
diary nerve  of  Wrisberg. 

The  course  of  the  filaments  of  the  chorda  tympani,  after  this  nerve  has 
joined  the  fifth,  is  shown  by  the  effect  upon  the  sense  of  taste  and  the  altera- 
tion of  the  nerve-fibres  following  its  division.  Vulpian  and  Prevost,  by  the 
so-called  Wallerian  method,  after  dividing  the  chorda  tympani,  found  degen- 
erated fibres  at  the  terminations  of  the  lingual  branch  of  the  fifth,  in  the 
mucous  membrane  of  the  tongue,  the  fibres  being  examined  ten  days  or 
more  after  the  section.  Observations  upon  the  sense  of  taste  show  that  the 
chorda  tympani  is  distributed  to  the  anterior  two-thirds  of  the  tongue. 

The  general  properties  of  the  chorda  tympani  have  been  ascertained  only 
by  observations  made  after  its  paralysis  or  division.  All  experiments  in 
which  a  stimulus  has  been  applied  directly  to  the  nerve  in  living  animals 
have  been  negative  in  their  results.  According  to  Longet,  when  the  nerve 
has  been  isolated  as  completely  as  possible  and  all  reflex  action  is  excluded, 
its  stimulation  produces  no  movement  in  the  tongue. 

In  cases  of  facial  palsy  in  which  the  lesion  affects  the  root  so  deeply  as 
to  involve  the  chorda  tympani,  there  is  loss  of  taste  in  the  anterior  two- 
thirds  of  the  tongue,  tactile  sensibility  being  unaffected ;  and  many  cases 
illustrating  this  fact  have  been  recorded.  Aside  from  cases  of  paralysis  of 
the  facial  with  impairment  of  taste,  in  which  the  general  sensibility  of  the 
tongue  is  intact,  instances  are  on  record  of  affections  of  the  fifth  pair,  in 
which  the  tongue  was  absolutely  insensible  to  ordinary  impressions,  the 
sense  of  taste  being  preserved.  A  number  of  such  cases  have  been  reported, 
which  show  conclusively  that  the  fifth  pair  presides  over  general  sensibility 
only,  and  that  it  is  not  a  gustatory  nerve,  except  by  virtue  of  filaments  de- 
rived from  the  chorda  tympani. 

Passing  from  the  consideration  of  pathological  facts  to  experiments 
upon  living  animals,  the  results  are  equally  satisfactory.  Although  it  is 
somewhat  difficult  to  observe  impairment  of  taste  in  animals,  Bernard  and 
others  have  succeeded  in  training  dogs  and  cats  so  as  to  observe  the  effects 
of  colocynth  and  various  sapid  substances  applied  to  the  tongue.  In  a  great 
number  of  experiments  of  this  kind,  it  has  been  observed  that  after  section 
of  the  chorda  tympani,  or  of  the  facial  so  as  to  involve  the  chorda  tympani, 


GLOSSO-PHARYNGEAL  NERVES.  665 

the  sense  of  taste  is  abolished  in  the  anterior  two-thirds  of  the  tongue  on 
the  side  of  the  section.  In  a  case  reported  by  Moos,  the  introduction  of  an 
artificial  membrana  tympani  in  the  human  subject  was  followed  by  loss  of 
taste  upon  the  corresponding  side  of  the  tongue,  and  upon  both  sides,  when 
a  membrane  was  introduced  into  each  ear.  This  disappeared  when  the 
membranes  were  removed,  and  the  phenomena  were  referred  to  pressure 
upon  the  chorda  tympaui.  Other  instances  of  this  kind  are  on  record. 

As  regards  the  gustatory  propsrties  of  the  anterior  two-thirds  of  the 
tongue,  certainly  in  the  human  subject,  it  may  be  stated  without  reserve,  that 
these  properties  depend  upon  the  chorda  tympani,  its  gustatory  filaments 
being  derived  from  the  facial  and  taking  their  course  to  the  tongue  with 
the  lingual  branch  of  the  inferior  maxillary  division  of  the  fifth.  In  addi- 
tion, the  lingual  branch  of  the  fifth  contains  filaments,  derived  from  the 
large  root  of  this  nerve,  which  give  general  sensibility  to  the  mucous  mem- 
brane. 

GLOSSO-PHARYNGEAL  (NINTH  NERVE). 

The  glosso-pharyngeal  is  distributed  to  those  portions  of  the  gustatory 
mucous  membrane  not  supplied  by  filaments  from  the  chorda  tympani.  It 
is  undoubtedly  a  nerve  of  taste ;  and  the  question  of  its  other  uses  will  be 
considered  in  connection  with  its  general  properties,  as  well  as  the  differences 
between  this  nerve  and  the  chorda  tympani. 

Physiological  Anatomy. — The  apparent  origin  of  the  glosso-pharyngeal 
is  from  the  groove  between  the  olivary  and  restiform  bodies  of  the  medulla 
oblongata,  between  the  roots  of  the  auditory  nerve  above  and  the  pneumo- 
gastric  below.  The  deep  origin  is  in  a  gray  nucleus  in  the  lower  part  of  the 
floor  of  the  fourth  ventricle,  between  the  nucleus  of  the  auditory  nerve  and 
the  nucleus  of  the  pneumogastric.  From  this  origin  the  filaments  pass  for- 
ward and  outward,  to  the  posterior  foramen  lacerum,  by  which  the  nerve 
emerges  with  the  pneumogastric,  the  spinal  accessory  and  the  internal  jugu- 
lar vein.  At  the  upper  portion  of  the  foramen,  is  a  small  ganglion,  the 
jugular  ganglion,  including  only  a  portion  of  the  root.  Within  the  foramen, 
is  the  main  ganglion,  including  all  of  the  filaments  of  the  trunk,  called  the 
petrous  ganglion,  or  the  ganglion  of  Andersch. 

At  or  near  the  ganglion  of  Andersch  the  glosso-pharyngeal  usually 
receives  a  delicate  filament  from  the  pneumogastric.  This  communication 
is  sometimes  wanting.  The  same  may  be  said  of  a  small  filament  passing  to 
the  glosso-pharyngeal  from  the  facial,  which  is  not  constant.  Branches  from 
the  glosso-pharyngeal  go  to  the  otic  ganglion  and  to  the  carotid  plexus  of  the 
sympathetic. 

The  distribution  of  the  glosso-pharyngeal  is  quite  extensive.  The  tym- 
panic branch,  the  nerve  of  Jacobson,  arises  from  the  anterior  and  external 
part  of  the  ganglion  of  Andersch,  and  enters  the  cavity  of  the  tympanum, 
where  it  divides  into  six  branches.  Of  these  six  branches,  two  posterior  are 
distributed  to  the  mucous  membrane  of  the  fenestra  rotunda  and  the  mem- 
brane surrounding  the  fenestra  ovalis ;  two  anterior  are  distributed,  one  to 


666 


SPECIAL  SENSES. 


the  carotid  canal,  where  it  anastomoses  with  a  branch  from  the  superior  cer- 
vical ganglion,  and  the  other  to  the  mucous  membrane  of  the  Eustachian 


FIG.  237.— Olosso-pharyngeal  nerve  (Sappey). 

I,  large  root  of  the  fifth  nerve  :  2,  ganglion  of  Gasser  ;  3,  ophthalmic  division  of  the  fifth  ;  4,  superior 
maxillary  division  ;  5,  inferior  maxillary  division  ;  6,  10,  lingual  branch  of  the  fifth,  containing  the 
filaments  of  the  chorda  tympani  ;  7,  branch  from  the  sublingual  to  the  lingual  branch  of  the  fifth  ; 
8,  chorda  tympani  ;  9,  inferior  dental  nerve  ;  11,  submaxillary  ganglion  ;  12,  mylo-hyoid  branch  of 
the  inferior  dental  nerve  ;  13,  anterior  belly  of  the  digastric  muscle  ;  14,  section  of  the  mylo-hyoid 
muscle  ;  15,  18,  glosso-pharyngeal  nerve  ,'  16,  ganglion  of  Andersch  ;  17,  branches  from  the  glosso- 
pharyngeal  to  the  stylo-glossus  and  the  stylo-pharyngeus  muscles ;  19,  19,  pneumogastric  ;  20,  21, 
ganglia  of  the  pneumogastric  ;  22,  22,  superior  laryngeal  nerve  ;  23,  spinal  accessory  ;  24,  25,  26,  27, 
28,  sublingual  nerve  and  branches. 

tube ;  two  superior  branches  are  distributed  to  the  otic  ganglion  and,  as  is 
stated  by  some  anatomists,  to  the  spheno-palatine  ganglion. 

A  little  below  the  posterior  foramen  lacerum  the  glosso-pharyngeal  sends 
branches  to  the  posterior  belly  of  the  digastric  and  to  the  stylo-hyoid  mus- 
cle. There  is  also  a  branch  which  joins  a  filament  from  the  facial  to  the 
stylo-glossus. 

Opposite  the  middle  constrictor  of  the  pharynx  three  or  four  branches 
join  branches  from  the  pneumogastric  and  the  sympathetic,  to  form  together 
the  pharyngeal  plexus.  This  plexus  contains  a  number  of  ganglionic  points, 
and  filaments  of  distribution  from  the  three  nerves  go  to  the  mucous  mem- 
brane and  to  the  constrictors  of  the  pharynx.  The  mucous  membrane  proba- 
bly is  supplied  by  the  glosso-pharyngeal.  It  is  probable,  also,  that  the  mus- 
cles of  the  pharynx  are  supplied  by  filaments  from  the  pneumogastric,  which 
are  derived  originally  from  the  spinal  accessory. 


MECHANISM  OF  GUSTATION.  667 

Near  the  base  of  the  tongue  branches  are  sent  to  the  mucous  membrane 
covering  the  tonsils  and  the  soft  palate. 

The  lingual  branches  penetrate  the  tongue  about  midway  between  its 
border  and  centre,  are  distributed  to  the  mucous  membrane  at  its  base  and 
are  connected  with  certain  of  the  papillae. 

General  Properties  of  the  Glosso-Pharyngeal. — To  ascertain  the  general 
properties  of  this  nerve,  it  must  be  stimulated  at  its  root,  before  it  has  con- 
tracted anastomoses  with  other  nerves,  and  the  nerve  must  be  divided  in 
order  to  avoid  reflex  phenomena.  Taking  these  precautions  it  has  been 
found  that  stimulation  of  the  peripheral  end  of  the  nerve  does  not  give  rise 
to  muscular  movements  (Longet).  There  can  be  no  doubt  of  the  fact  that 
the  nerve  is  sensory,  although  its  sensibility  is  somewhat  dull.  In  experi- 
ments in  which  the  nerve  has  seemed  to  be  insensible  to  ordinary  impressions, 
it  is  probable  that  the  animals  operated  upon  had  been  exhausted  more  or 
less  by  pain  and  loss  of  blood  in  the  operation  of  exposing  the  nerve,  which, 
it  is  well  known,  abolish  the  sensibility  of  some  of  the  nerves. 

Experiments  upon  the  glosso-pharyngeal  are  not  very  definite  and  satis- 
factory in  their  results  as  regards  the  general  sensibility  of  the  base  of  the 
tongue,  the  palate  and  the  pharynx.  The  sensibility  of  these  parts  seems  to 
depend  chiefly  upon  branches  of  the  fifth,  passing  to  the  mucous  membrane, 
through  Meckel's  ganglion.  Experiments  show,  also,  that  the  reflex  phe- 
nomena of  deglutition  take  place  mainly  through  these  branches  of  the  fifth, 
and  that  the  glosso-pharyngeal  has  little  or  nothing  to  do  with  the  process. 
In  fact  after  division  of  both  glosso-pharyngeal  nerves,  deglutition  does  not 
seem  to  be  affected. 

Relations  of  the  Glosso-Pharyngeal  Nerves  to  Gustation. — Relying  upon 
experiments  on  the  inferior  animals,  particularly  dogs,  it  seems  certain  that 
there  are  two  nerves  presiding  over  the  sense  of  taste :  The  chorda  tympani 
gives  this  sense  to  the  anterior  two-thirds  portion  of  the  tongue  exclusively ; 
the  glosso-pharyngeal  supplies  this  sense  to  the  posterior  portion  of  the 
tongue ;  the  chorda  tympani  seems  to  have  nothing  to  do  with  general  sensi- 
bility ;  while  the  glosso-pharyngeal  is  an  ordinary  sensory  nerve,  as  well  as  a 
nerve  of  special  sense. 

Where  there  are  such  differences  in  the  delicacy  of  the  sense  of  taste  as 
exist  usually  in  different  individuals,  it  must  be  difficult  to  describe  with 
accuracy  delicate  shades  of  savor,  particularly  in  alimentary  substances ;  but 
the  distinct  impressions  of  acidity  or  of  bitter  quality  are  easily  recognizable. 
It  is  certain,  however,  that  saline,  acid  and  styptic  tastes  are  best  appreciated 
through  the  chorda  tympani,  and  that  sweet,  alkaline,  bitter  and  metallic 
impressions  are  received  mainly  by  the  glosso-pharyngeal. 

Mechanism  of  Gustation. — Articles  which  make  the  special  impression 
upon  the  gustatory  organ  are  in  solution ;  introduced  into  the  mouth,  they 
increase  the  flow  of  saliva,  the  reflex  action  involving  chiefly  the  submaxillary 
and  sublingual  glands ;  there  is  usually  more  or  less  mastication,  which  in- 
creases the  flow  of  the  parotid  saliva ;  and  during  the  acts  of  mastication  and 
the  first  stages  of  deglutition,  the  sapid  substances  are  distributed  over  the 


G68 


SPECIAL  SENSES. 


gustatory  membrane,  so  extensively,  indeed,  that  it  is  difficult  to  exactly  locate 
the  seat  of  the  special  impression.  In  this  way,  by  the  movements  of  the 
tongue,  aided  by  an  increased  flow  of  saliva,  the  actual  contact  of  the  savory 
articles  is  rapidly  effected.  The  thorough  distribution  of  these  substances 
over  the  tongue  and  the  mucous  membrane  of  the  general  buccal  cavity  leads 
to  some  confusion  in  the  appreciation  of  the  special  impressions;  and  in 
order  to  ascertain  if  different  portions  of  the  membrane  possess  different 
properties,  it  is  necessary  to  make  careful  experiments,  limiting  the  points 
of  contact  as  exactly  as  possible.  This  has  been  done,  with  the  result  of 
showing  that  the  true  gustatory  organ  is  quite  restricted  in  its  extent. 

Physiological  Anatomy  of  the  Organ  of  Taste. — Anatomical  and  physio- 
logical researches 
have  shown  that, 
at  least  in  the  hu- 
man subject,  the 
organ  of  taste 
probably  is  con- 
fined to  the  dorsal 
surface  of  the 
tongue  and  the 
lateral  portion  of 
the  soft  palate. 
The  upper  surface 
of  the  tongue  pre- 
sents a  large  num- 
ber of  special  pa- 
pillse,  called,  in 
contradistinction 
to  the  filiform  pa- 
pillae, fungiform 
and  circumval- 
late.  These  are 
not  found  on  its 
under  surface  or 
anywhere  except 
on  the  superior 
portion ;  and  it  is 
now  well  estab- 
lished that  the 
circumvallate  and 
fungiform  papillae 

FIG.  238.—  Papillae  of  the  tongue  (Sappey).  . 

1, 1,  circumvallate  papillae ;  2,  median  circumvallate  papilla,  which  entirely  alone  Contain    the 

fills  the  foramen  caecum  ;  3,  3,  3,  3,  fungiform  papillae  ;  4,  4,  filiform  pa-  n   „„„„     ^.f     -i-aefa 

pillae  ;  5,  5,  vertical  folds  and  furrows  of  the  border  of  the  tongue  ;  G,  6,  6,  Olgdllb  UtblU 

6,  glands  at  the  base  of  the  tongue  ;  7,  7,  tonsils  ;  8,  epiglottis  ;  9,  median  TTI „„«   •  mmta    n-r» 
glosso-epiglottidean  fold. 

on  the  gustatory 
organs,  by  the  application  of  solutions  to  different  parts  through  fine,  glass 


MECHANISM  OF  GUSTATION.  669 

tubes,  have  shown  that  the  mucous  membrane  around  a  papilla  has  no  gusta- 
tory sensibility,  but  that  different  savors  can  be  distinguished  when  a  single 
papilla  is  touched  (Camerer). 

In  Fig.  238,  which  represents  the  dorsal  surface  of  the  tongue,  the  large, 
circumvallate  papillae,  usually  seven  to  twelve  in  number,  are  seen  in  the 
form  of  an  inverted  V,  occupying  the  base  of  the  tongue.  The  fungiform 
papillae  are  scattered  over  the  surface  but  are  most  abundant  at  the  point  and 
near  the  borders.  Both  of  these  varieties  of  papillae  are  distinguishable  by 
the  naked  eye. 

The  circumvallate  papillae  simply  are  enlarged,  fungiform  papillae,  each 
one  surrounded  by  a  circular  ridge,  or  wall,  and  covered  by  small,  secondary 


FIG.  239. — Medium-sized  circumvallate  FIG.  240.— Fungiform,  filiform,  and  heini- 

papilla  (Sappey).  spherical  papillae  (Sappey). 

FIG.  239.— 1.  papilla,  the  base  only  being  apparent  (it  is  seen  that  the  base  is  covered  with  secondary 

papillae) ;  2,  groove  between  the  papilla  and  the  surrounding  wall :  3,  3,  wall  of  the  papilla. 
FIG.  240.— 1,  1,  two  fungiform  papillae  covered  with  secondary  papillae  ;  2.  2.  2,  filiform  papillae  ;  3,  a 
filiform  papilla,  the  prolongations  of  which  are  turned  outward  ;  4,  a  filiform  papilla  with  vertical 
prolongations  ;  5,  5,  small  filiform  papillae  with  the  prolongations  turned  inward  ;  6,  6,  filiform 
papillae  with  striations  at  their  bases  ;  7,  7.  hemispherical  papillae,  slightly  apparent,  situated 
between  the  fungiform  and  the  filiform  papillae. 

papillae.  The  fungiform  papillae  have  each  a  short,  thick  pedicle  and  an  en- 
larged, rounded  extremity.  According  to  Sappey,  one  hundred  and  fifty  to 
two  hundred  of  these  can  easily  be  counted.  These,  also,  present  small,  sec- 
ondary papillae  on  their  surface.  When  the  mucous  membrane  of  the  tongue 
is  examined  with  a  low  magnifying  power,  particularly  after  maceration  in 
acetic  or  in  dilute  hydrochloric  acid,  their  structure  is  readily  observed. 
They  are  abundantly  supplied  with  blood-vessels  and  nerves. 

Several  glandular  structures  are  found  beneath  the  mucous  membrane  of 
the  tongue.  On  either  side  of  the  frenum,  near  the  point,  is  a  gland  about 
three-quarters  of  an  inch  (20  mm.)  long  and  one-third  of  an  inch  (8'5  mm.) 
broad,  which  has  five  or  six  little  openings  on  the  under  surface  of  the 
tongue  (Blandin  and  Nuhn).  Near  the  taste-beakers,  are  small,  racemose 
glands,  which  discharge  a  watery  secretion,  by  minute  ducts  which  open  into 
the  grooves  within  the  walls  of  the  circumvallate  papillae  (Ebner). 

Taste-Beakers. — Loven  and  Schwalbe  (1867)  described,  under  this  name, 
peculiar  structures  which  are  supposed  to  be  the  true  organs  of  taste.  They 
are  found  on  the  lateral  slopes  of  the  circumvallate  papillae  and  occasionally 

44 


6*^/\ 
(0 


SPECIAL  SENSES. 


on  the  fungiform  papillae.  Their  structure  is  very  simple.  They  consist  of 
flask-like  collections  of  spindle-shaped  cells,  which  are  received  into  little 
excavations  in  the  epithelial  covering  of  the  mucous  membrane,  the  bottom 
resting  upon  the  connective-tissue  layer.  Their  form  is  ovoid,  and  at  the 
neck  of  each  flask,  is  a  rounded  opening,  called  the  taste-pore.  Their  length 
ig  sH  to  -5-^7  of  an  inch  (71  to  83  /u,),  and  their  transverse  diameter,  about 
^-J^  of  an  inch  (41  p.}.  The  cavity  of  the  taste-beakers  is  filled  with  cells,  of 
which  two  kinds  are  described.  The  first  variety,  the  outer  cells,  or  the  cover- 
cells,  are  spindle-shaped,  and  curved  to  correspond  to  the  wall  of  the  beaker. 
These  come  to  a  point  at  the  taste-pore.  In  the  interior  of  the  beaker  are 
elongated  cells,  with  large,  clear  nuclei^which  are  called  taste-cells.  Accord- 
ing to  Engelmann,  delicate,  hair-like  processes  are  connected  with  the  taste- 
cells  and  extend  through  the  taste-pores,  in  the  form  of  very  fine  filaments. 

Bodies  similar  to  the  taste-beak- 
ers have  been  found  on  the  pa- 
pilla3  of  the  soft  palate  and  uvula, 
the  mucous  membrane  of  the  epi- 
glottis and  some  parts  of  the  top 
of  the  larynx.  As  regards  these 
structures  in  the  tongue,  it  has 
been  found  that  four  or  five 
months  after  section  of  the  glosso- 
pharyngeal  on  one  side  in  rabbits, 

Fm.  241.-Tasfe-6mfcerS,  from  the  lateral  taste-organ  of    the  taste-buds  On  the  Correspond- 
the  rabbit  (Engelmann).  jng  gjde  Qf  tne  posterior  portion  of 

the  tongue  disappear,  while  they  remain  perfect  on  the  sound  side  (Vintsch- 
gau  and  Honigschmied). 

According  to  the  views  of  those  who  have  described  the  so-called  taste- 
beakers,  sapid  solutions  find  their  way  into  the  interior  of  these  structures 
through  the  taste-pores  and  come  in  contact  with  the  taste-cells,  these  cells 
being  directly  connected  with  the  terminal  filaments  of  the  gustatory  nerves. 

Ferrier  has  described  a  taste-centre  near  the  so-called  olfactory  centre  in 
the  unicate  gyrus ;  but  his  observations  are  not  very  definite,  and  the  location 
of  a  centre  for  gustation  must  be  regarded  as  undetermined. 


OPTIC  NERVES.  671 

CHAPTER   XXII. 

VISION. 

General  considerations— Optic  (second  nerve) — General  properties  of  the  optic  nerves — Physiological  anat- 
omy of  the  eyeball— Sclerotic  coat — Cornea— Choroid  coat— Ciliary  muscle— Iris— Pupillary  membrane 
—Retina— Crystalline  lens — Aqueous  humor — Chambers  of  the  eye— Vitreous  humor— Summary  of  the 
anatomy  of  the  globe — The  eye  as  an  optical  instrument— Certain  laws  of  refraction,  dispersion  etc., 
bearing  upon  the  physiology  of  vision — Refraction  by  lenses — Visual  purple  and  visual  yellow  and  ac- 
commodation of  the  eye  for  different  degrees  of  illumination— Formation  of  images  in  the  eye— Mechan- 
ism of  refraction  in  the  eye — Astigmatism— Movements  of  the  iris— Direct  action  of  light  upon  the  iris 
—Action  of  the  nervous  system  upon  the  iris— Mechanism  of  the  movements  of  the  iris— Accommoda- 
tion of  the  eye  for  vision  at  different  distances — Changes  in  the  crystalline  lens  in  accommodation — 
Changes  in  the  iris  in  accommodation — Erect  impressions  produced  by  images  inverted  upon  the  retina 
— Field  of  indirect  vision — The  perimeter — Binocular  vision — Corresponding  points — The  horopter — 
Duration  of  luminous  impressions  (after-images)— Irradiation— Movements  of  the  eyeball— Muscles  of 
the  eyeball — Centres  for  vision— Parts  for  the  protection  of  the  eyeball — Conjunctival  mucous  membrane 
.—Lachrymal  apparatus — Composition  of  the  tears. 

THE  chief  important  points  to  be  considered  in  the  physiology  of  vision 
are  the  following : 

1.  The  physiological  anatomy  and  the  general  properties  and  uses  of  the 
optic  nerves. 

2.  The  physiological  anatomy  of  the  parts  essential  to  correct  vision. 

3.  The  laws  of  refraction,  diffusion  etc.,  bearing  upon  the  physiology  of 
vision. 

4.  The  action  of  the  different  parts  of  the  eye  in  the  production  and 
appreciation  of  correct  images. 

5.  Binocular  vision. 

6.  The  physiological  anatomy  and  uses  of  accessory  parts,  as  the  muscles 
which  move  the  eyeball. 

7.  The  physiological  anatomy  and  uses  of  the  parts  which  protect  the 
eye,  as  the  lachrymal  glands,  eyelids  etc. 

OPTIC  (SECOND  NERVE). 

The  bands  which  pass  from  the  tubercula  quadrigemina  to  the  eyes  are 
divided  into  the  optic  tracts,  which  extend  from  the  tubercula  on  either  side 
to  the  chiasm,  or  commissure ;  the  chiasm,  or  the  decussating  portion ;  and 
the  optic  nerves,  which  pass  from  the  chiasm  to  the  eyes. 

The  optic  tracts  arise  each  one  by  two  roots,  internal  and  external.  The 
internal  roots,  which  are  the  smaller,  arise  from  the  anterior  tubercula  quadri- 
gemina, and  pass  through  the  internal  corpora  geniculata,  to  the  optic  chiasm. 
The  external  roots,  which  are  the  larger,  arise  from  the  posterior  part  of  the 
optic  thalami,  pass  to  the  external  corpora  geniculata,  from  which  they  receive 
fibres,  and  thence  to  the  chiasm. 

Partly  by  anatomical  researches  (Wernicke)  and  partly  by  experiments  on 
the  cerebral  cortex  in  the  lower  animals  and  pathological  observations  on  the 
human  subject,  it  has  been  shown  that  fibres  from  the  apparent  origin  of  the 
optic  tracts  pass  backward  to  the  gray  matter  of  the  occipital  lobes  of  the 
cerebrum.  It  has  also  been  stated  by  Stilling  that  fibres  pass  to  the  medulla 


672 


SPECIAL  SENSES. 


oblongata,  extend  down  as  far  as  the  decussation  of  the  pyramids,  and  proba- 
bly are  concerned  in  the  reflex  movements  of  the  iris. 

The  two  roots  of  each  optic  tract  unite 
above  the  external  corpus  geniculatum,  form- 
ing a  flattened  band,  which  takes  an  oblique 
course  around  the  under  surface  of  the  crus 
cerebri,  to  the  optic  commissure. 

The  optic  commissure,  or  chiasm,  is  situ- 
ated just  in  front  of  the  corpus  cinereum, 
resting  upon  the  olivary  process  of  the  sphe- 
noid bone.  As  its  name  implies,  this  is  the 
point  of  union  between  the  nerves  of  the  two 
sides.  At  the  commissure  the  fibres  from  the 
optic  tracts  take  three  directions ;  and  in  ad- 
dition, the  commissure  contains  filaments  pass- 
ing from  one  eye  to  the  other,  which  have  no 
connection  with  the  optic  tracts.  The  four 
sets  of  fibres  in  the  optic  commissure  are  the 
following : 

1.  Decussating  fibres,  passing  from  the  op- 
tic tract  upon  either  side  to  the  eye  of  the  op- 
posite side.      The  greatest  part  of  the  fibres 
take  this  direction.     Their  relative  situation  is 
internal. 

2.  External  fibres,  fewer  than  the  preced- 
ing, which  pass  from  the  optic  tract  to  the  eye 
upon  the  same  side. 

3.  Fibres  situated  on  the  posterior  boundary  of  the  commissure,  which 
pass  from  one  optic  tract  to  the  other  and  do  not  go  to  the  eyes.    These  fibres 
are  scanty  and  are  sometimes  wanting. 

4.  Fibres  situated  on  the  anterior  border  of  the  commissure,  greater  in 
number  than  the  preceding,  which  pass  from  one 

eye  to  the  other  and  which  have  no  connection 
with  the  optic  tracts. 

The  fibres  of  the  optic  tracts  upon  the  two 
sides  are  connected  with  distinct  portions  of  the 
retina.  This  fact  is  illustrated  in  cases  of  hemi- 
anopsia,  which  show  that  the  decussating  fibres 
have  the  following  directions  and  distribution : 

From  the  left  side  of  the  encephalon,  fibres 
pass  to  the  right  eye,  supplying  the  inner,  or  na- 
sal  mathematical  half  of  the  retina,  from  a  ver-  The  dottec>  lines ,t*°w*I?e  four di' 

rections  of  the  fibres. 

tical  line  passing  through  the  macula  lutea.     Fi- 
bres also  pass  to  the  left  eye,  supplying  the  outer,  or  temporal  half  of  the 
retina.     The  macula  lutea,  then,  and  not  the  point  of  entrance  of  the  optic 
nerve,  is  in  the  true  line  of  division  of  the  retina. 


FIG.  342. — Optic  tracts,  commissure 
and  nerves  (Hirschfeld). 

1,  infundibulum  ;  2,  corpus  cinereum  ; 
3,  corpora  albicantia  ;  4,  cerebral 
peduncle  ;  5,  pons  Varolii ;  6,  optic 
tracts  and  nerves,  decussating  at 
the  commissure,  or  chiasm  ;  7,  mo- 
tor oculi  communis  ;  8,  patheticus  ; 
9,  fifth  nerve  ;  10,  motor  oculi  ex- 
ternus  ;  11,  facial  nerve  ;  12,  aud- 
itory nerve  ;  13,  nerve  of  Wris- 
berg  ;  14,  glosso-pharyngeal  nerve; 
15,  pneumogastric  ;  16,  spinal  ac- 
cessory ;  17,  sublingual  nerve. 


243. — Diagram  of  the  decusna- 
ion  of  fibres  at  the  optic  com- 


OPTIC  NERVES.  673 

With  the  exception  of  a  few  grayish  filaments,  the  fibres  of  the  optic 
tracts  and  the  optic  nerves  are  of  the  ordinary,  medallated  variety,  and  they 
present  no  differences  in  structure  from  the  general  cerebro-spinal  nerves. 

The  optic  commissure  is  covered  with  a  fibrous  membrane  and  is  more 
resisting  than  the  optic  tracts.  The  optic  nerves  are  rounded  and  are  enclosed 
in  a  double  sheath  derived  from  the  dura  mater  and  the  arachnoid.  They 
pass  into  the  orbit  upon  either  side  and  penetrate  the  sclerotic,  at  the  pos- 
terior, inferior  and  internal  portion  of  the  globe.  As  the  nerves  enter  the 
globe,  they  lose  their  coverings  from  the  dura  mater  and  arachnoid.  The 
sheath  derived  from  the  dura  mater  is  adherent  to  the  periosteum  of  the  orbit, 
at  the  sphenoidal  fissure,  and  when  it  reaches  the  globe,  it  fuses  with  the 
sclerotic  coat.  Just  before  the  nerves  penetrate  the  globe  they  each  present 
a  well  marked  constriction.  At  the  point  of  penetration  there  is  a  thin  but 
strong  membrane,  presenting  a  number  of  perforations  for  the  passage  of  the 
nervous  filaments.  This  membrane,  the  lamina  cribrosa,  is  in  part  derived 
from  the  sclerotic,  and  in  part,  from  the  coverings  of  the  individual  nerve- 
fibres,  which  lose  their  investing  membranes  at  this  point.  In  the  interior 
of  each  eye  there  is  a  little,  mammillated  eminence,  formed  by  the  united 
fibres  of  the  nerve.  The  retina,  with  which  the  optic  nerve  is  connected,  will 
be  described  as  one  of  the  coats  of  the  eye. 

In  the  centre  of  the  optic  nerve,  is  a  minute  canal,  lined  by  fibrous  tissue, 
in  which  are  lodged  the  central  artery  of  the  retina  and  its  corresponding 
vein,  with  a  delicate  nervous  filament  from  the  ophthalmic  ganglion.  The 
vessels  penetrate  the  optic  nerve  £  to  f  of  an  inch  (8*5  to  19-1  mm.)  behind 
the  globe.  The  central  canal  does  not  exist  behind  these  vessels. 

General  Properties  of  the  Optic  Nerves. — There  is  very  little  to  be  said 
regarding  the  general  properties  of  the  optic  nerves,  except  that  they  are  the 
only  nerves  capable  of  conveying  to  the  cerebrum  the  special  impressions  of 
sight,  and  that  they  are  not  endowed  with  general  sensibility. 

That  the  optic  nerves  are  the  only  nerves  of  sight,  there  can  be  no  doubt. 
Their  division  or  injury  always  involves  loss  or  impairment  of  vision,  directly 
corresponding  with  the  extent  of  the  lesion.  It  is  important,  however,  to 
note  that  they  are  absolutely  insensible  to  ordinary  impressions.  "  We  can, 
in  a  living  animal,  pinch,  cauterize,  cut,  destroy  in  any  way  the  optic  nerve 
without  giving  rise  to  the  slightest  painful  sensation ;  whether  it  be  taken 
before  or  after  its  decussation,  it  seems  completely  insensible  in  its  entire 
length  "  (Longet). 

Not  only  are  the  optic  nerve  and  retina  insensible  to  pain,  but  their 
stimulation  produces  luminous  impressions.  This  was  stated  in  the  remark- 
able paper,  Idea  of  a  New  Anatomy  of  the  Brain,  printed  by  Charles  Bell, 
in  1811.  A  few  years  later,  Magendie,  in  operating  for  cataract,  passed  the 
needle  to  the  bottom  of  the  eye  and  irritated  the  retina,  in  two  persons.  The 
patients  experienced  no  pain  but  merely  an  impression  of  flashes  of  light. 
The  insensibility  of  the  optic  nerves  has  also  been  repeatedly  noted  in  surgical 
operations  in  which  the  nerves  have  been  exposed.  If  an  electric  current  be 
passed  through  the  optic  nerves,  a  sensation  of  light  is  experienced.  The 


674  SPECIAL  SENSES. 

same  phenomenon  is  observed  when  the  eyeball  is  pressed  upon  or  contused, 
a  fact  which  is  sufficiently  familiar. 

PHYSIOLOGICAL  ANATOMY  OF  THE  EYEBALL. 

The  eyeball  is  a  spheroidal  body,  partially  embedded  in  a  cushion  of  fat 
in  the  orbit,  protected  by  the  surrounding  bony  structures  and  the  eyelids, 
its  surface  bathed  by  the  secretion  of  the  lachrymal  gland,  and  movable  in 
various  directions  by  the  action  of  certain  muscles.  It  is  surrounded  by  a 
thin,  serous  sac,  the  capsule  of  Tenon,  which  exists  in  two  layers.  The  outer 
layer  lies  next  the  fatty  layer  in  which  the  globe  is  embedded,  and  the  inner 
layer  invests  the  sclerotic  coat.  When  the  axis  of  the  eye  is  directed  for- 
ward, the  globe  has  the  form  of  a  sphere,  in  its  posterior  five-sixths,  with  the 
segment  of  a  smaller  sphere  occupying  its  anterior  sixth.  The  segment  of 
the  smaller  sphere,  bounded  externally  by  the  cornea,  is  more  prominent 
than  the  rest  of  the  surface. 

The  eyeball  is  made  up  of  several  coats  enclosing  certain  refracting 
media.  The  external  coat  is  the  sclerotic,  covering  the  posterior  five-sixths 
of  the  globe,  which  is  continuous  with  the  cornea,  covering  the  anterior 
sixth.  This  is  a  dense,  opaque,  fibrous  membrane,  for  the  protection  of  the 
inner  coats  and  the  contents  of  the  globe.  The  cornea  is  dense,  resisting 
and  perfectly  transparent.  The  muscles  that  move  the  globe  of  the  eye  are 
attached  to  the  sclerotic  coat. 

Were  it  not  for  the  prominence  of  the  cornea,  the  eyeball  would  present 
very  nearly  the  form  of  a  perfect  sphere,  as  will  be  seen  by  the  following 
measurements  of  its  various  diameters ;  but  the  prominence  of  its  anterior 
.sixth  gives  the  greatest  diameter  in  the  antero-posterior  direction. 

The  form  and  dimensions  of  the  globe  are  subject  to  considerable  varia- 
tions after  death,  by  evaporation  of  the  humors,  emptying  of  vessels,  etc., 
and  there  is  no  way  in  which  the  normal  conditions  can  be  restored.  The 
most  exact  measurements  are  those  made  by  Sappey.  As  an  illustration  of 
the  post-mortem  changes  in  the  eye,  Sappey  has  given  comparative  measure- 
ments made  three  hours  and  twenty-four  hours  after  death,  the  results  of 
which  presented  very  considerable  differences. 

In  measurements  made  by  Sappey,  one  to  four  hours  after  death,  of  the 
eyes  of  twelve  adult  females  and  fourteen  adult  males,  of  different  ages,  the 
following  mean  results  were  obtained  : 


SUBJECTS  EXAMINED. 

Diameters  (inch,  and  mm.  in  parentheses). 

Antero-poeterior. 

Tnnsversc. 

Vertical. 

Oblique. 

Mean  of  12  females,  18  to  81  years  of  a£*e. 
Mean  of  14  males,.  20  to  79  years  of  age  .  . 

0-941  (2,3-9  mm.) 
0-968  (24-6  mm.) 

0-911  (23-4  mm.) 
0-941  (23-9  mm.) 

0-905  (23'0  mm.) 
0-925  (23'5  mm.) 

0-937  (23'8  mm.) 
0-949  (24-1  mm.) 

From  these  results  it  is  seen  that  all  the  diameters  are  less  in  the  female 
than  in  the  male.  The  antero-posterior  diameter  is  the  greatest  of  all,  and 
the  vertical  diameter  is  the  shortest.  The  measurements  at  different  ages, 


ANATOMY  OF  THE  EYEBALL.  675 

not  cited  in  the  table  just  given,  show  that  the  excess  of  the  antero-posterior 
diameter  over  the  others  is  diminished  by  age. 

Sclerotic  Coat. — The  sclerotic  is  the  dense,  opaque,  fibrous  covering  of 
the  posterior  five-sixths  of  the  eyeball.  Its  thickness  is  different  in  different 
portions.  At  the  point  of  penetration  of  the  optic  nerve,  it  measures  fa  of 
an  inch  (1  mm.)  It  is  thinnest  at  the  middle  portion  of  the  eye,  measuring 
about  fa  of  an  inch  (O5  mm.),  and  is  a  little  thicker  again  near  the  cornea. 
This  membrane  is  composed  chiefly  of  bundles  of  ordinary  connective  tissue. 
The  fibres  are  slightly  wavy,  and  are  arranged  in  flattened  bands,  which  are 
alternately  longitudinal  and  transverse,  giving  the  membrane  a  lamellated 
appearance,  although  it  can  not  be  separated  into  distinct  layers.  Mixed 
with  these  bands  of  connective-tissue  fibres,  are  small  fibres  of  elastic  tissue. 
The  vessels  of  the  sclerotic  are  scanty.  They  are  derived  from  the  ciliary 
vessels  and  the  vessels  of  the  muscles  of  the  eyeball.  The  tissue  of  the  scle- 
rotic yields  gelatine  on  boiling. 

Cornea. — The  cornea  is  the  transparent  membrane  which  covers  about 
the  anterior  sixth  of  the  globe  of  the  eye.  As  before  remarked,  this  is  the 
most  prominent  portion  of  the  eyeball.  It  is  in  the  form  of  a  segment  of  a 
sphere,  attached  by  its  borders  to  the  segment  of  the  larger  sphere  formed 
by  the  sclerotic.  The  thickness  of  the  cornea  is  about  -fa  of  an  inch  (0*8  mm.), 
in  its  central  portion,  and  about  fa  of  an  inch  (1  mm.)  near  its  periphery.  "Its 
substance  is  composed  of  transparent  fibres,  arranged  in  incomplete  layers, 
something  like  the  layers  of  the  sclerotic.  It  yields  chondrine  instead  of 
gelatine  on  boiling. 

Upon  the  external,  or  convex  surface  of  the  cornea,  are  several  layers  of 
delicate,  transparent,  nucleated  epithelium.  The  most  superficial  cells  are 
flattened,  the  middle  cells  are  rounded,  and  the  deepest  cells  are  elongated 
and  arranged  perpendicularly.  These  cells  become  slightly  opaque  and  whit- 
ish after  death.  Just  beneath  the  epithelial  covering  of  the  cornea,  is  a  very 
thin,  transparent  membrane,  described  by  Bowman  under  the  name  of  the 
"anterior  elastic  lamella."  This  membrane,  with  its  cells,  is  a  continuation 
of  the  conjunctiva. 

The  proper  corneal  membrane  is  composed  of  very  pale,  flattened  bun- 
dles of  fibres,  interlacing  with  each  other  in  every  direction.  Their  arrange- 
ment is  lamellated,  although  they  can  not  be  separated  into  complete  and 
distinct  layers.  Between  the  bundles  of  fibres,  lie  a  great  number  of  stellate, 
anastomosing,  connective-tissue  corpuscles.  In  these  cells  and  in  the  inter- 
vals between  the  fibres,  there  is  a  considerable  quantity  of  transparent  liquid. 
The  fibres  constituting  the  substance  of  the  cornea  are  continuous  with  the 
fibrous  structure  of  the  sclerotic,  from  which  they  can  not  be  separated  by 
maceration.  At  the  margin  of  the  cornea  the  opaque  fibres  of  the  sclerotic 
abruptly  become  transparent.  The  corneal  substance  is  very  tough,  and  it 
will  resist  a  pressure  sufficient  to  rupture  the  sclerotic. 

Upon  the  posterior,  or  concave  surface  of  the  cornea,  is  the  membrane  of 
Descemet  or  of  Demours.  This  is  elastic,  transparent,  structureless,  rather 
loosely  attached,  and  covered  with  a  single  layer  of  regularly  polygonal,  nu- 


SPECIAL  SENSES. 


cleated  epithelium.  At  the  circumference  of  the  cornea,  a  portion  of  this 
membrane  passes  to  the  anterior  surface  of  the  iris,  in  the  form  of  a  number 
of  processes  which  constitute  the  ligamentum  iridis  pectinatum,  a  portion 
passes  into  the  substance  of  the  ciliary  muscle,  and  a  portion  is  continuous 
with  the  fibrous  structure  of  the  sclerotic. 

In  the  adult  the  cornea  is  almost  without  blood-vessels,  but  in  foetal  life 
it  presents  a  rich  plexus  extending  nearly  to  the  centre.  These  disappear, 
however,  before  birth,  leaving  a  very  few  delicate,  looped  vessels  at  the  ex- 
treme edge. 

In  the  cornea  fine  nerve-fibres  terminate  in  the  nuclei  of  the  posterior 
layer  of  the  epithelium  of  its  convex  surface.  The  cornea  also  contains 
lymph-spaces  and  the  so-called  "  wandering  cells,"  The  surface  of  the  cor- 
nea is  exquisitely  sensitive. 

Choroid  Coat. — Calling  the  sclerotic  and  the  cornea  the  first  coat  of  the 
eyeball,  the  second  is  the  choroid,  with  the  ciliary  processes,  the  ciliary  mus- 
cle and  the  iris.  This  was 
called  by  the  older  anato- 
mists the  uvea,  a  name 
which  was  later  applied, 
sometimes  to  the  entire  iris, 
and  sometimes  to  its  pos- 
terior, or  pigmentary  layer. 
The  choroid  and  ciliary 
processes  will  be  described 
together  as  the  second  coat. 
The  ciliary  muscle  and  the 
iris  will  be  described  sepa- 
rately. 

The  choroid  is  distin- 
guished from  the  other  coats 
of  the  eye  by  its  dark  color 
and  its  great  vascularity.  It 

FIG.  244.— Choroid  coat  of  the  eye  (Sappey).  .  . 

1,  optic  nerve  ;  2, 2,  2, 2,  3,  3.  3,  4,  sclerotic  coat,  divided  and  turned  OCCUpieS  that  portion  01  the 

back  to  show  the  choroid  ;  5,  5,  5,  5,  the  cornea,  divided  into  pVpK,,]l  pnrrocr>nnrlino-  +r>  tV.o 

oed  back  ;  6,  6,  canal  of  Schlemm  :  7,  eyeDdll  Corresponding  to  the 

sclerotic.  It  is  perforated 
posteriorly  by  the  optic 
nerve  and  is  connected  in 
front  with  the  iris.  It  is 
very  delicate  in  its  structure  and  is  composed  of  two  or  three  distinct  layers. 
Its  thickness  is  -fa  to  ^  of  an  inch  (0-3  to  1  mm.)  Its  thinnest  portion  is 
at  about  the  middle  of  the  eye.  Posteriorly  it  is  a  little  thicker.  Its  thick- 
est portion  is  at  its  anterior  border.- 

The  external  surface  of  the  choroid  is  connected  with  the  sclerotic  by 
vessels  and  nerves  (the  long  ciliary  arteries  and  the  ciliary  nerves),  and  very 
loose,  connective  tissue.  This  is  sometimes  called  the  membrana  fusca,  al- 
though it  can  hardly  be  regarded  as  a  distinct  layer.  It  contains,  in  addi- 


four  portions  and  turne 
external  surface  of  the  choroid,  traversed  by  the  ciliary 
nerves  and  one  of  the  long  ciliary  arteries  ;  8,  central  vessel, 
into  which  open  the  vasa  vorticosa  :  9,  9, 10, 10,  choroid  zone  ; 
11,  11,  ciliary  nerves  :  12,  long  ciliary  artery  ;  13,  13,  13.  13, 
anterior  ciliary  arteries  ;  14,  iris  ;  15, 15,  vascular  circle  of  the 
iris  ;  16,  pupil. 


ANATOMY  OF  THE  EYEBALL.  677 

tion  to  blood-vessels,  nerves  and  fibrous  tissue,  a  few  irregularly  shaped  pig- 
ment-cells. 

The  vascular  layer  of  the  choroid  consists  of  arteries,  veins  and  capillaries, 
arranged  in  a  peculiar  manner.  The  layer  of  capillary  vessels,  which  is 
internal,  is  sometimes  called  the  tunica  Ruyschiana.  The  arteries,  which 
are  derived  from  the  posterior  short  ciliary  arteries  and  are  connected  with 
the  capillary  plexus,  lie  just  beneath  the  pigmentary  layer  of  the  retina. 
The  plexus  of  capillaries  is  closest  at  the  posterior  portion  of  the  membrane. 
The  veins  are  external  to  the  other  vessels.  They  are  very  abundant  and  are 
disposed  in  curves  converging  to  four  trunks.  This  arrangement  gives  the 
veins  a  very  peculiar  appearance,  and  they  have  been  called  the  vasa  vorti- 
cosa.  The  pigmentary  portion  is  composed,  over  the  greatest  part  of  the 
choroid,  of  a  single  layer  of  regularly  polygonal  cells,  somewhat  flattened, 
measuring  -g-gV^  to  y-gVff  °f  an  inch  (12  to  16  /A)  in  diameter.  These  cells  are 
filled  with  pigmentary  granulations  of  uniform  size,  and  they  give  to  the 
membrane  its  characteristic  dark-brown  or  chocolate  color.  The  pigmentary 
granules  in  the  cells  are  less  abundant  near  their  centre,  where  a  clear  nucleus 
can  readily  be  observed.  In  the  anterior  portion  of  the  membrane,  in  front 
of  the  anterior  limit  of  the  retina,  the  cells  are  smaller,  more  rounded,  more 
completely  filled  with  pigment,  and  present  several  layers.  Beneath  the  layer 
of  hexagonal  pigment-cells,  the  intervascular  spaces  of  the  choroid  are  occu- 
pied by  stellate  pigment-cells.  The  cells  next  the  layer  of  rods  and  cones 
are  regarded  as  constituting  the  outer,  or  pigmentary  layer  of  the  retina. 
These  cells  send  little,  hair-like  processes  downward  between  the  rods  and 
cones. 

Ciliary  Processes. — The  anterior  portion  of  the  choroid  is  arranged  in 
the  form  of  folds  or  plaits  projecting  internally,  called  the  ciliary  processes. 
The  largest  of  these  folds  are  about  fa  of  an  inch  (2-5  mm.)  in  length.  They 
are  sixty  to  eighty  in  number.  The  larger  folds  are  of  nearly  uniform  size 
and  are  regularly  arranged  around  the  margin  of  the  crystalline  lens.  Be- 
tween these  folds,  which  constitute  about  two-thirds  of  the  entire  number, 
are  smaller  folds,  lying,  without  any  regular  alternation,  between  the  larger. 
Within  the  folds,  are  received  corresponding  folds  of  the  thick  membrane, 
continuous  anteriorly  with  the  hyaloid  membrane  of  the  vitreous  humor, 
called  the  zone  of  Zinn. 

The  ciliary  processes  present  blood-vessels,  which  are  somewhat  larger 
than  those  of  the  rest  of  the  choroid.  The  pigmentary  cells  are  smaller  and 
are  arranged  in  several  layers.  The  anterior  border  of  the  processes  is  free 
and  contains  little  or  no  pigment. 

Ciliary  Muscle. — This  muscle,  formerly  known  as  the  ciliary  ligament 
and  now  sometimes  called  the  tensor  of  the  choroid,  is  the  agent  for  the 
accommodation  of  the  eye  to  vision  at  different  distances.  Under  this  view, 
the  ciliary  muscle  is  an  organ  of  great  importance,  and  it  is  essential,  in  the 
study  of  accommodation,  to  have  an  exact  idea  of  its  relations  to  the  coats 
of  the  eye  and  to  the  crystalline  lens. 

The  form  and  situation  of  the  ciliary  muscle  are  as  follows :  It  surrounds 


678 


SPECIAL  SENSES. 


the  anterior  margin  of  the  choroid,  in  the  form  of  a  ring  about  £  of  an  inch 
(3-2  mm.)  wide  and  ^  of  an  inch  (0-5  mm.)  in  thickness  at  its  thickest  por- 


FIG.  245.—  Ciliary  muscle  ;  magnified  10  diameters  (Sappey). 

1,  1,  crystalline  lens  ;  3,  hyaloid  membrane  ;  3,  zone  of  Zinn  ;  4,  iris  ;  5.  5,  one  of  the  ciliary  processes  ; 
6,  6,  radiating  fibres  of  the  ciliary  muscle  ;  7,  section  of  the  circular  portion  of  the  ciliary  muscle  ; 
8,  venous  plexus  of  the  ciliary  process  ;  9,  10,  sclerotic  coat ;  11,  12,  cornea  ;  13,  epithelial  layer  of 
the  cornea ;  14,  membrane  of  Deseemet  ;  15,  ligamentum  iridis  pectinatum  ;  16,  epithelium  of  the 
membrane  of  Descemet ;  1~,  union  of  the  sclerotic  coat  with  the  cornea  ;  18,  section  of  the  canal  of 
Schlemm. 

tion,  which  is  its  anterior  border.  It  becomes  thinner  from  before  backward, 
until  its  posterior  border  apparently  fuses  with  the  fibrous  structure  of  the 
choroid.  It  is  semi-transparent  and  of  a  grayish  color.  Its  situation  is  just 
outside  of  the  ciliary  processes,  these  processes  projecting  in  front  of  its 
anterior  border,  about  -£%  of  an  inch  (1  mm.).  Regarding  the  anterior  border 
of  this  muscle  as  its  origin  and  the  posterior  border  as  its  insertion,  it  arises 
in  front,  from  the  circular  line  of  junction  of  the  cornea  and  sclerotic,  from 
the  border  of  the  membrane  of  Descemet,  and  the  ligamentum  iridis  pecti- 
natum. Its  fibres,  which  are  chiefly  longitudinal,  pass  backward  and  are  lost 
in  the  choroid,  extending  somewhat  farther  back  than  the  anterior  limit  of 
the  retina.  In  addition  a  net- work  of  circular  muscular  fibres  has  been 
described,  lying  over  the  anterior  portion  of  the  ciliary  body,  at  the  periphery 
of  the  iris,  beneath  the  longitudinal  fibres.  Some  of  these  fibres  have  an 
oblique  direction. 

The  ciliary  muscle  is  composed  mainly  of  muscular  fibres.  These  fibres, 
anatomically  considered,  belong  to  the  non-striated  variety.  They  are  pale, 
present  a  number  of  oval,  longitudinal  nuclei,  and  have  no  striae. 


ANATOMY  OF  THE  EYEBALL.  679 

It  is  evident,  from  the  arrangement  of  the  fibres  of  the  ciliary  muscle, 
that  its  action  must  be  to  approximate  the  border  of  connection  of  the  scle- 
rotic and  cornea  and  the  circumference  of  the  choroid,  compressing  the  vitre- 
ous humor  and  relaxing  the  suspensory  ligament  of  the  crystalline  lens.  This 
action  enables  the  lens  to  change  its  form,  and  it  adapts  the  curvature  of  the 
lens  to  vision  at  different  distances.  The  nerves  of  the  ciliary  muscle  are 
derived  from  the  long  and  the  short  ciliary. 

Iris. — The  iris  corresponds  to  the  diaphragm  of  optical  instruments.  It 
is  a  circular  membrane,  situated  just  in  front  of  the  crystalline  lens,  with  a 
round  perforation,  the  pupil,  near  its  centre. 

The  attachment  of  the  greater  circumference  of  the  iris  is  to  the  line  of 
junction  of  the  cornea  and  sclerotic,  near  the  origin  of  the  ciliary  muscle,  the 
latter  passing  backward  to  be  inserted  into  the  choroid,  and  the  former  pass- 
ing directly  over  the  crystalline  lens.  The  diameter  of  the  iris  is  about  half 
an  inch  (12'5  mm.).  The  pupil  is  subject  to  considerable  variations  in  size. 
When  at  its  medium  of  dilatation,  the  diameter  of  the  pupil  is  ^  to  -^  of  an 
inch  (3'2  to  4-2  mm.).  The  pupillary  orifice  is  not  in  the  mathematical  cen- 
tre of  the  iris,  but  is  situated  a  little  toward  the  nasal  side.  The  thickness  of 
the  iris  is  a  little  greater  than  that  of  the  choroid,  but  it  is  unequal  in  differ- 
ent parts,  the  membrane  being  thinnest  at  its  great  circumference  and  its 
pupillary  border,  and  thickest  at  about  the  junction  of  its  inner  third  with 
the  outer  two-thirds.  It  slightly  projects  anteriorly  and  divides  the  space 
between  the  lens  and  the  cornea  into  two  chambers,  anterior  and  posterior, 
the  anterior  chamber  being  much  the  larger.  Taking  advantage  of  a  prop- 
erty of  the  crystalline  lens,  called  fluorescence,  which  enables  an  observer,  by 
concentrating  upon  it  a  blue  light,  to  see  the  boundaries  in  the  living  eye, 
Helmholtz  has  demonstrated  that  the  posterior  surface  of  the  iris  and  the 
anterior  surface  of  the  lens  are  actually  in  contact,  except,  perhaps,  for  a 
certain  distance  near  the  periphery  of  the  iris.  This  being  the  case,  the 
posterior  chamber  is  very  small  and  exists  only  near  the  margins  of  the  lens 
and  the  iris. 

The  color  of  the  iris  is  different  in  different  individuals.  Its  anterior 
surface  is  generally  very  dark  near  the  pupil  and  presents  colored  radiations 
toward  its  periphery.  Its  posterior  surface  is  of  a  dark-purple  color  and  is 
covered  with  pigmentary  cells. 

The  entire  iris  presents  three  layers.  The  anterior  layer  is  continuous 
with  the  membrane  of  the  aqueous  humor.  At  the  great  circumference,  it 
presents  little,  fibrous  prolongations,  forming  a  delicate,  dentated  membrane, 
called  the  ligamentum  iridis  pectinatum.  The  membrane  covering  the  gen- 
eral anterior  surface  of  the  iris  is  extremely  thin  and  is  covered  by  cells  of 
tessellated  epithelium.  Just  beneath  this  membrane  are  a  number  of  irregu 
larly  shaped,  pigmentary  cells. 

The  posterior  layer  of  the  iris  is  very  thin,  easily  detached  from  the  middle 
layer,  and  contains  a  number  of  small  cells  rich  in  pigmentary  granules. 
Some  anatomists  recognize  this  membrane  only  as  the  uvea. 

The  middle  layer  constitutes  by  far  the  greatest  part  of  the  substance  of 


680  SPECIAL  SENSES. 

the  iris.  It  is  composed  of  connective  tissue,  muscular  fibres  of  the  non- 
striated  variety,  many  blood-vessels,  and  probably  nerve-terminations.  Di- 
rectly surrounding  the  pupil,  forming  a  band  about  -g^  of  an  inch  (0*5  mm.) 
in  width,  is  a  layer  of  non-striated  muscular  fibres,  called  the  sphincter  of  the 
iris.  The  existence  of  these  fibres  is  admitted  by  all  anatomists.  It  is  differ- 
ent, however,  for  the  radiating  muscular  fibres.  Most  anatomists  describe, 
in  addition  to  the  sphincter,  non-striated  fibres,  which  can  be  traced  from 
near  the  great  circumference  of  the  iris  almost  to  its  pupillary  border,  ly- 
ing both  in  front  of  and  behind  the  circular  fibres.  A  few  observers  deny 
that  these  fibres  are  muscular ;  but  they  recognize  a  thick,  muscular  layer 
surrounding  the  arteries  of  the  iris.  This  is  merely  a  question  of  observa- 
tion ;  but  the  weight  of  anatomical  authority  is  in  favor  of  the  existence  of 
the  radiating  fibres,  and  their  presence  explains  certain  of  the  phenomena  of 
dilatation  of  the  iris  which  would  otherwise  be  difficult  to  understand. 

The  blood-vessels  of  the  iris  are  derived  from  the  arteries  of  the  choroid, 
from  the  long  posterior  ciliary  and  from  the  anterior  ciliary  arteries.  The 
long  ciliary  arteries  are  two  branches,  running  along  the  sides  of  the  eyeball, 
between  the  sclerotic  and  choroid,  to  form  finally  a  circle  surrounding  the 
iris.  The  anterior  ciliary  arteries  are  derived  from  the  muscular  branches  of 
the  ophthalmic.  They  penetrate  the  sclerotic,  a  little  behind  the  iris,  and 
join  the  long  ciliary  arteries,  in  the  vascular  circle.  From  this  circle,  the  ves- 
sels branch  and  pass  into  the  iris,  to  form  a  smaller  arterial  circle  around  the 
pupil.  The  veins  from  the  iris  empty  into  a  circular  sinus  situated  at  the 
junction  of  the  cornea  with  the  sclerotic.  This  is  sometimes  spoken  of  as 
the  circular  venous  sinus,  or  the  canal  of  Schlemm. 

The  nerves  of  the  iris  are  the  long  ciliary,  from  the  fifth  cranial,  and  the 
short  ciliary,  from  the  ophthalmic  ganglion. 

Pupillary  Membrane. — At  a  certain  period  of  foetal  life  the  pupil  is 
closed  by  a  membrane  connected  with  the  lesser  circumference  of  the  iris, 
called  the  pupillary  membrane.  This  is  not  distinct  during  the  first  months ; 
but  between  the  third  and  the  fourth  months,  it  is  readily  seen.  It  is  most 
distinct  at  the  sixth  month.  The  membrane  is  thin  and  transparent,  and  it 
completely  separates  the  anterior  from  the  posterior  chamber  of  the  eye.  It 
is  provided  with  vessels  derived  from  the  arteries  of  the  iris,  anastomosing 
with  each  other  and  turning  back  in  the  form  of  loops  near  the  centre.  At 
about  the  seventh  month,  it  begins  to  give  way  at  the  centre,  gradually  atro- 
phies, and  scarcely  a  trace  of  it  can  be  seen  at  birth. 

Retina. — The  retina  is  described  by  anatomists  as  the  third  tunic  of  the 
eye.  It  is  closely  connected  with  the  optic  nerve,  and  the  most  important 
structures  entering  into  its  composition  are  probably  continuous  with  pro- 
longations from  the  nerve-cells.  This  is  the  membrane  endowed  with  the 
special  sense  of  sight,  the  other  structures  in  the  eye  being  accessory. 

If  the  sclerotic  and  choroid  be  removed  from  the  eye  under  water,  the 
retina  is  seen,  in  perfectly  fresh  specimens,  in  the  form  of  a  delicate,  trans- 
parent membrane  covering  the  posterior  portion  of  the  vitreous  humor.  A 
short  time  after  death  it  becomes  slightly  opaline.  It  extends  over  the  pos- 


ANATOMY  OF  THE  RETINA.  681 

terior  portion  of  the  eyeball,  to  a  distance  of  about  ^  of  an  inch  (1/7  mm.) 
behind  the  ciliary  processes.  When  torn  from  its  anterior  attachment,  it 
presents  a  finely  serrated  edge,  called  the  ora  serrata.  This  edge  adheres 
very  closely,  by  mutual  interlacement  of  fibres,  to  the  zone  of  Zinn.  In  the 
middle  of  the  membrane,  its  thickness  is  about  T^  of  an  inch  (200  /*).  It 
becomes  thinner  nearer  the  anterior  margin,  where  it  measures  only  about  y^- 
of  an  inch  (80  /*,).  Its  external  surface  is  in  contact  with  the  choroid,  and 
its  internal,  with  the  hyaloid  membrane  of  the  vitreous  humor. 

The  optic  nerve  penetrates  the  retina  about  ^  of  an  inch  (3-2  mm.)  within 
and  ^  of  an  inch  (2*1  mm.)  below  the  antero-posterior  axis  of  the  globe, 
presenting  at  this  point  a  small,  rounded  elevation  upon  the  internal  sur- 
face of  the  membrane,  perforated  in  its  centre  for  the  passage  of  the  central 
artery  of  the  retina.  At  a  point  ^  to  -J  of  an  inch  (2-1  to  3-2  mm.)  external 
to  the  point  of  penetration  of  the  nerve,  is  an  elliptic  spot,  its  long  diameter 
being  horizontal,  about  %  of  an  inch  (2'1  mm.)  long  and  ^  of  an  inch  (0'7 
mm.)  broad,  called  the  yellow  spot  of  Sommerring,  or  the  macula  lutea.  In 
the  centre  of  this  spot,  is  a  depression,  called  the  fovea  centralis.  This  de- 
pression is  exactly  in  the  axis  of  distinct  vision.  The  yellow  spot  exists  only 
in  man  and  the  quadrumana. 

The  structures  in  the  retina  which  present  the  greatest  physiological  im- 
portance are  the  external  layer,  formed  of  rods  and  cones,  the  layer  of  nerve- 
cells,  and  the  filaments  which  connect  the  rods  and  cones  with  the  cells. 
These  are  the  only  anatomical  elements  of  the  retina,  as  far  as  is  known, 
except  the  pigment  cells,  that  are  directly  concerned  in  the  reception  of 
optical  impressions,  and  they  will  be  described  rather  minutely,  while  the 
intermediate  layers  will  be  considered  more  briefly. 

Most  anatomists  recognize  nine  layers  in  the  retina : 

1.  Layer  of   pigment-cells   (already  described  in  connection  with   the 
choroid). 

2.  Jacob's  membrane,  the  bacillar  membrane,  or  the  layer  of  rods  and 
cones. 

3.  The  external  granule-layer. 

4.  The  inter-granule  layer  (cone-fibre  plexus  of  liulke). 

5.  The  internal  granule-layer. 

6.  The  granular  layer. 

7.  The  layer  of  nerve-cells  (ganglion-layer). 

8.  The  expansion  of  the  fibres  of  the  optic  nerve. 

9.  The  limitary  membrane. 

The  layer  of  rods  and  cones  is  composed  of  rods,  or  cylinders,  extending 
through  its  entire  thickness,  closely  packed,  and  giving  to  the  external  sur- 
face a  regular,  mosaic  appearance ;  and  between  these,  are  a  greater  or  less 
number  of  flask-shaped  bodies,  the  cones.  This  layer  is  about  -^  of  an  inch 
(76  p.)  in  thickness  at  the  middle  of  the  retina ;  j-i^-  of  an  inch  (62  /*),  about 
midway  between  the  centre  and  the  periphery;  and  near  the  periphery, 
about  ^^5-  of  an  inch  (55  /*).  At  the  macula  lutea  the  rods  are  wanting,  and 
the  layer  is  composed  entirely  of  cones,  which  are  here  very  much  elongated. 


682 


SPECIAL  SENSES. 


FIG.  846.— Rods  of  the  retina 

(Schultze). 


Over  the  rest  of  the  membrane  the  rods  predominate,  and  the  cones  be- 
come less  and  less  frequent  toward  the  periphery. 

The  rods  are  regular  cylinders,  their  length  corresponding  to  the  thick- 
ness of  the  layer,  terminating  above  in  truncated  extremities,  and  below  in 
points  which  are  probably  continuous  with  the  filaments  of  connection  with 
the  nerve-cells.  Their  diameter  is  about  13^06  of  an  inch  (2  /x).  They 

are  clear,  of  rather  a  fatty  lustre,  soft  and  plia- 
ble, but  somewhat  brittle,  and  so  alterable  that 
they  are  with  difficulty  seen  in  a  natural  state. 
They  should  be  examined  in  perfectly  fresh  prep- 
arations, moistened  with  liquid  from  the  vitreous 
humor  or  with  serum.  When  perfectly  fresh  it 
is  difficult  to  make  out  any  thing  but  an  entirely 
homogeneous  structure ;  but  shortly  after  death 
each  rod  seems  to  be  divided  by  a  delicate  line 
into  an  outer  and  an  inner  segment,  the  outer 
being  a  little  the  longer.  At  the  upper  extrem- 
ity of  the  inner  segment,  is  a  hemispherical  body, 
with  its  convexity  presenting  inward,  called  the 
lentiform  body  (linsenformiqer  Korper).  The 

From  the  monkey.— A.  Rods,  after  .  J 

maceration  in  iodized  serum,  the   entire  inner  segment  is  somewhat  granular,  and 

outer  segment  (b)  truncated,  the     .  . 

inner  segment  (a)  coagulated,    it  often  presents  a  granular  nucleus  at  its  inner 

granular,   and   somewhat  swol- 
len ;  c,  filament  of  the  rods  ;  d,     extremity, 
nucleus. 

B.  Rods  from  the  frog:  1.  Fresh 
magnified  500  diameters  ;  a.  in 
ner  segment ;  b,  outer  segment 
c,  lentiform  body;  d,  nucleus  •,-,  -,••,  ,  ,.  . -.  , -, 

2  Treated  with  dilute  acetic  acid  with  dilute  acetic  acid,  the  outer  segment  be- 
comes broken  up  transversely  into  thin  disks. 

The  cones  are  probably  of  the  same  constitution  as  the  rods,  but  that 
portion  called  the  inner  segment  is  pyriform.  The  straight  portion  above 
(the  outer  segment)  is  sometimes  called  the  cone-rod.  The  entire  cones  are 
about  half  the  length  of  the  rods  and  occupy  the  inner  portion  of  the  layer. 
The  outer  segment  is  in  its  constitution  precisely  like  the  outer  segment  of 
the  rods.  The  inner  segment  is  slightly  granular  and  contains  a  nucleus. 
The  cones  are  connected  below  with  filaments  passing  into  the  deeper  layers 
of  the  retina.  The  arrangement  of  the  rods  and  cones  is  seen  in  Fig.  247, 
which  shows  the  different  layers  of  the  retina. 

At  the  fovea  centralis,  Jacob's  membrane  is  composed  entirely  of  elon- 
gated cones,  with  no  rods.  These  are  slightly  increased  in  thickness  at  the 
macula  lutea,  but  are  diminished  again  in  thickness,  by  about  one-half,  at  the 
fovea  centralis.  At  the  fovea  the  optic  nerve-fibres  are  wanting ;  and  the 
ganglion-cells,  which  exist  in  a  single  layer  over  other  portions  of  the  retina, 
here  present  six  to  eight  layers,  except  at  the  very  centre,  where  there  are 
but  three  layers.  Of  the  layers  between  the  cones  and  the  ganglion  cells, 
the  external  granule-layer  and  the  inter-granule  layer  (cone-fibre  plexus)  re- 
main, in  the  fovea,  while  the  internal  granule-layer  and  the  granular  layer  are 
wanting.  At  the  fovea,  indeed,  those  elements  of  the  retina  which  may  be 


The  outer  segment  apparently  differs 
in  its  constitution  from  the  inner  segment  and 
is  not  similarly  affected  by  reagents.  Treated 


ANATOMY  OF  THE  KETINA. 


683 


regarded  as  purely  accessory  disappear,  leaving  only  the  structures  that  are 
concerned  directly  in  the  reception  of  visual  impressions. 

The  external  granule-layer  is  composed  of  large  granules,  looking  like 
cells,  which  are  each  nearly  filled  with  a  single  nucleus.  These  are  connected 
with  the  filaments  from  the  rods  and  cones.  They  are  rounded  or  ovoid 
and  measure  from  TT£OTF  to  6o*00  of  an  inch  (2  to  4  /u)  in  diameter.  The 
inter-granule  layer  (cone-fibre  plexus)  is  composed  apparently  of  minute 
fibrillae  and  a  few  nuclei.  The  internal  granule-layer  is  composed  of  cells 
nearly  like  those  of  the  external  granule-layer,  but  a  little  larger,  and  prob- 


FIG.  247.— Vertical  section  of  the  retina       Fio.  848.—  Connection  of  the  rods  and  cones 
(H.  Muller;.  of  the  retina  with  the  nervous  elements 

(Sappey). 

FIG.  247. — 1,  1,  layer  of  rods  and  cones  ;  2,  rods  ;  3,  cones  ;  4,  4,  5,  6,  external  granule-layer  ;  7,  inter- 
granule  layer  (cone-fibre  plexus) ;  8,  internal  granule-layer  ;  9,  10.  finely  granular,  gray  layer  ;  11, 
layer  of  nerve-cells  :  12,  12, 12,  12,  14.  14,  fibres  of  the  optic  nerve  ;  13,  membrana  limitans.  (The  pig- 
mentary layer  is  not  shown  in  this  figure.) 

FIG.  248.— 1.  1,  2,  3,  rods  and  cones,  front  view;  4,  5,  6,  rods,  side  view;  7,  7,  8,  8.  cells  of  the  external  and 
internal  granule-layers  ;  9,  cell,  connected  by  a  filament  with  subjacent  cells  ;  10. 13,  nerve-cells  con- 
nected with  cells  of  the  granule-layers  ;  11,  21,  filaments  connecting  cells  of  the  external  and  internal 
granule-layers  (12  is  not  in  the  figure):  14,  15.  16,  17,  18,  19,  20.  22,  23,  24.  25,  26,  a  rod  and  a  cone,  con- 
nected with  the  cells  of  the  granule-layers,  with  the  nerve-cells  and  with  the  nerve-fibres. 

ably  connected  with  the  filaments  of  the  rods  and  cones.     The  granular 
layer  is  situated  next  the  layer  of  ganglion-cells. 

The  layer  of  ganglion-cells  is  composed  of  multipolar  nerve-cells,  measuring 
ToVrr  to  -^  of  an  inch  (8  to  32  p.)  in  diameter.  In  the  centre  of  the  retina, 
at  the  macula  lutea,  the  cells  present  eight  layers,  and  they  diminish  to  a 
single  layer  near  the  periphery.  The  smaller  cells  are  situated  near  the  cen- 


684  SPECIAL  SENSES. 

tre,  and  the  larger,  near  the  periphery.  Each  cell  sends  off  several  fila- 
ments (two  to  twenty-five),  probably  going  to  the  layer  of  rods  and  cones,  and 
a  single  filament  which  becomes  continuous  with  one  of  the  filaments  of  the 
optic  nerve. 

The  layer  formed  by  the  expansion  of  the  optic  nerve  is  composed  of 
pale,  transparent  nerve-fibres,  -gQ&0o  to  ^Tornr  °^  an  incn  (0'5  to  1  /u.)  in 
diameter.  These  do  not  require  special  description. 

The  limitary  membrane  is  a  delicate  structure,  with  fine  striae  and  nuclei, 
composed  of  connective-tissue  elements.  It  is  about  2S^66  of  an  inch  (1  ft) 
in  thickness.  From  this  membrane,  connective-tissue  elements  are  sent  into 
the  various  layers  of  the  retina,  where  they  form  a  framework  for  the  sup- 
port of  the  other  structures. 

The  retina  becomes  progressively  thinner  from  the  centre  to  the  periphery. 
The  granular  layers  and  the  nervous  layers  rapidly  disappear  in  the  anterior 
half  of  the  membrane. 

The  following  is  the  probable  mode  of  connection  between  the  rods  and 
cones  and  the  ganglion-cells  :  The  filaments  from  the  bases  of  the  rods  and 
cones  pass  inward,  presenting  in  their  course  the  corpuscles  which  have 
been  described  in  the  granule-layers,  and  finally  become,  as  is  thought, 
directly  continuous  with  the  poles  of  the  ganglion-cells.  The  cells  send 
filaments  to  the  layer  formed  by  the  expansion  of  the  optic  nerve,  which 
are  continuous  with  the  nerve-fibres.  This  arrangement  is  shown  in  Fig. 
248. 

The  following  description  of  the  blood-vessels  of  the  retina,  with  Fig. 
249,  was  furnished  by  Loring : 

"  The  arteries  and  veins  of  the  retina  are  subdivisions  of  the  arteria  and 
vena  centralis.  The  larger  branches  run  in  the  nerve-fibre  layer  and  are 
immediately  beneath  the  limitary  membrane.  The  vessels  lie  so  superficially 
that  in  a  cross-section  examined  with  the  microscope,  they  are  seen  to  pro- 
ject above  the  general  level  of  the  retina,  toward  the  vitreous  humor.  While 
the  large  vessels  are  in  the  plane  of  the  inner  surface  of  the  retina,  the 
smaller  branches  penetrate  the  substance  of  the  retina,  to  the  inter-granule 
layer.  They  do  not  extend,  however,  as  far  as  the  external  granule-layer 
and  the  layer  of  rods  and  cones.  These  two  layers,  therefore,  have  no  blood- 
vessels. 

"  The  ramifications  of  the  vessels  present  a  beautifully  arborescent  appear- 
ance when  seen  with  the  ophthalmoscope.  The  manner  in  which  the  vessels 
are  distributed  and  the  way  in  which  the  circulation  is  carried  on  can  be 
better  understood  by  a  study  of  Fig.  249  than  by  any  detailed  description. 
The  figure  represents  the  ophthalmoscopic  appearance  of  a  normal  eye  in 
young,  adult  life.  The  darker  vessels  are  the  veins,  and  the  lighter  vessels, 
the  arteries.  The  dotted  oval  line  is  diagrammatic  and  marks  the  position 
and  extent  of  the  macula  lutea.  It  is  seen  that  this  oval  space  contains  a 
number  of  fine  vascular  twigs  which,  coming  from  above  and  below,  extend 
toward  the  spot  in  the  centre  of  the  oval  which  marks  the  position  of  the 
fovea  centralis.  In  opposition,  then,  to  the  general  opinion,  which  is  that 


CRYSTALLINE  LENS. 


685 


the  macula  lutea  has  no  blood-vessels,  it  is  the  spot  of  all  others  in  the  retina 
which  is  most  abundantly  supplied  with  minute  vascular  branches.  These 
vessels  can  be  dis- 
tinctly seen  even 
with  the  ophthal- 
moscope ;  and  mi- 
croscopical exam- 
ination shows  that 
the  capillary  plex- 
us in  the  macula 
lutea  is  closer  and 
richer  than  in  any 
other  part  of  the 
retina." 

The  arteries  of 
the  retina  send 
branches  to  the 
periphery,  where 
they  supply  a  wide 
plexus  of  very 
small  capillaries  in 
the  ora  serrata- 
These  capillaries 
empty  into  an  in- 
complete venous 

circle,  branches  from  which  pass  back  by  the  sides  of  the  arteries,  to  the  vena 
centralis. 

Crystalline  Lens. — The  crystalline  is  a  double-convex  lens,  which  is  per- 
fectly transparent  and  very  elastic.  Its  action  in  the  refraction  of  the  rays 
of  light  is  analogous  to  that  of  convex  lenses  in  optical  instruments.  It  is 
situated  behind  the  pupil,  in  what  is  called  the  hyaloid  fossa  of  the  vitreous 
humor,  which  is  exactly  moulded  to  its  posterior  convexity.  In  the  foetus 
the  capsule  of  the  lens  receives  a  branch  from  the  arteria  centralis,  but  it  is 
non-vascular  in  the  adult.  The  anterior  convexity  of  the  lens  is  just  behind 
the  iris,  and  its  borders  are  in  relation  with  what  is  known  as  the  suspensory 
ligament.  The  convexities  do  not  present  regular  curves,  and  they  are  so 
subject  to  variations  after  death  that  the  measurements,  post  mortem,  are  of 
little  value.  During  life,  however,  they  have  been  measured  very  exactly  in 
the  various  conditions  of  accommodation.  The  diameters  of  the  lens  in  the 
adult  are  about  ^  of  an  inch  (8'5  mm.)  transversely  and  \  of  an  inch  (6'4  mm.) 
antero-posteriorly.  The  convexity  is  greater  on  its  posterior  than  on  its 
anterior  surface.  In  foetal  life  the  convexities  of  the  lens  are  greater  than 
in  the  adult  and  its  structure  is  much  softer.  In  old  age  the  convexities 
are  diminished  and  the  lens  becomes  harder  and  less  elastic.  The  substance 
of  the  lens  is  made  up  of  layers  of  fibres  of  different  degrees  of  density,  and 
the  whole  is  enveloped  in  a  delicate  membrane,  called  the  capsule. 

45 


Fio.  249.— Blood-vessels  of  the  retina ;  magnified  7J  diameters  (Loring). 


686 


SPECIAL  SENSES. 


FIG.  230.  —  Crystalline  lens  :  anterior  view  (Babuehin). 


The  capsule  of  the  lens  is  a  thin,  transparent  membrane,  which  is  very 
elastic.     This  membrane  generally  is  from  ^Vff  to  yrVtr  °f  an  inch  (10  to 

17  /A)  thick;  but  it  is  very 
thin  at  the  periphery,  meas- 
uring here  only  ^jVo-  of  an 
inch  (4  /A).  Its  thickness  is 
increased  in  old  age.  The 
anterior  portion  of  the  cap- 
sule is  lined  on  its  inner  sur- 
face with  a  layer  of  exceed- 
ingly delicate,  nucleated  epi- 
thelial cells.  The  posterior 
half  of  the  capsule  has  no 
epithelial  lining.  The  cells 
are  regularly  polygonal, 
measuring  -^  to  y^T  of 
an  inch  (12  to  20  //.)  in  di- 
ameter, with  large,  round 
nuclei.  After  death,  they 
are  said  to  break  down  into 

,.       .  ,    ,  .,       ,  .       .  , 

a  liquid,  known  as  the  liquid 
of  Morgagni,  though  by  some  this  liquid  is  supposed  to  be  exuded  from  the 
substance  of  the  lens.  At  all  events,  the  cells  disappear  soon  after  death. 

If  the  lens  be  viewed  entire  with  a  low 
magnifying  power,  it  presents  upon  either  of 
its  surfaces,  a  star  with  nine  to  sixteen  radi- 
ations extending  from  the  centre  to  about 
half  or  two-thirds  of  the  distance  to  the  pe- 
riphery. The  stars  seen  upon  the  two  surfaces 
are  not  coincident,  the  rays  of  one  being  situ- 
ated between  the  rays  of  the  other.  In  the 
foetus  the  stars  are  more  simple,  presenting 
only  three  radiations  upon  either  surface. 
These  stars  are  not  fibrous,  like  the  rest  of 
the  lens,  but  are  composed  of  a  homogeneous 
substance,  which  extends,  also,  between  the 
fibres. 

The  greatest  part  of  the  substance  of  the 
lens  is  composed  of  very  delicate,  soft  and  plia- 
ble fibres,  which  are  transparent,  but  perfect- 
ly distinct.  These  fibres  are  flattened,  six- 
sided  prisms,  closely  packed  together,  so  that 
their  transverse  section  presents  a  regularly 
tesselated  appearance.  They  are  -g-g^ff  to  ^^r 
and  i  3  \  6  6  to  -g-gVg-  of  an  inch  (2  to  3  ^ 
parallel  with  the  surface  of  the  lens. 


FlG-  m-- 


*  lens 


an  incn  (5  to  10  /x)  broad, 
in  thickness.  Their  flat  surfaces  are 
The  direction  of  the  fibres  is  from 


CRYSTALLINE  LENS.  687 

the  centre  and  from  the  rays  of  the  stellate  figures  to  the  periphery,  where 
they  turn  and  pass  to  the  star  upon  the  opposite  side.  The  outer  layers  of 
fibres  near  the  equator,  or  circumference  of  the  lens,  contain  exceedingly 
distinct,  oval  nuclei,  with  one  or  two  nucleoli.  These  become  smaller  in 
passing  more  deeply  into  the  substance  of  the  lens,  and  gradually  they  dis- 
appear. 

The  regular  arrangement  of  the  fibres  of  the  lens  makes  it  possible  to 
separate  its  substance  into  laminae,  which  have  been  compared  by  anatomists 
to  the  layers  of  an  onion  ;  but  this  separation  is  entirely  artificial,  and  the 
number  of  apparent  layers  depends  upon  the  dexterity  of  the  manipulator. 
It  is  to  be  noted,  however,  that  the  external  portions  of  the  lens  are  soft, 
even  gelatinous,  and  that  the  central  layers  are  much  harder,  forming  a  sort 
of  central  kernel,  or  nucleus. 

The  lens  is  composed  of  a  nitrogenized  substance,  called  crystalline,  com- 
bined with  various  inorganic  salts.  One  of  the  constant  constituents  of  this 
body  is  cholesterine.  In  an  examination  of  four  fresh 
crystalline  lenses  of  the  ox,  cholesterine  was  found  in  the 
proportion  of  0*907  of  a  part  per  1,000  (Flint).  In  some 
cases  of  cataract  cholesterine  exists  in  the  lens  in  a  crys- 
talline form  ;  but  under  normal  conditions  it  is  united 
with  the  other  constituents. 

Suspensory  Ligament  of  the  Lens  (Zone  of  Zinn}.  — 
The  vitreous  humor  occupies  about  the  posterior  two-  FIG.  252.—  zone  ofzinn 
thirds  of  the  globe,  and  is  enveloped  in  a  delicate  capsule,  lt  crystainnMens  ;  2,  2, 


called  the  hyaloid  membrane.     In  the  region  of  the  ora 

serrata  of  the  retina,  this  membrane  divides  into  two 

layers.     The  posterior  layer  lines  the  depression  in  the     terfor'and  middle  por- 

vitreous  humor  into  which  the  lens  is  received.     The  an-     t1?"8  of  the  zone  of 

^uim. 

terior  layer  passes  forward  toward  the  lens  and  divides  into 
two  secondary  layers,  one  of  which  passes  forward,  to  become  continuous  with 
the  anterior  portion  of  the  capsule  of  the  lens,  while  the  other  passes  to  the  pos- 
terior surface  of  the  lens,  to  become  continuous  with  this  portion  of  its  capsule. 
The  anterior  of  these  layers  is  corrugated  or  thrown  into  folds  which  correspond 
with  the  ciliary  processes,  with  which  it  is  in  contact.  This  corrugated  portion 
is  called  the  zone  of  Zinn.  The  two  layers  thus  surround  the  lens  and  are 
properly  called  its  suspensory  ligament.  As  the  two  layers  of  the  suspensory 
ligament  separate  at  a  certain  distance  from  the  lens,  one  passing  to  the  ante- 
rior and  the  other  to  the  posterior  portion  of  the  capsule,  there  remains  a 
triangular  canal,  about  ^  of  an  inch  (2'5  mm.)  wide,  surrounding  the  border 
of  the  lens,  called  the  canal  of  Petit.  Under  natural  conditions  the  walls  of 
this  canal  are  nearly  in  apposition,  and  it  contains  a  very  small  quantity  of 
clear  liquid. 

The  membrane  forming  the  suspensory  ligament  is  composed  of  pale,  lon- 
gitudinal and  transverse  fibres  of  rather  a  peculiar  appearance,  which  are 
much  less  affected  by  acetic  acid  than  the  ordinary  fibres  of  connective  tissue. 

Aqueous  Humor.  —  The  space  bounded  in  front  by  the  cornea,  posteriorly, 


688  SPECIAL  SENSES. 

by  the  crystalline  lens  and  the  anterior  face  of  its  suspensory  ligament,  and 
at  its  circumference,  by  the  tips  of  the  ciliary  processes,  is  known  as  the  aque- 
ous chamber.  This  contains  a  clear  liquid  called  the  aqueous  humor.  The 
iris  separates  this  space  into  two  divisions,  which  communicate  with  each 
other  through  the  pupil ;  viz.,  the  anterior  chamber,  situated  between  the 
anterior  face  of  the  iris  and  the  cornea,  and  the  posterior  chamber,  between 
the  posterior  face  of  the  iris  and  the  crystalline.  It  is  evident,  from  the  posi- 
tion of  the  iris,  that  the  anterior  chamber  is  much  the  larger ;  and,  indeed, 
the  posterior  surface  of  the  iris  and  the  anterior  surface  of  the  lens  are  in 
contact,  except,  perhaps,  near  their  periphery  or  when  the  iris  is  very  much 
dilated.  The  liquid  filling  the  chambers  of  the  eye  is  rapidly  reproduced 
after  it  has  been  evacuated,  as  occurs  in  many  surgical  operations  upon 
the  eye. 

The  aqueous  humor  is  colorless  and  transparent,  faintly  alkaline,  of  a 
specific  gravity  of  about  1005,  and  with  the  same  index  of  refraction  as  that 
of  the  cornea  and  the  vitreous  humor.  It  contains  a  small  quantity  of  an 
albuminoid  matter,  but  it  is  not  rendered  turbid  by  heat  or  other  agents 
which  coagulate  albumen.  Various  inorganic  salts  (the  chlorides,  sulphates, 
phosphates  and  carbonates)  exist  in  small  proportions  in  this  liquid.  It  also 
contains  traces  of  urea  and  glucose. 

The  anterior  and  posterior  chambers  of  the  eye  are  regarded  as  lymph- 
spaces  communicating  with  the  lymphatics  of  the  conjunctiva,  cornea,  iris 
and  ciliary  processes.  In  addition  a  lymph-space  is  described  as  existing  be- 
tween the  choroid  and  the  sclerotic.  This  space  is  supposed  to  communicate 
with  a  perivascular  canal-system  around  the  vasa  vorticosa,  and  through  these 
vessels,  with  the  space  between  the  capsule  of  Tenon  and  the  sclerotic 
(Schwalbe).  The  latter  is  connected  with  lymph-channels  which  surround 
the  optic  nerve  (Key  and  Retzius). 

Vitreous  Humor. — The  vitreous  humor  is  a  clear,  glassy  substance,  occupy- 
ing about  the  posterior  two-thirds  of  the  globe.  It  is  enveloped  in  a  delicate, 
structureless  capsule,  called  the  hyaloid  membrane,  which  is  about  ^-^Vo  of 
an  inch  (4  /*)  in  thickness.  This  membrane  adheres  rather  strongly  to  the 
limitary  membrane  of  the  retina.  In  front,  at  the  ora  serrata,  the  hyaloid 
membrane  is  thickened  and  becomes  continuous  with  the  suspensory  ligament 
of  the  lens. 

The  vitreous  humor  itself  is  gelatinous,  of  feeble  consistence  and  slightly 
alkaline  in  its  reaction,  with  a  specific  gravity  of  about  1005.  Upon  section 
there  oozes  from  it  a  watery  and  slightly  mucilaginous  liquid.  This  humor 
is  not  affected  by  heat  or  alcohol,  but  it  is  coagulated  by  certain  mineral 
salts,  especially  lead  acetate.  When  thus  solidified  it  presents  regular  layers, 
like  the  white  of  an  egg  boiled  in  its  shell ;  but  these  are  artificial.  In  the 
embryon  the  vitreous  humor  is  divided  into  a  number  of  little  cavities  and 
contains  cells  and  leucocytes.  It  is  also  penetrated  by  a  branch  from  the 
central  artery  of  the  retina,  which  passes  through  its  centre,  to  ramify  upon 
the  posterior  surface  of  the  crystalline  lens.  This  structure,  however,  is  not 
found  in  the  adult,  the  vitreous  humor  being  then  entirely  without  blood- 


SUMMAEY  OF  THE  ANATOMY  OF  THE  EYE. 


689 


vessels.  The  vitreous  humor  is  divided  into  compartments  formed  by  deli- 
cate membranes  radiating  from  the  point  of  penetration  of  the  optic  nerve 
to  the  anterior  boundary  where  the  hyaloid  membrane  is  in  contact  with  the 
capsule  of  the  lens.  In  this  way  the  humor  is  divided  up,  something  like 
the  half  of  an  orange,  by  about  one  hundred  and  eighty  membranous  pro- 
cesses of  extreme  delicacy,  which  do  not  interfere  with  its  transparency. 

SUMMARY  or  THE  ANATOMY  OF  THE  GLOBE  OF  THE  EYE. 

This  summary  is  intended  simply  to  indicate  the  relations  and  the  physio- 
logical importance  of  the  various  parts  of  the  eye,  in  connection  with  Fig. 
253. 

The  eyeball  is  nearly  spherical  in  its  posterior  five-sixths,  its  anterior  sixth 


SUPERIOR  RECTUS 


CHOROID 


OPTIC  NERVE 


CHOROID 


•-INFERIOR  RECTUS 
FIG.  253.—  Section  of  the  human  eye. 

being  formed  of  the  segment  of  a  smaller  sphere,  which  is  slightly  projecting. 
It  presents  the  following  parts,  indicated  in  the  figure. 

The  sclerotic ;  a  dense,  fibrous  membrane,  chiefly  for  the  protection  of 
the  more  delicate  structures  of  the  globe,  and  giving  attachment  to  the  mus- 
cles which  move  the  eyeball.  Attached  to  the  sclerotic  are  the  tendons  of 
the  recti  and  the  oblique  muscles. 

The  cornea;  a  transparent  structure,  forming  the  anterior,  projecting 
sixth  of  the  globe ;  dense  and  resisting,  allowing,  however,  the  passage  of 
light ;  covered,  on  its  convex  surface,  with  several  layers  of  transparent  epi- 
thelial cells. 

The  choroid  coat ;  lining  the  sclerotic  and  extending  only  as  far  forward 


690  SPECIAL  SENSES. 

as  the  cornea ;  connected  with  the  sclerotic  by  loose,  connective  tissue,  in 
which  ramify  blood-vessels  and  nerves,  and  presenting  an  external,  vascular 
layer  and  an  internal,  pigmentary  layer,  which  latter  gives  its  characteristic 
dark-brown  color. 

The  ciliary  processes ;  peculiar  folds  of  the  choroid,  which  form  its  ante- 
rior border  and  which  embrace  the  folds  of  the  suspensory  ligament  of  the 
lens. 

The  ciliary  muscle ;  situated  just  outside  of  the  ciliary  processes,  arising 
from  the  circular  line  of  junction  of  the  sclerotic  with  the  cornea,  passing 
over  the  ciliary  processes,  and  becoming  continuous  with  the  fibrous  tissue  of 
the  choroid.  The  action  of  this  muscle  is  to  tighten  the  choroid  over  the 
vitreous  humor  and  to  relax  the  ciliary  processes  and  the  suspensory  ligament 
of  the  lens,  when  the  lens,  by  virtue  of  its  elasticity,  becomes  more  convex. 
This  action  is  shown  by  the  dotted  lines  in  the  figure. 

The  iris ;  dividing  the  space  in  front  of  the  lens  into  two  chambers  occu- 
pied by  the  aqueous  humor.  The  anterior  chamber  is  much  the  larger. 
The  iris,  in  its  central  portion  surrounding  the  pupil,  is  in  contact  with  the 
lens.  Its  circumference  is  just  in  front  of  the  line  of  origin  of  the  ciliary 
muscle. 

The  retina ;  a  delicate,  transparent  membrane,  lining  the  choroid  and  ex- 
tending to  about  ^  of  an  inch  (!•?  mm.)  behind  the  ciliary  processes,  the 
anterior  margin  forming  the  ora  serrata.  The  optic  nerve  penetrates  the 
retina  a  little  internal  to  and  below  the  antero-posterior  axis  of  the  globe. 
The  layer  of  rods  and  cones  is  situated  next  the  pigmentary  layer,  which  is 
external.  Internal  to  the  layer  of  rods  and  cones,  are  the  four  granular  lay- 
ers ;  next,  the  layer  of  nerve-cells ;  next,  the  expansion  of  the  fibres  of  the 
optic  nerve ;  and  next,  in  apposition  with  the  hyaloid  membrane  of  the  vitre- 
ous humor,  is  the  limitary  membrane. 

The  crystalline  lens;  elastic,  transparent,  enveloped  in  its  capsule  and 
surrounded  by  the  suspensory  ligament. 

The  suspensory  ligament ;  the  anterior  layer  connected  with  the  anterior 
portion  of  the  capsule  of  the  lens,  and  the  posterior,  with  the  posterior  portion 
of  the  capsule.  The  folded  portion  of  this  ligament,  which  is  received  be- 
tween the  folds  of  the  ciliary  processes,  is  called  the  zone  of  Zinn.  The  tri- 
angular canal  between  the  anterior  and  the  posterior  layers  of  the  suspen- 
sory ligament  and  surrounding  the  equator  of  the  lens  is  called  the  canal  of 
Petit. 

The  vitreous  humor ;  enveloped  in  the  hyaloid  membrane,  which  mem- 
brane is  continuous  in  front,  with  the  suspensory  ligament  of  the  lens. 

KEFKACTION  IN  THE  EYE. 

In  applying  some  of  the  elementary  laws  of  refraction  of  light  to  the 
transparent  media  of  the  eye,  it  is  necessary  to  bear  in  mind  certain  general 
facts  with  regard  to  vision,  that  have  as  yet  been  referred  to  either  very  briefly 
or  not  at  all. 

The  eye  is  not  a  perfect  optical  instrument,  looking  at  it  from  a  purely 


REFEACTION  IN  THE  EYE.  691 

physical  point  of  view.  This  statement,  however,  should  not  be  understood 
as  implying  that  the  arrangement  of  the  parts  is  not  such  as  to  adapt  them 
perfectly  to  their  uses  in  connection  with  the  proper  appreciation  of  visual 
impressions.  By  physical  tests  it  can  be  demonstrated  that  the  eye  is  not 
entirely  achromatic ;  but  in  ordinary  vision  the  dispersion  of  colors  is  not 
appreciated.  There  is  but  a  single  point  in  the  retina,  the  fovea  centralis, 
where  vision  is  absolutely  distinct ;  and  it  is  upon  this  point  that  images  are 
made  to  fall  when  the  eye  is  directed  toward  any  particular  object. 

The  refracting  apparatus  is  not  exactly  centred,  a  condition  so  essential 
to  the  satisfactory  performance  of  perfect  optical  instruments.  For  example, 
in  a  compound  microscope  or  a  telescope,  the  centres  of  the  different  lenses 
entering  into  the  construction  of  the  instrument  are  all  situated  in  a  straight 
line.  Were  the  eye  a  perfect  optical  instrument,  the  line  of  vision  would 
coincide  exactly  with  the  axis  of  the  cornea ;  but  this  is  not  the  case.  The 
visual  line — a  line  drawn  from  an  object  to  its  image  on  the  fovea  centralis — 
deviates  from  the  axis  of  the  cornea,  in  normal  eyes,  to  the  nasal  side.  The 
visual  line,  therefore,  forms  an  angle  with  the  axis  of  the  cornea.  This  is 
known  as  the  angle  alpha.  This  deviation  of  the  visual  line  from  the  mathe- 
matical centre  of  the  eye  is  observed  both  in  the  horizontal  and  in  the  verti- 
cal planes.  The  horizontal  deviation  varies  by  two  to*  eight  degrees  (Schuer- 
man),  and  the  vertical,  by  one  to  three  degrees  (Mandelstamm).  Of  course 
this  want  of  exact  centring  of  the  optical  apparatus,,  in  normal  eyes,  does 
not  practically  affect  distinct  vision ;  for  when  the  eyes  are  directed  toward 
any  object,  this  object  is  brought  in  the  line  of  the  visual  axis ;  but  the  angle 
apha  is  an  important  element  to  be  taken  into  account  in  various  mathemati- 
cal calculations  connected  with  the  physics  of  the  eye. 

The  area  of  distinct  vision  is  quite  restricted ;  but  were  it  larger,  it  is 
probable  that  the  mind  would  become  confused  by  the  extent  and  variety  of 
the  impressions,  and  that  it  would  not  be  so  easy  to  observe  minute  details 
and  fix  the  attention  upon  small  objects. 

Although  certain  objects  are  seen  with  absolute  distinctness  only  in  a  re- 
stricted field,  the  angle  of  vision  is  very  wide,  and  rays  of  light  are  admitted 
from  an  area  equal  to  nearly  the  half  of  a  sphere.  Such  a  provision  is  emi- 
nently adapted  to  visual  requirements.  The  eyes  are  directed  to  a  particular 
point  and  a  certain  object  is  seen  distinctly,  with  the  advantage  of  an  image 
in  the  two  eyes,  exactly  at  the  points  of  distinct  vision ;  the  rays  coming  from 
without  the  area  of  distinct  vision  are  received  upon  different  portions  of  the 
surface  of  the  retina  and  produce  an  impression  more  or  less  indistinct,  not 
interfering  with  the  observation  of  the  particular  object  to  which  the  atten- 
tion is  for  the  moment  directed ;  but  even  while  looking  intently  at  any  ob- 
ject, the  attention  may  be  attracted  by  another  object  of  an  unusual  character, 
which  might,  for  example,  convey  an  idea  of  danger,  and  the  point  of  distinct 
vision  can  be  turned  in  its  direction.  Thus,  while  but  few  objects  are  seen 
distinctly  at  one  time,  the  area  of  indistinct  vision  is  very  large ;  and  the  at- 
tention may  readily  be  directed  to  unexpected  or  unusual  objects  that  come 
within  any  portion  of  the  field  of  view.  The  small  extent  of  the  area  of  dis- 


692  SPECIAL  SENSES. 

tinct  vision,  especially  for  near  objects,  may  readily  be  appreciated  in  watch- 
ing a  person  who  is  attentively  reading  a  book,  when  the  eyes  will  be  seen  to 
follow  the  lines  from  one  side  of  the  page  to  the  other  with  perfect  regular- 
ity. When  it  is  considered  that  in  addition  to  these  qualities,  which  are  not 
possible  in  artificial  optical  instruments,  the  eye  may  be  accommodated  at 
will  to  vision  at  different  distances,  and  that  there  is  correct  appreciation  of 
form,  etc.,  by  the  use  of  the  two  eyes,  it  is  evident  that  the  visual  organ  gains 
rather  than  loses  in  comparison  with  the  most  perfect  instruments  that  have 
been  constructed. 

Certain  Laws  of  Refraction,  Dispersion  etc.,  bearing  upon  the  Physiology 
of  Vision. — Physiologists  have  little  to  do  with  the  theory  of  light,  except  as 
regards  the  modifications  of  luminous  rays  in  passing  through  the  refracting 
media  of  the  eye.  It  will  be  sufficient  to  state  that  nearly  all  physicists  of 
the  present  day  agree  in  accepting  what  is  known  as  the  theory  of  undula- 
tion, rejecting  the  emission- theory  proposed  by  Newton.  It  is  necessary  to 
the  theory  of  undulation  to  assume  that  all  space  and  all  transparent  bodies 
are  permeated  with  what  has  been  called  a  luminiferous  ether ;  and  that  light 
is  propagated  by  a  vibration  or  an  undulation  of  this  hypothetical  substance. 
This  theory  assimilates  light  to  sound,  in  the  mechanism  of  its  propagation ; 
but  in  sound  the  waves  are  supposed  to  be  longitudinal,  or  to  follow  the  line 
of  propagation,  while  in  light  the  particles  are  supposed  to  vibrate  trans- 
versely, or  at  right  angles  to  the  line  of  propagation.  It  must  be  remem- 
bered, however,  that  the  undulatory  theory  of  sound  is  capable  of  positive 
demonstration,  and  that  the  propagation  of  sound  by  waves  can  take  place 
only  through  ponderable  matter,  the  vibrations  of  which  can  always  be  ob- 
served ;  but  the  theory  of  luminous  vibrations  involves  the  existence  of  an 
hypothetical  ether.  It  is  possible,  indeed,  that  scientific  facts  may  in  the 
future  render  the  existence  of  such  an  ether  improbable  or  its  supposition 
unnecessary;  but  at  present  the  theory  of  luminous  undulation  seems  to 
be  in  accord  with  the  optical  phenomena  that  have  thus  far  been  rec- 
ognized. 

The  different  calculations  of  physicists  with  regard  to  the  velocity  of  light 
have  been  remarkably  uniform  in  their  results.  The  lowest  calculations  put 
it  at  about  185,000  miles  (297,725  kilometres)  in  a  second,  and  the  highest, 
at  about  195,000  miles  (313,818  kilometres).  The  rate  of  propagation  is 
usually  assumed  to  be  about  192,000  miles  (309,000  kilometres). 

The  intensity  of  light  is  in  proportion  to  the  amplitude  of  the  vibrations. 
The  intensity  diminishes  as  the  distance  of  the  luminous  body  increases,  and 
is  in  inverse  ratio  to  the  square  of  the  distance. 

In  the  theory  of  the  colors  into  which  pure  white  light  may  be  decom- 
posed by  prisms,  it  is  assumed  to  be  a  matter  of  demonstration  that  the 
waves  of  the  different  colors  of  the  solar  spectrum  are  not  of  the  same  length. 
The  decomposition  of  light  is  produced  by  differences  in  the  refrangibility 
of  the  different  colored  rays  as  they  pass  through  a  medium  denser  than  the 
air. 

The  analysis  of  white  light  into  the  different  colors  of  the  spectrum  shows 


REFRACTION  IN  THE  EYE.  693 

that  it  is  compound ;  and  by  synthesis,  the  colored  rays  may  be  brought  to- 
gether, producing  white  light.  Colors  may  be  obtained  by  decomposition  of 
light  by  transparent  bodies,  the  different  colored  rays  being  refracted,  or  bent, 
by  a  prism,  at  different  angles.  It  is  not  in  this  way,  however,  that  the  colors 
of  different  objects  are  produced.  Certain  objects  have  the  property  of  re- 
flecting the  rays  of  light.  A  perfectly  smooth,  polished  surface,  like  a  mir- 
ror, may  reflect  all  of  the  rays ;  and  the  object  then  has  no  color,  only  the  re- 
flected light  being  appreciated  by  the  eye.  Certain  other  objects  do  not  reflect 
all  of  the  rays  of  light,  some  of  them  being  lost  to  view,  or  absorbed.  When 
an  object  absorbs  all  of  the  rays,  it  has  no  color  and  is  called  black.  When 
an  object  absorbs  the  rays  equally  and  reflects  a  portion  of  these  rays  without 
decomposition,  it  is  gray  or  white.  There  are  many  objects,  however,  that 
decompose  white  light,  absorbing  certain  rays  of  the  spectrum  and  reflecting 
others.  The  rays  not  absorbed,  but  returned  to  the  eye  by  reflection,  give 
color  to  the  object.  Thus,  if  an  object  absorb  all  of  the  rays  of  the  spectrum 
except  the  red,  the  red  rays  strike  the  eye,  and  the  color  of  the  object  is  red. 
So  it  is  with  objects  of  different  shades,  the  colors  of  which  are  given  simply 
by  the  unabsorbed  rays. 

A  mixture  of  different  colors  in  certain  proportions  will  result  in  white. 
Two  colors,  which,  when  mixed,  result  in  white,  are  called  complementary. 
The  following  colors  of  the  spectrum  bear  such  a  relation  to  each  other :  Ked 
and  greenish-blue ;  orange  and  cyanogen-blue ;  yellow  and  indigo-blue ; 
greenish-yellow  and  violet. 

The  fact  that  impressions  made  upon  the  retina  persist  for  an  appreciable 
length  of  time  affords  an  illustration  of  the  law  of  complementary  colors.  If 
a  disk,  presenting  divisions  with  two  complementary  colors,  be  made  to 
revolve  so  rapidly  that  the  impressions  made  by  the  two  colors  are  blended, 
the  resulting  color  is  white. 

Refraction  by  Lenses. — A  ray  of  light  is  an  imaginary  pencil,  so  small  as 
to  present  but  a  single  line ;  and  the  light  admitted  to  the  interior  of  the  eye 
by  the  pupil  is  supposed  to  consist  of  an  infinite  number  of  such  rays.  In 
studying  the  physiology  of  vision,  it  is  important  to  recognize  the  laws  of  re- 
fraction of  rays  by  transparent  bodies  bounded  by  curved  surfaces,  with  par- 
ticular reference  to  the  action  of  the  crystalline  lens. 

The  action  of  a  double-convex  lens,  like  the  crystalline,  in  the  refraction 
of  light,  may  readily  be  understood  by  a  "simple  application  of  the  well  known 
laws  of  refraction  by  prisms.  A  ray  of  light  falling  upon  the  side  of  a  prism 
at  an  angle  is  deviated  toward  a  line  perpendicular  to  the  surface  of  the  prism. 
As  the  ray  passes  from  the  prism  to  the  air,  it  is  again  refracted,  but  the  de- 
viation is  then  from  the  perpendicular  of  the  second  surface  of  the  prism. 
In  passing  through  a  prism,  therefore,  the  pencil  of  light  is  bent,  or  refracted, 
toward  the  base. 

A  circle  is  equivalent  to  a  polygon  with  an  infinite  number  of  sides.  A 
regular,  double-convex  lens  is  a  transparent  body  bounded  by  segments  of  a 
sphere.  Theoretically  a  double-convex  lens  may  be  assumed  to  be  composed 
of  an  infinite  number  of  sections  of  prisms  (Fig.  254, 1.),  or  to  make  the  com- 


694 


SPECIAL  SENSES. 


parison  with  prisms  more  striking,  although  less  accurate,  the  lens  may  be 
assumed  to  be  composed  of  prisms  (Fig.  254,  II.,  Weinhold). 

If  these  prisms  or  sections  of  prisms  be  infinitely  small,  so  that  the  sur- 
face of  each  receives  but  a  single  infinitely  small  pencil  of  light,  these  pencils 
will  be  refracted  toward  the  bases  of  the  prisms,  and  different  rays  of  light 
from  all  points  of  an  object  may  be  brought  to  an  infinite  number  of  foci,  all 
these  foci,  for  a  plane  object,  being  in  the  same  plane.  If  the  number  of 
sections  be  equal  on  every  side  of  the  centre  of  the  lens,  the  bases  looking 
toward  the  axis  of  the  lens,  the  rays  of  light  will  cross  at  a  certain  point,  and 
the  image  formed  by  the  lens  will  be  inverted.  This  is  illustrated  in  Fig. 


II 


FIG.  254.— Refraction  by  convex  lenses. 


254,  which  represents  a  section  of  a  lens  theoretically  dissected  into  six  sec- 
tions of  prisms. 

If  the  lens  A  B  (Fig.  254)  be  assumed  to  be  free  from  what  is  known  as 
spherical  aberration,  the  rays  from  the  point  C  will  be  refracted,  and  brought 
to  a  focus  at  the  point  D.  In  the  same  way  the  rays  from  E  will  be  brought 
to  a  focus  at  F,  the  two  sets  of  rays  crossing  before  they  reach  their  focal 
points.  The  same  is  true  for  all  the  rays  from  every  point  in  the  image  C  E, 
which  strike  the  lens  at  an  angle,  but  the  ray  G-  H,  which  is  perpendicular  to 
the  lens,  is  not  deviated.  The  rays  of  light  are  refracted  in  this  way  by  the 
cornea  and  by  the  crystalline  lens.  The  retina  is  normally  at  such  a  distance 
from  the  lens  that  the  rays  are  brought  to  a  focus  exactly  at  its  surface.  In- 
asmuch as  the  rays  cross  each  other  before  they  reach  the  retina,  the  image 
is  always  inverted. 

Supposing  the  crystalline  lens  to  be  free  from  spherical  and  chromatic 
aberration,  the  formation  of  a  perfect  image  depends  upon  the  following  con- 
ditions : 

The  object  must  be  at  a  certain  distance  from  the  lens.  If  the  object  be 
too  near,  the  rays,  as  they  strike  the  lens,  are  too  divergent  and  are  brought 
to  a  focus  beyond  the  plane  F  II  D,  or  behind  the  retina ;  and  as  a  conse- 
quence the  image  is  confused.  In  optical  instruments  the  adjustment  is 
made  for  objects  at  different  distances  by  moving  the  lens  itself.  In  the  eye, 


KEFRACTION  IN  THE  EYE.  695 

however,  the  adjustment  is  effected  by  increasing  or  diminishing  the  curva- 
tures of  the  lens,  so  that  the  rays  are  always  brought  to  a  focus  at  the  visual 
surface  of  the  retina.  The  faculty  of  thus  changing  the  curvatures  of  the 
crystalline  lens  is  called  accommodation.  This  power,  however,  is  restricted 
within  certain  well  defined  limits. 

In  some  individuals  the  antero-posterior  diameter  of  the  eye  is  too  long, 
and  the  rays,  for  most  objects,  come  to  a  focus  before  they  reach  the  retina. 
This  defect  may  be  remedied  by  placing  the  object  very  near  the  eye,  so  as 
to  increase  the  divergence  of  the  rays  as  they  strike  the  crystalline.  Such 
persons  are  said  to  be  near-sighted  (myopic),  and  objects  are  seen  distinctly, 
only  when  very  near  the  eye.  This  defect  may  be  remedied  for  distant  ob- 
jects, by  placing  concave  lenses  before  the  eyes,  by  which  the  rays  falling 
upon  the  crystalline  are  diverged.  The  opposite  condition,  in  which  the 
antero-posterior  diameter  is  too  short  (hypermetropia),  is  such  that  the  rays 
are  brought  to  a  focus  behind  the  retina.  This  is  corrected  by  converging 
the  rays  of  incidence,  by  placing  convex  lenses  before  the  eyes.  In  old  age 
the  crystalline  lens  becomes  flattened,  its  elasticity  is  diminished  and  the 
power  of  accommodation  is  lessened ;  conditions  which  also  tend  to  bring  the 
rays  to  a  focus  behind  the  retina.  This  condition  is  called  presbyopia.  To 
render  near  vision — as  in  reading — distinct,  objects  are  placed  farther  from 
the  eye  than  under  normal  conditions.  The  defect  may  be  remedied,  as  in 
hypermetropia,  by  placing  convex  lenses  before  the  eyes,  by  which  the  rays 
are  converged  before  they  fall  upon  the  crystalline  lens. 

The  mechanism  of  accommodation  will  be  fully  considered  in  connection 
with  the  physiology  of  the  crystalline  lens ;  and  at  present  it  is  sufficient  to 
state  that  in  looking  at  distant  objects,  the  rays  as  they  fall  upon  the  lens 
are  nearly  parallel.  The  lens  is  then  in  repose,  or  "  indolent."  It  is  only 
when  an  effort  is  made  to  see  near  objects  distinctly,  that  the  agents  of  ac- 
commodation are  called  into  action ;  and  then,  very  slight  changes  in  the 
curvature  of  the  lens  are  sufficient  to  bring  the  rays  to  a  focus  exactly  on  the 
visual  surface  of  the  retina. 

Spherical,  Monochromatic  Aberration. — In  a  convex  lens  in  which  the 
surfaces  are  segments  of  a  sphere,  the  rays  of  light  from  any  object  are  not 
converged  to  a  uniform  focus,  and  the  production  of  an  absolutely  distinct 
image  is  impossible.  For  example,  if  the  crystalline  lens  had  regular  curva- 
tures, the  rays  refracted  by  its  peripheral  portion  would  be  brought  to  a  focus 
in  front  of  the  retina ;  the  focus  of  the  rays  converged  by  the  lens  near  its 
centre  would  be  behind  the  retina ;  a  few,  only,  of  the  rays  would  have  their 
focus  at  the  retina  itself ;  and  as  a  consequence,  the  image  would  appear 
confused.  This  is  illustrated  in  imperfectly  corrected  lenses,  and  is  called 
spherical  aberration.  It  is  also  called  monochromatic  aberration,  because  it 
is  to  be  distinguished  from  an  aberration  which  involves  decomposition  of 
light  into  the  colors  of  the  spectrum.  If  an  object  be  examined  under  the 
microscope  with  an  imperfectly  corrected  objective,  it  is  evident  that  the  field 
of  view  is  not  uniform,  and  that  there  is  a  different  focal  adjustment  for  the 
central  and  the  peripheral  portions  cf  the  lens.  In  the  construction  cf 


696  SPECIAL  SENSES. 

optical  instruments,  this  difficulty  may  be  in  part  corrected  if  the  rays  of 
light  be  cut  off  from  the  periphery  of  the  lens,  by  a  diaphragm,  which  is  an 
opaque  screen  with  a  circular  perforation  allowing  the  rays  to  pass  to  a 
restricted  portion  of  the  lens,  near  its  centre.  The  iris  corresponds  to  the 
diaphragm  of  optical  instruments,  and  it  corrects  the  spherical  aberration  of 
the  crystalline  in  part,  by  eliminating  a  portion  of  the  rays  that  would  other- 
wise fall  upon  its  peripheral  portion.  This  correction,  however,  is  not  suffi- 
cient for  high  magnifying  powers  ;  and  it  is  only  by  the  more  or  less  perfect 
correction  of  this  kind  of  aberration  by  other  means,  that  powerful  lenses 
have  been  rendered  available  in  optics. 

The  spherical  aberration  of  lenses  which  diverge  the  rays  of  light  is  pre- 
cisely opposite  to  the  aberration  of  converging  lenses.  In  a  compound  lens, 
therefore,  it  is  possible  to  fulfill  the  conditions  necessary  to  the  convergence 
of  all  the  incident  rays  to  a  focus  on  a  uniform  plane,  so  that  the  image  pro- 
duced behind  the  lens  is  not  distorted.  Given,  for  example,  a  double-convex 
lens,  by  which  the  rays  are  brought  to  innumerable  focal  points  situated  in 
different  planes.  The  fact  that  but  a  few  of  these  focal  points  are  in  the 
plane  of  the  retina  renders  the  image  indistinct.  If  a  concave  or  a  plano- 
concave lens  be  placed  in  front  of  this  convex  lens,  which  will  diverge  the 
rays  more  or  less,  the  inequality  of  the  divergence  by  different  portions  of 
the  second  lens  will  have  the  following  effect :  As  the  angle  of  divergence 
gradually  increases  from  the  centre  toward  the  periphery,  the  rays  near  the 
periphery,  which  are  most  powerfully  converged  by  the  convex  lens,  will  be 
most  widely  diverged  by  the  peripheral  portion  of  the  concave  lens ;  so  that 
if  the  opposite  curvatures  be  accurately  adjusted,  the  aberrant  rays  may  be 
blended.  It  is  evident  that  if  all  the  rays  were  equally  converged  by  the  con- 
vex lens  and  equally  diverged  by  the  concave  lens,  the  action  of  the  latter 
would  be  simply  to  elongate  the  focal  distance ;  and  it  is  equally  evident  that 
if  the  aberration  of  the  one  be  exactly  opposite  to  the  aberration  of  the  other, 
there  will  be  perfect  correction.  Mechanical  art  has  not  effected  correction 
of  every  portion  of  very  powerful  convex  lenses  in  this  way ;  but  by  a  com- 
bination of  lenses  and  diaphragms  together,  highly  magnified  images,  nearly 
perfect,  have  been  produced.  Lenses  in  which  spherical  aberration  has  been 
corrected  are  called  aplanatic. 

It  is  evident  that  for  distinct  vision  at  different  distances,  the  crystalline 
lens  must  be  nearly  free  from  spherical  aberration.  This  is  not  effected  by  a 
combination  of  lenses,  as  in  ordinary  optical  instruments,  but  by  the  curva- 
tures of  the  lens  itself,  and  by  certain  differences  in  the  consistence  of  differ- 
ent portions  of  the  lens,  which  will  be  fully  considered  hereafter. 

Chromatic  Aberration. — A  refracting  medium  does  not  act  equally  upon 
the  different  colored  rays  into  which  pure  white  light  may  be  decom- 
posed ;  in  other  words,  as  the  pure  ray  falling  upon  the  inclined  surface  of 
a  glass  prism  is  bent,  it  is  decomposed  into  the  colors  of  the  spectrum.  As  a 
convex  lens  is  practically  composed  of  an  infinite  number  of  prisms,  the  same 
effect  would  be  expected.  Indeed,  a  simple  convex  lens,  even  if  the  spherical 
aberration  be  corrected,  always  produces  more  or  less  decomposition  of  light. 


REFRACTION  IN  THE  EYE.  697 

The  image  formed  by  such  a  lens  will  consequently  be  colored ;  and  this 
defect  in  simple  lenses  is  called  chromatic  aberration.  At  the  same  time  it 
is  evident  that  the  centre  of  the  different  rays  from  an  object  will  be  com- 
posed of  all  the  colors  of  the  spectrum  combined,  producing  the  effect  of 
white  light ;  but  at  the  borders  the  different  colors  will  be  separate  and  dis- 
tinct, and  an  image  produced  by  a  simple  convex  lens  will  thus  be  surrounded 
by  a  circle  of  colors,  like  a  rainbow. 

In  prisms  the  chromatic  dispersion  may  be  corrected  by  allowing  the 
colored  rays  from  one  prism  to  fall  upon  a  second  prism,  which  is  inverted, 
so  that  the  colors  will  be  brought  together  and  produce  white  light.  Two 
prisms  thus  applied  to  each  other  constitute,  in  fact,  a  flat  plate  of  glass,  and 
the  rays  of  light  pass  without  deviation.  If  this  law  be  applied  to  lenses,  it 
is  evident  that  the  dispersive  power  of  a  convex  lens  may  be  exactly  opposite 
to  that  of  a  concave  lens.  By  the  convex  lens  the  colored  rays  are  separated 
by  convergence  and  cross  each  other ;  and  in  the  concave  lens  the  colored 
rays  are  diverged  in  the  opposite  direction.  If,  then,  a  convex  be  combined 
with  a  concave  lens,  the  white  light  decomposed  by  the  one  will  be  recom- 
posed  by  the  other,  and  the  chromatic  aberration  will  thus  be  corrected  ;  but 
in  using  a  convex  and  a  concave  lens  composed  of  the  same  material,  the  con- 
vergence by  the  one  will  be  neutralized  by  the  divergence  of  the  other,  and 
there  will  be  no  amplification  of  the  object.  Newton  supposed  that  dis- 
persion, or  decomposition  of  light,  by  lenses  was  always  in  exact  proportion 
to  refraction,  so  that  it  would  be  impossible  to  correct  chromatic  aberration  and 
retain  magnifying  power ;  but  it  has  been  ascertained  that  there  are  great 
differences  in  the  dispersive  power  of  different  kinds  of  glass,  without  corre- 
sponding differences  in  refraction.  This  discovery  rendered  it  possible  to  con- 
struct achromatic  lenses  (Dollond,  1757).  According  to  Ganot,  Hall  was  the 
first  to  make  achromatic  lenses,  in  1753,  but  his  discovery  was  not  published. 
In  the  construction  of  modern  optical  instruments,  the  chromatic  aberra- 
tion is  corrected,  with  a  certain  diminution  in  the  amplification,  by  cement- 
ing together  lenses  made  of  different  material,  as  of  flint-glass  and  crown- 
glass.  Flint-glass  has  a  much  greater  dispersive  power  than  crown-glass.  If, 
therefore,  a  convex  lens  of  crown-glass  be  combined  with  a  concave  or  plano- 
concave lens  of  flint-glass,  the  chromatic  aberration  of  the  convex  lens  may 

be  corrected  by  a  concave  lens  with  a  curvature 
which  will  reduce  the  magnifying  power  about 
one-half.     A  compound  lens,  with  the  spherical 
.     aberration  of  the  convex  element  corrected  by  the 

FLINT  GLASS 

FIG.  255.— Achromatic  lens.       curvature  of  a  concave  lens,  and  the  chromatic 
aberration  corrected  in  part  by  the  curvature,  and 

in  part  by  the  superior  refractive  power  of  flint-glass  over  crown-glass,  will 
produce  a  perfect  image. 

Although  the  eye  is  not  absolutely  achromatic,  the  dispersion  of  light  is 
not  sufficient  to  interfere  with  distinct  vision ;  but  the  chromatic  aberration 
is  practically  corrected  in  the  crystalline  lens,  probably  by  differences  in  the 
consistence  and  in  the  refractive  power  of  its  different  layers. 


698  SPECIAL  SENSES. 


FORMATION  OF  IMAGES  IN  THE  EYE. 

It  is  necessary  only  to  call  to  mind  the  general  arrangement  of  the  differ- 
ent structures  in  the  eye  and  to  apply  the  simple  laws  of  refraction,  in  order 
to  comprehend  precisely  how  images  are  formed  upon  the  retina. 

The  eye  corresponds  to  a  camera  obscura.  Its  interior  is  lined  with  a 
dark,  pigmentary  membrane  (the  choroid),  the  immediate  action  of  which  is 
to  prevent  the  confusion  of  images  by  internal  reflection.  The  rays  of  light 
are  admitted  through  a  circular  opening  (the  pupil),  the  size  of  which  is 
regulated  by  the  movements  of  the  iris.  The  pupil  is  contracted  when  the 
light  striking  the  eye  is  intense,  and  is  dilated  as  the  quantity  of  light  is 
diminished.  In  the  accommodation  of  the  eye,  the  pupil  is  dilated  for  dis- 
tant objects  and  contracted  for  near  objects ;  for  in  looking  at  near  objects, 
the  aberrations  of  sphericity  and  achromatism  in  the  lens  are  more  marked, 
and  the  peripheral  portion  is  cut  off  by  the  action  of  this  movable  dia- 
phragm, thus  aiding  the  correction.  The  rays  of  light  from  an  object  pass 
through  the  cornea,  the  aqueous  humor,  the  crystalline  lens  and  the  vitreous 
humor,  and  they  are  refracted  with  so  little  spherical  and  chromatic  aberra- 
tion, that  the  image  formed  upon  the  retina  is  practically  perfect.  The  layer 
of  rods  and  cones  of  the  retina  is  the  only  portion  of  the  eye  endowed  directly 
with  special  sensibility,  the  impressions  of  light  being  conveyed  to  the  brain 
by  the  optic  nerves.  This  layer  is  situated  next  the  pigmentary  layer  of 
the  choroid,  but  the  other  layers  of  the  retina,  through  which  the  light 
passes  to  reach  the  rods  and  cones,  are  perfectly  transparent. 

It  has  been  shown  that  the  rods  and  cones  are  the  only  structures  capa- 
ble of  directly  receiving  visual  impressions,  by  the  following  experiment, 
first  made  by  Purkinje  :  With  a  convex  lens  of  short  focus,  an  intense  light 
is  concentrated  on  the  sclerotic,  at  a  point  as  far  as  possible  removed  from 
the  cornea.  This  passes  through  the  translucent  coverings  of  the  eye  at  this 
point,  and  the  image  of  the  light  reaches  the  retina.  In  then  looking  at  a 
dark  surface,  the  field  of  vision  presents  a  reddish-yellow  illumination,  with 
a  dark,  arborescent  appearance  produced  by  the  shadows  of  the  large  retinal 
vessels ;  and  as  the  lens  is  moved  slightly,  the  shadows  of  the  vessels  move 
with  it.  Without  going  elaborately  into  the  mechanism  of  this  phenomenon, 
it  is  sufficient  to  state  that  Heinrich  Muller  has  arrived  at  a  mathematical 
demonstration  that  the  shadows  of  the  vessels  are  formed  upon  the  layer  of 
rods  and  cones,  and  that  this  layer  alone  is  capable  of  receiving  impressions 
of  light.  His  explanation  is  generally  accepted  and  is  regarded  as  positive 
proof  of  the  peculiar  sensibility  of  this  portion  of  the  retina. 

Theoretically,  an  illuminated  object  placed  in  the  angle  of  vision  would 
form  upon  the  retina  an  image,  diminished  in  size  and  inverted.  This  fact 
is  capable  of  demonstration  by  means  of  the  ophthalmoscope ;  as  with  this 
instrument  the  retina  and  the  images  formed  upon  it  may  be  seen  during  life. 

All  parts  of  the  retina,  except  the  point  of  entrance  of  the  optic  nerve, 
are  sensitive  to  light;  and  the  arrangement  of  the  cornea  and  pupil  is  such, 
that  the  field  of  vision  is,  at  the  least  estimate,  equal  to  the  half  of  a  sphere. 


FORMATION  OF  IMAGES  IN  THE  EYE.  699 

If  a  ray  of  light  fall  upon  the  border  of  the  cornea,  at  a  right  angle  to  the 
axis  of  the  eye,  it  is  refracted  by  its  surface  and  will  pass  through  the  pupil 
to  the  opposite  border  of  the  retina.  Above  and  below,  the  circle  of  vision 
is  cut  off  by  the  overhanging  arch  of  the  orbit  and  the  malar  prominence ; 
but  externally  the  field  is  free.  With  the  two  eyes,  therefore,  the  lateral 
field  of  vision  must  be  equal  to  at  least  one  hundred  and  eighty  degrees. 
It  is  easy  to  demonstrate,  however,  by  the  ophthalmoscope,  as  well  as  by 
taking  cognizance  of  the  impressions  made  by  objects  far  removed  from  the 
axis  of  distinct  vision,  that  images  formed  upon  the  lateral  and  peripheral 
portions  of  the  retina  are  confused  and  imperfect.  One  has  a  knowledge 
of  the  presence  and  an  indefinite  idea  of  the  general  form  of  large  objects 
situated  outside  of  the  area  of  distinct  vision;  but  when  it  is  desired  to 
note  such  objects  exactly,  the  eyeball  is  turned  by  muscular  effort,  so  as  to 
bring  them  at  or  very  near  the  axis  of  the  globe.  This  fact,  with  what  is 
known  of  the  mechanism  of  refraction  by  the  cornea  and  lens,  makes  it 
evident  that  the  area  of  the  retina,  upon  which  images  are  formed  with 
perfect  distinctness,  is  quite  restricted.  A  moment's  reflection  is  sufficient 
to  convince  any  one  that  in  order  to  see  any  object  distinctly,  it  is  necessary 
to  bring  the  axis  of  the  eye  to  bear  upon  it  directly. 

In  examining  the  bottom  of  the  eye  with  the  ophthalmoscope,  the  yellow 
spot,  with  the  fovea  centralis,  can  be  seen,  free  from  large  blood-vessels,  and 
composed  chiefly  of  those  elements  of  the  retina  which  are  sensitive  to  light. 
If  at  the  same  time,  an  image  for  which  the  eye  is  perfectly  adjusted  be  ob- 
served, it  will  be  seen  that  this  image  is  perfect  only  at  the  fovea  centralis ; 
and  if  the  object  be  removed  from  the  axis  of  vision,  there  is  a  confused  image 
upon  the  retina,  removed  from  the  fovea,  at  the  same  time  that  the  subject 
is  conscious  of  indistinct  vision.  In  the  words  of  Helmholtz,  "  It  is  only  in 
the  immediate  vicinity  of  the  ocular  axis  that  the  retinal  image  possesses 
entire  distinctness  ;  beyond  this,  the  contours  are  less  defined.  It  is  in  part 
for  this  reason  that  in  general  we  see  distinctly  in  the  field  of  vision,  only 
the  point  that  we  fix.  All  the  others  are  seen  vaguely.  This  lack  of  dis- 
tinctness in  indirect  vision,  in  addition,  depends  also  upon  diminished  sensi- 
bility of  the  retina :  at  a  slight  distance  from  the  fixed  point,  the  distinct- 
ness of  vision  has  diminished  much  more  than  the  objective  distinctness 
of  retinal  images." 

At  the  point  of  penetration  of  the  optic  nerve,  the  retina  is  insensible  to 
luminous  impressions ;  or  at  least,  its  sensibility  is  here  so  obtuse  as  to  be 
entirely  inadequate  for  the  purposes  of  vision.  This  point  is  called  the  punc- 
tum  cascum ;  and  its  want  of  sensibility  was  demonstrated  many  years  ago 
(1668)  by  Mariotte.  The  classical  experiment  by  which  this  important  fact 
was  ascertained  is  generally  known  as  Mariotte's  experiment.  The  following 
account  is  quoted  verbatim : 

"  I  fasten'd  on  an  obscure  Wall  about  the  hight  of  my  Eye,  a  small  round 
paper,  to  serve  me  for  a  fixed  point  of  Vision ;  and  I  fastened  such  an  other 
on  the  side  thereof  towards  my  right  hand,  at  the  distance  of  about  2.  foot ; 
but  somewhat  lower  than  the  first,  to  the  end  that  it  might  strike  the  Optick 


700  SPECIAL  SENSES. 

Nerve  of  my  Right  Eye,  whilst  I  kept  my  Left  shut.  Then  I  plac'd  myself 
over  against  the  First  paper,  and  drew  back  by  little  and  little,  keeping  my 
Right  Eye  fixt  and  very  steddy  upon  the  same ;  and  being  about  10.  foot 
distant,  the  second  paper  totally  disappear'd." 

In  this  experiment  the  rays  of  light  from  the  paper  which  has  disap- 
peared from  view  are  received  upon  the  punctum  caecum,  at  the  point  of 
entrance  of  the  optic  nerve.  If  the  observer  withdraw  himself  still  farther, 
the  second  circle  will  reappear,  as  the  rays  are  removed  from  the  punctum 
caecum.  With  the  ophthalmoscope,  the  point  of  penetration  of  the  optic 
nerve  may  readily  be  seen  in  the  living  eye.  If  the  image  of  a  flame  be 
directed  upon  this  point,  the  sensation  of  light  is  either  not  perceived  or  it 
is  very  faint  and  indefinite,  and  it  is  then  probably  due  to  diffusion  to  other 
portions  of  the  retina. 

The  relative  sensibility  of  different  portions  of  the  retina  has  been  meas- 
ured by  Volkmann  and  has  been  found  to  be,  in  an  inverse  ratio,  equal  to 
about  the  square  of  the  distance  from  the  axis  of  most  perfect  vision.  This 
observer  calculated  the  distance  between  the  sensitive  elements  of  the  retina 
at  which  he  supposed  that  two  parallel  lines  would  appear  as  one.  In  the 
axis  of  vision,  the  distance  was  0-00029  inch  (7*366  ^),  and  at  a  deviation  in- 
ward of  8°,  it  was  0-03186  inch  (809-244  ^),  a  diminution  of  acuteness  of 
more  than  a  hundred  times. 

Visual  Purple  and  Visual  Yellow,  and  Accommodation  of  tlie  Eye  for 
Different  Degrees  of  Illumination. — The  outer  segments  of  the  rods  of  the 
retina  sometimes  present  a  peculiar  red  or  purple  color,  which  disappears 
after  ten  or  twelve  seconds  of  exposure  to  light.  This  was  first  observed  by 
Boll  (1876)  in  the  retinae  of  frogs  that  had  been  kept  for  a  certain  time  in 
the  dark.  From  his  preliminary  researches,  Boll  concluded  that  this  colora- 
tion of  the  retina  exists  only  during  life  and  persists  but  a  few  moments  after 
death ;  that  it  is  constantly  destroyed  during  life  by  the  action  of  light  and 
reappears  in  the  dark ;  and  finally  that  it  plays  an  important  part  in  the  act 
of  vision.  Kiihne  and  others  have  since  confirmed  and  extended  the  original 
observations  of  Boll ;  and  the  visual  purple  (rhodopsine)  has  been  noted  in 
the  mammalia  and  in  man.  It  has  been  extracted  from  the  retinse  of  frogs 
and  dissolved  in  a  five-per-cent.  solution  of  crystallized  ox-gall,  still  present- 
ing in  solution  its  remarkable  sensitiveness  to  light  (Ayres).  Finally  it  has 
been  found  possible  to  fix  images  of  simple  objects,  such  as  strips  of  black 
paper  pasted  upon  a  plate  of  ground  glass,  upon  the  retina,  by  a  process  very 
like  that,  of  photography. 

The  visual  purple  is  produced  by  the  cells  of  the  pigmentary  layer  of  the 
retina  and  from  them  is  absorbed  by  the  outer  segments  of  the  rods.  It  is 
not  present  in  any  part  of  the  cones  and  does  not  exist,  therefore,  in  the  area 
of  distinct  vision,  at  the  fovea  centralis.  The  rapid  disappearance  of  the 
color  under  the  influence  of  actinic  rays  of  light  renders  it  necessary  to  ex- 
amine the  retina  under  a  non-actinic  (monochromatic)  sodium-flame  (Ayres). 
When  thus  examined  and  gradually  exposed  to  actinic  rays,  the  color  quickly 
fades  into  a  yellow  and  finally  disappears,  being  restored,  however,  in  the  dark. 


VISUAL  PURPLE  AND  VISUAL  YELLOW.  701 

If  the  choroid  and  the  pigmentary  layer  of  the  retina  be  removed,  the  rods 
are  bleached,  and  the  color  is  restored  in  the  dark  when  the  choroid  is  re- 
placed. In  the  eye  of  the  frog,  kept  in  the  dark,  the  hair-like  processes 
which  extend  from  the  pigmentary  layer  of  the  retina  downward  between  the 
rods  and  cones  are  retracted,  and  the  pigment  is  then  contained  chiefly  in  the 
cells  themselves.  After  prolonged  exposure  of  the  retina  to  light,  these  pro- 
cesses, loaded  with  pigment,  extend  between  the  cones  as  far  as  the  limitary 
membrane  (Kiihne). 

The  fact  that  visual  purple  has  never  been  found  in  the  fovea  centralis  is 
opposed  to  the  theory  that  its  existence  is  directly  essential  to  distinct  vision ; 
nevertheless,  certain  phenomena  observed  in  passing  from  a  bright  light  to 
comparative  obscurity,  and  the  reverse,  show  that  the  purple  has,  at  least,  an 
important  indirect  action.  In  passing  from  the  dark  to  bright  light,  the  eye 
is  dazzled  and  distinct  vision  is  difficult.  It  may  be  assumed  that  this  is  due 
to  unusual  general  sensitiveness  of  the  retina  to  light,  on  account  of  the  ex- 
cessive quantity  of  visual  purple  which  has  accumulated  in  the  dark,  and 
that  distinct  vision  is  restored  when  the  retina  is  bleached  to  a  yellow,  which 
seems  to  be  the  most  favorable  condition  for  the  exact  appreciation  of  visual 
impressions,  under  full  illumination.  On  the  other  hand,  it  requires  time  for 
the  eye  to  become  accustomed  to  a  dim  light ;  and  during  this  time  the  yel- 
low is  changing  to  purple.  These  changes  in  the  color  of  the  retina  have 
been  actually  observed  (Ayres).  Investigations  of  the  absorption-spectra  of 
the  purple  and  yellow  have  shown  that  the  purple  allows  the  actinic  rays  to 
pass  perfectly,  while  the  yellow  completely  absorbs  these  rays  (Kiihne).  The 
existence  of  visual  purple  seems  to  be  most  favorable  to  the  imperfect  and 
shadowy  vision  which  occurs  under  dim  illumination,  when  the  exact  appre- 
ciation of  minute  details  is  impossible.  In  the  condition  known  as  night- 
blindness,  it  is  probable  that  the  visual  purple  has  become  exhausted  beyond 
the  possibility  of  prompt  restoration  such  as  is  normal ;  and  persons  so  affected 
can  not  see  at  night,  although  minute  vision  under  a  bright  light  may  not  be 
affected.  In  certain  cases  of  this  kind,  the  normal  conditions  may  be  re- 
stored by  a  few  days'  seclusion  in  the  dark.  What  is  called  functional  night- 
blindness  frequently  occurs  in  sailors  during  long,  tropical  voyages,  and  is 
due  to  the  excessive  action  of  diffused  light  upon  the  retina.  "  That  the 
affection  is  local,  is  shown  by  the  fact  that  darkening  one  eye,  with  a  band- 
age, during  the  day,  has  been  found  to  restore  its  sight  enough  for  the  ensuing 
night's  watch  on  board  ship,  the  unprotected  eye  remaining  as  bad  as  ever  " 
(Nettleship). 

The  change  of  the  visual  purple  to  yellow  is  readily  effected,  but  the 
farther  change  to  white  is  slower  and  more  difficult.  Conversely,  the  change 
from  white  to  yellow  is  slow  and  the  change  from  yellow  to  purple  is  com- 
paratively prompt.  One  use  of  the  colors  purple  and  yellow  seems  to  be  to 
accommodate  the  retina  for  vision  under  different  degrees  of  illumination. 
The  purple  adapts  the  eye  to  a  feeble  illumination,  and  the  yellow,  to  a  full 
illumination.  This  being  the  case,  it  is  manifestly  proper  to  speak  of  a 
visual  yellow  (Kiiline)  as  well  as  of  visual  purple. 

46 


702  SPECIAL  SENSES. 

That  the  accommodation  of  the  eye  to  different  degrees  of  illumination  is 
due  to  the  changes  in  the  colors  produced  by  the  pigmentary  layer  of  the 
retina  and  not  to  different  degrees  of  dilatation  of  the  pupil,  is  shown  by  the 
fact  that  a  person  does  not  see  better  in  the  dark  when  the  pupil  has  been 
dilated  by  atropine  (Loring).  In  a  very  dim  light  there  is  no  possibility  of 
exact  accommodation  for  near  objects,  which,  when  small,  can  not  be  seen 
distinctly ;  and  the  contraction  of  the  pupil  which  attends  accommodation 
for  near  vision  does  not  occur.  It  is  possible  that  under  dim  illumination, 
parts  outside  of  the  fovea,  which  are  insensible  to  vision  under  a  bright  light, 
receive  visual  impressions.  Under  these  conditions  the  pupil  is  dilated 
and  rays  impinge  on  portions  of  the  retina  not  used  in  direct  vision.  A 
natural  extension  of  this  idea  would  confine  distinct  vision  and  the  apprecia- 
tion of  minute  details  to  the  action  of  the  fovea  centralis,  in  which  there  is 
no  visual  purple,  other  parts  of  the  retina,  under  full  illumination,  not  being 
used.  To  express  this  in  a  few  words,  the  fovea  centralis  is  used  by  day,  and 
the  adjacent  parts  of  the  retina,  by  night. 

MECHANISM  OF  REFKACTION  IN  THE  EYE. 

An  object  that  is  seen  reflects  rays  from  every  point  of  its  surface,  to  the 
•cornea.  If  the  object  be  near,  the  rays  from  each  and  every  point  are  diver- 
gent as  they  strike  the  eye.  Rays  from  distant  objects  are  practically  parallel. 
It  is  evident  that  the  refraction  for  diverging  rays  must  be  greater  than  for 
parallel  rays,  as  a  necessity  of  distinct  vision ;  in  other  words,  the  eye  must 
be  accommodated  for  vision  at  different  distances.  Leaving,  however,  the 
mechanism  of  accommodation  for  future  consideration,  it  may  be  stated 
simply  that  the  important  agents  in  refraction  in  the  eye  are  the  surfaces 
of  the  cornea  and  the  crystalline  lens.  Calculations  have  shown  that  the 
index  of  refraction  of  the  aqueous  humor  is  sensibly  the  same  as  that  of 
the  substance  of  the  cornea,  so  that  practically  the  refraction  is  the  same 
as  if  the  cornea  and  the  aqueous  humor  were  one  and  the  same  substance. 
The  index  of  refraction  of  the  vitreous  humor  is  practically  the  same  as 
that  of  the  aqueous  humor,  both  being  about  equal  to  the  index  of  refrac- 
tion of  pure  water.  Refraction  by  the  crystalline  lens,  however,  is  more 
complex  in  its  mechanism ;  depending  first,  upon  the  curvatures  of  its  two 
surfaces,  and  again,  upon  the  differences  in  the  consistence  of  different  por- 
tions of  its  substance.  In  view  of  these  facts,  the  conditions  of  refraction 
in  the  eye  in  distinct  vision  may  be  simplified  by  assuming  the  following 
arrangement : 

The  cornea  presents  a  convex  surface  upon  which  the  rays  of  light  are 
received.  At  a  certain  distance  behind  its  anterior  border,  is  the  crystalline, 
a  double  convex  lens,  corrected  sufficiently  for  all  practical  purposes,  both  for 
spherical  and  chromatic  aberration.  This  lens  is  practically  suspended  in  a 
liquid  with  an  index  of  refraction  equal  to  that  of  pure  water,  as  both  the 
aqueous  humor  in  front  and  the  vitreous  humor  behind  have  the  same  refract- 
ive power.  Behind  the  lens,  in  its  axis  and  exactly  in  the  plane  upon  which 
the  rays  of  light  are  brought  to  a  focus  by  the  action  of  the  cornea  and  the 


MECHANISM  OF  REFRACTION  IN  THE  EYE.  703' 

lens,  is  the  fovea  centralis,  which  is  the  centre  of  distinct  vision.  The  an- 
atomical elements  of  the  fovea  are  capable  of  receiving  visual  impressions, 
which  are  conveyed  to  the  brain  by  the  optic  nerves.  All  impressions  made 
upon  other  portions  of  the  retina  are  comparatively  indistinct ;  and  the  point 
of  entrance  of  the  optic  nerve  is  insensible  to  light.  Inasmuch  as  the  punc- 
tum  caecum  is  situated  in  either  eye  upon  the  nasal  side  of  the  retina,  in  nor- 
mal vision,  rays  from  the  same  object  can  not  fall  upon  both  blind  points  at 
the  same  time.  Thus,  in  binocular  vision,  the  insensibility  of  the  punctum 
caecum  does  not  interfere  with  sight ;  and  the  movements  of  the  globe  pre- 
vent any  notable  interference  in  vision,  even  with  one  eye.  The  sclerotic 
coat  is  for  the  protection  of  its  contents  and  for  the  insertion  of  muscles. 
The  iris  has  an  action  similar  to  that  of  the  diaphragm  in  optical  instru- 
ments. The  suspensory  ligament  of  the  lens,  the  ciliary  body,  and  the  cili- 
ary muscle,  are  for  the  fixation  of  the  lens  and  its  accommodation  for  distinct 
vision  at  different  distances.  The  choroid  is  a  dark  membrane,  for  the  ab- 
sorption of  light,  preventing  confusion  of  vision  from  reflection  within  the  eye. 

Refraction  by  the  cornea  is  effected  simply  by  its  external  surface.  The 
rays  of  light  from  a  distant  point  are  deviated  by  its  convexity  so  that,  if 
they  were  not  again  refracted  by  the  crystalline  lens,  they  would  be  brought 
to  a  focus  at  a  point  situated  about  -fo  of  an  inch  (10  mm.)  behind  the 
retina.  Without  the  crystalline  lens,  therefore,  distinct,  unaided  vision  gen- 
erally is  impossible,  although  the  sensation  of  light  is  appreciated.  In  cases 
of  extraction  of  the  lens  for  cataract  (aphakia),  the  crystalline  is  supplied  by 
a  convex  lens  placed  before  the  eye. 

The  rays  of  light,  refracted  by  the  anterior  surface  of  the  cornea,  are 
received  upon  the  anterior  surface  of  the  crystalline  lens,  by  which  they  are 
still  farther  refracted.  Passing  through  the  substance  of  the  lens,  they 
undergo  certain  modifications  in  refraction,  dependent  upon  the  differences 
in  the  various  strata  of  the  lens.  These  modifications  have  not  been  accu- 
rately calculated ;  but  it  is  sufficient  to  state  that  they  contribute  to  the 
accuracy  of  the  formation  of  the  retinal  image  and  to  the  production  of  an 
image  practically  free  from  chromatic  dispersion.  As  the  rays  pass  out  of 
the  crystalline  lens,  they  are  again  refracted  by  its  posterior  curvature  and 
are  brought  to  a  focus  at  the  point  of  distinct  vision. 

The  rays  from  all  points  of  an  object  distinctly  seen  are  brought  to  a 
focus,  if  the  accommodation  of  the  lens  be  correct,  upon  a  restricted  surface 
in  the  macula  lutea;  but  the  rays  from  different  points  cross  each  other 
before  they  reach  the  retina,  and  the  image  is  inverted. 

Calculating  the  curvatures  of  the  refracting  surfaces  in  the  eye  and  the 
indices  of  refraction  of  its  transparent  media,  it  has  been  pretty  clearly 
shown,  by  mathematical  formulae,  that  the  eye — viewed  simply  as  an  optical 
instrument,  and  not  practically,  as  the  organ  of  vision — presents  a  certain 
degree  of  spherical  and  chromatic  aberration ;  but  these  calculations  are  not 
very  important  in  a  purely  physiological  consideration  of  the  sense  of  sight. 

In  most  calculations  of  the  size  of  images,  the  positions  of  conjugate  foci, 
etc.,  in  normal  and  abnormal  eyes,  a  schematic  eye  reduced  by  Bonders,  after 


704  SPECIAL  SENSES. 

the  example  of  Listing,  is  regarded  as  sufficiently  exact  for  all  practical  pur- 
poses. This  simple  scheme  represents  the  eye  as  reduced  to  a  single  refract- 
ing surface,  the  cornea,  and  a  single  liquid  assumed  to  have  an  index  of  re- 
fraction equal  to  that  of  pure  water.  The  distance  between  what  are  called 
the  two  nodal  points  and  between  the  two  principal  points  of  the  dioptric  sys- 
tem of  the  eye  is  so  small,  amounting  to  hardly  -^fa  of  an  inch  (0-254  mm.), 
that  it  can  be  neglected.  In  this  simple  eye,  there  is  assumed  to  be  a  radius 
of  curvature  of  the  cornea  of  about  \  of  an  inch  (5  mm.)  and  a  single  optical 
centre  situated  \  of  an  inch  (5  mm.)  back  of  the  cornea,  the  "  principal 
point "  being  in  the  cornea,  in  the  axis  of  vision.  The  posterior  focal  dis- 
tance, that  is,  the  focus,  at  the  bottom  of  the  eye,  for  rays  that  are  parallel  in 
the  air,  is  about  f  of  an  inch  (20  mm.).  The  anterior  focal  distance,  that  is, 
for  rays  parallel  in  the  vitreous  humor,  is  about  f  of  an  inch  (15  mm.).  The 
measurements  in  this  simple  schematic  eye  can  easily  be  remembered  and 
used  in  calculations. 

ASTIGMATISM. 

In  the  normal  human  eye  the  visual  line  does  not  coincide  exactly  with 
the  mathematical  axis;  but  there  is  still  another  normal  deviation  from 
mathematical  exactness  in  the  refraction  of  rays  by  the  cornea  and  the  crys- 
talline lens,  which  is  of  considerable  importance.  If  two  threads,  crossing 
each  other  at  right  angles  in  the  same  plane,  be  placed  before  the  eyes,  one 
of  these  threads  being  vertical,  and  the  other,  horizontal,  when  the  optical 
apparatus  is  adjusted  so  that  one  line  is  seen  with  perfect  distinctness,  the 
other  is  not  well  denned.  In  other  words,  when  the  eye  is  accommodated 
for  the  vertical  thread,  the  horizontal  thread  is  indistinct,  and  vice  versa.  If 
the  horizontal  line  be  seen  distinctly,  in  order  to  see  the  vertical  line  without 
modifying  the  accommodation,  it  must  be  removed  to  a  greater  distance. 
This  depends  chiefly  upon  a  difference  in  the  vertical  and  the  horizontal 
curvatures  of  the  cornea,  so  that  the  horizontal  meridian  has  a  focus  slightly 
different  from  the  focus  of  the  vertical  meridian.  A  condition  opposite  to 
that  observed  in  the  cornea  usually  exists  in  the  crystalline  lens ;  that  is,  the 
difference  which  exists  between  the  curvatures  of  the  lens  in  the  vertical  and 
the  horizontal  meridians  is  such  that  the  deepest  curvature  in  the  lens  is 
situated  in  the  meridian  of  the  shallowest  curvature  of  the  cornea.  In  this 
way,  in  normal  eyes,  the  aberration  of  the  lens  has  a  tendency  to  correct  the 
aberration  in  the  cornea ;  but  this  correction  is  incomplete,  and  there  still 
remains,  in  all  degrees  of  accommodation,  a  certain  difference  in  vision,  as 
regards  vertical  and  horizontal  lines. 

The  condition  just  described  is  known  under  the  name  of  normal,  regular 
astigmatism  ;  but  the  aberration  is  not  sufficiently  great  to  interfere  with  dis- 
tinct vision.  The  degree  of  regular  astigmatism  presents  normal  variations 
in  different  eyes.  In  some  eyes  there  is  no  astigmatism ;  but  this  is  rare. 
According  to  Donders,  if  the  astigmatism  amount  to  ^  or  more,  it  is  to  be 
considered  abnormal ;  which  simply  means  that  beyond  this  point  the  aber- 
ration interferes  with  distinct  vision. 

From  the  simple  definition  of  regular  astigmatism,  it  is  evident  that  this 


MOVEMENTS  OF  THE  IRIS.  T05 

condition  and  the  degree  to  which  it  exists  may  easily  be  determined  by 
noting  the  differences  in  the  foci  for  vertical  and  horizontal  lines,  and  it  may 
be  exactly  corrected  by  the  application  of  cylindrical  glasses  of  proper  curva- 
ture. Indeed,  the  curvature  of  a  cylindrical  glass  which  will  enable  a  person 
to  distinguish  vertical  and  horizontal  lines  with  perfect  distinctness  at  the 
same  time,  is  an  exact  indication  of  the  degree  of  aberration.  Regular 
astigmatism,  such  as  just  described,  may  be  so  exaggerated  as  to  interfere 
very  seriously  with  vision,  when  it  becomes  abnormal.  This  kind  of  aberra- 
tion, however,  which  is  dependent  upon  an  abnormal  condition  of  the  cornea, 
is  remediable  by  the  use  of  properly  adjusted,  cylindrical  glasses. 

Irregular  astigmatism,  excluding  cases  of  pathological  deformation, 
opaque  spots  etc.,  in  the  cornea,  depends  upon  irregularity  in  the  different 
sectors  of  the  crystalline  lens.  Instead  of  a  simple  and  regular  aberration, 
consisting  in  a  difference  between  the  depth  of  the  vertical  and  the  horizontal 
curvatures  of  the  cornea  and  lens,  there  are  irregular  variations  in  the  curva- 
tures of  different  sectors  of  the  lens.  As  a  consequence  of  this,  when  the 
irregularities  are  very  great,  there  is  impairment  of  the  sharpness  of  vision. 
The  circles  of  diffusion,  which  are  regular  in  normal  vision,  become  irregu- 
larly radiated,  and  single  points  appear  multiple,  an  irregularity  described 
under  the  name  of  polyopia  monocularis.  Accurate  observations  have  shown 
that  this  condition  exists  to  a  very  moderate  degree  in  normal  eyes ;  but  it  is 
so  slight  as  not  to  interfere  with  ordinary  vision.  In  what  is  called  normal, 
irregular  astigmatism,  the  irregularity  depends  entirely  upon  the  crystalline 
lens.  If  a  card  with  a  very  small  opening  be  placed  before  the  eye  and  be 
moved  in  front  of  the  lens,  so  that  the  pencil  of  light  falls  successively  upon 
different  sectors,  it  can  be  shown  that  the  focal  distance  is  different  for  dif- 
ferent portions.  The  radiating  lines  of  light  observed  in  looking  at  remote, 
luminous  points,  as  the  fixed  stars,  are  produced  by  this  irregularity  in  the 
curvatures  of  the  different  sectors  of  the  lens. 

While  regular  astigmatism,  both  normal  and  abnormal,  may  be  perfectly 
corrected  by  placing  cylindrical  glasses  before  the  eyes,  it  is  impossible,  in  the 
great  majority  of  cases,  to  construct  glasses  which  will  remedy  what  has  been 
called  irregular  astigmatism. 

MOVEMENTS  OF  THE  IRIS. 

There  are  two  physiological  conditions  under  which  the  size  of  the  pupil 
is  modified :  The  first  of  these  depends  upon  the  degree  of  illumination  to 
which  the  eye  is  exposed.  When  the  illumination  is  dim,  the  pupil  is  widely 
dilated.  When  the  eye  is  exposed  to  a  bright  light,  the  retina  is  protected 
by  contraction  of  the  iris.  The  muscular  action  by  which  the  iris  is  con- 
tracted is  characteristic  of  the  smooth  muscular  fibres,  as  can  be  readily  seen 
by  exposing  an  eye,  in  which  the  pupil  is  dilated,  to  a  bright  light.  Con- 
traction does  not  take  place  instantly,  but  an  appreciable  interval  elapses  after 
the  exposure,  and  a  more  or  less  gradual  diminution  in  the  size  of  the  pupil 
is  observed.  This  is  seen  both  in  solar  and  in  artificial  light.  The  second 
of  these  conditions  depends  indirectly  upon  the  voluntary  action  of  muscles. 


706  SPECIAL  SENSES. 

The  effort  of  converging  the  axes  of  the  eyes,  by  looking  at  a  very  near  ob- 
ject, contracts  the  pupils ;  and  accommodation '  of  the  eye  for  near  objects 
produces  the  same  effect,  even  when  the  eyes  are  not  converged.  This  action 
will  be  fully  considered  under  the  head  of  accommodation. 

Direct  Action  of  Light  upon  the  Iris. — The  variations  in  the  size  of  the 
pupil  under  different  physiological  conditions  are  effected  almost  exclusively 
through  the  nervous  system,  either  by  reflex  action  from  variations  in  the 
intensity  of  light,  or  by  a  direct  influence,  as  in  accommodation  for  dis- 
tances ;  but  it  is  nevertheless  true  that  the  muscular  tissue  of  the  iris  will 
respond  directly  to  the  stimulus  of  light.  Harless  noted,  in  subjects  dead  of 
various  diseases,  five  to  thirty  hours  after  death,  that  the  iris  contracted  un- 
der the  stimulus  of  light ;  and  he  regarded  this  as  probably  due  to  direct 
action  upon  its  muscular  tissue.  It  is  not  reflex,  for  the  reason  that  the  irri- 
tability of  the  nerves  in  warm-blooded  animals  disappears  certainly  in  twenty 
hours  after  death.  The  experiments  of  Harless  were  made  upon  the  two 
eyes,  one  being  exposed  to  the  light,  while  the  other  was  closed.  The  con- 
traction, however,  took  place  very  slowly,  requiring  an  exposure  of  several 
hours.  This  mode  of  contraction  is  very  different  from  the  action  of  the  iris 
during  life,  but  it  is  precisely  like  the  contraction  observed  after  division  of 
the  motor  oculi  communis,  which  is  slow  and  gradual  and  depends  upon  the 
direct  action  of  light  upon  the  muscular  fibres. 

Action  of  the  Nervous  System  upon  the  Iris. — This  subject,  as  far  as  it 
relates  to  the  third  pair,  has  been  considered  in  connection  with  the  physi- 
ology of  these  nerves ;  and  it  is  unnecessary  to  refer  again  in  detail  to  the 
experiments  which  have  already  been  cited.  The  reflex  phenomena  observed 
are  sufficiently  distinct.  When  light  is  admitted  to  the  retina,  the  pupil  con- 
tracts, and  the  same  result  follows  mechanical  irritation  of  the  optic  nerves. 
When  the  third  pair  of  nerves  has  been  divided,  no  such  reflex  phenomena 
are  observed.  It  is  well  known,  also,  that  division  of  the  third  nerves  in  the 
lower  animals  or  their  paralysis  in  the  human  subject  produces  permanent 
dilatation  of  the  pupil,  the  iris  responding,  only  in  the  slow  and  gradual  man- 
ner already  indicated,  to  the  direct  action  of  light. 

Taking  all  the  experimental  facts  into  consideration,  it  is  certain  that  the 
third  nerve  has  an  important  influence  upon  the  iris.  Filaments  from  the 
ophthalmic  ganglion  animate  the  circular  fibres,  or  sphincter,  and  these  fila- 
ments are  derived  from  the  third  cranial  nerve.  If  this  nerve  be  divided, 
the  iris  becomes  permanently  dilated  and  is  immovable,  except  that  it  re- 
sponds very  slowly  to  the  direct  action  of  light.  The  reflex  action  by 
which  the  pupil  is  contracted  under  the  stimulus  of  light  operates  through 
the  third  nerve,  and  no  such  action  can  take  place  after  this  nerve  has  been 
divided.  In  view  of  these  facts,  there  can  be  no  doubt  with  regard  to  the 
nervous  action  upon  the  sphincter  of  the  pupil,  this  muscle  being  animated 
exclusively  by  filaments  from  the  motor  oculi  communis,  coming  through  the 
ophthalmic  ganglion. 

Most  anatomists  admit  the  existence  of  radiating  muscular  fibres  in  the 
iris,  the  action  of  which  is  antagonistic  to  the  circular  fibres,  and  which  dilate 


MOVEMENTS  OF  THE  IRIS.  707 

the  pupil.  That  these  fibres  are  subjected  to  nervous  influence,  is  rendered 
certain  by  experiments  upon  the  sympathetic  system.  There  can  be  no  doubt 
that  the  action  of  the  sympathetic  upon  the  pupil  is  directly  antagonistic  to 
that  of  the  third  pair,  the  former  presiding  over  the  radiating  muscular  fibres ; 
and  the  only  question  to  determine  is  the  course  taken  by  the  sympathetic 
filaments  to  the  iris.  Experiments  on  the  influence  of  the  fifth  pair  upon  the 
pupil  have  been  somewhat  contradictory  in  different  animals.  In  rabbits  sec- 
tion of  this  nerve  in  the  cranial  cavity  produces  contraction  of  the  pupil ; 
but  in  dogs  and  cats  the  same  operation  produces  dilatation.  In  the  human 
subject,  of  course,  it  is  impossible  to  determine  this  point  by  direct  experi- 
ment ;  and  the  varying  results  obtained  in  observations  upon  different  ani- 
mals probably  depend  upon  differences  in  the  anatomical  relations  of  the 
nerves.  It  is  probable,  however,  that  the  filaments  of  the  sympathetic  which 
animate  the  radiating  fibres  join  the  fifth  nerve  near  the  ganglion  of  Gasser, 
and  from  this  nerve  pass  to  the  iris. 

There  seem  to  be  two  distinct  nerve-centres  corresponding  to  the  two  sets 
of  nerves  which  regulate  the  movements  of  the  iris.  One  of  these  centres 
presides  over  the  reflex  contractions  of  the  iris,  and  the  other  is  the  centre  of 
origin  of  the  nervous  influence  through  which  the  pupil  is  dilated. 

The  mechanism  of  reflex  contraction  of  the  iris  under  the  stimulus  of 
light  is  sufficiently  simple.  An  impression  is  made  upon  the  retina,  which  is 
conveyed  by  the  optic  nerves  to  the  centre,  and  in  obedience  to  this  impres- 
sion, the  sphincter  of  the  iris  contracts.  If  the  optic  nerves  be  divided,  so 
that  the  impression  can  not  be  conveyed  to  the  centre,  or  if  the  third  nerve 
be  divided,  no  movements  of  the  iris  can  take  place.  The  centres  which 
preside  over  the  reflex  phenomena  of  contraction  of  the  pupil  are  situated  in 
the  medulla  oblongata.  The  action  of  these  centres  is  crossed  in  animals  in 
which  the  decussation  of  the  optic  nerves  is  complete.  In  man  the  axes  of 
both  eyes  are  habitually  brought  to  bear  upon  objects,  and  it  is  well  known 
that  there  is  a  physiological  unity  in  the  action  of  the  two  eyes  in  ordinary 
vision.  It  has  been  observed  that  when  one  eye  only  is  exposed  to  light,  the 
pupil  becoming  contracted  under  this  stimulus,  the  pupil  of  the  other  eye 
also  contracts.  There  is,  indeed,  a  direct  contraction  and  dilatation  of  the 
pupil  of  the  eye  which  is  exposed  to  the  light,  and  an  indirect,  or  "  consen- 
sual "  movement  of  the  iris  upon  the  opposite  side.  The  consensual  con- 
traction occurs  about  f  of  a  second  later  than  the  direct  action,  and  the  con- 
sensual dilatation,  about  £  of  a  second  later  (Bonders). 

Budge  and  Waller  have  shown  that  the  filaments  of  the  sympathetic 
which  produce  dilatation  of  the  pupil  take  their  origin  from  the  spinal  cord. 
In  the  spinal  cord,  between  the  sixth  cervical  and  the  second  thoracic  nerves, 
is  the  inferior  cilio-spinal  centre.  When  the  spinal  cord  is  stimulated  in  this 
situation,  both  pupils  become  dilated.  If  the  cord  be  divided  longitudinally 
and  the  two  halves  be  separated  from  each  other  by  a  glass  plate,  stimulation 
of  the  right  half  produces  dilatation  of  the  right  pupil,  and  vice  versa.  This 
does  not  occur  when  the  sympathetic  in  the  neck  has  been  divided.  In  ad- 
dition to  the  inferior  cilio-spinal  centre,  there  is  a  superior  centre,  which  is 


708  SPECIAL  SENSES. 

in  communication  with  the  superior  cervical  ganglion  and  is  situated  near 
the  sublingual  nerve.  The  influence  of  this  centre  over  the  pupil  can  not  be 
demonstrated  by  direct  stimulation,  because  it  is  too  near  the  origin  of  the 
fifth,  irritation  of  which  affects  the  iris ;  but  it  is  shown  by  division  of  its 
filaments  of  communication  with  the  iris. 

ACCOMMODATION  OF  THE  EYE  FOR  VISION  AT  DIFFERENT  DISTANCES. 

Supposing  the  eye  to  be  adapted  to  vision  at  an  infinite  distance,  in  which 
the  rays  from  an  object,  as  they  strike  the  cornea,  are  practically  parallel,  it  is 
evident  that  the  foci  of  the  rays,  as  they  form  a  distinct  image  upon  the  reti- 
na, are  all  situated  at  the  proper  plane.  Under  these  conditions,  in  a  perfectly 
normal  eye,  the  image,  appreciated  by  the  individual  or  seen  by  means  of  the 
ophthalmoscope,  is  perfectly  clear  and  distinct.  If  the  foci  be  situated  in 
front  of  the  retina,  the  rays,  instead  of  coming  to  a  focus  upon  a  point  in  the 
retina,  will  cross,  and  from  their  diffusion  or  dispersion,  will  produce  indis- 
tinct vision.  Under  these  conditions  a  distinct  point  is  not  perceived,  but 
every  point  in  the  image  is  surrounded  by  an  indistinct  circle.  These  are 
called  "  circles  of  diffusion."  If,  now,  the  eye,  adjusted  for  vision  at  an  infi- 
nite distance,  be  brought  to  bear  upon  a  near  object,  the  rays  from  which  are 
divergent  as  they  strike  the  cornea,  the  image  will  be  no  longer  distinct,  but 
will  be  obscured  by  circles  of  diffusion.  It  is  the  adjustment  by  which  these 
circles  of  diffusion  are  removed,  that  constitutes  accommodation.  This  fact 
has  been  demonstrated  by  Helmholtz  by  means  of  the  ophthalmoscope.  "  If 
the  eye  be  adjusted  to  the  observation  of  an  object  placed  at  a  certain  dis- 
tance, it  is  found  that  the  image  of  a  flame,  placed  at  the  same  distance,  is 
produced  with  perfect  distinctness  upon  the  retina,  and,  at  the  same  time, 
upon  the  illuminated  plane  of  the  image,  the  vessels  and  the  other  anatomi- 
cal details  of  the  retina  are  seen  with  equal  distinctness.  But,  when  the 
flame  is  brought  considerably  nearer,  its  image  becomes  confused,  while  the 
details  of  the  structure  of  the  retina  remain  perfectly  distinct." 

It  is  evident  that  there  is  a  certain  condition  of  the  eyes  adapted  to  vision 
at  an  infinite  distance,  and  that  for  the  distinct  perception  of  near  objects, 
the  transparent  media  must  be  so  altered  in  their  arrangement  or  in  the  cur- 
vatures of  their  surfaces,  that  the  refraction  will  be  greater ;  for  without  this, 
the  rays  would  be  brought  to  a  focus  beyond  the  retina. 

The  changes  in  the  eye  by  which  accommodation  is  effected  are  now 
known  to  consist  mainly  in  an  increased  convexity  of  the  lens  for  near  ob- 
jects ;  and  the  only  points  in  dispute  are  a  few  unimportant  details  in  the 
mechanism  of  this  action.  The  simple  facts  to  be  borne  in  mind  in  study- 
ing this  question  are  the  following  : 

When  the  eye  is  accommodated  to  vision  at  an  infinite  distance,  the  parts 
are  passive. 

In  the  adjustment  of  the  eye  for  near  objects,  the  convexities  of  the  lens 
are  increased  by  muscular  action. 

In  accommodation  for  near  objects,  the  pupil  is  contracted;  but  this 
action  is  merely  accessory  and  is  not  essential. 


VISUAL  ACCOMMODATION. 


709 


The  ordinary  range  of  accommodation  varies  between  a  distance  of  about 
five  inches  (12'7  centimetres)  and  infinity. 

Changes  in  the  Crystalline  Lens  in  Accommodation. — It  is  important  to 
determine  the  extent  and  nature  of  the  changes  of  the  lens  in  accommoda- 
tion ;  and  these  changes  have  been  accurately  measured  in  the  living  subject. 
As  the  general  results  of  these  measurements  (Helmholtz),  it  was  ascertained 
that  the  lens  becomes  increased  in  thickness  in  accommodation  for  near 
objects,  chiefly  by  an  increase  in  its  anterior  curvature,  by  which  this  surface 
of  the  lens  is  made  to  project  toward  the  cornea.  As  the  iris  is  in  contact 
with  the  anterior  surface  of  the  lens,  this  membrane  is  made  to  project  in 
the  act  of  accommodation.  The  posterior  curvature  of  the  lens  is  also  in- 
creased, but  this  is  slight  as  compared  with  the  increase  of  the  curvature  of 
its  anterior  surface.  The  distance  between  the  posterior  surface  of  the  lens 
and  the  cornea  is  not  sensibly  altered.  It  is  unnecessary  to  describe  minutely 
the  methods  employed  in  making  these  calculations,  and  it  is  sufficient  to 
state  that  it  is  done  by  accurately  measuring  the  comparative  size  of  images 
formed  by  reflection  from  the  anterior  surface  of  the  lens.  The  results 
obtained  by  Helmholtz,  in  observations  upon  two  persons,  are  as  follows : 


Persons  examined. 

Radius  of  curvature  of  the  anterior  surface  of 
the  lens. 

Displacement  of  the  pupil  in  ac- 
commodation for  near  objects. 

Distant  vision. 

Near  vision. 

0.  H. 
B.  P. 

0-4641  in.  (11-9  mm.) 
0-3432  in.  (8-8  mm.) 

0-3354  in.  (8-6  mm.) 
0-2701  in.  (5-9  mm.) 

0-0140  in.  (0-36  mm.) 
0-0172  in.  (0-44  mm.) 

The  mechanism  of  the  changes  in  the  thickness  and  in  the  curvatures  of 
the  lens  in  accommodation  can  be  understood  only  by  keeping  clearly  in 
mind  the  physical  properties  of  the  lens  itself  and  its  anatomical  relations. 
In  situ,  in  what  has  been  called  the  indolent  state  of  the  eye,  the  lens  is  ad- 
justed to  vision  at  an  infinite  distance  and  is  flattened  by  the  tension  of  its 
suspensory  ligament.  After  death,  indeed,  it  is  easy  to  produce  changes  in 
its  form  by  applying  traction  to  the  zone  of  Zinn.  Eemembering  the  exact 
relations  of  the  suspensory  ligament,  the  ciliary  muscle  and  the  lens,  and 
keeping  in  mind  the  tension  within  the  globe,  it  is  evident  that  when  the 
ciliary  muscle  is  in  repose,  the  capsule  will  compress  the  lens,  increasing  its 
diameter  and  diminishing  its  convexity.  It  is  in  this  condition  that  the  eye 
is  adapted  to  vision  at  an  infinite  distance.  It  is  evident,  also,  that  very 
slight  changes  in  the  convexity  of  the  lens  will  be  sufficient  for  the  range  of 
accommodation  required.  If  any  near  object  be  fixed  with  the  eye  there  is 
a  conscious  effort,  and  the  prolonged  vision  of  near  objects  produces  a  sense 
of  fatigue.  This  may  be  illustrated  by  the  very  familiar  experiment  of  look- 
ing at  a  distant  object  through  a  gauze.  When  the  object  is  seen  distinctly, 
the  gauze  is  scarcely  perceived ;  but  by  an  effort  the  eye  can  be  brought  to 
see  the  meshes  of  the  gauze  distinctly,  when  the  impression  of  the  distant 
object  is  either  lost  or  becomes  very  indistinct. 


710 


SPECIAL  SENSES. 


The  ciliary  muscle  arises  from  the  circular  line  of  junction  of  the  cornea 
and  sclerotic,  passes  backward,  and  is  lost  in  the  tissue  of  the  choroid,  ex- 
tending as  far  as  the  anterior  border  of  the  retina.  Most  of  the  fibres  pass 
directly  backward,  but  some  become  circular  or  spiral.  When  this  muscle 
contracts,  the  choroid  is  drawn  forward,  with  probably  a  slightly  spiral 
motion  of  the  lens,  the  contents  of  the  globe,  situated  behind  the  lens,  are 
compressed,  and  the  suspensory  ligament  is  relaxed.  The  lens  itself,  the 
compressing  and  flattening  action  of  the  suspensory  ligament  being  dimin- 


N 


FIG.  256. — Section  of  the  lens  etc.,  showing  the  mechanism  of  accommodation  (Kick). 
The  left  side  of  the  figure  (F)  shows  the  lens  adapted  to  vision  at  infinite  distances.    The  right  side  of 
the  figure  (N)  shows  the  lens  adapted  to  the  vision  of  near  objects,  the  ciliary  muscle  being  con- 
tracted and  the  suspensory  ligament  of  the  lens  consequently  relaxed. 

ished,  becomes  thicker  and  more  convex,  by  virtue  of  its  own  elasticity,  in 
the  same  way  that  it  becomes  thicker  after  death,  when  the  tension  of  the 
ligament  is  artificially  diminished. 

This  is  in  brief  the4  mechanism  of  accommodation.  Near  objects  are 
seen  distinctly  by  a  voluntary  contraction  of  the  ciliary  muscle,  the  action  of 
which  is  perfectly  adapted  to  the  requirements  of  vision.  In  early  life  the 
lens  is  soft  and  elastic,  and  the  accommodating  power  is  at  its  maximum ; 
but  in  old  age  the  lens  becomes  flattened,  harder  and  less  elastic,  and  the 
power  of  accommodation  necessarily  is  diminished. 

Changes  in  the  Iris  in  Accommodation. — The  size  of  the  pupil  is  sensibly 
diminished  in  accommodation  of  the  eye  for  near  objects.  Although  the 
movements  of  the  iris  are  directly  associated  with  the  muscular  effort  by 
which  the  form  of  the  lens  is  modified,  the  contraction  of  the  pupil  is  not 
one  of  the  essential  conditions  of  accommodation.  Helmholtz  reported  a 
case  in  which  the  iris  was  completely  paralyzed,  the  power  of  accommoda- 
tion remaining  perfect ;  and  he  described  another  case,  reported  by  Von 
Graefe,  in  which  accommodation  was  not  disturbed  after  loss  of  the  entire 
iris. 

It  has  already  been  noted  that  the  pupil  contracts  when  the  eyes  are  made 
to  converge  by  the  action  of  the  muscles  animated  by  the  third  pair  of  nerves ; 
and  it  is  evident  that  convergence  of  the  eyes  occurs  in  looking  at  very  near  ob- 
jects. It  has  been  shown  by  Bonders,  that  increased  convergence  of  the  vis- 
ual lines  without  change  of  accommodation  makes  the  pupil  contract,  as  is 
easily  proved  by  simple  experiments  with  prismatic  glasses,  and  that  when 


VISUAL  ACCOMMODATION.  Til 

accommodation  is  effected  without  converging  the  visual  axes,  "  each  stronger 
tension  is  combined  with  contraction  of  the  pupil."  Contraction  of  the 
pupil,  therefore,  occurs  both  in  convergence  of  the  visual  axes  without  ac- 
commodation and  in  accommodation  for  near  objects  without  convergence  of 
the  eyes. 

The  action  of  the  iris,  as  is  evident  from  the  facts  just  stated,  is  to  a  cer- 
tain extent  under  the  control  of  the  will ;  but  it  can  not  be  disassociated, 
first,  from  the  voluntary  action  of  the  muscles  which  converge  the  visual 
axes,  and  second,  from  the  action  of  the  ciliary  muscle.  Bonders,  by  alter- 
nating the  accommodation  for  a  remote  and  a  near  object,  was  able  to  volun- 
tarily contract  and  dilate  the  pupil  more  than  thirty  times  in  a  minute. 
Brown-Sequard,  in  discussing  the  voluntary  movements  of  the  iris,  has  men- 
tioned a  case  in  which  "  the  pupil  could  be  contracted  or  dilated  without 
changing  the  position  of  the  eye  or  making  an  effort  of  adaptation  for  a  long 
or  a  short  distance."  As  a  farther  evidence  of  the  connection  of  accommoda- 
tion with  muscular  action,  cases  are  cited  in  works  on  ophthalmology,  in 
which  there  is  paralysis  of  the  ciliary  muscle,  as  well  as  cases  in  which  the 
act  of  accommodation  is  painful. 

A  curious  phenomenon  connected  with  accommodation  may  be  observed 
in  looking  at  a  near  object  through  a  very  small  orifice,  like  a  pinhole.  The 
shortest  distance  at  which  one  can  see  a  small  object  distinctly  is  about  five 
inches  (12'7  centimetres) ;  but  in  looking  at  the  same  object  through  a  pin- 
hole  in  a  card,  it  can  be  seen  distinctly  at  the  distance  of  about  one  inch 
(25'4  mm.),  and  it  then  appears  considerably  magnified.  In  this  experiment, 
the  card  serves  as  a  diaphragm  with  a  very  small  opening,  so  that  the  centre 
of  the  lens  only  is  used ;  and  the  apparent  increase  in  the  size  of  the  object 
probably  is  due  to  the  fact  that  its  distance  from  the  eye  is  many  times  less 
than  the  distance  at  which  distinct  vision  is  possible  under  ordinary  condi- 
tions. It  is  well  known  that  myopic  persons,  by  being  able  to  bring  the  eye 
nearer  to  objects  than  is  possible  in  ordinary  vision,  can  see  minute  details 
with  peculiar  distinctness. 

Erect  Impressions  produced  by  Images  inverted  upon  the  Retina. — The 
images  which  make  visual  impressions  are  necessarily  inverted  upon  the 
retina ;  but  the  cerebral  visual  centre  takes  no  cognizance  of  this,  and  objects 
are  seen  in  their  actual  position.  It  seems  almost  absurd  to  enter  into  a  seri- 
ous discussion  of  this  fact.  In  the  words  of  Helmholtz,  "  our  natural  con- 
sciousness is  completely  ignorant  even  of  the  existence  of  the  retina  and  of 
the  formation  of  images :  how  should  it  know  any  thing  of  the  position  of 
images  formed  upon  it  ?  " 

Field  of  Indirect  Vision. — If  the  eye  be  kept  fixed  upon  a  certain  point, 
and  an  object  be  moved  from  this  point  as  a  centre  in  lines  radiating  in  dif- 
ferent directions  until  it  passes  from  the  field  of  view,  the  limits  of  indirect 
vision  are  indicated.  Eight  or  ten  such  points  of  limit,  connected  by  a 
curved  line,  give  a  map  of  the  visual  field.  This  may  be  done  roughly  upon  a 
flat  surface,  such  as  a  blackboard,  placed  at  a  distance  of  twelve  to  eighteen 
inches  (3  to  4-5  centimetres)  from  the  eye,  or  a  chart  may  be  made  with  an 


712 


SPECIAL  SENSES. 


instrument  called  the  perimeter,  by  which  the  field  is  marked  on  the  inner 
surface  of  a  hemisphere.     The  field  of  vision  thus  delineated  is  an  irregular 

oval,  extending  from  the 
fixed  point,  farther  to 
the  temporal  side  than 
to  either  the  nasal  side 
or  above  and  below.  The 
extent  from  the  fixed 
point  is  about  90°  on 
the  temporal  side,  and 
about  70°  to  the  nasal 
side  and  above  and  be- 
low. The  field  for  white 
is  larger  than  for  colors, 
especially  on  its  nasal 
side,  as  is  seen  in  Fig. 
257.  The  field  is  small- 
est for  green,  a  little 
larger  for  red,  and  is 
larger  still  for  blue.  In- 
vestigation of  the  field 


FIG.  257. — Field  of  vision  of  the  right  eye,  as  projected  by  the  pa- 
tient on  the  inner  surface  of  a  hemisphere,  the  pole  of  which 
forms  the  object  of  regard  —  semi-diagrammatic  (Nettleship, 
after  Landolt). 

T,  temporal  side  ;  N,  nasal  side  ;  w,  boundary  for  white  ;  B,  bound- 
ary for  blue  ;  R,  boundary  for  red  ;  G,  boundary  for  green. 

ological  interest,  as  regards  the  sensibility  of  the 
direct  vision. 

BIXOCULAR  Vision. 


of  indirect  vision  with 
the  perimeter  is  very 
useful  in  ophthalmolo- 
gy, but  the  chief  physi- 
retina,  is  connected  with 


Thus  far  the  mechanism  of  the  eye  and  its  action  as  an  optical  instru- 
ment, in  monocular  vision  only,  have  been  described ;  but  it  is  evident  that 
both  eyes  are  habitually  used,  and  that  their  axes  are  practically  parallel  in 
looking  at  distant  objects  and  are  converged  when  objects  are  approached  to 
the  nearest  point  at  which  there  is  distinct  vision.  In  fact  an  image  is 
formed  simultaneously  upon  the  retina  of  each  eye,  but  it  is  nevertheless 
appreciated  as  a  unit.  If  the  axis  of  one  eye  be  slightly  deviated  by  pressure 
upon  the  globe,  so  that  the  images  are  not  formed  upon  corresponding  points 
in  the  retina  of  each  eye,  vision  is  more  or  less  indistinct  and  is  double.  In 
strabismus,  when  this  condition  is  recent,  temporary  or  periodical,  as  in  recent 
cases  of  paralysis  of  the  external  rectus  muscle,  when  both  eyes  are  normal, 
there  is  double  vision.  When  the  strabismus  is  permanent  and  has  existed 
for  a  long  time,  double  vision  may  not  be  observed,  unless  the  subject  direct 
the  attention  strongly  to  this  point.  As  but  one  eye  is  capable  of  fixing 
objects  accurately,  images  are  formed  upon  the  fovea  of  this  eye  only.  Images 
formed  upon  the  retina  of  the  other  eye  are  indistinct,  and  in  many  instances 
are  habitually  disregarded ;  so  that  practically  the  subject  uses  but  one  eye, 


BINOCULAE  VISION.  713 

and  presents  the  errors  of  appreciation  which  attend  monocular  vision,  such 
as  a  want  of  exact  estimation  of  the  solidity  and  distance  of  objects.  It  is 
stated  as  the  rule  that  when  strabismus  of  long  standing  is  remedied,  as  far 
as  the  axes  of  the  eyes  are  concerned,  by  an  operation,  binocular  vision  is  not 
restored.  This  is  explained  upon  the  supposition  that  the  perceptive  power 
of  the  retina  of  the  affected  eye  has  been  gradually  and  irrecoverably  lost 
from  disuse.  In  normal  binocular  vision  the  images  are  formed  upon  the 
fovea  centralis  of  each  eye ;  that  is,  upon  corresponding  points,  which  are, 
for  each  eye,  the  centres  of  distinct  vision.  The  concurrence  of  both  eyes  is 
necessary  to  the  exact  appreciation  of  distance  and  form ;  and  when  the  two 
images  are  formed  upon  corresponding  points,  the  visual  centre  receives  a 
correct  impression  of  a  single  object.  When  vision  is  perfect,  the  sensation 
of  the  situation  of  any  single  object  is  referred  to  one  and  the  same  point ; 
and  the  impression  of  a  double  image  can  not  be  received  unless  the  condi- 
tions of  vision  be  abnormal. 

Corresponding  Points. — While  it  is  evident,  after  the  statements  just 
made,  that  an  image  must  be  formed  upon  the  fovea  of  each  eye  in  order  to 
produce  the  effect  of  a  single  object,  it  becomes  important  to  ascertain  how 
far  it  is  necessary  that  the  correspondence  of  points  be  carried  out  in  the 
retina.  It  is  almost  certain  that  for  absolutely  perfect,  single  vision  with  the 
two  eyes,  the  impressions  must  be  made  upon  exactly  corresponding  points, 
even  to  the  ultimate,  sensitive  elements  of  the  retina.  It  may  be  assumed, 
indeed,  that  each  rod  and  each  cone  of  one  eye  has  its  corresponding  rod  and 
cone  in  the  other,  situated  at  exactly  the  same  distance  and  in  correspond- 
ing directions  from  the  visual  axis.  When  the  two  images  of  an  object  are 
formed  upon  these  corresponding  points,  they  appear  as  one ;  but  when  the 
images  do  not  correspond,  the  impression  is  as  though  the  images  were 
formed  upon  different  points  in  one  retina,  and  of  necessity  they  appear 
double. 

The  effect  of  a  slight  deviation  from  the  corresponding  points  may  be 
illustrated  by  the  following  experiment :  If  a  small  object,  like  a  lead-pencil, 
held  at  a  distance  of  a  few  inches,  be  fixed  with  the  eyes,  it  is  seen  distinctly 
as  a  single  object.  Holding  another  small  object  in  the  same  line,  a  few 
inches  farther  removed,  when  the  first  is  seen  distinctly,  the  second  appears 
double.  If  the  second  object  be  fixed  with  the  eyes,  the  first  appears  double. 
It  is  evident  here,  that  when  the  axes  of  the  eyes  bear  upon  one  of  these  ob- 
jects, the  images  of  the  other  must  be  formed  at  a  certain  distance  from  the 
corresponding  retinal  points. 

The  Horopter. — The  above-mentioned  experiment  affords  an  explanation 
of  the  horopter.  If  both  eyes  be  fixed  upon  a  point  directly  in  front  and  be 
kept  in  this  position,  an  object  moved  to  one  side  or  the  other,  within  a  cer- 
tain area,  may  be  seen  without  any  change  in  the  direction  of  the  axis  of  vis- 
ion ;  but  the  distance  from  the  eye  at  which  there  is  single  vision  of  this 
object  is  fixed,  and  at  any  other  distance  the  object  appears  double.  The 
explanation  of  this  is  that  at  a  certain  distance  from  the  eye,  the  images  are 
formed  upon  corresponding  points  in  the  retina ;  but  at  a  shorter  or  longer 


714  SPECIAL  SENSES. 

distance,  this  can  not  occur.  This  illustrates  the  fact  that  there  are  corre- 
sponding points  in  a  large  part  of  the  sensitive  layer  of  the  retina,  as  well  as 
in  the  fovea  centralis.  By  these  experiments,  the  following  facts  have  been 
ascertained :  With  both  eyes  fixed  upon  an  object,  another  object  moved  to 
one  side  or  the  other  can  be  distinctly  seen  only  when  it  is  carried  in  a  cer- 
tain curved  line.  On  either  side  of  this  line,  the  object  appears  double. 
This  line,  or  area — for  the  line  may  have  any  direction — is  called  the  horop- 
ter.  It  was  supposed  at  one  time  to  be  a  regular  curve,  or  a  portion  of  a  circle 
drawn  through  the  fixed  point  and  the  points  of  intersection  of  the  rays  of 
light  in  each  eye.  Although  it  has  been  ascertained  that  the  line  varies 
somewhat  from  a  regular  curve,  and  also  varies  in  different  meridians,  this  is 
due  to  differences  in  refraction,  etc.,  and  the  principle  is  not  altered. 

If  the  visual  areas  of  the  two  retinae  be  superimposed,  the  fixation-points 
coinciding,  it  becomes  evident  that  a  portion  only  of  the  two  fields  can  have 

corresponding  points.  This 
is  the  light  portion  shown  in 
Fig.  258,  which  may  be  called 
the  binocular  field  of  vision. 
Binocular  vision  must  be  im- 
possible in  the  temporal  por- 
tion of  each  visual  area  (Net- 
tleship). 

It  is  undoubtedly  true  that 
education  and  habit  have  a 
great  deal  to  do  with  the  cor- 

FIG.  258.— Binncular  Held  of  vision  (Nettleship,  after  Forster.)    rpptinn    nf    vJcnnl  imnrpsainna 
F,  fixation-point ;  B,  B,  blind  spots. 

and  the  just  appreciation  of 

the  size,  form  and  distance  of  objects.  In  the  remarkable  case  of  Casper 
Hauser,  who  is  said  to  have  been  kept  in  total  darkness  and  seclusion,  from 
the  age  of  five  months  until  he  was  nearly  seventeen  years  old,  the  appreciation 
of  size,  form  and  distance  were  acquired  by  correcting  and  supplementing  the 
sense  of  sight,  by  experience.  This  boy  at  first  had  no  idea  of  the  form  of 
objects  or  of  distance,  until  he  had  learned  by  touch,  by  walking  etc.,  that 
certain  objects  were  round  and  others  were  square,  and  had  actually  traversed 
the  distance  from  one  object  to  another.  At  first  all  objects  appeared  as  if 
painted  upon  a  screen.  Such  points  as  these  it  would  be  impossible  to  accu- 
rately observe  in  infants ;  but  young  children  often  grasp  at  remote  objects, 
apparently  under  the  impression  that  they  were  within  reach.  It  must  be 
admitted,  however,  that  the  account  of  the  case  of  Casper  Hauser  is  rather 
indefinite ;  but  it  is  certain  that  even  in  the  adult,  education  and  habit 
greatly  improve  the  faculty  of  estimating  distances. 

Careful  observations  leave  no  doubt  of  the  fact  that  monocular  vision  is 
incomplete  and  inaccurate,  and  that  it  is  only  when  two  images  are  formed, 
one  upon  either  retina,  that  vision  is  absolutely  perfect.  The  sum  of  actual 
knowledge  upon  this  important  point  is  expressed  in  the  following  quotation 
from  Giraud-Teulon  : 


BINOCULAR  VISION.  715 

"  Monocular  vision  only  indicates  to  us  immediately,  visual  direction,  and 
not  precise  locality.  At  whatever  distance  a  luminous  point  may  be  situated 
in  the  line  of  direction,  it  forms  its  image  upon  the  same  point  in  the  retina. 

"  In  the  physiological  action  of  a  single  eye,  in  order  to  arrive  at  an  idea 
of  the  distance  of  a  point  in  a  definite  direction,  we  have  only  the  following 
elements  : 

"  1.  The  consciousness  of  an  effort  of  accommodation. 

"  2.  Our  own  movement  in  its  relations  to  the  point  observed. 

"3.  Facts  brought  to  bear  from  recollection,  education,  our  acquired 
knowledge  with  regard  to  the  form  and  size  of  objects :  in  a  word,  experi- 
ence. 

"  4.  The  geometric  perspective  of  form  and  position. 

"  5.  Aerial  perspective. 

"  All  these  are  elements  wanting  in  precision  and  leaving  the  problem 
without  a  decisive  solution. 

"  And,  indeed : 

"  We  place  before  one  of  our  eyes,  the  other  being  closed,  the  excavated 
mould  of  a  medallion :  we  do  not  hesitate,  after  a  few  seconds,  to  mistake  it 
for  the  relief  of  the  medallion.  This  illusion  ceases  at  the  instant  that  both 
eyes  are  opened. 

"  Or  again : 

"  A  miniature,  a  photograph,  a  picture,  produces  for  a  single  eye  a  perfect 
illusion ;  but  if  both  eyes  be  open,  the  picture  becomes  flat,  the  prominences 
and  the  depressions  are  effaced. 

"  "We  may  repeat  the  following  experiment  described  by  Malebranche : 
'  Suspend  by  a  thread  a  ring,  the  opening  of  which  is  not  directed  toward 
us ;  step  back  two  or  three  paces ;  take  in  the  hand  a  stick  curved  at  the 
end ;  then,  closing  one  eye  with  the  hand,  endeavor  to  insert  the  curved  end 
of  the  stick  within  the  ring,  and  we  shall  be  surprised  at  being  unable  to  do 
in  a  hundred  trials  what  we  should  believe  to  be  very  easy.  If,  indeed,  we 
abandon  the  stick  and  endeavor  to  pass  one  of  the  fingers  through  the  ring, 
we  shall  experience  a  certain  degree  of  difficulty,  although  it  is  very  near. 
This  difficulty  ceases  at  the  instant  that  both  eyes  are  opened.' 

"  As  regards  precision,  exactitude  of  information  concerning  the  relative 
distance  of  objects,  that  is  to  say,  the  idea  of  the  third  dimension,  or  of  depth, 
there  is  then  a  notable  difference  between  binocular  vision  and  that  which  is 
obtained  by  means  of  one  eye  alone." 

It  is  evident  that  an  accurate  idea  of  the  distance  of  near  objects  can 
not  be  obtained  except  by  the  use  of  both  eyes,,  and  this  fact  will  partly  ex- 
plain the  errors  of  monocular  vision  in  looking  with  one  eye  upon  objects  in 
relief ;  for  under  these  conditions,  it  is  impossible  to  determine  with  accu- 
racy whether  the  points  in  relief  be  nearer  or  farther  from  the  eye  than  the 
plane  surface.  This  will  not  fully  explain,  however,  the  idea  of  solidity  of 
objects,  which  is  obtained  by  the  use  of  both  eyes ;  for  the  estimation  of  dis- 
tance is  obtained  by  bringing  the  axes  of  both  eyes  to  bear  upon  a  single 
object,  be  it  near  or  remote.  The  fact  is — as  was  distinctly  stated  by  Galen, 


716  SPECIAL  SENSES. 

in  the  second  century — that  in  looking  at  any  solid  object  not  so  far  re- 
moved as  to  render  the  visual  axes  practically  parallel,  a  portion  of  the  sur- 
face, seen  with  the  right  eye,  is  not  seen  with  the  left  eye,  and  vice  versd. 
The  two  impressions,  therefore,  are  not  identical  for  each  retina ;  the  image 
upon  the  left  retina  including  a  portion  of  the  left  side  of  the  object,  not 
seen  by  the  right  eye,  the  right  image  in  the  same  way  including  a  portion 
of  the  right  surface,  not  seen  by  the  left  eye.  These  slightly  dissimilar 
impressions  are  fused  and  produce  the  impression  of  a  single  image,  when 
vision  is  perfectly  normal ;  and  this  gives  the  idea  of  relief  or  solidity,  and 
an  exact  appreciation  of  the  form  of  objects,  when  they  are  not  too  remote. 

The  fact  just  stated  is  of  course  a  mathematical  necessity  in  binocular 
vision  for  near  objects ;  but  the  actual  demonstration  of  the  fusion  of  two 
dissimilar  images  and  the  consequent  formation  of  a  single  image  giving  the 
impression  of  solidity  was  made  by  the  invention  of  the  stereoscope,  by 
Wheatstone.  The  principle  of  this  instrument  is  very  simple.  Two  pictures 
are  made,  representing  a  solid  object,  one  viewed  slightly  from  the  right 
side,  and  the  other,  slightly  from  the  left,  so  as  to  imitate  the  differences  in 
the  images  formed  upon  the  two  retinae.  These  pictures  are  so  placed  in  a 
box  that  the  image  of  one  is  formed  upon  the  right  retina,  and  the  other, 
upon  the  left.  When  these  conditions  are  accurately  fulfilled,  but  a  single 
image  is  seen,  and  this  conveys  to  the  mind  the  perfect  illusion  of  a  solid 
object.  Experiments  with  the  stereoscope  are  so  familiar  that  they  need 
hardly  be  dwelt  upon.  Experience,  the  aid  of  the  sense  of  touch  etc.,  enable 
persons  with  but  one  eye  to  get  a  notion  of  form,  but  the  impressions  are 
never  entirely  accurate  in  this  regard,  although,  from  habit,  this  defect  occa- 
sions little  or  no  inconvenience. 

Although  an  opposite  opinion  is  held  by  some  experimenters,  Helmholtz, 
with  many  others,  has  stated  that  when  one  color  is  seen  with  one  eye  and 
another  color,  with  the  other  eye,  in  the  stereoscope,  the  impression  is  not  of  a 
single  color  resulting  from  the  combination  of  the  two.  It  is  true  that  there 
is  an  imperfect  mingling  of  the  two  colors,  but  this  is  very  different  from  the 
resulting  color  produced  by  the  actual  fusion  of  the  two.  There  is,  in  other 
words,  a  sort  of  confusion  of  colors,  without  the  complete  combination  ob- 
served in  ordinary  experiments.  One  additional  point  of  importance,  how- 
ever, is  that  the  binocular  fusion  of  two  pictures,  unequally  illuminated  or  of 
different  colors,  produces  a  single  image  of  a  peculiar  lustre,  even  when  both 
surfaces  are  dull.  This  may  be  shown  by  making  a  stereoscopic  combination 
of  images  of  crystals,  one  with  black  lines  on  a  white  ground,  and  the  other 
with  white  lines  on  a  black  ground.  The  resulting  image  has  then  the  ap- 
pearance of  dark,  brilliant  crystals,  like  graphite. 

Duration  of  Luminous  Impressions  (After- Images}. — The  time  re- 
quired for  a  single  visual  stimulation  of  the  retina  is  exceedingly  short.  The 
letters  on  a  printed  page  are  distinctly  seen  when  illuminated  by  an  electric 
spark,  the  duration  of  which  is  not  more  than  forty  billionths  of  a  second 
(Rood).  An  impression  made  upon  the  retina,  however,  endures  for  a  length 
of  time  that  bears  a  certain  relation  to  the  intensity  of  the  luminous  excita- 


IRRADIATION.  717 

tion.  If  the  eyes  be  closed  after  looking  steadily  at  a  very  bright  object,  the 
object  is  more  or  less  distinctly  seen  after  the  rays  have  ceased  to  pass  to  the 
eye,  and  the  image  fades  away  gradually.  When  there  is  a  rapid  succession 
of  images,  they  may  be  fused  into  one,  as  the  spokes  of  a  rapidly  revolving 
wheel  are  indistinct  and  produce  a  single  impression.  This  is  due  to  the 
persistence  of  the  successive  retinal  impressions ;  for  if  a  revolving  wheel  or 
even  a  falling  body  be  illuminated  for  the  brief  duration  of  an  electric  spark, 
it  appears  absolutely  stationary,  as  the  period  of  time  necessary  for  perfectly 
distinct  vision  and  the  duration  of  the  illumination  are  so  short,  that  there  is 
no  time  for  any  appreciable  movement  of  the  object.  The  familiar  experi- 
ments made  with  revolving  disks  illustrate  these  points.  In  a  disk  marked 
with  alternate,  radiating  lines  of  black  and  white,  the  rays  become  entirely 
indistinguishable  during  rapid  revolution,  and  the  disk  appears  of  a  uniform 
color,  such  as  would  be  produced  by  a  combination  of  the  black  and  white. 
The  effects  of  an  artificial  combination  of  colors  may  be  produced  in  this  way, 
the  resultant  color  appearing  precisely  as  if  the  individual  colors  had  been 
ground  together.  The  duration  of  retinal  impressions  varies  considerably 
for  the  different  colors.  According  to  Emsmann,  the  duration  for  yellow  is 
0-25  of  a  second ;  for  white,  0'25  of  a  second ;  for  red,  O22  of  a  second  ;  and 
for  blue,  O21  of  a  second. 

The  impressions  which  remain  on  the  retina  after  an  object  has  been 
looked  at  steadily  are  called  after-images.  When  these  are  bright  and  of  the 
same  character  as  the  object,  they  are  called  positive  after-images.  When 
the  stimulation  of  the  retina  has  been  very  powerful  and  prolonged,  the 
after-image  frequently  is  dark.  Such  images  are  called  negative  after-images. 

It  is  unnecessary  to  describe  farther  in  detail  the  well  known  phenomena 
which  illustrate  the  point  under  consideration.  The  circle  of  light  produced 
by  rapidly  revolving  a  burning  coal,  the  track  of  a  meteor,  and  other  illustra- 
tions, are  sufficiently  familiar,  as  well  as  many  scientific  toys  producing  opti- 
cal illusions  of  various  kinds. 

Irradiation. — It  has  been  observed  that  luminous  impressions  are  not 
always  confined  to  the  elements  of  the  retina  directly  involved,  but  are  some- 
times propagated  to  those  immediately  adjacent.  This  gives  to  objects  a 
certain  degree  of  amplification,  which  is  generally  in  proportion  to  their 
brightness.  An  illustration  of  this  is  afforded  by  the  simple  experiment  of 
looking  at  two  circles,  one  black  on  a  white  ground,  and  the  other  white  on 
a  black  ground.  Although  the  actual  dimensions  of  the  two  circles  are  iden- 
tical, the  irradiation  of  rays  from  the  white  circle  makes  this  appear  the 
larger.  In  a  circle  with  one  half  black  and  the  other  white,  the  white  por- 
tion will  appear  larger,  for  the  same  reason.  These  phenomena  are  due  to 
what  has  been  called  irradiation ;  and  their  explanation  is  very  simple.  It  is 
probable  that  luminous  impressions  are  never  confined  absolutely  to  those 
parts  of  the  retina  upon  which  the  rays  of  light  directly  impinge,  but  that 
the  sensitive  elements  immediately  contiguous  are  always  more  or  less  in- 
volved. In  looking  at  powerfully  illuminated  objects,  the  irradiation  is  con- 
siderable, as  compared  with  objects  which  send  fewer  luminous  rays  to  the  eye. 
47 


718 


SPECIAL  SENSES. 


In  experiments  analogous  to  those  just  described,  made  with  strongly 
colored  objects,  it  has  been  observed  that  the  border  of  irradiation  takes  a 
color  complementary  to  that  of  the  object  itself.  This  is  particularly  well 
marked  when  the  objects  are  steadily  looked  at  for  some  time.  Illustrations 
of  this  point  also  are  very  simple.  In  looking  steadily  at  a  red  spot  or  figure 
on  a  white  ground,  a  faint  areola  of  a  pale-green  soon  appears  surrounding 
the  red  object ;  or  if  the  image  be  yellow,  the  areola  will  appear  pale-blue. 
These  appearances  have  been  called  accidental  areolae. 

MOVEMENTS  OF  THE  EYEBALL. 

The  eyeball  nearly  fills  the  cavity  of  the  orbit,  resting,  by  its  posterior  por- 
tion, upon  a  bed  of  adipose  tissue,  which  is  never  absent,  even  in  extreme 
emaciation.  Outside  of  the  sclerotic,  is  a  fibrous  membrane,  the  tunica  vag- 
inalis  oculi,  or  capsule  of  Tenon,  which  is  useful  in  maintaining  the  equilib- 
rium of  the  globe.  This  fibrous  membrane  surrounds  the  posterior  two- 
thirds  of  the  globe  and  is  loosely  attached  to  the  sclerotic.  It  is  perforated 
by  the  optic  nerve  posteriorly,  and  by  the  tendons  of  the  recti  and  oblique 
muscles  of  the  eyeball  in  front,  being  reflected  over  these  muscles.  It  is 
also  continuous  with  the  palpebral  ligaments  and  is  attached  by  two  tendin- 
ous bands,  to  the  border  of  the  orbit,  at  the  internal  and  the  external  angles 
of  the  lids. 

The  muscles  which  move  the  globe  are  six  in  number  for  each  eye.  These 
are  the  external  and  internal  recti,  the  superior  and  inferior  recti  and  the 


FIG.  259.— Muscles  of  the  eyeball  (Sappey). 

1,  attachment  of  the  tendon  connected  with  the  inferior  rectus,  internal  rectus  and  external  rectus  ;  2, 
external  rectus,  divided  and  turned  downward,  to  expose  the  inferior  rectus  :  3,  internal  rectus  :  4, 
inferior  rectus  :  5,  superior  rectus  ;  6,  superior  oblique  ;  7.  pulley  and  reflected  portion  of  the  supe- 
rior oblique  :  8,  inferior  oblique  ;  9,  levator  palpebri  superioris  ;  10, 10,  middle  portion  of  the  levator 
palpebri  superioris  ;  11,  optic  nerve. 

two  oblique  muscles.     The  four  recti  muscles  and  the  superior  oblique  arise 
posteriorly  from  the  apex  of  the  orbit.     The  recti  pass  directly  forward  by 


MOVEMENTS  OF  THE  EYEBALL.  719 

the  sides  of  the  globe  and  are  inserted  by  short,  tendinous  bands  into  the  scle- 
rotic, at  a  distance  of  one-fourth  to  one-third  of  an  inch  (6-4  to  8'5  mm.) 
from  the  margin  of  the  cornea.  The  superior  oblique,  or  trochlearis  muscle 
passes  along  the  upper  and  inner  wall  of  the  orbit,  to  a  point  near  the  inner 
angle.  It  here  presents  a  rounded  tendon,  which  passes  through  a  ring,  or 
pulley  of  fibro-cartilage ;  and  it  is  from  this  point  that  its  action  is  exerted 
upon  the  globe.  From  the  pulley,  or  trochlea,  the  tendon  becomes  flattened, 
passes  outward  and  backward  beneath  the  superior  rectus,  and  is  inserted 
into  the  sclerotic,  about  midway  between  the  superior  and  the  external  rectus 
and  just  behind  the  equator  of  the  globe.  The  inferior  oblique  muscle  arises 
just  within  the  anterior  margin  of  the  orbit,  near  the  inner  angle  of  the  eye, 
and  passes  around  the  anterior  portion  of  the  globe,  beneath  the  inferior  rec- 
tus and  between  the  external  rectus  and  the  eyeball,  taking  a  direction  out- 
ward and  slightly  backward.  Its  tendon  is  inserted  into  the  sclerotic,  a  little 
below  the  insertion  of  the  superior  oblique.  The  general  arrangement  of  these 
muscles  is  shown  in  Fig.  259. 

The  various  movements  of  the  eyeball  are  easily  understood  by  a  study  of 
the  associated  movements  of  the  muscles  just  enumerated,  at  least  as  far  as 
is  necessary  to  the  comprehension  of  the  mechanism  by  which  the  eyes  are 
directed  toward  any  particular  object.  The  centre  of  exact  vision  is  in  the 
f ovea ;  and  it  is  evident  that  in  order  to  see  any  object  distinctly,  it  is  neces- 
sary to  bring  it  within  the  axes  of  vision  of  both  eyes.  As  the  globe  is  so 
balanced  in  the  orbit  as  to  be  capable  of  rotation,  within  certain  limits,  in 
every  direction,  it  is  necessary  only  to  note  the  exact  mode  of  action  of  each 
of  the  muscles,  in  order  to  comprehend  how  the  different  movements  are 
accomplished ;  and  it  is  sufficient  for  practical  purposes  to  admit  that  ap- 
proximately there  is  a  common  axis  of  rotation  for  each  pair  of  muscles. 

Under  ordinary  conditions,  in  the  human  subject,  the  action  of  the  six 
ocular  muscles  is  confined  to  the  movements  of  rotation  and  torsion  of  the 
globe.  It  is  said  that  in  the  human  subject,  there  is  no  such  thing  as  pro- 
trusion of  the  eye  from  general  relaxation  of  these  muscles,  and  that  it  is 
impossible,  by  a  combined  action  of  the  four  recti  muscles,  to  retract  the 
globe  in  the  orbit ;  but  those  who  have  operated  upon  the  eyes  assert  posi- 
tively that  this  statement  is  erroneous,  and  that  the  globe  is  almost  always 
suddenly  and  powerfully  drawn  within  the  orbit,  when  a  painful  impression 
is  made  upon  the  cornea.  This  is  stated  as  a  matter  of  common  observation 
by  ophthalmic  surgeons. 

The  extent  to  which  the  line  of  vision  may  be  turned  by  a  voluntary  effort 
varies  in  different  individuals,  even  when  the  eyes  are  perfectly  normal.  In 
myopic  eyes,  the  centre  of  rotation  is  deeper  in  the  orbit  than  normal,  and 
the  extent  of  the  possible  deviation  of  the  visual  line  is  correspondingly  di- 
minished. Helmholtz  stated  that,  in  -his  own  person,  with  the  greatest  effort 
that  he  was  capable  of  making,  he  could  move  the  line  of  vision  in  the  hori- 
zontal plane  to  the  extent  of  about  fifty  degrees,  and  in  the  vertical  plane,  about 
forty- five  degrees;  but  he  added  that  these  extreme  rotations  were  very 
forced,  and  that  they  could  not  be  sustained  for  any  considerable  length  of 


720 


SPECIAL  SENSES. 


time.  It  is  probable  that  the  eyeball  is  seldom  moved  to  an  angle  of  forty- 
five  degrees,  the  direction  of  the  visual  line  being  more  easily  accomplished 
by  movements  of  the  head. 

Action  of  the  Recti  Muscles. — The  internal  and  external  recti  rotate  the 
globe  upon  a  vertical  axis,  which  is  perpendicular  to  the  axis  of  the  eye.  The 
isolated  action  of  these  muscles,  particularly  of  the  external  rectus,  is  often 
illustrated  in  certain  forms  of  paralysis,  which  have  been  alluded  to  in  con- 
nection with  the  history  of  the  cranial  nerves. 

The  superior  and  inferior  recti  rotate  the  globe  upon  an  horizontal  axis, 
which  is  not  at  right  angles  with  the  axis  of  the  eye,  but  is  inclined  from  the 
nasal  side,  slightly  backward.  The  line  which  serves  as  the  axis  of  rotation 
for  these  muscles  forms  an  angle  of  about  seventy  degrees  with  the  axis  of 
the  globe ;  and  as  a  consequence  of  this  arrangement,  their  action  is  not  so 
simple  as  that  of  the  internal  and  external  recti.  The  insertion  of  the  supe- 
rior rectus  in  such,  that  when  it  contracts,  the  pupil  is  directed  upward  and 
inward,  the  inferior  rectus  directing  the  pupil  downward  and  inward. 

The  above  represents  the  simple,  isolated  action  of  each  pair  of  recti 
muscles ;  but  it  is  easy  to  see  how,  without  necessarily  involving  the  action 

of  the  oblique  muscles,  the  globe  may 
be  made  to  perform  a  great  variety 
of  rotations,  and  the  line  of  vision 
may  be  turned  in  nearly  every  direc- 
tion, by  the  action  of  the  recti  mus- 
cles alone. 

Action  of  the  Oblique  Muscles. — 
It  is  sufficient  for  all  practical  pur- 
poses to  assume  that  the  superior  and 
the  inferior  oblique  muscles  act  as 
direct  antagonists  to  each  other. 
The  most  exact  measurements  show 
that  the  axis  of  rotation  for  these 
muscles  is  horizontal  and  has  an  ob- 
lique direction  from  before  backward 
and  from  without  inward.  The  an- 
gle formed  by  the  axis  of  rotation  of 
the  oblique  muscles  with  the  axis  of 
the  globe  is  thirty-five  degrees;  and 
the  angle  between  the  axis  of  the 
oblique  muscles  and  the  axis  of  the 
superior  and  inferior  recti  muscles'  is 

FIG.  260.— Diagram  illustrating  the  action  of  the    a0T-OT,f,r  fi~0  /Inrrvaaa 
muscles  of  the  eyeball  (Fick).  Sev  eilty-nve  degrees. 

The  heavy  lines  represent  the  muscles  of  the  eye-  Given  the  direction  of  the  axis  of 

rotation  and  the  direction  of  the  su- 
perior oblique  muscle,  it  is  easy  to 
understand  the  effects  of  its  contraction.  As  this  muscle,  passing  obliquely 
backward  and  forward  over  the  globe,  acts  from  the  pulley  near  the  inner 


ball,  and  the  fine  lines,  the  axes  of  the  superior 
and  the  inferior  recti  and  the  axes  of  the  oblique 
muscles. 


MOVEMENTS  OF  THE  EYEBALL.  721 

angle  of  the  eye,  to  its  insertion  just  behind  the  anterior  half  of  the  globe  on 
its  external  and  superior  surface  (7,  Fig.  259),  it  must  rotate  the  globe  so  as 
to  direct  the  pupil  downward  and  outward. 

The  inferior  oblique,  passing  outward  and  slightly  backward  under  the 
globe,  acts  from  its  origin,  at  the  margin  of  the  orbit  near  the  inner  angle  of 
the  eye,  to  its  insertion,  which  is  just  below  the  insertion  of  the  superior 
oblique.  This  muscle  rotates  the  globe  so  as  to  direct  the  pupil  upward  and 
outward. 

The  action  of  the  oblique  muscles  seems  to  be  specially  connected  with 
the  movements  of  torsion  of  the  globe.  It  is  necessary  to  distinct,  single 
vision  with  both  eyes,  that  the  images  should  be  formed  upon  exactly  corre- 
sponding points  on  the  retina,  and  that  they  should  bear,  for  the  two  eyes, 
corresponding  relations  to  the  perpendicular.  Thus  it  is  that  when  the  head 
is  inclined  to  one  side,  the  eyes  are  twisted  upon  an  oblique,  antero-posterior 
axis ;  as  can  be  readily  seen  by  observing  little  spots  upon  the  iris,  during 
these  movements. 

The  superior  oblique  muscle  is  supplied  by  a  single  nerve,  the  patheticus. 
When  this  muscle  is  paralyzed,  the  inferior  oblique  acts  without  its  antago- 
nist, and  the  eyeball  is  immovable,  as  far  as  the  twisting  of  the  globe,  just 
describsd,  is  concerned.  When  the  head  is  moved  toward  the  shoulder,  the 
globe  can  not  rotate  to  maintain  a  position  corresponding  to  that  of  the  other 
eye,  and  there  is  double  vision.  This  point  has  already  been  touched  upon 
in  connection  with  the  physiology  of  the  nerves  of  the  eyeball  and  the  situa- 
tion of  corresponding  points  in  the  retina. 

Associated  Action  of  the  Different  Muscles  of  the  Eyeball. — It  is  almost 
unnecessary  to  add,  after  the  description  just  given  of  the  actions  of  the  indi- 
vidual muscles  of  the  globe,  that  their  contractions  may  be  associated  so  as 
to  produce  a  great  variety  of  movements.  There  is  no  consciousness,  under 
ordinary  conditions,  of  the  muscular  action  by  which  the  globe  is  rotated 
and  twisted  in  various  directions,  except  that  by  an  effort  of  the  will  the  line 
of  vision  is  directed  toward  different  objects.  By  a  strong  effort  the  axis  of 
the  eyes  may  be  converged  by  contracting  both  internal  recti,  and  some  per- 
sons can  produce  extreme  divergence  by  using  both  external  recti ;  but  this 
is  abnormal. 

In  looking  at  distant  objects  the  axes  of  vision  are  practically  parallel. 
In  looking  at  near  objects  the  effort  of  accommodation  is  attended  with  the 
degree  of  convergence  necessary  to  bring  the  visual  axes  to  bear  upon  iden- 
tical points.  In  looking  around  at  different  objects  the  head  is  moved  more 
or  less  and  the  globes  are  rotated  in  various  directions.  In  the-  movements 
of  the  globes  vertically  the  axes  are  kept  parallel,  or  at  the  proper  angle,  by 
the  internal  and  external  recti,  and  the  superior  and  inferior  recti  upon  the 
two  sides  act  together.  In  rotating  the  globe  from  one  side  to  the  other, 
upon  a  vertical  axis,  the  external  rectus  upon  one  side  acts  with  the  internal 
rectus  upon  the  other.  In  the  movements  of  torsion  upon  an  antero-poste- 
rior axis  there  must  be  an  associated  action  of  the  oblique  muscles  and 
the  recti. 


722  SPECIAL  SENSES. 

An  important  point,  not  to  be  lost  sight  of  in  the  study  of  the  associated 
action  of  the  muscles  of  the  globe,  relates  to  the  associated  movements  of  the 
two  eyes.  Perfect,  binocular  vision  is  possible  only  when  impressions  are 
made  upon  exactly  corresponding  points  in  the  retina  of  each  eye.  If  one 
eye  be  deviated  in  the  horizontal  plane,  the  points  no  longer  correspond,  and 
there  is  double  vision,  the  same  as  if  two  impressions  were  made  upon  one 
retina;  for  when  the  impressions  exactly  correspond,  the  two  retinae  act 
practically  as  a  single  organ.  The  same  is  true  in  deviation  of  the  globe  in 
the  vertical  plane.  If  it  be  supposed,  for  the  sake  of  argument,  that  the 
retina  is  square,  it  is  evident  that  a  torsion,  or  twisting  of  one  globe  upon  an 
antero-posterior  axis,  must  be  attended  with  an  analogous  movement  of  the 
other  globe,  in  order  to  bring  the  visual  rays  to  bear  upon  the  corresponding 
points ;  in  other  words,  the  obliquity  of  the  assumed  square  of  the  retina 
must  be  exactly  the  same  for  the  two  eyes,  or  the  coincidence  of  the  corre- 
sponding points  would  be  disturbed  and  there  would  be  double  vision.  De- 
viation of  one  eye  in  the  horizontal  or  the  vertical  plane  disturbs  the  relation 
of  the  corresponding  points,  and  a  deviation  from  exact  coincidence  of  action 
in  torsion  of  the  globes,  twists,  as  it  were,  the  corresponding  points,  so  that 
their  relation  is  also  disturbed.  It  is  evident,  therefore,  that  the  varied  move- 
ments of  the  globes,  by  the  combined  action  of  the  recti  and  oblique  muscles, 
must  correspond  for  each  eye,  in,  the  movements  of  torsion  upon  an  antero- 
posterior  axis  as  well  as  in  movements  of  rotation  upon  the  horizontal  or  the 
vertical  axis. 

CENTRES  FOB  VISION. 

Experiments  have  been  made  upon  the  lower  animals  by  Ferrier,  Munk, 
Exner,  Dalton  and  many  others,  with  the  object  of  locating  in  the  cerebrum 
a  centre  for  vision.  It  is  important,  however,  to  compare  the  results  of  such 
experiments  with  cases  of  cerebral  lesions  in  the  human  subject.  As  the 
general  result  of  experiments,  both  on  dogs  and  monkeys,  and  of  pathological 
observations,  the  present  opinion  is  that  the  centres  for  vision  are  in  the 
occipital  lobes.  The  lower  half  of  the  cuneus  and  the  adjacent  portions  of 
the  middle  occipital  convolutions  (compare  Figs.  221  and  222)  seem  to  be 
the  cerebral  terminations  of  fibres  that  are  continuous  with  the  optic  tracts. 
These  fibres  are  not  crossed  in  the  cerebrum,  but  the  conductors  decussate 
at  the  optic  chiasm,  as  they  pass  to  the  eyes.  Cases  have  been  observed  in 
the  human  subject,  in  which  lesion  of  these  parts  on  one  side  has  been  fol- 
lowed by  loss  of  vision  in  one  lateral  half  of  the  retina  in  either  eye.  This 
condition  is  called  hemianopsia.  In  these  instances  the  blindness  is  confined 
to  the  temporal  side  of  the  retina  corresponding  to  the  lesion  and  the  nasal 
side  of  the  retina  of  the  opposite  eye.  This  is  called  lateral,  homonymous 
hemianopsia,  and  this  is  the  form  which  always  occurs  in  unilateral,  cerebral 
lesion.  In  dogs  and  in  monkeys  destruction  of  both  occipital  lobes  and  both 
angular  convolutions  produces  total  and  permanent  blindness  of  both  eyes. 

The  complete  and  perfect  perception  of  visual  impressions  involves  intel- 
lectual action  connected  with  the  simple  visual  sense.  An  individual  may 


PARTS  FOR  THE  PROTECTION  OF  THE  EYEBALL.    723 

see  objects  and  yet  not  be  able  to  appreciate  their  significance.  In  the  con- 
dition known  as  word-blindness,  words  are  seen,  but  they  convey  no  idea. 
A  dog  with  part  of  the  occipital  lobes  removed  may  see  objects,  such  as  food, 
but  does  not  recognize  their  character.  There  are,  apparently,  psychical 
centres,  which  elaborate  the  impressions  received  by  the  visual  centres. 

What  seems  at  present  to  be  the  most  rational  view  to  take  with  regard 
to  the  location  and  action  of  the  visual  centres  is  the  following,  which  has 
been  adopted  and  formulated  by  Hun : 

1.  In  the  lower  half  of  the  cuneus  and  the  adjacent  part  of  the  median 
occipito-temporal  convolution  (lobulus  lingualis — see  Fig.  222,  page  605),  is 
the  centre  for  simple  visual  sensation.     This  part  is  connected  with  fibres 
from  homonymous  halves  of  the  retina  of  each  eye,  the  temporal  half  of  the 
retina  of  the  same  side  and  the  nasal  half  of  the  retina  of  the  opposite  side. 

2.  The  action  of  the  cortex  of  the  convex  surface  of  the  temporal  lobe 
(perhaps  only  on  the  left  side)  "  is  necessary  for  full  visual  perception  and 
recognition,  and  for  the  production  of  visual  memories."    This  may  be  called 
the  psychical,  visual  centre.     Psychical  blindness  may  exist,  indeed,  without 
loss  of  visual  sensation. 

3.  The  angular  convolution  is  not  a  visual  centre,  as  was  claimed  by  Fer- 
rier.     It  is  related  to  visual  perception  only  in  so  far  as  it  affects  "  the 
memories  of  the  appearance  of  written  or  printed  words."    In  cases  of  word- 
blindness  lesions  have  been  found  in  this  situation  (Stirling). 

The  situation  of  the  visual  centres,  as  indicated  above,  is  in  parts  supplied 
by  the  third  branch  of  the  posterior  cerebral  artery. 

Perception  of  Colors. — Physical  researches  have  shown  that  different  colors 
have  different  wave-lengths.  It  is  evident  that  they  are  appreciated  by  the 
visual  centres,  as  distinct  impressions  for  each  color  and  shade  of  color,  al- 
though, under  what  may  be  called  normal  conditions,  the  delicacy  of  color- 
perception  varies  in  different  individuals.  Color-blindness  is  an  abnormal 
condition,  in  which  the  power  of  discrimination  between  different  colors  is 
impaired  or  lost.  Some  persons  are  entirely  insensible  to  colors ;  and  cases 
have  been  reported  in  which  one  eye  was  color-blind,  while  the  other  eye  was 
normal  (Becker  and  Hippel).  The  latter  is  called  unilateral  color-blindness. 

Before  the  cerebral  visual  centres  had  been  described,  various  theories 
were  proposed  to  account  for  the  perception  of  colors.  Some  physiologists 
assumed  the  existence  of  separate  and  distinct  elements  in  the  retina  for  the 
reception  of  impressions  made  by  different  colors ;  but  this  and  other  theories 
have  been  far  from  satisfactory.  Cases  of  disease  of  the  brain,  in  which  ordi- 
nary visual  sensations  remain  but  the  sense  of  color  is  destroyed,  seem  to 
show  that  a  part  of  the  visual  centre  is  specially  connected  with  the  apprecia- 
tion of  colors.  Beyond  this,  nothing  is  known  of  the  mechanism  of  color- 
perception. 

PARTS  FOR  THE  PROTECTION  OF  THE  EYEBALL. 

The  orbit,  formed  by  the  union  of  certain  of  the  bones  of  the  face,  re- 
ceives the  eyeball,  the  ocular  muscles,  the  muscle  of  the  upper  1-id,  blood-ves- 


724:  SPECIAL  SENSES. 

sels,  nerves  and  a  part  of  the  lachrymal  apparatus ;  and  it  contains,  also,  a  cer- 
tain quantity  of  adipose  tissue,  which  latter  never  disappears,  even  in  extreme 
marasmus.  The  bony  walls  of  this  cavity  protect  the  globe  and  lodge  the 
parts  above  enumerated.  The  internal,  or  nasal  wall  of  the  orbit  projects 
considerably  beyond  the  external  wall,  so  that  the  extent  of  vision  is  far 
greater  in  the  outward  than  in  the  inward  direction.  As  the  globe  is  more 
exposed  to  accidental  injury  from  an  outward  direction,  the  external  wall  of 
the  orbit  is  strong,  while  the  bones  which  form  its  internal  wall  are  compara- 
tively fragile.  The  upper  border  of  the  orbit  (the  superciliary  ridge)  is  pro- 
vided with  short,  stiff  hairs  (the  eyebrows)  which  serve  to  shade  the  eye  from 
excessive  light  and  to  protect  the  eyelids  from  perspiration  from  the  fore- 
head. 

The  eyelids  are  covered  by  a  very  thin  integument  and  are  lined  by  the 
conjunctival  mucous  membrane.  The  subcutaneous  connective  tissue  is  thin 
and  loose  and  is  entirely  free  from  fat.  The  skin  presents  a  large  number  of 
short  papillae  and  small,  sudoriparous  glands.  At  the  borders  of  the  lids,  are 
short,  stiff,  curved  hairs,  arranged  in  two  or  more  rows,  called  the  eyelashes 
or  cilia.  Those  of  the  upper  lid  are  in  greater  number  and  longer  than  the 
lower  cilia.  The  curve  of  the  lashes  is  from  the  eyeball.  They  serve  to  pro- 
tect the  globe  from  dust,  and  to  a  certain  extent,  to  shade  the  eye. 

The  tarsal  cartilages  are  small,  elongated,  semilunar  plates,  extending 
from  the  edges  of  the  lids  toward  the  margin  of  the  orbit,  between  the  skin 
and  the  mucous  membrane.  Their  length  is  about  an  inch  (25-4  mm.).  The 
central  portion  of  the  upper  cartilage  is  about  one-third  of  an  inch  (8'5  mm.) 
broad,  and  the  corresponding  part  of  the  lower  cartilage  measures  about  one- 
sixth  of  an  inch  (4-2  mm.).  At  the  inner  canthus,  or  angle  of  the  eye,  is  a 
small,  delicate  ligament,  or  tendon,  the  tendo  palpebrarum,  which  is  attached 
to  the  lachrymal  groove  internally,  passes  outward,  and  divides  into  two 
lamellae,  which  are  attached  to  the  two  tarsal  cartilages.  At  the  outer  can- 
thus  the  cartilages  are  attached  to  the  malar  bone,  by  the  external  tarsal  liga- 
ment. The  tarsal  cartilages  receive  additional  support  from  the  palpebral 
ligament,  a  fibrous  membrane  attached  to  the  margin  of  the  orbit  and  the 
convex  border  of  the  cartilages  and  lying  beneath  the  orbicularis  muscle. 
This  membrane  is  strongest  near  the  outer  angle  of  the  eye. 

On  the  posterior  surface  of  the  tarsal  cartilages,  partly  embedded  in  them 
and  lying  just  beneath  the  conjunctiva,  are  the  Meibomian  glands.  The 
structure  and  uses  of  these  glands  have  already  been  described  in  connec- 
tion with  the  physiology  of  secretion.  They  produce  an  oily  fluid,  which 
smears  the  edges  of  the  eyelids  and  prevents  the  overflow  of  tears. 

Muscles  which  open  and  close  the  Eyelids. — The  corrugator  supercilii 
draws  the  skin  of  the  forehead  downward  and  inward ;  the  orbicularis  palpe- 
brarum closes  the  lids ;  and  the  levator  palpebrae  superioris  raises  the  upper 
lid.  The  tensor  tarsi,  called  the  muscle  of  Homer,  is  a  very  thin,  delicate 
muscle,  which  is  regarded  by  some  anatomists  as  a  deep  portion  of  the  orbic- 
ularis. Considering  this  as  a  distinct  muscle,  it  consists  of  two  delicate 
slips,  which  pass  from  either  eyelid,  behind  the  lachrymal  sac,  uniting  here 


CONJUNCTIVAL  MUCOUS  MEMBRANE.  725 

to  go  to  its  attachment  at  the  posterior  portion  of  the  lachrymal  bone.  When 
this  acts  with  the  orbicularis,  it  compresses  the  lachrymal  sac. 

The  orbicularis  palpebrarum  is  a  broad,  thin  muscle,  closely  attached  to 
the  skin,  surrounding  the  free  margin  of  the  lids,  and  extending  a  short  dis- 
tance over  the  bones,  beyond  the  margin  of  the  orbit.  This  muscle  may  be 
described  as  arising  from  the  tendo  palpebrarum,  the  surface  of  the  nasal 
process  of  the  superior  maxillary  bone  and  the  internal  angular  process  of 
the  os  frontis.  From  this  origin  at  the  inner  angle  of  the  eye,  its  fibres  pass 
elliptically  around  the  fissure  of  the  lids,  as  above  indicated.  Its  action  is  to 
close  the  lids.  In  the  ordinary,  moderate  contraction  of  this  muscle,  only 
the  upper  lid  is  moved;  but  in  forcible  contraction,  the  lower  lid  moves 
slightly  and  the  lids  are  drawn  toward  the  nose. 

The  levator  palpebrse  superioris  is  situated  within  the  orbit.  It  arises 
from  a  point  a  little  above  and  in  front  of  the  optic  foramen,  at  the  apex  of 
the  orbit,  passes  forward  above  the  eyeball,  and  spreads  into  a  thin  tendon, 
which  is  inserted  into  the  anterior  surface  of  the  superior  tarsal  cartilage. 
Its  action  is  to  raise  the  upper  lid.  This  muscle  and  its  relations  are  shown 
in  Fig.  259  (9,  10,  10),  page  718. 

In  the  act  of  opening  the  eyes  the  levator  muscles  alone  are  brought  into 
play.  Closing  of  the  lids  is  accomplished  by  the  orbicular  muscles.  Both  of 
these  sets  of  muscles  act  to  a  great  extent  without  the  intervention  of  the 
will.  The  eyes  are  kept  open  almost  involuntarily,  except  in  extreme 
fatigue ;  although  when  the  will  ceases  to  act  the  lids  are  closed.  Never- 
theless there  is  hardly  a  conscious  effort  usually  in  keeping  the  eyes  open, 
and  an  effort  is  required  to  close  the  eyes.  During  sleep  the  eyes  are  closed 
and  the  globes  are  turned  upward.  The  contractions  of  the  orbicular  mus- 
cles which  take  place  in  winking  usually  are  involuntary.  This  act  occurs  at 
short  intervals,  and  it  is  useful  in  spreading  the  lachrymal  secretion  over  the 
exposed  portions  of  the  globes.  The  action  of  both  sets  of  muscles  usually  is 
simultaneous,  although  they  may  be  educated  so  as  to  close  one  eye  while  the 
other  is  kept  open.  The  action  of  the  orbicularis  is  so  far  removed  from  the 
control  of  the  will,  that  when  the  surface  of  the  globe  is  touched  or  irritated 
or  when  the  impression  of  light  produces  intense  pain,  it  is  impossible  to  keep 
the  eye  open. 

Conjunctival  Mucous  Membrane. — The  entire  inner  surface  of  the  upper 
and  lower  eyelids  is  lined  by  a  mucous  membrane,  which  is  reflected  forward, 
from  the  inner  periphery  of  the  lids,  over  the  eyeball.  The  membrane  lining 
the  lids  is  called  the  palpebral  conjunctiva,  and  that  covering  the  eyeball,  the 
ocular  conjunctiva.  The  latter  presents  a  sclerotic  and  a  corneal  portion. 
The  conjunctiva  presents  a  superior  and  an  inferior  fold,  where  it  is  reflected 
upon  the  globe.  In  the  superior  conjunctival  fold,  are  glandular  follicles,  or 
accessory  lachrymal  glands,  which  secrete  a  certain  portion  of  the  fluid  which 
moistens  the  surface  of  the  eyeball.  These  are  generally  described  as  form- 
ing a  part  of  the  lachrymal  gland.  At  the  inner  canthus  there  is  a  vertical 
fold,  the  plica  semilunaris,  with  a  reddish,  spongy  elevation  at  its  inner  por- 
tion, called  the  caruncula  lacrymalis.  The  caruncula  presents  a  collection  of 


726 


SPECIAL  SENSES. 


follicular  glands,  with  a  few  delicate  hairs  on  its  surface.  The  conjunctiva 
is  continuous  with  the  membrane  of  the  lachrymal  ducts,  of  the  puncta  lacry- 
malia  and  of  the  Meibomian  glands.  Beneath  the  conjunctiva,  except  in  the 
corneal  portion,  is  a  loose,  connective  tissue. 

The  palpebral  conjunctiva  is  reddish,  thicker  than  the  ocular  portion,  fur- 
rowed, and  presents  small,  isolated  papillae  near  the  borders  of  the  lids,  which 
increase  in  number  and  size  toward  the  folds.  This  portion  of  the  membrane 
presents  large,  capillary  blood-vessels  and  lymphatics  and  is  covered  with  a 
layer  of  cells  of  flattened  epithelium.  The  sclerotic  portion  is  thinner,  less 
vascular,  and  has  no  papillae.  It  is  covered  by  conical  and  rounded  epithelial 
cells,  in  two  to  four  layers.  Over  the  cornea  the  epithelium  of  the  sclerotic 
portion  is  continued  in  delicate,  transparent  layers,  without  a  distinct  base- 
ment-membrane. 

The  Lachrymal  Apparatus. — The  eyeball  is  constantly  bathed  in  a  thin, 
watery  fluid,  which  is  secreted  by  the  lachrymal  gland,  is  spread  over  the 
globe  by  the  movements  of  the  lids  and  of  the  eyeball,  and  is  prevented, 
under  ordinary  conditions,  from  overflowing  upon  the  cheek,  by  the  Meibo- 
mian secretion.  The  excess  of  this  fluid  is  collected  into  the  lachrymal  sac, 
and  is  carried  into  the  nose,  by  the  nasal  duct.  The  lachrymal  gland,  the 
lachrymal  canals,  duct  and  sac,  and  the  nasal  duct  constitute  the  lachrymal 
apparatus. 

The  lachrymal  gland  is  an  ovoid,  flattened  gland  of  the  racemose  variety, 
resembling  the  salivary  glands  in  its  general  structure.  It  is  about  the  size 

of  a  small  almond  and 
is  lodged  in  a  shallow 
depression  in  the  bones 
of  the  orbit,  at  its  upper 
and  outer  portion.  It 
is  closely  attached  to  the 
periosteum,  by  its  upper 
surface,  and  is  moulded 
below  to  the  convexity 
of  the  globe.  Its  ante- 
rior portion  is  separated 
from  the  rest  by  a  well 
marked  groove,  is  com- 
paratively thin  and  ad- 
heres to  the  upper  lid. 
It  presents  six  to  eight 
(usually  seven)  ducts, 
which  form  a  row  of 
openings  into  the  con- 
junctival  fold.  Five  or 
six  of  these  orifices  are  situated  above  the  outer  canthus,  and  two  or  three 
open  below.  In  its  minute  structure  this  gland  presents  no  points  of  special 
physiological  importance  as  distinguished  from  the  ordinary  racemose  glands. 


FIG.  261. — Lachrymal  and  Meibomian  glands  (Sappey). 
1,1,  internal  wall  of  the  orbit ;  2,  2.  internal  portion  of  the  orbicularis 
palpebrarum  ;   3,  3,  attachment  of  this  muscle  to  the  orbit ;   4, 
orifice  for  the  passage  of  the  nasal  artery  ;  5,  muscle  of  Horner  ; 

6,  6,  posterior  surface  of  the  eyelids,  with  the  Meibomian  glands  ; 

7,  7,  8,  8,  9,  9,  10,  lachrymal  gland  and  ducts ;  11,  openings  of  the 
lachrymal  ducts. 


THE  LACHRYMAL  APPARATUS. 


•27 


It  receives  nervous   filaments  from  the  fifth  cranial  nerve  and  the  sympa- 
thetic. 

The  channels  by  which  the  excess  of  tears  is  conducted  into  the  nose  be- 
gin by  two  little  points,  situated  on  the  margin  of  the  upper  and  the  lower 
lid,  near  the  inner  canthus,  called  the  puncta  lacrymalia,  which  present  each 
a  minute  orifice.  These  orifices  open  respectively  into  the  upper  and  the 
lower  lachrymal  canals,  which  together  surround  the  caruncula  lacrymalis. 
At  the  inner  angle,  just  beyond  the  caruncula,  the  two  canals  join,  to  empty 
into  the  lachrymal  sac,  which  is  the  dilated  upper  extremity  of  the  nasal 
duct.  The  duct  is  about  half  an  inch  (12'7  mm.)  in  length  and  empties 
into  the  inferior  meatus  of  the  nose,  taking  a  direction  nearly  vertical 
and  inclined  slightly  outward  and  backward.  This  portion  of  the  lachrymal 
apparatus  is  fibrous  and  is  lined  by  a  reddish,  mucous  membrane,  which 
presents  several  well  marked  folds.  Near  the  puncta,  are  two  folds,  one 
for  each  lachrymal  canal.  Another  pair  of  folds  exists  near  the  horizontal 
portions  of  the  canals.  At  the  opening  of  the  duct  into  the  nose,  is  an  over- 
hanging fold  of  the  nasal,  mucous  membrane.  These  folds  are  supposed  to 
prevent  the  reflux  of  fluid  from  the  lachrymal  canals  and  the  entrance  of 
air  from  the  nose.  The  mucous  membrane  of  the  lachrymal  canals  is  cov- 
ered by  a  flattened  epithelium,  like  that  of  the  conjunctiva.  The  lachrymal 
sac  and  duct  are  lined  by  a  continuation  of  the  ciliated  epithelium  of  the 
nose.  The  disposition  of  the  apparatus  just  described  is  shown  in  Fig. 
262. 

The  Tears. — The  secretion  of  the  lachrymal  glands  is  constant,  although 
the  quantity  of  fluid  may  be  increased  under  various  conditions.  The  actual 
quantity  of  the  secretion  has  never  been  estimated.  During  sleep  it  is  much 
diminished  ;  and  when  the  eyes  are  open,  the  quantity 
is  sufficient  to  moisten  the  eyeball,  the  excess  being 
carried  into  the  nose  so  gradually  that  this  process  is 
not  appreciated.  That  this  drainage  of  the  excess  of 
tears  takes  place,  is  shown  by  cases  of  obstruction  of 
the  nasal  duct,  when  the  liquid  constantly  overflows 
upon  the  cheeks,  producing  considerable  inconven- 
ience. 

It  is  probable  that  the  openings  at  the  puncta 
lacrymalia  take  up  the  lachrymal  fluid,  like  delicate 
pipettes,  this  action  being  aided  by  the  movements  in 
winking,  by  which,  when  the  lids  are  closed,  the 
points  are  compressed  and  turned  backward,  opening 
and  drawing  in  the  tears  when  the  lids  are  opened. 
It  is  possible  that  the  lachrymal  sac  is  compressed 
in  the  act  of  winking,  by  the  contractions  of  the  mus- 
cle of  Horner,  and  that  this,  while  it  empties  the  sac, 
may  in  the  subsequent  relaxation  assist  the  intro- 
duction of  liquid  from  the  orbit. 

Very  little  is  known  with  regard  to  the  chemical  composition  of  tears,  be- 


FIG.  262.— Lachrymal  canals, 
lachrymal  sac  and  nasal 
canal,  opened  by  their  ante- 
rior portion  (Sappey). 

1,  walls  of  the  lachrymal  pas- 
sages, smooth  and  adher- 
ent ;  2,  2,  walls  of  the  lach- 
rymal sac,  presenting  deli- 
cate folds  of  the  mucous 
membrane :  3.  a  similar  fold 
belonging  to  the  nasal  mu- 
cous membrane. 


728  SPECIAL  SENSES. 

yond  the  analysis  made  many  years  ago  by  Frerichs.      According  to  this 
observer  the  following  is  the  composition  of  the  lachrymal  secretion  : 

COMPOSITION    OF   THE   TEARS. 

Water 990'GO    to      987-00 

Epithelium 1'40     "  3-20 

Albumin 0'80     "  1-00 

Sodium  chloride. . . .  ") 
Alkaline  phosphates,  j 

Earthy  phosphates.,   f-   7-20     "  8'80 

Mucus j 

Fat J 

1,000-00  1,000-00 

The  specific  gravity  of  the  tears  has  never  been  ascertained.  The  liquid 
is  perfectly  clear,  colorless,  of  a  saltish  taste  and  a  feebly  alkaline  reaction. 
The  albumin  given  in  the  table  is  called  by  some  authors,  lachrymine,  thrae- 
nine  or  dacryoline.  This  substance,  whatever  it  may  be  called,  resembles 
mucus  in  many  regards  and  probably  is  secreted  by  the  conjunctiva  and  not 
by  the  lachrymal  glands.  Unlike  ordinary  mucus,  it  is  coagulated  by  water. 

The  secretion  of  tears  is  readily  influenced  through  the  nervous  system. 
Aside  from  the  increased  flow  of  this  secretion  from  emotional  causes,  which 
probably  operate  through  the  sympathetic,  a  hypersecretion  almost  imme- 
diately follows  irritation  of  the  mucous  membrane  of  the  conjunctiva  or  of 
the  nose.  The  same  result  follows  violent  muscular  effort,  laughing,  cough- 
ing, sneezing  etc.  The  secretion  of  tears  following  stimulation  of  the  mu- 
cous membrane  is  reflex. 


CHAPTER  XXIII. 

A  UDITION. 

Auditory  (eighth  nerve)— General  properties  of  the  auditory  nerves— Topographical  anatomy  of  the  parts 
essential  to  the  appreciation  of  sound — The  external  ear — General  arrangement  of  the  parts  composing 
the  middle  ear— Anatomy  of  the  tympanum— Arrangement  of  the  ossicles  of  the  ear— Muscles  of  the 
middle  ear— Mastoid  cells— Eustachian  tube— Muscles  of  the  Eustachian  tube — General  arrangement  of 
the  bony  labyrinth— Physics  of  sound— Noise  and  musical  sounds— Pitch  of  musical  sounds— Musical 
scale— Quality  of  musical  sounds — Harmonics,  or  overtones— Resultant  tones — Summation  tones— Har- 
mony—Discords— Tones  by  influence— Uses  of  different  parts  of  the  auditory  apparatus— Structure  of  the 
membrana  tympani — Uses  of  themembrana  tympani — Mechanism  of  the  ossicles  of  the  ear — Physiologi- 
cal anatomy  of  the  internal  ear— General  arrangement  of  the  membranous  labyrinth— Liquids  of  the 
labyrinth— Distribution  of  nerves  in  the  labyrinth— Organ  of  Corti— Uses  of  different  parts  of  the  inter- 
nal ear— Centres  for  audition. 

IMPRESSIONS  of  sound  are  conveyed  to  the  brain  by  special  nerves;  but 
in  order  that  these  impressions  shall  reach  these  nerves  so  as  to  be  properly 
appreciated,  a  complex  accessory  apparatus  is  required,  the  integrity  of  which 
is  essential  to  perfect  audition.  The  study  of  the  arrangement  and  action 
of  these  accessory  parts  is  even  more  important  and  is  far  more  intricate  than 


AUDITORY  NERVES.  729 

the  physiology  of  the  auditory  nerves.  The  auditory  nerves  conduct  impres- 
sions of  sound,  as  the  optic  nerves  conduct  impressions  of  light ;  but  there 
is  an  elaborate  arrangement  of  parts  by  which  the  waves  are  collected,  con- 
veyed to  a  membrane  capable  of  vibration,  and  finally  carried  to  the  nerves, 
by  which  the  intensity  and  the  varied  qualities  of  sound  are  appreciated. 

AUDITORY  (EIGHTH  XERVE). 

The  origin  of  the  auditory  nerve  can  easily  be  traced  to  the  floor  of  the 
fourth  ventricle,  where  it  presents  two  roots.  The  external,  or  superficial 
root,  sometimes  called  the  posterior  root,  can  be  seen  usually  without  prepara- 
tion. It  consists  of  five  to  seven  grayish  filaments,  which  decussate  in  the 
median  line,  and  pass  outward,  winding  from  the  fourth  ventricle  around 
the  restiform  body.  The  deep  root  consists  of  a  number  of  distinct  filaments 
arising  from  the  gray  matter  of  the  fourth  ventricle,  two  or  three  of  which 
pass  to  the  median  line,  to  decussate  with  corresponding  filaments  from  the 
opposite  side.  Filaments  from  this  root  have  been  traced  to  a  gray  nucleus 
in  the  inferior  peduncle  of  the  cerebellum  and  thence  to  the  white  substance 
of  the  cerebellum  itself.  The  deep  root  passes  around  the  restiform  body 
inward,  so  that  this  portion  of  the  medulla  is  encircled  by  the  two  roots. 
Passing  from  the  superior  and  lateral  portion  of  the  medulla  oblongata, 
the  trunk  of  the  nerve  is  applied  to  the  superior  and  anterior  surface  of 
the  facial.  It  then  passes  around  the  middle  peduncle  of  the  cerebellum, 
and  receives  a  process  from  the  arachnoid  membrane,  which  envelops  it  in 
a  common  sheath  with  the  facial.  It  finally  penetrates  the  internal  audi- 
tory meatus.  In  its  course  it  receives  filaments  from  the  restiform  body 
and  possibly  from  the  pons  Varolii.  Within  the  meatus  the  nerve  divides 
into  an  anterior  and  a  posterior  branch,  the  anterior  being  distributed  to  the 
cochlea,  and  the  posterior,  to  the  vestibule  and  semicircular  canals.  The 
distribution  of  these  branches  will  be  fully  described  in  connection  with  the 
anatomy  of  the  internal  ear. 

The  auditory  nerves  are  grayish  in  color,  and  their  consistence  is  soft, 
thus  differing  from  the  ordinary  cerebro-spinal  nerves,  and  resembling  to  a 
certain  extent  the  other  nerves  of  special  sense.  On  the  external,  or  super- 
ficial root,  is  a  small,  ganglioform  enlargement,  containing  fusiform  nerve- 
cells.  The  filaments  of  the  trunk  of  the  nerve  consist  of  very  large  axis- 
cylinders,  surrounded  by  a  medullary  sheath,  but  having  no  tubular  mem- 
brane. In  the  course  of  these  fibres,  are  found  small,  nucleated,  ganglionic 
enlargements. 

General  Properties  of  the  Auditory  Nerves. — There  can  be  no  doubt,  as 
regards  the  eighth,  that  it  is  the  only  nerve  capable  of  receiving  and  convey- 
ing to  the  brain  the  special  impressions  produced  by  waves  of  sound ;  but  it 
is  an  important  question  to  determine  whether  this  nerve  be  endowed  also 
with  general  sensibility.  Analogy  with  most  of  the  other  nerves  of  special 
sense  would  indicate  that  the  auditory  nerves  are  insensible  to  ordinary 
impressions;  and  this  view  has  been  sustained  by  direct  experiments.  In 
experiments  made  by  passing  electric  currents  through  the  ears,  some  physi- 


730  SPECIAL  SENSES. 

ologists  have  thought  that  auditory  sensations  were  produced  ;  but  it  is  proba- 
ble that  the  sensations  observed  were  due  to  clonic  spasm  of  the  stapedius 
muscle  and  not  to  impressions  of  sound  produced  by  the  action  of  the  stimu- 
lus upon  the  auditory  nerves.  In  cases  of  complete  facial  paralysis  from 
otitis,  in  which  paralysis  of  the  auditory  nerve  could  be  positively  excluded, 
it  has  not  been  possible  to  produce  subjective  auditory  sensations,  even  by 
powerful  Faradization  by  means  of  a  catheter  passed  through  the  Eustachian 
tube  into  the  tympanic  cavity  or  by  the  external  meatus  (Wreden).  In  addi- 
tion there  are  well  established  clinical  observations  which  sustain  the  theory 
of  muscular  contraction  and  are  opposed  to  the  idea  of  impressions  of  sound 
produced  by  direct  stimulation  of  the  auditory  nerves.  The  results,  then, 
as  regards  stimulation  of  the  auditory  nerves,  have  been  simply  negative. 
Were  it  practicable  to  subject  the  nerves  to  mechanical  or  electric  stimula- 
tion, in  the  human  subject,  without  involving  other  parts,  it  might  be  pos- 
sible to  arrive  at  a  definite  conclusion ;  but  the  difficulties  in  the  way  of 
such  an  experiment  have  thus  far  proved  insurmountable. 

TOPOGRAPHICAL  ANATOMY  OF  THE  PARTS  ESSENTIAL  TO  THE  APPRE- 
CIATION OF  SOUND. 

Perfect  audition  involves  the  anatomical  integrity  of  a  complex  appa- 
ratus, which,  for  convenience  of  anatomical  description,  may  be  divided  into 
the  external,  middle  and  internal  ear. 

1.  The  external  ear  includes  the  pinna  and  the  external  auditory  meatus, 
and  is  bounded  internally  by  the  membrana  tympani. 

2.  The  middle  ear  includes  the  cavity  of  the  tympanum,  or  drum,  with 
its  boundaries.     The  parts  here  to  be  described  are  the  membrana  tympani, 
the  form  of  the  tympanic  cavity,  its  openings,  its  lining  membrane,  and  the 
small  bones  of  the  ear,  or  ossicles,  with  their  ligaments,  muscles  and  nerves. 
The  cavity  of  the  tympanum  communicates  by  the  Eustachian  tube  with  the 
pharynx,  and  it  also  presents  openings  into  the  mastoid  cells. 

3.  The  internal  ear  contains  the  terminal  filaments  of  the  auditory  nerve. 
It  includes  the  vestibule,  the  three  semicircular  canals  and  the  cochlea,  which 
together  form  the  labyrinth. 

The  pinna  and  the  external  meatus  simply  conduct  the  waves  of  sound 
to  the  tympanum.  The  parts  entering  into  the  structure  of  the  middle  ear 
are  accessory,  and  are  analogous  in  their  uses  to  the  refracting  media  of  the 
eye.  Structures  contained  in  the  labyrinth  constitute  the  true  sensory  organ. 

The  External  Ear. — The  pinna,  or  auricle,  is  that  portion  projecting  from 
the  head,  which  first  receives  the  waves  of  sound.  The  outer  ridge  of  the 
pinna  is  called  the  helix.  Just  within  this,  is  a  groove  called  the  fossa  of 
the  helix.  This  fossa  is  bounded  anteriorly  by  a  prominent  but  shorter  ridge, 
called  the  antihelix ;  and  above  the  concha,  between  the  superior  portion  of 
the  antihelix  and  the  anterior  portion  of  the  helix,  is  a  shallow  fossa,  called 
the  fossa  of  the  antihelix.  The  deep  fossa,  immediately  surrounding  the 
opening  of  the  meatus,  is  called  the  concha.  A  small  lobe  projects  pos- 
teriorly, covering  the  anterior  portion  of  the  concha,  which  is  called  the 


THE  EXTERNAL  EAR.  Y31 

tragus ;  and  the  projection  at  the  lower  extremity  of  the  antihelix  is  called 
the  anti tragus.  The  fleshy,  dependent  portion  of  the  pinna  is  called  the 
lobule  of  the  ear. 

The  form  of  the  pinna  and  its  consistence  depend  upon  the  presence  of 
fibro-cartilage,  which  occupies  the  whole  of  the  external  ear  except  the  lobule. 
The  structure  of  this  kind  of  cartilage  has  already  been  described. 

The  integument  covering  the  ear  does  not  vary  much  from  the  integu- 
ment of  the  general  surface.  It  is  thin,  closely  attached  to  the  subjacent 
parts,  and  possesses  small,  rudimentary  hairs,  with  sudoriparous  and  seba- 
ceous glands'. 

The  muscles  of  the  external  ear  are  not  important  in  the  human  subject ; 
and  excluding  a  few  exceptional  cases,  they  are  not  under  the  control  of  the 
will.  The  extrinsic  muscles  are  the  superior,  or  attollens,  the  anterior,  or 
attrahens,  and  the  posterior,  or  retrahens  aurem.  In  addition  there  are  the 
six  small  intrinsic  muscles,  situated  between  the  ridges  upon  the  cartilagi- 
nous surface.  The  pinna  is  attached  to  the  sides  of  the  head,  by  two  distinct 
ligaments  and  a  few  delicate,  ligamentous  fibres. 

The  external  auditory  meatus  is  about  an  inch  and  a  quarter  (3T8  mm.) 
in  length  and  extends  from  the  concha  to  the  membrana  tympani.  Its  course 
is  somewhat  tortuous.  Passing  from  without  inward,  its  direction  is  at  first 
somewhat  upward,  turning  abruptly  over  a  bony  prominence  near  the  middle, 
from  which  it  has  a  slightly  downward  direction,  to  the  membrana  tympani. 
Its  general  course  is  from  without  inward  and  slightly  forward.  The  inner 
termination  of  the  canal  is  the  membrana  tympani,  which  is  quite  oblique,  the 
upper  portion  being  inclined  outward,  so  that  the  inferior  wall  of  the  meatus 
is  considerably  longer  than  the  superior. 

The  walls  of  the  external  meatus  are  partly  cartilaginous  and  fibrous,  and 
partly  bony.  The  cartilaginous  and  fibrous  portion  occupies  a  little  less  than 
one-half  of  the  entire  length  and  consists  of  a  continuation  of  the  cartilage 
of  the  pinna,  with  fibrous  tissue.  The  lower  two-thirds  of  this  portion  of 
the  canal  is  cartilaginous,  the  upper  third  being  fibrous.  The  rest  of  the 
tube  is  osseous  and  is  a  little  longer  and  narrower  than  the  cartilaginous  por- 
tion. Around  the  inner  extremity  of  the  canal,  except  at  its  superior  por- 
tion, is  a  narrow  groove,  which  receives  the  greater  portion  of  the  margin  of 
the  membrana  tympani. 

The  skin  of  the  external  meatus  is  continuous  with  the  integument  cover- 
ing the  pinna.  It  is  very  delicate,  becoming  thinner  from  without  inward. 
In  the  osseous  portion  it  adheres  very  closely  to  the  periosteum,  and  at  the 
bottom  of  the  canal  it  is  reflected  over  the  membrana  tympani,  forming  its 
outer  layer.  In  the  cartilaginous  and  fibrous  portion,  are  short,  stiff  hairs, 
with  sebaceous  glands  attached  to  their  follicles,  and  the  coiled  tubes  known 
as  the  ceruminous  glands.  The  structure  of  these  glands  and  the  properties 
and  composition  of  the  cerumen  have  already  been  described  in  connection 
with  the  physiology  of  the  glands  of  the  skin. 

General  Arrangement  of  the  Parts  composing  the  Middle  Ear. — Without 
a  very  elaborate  description,  fully  illustrated  by  plates,  it  is  difficult  to  give  a 


732 


SPECIAL  SENSES. 


clear  idea  of  the  structure  and  relations  of  the  complex  anatomical  parts  in 
the  middle  and  the  internal  ear.  Such  a  minute  and  purely  anatomical  de- 
scription would  be  out  of  .place  in  this  work,  where  it  is  desired  only  to  give 
such  an  account  of  the  anatomy  as  will  enable  the  student  to  comprehend  the 
physiology  of  the  ear,  reserving  for  special  description  certain  of  the  most 
important  structures.  It  will  be  useful,  however,  to  give  a  general  outline  of 
the  different  parts,  with  their  names. 

The  arrangement  of  the  parts  constituting  the  external  ear  is  sufficiently 
simple.  The  middle  ear  presents  a  narrow  cavity  (Fig.  263,  11),  of  irregular 
shape,  situated  between  the  external  ear  and  the  labyrinth,  in  the  petrous 
portion  of  the  temporal  bone.  The  general  arrangement  of  its  parts  is  shown 
in  Fig.  263.  The  outer  wall  of  the  tympanic  cavity  is  formed  by  the  mem- 
brana  tympani  (Fig.  263,  6).  This  membrane  is  concave,  its  concavity  look- 
ing outward,  and  oblique,  inclining  usually  at  an  angle  of  forty-five  degrees 

with  the  perpendicu- 
lar. This  angle,  how- 
ever, varies  considera- 
bly in  different  indi- 
viduals. The  roof  is 
formed  by  a  thin  plate 
of  bone.  The  floor  is 
bony  and  is  much  nar- 
rower than  the  roof. 
The  inner  wall,  sepa- 
rating the  tympanic 
cavity  from  the  laby- 
rinth, is  irregular,  pre- 
senting several  small 
elevations  and  forami- 
na. The  f  enestra  ova- 
lis,  an  ovoid  opening 

FIG.  263.  —  General  view  of  the  organ  of  hearing  (Sappey). 

1,  pinna  ;  2,  cavity  of  the  concha,  on  the  walls  of  which  are  seen  the    n©ar  its  Upper  portion, 
orifices  of  a  great  number  of  sebaceous  glands  ;  3,  external  auditory 
meatus  ;  4,  angular  projection  formed  by  the  union  of  the  anterior 


to  the  cavity  of 
the  vestibule.     This  is 
closed   in  the  natural 
base  of  the 


c    •> 
flip 


portion  of  the  concha  with  the  posterior  wall  of  the  auditory  canal  ; 

5,  openings  of  the  ceruminous  glands,  the  most  internal  of  which 

form  a  curved  line  which  corresponds  with  the  beginning  of  the 

osseous  portion  of  the  external  meatus  :  6,  membrana  tympani  and 

the  elastic  fibrous  membrane  which  forms  its  border  ;  7,  anterior    0+QfQ  V.,, 

portion  of  the  incus  :  8,  malleus;  9,  handle  of  the  malleus,  applied  to    buue  UJ 

the  internal  surface  of  the  membrana  tympani,  which  it  draws  in-    ctonoc  -inrl    Uo 

ward  toward  the  projection  of  the  promontory  ;  10,  tensor  tympani    feualjt;i 

muscle,  the  tendon  of  which  is  reflected  at  a  fight  angle,  to  become    lirrarnonf 

attached  to  the  superior  portion  of  the  handle  of  the  malleus;  11,    116<11J 

tympanic  cavity;  12,  Eustachian  tube,  the  internal,  or  pharyngeal    emnllpr     rmprmio- 

extremity  of  which  has  been  removed  by  a  section  perpendicular  to  *    & 

its  curve  ;  13,  superior  semicircular  canal  ;  14,  posterior  semicircu-    fpnperm  rnrnnrlfl  wliir-Vi 

lar  canal  ;  15,  external  semicircular  canal  ;  16,  cochlea  ;  17,  internal  U<l,Wl 

auditory  canal;   18,  facial  nerve;  19,  large  petrosal  branch,  given    Ipnfja     to     flip     Pnrlilpfl 

off  from  the  ganglioform  enlargement  of  the  facial  and  passing  - 

below  the  cochlea,  to  go  to  its  distribution  :  20,  vestibular  branch  of    This    is    closed    in    the 

the  auditory  nerve  ;  21,  cochlear  branch  of  the  auditory  nerve. 

natural     state     by    a 

membrane  called  the  secondary  membrana  tympani.  In  addition  the  poste- 
rior wall  presents  several  small  foramina  leading  to  the  mastoid  cells,  which 
cells  are  lined  by  a  continuation  of  the  mucous  membrane  of  the  tympanic 


THE  MIDDLE  EAR. 


733 


cavity.  The  tympanic  cavity  also  presents  an  opening  leading  to  the  Eusta- 
chian  tube,  and  a  small  foramen  which  gives  passage  to  the  tendon  of  the 
stapedius  muscle.  The  Eustachian  tube  extends  from  the  upper  part  of  the 
pharynx  to  the  tympanum. 

The  small  bones  of  the  ear  are  three  in  number ;  the  malleus,  the  incus, 
and  the  stapes,  forming  a  chain  and  connected  together  by  ligaments  (D,  Fig. 
264).  These  bones  are  situated  in  the  upper  part  of  the  tympanic  cavity.  The 
handle  of  the  malleus  (A,  2,  Fig.  264)  is  closely  attached  to  the  membrana 
tympani,  and  the  long  process  (A,  3,  Fig.  264)  is  attached  to  the  Glasserian 
fissure  of  the  temporal  bone.  The  malleus  is  articulated  with  the  incus.  The 
incus  (B,  Fig.  264)  is  connected  with  the  posterior  wall  of  the  tympanic  cav- 
ity, near  the  openings  of  the  mastoid  cells.  It  is  articulated  with  the  malleus, 
and  by  the  extremity  of  its  long  process  (B,  2,  Fig.  264),  with  the  stapes. 
The  stapes  (C,  Fig.  264)  is  the  most  internal  bone  of  the  middle  ear.  It  is 
articulated  by  its  smaller  extremity  with  the  long  process  of  the  incus.  Its 
base  is  oval  (C',  Fig.  264)  and  with  its  annular  ligament,  is  applied  to  the 
fenestra  ovalis.  The  direction  of  the  stapes  is  nearly  at  a  right  angle  with 
the  long  process  of  the  incus,  in  the  natural  state  (8,  Fig.  265).  Some  anato- 
mists describe  a  fourth  bone  as  existing  between  the  long  process  of  the  incus 
and  the  stapes,  but  this  is  seldom  dis- 
tinct, usually  being  united  either  with 
the  incus  or  with  the  stapes. 

There  are  two  well  defined  muscles 
connected  with  the  ossicles  of  the  mid- 
dle ear.  One  of  these  is  attached  to  the 
malleus,  and  the  other,  to  the  stapes. 
The  so-called  laxator  tympani  probably 
is  not  composed  of  muscular  fibres  and 
should  not  be  enumerated  with  the  mus- 
cles of  the  tympanum. 

The  larger  of  the  two  muscles  is  the 
tensor  tympani.  Its  fibres  arise  from 
the  cartilaginous  portion  of  the  Eusta- 
chian tube,  the  spinous  process  of  the 
sphenoid  bone  and  the  adjacent  portion 
of  the  temporal.  From  this  origin  it 
passes  backward,  almost  horizontally,  to 
the  tympanic  cavity.  In  front  of  the 
fenestra  ovalis  it  turns  nearly  at  a  right 
angle  over  a  bony  process,  and  its  ten- 
don is  inserted  into  the  handle  of  the  malleus,  at  its  inner  surface  near  the 
root.  The  tendon  is  very  delicate,  and  the  muscular  portion  is  about  half 
an  inch  (12'7  mm.)  in  length  (10,  Fig.  263).  The  muscle  and  its  tendon  are 
enclosed  in  a  distinct,  fibrous  sheath.  The  action  of  this  muscle  is  to  draw 
the  handle  of  the  malleus  inward,  pressing  the  base  of  the  stapes  against 
the  membrane  of  the  fenestra  ovalis  and  producing  tension  of  the  membrana 

48 


FIG.  264.— Ossicles  of  the  tympanum  of  the,  right 
side  ;  magnified  2  diameters  (Arnold). 

A,  malleus  ;  1,  its  head  ;  2,  the  handle  ;  3.  long, 
or  slender  process  ;  4,  short  process  ;  B,  in- 
cus ;  1.  its  body ;  2,  the  long  process,  with  the 
orbicular  process  ;  3.  short,  or  posterior  pro- 
cess ;  4,  articular  surf  ace,  receiving  the  head 
of  the  malleus  ;  C,  stapes  ;  1,  head  ;  2,  pos- 
terior crus ;  3,  anterior  crus ;  4,  base ;  C'. 
base  of  the  stapes;  D,  the  three  bones  in  their 
natural  connection,  as  seen  from  the  outside; 
A,  malleus  ;  B,  incus  ;  C,  stapes. 


734 


SPECIAL  SENSES. 


tympani.     The  fibres  of  this,  and  of  all  the  muscles  of  the  middle  ear,  are  of 
the  striated  variety.     The  tensor  tympani  is  supplied  with  motor  filaments 

from  the  otic  ganglion,  which 
are  probably  derived  from  the 
facial  nerve. 

The  stapedius  muscle  is  sit- 
uated in  the  descending  por- 
tion of  the  acquaeductus  Fallo- 
pii  and  in  the  cavity  of  the 
pyramid  on  the  posterior  wall 
of  the  tympanic  cavity.  Its 
tendon  emerges  from  a  fora- 
men at  the  summit  of  the  pyra- 
mid. In  the  canal  in  which 
this  muscle  is  lodged,  its  direc- 
tion is  vertical.  At  the  sum- 
mit of  the  pyramid,  it  turns  at 
nearly  a  right  angle,  its  tendon 
passing  horizontally  forward,  to 
be  attached  to  the  head  of  the 
stapes.  Like  the  other  mus- 
cles of  the  ear,  this  is  enveloped 
in  a  fibrous  sheath.  Its  action 
is  to  draw  the  head  of  the 
stapes  backward,  relaxing  the 
membrana  tympani.  This  muscle  receives  filaments  from  the  facial  nerve, 
by  a  distinct  branch,  the  tympanic. 

The  posterior  wall  of  the  tympanic  cavity  presents  several  foramina,  which 
open  directly  into  a  number  of  irregularly  shaped  cavities  communicating 
freely  with  each  other  in  the  mastoid  process  of  the  temporal  bone.  These 
are  called  the  mastoid  cells.  They  are  lined  by  a  continuation  of  the  mucous 
membrane  of  the  tympanum.  There  is  under  certain  conditions  a  free  cir- 
culation of  air  between  the  pharynx  and  the  cavity  of  the  tympanum,  through 
the  Eustachian  tube,  and  from  the  tympanum  to  the  mastoid  cells. 

The  Eustachian  tube  (12,  Fig.  263)  is  partly  bony  and  partly  cartilagi- 
nous. Following  its  direction  from  the  tympanic  cavity,  it  passes  forward, 
inward  and  slightly  downward.  Its  entire  length  is  about  an  inch  and  a 
half  (38*1  mm.).  Its  caliber  gradually  contracts  from  the  tympanum  to  the 
spine  of  the  sphenoid,  and  from  this  constricted  portion  it  gradually  dilates 
to  its  opening  into  the  pharynx,  the  entire  canal  presenting  the  appearance 
of  two  cones.  The  osseous  portion  extends  from  the  tympanum  to  the  spine 
of  the  sphenoid  bone.  The  cartilaginous  portion  is  an  irregularly  trian- 
gular cartilage,  bent  upon  itself  above,  forming  a  furrow  with  its  concav- 
ity presenting  downward  and  outward.  The  fibrous  portion  occupies  about 
half  of  the  tube  beyond  the  osseous  portion,  and  completes  the  canal, 
forming  its  inferior  and  external  portion.  In  its  structure  the  cartilage 


FIG.  265.— The  right  temporal  bone,  the.  petrosal  portion  re- 
moved, showing  the  ossicles  seen  from  within.  From  a 
photograph  (RUdinger). 

4,  the  incus,  the  short  process  of  which  is  directed  nearly 
in  a  horizontal  direction  backward  ;  5,  the  long  process 
of  tha  incus,  free  in  the  tympanic  cavity,  articulated 
with  the  stapes ;  6,  the  malleus,  articulated  with  the 
incus:  7,  the  long  process  of  the  malleus,  in  the  Glasse- 
rian  fissure :  8,  the  stapes,  articulated  with  the  incus. 
This  is  drawn  somewhat  outward  ;  otherwise  the  base 
of  the  stapes  alone  would  be  visible.  This  figure  shows 
the  handle  of  the  malleus,  attached  to  the  membrana 
tympani. 


GENERAL  ARRANGEMENT  OF  THE  BONY  LABYRINTH.         735 

of  the  Eustachian  tube  is  intermediate  between  the  hyaline  and  the  fibro- 
cartilage. 

The  circumflexus,  or  tensor  palati  muscle,  which  has  already  been  de- 
scribed in  connection  with  deglutition,  is  attached  to  the  anterior  margin, 
or  the  hook  of  the  cartilage.  The  attachments  of  this  muscle  have  been  ac- 
curately described  by  Eiidinger,  who  called  it  the  dilator  of  the  tube. 

The  action  of  certain  of  the  muscles  of  deglutition  dilates  the  pharyngeal 
opening  of  the  Eustachian  tube.  If  the  mouth  and  nostrils  be  closed  and 
several  repeated  acts  of  deglutition  be  made,  air  is  drawn  from  the  tympanic 
cavity,  and  the  atmospheric  pressure  renders  the  membrane  of  the  tympanum 
tense,  increasing  its  concavity.  By  one  or  two  lateral  movements  of  the 
jaws,  the  tube  is  opened,  the  pressure  of  air  is  equalized  and  the  ear  returns 
to  its  normal  condition.  The  nerves  animating  the  dilator  tubae  come  from 
the  pneumogastric  and  are  derived  from  the  spinal  accessory. 

A  smooth,  mucous  membrane  forms  a  continuous  lining  for  the  Eusta- 
chian tube,  the  cavity  of  the  tympanum  and  the  mastoid  cells.  In  all  parts 
it  is  closely  adherent  to  the  subjacent  tissues,  and  in  the  cavity  of  the  tym- 
panum it  is  very  thin.  In  the  cartilaginous  portion  of  the  Eustachian  tube 
there  are  mucous  glands,  which  are  most  abundant  near  the  pharyngeal  ori- 
fice and  gradually  diminish  in  number  toward  the  osseous  portion,  in  which 
there  are  no  glands.  Throughout  the  tube  the  surface  of  the  mucous  mem- 
brane is  covered  with  conoidal  cells  of  ciliated  epithelium.  The  mucous 
membrane  of  the  tympanic  cavity  is  very  thin,  consisting  of  little  more  than 
epithelium  and  a  layer  of  connective  tissue.  It  lines  the  walls  of  the  cavity 
and  the  inner  surface  of  the  membrana  tympani,  is  prolonged  into  the  mas- 
toid cells  and  covers  the  ossicles  and  those  portions  of  the  muscles  and  ten- 
dons which  pass  through  the  tympanum.  On  the  floor  of  the  tympanic 
cavity  and  on  its  anterior,  inner  and  posterior  walls,  the  epithelium  is  of  the 
conoidal,  ciliated  variety.  On  the  promontory,  roof,  ossicles  and  muscles,  the 
cells  are  of  the  pavement- variety  and  not  ciliated,  the  transition  from  one 
form  to  the  other  being  gradual.  The  entire  mucous  membrane  contains 
lymphatics,  a  plexus  of  nerve-fibres  and  nerve-cells,  with  some  peculiar  cells, 
the  physiology  of  which  is  not  understood. 

The  above  is  merely  a  general  sketch  of  the  physiological  anatomy  of  the 
middle  ear,  and  it  will  not  be  necessary  to  treat  more  fully  of  the  cavity  of 
the  tympanum,  the  mastoid  cells  or  the  Eustachian  tube,  except  as  regards 
certain  points  in  their  physiology.  The  minute  anatomy  of  the  membrana 
tympani  and  the  articulations  of  the  ossicles  can  be  more  conveniently  con- 
sidered in  connection  with  the  physiology  of  these  parts. 

General  Arrangement  of  the  Bony  Labyrinth. — The  internal  portion  of 
the  auditory  apparatus  is  contained  in  the  petrous  portion  of  the  temporal 
bone.  It  consists  of  an  irregular  cavity,  called  the  vestibule,  the  three  semi- 
circular canals  (13,  14,  15,  Fig.  263)  and  the  cochlea  (16,  Fig.  263).  The 
general  arrangement  of  these  parts  in  situ  and  their  relations  to  the  adja- 
cent structures  are  shown  in  Fig.  263.  Fig.  266,  showing  the  bony  labyrinth 
isolated,  is  from  a  photograph  in  Riidinger's  atlas. 


736  SPECIAL  SENSES. 

The  vestibule  is  the  central  chamber  of  the  labyrinth,  communicating 
with  the  tympanic  cavity  by  the  fenestra  ovalis,  which  is  closed  in  the  nat- 
ural state  by  the  base  of  the  stapes.  This  is  the  central,  ovoid  opening 
shown  in  Fig.  266.  The  inner  wall  of  the  vestibule  presents  a  round  depres- 
sion, the  fovea  hemispherica,  perforated  by  a  number  of  small  foramina, 
through  which  pass  nervous  filaments  from  the  internal  auditory  meatus. 
Behind  this  depression  is  the  opening  of  the  aqueduct  of  the  vestibule.  In 
the  posterior  wall  of  the  vestibule  are  five  small,  round  openings  leading  to 
the  semicircular  canals,  with  a  larger  opening  below,  leading  to  the  cochlea. 

The  general  arrangement  of  the  semicircular  canals  is  shown  in  Fig.  266 
(6,  7,  8,  9,  10,  11,  12). 

The  arrangement  of  the  cochlea,  the  anterior  division  of  the  labyrinth,  is 
shown  in  Fig.  266  (1,  3,  4).  This  is  a  spiral  canal,  about  an  inch  and  a  half 
(38*1  mm.)  long,  and  one-tenth  of  an  inch  (2'5  mm.)  wide  at  its  beginning, 
gradually  tapering  to  the  apex,  and  making  in  its  course,  two  and  a  half 
turns.  Its  anterior  presents  a  central  pillar,  around  which  winds  a  spiral 
lamina  of  bone.  The  fenestra  rotunda  (2,  Fig.  266),  closed  in  the  natural 
state  by  a  membrane  (the  secondary  membrana  tympani),  lies  between  the 
lower  portion  of  the  cochlea  and  the  cavity  of  the  tympanum. 


FIG.  266.— The  left  bony  labyrinth  of  a  new-born  child,  forward  and  outward  view.  From  a  photograph 

(Rudinger). 

1,  the  wide  canal,  the  beginning  of  the  spiral  canal  of  the  cochlea  ;  2,  the  fenestra  rotunda  ;  3,  the  sec- 
ond turn  of  the  cochlea  ;  4,  the  final  half-turn  of  the  cochlea  :  5,  the  border  of  the  bony  wall  of  the 
vestibule,  situated  between  the  cochlea  and  the  semicircular  canals  ;  6,  the  superior,  or  sagittal 
semicircular  canal;  T,  the  portion  of  the  semicircular  canal  bent  outward;  8,  the  posterior,  or  trans- 
verse semicircular  canal :  9,  the  portion  of  the  posterior  connected  with  the  superior  semicircular 
canal ;  10,  point  of  junction  of  the  superior  and  the  posterior  semicircular  canals  ;  11,  the  ampulla 
ossea  externa ;  12,  the  horizontal,  or  external  semicircular  canal.  The  explanation  of  this  figure 
has  been  modified  and  condensed  from  Rudinger. 

What  is  called  the  membranous  labyrinth  is  contained  within  the  bony 
parts  just  described.  Some  of  the  anatomical  points  connected  with  its 
structure  and  the  distribution  and  connections  of  the  auditory  Yierve  have 


PHYSICS  OF  SOUND.  737 

direct  and  important  relations  to  the  physiology  of  hearing,  while  many  are 
of  purely  anatomical  interest.  Such  facts  as  bear  directly  upon  physiology 
will  be  considered  fully  in  connection  with  the  uses  of  the  internal  ear. 

PHYSICS  OF  SOUND. 

The  sketch  just  given  of  the  general  anatomical  arrangement  of  the 
auditory  apparatus  conveys  a  general  idea  of  the  uses  of  the  different  parts  of 
the  ear.  The  waves  of  sound  must  be  transmitted  to  the  terminal  extremi- 
ties of  the  auditory  nerve  in  the  labyrinth.  These  waves  are  collected  by  the 
pinna,  are  conducted  to  the  membrana  tympani  through  the  external  auditory 
meatus,  produce  vibrations  of  the  membrana  tympani,  are  conducted  by  the 
chain  of  ossicles  to  the  openings  in  the  labyrinth  and  are  communicated 
through  the  fluids  of  the  labyrinth  to  the  ultimate  nervous  filaments.  The 
free  passage  of  air  through  the  external  meatus  and  the  communications 
of  the  cavity  of  the  tympanum  with  the  mastoid  cells,  and  by  the  Eustachian 
tube,  with  the  pharynx,  are  necessary  to  the  proper  vibration  of  the  mem- 
brana tympani ;  the  integrity  of  the  ossicles  and  of  their  ligaments  and  mus- 
cles is  essential  to  the  proper  conduction  of  sound  to  the  labyrinth;  the 
presence  of  liquid  in  the  labyrinth  is  a  condition  essential  to  the  conduction 
of  the  waves  to  the  filaments  of  distribution  of  the  auditory  nerves ;  and 
finally,  from  the  labyrinth,  the  nerves  pass  through  the  internal  auditory  mea- 
tus, to  the  auditory  centre  in  the  brain,  where  the  auditory  impressions  are 
appreciated. 

Most  of  the  points  in  acoustics  which  are  essential  to  the  comprehension 
of  the  physiology  of  audition  are  definitely  settled.  The  theories  of  the  prop- 
agation of  sound  involve  wave-action,  concerning  which  there  is  no  dispute 
among  physicists.  For  the  conduction  of  sound  a  ponderable  medium  is 
essential ;  and  it  is  not  necessary,  as  in  the  case  of  the  undulatory  theory  of 
light,  to  assume  the  existence  of  an  imponderable  ether.  The  human  ear, 
though  perhaps  not  so  acute  as  th6  auditory  apparatus  of  some  of  the  inferior 
animals,  not  only  appreciates  irregular  waves,  such  as  produce  noise  as  distin- 
guished from  sounds  called  musical,  but  is  capable  of  distinguishing  regular 
waves,  as  in  simple,  musical  sounds,  and  harmonious  combinations. 

In  music  certain  successions  of  regular  sounds  are  agreeable  to  the  ear 
and  constitute  what  is  called  melody.  Again,  there  is  appreciation,  not  only 
of  the  intensity  of  sounds,  both  noisy  and  musical,  but  of  pitch  and  different 
qualities,  particularly  in  music.  Still  farther,  musical  notes  may  be  resolved 
into  certain  invariable  component  parts,  such  as  the  octave,  the  third,  fifth 
etc.  These  components  of  what  were  formerly  supposed  to  be  simple  sounds 
—which  may  be  isolated  by  artificial  means,  to  be  described  farther  on — are 
called  tones;  while  the  sounds  themselves,  produced  by  the  union  of  the 
different  tones,  are  called  notes,  which  may  themselves  be  combined  to  form 
chords. 

The  quality  of  musical  sounds  may  be  modified  by  the  simultaneous  pro- 
duction of  others  which  correspond  to  certain  of  the  components  of  the  pre- 
dominating note.  For  example,  if  there  be  added  to  a  single  note,  the  third, 


Y38  SPECIAL  SENSES. 

fifth  and  octave,  the  result  is  a  major  chord,  the  sound  of  which  is  very  dif- 
ferent from  that  of  a  single  note  or  of  a  note  with  its  octave.  If  the  third 
be  diminished  by  a  semitone,  there  is  a  different  quality,  which  is  peculiar  to 
minor  chords.  In  this  way  a  great  variety  of  musical  sounds  may  be  made 
upon  a  single  instrument,  as  the  piano ;  and  by  the  harmonious  combinations 
of  the  notes  of  different  instruments  and  of  different  registers  of  the  human 
voice,  as  in  choral  and  orchestral  compositions,  shades  of  effect,  almost  in- 
numerable, may  be  produced.  The  modification  of  sounds  in  this  way  con- 
stitutes harmony ;  and  an  educated  ear  not  only  experiences  pleasure  from 
these  musical  combinations,  but  can  distinguish  their  different  component 
parts. 

A  chord  may  convey  to  the  ear  the  sensation  of  completeness  in  itself  or 
it  may  lead  to  a  succession  of  notes  before  this  sense  of  completeness  is 
attained.  Different  chords  of  the  same  key  may  be  made  to  follow  each 
other,  or  by  transition-notes,  may  pass  to  the  chords  of  other  keys.  Each 
key  has  its  fundamental  note,  and  the  transition  from  one  key  to  another,  in 
order  to  be  agreeable  to  the  ear,  must  be  made  in  certain  ways.  These 
regular  transitions  constitute  modulation.  The  ear  becomes  fatigued  by  long 
successions  of  notes  or  chords  always  in  one  key,  and  modulation  is  essential 
to  the  enjoyment  of  elaborate  musical  compositions;  otherwise  the  notes 
would  not  only  become  monotonous,  but  their  correct  appreciation  would  be 
impaired,  as  the  appreciation  of  colors  becomes  less  distinct  after  looking  for 
a  long  time  at  an  object  presenting  a  single  vivid  tint. 

Laws  of  Sonorous  Vibrations. — Sound  is  produced  by  vibrations  in  a 
ponderable  medium ;  and  the  sounds  ordinarily  heard  are  transmitted  to  the 
ear  by  means  of  vibrations  of  the  atmosphere.  A  simple  and  very  common 
illustration  of  this  fact  is  afforded  by  the  experiment  of  striking  a  bell  care- 
fully arranged  in  vacua.  Although  the  stroke  and  the  vibration  can  readily 
be  seen,  there  is  no  sound ;  and  if  air  be  gradually  introduced,  the  sound  will 
become  appreciable,  and  progressively  more  intense  as  the  surrounding 
medium  is  increased  in  density.  The  oscillations  of  sound  are  to  and  fro  in 
the  direction  of  the  line  of  conduction  and  are  said  to  be  longitudinal.  In 
the  uridulatory  theory  of  light,  the  vibrations  are  supposed  to  be  at  right 
angles  to  the  line  of  propagation,  or  transversal.  A  complete  oscillation  to 
and  fro  is  called  a  sound-wave. 

It  is  evident  that  vibrating  bodies  may  be  made  to  perform  and  impart  to 
the  atmosphere  oscillations  of  greater  or  less  amplitude.  The  intensity  of 
sound  is  in  proportion  to  the  amplitude  of  the  vibrations.  In  a  vibrating 
body  capable  of  producing  a  definite  number  of  waves  of  sound  in  a  second, 
it  is  evident  that  the  greater  the  amplitude  of  the  wave,  the  greater  is  the 
velocity  of  the  particles  thrown  into  vibration.  It  has  been  ascertained  that 
there  is  an  invariable  mathematical  relation  between  the  intensity  of  sound, 
the  velocity  of  the  conducting  particles  and  the  amplitude  of  the  waves ;  and 
this  is  expressed  by  the  formula,  that  the  intensity  is  proportional  to  the 
square  of  the  amplitude.  It  is  evident,  also,  that  the  intensity  of  sound  is 
diminished  by  distance.  The  sound,  as  the  waves  recede  from  the  sonorous 


LAWS  OF  SONOROUS  VIBRATIONS.  739 

body,  becomes  distributed  over  an  increased  area.  The  propagation  of  sound 
has  been  reduced  also  to  the  formula,  that  the  intensity  diminishes  in  pro- 
portion to  the  square  of  the  distance. 

Sonorous  vibrations  are  subject  to  many  of  the  laws  of  reflection  of  light. 
Sound  may  be  absorbed  by  soft  and  non-vibrating  surfaces,  in  the  same  way 
that  certain  surfaces  aborb  the  rays  of  light.  By  carefully  arranged  convex 
surfaces,  the  waves  of  sound  may  readily  be  collected  to  a  focus.  These  laws 
of  the  reflection  of  sonorous  waves  explain  echoes  and  the  conduction  of 
sound  by  confined  strata  of  air,  as  in  tubes.  To  make  the  parallel  between 
sonorous  and  luminous  transmission  more  complete,  it  has  been  ascertained 
that  the  waves  of  sound  may  be  refracted  to  a  focus,  by  being  made  to  pass 
through  an  acoustic  lens,  as  a  balloon  filled  with  carbon  dioxide.  The  waves 
of  sound  may  also  be  deflected  around  solid  bodies,  when  they  produce  what 
have  been  called  by  Tyndall,  shadows  of  sound. 

Any  one  observing  the  sound  produced  by  the  blow  of  an  axe  can  note 
the  fact  that  sound  is  transmitted  with  much  less  rapidity  than  light.  At  a 
short  distance  the  view  of  the  body  is  practically  instantaneous ;  but  there  is 
a  considerable  interval  between  the  blow  and  the  sound.  This  interval  re- 
presents the  velocity  of  sonorous  conduction.  This  fact  is  also  illustrated  by 
the  interval  between  a  flash  of  lightning  and  the  sound  of  thunder.  The 
velocity  of  sound  depends  upon  the  density  and  elasticity  of  the  conducting 
medium.  The  rate  of  conduction  of  sound,  by  atmospheric  air  at  the  freezing- 
point  of  water,  is  about  1,090  feet  (332  metres)  per  second.  This  rate  pre- 
sents comparatively  slight  variations  for  the  different  gases,  but  it  is  very 
much  more  rapid  in  liquids  and  in  solids. 

Noise  and  Musical  Sounds. — There  is  a  well  defined  physical  as  well  as 
an  aesthetic  distinction  between  noise  and  music.  Taking  as  examples,  sin- 
gle sounds,  a  sound  becomes  noise  when  the  air  is  thrown  into  confused  and 
irregular  vibrations.  A  noise  may  be  composed  of  musical  sounds,  when 
these  are  not  in  accord  with  each  other,  and  sounds  called  musical  are  not 
always  entirely  free  from  discordant  vibrations.  A  noise  possesses  intensity, 
varying  with  the  amplitude  of  the  vibrations,  and  it  may  have  different 
qualities  depending  upon  the  form  of  its  vibrations.  A  noise  may  be  called 
dull,  sharp,  ringing,  metallic,  hollow  etc.,  these  terms  expressing  qualities 
that  are  readily  understood.  A  noise  may  also  be  called  sharp  or  low  in 
pitch,  as  the  rapid  or  slow  vibrations  predominate,  without  answering  the 
requirements  of  musical  sounds. 

A  musical  sound  consists  of  vibrations  following  each  other  at  regular  in- 
tervals, provided  that  the  succession  of  waves  be  not  too  slow  or  too  rapid. 
When  the  vibrations  are  too  slow,  there  is  an  appreciable  succession  of  im- 
pulses, and  the  sound  is  not  musical.  When  they  are  too  rapid,  the  sound 
is  excessively  sharp,  but  it  is  painfully  acute  and  has  no  pitch  that  can  be  ac- 
curately determined  by  the  auditory  apparatus.  Such  sounds  may  be  occa- 
sionally employed  in  musical  compositions,  but  in  themselves  they  are  not 
strictly  musical. 

Musical  sounds  have  the  characters  of    duration,  intensity,  pitch  and 


740  SPECIAL  SENSES. 

quality.  Duration  depends  simply  upon  the  length  of  time  during  which 
the  vibrating  body  continues  in  action.  Intensity  depends  upon  the  ampli- 
tude of  the  vibrations,  and  it  has  no  relation  whatsoever  to  pitch.  Pitch  de- 
pends absolutely  upon  the  rapidity  of  the  regular  vibrations,  and  quality, 
upon  the  combinations  of  different  notes  in  harmony,  the  character  of  the 
harmonics  of  fundamental  tones  and  the  form  of  the  vibrations. 

Pitch  of  Musical  Sounds. — Pitch  depends  upon  the  number  of  vibrations. 
A  musical  sound  may  be  of  greater  or  less  intensity ;  it  may  at  first  be  quite 
loud  and  gradually  die  away ;  but  the  number  of  vibrations  in  a  definite  note 
is  invariable,  be  it  weak  or  powerful.  The  rapidity  of  the  conduction  of 
sound  does  not  vary  with  its  intensity  or  pitch,  and  in  the  harmonious  com- 
bination of  the  sounds  of  different  instruments,  be  they  high  or  low  in  pitch, 
intense  or  feeble,  it  is  always  the  same  in  the  same  conducting  medium. 
Distinct  musical  notes  may  present  a  great  variety  of  qualities,  but  all  notes 
of  the  same  pitch  have  absolutely  equal  rates  of  vibration.  Notes  equal  in 
pitch  are  said  to  be  in  unison.  An  educated  ear  can  distinguish  slight  differ- 
ences in  pitch  in  ordinary  musical  notes;  but  this  power  of  appreciation  of 
pitch  is  restricted  within  well  defined  limits,  which  vary  slightly  in  different 
.individuals.  According  to  Helmholtz,  the  range  of  sounds  that  can  be  legit- 
imately employed  in  music  is  between  40  and  4,000  vibrations  in  a  second, 
•  embracing  about  seven  octaves.  In  an  orchestra  the  double  bass  gives  the 
•lowest  note,  which  has  40-25  vibrations  in  a  second,  and  the  highest  note, 
•given  by  the  small  flute,  has  4,752  vibrations.  In  grand  organs  there  is  a 
,pipe  which  gives  a  note  of  16*5  vibrations,  and  the  deepest  note  of  modern 
pianos  has  27*5  vibrations ;  but  delicate  shades  of  pitch  in  these  low  notes 
.are  not  appreciable  to  most  persons.  Sounds  above  the  limits  just  indicated 
.  are  painfully  sharp,  and  their  pitch  can  not  be  exactly  appreciated  by  the 
ear. 

Musical  Scale. — A  knowledge  of  the  relations  of  different  notes  to  each 
other  lies  at  the  foundation  of  the  science  of  music ;  and  without  a  clear 
idea  of  certain  of  the  fundamental  laws  of  music,  it  is  impossible  to  thor- 
oughly comprehend  the  mechanism  of  audition. 

It  requires  very  little  cultivation  of  the  ear  to  enable  one  to  comprehend 
the  fact  that  the  successions  and  combinations  of  notes  must  obey  certain 
fixed  laws ;  and  long  before  these  laws  were  subjects  of  mathematical  demon- 
stration, the  relations  of  the  different  notes  of  the  scale  were  established, 
merely  because  certain  successions  and  combinations  were  agreeable  to  the 
ear,  while  others  were  discordant  and  apparently  unnatural. 

The  most  convenient  sounds  for  study  are  those  produced  by  vibrating 
strings,  and  the  phenomena  here  observed  are  essentially  the  same  for  all 
musical  sounds ;  for  it  is  by  means  of  vibrations  communicated  to  the  air 
that  the  waves  of  sound  find  their  way  to  the  auditory  apparatus.  Take,  to 
begin  with,  a  string  vibrating  48  times  in  a  second.  If  this  string  be  divided 
into  two  equal  parts,  each  part  will  vibrate  96  times  in  a  second.  The  note 
thus  produced  is  the  octave,  or  the  8th  of  the  primary  note,  called  the  8th, 
because  the  natural  scale  contains  eight  notes,  of  which  the  first  is  the  low- 


LAWS  OF  SONOROUS  VIBRATIONS.  741 

est,  and  the  last,  the  highest.  The  half  may  be  divided  again,  producing  a 
second  octave,  and  so  on,  within  the  limits  of  appreciation  of  musical  sounds. 
If  the  string  be  divided  so  that  f  of  its  length  will  vibrate,  there  are  72  vibra- 
tions in  a  second,  and  this  note  is  the  5th  in  the  scale.  If  the  string  be 
divided  again,  so  as  to  leave  £  of  its  length,  there  are  60  vibrations,  which 
give  the  3d  note  in  the  scale.  These  are  the  most  natural  subdivisions  of 
the  note ;  and  the  1st,  3d,  5th  and  8th,  when  sounded  together,  make  what 
is  known  as  the  common  major  chord.  Three-fourths  of  the  length  of  the 
original  string  make  64  vibrations,  and  give  the  4th  note  in  the  scale. 
With  |  of  the  string,  there  are  54  vibrations,  and  the  note  is  the  2d  in  the  scale. 
With  f  of  the  string,  there  are  80  vibrations,  or  the  6th  note  in  the  scale. 
With  T\  of  the  string,  there  are  90  vibrations,  or  the  7th  note  in  the  scale. 
The  original  note,  which  may  be  called  C,  is  the  key-note,  or  the  tonic.  In 
this  scale,  which  is  called  the  natural,  or  diatonic,  there  is  a  regular  mathe- 
matical progression  from  the  1st  to  the  8th.  This  is  called  the  major  key. 
Melody  consists  in  an  agreeable  succession  of  notes,  which  may  be  assumed, 
for  the  sake  of  simplicity,  to  be  pure.  In  a  simple  melody  every  note  must 
be  one  of  those  in  the  scale.  When  a  different  note  is  sounded,  the  melody 
passes  into  a  key  which  has  a  different  fundamental  note,  or  tonic,  with  a 
different  succession  of  3ds,  5ths  etc.  Every  key,  therefore,  has  its  1st,  3d, 
5th  and  8th,  as  well  as  the  intermediate  notes.  If  a  note  formed  by  a  string  |- 
the  length  of  the  tonic  instead  of  £,  be  substituted  for  the  major  3d,  the  key 
is  converted  into  the  minor.  The  minor  chord,  consisting  of  the  1st,  the 
diminished  3d,  the  5th  and  the  8th,  is  perfectly  harmonious,  but  it  has  a 
quality  quite  different  from  that  of  the  major  chord.  The  notes  of  a  melody 
may  progress  in  the  minor  key  as  well  as  in  the  major.  Taking  the  small 
numbers  of  vibrations  merely  for  convenience,  the  following  is  the  mode  of 
progression  in  the  natural  scale,  which  may  be  assumed  to  be  the  scale  of  C 
major : 

1st.       2d.       3d.      4th.      5th.      6th.    7th.       8th. 

Note CDEFGAB        C 

Lengths  of  the  string IfifiiAi 

Number  of  vibrations 48      54      60      64      72      80     90       96 

The  intervals  between  the  notes  of  the  scale,  it  is  seen,  are  not  equal. 
The  smallest,  between  the  3d  and  4th  and  the  7th  and  8th,  are  called  semi- 
tones. The  other  intervals  are  either  full  perfect  tones  or  small  perfect 
tones.  Although  there  are  semitones,  not  belonging  to  the  key  of  C,  between 
C  and  D,  D  and  E,  F  and  G,  G  and  A,  and  A  and  B,  these  intervals  are  not 
all  composed  of  exactly  the  same  number  of  vibrations ;  so  that,  taking  the 
notes  on  a  piano,  with  D  as  the  tonic,  the  5th  would  be  A.  It  is  assumed 
that  D  has  54  vibrations,  and  A,  80,  giving  a  difference  of  26.  With  C  as 
the  tonic  and  G  as  the  fifth,  there  is  a  difference  of  24.  It  is  on  account  of 
these  differences  in  the  intervals,  that  each  key  in  music  has  a  more  or  less 
peculiar  and  distinctive  character. 

Even  in  melody,  and  still  more  in  harmony,  in  long  compositions,  the  ear 
becomes  fatigued  by  a  single  key,  and  it  is  necessary,  in  order  to  produce  the 


742      .  SPECIAL  SENSES. 

most  pleasing  effects,  to  change  the  tonic,  by  what  is  called  modulation,  re- 
turning afterward  to  the  original  key. 

Quality  of  Musical  Sounds. — Nearly  all  musical  sounds,  which  seem  at 
first  to  be  simple,  can  be  resolved  into  certain  well  defined  constituents ;  but 
with  the  exception  of  the  notes  of  great  stopped  pipes  in  the  organ,  there  are 
few  absolutely  simple  sounds  used  in  music.  These  simple  sounds  are  pure, 
but  are  of  an  unsatisfactory  quality  and  wanting  in  richness.  Almost  all 
other  musical  sounds  have  a  fundamental  tone,  which  is  at  once  recognized ; 
but  this  tone  is  accompanied  by  harmonics  caused  by  secondary  vibrations  of 
subdivisions  of  the  sonorous  body.  The  number,  pitch  and  intensity  of  these 
harmonic,  or  aliquot  vibrations  affect  what  is  called  the  quality,  or  timbre  of 
musical  notes,  by  modifying  the  form  of  the  sonorous  waves.  A  string  vi- 
brating a  certain  number  of  times  in  a  second,  if  the  vibrations  were  abso- 
lutely simple,  would  produce,  according  to  the  laws  of  vibrating  bodies,  a 
simple,  musical  tone ;  but  as  the  string  subdivides  itself  into  different  por- 
tions, one  of  which  gives  the  3d,  another,  the  5th,  and  so  on,  of  the  funda- 
mental tone,  it  is  evident  that  the  form  of  the  vibrations  must  be  consid- 
erably modified,  and  with  these  modifications  in  form,  the  quality,  or  timbre 
of  the  note  is  changed. 

From  what  has  just  been  stated,  it  follows  that  nearly  all  musical  notes 
consist,  not  only  of  a  fundamental  sound,  but  of  harmonic  vibrations,  sub- 
ordinate to  the  fundamental  and  qualifying  it  in  a  particular  way.  These 
harmonics  may  be  feeble  or  intense  ;  certain  of  them  may  predominate  over 
others ;  some  that  are  usually  present  may  be  eliminated ;  and  in  short,  there 
may  be  a  great  diversity  in  their  arrangement,  and  thus  the  timbre  may  pre- 
sent an  infinite  variety.  This  is  one  of  the  elements  entering  into  the  com- 
position of  notes,  and  it  affords  a  partial  explanation  of  quality. 

Another  element  in  the  quality  of  notes  depends  upon  their  re-enforce- 
ment by  resonance.  The  vibrations  of  a  stretched  string  not  connected  with 
a  resonant  body  are  almost  inaudible.  In  musical  instruments  the  sound  is 
taken  up  by  some  mechanical  arrangement,  as  the  sound-board  of  the  organ, 
piano,  violin,  harp  or  guitar.  In  the  violin,  for  example,  the  sweetness  of 
the  notes  depends  chiefly  upon  the  construction  of  the  resonant  part  of  the 
instrument,  and  but  little  upon  the  strings  themselves,  which  latter  are 
frequently  changed ;  and  the  same  is  true  of  the  human  voice. 

In  addition  to  the  harmonic  tones  of  sonorous  bodies,  various  discordant 
sounds  are  generally  present,  which  modify  the  timbre,  producing,  usually,  a 
certain  roughness,  such  as  the  grating  of  a  violin-bow,  the  friction  of  the 
columns  of  air  against  the  angles  in  wind-instruments,  etc.  All  of  these 
conditions  have  their  effect  upon  the  quality  of  tones ;  and  these  discordant 
sounds  may  exist  in  infinite  number  and  variety.  These  sounds  are  composed 
"of  irregular  vibrations  and  consequently  are  inharmonious.  Nearly  all  notes 
that  are  spoken  of  in  general  terms  as  musical  are  composed  of  musical,  or 
harmonic,  aliquot  tones  with  the  discordant  elements  to  which  allusion  has 
just  been  made. 

Aside  from  the  relations  of  the  various  component  parts  of  musical  notes, 


LAWS  OF  SONOROUS  VIBRATIONS.  743 

the  quality  depends  largely  upon  the  form  of  the  vibrations.  To  quote  the 
words  of  Helmholtz,  "  the  more  uniformly  rounded  the  form  of  the  wave, 
the  softer  and  milder  is  the  quality  of  the  sound.  The  more  jerking  and 
angular  the  wave-form,  the  more  piercing  the  quality.  Tuning-forks,  with 
their  rounded  forms  of  wave,  have  an  extraordinarily  soft  quality ;  and  the 
qualities  of  sound  generated  by  the  zither  and  violin  resemble  in  harshness 
the  angularity  of  their  wave-forms." 

Harmonics,  or  Overtones. — As  before  stated,  nearly  all  sounds  are  compos- 
ite, but  some  contain  many  more  aliquot,  or  secondary  vibrations  than  others. 
The  notes  of  vibrating  strings  are  peculiarly  rich  in  harmonics,  and  these 
may  be  used  for  illustration,  remembering  that  the  phenomena  here  observed 
have  their  analogies  in  nearly  all  varieties  of  musical  sounds.  If  a  stretched 
string  be  made  to  vibrate,  the  secondary  tones,  which  qualify  the  funda- 
mental, are  called  harmonics,  or  overtones. 

While  it  is  difficult  at  all  times  to  distinguish  by  the  ear  the  individual 
overtones  of  vibrating  strings,  their  existence  can  be  demonstrated  by  certain 
simple  experiments.  Take,  for  example,  a  string,  the  fundamental  tone  of 
which  is  C.  If  this  string  be  damped  with  a  feather  at  one-fourth  of  its 
length  and  a  violin-bow  be  drawn  across  the  smaller  section,  not  only  the 
fourth  part  of  the  string  across  which  the  Jbow  is  drawn  is  made  to  vibrate, 
but  the  remaining  three-fourths ;  and  if  little  riders  of  paper  be  placed  upon 
the  longer  segment  at  distances  equal  to  one-fourth  of  the  entire  string,  they 
will  remain  undisturbed,  while  riders  placed  at  any  other  points  on  the  string 
will  be  thrown  off.  This  experiment  shows  that  the  three-fourths  of  the 
string  have  been  divided.  This  may  be  illustrated  by  connecting  one  end  of 
the  string  with  a  tuning-fork.  When  this  is  done  and  the  string  is  brought 
to  the  proper  degree  of  tension,  it  will  first  vibrate  as  a  whole,  then,  when  a 
little  tighter,  will  spontaneously  divide  into  two  equal  parts,  and  under  in- 
creased tension,  into  three,  four,  and  so  on.  By  damping  a  string  with  the 
light  touch  of  a  feather,  it  is  possible  to  suppress  the  fundamental  tone  and 
bring  out  the  overtones,  which  exist  in  all  vibrating  strings  but  are  usually 
concealed  by  the  fundamental.  The  points  which  mark  the  subdivisions  of 
the  string  into  segments  of  secondary  vibrations  are  called  nodes.  When  the 
string  is  damped  at  its  centre,  the  fundamental  tone  is  quenched  and  there 
are  overtones  an  octave  above ;  damping  it  at  a  distance  of  one-fourth,  there 
is  the  second  octave  above,  and  so  on.  When  the  string  is  damped  at  a  dis- 
tance of  one-fifth  from  the  end,  the  four-fifths  sound  the  3d  of  the  funda- 
mental, with  the  second  octave  of  the  3d.  If  it  be  damped  at  a  distance  of 
two-thirds,  there  is  the  5th  of  the  fundamental,  with  the  octave  of  the  5th. 
Every  vibrating  string  thus  possesses  a  fundamental  tone  and  overtones. 
Qualifying  the  fundamental  there  is  first,  as  the  most  simple,  a  series  of 
octaves ;  next,  a  series  of  oths  of  the  fundamental  and  their  octaves ;  and 
next,  a  series  of  3ds.  These  are  the  most  powerful  overtones,  and  they  form 
the  common  chord  of  the  fundamental ;  but  they  are  so  far  concealed  by  the 
greater  intensity  of  the  fundamental,  that  they  can  not  easily  be  distinguished 
by  the  unaided  ear,  unless  the  fundamental  be  quenched  in  some  way.  In 


744 


SPECIAL  SENSES. 


the  same  way  the  harmonic  5ths  and  3ds  overpower  other  overtones ;  for  the 
string  is  subdivided  again  and  again  into  overtones,  which  are  not  harmonious 
like  the  notes  of  the  common  chord  of  the  fundamental. 

The  presence  of  overtones,  resultant  tones  and  additional  tones,  which 
latter  will  be  described  hereafter,  can  be  demonstrated,  without  damping  the 
strings,  by  resonators.  It  is  well  known  that  if  a  glass  tube,  closed  at  one 
end,  which  contains  a  column  of  air  of  a  certain  length,  be  brought  near  a 
resounding  body  emitting  a  note  identical  with  that  produced  by  the  vibra- 
tions of  the  column  of  air,  the  air  in  the  tube  will  resound  in  consonance 
with  the  note,  while  no  other  note  will  have  this  effect.  The  resonators  of 
Helmholtz  are  constructed  upon  this  principle.  A  glass  globe  or  tube  (Fig. 
267)  is  constructed  so  as  to  produce  a  certain  note.  This  has  a  larger  open- 
ing (a)  and  a  smaller  opening  (b),  which  latter  is  fitted  in  the  ear  by  warm 
sealing-wax,  the  other  ear  being  closed.  When  the  proper  note  is  sounded, 
it  is  re-enforced  by  the  resonator  and  is  greatly  increased  in  intensity,  while 
all  other  notes  are  heard  very  faintly.  By  using  resonators  graduated  to  the 
musical  scale,  it  is  easy  to  analyze  a  note  and  distinguish  its  overtones.  The 
resonators  of  Helmholtz,  which  are  open  at  the  larger  extremity,  are  much 
more  delicate  than  those  in  which  this  is  closed  by  a  membrane. 

A  very  striking  and  instructive  point  in  the  present  discussion  is  the  fol- 
lowing :  All  the  overtones  are  produced  by  vibrations  of  divisions  of  the 
string,  included  between  the  comparatively  still  points,  called  nodes ;  and  if 
a  string  be  thrown  into  vibration  by  plucking  or  striking  it  at  one  of  these 

nodal  points,  the  overtones 
which  vibrate  from  this 
node  at  a  fixed  point  are 
abolished.  It  is  readily 
understood  that  when  a 
string  is  plucked  at  any 
point,  it  will  vibrate  so  vig- 
orously at  this  point  that 
no  node  can  be  formed. 
This  fact  has  long  been 
recognized  by  practical 
musicians,  although  many 
are  probably  unacquainted 
with  its  scientific  explana- 
tion. Performers  upon 
stringed  instruments  ha- 
bitually attack  the  strings  near  their  extremities.  In  the  piano,  where  the 
strings  may  be  struck  at  almost  any  point,  the  hammers  are  placed  at  a  dis- 
tance of  -J-  to  |  of  the  length  of  the  strings,  from  their  extremities ;  and  it  has 
been  ascertained  by  experience  that  this  arrangement  gives  the  richest  notes. 
The  nodes  formed  at  these  points  would  produce  the  7ths  and  9ths  as  over- 
tones, which  do  not  belong  to  the  perfect  major  chord,  while  the  nodes  for 
the  harmonious  overtones  are  undisturbed.  The  reason,  then,  why  the  notes 


FIG.  267.— Resonators  of  Helmholtz. 


LAWS  OF  SONOROUS  VIBRATIONS.  745 

are  richer  and  more  perfect  when  the  strings  are  attacked  at  this  point,  is 
that  the  harmonious  overtones  are  full  and  perfect,  and  certain  of  the  dis- 
cordant overtones  are  suppressed. 

When  two  harmonious  notes  are  produced  under  favorable  conditions, 
one  can  hear,  in  addition  to  the  two  sounds,  a  sound  differing  from  both  and 
much  lower  than  the  lower  of  the  two.  This  sound  is  too  low  for  a  har- 
monic, and  it  has  been  called  a  resultant  tone.  The  formation  of  a  new 
sound  by  combining  two  sounds  of  different  pitch  is  analogous  to  the  blend- 
ing of  colors  in  optics,  except  that  the  primary  sounds  are  not  lost.  The 
laws  of  the  production  of  these  resultant  sounds  are  very  simple.  When  two 
notes  in  harmony  are  sounded,  the  resultant  tone  is  equal  to  the  difference 
between  the  two  primaries.  For  example,  C,  with  48  vibrations,  and  its  5th, 
with  72  vibrations  in  a*second,  give  a  resultant  tone  equal  to  the  difference, 
which  is  24  vibrations,  and  it  is  consequently  the  octave  below  C.  These  result- 
ant tones  are  very  feeble  as  compared  with  the  primary  tones,  and  they  can 
be  heard  under  only  the  most  favorable  experimental  conditions.  In  addition 
to  these  sounds,  Helmholtz  has  discovered  sounds,  even  more  feeble,  which  he 
calls  additional,  or  summation  tones.  The  value  of  these  is  equal  to  the  sum 
of  vibrations  of  the  primary  tones.  For  example,  C  (48)  and  its  5th  (72) 
would  give  a  summation  tone  of  120  vibrations,  or  the  octave  of  the  3d ;  and 
C  (48)  with  its  3d  (60)  would  give  108  vibrations,  the  octave  of  the  2d. 
These  tones  can  be  distinguished  by  means  of  resonators. 

.It  is  thus  seen  that  musical  sounds  are  complex.  With  single  sounds 
there  is  an  infinite  variety  and  number  of  harmonics,  or  overtones,  and  in 
chords  there  are  series  of  resultants,  which  are  lower  than  the  primary 
notes,  and  series  of  additional,  or  summation  tones,  which  are  higher ;  but 
both  the  resultant  and  the  summation  tones  bear  exact  mathematical  relations 
to  the  primary  notes  of  the  chord. 

Harmony. — Overtones,  resultant  tones  and  summation  tones  of  strings 
have  been  discussed  rather  fully,  for  the  reason  that  in  studying  the  physiol- 
ogy of  audition,  it  will  be  seen  that  the  ear  is  capable  of  recognizing  single 
sounds  or  successions  of  single  sounds ;  but  at  the  same  time  certain  com- 
binations of  sounds  are  appreciated  and  are  even  more  agreeable  than  those 
which  are  apparently  produced  by  simple  vibrations.  Combinations  of  tones 
which  thus  produce  an  agreeable  impression  are  called  harmonious.  They 
seem  to  become  blended  with  each  other  into  a  complete  sound  of  peculiar 
quality,  all  of  the  different  vibrations  entering  into  their  composition  being 
simultaneously  appreciated  by  the  ear.  The  blending  of  tones  which  bear 
to  each  other  certain  mathematical  relations  is  called  harmony ;  but  two  or 
more  tones,  though  each  one  be  musical,  are  not  necessarily  harmonious. 
The  most  prominent  overtone,  except  the  octave,  is  the  5th,  with  its  octaves, 
and  this  is  called  the  dominant.  The  next  is  the  3d,  with  its  octaves.  The 
other  overtones  are  comparatively  feeble.  Eeasoning,  now,  from  a  knowledge 
of  the  relations  of  overtones,  it  might  be  inferred  that  the  re-enforcement 
of  the  5th  and  3d  by  other  notes  bearing  similar  relations  to  the  tonic  would 
be  agreeable.  This  is  the  fact,  and  it  was  ascertained  empirically  long  before 


74-G  SPECIAL  SENSES. 

the  pleasing  impression  produced  by  such  combinations  was  explained  mathe- 
matically. 

It  is  a  law  in  music  that  the  more  simple  the  ratio  between  the  number 
of  vibrations  in  two  sounds,  the  more  perfect  is  the  harmony.  The  simplest 
relation,  of  course,  is  1 : 1,  when  the  two  sounds  are  said  to  be  in  unison.  The 
next  in  order  is  1  :  2.  In  sounding  C  and  its  8th,  for  example,  there  are  48 
vibrations  of  one  to  96  of  the  other.  These  sounds  can  produce  no  discord, 
because  the  waves  never  interfere  with  each  other,  and  the  two  sounds  can  be 
prolonged  indefinitely,  always  maintaining  the  same  relations.  The  combined 
impression  is  therefore  continuous.  The  next  in  order  is  the  1st  and  5th, 
their  relations  being  2:3.  In  other  words,  with  the  1st  and  5th,  for  two 
waves  of  the  1st  there  are  three  waves  of  the  5th.  The  two  sounds  may  thus 
progress  indefinitely,  for  the  waves  coincide  for  every*second  wave  of  the  1st 
and  every  third  wave  of  the  5th.  The  next  in  order  is  the  3d.  The  3d  of 
C  has  the  8th  of  C  for  its  5th,  and  the  5th  of  C  for  its  minor  3d.  The  1st, 
3d,  5th  and  8th  form  the  common  major  chord ;  and  the  waves  of  each  tone 
blend  with  each  other  at  such  short  intervals  of  time  that  the  ear  experiences 
a  continuous  impression,  and  no  discord  is  appreciated.  This  explanation  of 
the  common  major  chord  illustrates  the  law  that  the  smaller  the  ratio  of  vi- 
bration between  different  tones,  the  more  perfect  is  their  harmony.  Sounded 
with  the  1st,  the  4th  is  more  harmonious  than  the  3d ;  but  its  want  of  har- 
mony with  the  5th  excludes  it  from  the  common  chord.  The  1st,  4th  and 
8th  are  harmonious,  but  to  make  a  complete  chord  the  6th  must  be  added. 

Discords. — A  knowledge  of  the  mechanism  of  simple  accords  leads  natu- 
rally to  a  comprehension  of  the  rationale  of  discords.  The  fact  that  certain 
combinations  of  musical  notes  produce  a  disagreeable  impression  was  ascer- 
tained empirically,  with  no  knowledge  of  the  exact  cause  of  the  dissonance ; 
but  the  mechanism  of  discord  may  now  be  regarded  as  settled. 

The  sounds  produced  by  two  tuning-forks  giving  precisely  the  same  num- 
ber of  vibrations  in  a  second  are  in  perfect  unison.  If  one  of  the  forks  be 
loaded  with  a  bit  of  wax,  so  that  its  vibrations  are  slightly  reduced,  and  if 
both  be  put  in  vibration  at  the  same  instant,  there  is  discord.  Taking  the 
illustration  given  by  Tyndall,  it  may  be  assumed  that  one  fork  has  256,  and 
the  other,  255  vibrations  in  a  second.  While  these  two  forks  are  vibrating, 
one  is  gradually  gaining  upon  the  other;  but  at  the  end  of  half  a  second,  one 
will  have  made  128  vibrations,  while  the  other  will  have  made  127|.  At  this 
point  the  two  waves  are  moving  in  exactly  opposite  directions ;  and  as  a  con- 
sequence, the  sounds  neutralize  each  other,  and  there  is  an  instant  of  silence. 
The  perfect  sounds,  as  the  two  forks  continue  to  vibrate,  are  thus  alternately 
re -enforced  and  diminished,  and  this  produces  what  is  known  in  music  as  beats. 
As  the  difference  in  the  number  of  vibrations  in  a  second  is  one,  the  instants 
of  silence  occur  once  in  a  second ;  and  in  this  illustration  the  beats  occur 
once  a  second.  Unison  takes  place  when  two  sounds  can  follow  each  other 
indefinitely,  their  waves  blending  perfectly;  and  dissonance  is  marked  by 
successive  beats,  or  pulses.  If  the  forks  be  loaded  so  that  one  will  vibrate 
240  times  in  a  second,  and  the  other  234,  there  will  be  six  times  in  a  second 


LAWS  OF  SONOROUS  VIBRATIONS.  747 

when  the  interference  will  be  manifest ;  or  in  other  words  in  ^  of  a  second, 
one  fork  will  make  40  vibrations,  while  the  other  is  making  39.  This  will 
give  6  beats  in  a  second.  From  these  experiments  the  law  may  be  deduced, 
that  the  number  of  beats  produced  by  two  tones  not  in  harmony  is  equal  to 
the  difference  between  the  two  rates  of  vibration.  An  analogous  interference 
of  undulations  is  observed  in  optics,  when  waves  of  light  are  made  to  inter- 
fere and  produce  darkness. 

It  is  evident  that  the  number  of  beats  will  increase  as  two  discordant 
notes  are  produced  higher  and  higher  in  the  scale.  According  to  llelmholtz, 
the  beats  can  be  recognized  up  to  132  in  a  second.  Beyond  that  point  they 
become  confused,  and  there  is  only  a  general  sensation  of  dissonance.  Beats, 
then,  are  due  to  interference  of  sound-waves.  There  is  no  interference  of  the 
waves  of  tones  in  unison,  provided  that  waves  start  at  the  same  instant ;  the 
intensity  of  the  sound  being  increased  by  re-enforcement.  The  differences 
between  the  1st  and  8th,  the  1st  and  5th,  the  1st  and  3d,  and  other  harmo- 
nious combinations,  is  so  great  that  there  are  no  beats  and  no  discord,  the 
more  rapid  waves  re-enforcing  the  harmonics  of  the  primary  sound.  It  is 
important  to  remember  in  this  connection,  that  resultant  tones  are  equal  to 
the  difference  in  the  rates  of  vibration  of  two  harmonious  tones.  Taking  a 
note  of  240  vibrations,  and  its  5th,  with  300  vibrations,  these  two  have  a 
difference  of  120,  which  is  the  lower  octave  of  the  1st  and  is  an.  harmonious 
tone. 

It  is  evident  that  the  laws  just  stated  are  applicable  to  overtones,  resultant 
tones  and  additional  tones,  which,  like  the  primary  notes,  have  their  beats 
and  dissonances. 

Tones  by  Influence. — After  what  has  been  stated  in  regard  to  the  laws  of 
musical  vibrations,  it  will  be  easy  to  comprehend  the  production  of  sounds 
by  influence.  If  a  key  of  the  piano  be  lightly  touched,  so  as  to  raise  the 
damper  but  not  to  sound  the  string,  and  then  a  note  be  sung  in  unison,  the 
string  will  return  the  sound,  by  the  influence  of  the  sound-waves  of  the  voice. 
The  sound  thus  produced  by  the  string  will  have  its  fundamental  tone  and 
overtones ;  but  the  series  of  overtones  will  be  complete,  for  none  of  the  nodes 
are  abolished,  as  in  striking  or  plucking  a  string  at  any  particular  point.  If 
instead  of  a  note  in  unison,  any  of  the  octaves  be  sounded,  the  string  will  re- 
turn the  exact  note  sung ;  and  the  same  is  true  of  the  3d,  5th  etc.  If  a 
chord  in  harmony  with  the  undamped  string  be  struck,  this  chord  will  be 
exactly  returned  by  influence.  In  other  words,  a  string  may  be  made  to 
sound  by  influence,  its  fundamental  tone,  its  harmonics  and  harmonious  com- 
binations. To  carry  the  observation  still  farther,  the  string  will  return,  not 
only  a  note  of  its  exact  pitch  and  its  harmonics,  but  notes  of  the  peculiar 
quality  of  the  primary  note.  This  is  a  very  important  point  in  its  applica- 
tions to  the  physiology  of  hearing  and  can  be  readily  illustrated.  Taking 
identical  notes  in  succession,  produced  by  the  voice,  trumpet,  violin,  clarinet 
or  any  other  musical  instrument,  it  can  easily  be  noted  that  the  quality  of  the 
note,  as  well  as  the  pitch,  is  rendered  by  a  resounding  string ;  and  the  same 
is  true  of  combinations  of  notes.  These  laws  of  tones  by  influence  have  been 


748  SPECIAL  SENSES. 

illustrated  by  strings  merely  for  the  sake  of  simplicity ;  but  they  have  a  more 
or  less  perfect  application  to  all  bodies  capable  of  producing  musical  tones, 
except  that  some  are  thrown  into  vibration  with  more  difficulty  than  others. 
A  thin  membrane,  like  a  piece  of  bladder  or  thin  rubber,  stretched  over  a 
circular  orifice,  such  as  the  mouth  of  a  wide  bottle,  may  readily  be  tuned  to 
a  certain  note.  When  arranged  in  this  way,  the  membrane  can  be  made  to 
sound  its  fundamental  note  by  influence.  In  addition,  the  membrane,  like  a 
string,  will  divide  itself  so  as  to  sound  the  harmonics  of  the  fundamental, 
and  it  will  likewise  be  thrown  into  vibration  by  the  5th,  3d  etc.,  of  its  funda- 
mental, thus  obeying  the  laws  of  vibrations  of  strings,  although  the  har- 
monic sounds  are  produced  with  greater  difficulty. 

The  account  just  given  of  some  of  the  laws  of  sonorous  vibrations  and 
their  relations  to  musical  effects  and  combinations,  although'  by  no  means 
complete,  may  seem  rather  extended  for  a  work  on  physiology ;  but  it  should 
be  borne  in  mind  that  the  mechanism  of  the  appreciation  of  musical  sounds 
includes  the  entire  physiology  of  audition.  This  subject  can  not  be  compre- 
hended without  a  general  knowledge  of  the  physics  of  sound  and  of  some  of 
the  laws  of  harmony ;  for  not  only  is  there  a  perception  of  single  notes  by 
the  auditory  apparatus,  but  the  most  intricate  combinations  of  sounds  in 
harmony  are  all  appreciated  together  and  at  one  and  the  same  instant,  as  will 
be  seen  in  studying  the  action  and  uses  of  different  parts  concerned  in  audi- 
tion. Many  of  the  laws  of  musical  combinations  are  directly  applicable  to 
the  physiology  of  hearing. 

USES  OF  DIFFERENT  PARTS  OF  THE  MIDDLE  EAR. 

The  uses  of  the  pavilion  and  of  the  external  auditory  meatus  are  suffi- 
ciently apparent.  The  pavilion  serves  to  collect  the  waves  of  sound,  and 
probably  it  inclines  them  toward  the  external  meatus  as  they  come  from  vari- 
ous directions.  Although  this  action  is  simple,  it  has  a  certain  degree  of 
importance,  and  the  various  curves  of  the  concavity  of  the  pavilion  tend  more 
or  less  to  concentrate  sonorous  vibrations.  Such  has  long  been  the  opinion 
of  physiologists,  and  this  seems  to  be  carried  out  by  experiments  in  which 
the  concavities  of  the  external  ear  have  been  obliterated  by  wax.  There 
probably  is  no  resonance  or  vibration  of  much  importance  until  the  waves  of 
sound  strike  the  membrana  tympani.  The  same  remarks  may  be  made  with 
regard  to  the  external  auditory  meatus.  It  is  not  known  precisely  how  the 
obliquity  and  the  curves  of  this  canal  affect  the  waves  of  sound,  but  it  is 
probable  that  the  deviation  from  a  straight  course  protects,  to  a  certain 
extent,  the  tympanic  membrane  from  impressions  that  might  otherwise  be 
too  violent. 

Structure  of  the  Membrana  Tympani. — The  general  arrangement  of  the 
membrana  tympani  has  already  been  described  in  connection  with  the  topo- 
graphical anatomy  of  the  auditory  apparatus.  The  membrane  is  elastic, 
about  the  thickness  of  ordinary  gold-beater's  skin,  and  is  subject  to  various 
degrees  of  tension  by  the  action  of  the  muscles  of  the  middle  ear  and  under 


STRUCTURE  OF  THE  MEMBRANA  TYMPANI. 


749 


different  conditions  of  atmospheric  pressure  vithin  and  without  the  tympanic 
cavity.  Its  form  is  nearly  circular;  and  it  has  a  diameter  in  the  adult, 
according  to  Sappey,  of  a  little  more  than  \  of  an  inch  (10  to  11  mm.)  verti- 
cally and  about  f  of  an  inch 
(10  mm.)  antero-posteriorly. 
The  excess  of  the  vertical 
over  the  horizontal  diame- 
ter is  about  -5*0  of  an  inch 
(0*5  mm.) 

The  periphery  of  the 
tympanic  membrane  is  re- 
ceived into  a  little  ring  of 
bone,  which  may  be  sepa- 
rated by  maceration  in  early 
life,  but  which  is  consoli- 
dated with  the  adjacent 
bony  structures  in  the  adult. 
This  bony  ring  is  incom- 
plete at  its  superior  portion, 
but  aside  from  this,  it  re- 
sembles the  groove  which 
receives  the  crystal  of  a 
watch.  At  the  periphery 
of  the  membrane,  is  a  ring 
of  condensed,  fibrous  tissue, 
which  is  received  into  the 
bony  ring.  This  ring  also 
presents  a  break  at  its  supe- 
rior portion. 

The  concavity  of  the 
membrana  tympani  presents 
outward,  and  it  may  be  in- 
creased or  diminished  by 
the  action  of  the  muscles  of  the  middle  ear.  The  point  of  greatest  concav- 
ity, where  the  extremity  of  the  handle  of  the  malleus  is  attached,  is  called 
the  umbo.  Upon  the  inner  surface  of  the  membrane  are  two  pouches,  or 
pockets.  One  is  formed  by  a  small,  irregular,  triangular  fold,  situated  at  the 
upper  part  of  its  posterior  half  and  consisting  of  a  process  of  the  fibrous 
layer.  This,  which  is  called  the  posterior  pocket,  is  open  below  and  extends 
from  the  posterior  upper  border  of  the  membrane,  to  the  handle  of  the  mal- 
leus, which  it  assists  in  holding  in  position.  "  After  it  has  been  divided,  the 
bone  is  much  more  movable  than  before  "  (Troltsch).  The  anterior  pocket 
is  lower  and  shorter  than  the  posterior.  It  is  formed  by  a  small,  bony  pro- 
cess turned  toward  the  neck  of  the  malleus,  by  the  mucous  membrane,  by  the 
bony  process  of  the  malleus,  by  its  anterior  ligament,  the  chorda  tympani 
and  the  anterior  tympanic  artery.  The  handle  of  the  malleus  is  inserted 

49 


FIG.  868. — Right  membrana  tympani,  seen  from  within.  From 
a  photograph,  and  somewhat  reduced  (Riidinger). 

1,  head  of  the  malleus,  divided  ;  2,  neck  of  the  malleus  :  3.  han- 
dle of  the  malleus,  with  the  tendon  of  the  tensor  tympani 
muscle  ;  4,  divided  tendon  of  the  tensor  tympani ;  5,  6.  por- 
tion of  the  malleus  between  the  layers  of  the  membrana 
tympani ;  7,  outer  (radiating)  and  inner  (circular)  fibres  of 
the  membrana  tympani ;  8,  fibrous  ring  of  the  membrana 
tympani;  9, 14, 15,  dentated  fibres,  discovered  by  Gruber:  10, 
posterior  pocket;  11,  connection  of  the  posterior  pocket  with 
the  malleus;  12,  anterior  pocket;  13,  chorda  tympani  nerve. 


750  SPECIAL  SENSES. 

between  the  two  layers  of  the  fibrous  structure  of  the  membrana  tympani 
and  occupies  the  upper  half  of  its  vertical  diameter,  extending  from  the  pe- 
riphery to  the  umbo. 

The  membrana  tympani,  though  thin  and  translucent,  presents  three  dis- 
tinct layers.  Its  outer  layer  is  a  very  thin  extension  of  the  integument  lining 
the  external  meatus,  presenting,  however,  neither  papillae  nor  glands.  The 
inner  layer  is  a  delicate  continuation  of  the  mucous  membrane  lining  the 
tympanic  cavity  and  is  covered  by  tessellated  epithelial  cells.  The  fibrous 
portion,  or  lamina  propria,  is  formed  of  two  layers.  The  outer  layer  consists 
of  fibres  radiating  from  the  handle  of  the  malleus  to  the  periphery.  These 
are  best  seen  near  the  centre.  The  inner  layer  is  composed  of  circular  fibres, 
which  are  most  abundant  near  the  periphery  and  diminish  in  number  toward 
the  centre. 

The  color  of  the  membrana  tympani,  when  it  is  examined  with  an  aural 
speculum  by  daylight,  is  peculiar,  and  it  is  rather  difficult  to  describe,  as  it 
varies  in  the  normal  ear  in  different  individuals.  Politzer  described  the  mem- 
brane, examined  in  this  way,  as  translucent,  and  of  a  color  which  "  most 
nearly  approaches  a  neutral  gray,  mingled  with  a  weaker  tint  of  violet  and 
light  yellowish-brown."  This  color  is  modified,  in  certain  portions  of  the 
membrane,  by  the  chorda  tympani  and  the  bones  of  the  ear,  which  produce 
some  opacity.  The  entire  membrane  in  health  has  a  soft  lustre.  In  addi- 
tion there  is  seen,  with  proper  illumination,  a  well-marked,  triangular  cone 
of  light,  with  its  apex  at  the  end  of  the  handle  of  the  malleus,  spreading  out 
in  a  downward  and  forward  direction,  and  ^  to  ^  of  an  inch  (1'6  to 
2*1  mm.)  broad  at  its  base.  This  appearance  is  regarded  by  physiologists  as 
very  important,  as  indicating  a  normal  condition  of  the  membrane.  It  is 
undoubtedly  due  to  reflection  of  light  and  not  to  a  peculiar  structure  of  that 
portion  of  the  membrane  upon  which  it  is  seen. 

Uses  of  the  Membrana  Tympani. — Jt  is  unquestionable  that  the  mem- 
brana tympani  is  very  important  in  audition.  In  cases  of  disease  in  which 
the  membrane  is  thickened,  perforated  or  destroyed,  the  acuteness  of  hearing 
is  always  more  or  less  affected.  That  this  is  in  great  part  due  to  the  absence 
of  a  vibrating  surface  for  the  reception  of  waves  of  sound,  is  shown  by  the 
relief  which  is  experienced  by  those  patients  who  can  tolerate  the  presence  of 
an  artificial  membrane  of  rubber.  As  regards  the  mere  acuteness  of  hearing, 
aside  from  the  pitch  of  sounds,  the  explanation  of  the  action  of  the  mem- 
brane is  very  simple.  Sonorous  vibrations  are  not  readily  transmitted  through 
the  atmosphere  to  solid  bodies,  like  the  bones  of  the  ear ;  and  when  they  are 
thus  transmitted  they  lose  considerably  in  intensity.  When,  however,  the 
aerial  vibrations  are  received  by  a  membrane,  under  the  conditions  of  the 
membrana  tympani,  they  are  transmitted  with  very  little  loss  of  intensity ; 
and  if  this  membrane  be  connected  with  solid  bodies,  like  the  bones  of  the 
middle  ear,  the  vibrations  are  readily  conveyed  to  the  sensory  portions  of  the 
auditory  apparatus.  The  parts  composing  the  middle  ear  are  well  adapted 
to  the  transmission  of  sonorous  waves  to  the  auditory  nerves.  The  membrane 
of  the  tympanum  is  delicate  in  structure,  stretched  to  the  proper  degree  of 


USES  OF  THE  MEMBRANA  TYMPANI.  751 

tension,  and  vibrates  under  the  influence  of  the  waves  of  sound.  Attached 
to  this  membrane,  is  the  angular  chain  of  bones,  which  conducts  its  vibra- 
tions, like  the  bridge  of  a  violin,  to  the  liquid  of  the  labyrinth.  The  mem- 
brane is  fixed  at  its  periphery  and  has  air  upon  both  sides,  so  that  it  is  under 
favorable  conditions  for  vibration. 

A  study  of  the  mechanism  of  the  ossicles  and.  muscles  of  the  middle  ear 
shows  that  the  membrana  tympani  is  subject  to  certain  physiological  varia- 
tions in  tension,  due  to  the  contraction  of  the  tensor  tympani.  It  is  also  evi- 
dent that  this  membrane  may  be  drawn  in  and  rendered  tense  by  exhausting 
or  rarefying  the  air  in  the  drum.  If  the  mouth  and  nose  be  closed  and  an 
attempt  be  made  to  breathe  forcibly  by  expanding  the  chest,  the  external 
pressure  tightens  the  membrane.  In  this  condition  the  ear  is  rendered  in- 
sensible to  grave  sounds,  but  high-pitched  sounds  appear  to  be  more  intense. 
If  the  tension  be  removed,  as  may  be  done  by  an  act  of  swallowing,  the  grave 
sounds  are  heard  with  normal  distinctness.  This  experiment,  tried  at  a  con- 
cert, produces  the  curious  effect  of  abolishing  a  great  number  of  the  lowest 
tones,  while  the  shrill  sounds  are  heard  very  acutely.  The  same  phenomena 
are  observed  when  the  external  pressure  is  increased  by  descent  in  a  diving- 
bell. 

Undoubted  cases  of  voluntary  contraction  of  the  -tensor  tympani  have 
been  observed  by  otologists ;  and  in  these,  by  bringing  this  muscle  into  action, 
the  limit  of  the  perception  of  high  tones  is  greatly  increased.  In  two  in- 
stances of  this  kind,  recorded  by  Blake,  the  ordinary  limit  of  perception  was 
found  to  be  three  thousand  single  vibrations,  and  by  contraction  of  the  mus- 
cle, this  was  increased  to  five  thousand  single  vibrations. 

The  concave  form  of  the  membrana  tympani  and  the  presence  of  a  bony 
process  between  its  layers,  which  is  part  of  the  chain  of  bones  of  the  middle 
ear,  are  conditions  under  which  it  is  impossible  that  it  should  have  a  single, 
fundamental  tone.  This  has  been  shown  by  experiments  with  stretched 
membranes  depressed  in  their  central  portion  by  means  of  a  solid  rod.  No 
membrane  can  have  a  single,  fundamental  tone  unless  it  be  in  a  condition  of 
uniform  tension,  like  a  string,  and  this  is  impossible  in  the  membrana  tym- 
pani. Nevertheless  the  membrana  tympani  repeats  sounds  by  influence,  and 
it  is  capable  of  repeating  in  this  way  a  much  greater  variety  of  sounds  than 
if  it  had  itself  a  fundamental  tone  and  were  capable  of  a  uniform  degree  of 
tension.  This  has  been  shown  by  experiments  with  stretched,  elastic  mem- 
branes made  to  assume  a  concave  form.  If  the  membrana  tympani  had  a 
single,  fundamental  tone,  it  would  vibrate  by  influence  only  with  certain  tones 
in  unison  with  it,  and  the  overtones  would  be  eliminated.  It  would  then  act 
like  a  resonator  closed  by  a  membrane,  and  the  tone  with  which  it  happened 
to  be-in  unison  would  overpower  all  other  tones.  The  fact  is  that  all  tones, 
the  vibrations  of  which  reach  the  membrane,  are  appreciated  at  their  proper 
value  as  regards  intensity.  Again,  if  the  membrana  tympani  had  its  own 
fundamental  tone,  it  would  have  overtones  of  the  fundamental,  which  would 
produce  errors  and  confusion  in  auditory  appreciation.  The  chain  of  bones, 
also,  attached  to  the  membrane,  acts  as  a  damper  and  prevents  the  persist- 


752  SPECIAL  SENSES. 

ence  of  vibrations  after  the  waves  of  sound  cease  in  the  air.  This  provision 
enables  rapid  successions  of  sounds  to  be  distinctly  and  acurately  repeated. 

The  arrangement  of  the  muscles  and  bones  of  the  middle  ear  is  such  that 
the  tension  of  the  membnma  tympani  may  be  regulated  and  graduated  with 
great  nicety.  It  does  not  seem  to  be  necessary  to  perfect  audition  that  this 
should  be  done  for  every  single  note  or  combination  of  notes,  but  the  mem- 
brane probably  is  brought  by  voluntary  effort  to  a  definite  degree  of  tension 
for  notes  within  a  certain  range  as  regards  pitch  or  for  successions  and  pro- 
gressions of  sounds  in  a  particular  key.  As  far  as  the  consciousness  of  this 
muscular  action  is  concerned,  it  may  be  revealed  only  by  the  fact  of  the  cor- 
rect appreciation  of  certain  musical  sounds.  Some  persons  can  educate  the 
ear  so  as  to  acquire  what  is  called  the  faculty  of  absolute  pitch ;  that  is,  with- 
out the  aid  of  a  tuning-fork  or  any  musical  instrument,  they  can  give  the  ex- 
act musical  value  of  any  given  note.  A  possible  explanation  of  this  is  that 
;such  persons  may  have  educated  the  muscles  of  the  ear  so  as  to  put  the  tym- 
panic membrane  in  such  a  condition  of  tension  as  to  respond  to  a  given  note 
and  to  recognize  the  position  of  this  note  in  the  musical  scale.  Finally,  an 
accomplished  musician,  in  conducting  an  orchestra,  can  by  a  voluntary  effort, 
direct  his  attention  to  certain  instruments  and  hear  their  notes  distinctly, 
separating  them  from  the  general  volume  of  sound,  can  distinguish  the 
faintest  discords  and  can  designate  a  single  instrument  making  a  false  note. 

Destruction  of  both  tympanic  membranes  does  not  necessarily  produce 
total  deafness,  although  this  condition  involves  considerable  impairment  of 
hearing.  So  long  as  there  is  simple  destruction  of  these  membranes,  the 
bones  of  the  middle  ear  and  the  other  parts  of  the  auditory  apparatus  being 
intact,  the  waves  of  sound  are  conducted  to  the  auditory  nerves,  although 
this  is  done  imperfectly.  In  a  case  reported  by  Astley  Cooper,  one  membrana 
tympani  was  entirely  destroyed,  and  the  other  was  nearly  gone,  there  being 
.some  parts  of  its  periphery  remaining.  In  this  person  the  hearing  was  some- 
what impaired,  although  he  could  distinguish  ordinary  conversation  without 
much  difficulty.  Fortunately  he  had  considerable  musical  taste,  and  it  was 
ascertained  that  his  musical  ear  was  not  seriously  impaired ;  "  for  he  played 
well  on  the  flute  and  had  frequently  borne  a  part  in  a  concert.  I  speak  this, 
not  from  his  authority  only,  but  also  from  that  of  his  father,  who  is  an  ex- 
cellent judge  of  music,  and  plays  well  on  the  violin  :  he  told  me,  that  his  son, 
besides  playing  on  the  flute,  sung  with  much  taste,  and  perfectly  in  tune." 

There  is  an  important  consideration  that  must  be  kept  in  view  in  study- 
ing the  uses  of  any  distinct  portion  of  the  auditory  apparatus,  like  the 
^membrana  tympani.  This  membrane,  like  all  other  parts  of  the  apparatus, 
except  the  auditory  nerves  themselves,  has  simply  an  accessory  action.  If  the 
regular  waves  of  a  musical  sound  be  conveyed  to  the  terminal  filaments  of 
the  auditory  nerves,  these  waves  make  their  impression  and  the  sound  is  cor- 
rectly appreciated.  It  makes  no  difference,  except  as  regards  intensity,  how 
these  waves  are  conducted ;  the  sound  is  appreciated  by  the  impression  made 
upon  the  nerves,  and  the  nerves  only.  The  waves  of  sound  are  not  like  the 
waves  of  light,  refracted,  decomposed,  perhaps,  and  necessarily  brought  to  a 


MECHANISM  OF  THE  OSSICLES  OF  THE  EAR.  753 

focus  as  they  impinge  upon  the  retina ;  but  as  far  as  the  action  of  the  acces- 
sory parts  of  the  ear  are  concerned,  the  waves  of  sound  are  unaltered  ;  that 
is,  the  rate  of  their  succession  remains  absolutely  the  same,  though  they  be 
reflected  by  the  concavities  of  the  concha  and  repeated  by  the  tympanic 
membrane.  Even  if  it  be  assumed  that  the  membrane  under  normal  condi- 
tions repeats  musical  sounds  by  vibrations  produced  by  influence,  and  that 
sounds  are  exactly  repeated,  the  position  of  these  sounds  in  the  musical  scale 
is  not  and  can  not  be  altered  by  the  action  of  any  of  the  accessory  organs  of 
hearing.  The  fact  that  a  person  may  retain  his  musical  ear  with  both  mem- 
branes destroyed  is  not  really  an  argument  against  the  view  that  the  mem- 
brane repeats  sounds  by  influence ;  for  if  musical  sounds  or  noisy  vibrations 
be  conducted  to  the  auditory  nerves,  the  impression  produced  must  of  neces- 
sity be  dependent  exclusively  upon  the  character,  regularity  and  number  of 
the  sonorous  vibrations.  And,  again,  the  physical  laws  of  sound  teach  that 
a  membrane,  like  the  membrana  tympani,  must  reproduce  sounds  with  which 
it  is  more  or  less  in  unison  much  more  perfectly  than  discordant  or  irregular 
vibrations.  In  a  loud  confusion  of  noisy  sounds,  one  can  readily  distinguish 
melody  or  harmony,  even  when  the  vibrations  of  the  latter  are  comparatively 
feeble. 

It  has  been  shown  that  the  appreciation  of  the  pitch  of  sounds  bears  a 
certain  relation  to  the  degree  of  tension  of  the  tympanic  membrane.  When 
the  membrane  is  rendered  tense,  there  is  insensibility  to  low  notes.  When 
the  membrane  is  brought  to  the  highest  degree  of  tension  by  voluntary  con- 
traction of  the  tensor  tympani,  the  limit  of  appreciation  of  high  notes  may 
be  raised  from  three  thousand  to  five  thousand  vibrations.  It  is  a  fact  in  the 
physics  of  the  membrana  tympani  that  the  vibrations  are  more  intense  the 
nearer  the  membrane  approaches  to  a  vertical  position ;  and  it  has  been  ob- 
served that  the  membrane  has  a  position  more  nearly  vertical  in  musicians 
than  in  persons  with  an  imperfect  musical  ear  (Troltsch). 

Experiments  have  shown  that  the  tympanic  membrane  vibrates  more 
forcibly  when  relaxed  than  when  it  is  tense.  In  certain  cases  of  facial  palsy, 
in  which  it  is  probable  that  the  branch  of  the  facial  going  to  the  tensor  tym- 
pani was  affected,  the  ear  has  been  found  painfully  sensitive  to  powerful  im- 
pressions of  sound.  This  probably  has  no  relation  to  pitch,  and  most  sounds 
that  are  painfully  loud  are  comparatively  grave.  Artillerists  are  in  danger  of 
rupture  of  the  membrana  tympani  from  sudden  concussions.  To  guard 
against  this  injury,  it  is  recommended  to  stop  the  ear,  draw  the  shoulder  up 
against  the  ear  most  in  danger,  and  particularly  to  inflate  the  middle  ear 
after  Valsalva's  method.  "  This  method  consists  in  making  a  powerful  ex- 
piration, with  the  mouth  and  nostrils  closed  "  (Troltsch). 

Mechanism  of  the  Ossicles  of  the  Ear. — The  ossicles  of  the  middle  ear,  in 
connection  with  the  muscles,  have  a  twofold  office :  First,  by  the  action  of 
the  muscles  the  membrana  tympani  may  be  brought  to  different  degrees  of 
tension.  Second,  the  angular  chain  of  bones  serves  to  conduct  sonorous 
vibrations  to  the  labyrinth.  It  must  be  remembered  that  the  handle  of  the 
malleus  is  closely  attached  to  the  membrana  tympani,  especially  near  its 


754  SPECIAL  SENSES. 

lower  end.  Near  the  short  process — which  is  a  little,  conical  projection  at 
the  root  of  the  handle — the  attachment  is  looser  and  there  is  even  an  incom- 
plete joint-space  at  this  point.  The  long  process  is  attached  closely  to  the 
Glasserian  fissure  of  the  temporal  bone. ' 

The  malleus  is  articulated  with  the  incus  by  a  very  peculiar  joint.  This 
joint  is  so  arranged,  presenting  a  sort  of  cog,  that  the  handle  of  the  malleus 
can  rotate  only  outward ;  and  when  a  force  is  applied  which  would  have  a 
tendency  to  produce  a  rotation  inward,  the  malleus  must  carry  the  incus  with 
it.  This  mechanism  has  been  compared  to  that  of  a  watch-key  with  cogs 
which  are  fitted  together  and  allow  the  whole  key  to  turn  in  one  direction, 
but  are  separated  so  that  only  the  upper  portion  of  the  key  turns  when  the 
force  is  applied  in  the  opposite  direction  (Helmholtz).  In  the  articulation 
between  the  malleus  and  the  incus,  the  only  difference  is  that  there  is  but 
one  cog;  but  this  is  sufficient  to  prevent  an  independent  rotation  of  the 
malleus  inward. 

The  body  of  the  incus  is  attached  to  the  posterior  bony  wall  of  the  tym- 
panic cavity.  Its  articulation  with  the  malleus  has  just  been  indicated.  By 
the  extremity  of  its  long  process,  it  is  also  articulated  with  the  stapes,  which 
completes  the  chain.  In  situ,  the  stapes  forms  nearly  a  right  angle  with  the 
long  process  of  the  incus. 

The  stapes  is  articulated  with  the  incus,  as  indicated  above,  and  its  oval 
base  is  applied  to  the  fenestra  ovalis.  Surrounding  the  base  of  the  stapes,  is 
a  ring  of  elastic  fibro-cartilage,  which  is  closely  united  to  the  bony  wall  of  the 
labyrinth,  by  an  extension  of  the  periosteum. 

The  articulations  between  the  malleus  and  the  incus  and  between  the 
incus  and  the  stapes  are  so  arranged  that  when  the  membrana  tympani  is 
forced  outward,  as  it  may  be  by  inflation  of  the  tympanic  cavity,  there  is  no 
danger  of  tearing  the  stapes  from  its  attachment  to  the  fenestra  ovalis ;  for 
when  the  handle  of  the  malleus  is  drawn  outward,  the  cog-joint  between  the 
malleus  and  the  incus  is  loosened  and  no  considerable  traction  can  be  exerted 
upon  the  stapes. 

The  tensor  tympani  is  by  far  the  more  important  of  the  two  muscles  of 
the  middle  ear.  Its  action  is  to  tighten  the  cog-like  joint  between  the  malleus 
and  the  incus,  to  tighten,  also,  all  the  ligaments  of  the  incus,  to  draw  the 
long  process  of  the  malleus  inward,  thereby  increasing  the  tension  of  the 
membrana  tympani,  and  to  press  the  base  of  the  stapes  against  the  fenestra 
ovalis.  By  the  action  of  this  muscle  the  chain  of  ossicles  becomes  prac- 
tically a  solid  and  continuous,  angular,  bony  rod. 

Although  experiments  have  demonstrated  the  mechanism  of  the  ossicles 
and  the  action  of  the  tensor  tympani,  both  as  regards  the  chain  of  bones  and 
the  membrana  tympani,  direct  observations  are  wanting,  to  show  the  exact 
relations  of  these  different  conditions  of  the  ossicles  and  of  the  membrane  to 
the  physiology  of  audition.  One  very  important  physical  point,  however, 
which  has  been  the  subject  of  much  discussion,  is  settled.  The  chain  of 
bones  acts  as  a  single,  solid  body  in  conducting  vibrations  to  the  labyrinth. 
It  is  a  matter  of  physical  demonstration  that  vibrations  of  the  bones  them- 


PHYSIOLOGICAL  ANATOMY  OF  THE  INTERNAL  EAE.      755 

selves  would  be  infinitely  rapid  as  compared  with  the  highest  tones  which  can 
be  appreciated  by  the  ear,  if  it  were  possible  to  induce  in  these  bones  regular 
vibrations.  Practically,  then,  the  ossicles  have  no  independent  vibrations 
that  can  be  appreciated.  This  being  the  fact,  the  ossicles  simply  conduct  to 
the  labyrinth  the  vibrations  induced  in  the  membrana  tympani  by  sound- 
waves ;  and  their  arrangement  is  such  that  these  vibrations  lose  very  little  in 
intensity.  While  it  has  been  shown  experimentally  that  the  amplitude  of 
vibration  in  the  membrana  tympani  and  the  ossicles  diminishes  as  the  tension 
of  the  membrane  is  increased,  it  would  seem  that  when  the  tensor  tympani 
contracts,  it  must  render  the  conduction  of  sound-waves  to  the  labyrinth 
more  delicate  than  when  the  auditory  apparatus  is  in  a  relaxed  condition, 
which  may  be  compared  with  the  "  indolent "  condition  of  accommodation  of 
the  eye.  When  the  membrana  tympani  is  relaxed  and  the  cog-like  articula- 
tion between  the  malleus  and  the  incus  is  loosened,  the  vibrations  of  the 
membrane  and  of  the  malleus  may  have  a  greater  amplitude ;  but  when  the 
malleo-incudal  joint  is  tightened  and  the  stapes  is  pressed  against  the  fenestra 
ovalis,  the  loss  of  intensity  of  vibration,  in  conduction  through  the  bones  to 
the  labyrinth,  must  be  reduced  to  the  minimum.  With  this  view,  the  tensor 
tympani  muscle,  while  it  contracts  to  secure  for  the  membrana  tympani  the 
degree  of  tension  most  favorable  for  vibration  under  the  influence  of  certain 
sounds,  puts  the  chain  of  bones  in  the  condition  best  adapted  to  the  conduc- 
tion of  the  vibrations  of  the  membrane  to  the  labyrinth,  with  the  smallest 
possible  loss  of  intensity. 

PHYSIOLOGICAL  AXATOMY  OF  THE  INTERNAL  EAR. 

The  internal  ear  consists  of  the  labyrinth,  which  is  divided  into  the  vesti- 
bule, semicircular  canals  and  cochlea.  The  general  arrangement  of  these 
parts  has  already  been  described ;  and  it  remains  only  to  study  the  structures 
contained  within  the  bony  labyrinth,  in  so  far  as  their  anatomy  bears  directly 
upon  the  physiology  of  audition.  Passing  inward  from  the  tympanum,  the 
first  division  of  the  internal  ear  is  the  vestibule.  This  cavity  communicates 
with  the  tympanum,  by  the  fenestra  ovalis,  which  is  closed  in  the  natural 
state  by  the  base  of  the  stapes.  It  communicates,  also,  with  the  semicircular 
canals  and  with  the  cochlea. 

General  Arrangement  of  the  Membranous  Labyrinth — The  bony  labyrinth 
is  lined  by  a  moderately  thick  periosteum,  consisting  of  connective  tissue,  a 
few  delicate  elastic  fibres,  nuclei  and  blood-vessels,  with  spots  of  calcareous 
concretions.  This  membrane  adheres  closely  to  the  bone  and  extends  over 
the  fenestra  ovalis  and  the  fenestra  rotunda.  Its  inner  surface  is  smooth  and 
is  covered  with  a  single  layer  of  cells  of  endothelium,  which  in  some  parts  is 
segmented  and  in  others  forms  a  continuous,  nucleated  sheet.  In  certain 
portions  of  the  vestibule  and  semicircular  canals,  the  periosteum  is  united 
to  the  membranous  labyrinth,  more  or  less  closely,  by  fibrous  bands,  which 
have  been  called  ligaments  of  the  labyrinth.  The  fenestra  rotunda,  which 
lies  between  the  cavity  of  the  tympanum  and  the  cochlea,  is  closed  by  a 
membrane  formed  by  an  extension  of  the  periosteum  lining  the  cochlea, 


756 


SPECIAL  SENSES. 


on  one  side,  and  the  mucous  membrane  lining  the  tympanic  cavity,  on  the 
other. 

In  the  bony  vestibule,  occupying  about  two-thirds  of  its  cavity,  are  two 
distinct  sacs ;  a  large,  ovoid  sac,  the  utricle,  situated  in  the  upper  and  pos- 
terior portion  of  the  cavity,  and  a  smaller,  rounded  sac,  the  saccule,  situated 
in  its  lower  and  anterior  portion.  These  two  sacs  communicate  with  each 

other  through  a  small 
canal  in  the  form  of 
the  letter  Y,  which  is 
represented  in  the  up- 
per diagram  in  Fig. 
269.  The  utricle  com- 
municates with  the 
semicircular  canals, 
and  the  saccule  opens 
into  the  membranous 
canal  of  the  cochlea,  by 
the  canalis  reuniens. 
At  a  point  in  the  utri- 
cle corresponding  to  the 
entrance  of  a  branch  of 
the  auditory  nerve,  is  a 
round,  whitish  spot, 
called  the  acoustic  spot 
(macula  acustica),  con- 
taining otoliths,  or  oto- 
conia,  which  are  at- 
tached to  the  inner  sur- 
face of  the  membrane. 
A  similar  spot,  contain- 
ing otoliths,  exists  in 
the  saccule,  at  the  point 
of  entrance  of  its  nerve. 
Otoliths  are  also  found 
in  the  ampullas  of  the 
semicircular  canals. 
These  calcareous  masses  are  composed  of  crystals  of  calcium  carbonate,  which 
are  hexagonal  and  pointed  at  their  extremities.  Nothing  definite  is  known 
of  the  uses  of  these  calcareous  bodies,  which  exist  in  man,  mammals,  birds 
and  reptiles. 

The  membranous  semicircular  canals  occupy  about  one-third  of  the  cavity 
of  the  bony  canals.  They  present  small,  ovoid  dilatations,  called  ampulla?, 
corresponding  to  the  ampullary  enlargements  of  the  bony  canals.  They  are 
held  in  place  by  a  large  number  of  little,  fibrous  bands  extending  to  the  bony 
labyrinth. 

The  membrane  of  the  cochlea,  including  the  lining  periosteum,  occupies 


FIG.  269.— Diagram  of  the  labyrinth  (vestibule  and  semicircular 
canals).  From  a  photograph,  and  somewhat  reduced  (RUdinger). 

Upper  figure:  1,  utricle  ;  2.  saccule  ;  3,  5,  membranous  cochlea  ;  4, 
canalis  reuniens  :  6.  semicircular  canals. 

Lower  figure  :  1,  utricle  ;  2.  saccule  :  3,  4,  6.  ampullae  :  5,  7.  8.  9,  semi- 
circular canals  :  10,  auditory  nerve  (partly  diagrammatic):  11,12, 
13,  14,  15,  distribution  of  the  branches  of  the  nerve,  to  the  vesti- 
bule and  the  semicircular  canals. 


PHYSIOLOGICAL  ANATOMY  OF  THE  INTERNAL  EAR.      757 


the  spiral  canal  of  the  cochlea,  which  it  fills  completely.  Viewed  externally, 
it  appears  as  a  single  tube,  following  the  turns  of  the  bony  cochlea,  beginning 
below,  at  the  first  turn,  by  a  blind  extremity,  and  terminating  in  a  blind 
extremity  at  the  summit  of  the  cochlea.  If  a  section  of  the  cochlea  be  made 
in  a  direction  vertical  to  the  spiral,  it  will  be  seen  that  this  canal  is  divided, 
partly  by  bone  and  partly  by  membrane,  into  an  inferior  portion,  a  superior 
portion,  and  a  triangular  canal,  lying  between  the  two,  which  is  external. 
The  bony  septum  is  in  the  form  of  a  spiral  plate,  extending  from  the  central 
column  (the  modiolus)  into  the  cavity  of  the  cochlea,  about  half-way  to  its 
external  wall,  and  terminating  above  in  a  hook-shaped  extremity,  called  the 
hamulus.  The  free  edge  of  this  bony  lamina  is  thin  and  dense.  Near  the 
central  column  it  divides  into  two  plates,  with  an  intermediate,  spongy  struct- 
ure, in  which  are  lodged 
vessels  and  nerves.  The 
surface  of  the  bony  lamina 
looking  toward  the  base 
of  the  cochlea  is  marked 
by  a  number  of  regular, 
transverse  ridges,  or  striae. 

Attached  to  the  free 
margin  of  the  bony  lam- 
ina, is  a  membrane,  the 
membrana  basilaris,which 
extends  to  the  outer  wall 
of  the  cochlea.  In  this 
way  the  canal  of  the  coch- 
lea is  divided  into  two 
portions,  one  above  and 
the  other  below  the  sep- 
tum. The  portion  below 
begins  at  the  fenestra  ro- 
tunda and  is  called  the 
scala  tympani.  The  por- 
tion above,  exclusive  of  the  triangular  canal  of  the  cochlea,  communicates 
with  the  vestibule  and  is  called  the  scala  vestibuli. 

Above  the  membrana  basilaris,  is  a  membrane,  the  limbus  laminfe  spiralis, 
the  external  continuation  of  which  is  called  the  membrana  tectoria,  or  the 
membrane  of  Corti.  Between  the  membrana  tectoria  and  the  membrana 
basilaris,  is  the  organ  of  Corti.  The  membrane  of  Reissner  extends  from 
the  inner  portion  of  the  limbus  upward  and  outward  to  the  outer  wall  of  the 
cochlea.  This  divides  the  portion  of  the  cochlea  situated  above  the  scala 
tympani  into  two  portions ;  an  internal  portion,  the  scala  vestibuli,  and  an 
external,  triangular  canal,  called  the  canalis  cochlea?,  or  the  membranous 
cochlea. 

In  the  anatomical  description  of  the  contents  of  the  bony  cochlea,  the 
membranous  parts  may  be  designated  as  follows : 


FIG.  270.— Otolithsfrom  various  animals  (Riidinger). 
from  the  goat :  2,  from  the  herring :  3.  from  the  devil-fish  ;  4 
from  the  mackerel ;  5,  from  the  flying-fish  ;  6,  from  the  pike  :  7, 
from  the  carp  ;  8,  from  the  ray  ;  9,  from  the  shark  ;  10,  from 
the  grouse. 


758  SPECIAL  SENSES. 

1.  The  portion  below  the  bony  and  membranous  septum,  called  the  scala 
tympani.     This  is  formed  by  the  periosteum  lining  the  corresponding  por- 
tion of  the  cochlea  and  the  under  surface  of  the  bony  lamina,  and  the  mem- 
brana  basilaris. 

2.  The  scali  vestibuli.     This  is  formed  by  the  periosteum  lining  the  cor- 


Fio.  271.— Section  of  the  first  turn  of  the  spiral  canal  of  a  cat  newly-born.— Section  of  the  cochlea  of  a 
human  foetus  at  the  fourth  month.  From  a  photograph,  and  somewhat  reduced  (Rudinger). 

Upper  figure  :  1,  2,  6,  lamina  spiralis ;  2,  lower  plate  ;  3,  4,  5.  5,  nervus  cochlearis  ;  7.  membrane  of 
Reissner  ;  8,  membrana  tectoria  ;  9,  epithelium  ;  10,  11.  pillars  of  Corti  :  12  inner  hair-cells  •  13 
outer  hair-cells  ;  14,  16,  membrana  basilaris  ;  15,  epithelium  in  the  sulcus  spiralis  ;  17,  18,  19,  liga- 
mentum  spirale  ;  20.  spiral  canal,  below  the  membrana  basilaris 

Lower  figure  :  8  T,  S  T,  5.  5,  7,  7,  8,  8,  scala  tympani  ;  S  V,  S  V,  9.  9.  scala  vestibuli  ;  1,  base  of  the  coch- 
lea ;  2,  apex;  3,  4,  central  column;  10,  10,  10,  10,  ductus  cochlearis;  11,  branches  of  the  nervus 
cochlearis ;  12,  12,  12,  spiral  ganglion  ;  18,  14.  limbus  laminae  spiralis  ;  15,  membrane  of  Reissner  ; 
16,  epithelium;  17.  outer  hair-cells;  18,  epithelium  of  the  membrana  basilaris:  19,  nervous  filaments: 
20,  union  of  the  membrana  basilaris  with  the  ligamentum  spirale  :  21,  epithelium  of  the  peripheral 
wall  of  the  ductus  cochlearis ;  22,  23,  membrana  tectoria  ;  24,  spiral  canal  below  the  membrana 
basilaris. 

responding  portion  of  the  bony  cochlea  and  the  upper  surface  of  the  bony 
septum  and  is  bounded  externally  by  the  membrane  of  Reissner. 

3.  The  true  membranous  cochlea.     This  is  the  spiral,  triangular  canal, 


PHYSIOLOGICAL  ANATOMY  OF  THE  INTERNAL  EAR.      759 

bounded  externally  by  the  periosteum  of  the  corresponding  portion  of  the 
wall  of  the  cochlea,  internally,  by  the  membrane  of  Reissner,  and  on  the 
other  side,  by  the  membrana  basilaris.  What  is  thus  called  the  membranous 
cochlea  is  divided  by  the  limbus  laminae  spiralis  and  the  membrana  tectoria 
into  two  portions ;  a  triangular  canal  above,  which  is  the  larger,  and  a  quadri- 
lateral canal  below,  between  the  limbus  and  membrana  tectoria  and  the  mem- 
brana basilaris.  The  quadrilateral  canal  contains  the  organ  of  Corti  and 
various  complex  anatomical  structures.  The  relations  of  these  divisions  of 
the  cochlea  are  shown  in  Fig.  272. 

The  membranous  cochlea,  as  described  above,  follows  the  spiral  course  of 
the  cochlea,  terminates  superiorly  in  a  blind,  pointed  extremity,  at  the  cupola, 
beyond  the  hamulus,  and  is  connected  below  with  the  saccule  of  the  vestibule, 
by  the  canalis  reuniens.  The  relations  of  the  different  portions  of  the  mem- 
branous cochlea  to  each  other  and  to  the  scalae  of  the  cochlea  are  shown  in 
Fig.  271. 

Liquids  of  the  Labyrinth. — The  labyrinth  contains  a  certain  quantity  of  a 
clear,  watery  liquid,  called  the  humor  of  Cotugno  or  of  Valsalva.  A  portion 
of  this  liquid  surrounds  the  membranous  sacs  of  the  vestibule,  the  semicircu- 
lar canals  and  the  membranous  cochlea,  and  this  is  known  as  the  perilymph 
of  Breschet.  Another  portion  of  the  liquid  fills  the  membranous  labyrinth  ; 
and  this  is  sometimes  called  the  humor  of  Scarpa,  but  it  is  known  more  gen- 
erally as  the  endolymph  of  Breschet.  The  perilymph  occupies  about  one- 
third  of  the  cavity  of  the  bony  vestibule  and  semicircular  canals  and  both 
scalae  of  the  cochlea.  Both  this  liquid  and  the  endolymph  are  clear  and  wat- 
ery, becoming  somewhat  opalescent  on  the  addition  of  alcohol.  The  spaces 
in  the  labyrinth  are  directly  connected  with  the  lymphatic  system.  The 
space  occupied  by  the  perilymph  communicates  with  lymphatics,  chiefly 
through  the  aqueduct  of  the  cochlea,  but  there  is  also  a  communication 
through  the  internal  auditory  meatus,  with  the  space  beneath  the  dura  mater. 
The  endolymph  passes  to  the  subarachnoid  space,  beneath  the  arachnoid  cov- 
ering of  the  auditory  nerve.  As  far  as  is  known,  the  uses  of  the  liquid  of  the 
internal  ear  are  to  sustain  the  delicate  structures  contained  in  this  portion 
of  the  auditory  apparatus  and  to  conduct  sonorous  vibrations  to  the  terminal 
filaments  of  the  auditory  nerves  and  the  parts  with  which  they  are  con- 
nected. 

Distribution  of  the  Nerves  in  the  Labyrinth. — As  the  auditory  nerves 
enter  the  internal  auditory  meatus,  they  divide  into  an  anterior,  or  cochlear, 
and  a  posterior,  or  vestibular  branch.  The  vestibular  branch  divides  into 
three  smaller  branches,  a  superior  and  anterior,  a  middle,  and  a  posterior 
branch.  The  superior  and  anterior  branch,  the  largest  of  the  three,  is  dis- 
tributed to  the  utricle,  the  superior  semicircular  canal  and  the  external  semi- 
circular canal.  The  middle  branch  is  distributed  to  the  saccule.  The  pos- 
terior branch  passes  to  the  posterior  semicircular  canal.  The  nerves  distrib- 
uted to  the  utricle  and  saccule  penetrate  at  the  points  occupied  by  the 
otoliths,  and  the  nerves  going  to  the  semicircular  canals  pass  to  the  ampullae, 
which  also  contain  otoliths.  (See  Fig.  2G9.)  In  each  ampulla,  at  the  point 


760 


SPECIAL  SENSES. 


where  the  nerve  enters,  is  a  transverse  fold,  projecting  into  the  canal  and 
occupying  about  one-third  of  its  circumference,  called  the  septum  trans- 
versum. 

The  nerves  terminate  in  essentially  the  same  way  in  the  sacs  of  the  ves- 
tibule and  the  ampullae  of  the  semicircular  canals.  At  the  points  where  the 
nerves  enter,  in  addition  to  the  otoliths,  are  cylindrical  cells  of  various  forms, 
which  pass  gradually  into  the  general  endothelium  of  the  .cavities.  In  addi- 
tion to  these  cells,  are  fusiform,  nucleated  bodies,  the  free  ends  of  which  are 
provided  with  hair-like  processes,  called  fila  acustica.  These  are  about  ^^ 
of  an  inch  (31  //.)  in  length  and  are  distributed  in  quite  a  regular  manner 
around  the  otoliths.  The  nerves  form  an  anastomosing  plexus  beneath  the 
endothelium,  and  they  probably  terminate  in  the  fusiform  bodies  just  de- 
scribed as  presenting  the  fila  acustica  at  their  free  extremities.  In  the  sacs 
of  the  vestibule  and  in  the  semicircular  canals,  nerves  exist  only  in  the 
maculae  acusticae  and  the  ampullae. 

The  cochlear  division  of  the  auditory  nerve  breaks  up  into  a  number  of 
small  branches,  which  pass  through  foramina  at  the  base  of  the  cochlear,  in 
what  is  called  the  tractus  spiralis  foraniinulentus.  These  follow  the  axis  of 

the  cochlea  and  pass  in 
their  course  toward  the 
apex,  between  the  plates  of 
the  bony  spiral  lamina. 
Between  these  plates  of 
bone,  the  dark  -  bordered 
nerve-fibres  pass  each  one 
through  a  bipolar  cell,  these 
cells  together  forming  a 
spiral  ganglion,  known  as 
the  ganglion  of  Corti.  Be- 
yond this  ganglion  the 
nerves  form  an  anastomos- 
ing plexus  and  finally  enter 

FIG.  272.— Distribution  of  the  cochlear  nerve  in  the  spirallamina    +V.,.    r,,!,,^,,;!.,^  £.„,,!    ^QT1Ql     nv 
of  the  cochlea.    The  cochlea  is  from  the  right  side  and  is  seen     l  udl>    u 

from  itsantero-inferior  part  "(Sappey).  the  }     f  CoftL      Ag  th 

1,  trunk  of  the  cochlear  nerve  :  2.  2.  2,  membranous  zone  of  the 

spiral  lamina  :  3,  3,  3,  terminal  expansion  of  the  cochlear    paSS    into    this    Canal     theV 
nerve,  exposed  in  its  whole  extent  by  the  removal  of  the  su-          • 

perior  plate  of  the  lamina  sniralis  :' 4.  orifice  of  communica-    Suddenly   become    pale    and 
tion  of  the  scala  tympani  with  the  scala  vestibuli.  J 

exceedingly     fine.        They 

probably  are  connected  finally  with  the  organ  of  Corti,  although  their  exact 
mode  of  termination  has  not  yet  been  determined.  The  course  of  the  nerve- 
fibres  to  their  distribution  in  the  cochlea  is  shown  in  Fig.  272. 

Organ  of  Corti. — In  the  quadrilateral  canal,  bathed  in  the  endolymph, 
throughout  its  entire,  spiral  course,  is  an  arrangement  of  pillars,  or  rods,  which 
are  regular,  like  the  strings  of  a  harp  in  miniature.  These  are  the  pillars  of 
Corti.  These  pillars  are  external  and  internal,  with  their  bases  attached  to  the 
basilar  membrane  and  their  summits  articulated  above,  so  as  to  form  a  regu- 
lar, spiral  arcade,  enclosing  a  triangular  space  which  is  bounded  below  by  the 


ORGAN  OF  CORTI. 


761 


basilar  membrane.  The  number  of  the  elements  of  the  organ  of  Corti  is  es- 
timated at  about  4,500,  for  the  outer,  and  6,500,  for  the  inner  rods.  The 
relations  of  these  structures  to  the  membranous  labyrinth  are  seen  in  Fig. 
271.  The  external  pillars  are  longer,  more  delicate  and  more  rounded  than 


FIG.  273.— The  two  pillars  of  the  organ  of  Corti  (Sappey). 

A,  external  pillar  of  the  organ  of  Corti :  1,  body,  or  middle  portion  ;  2,  posterior  extremity,  or  base  :  3, 

cell  on  its  internal  side  ;  4,  anterior  extremity  ;  5,  convex  surface,  by  which  it  is  joined  to  the  inter- 
nal pillar  ;  t>,  prolongation  of  this  extremity. 

B,  internal  pillar  of  the  organ  of  Corti :  1,  body,  or  middle  portion  ;  2,  posterior  extremity  ;  3,  cell  on  its 

external  side  ;  4,  anterior  extremity  ;  5,  concave  surface,  by  which  it  is  joined  to  the  external  pillar  ; 
6,  prolongation,  lying  above  the  corresponding  prolongation  of  the  external  pillar. 

C,  the  two  pillars  of  the  organ  of  Corti,  united  by  their  anterior  extremity,  and  forming  an  arcade,  the 

concavity  of  which  presents  outward :  1,1,  body,  or  middle  portion  of  the  pillars ;  2,  2,  posterior 
extremities  ;  3,  3,  cells  attached  to  the  posterior  extremities  ;  4,  4,  anterior  extremities  joined 
together  ;  5,  terminal  prolongation  of  this  extremity. 

the  internal  pillars.  The  form  of  the  pillars  is  more  exactly  shown  in  Figs. 
273  and  274,  the  latter  figure,  however,  exhibiting  other  structures  which 
enter  into  the  constitution  of  the  organ  of  Corti.  It  will  be  remarked  that 


FIG.  274.— Vertical  section  of  the  organ  of  Corti  of  the  dog ;  magnified  800  diameters  (Waldeyer). 
0-6,  homogeneous  layer  of  the  basilar  membrane  ;  v,  t3rmpanic  layer,  with  nuclei,  granular  cell-proto- 
plasm and  connective  tissue  ;  a,,  tympanic  lip  of  the  crista  spiralis  ;  c,  thickened  portion  of  the 
basilar  membrane  ;  d.  spiral  vessel  ;  e,  blood-vessel :  /,  h.  bundle  of  nerves  ;  g,  epithelium  ;  t.  inner 
hair-cell,  with  its  basilar  process,  fc  ;  Z,  head-plate  of  the  inner  pillar  ;  m,  union  of  the  two  pillars  ; 
n.  base  of  the  inner  pillar ;  o,  base  of  the  outer  pillar  :  p,  g,  r,  outer  hair-cells,  with  traces  of  the 
cilia  :  t,  bases  of  two  other  hair-cells  ;  z,  Hensen's  prop-cell ;  /-/i,  lamina  reticularis  ;  w,  nerve-fibre 
passing  to  the  first  hair-cell,  p. 

a  small,  nucleated  body  is  attached  to  the  base  of  each  pillar.  At  the  summit, 
Avhere  the  internal  and  the  external  pillars  are  joined  together,  is  a  delicate 
prolongation,  directed  outward,  which  is  attached  to  the  covering  of  the 
quadrilateral  canal. 

The  above  description  comprises  about  all  that  is  definitely  known  of  the 


762  SPECIAL  SENSES. 

arrangement  of  the  pillars,  or  rods  of  Corti.  They  are  nearly  homogeneous, 
except  when  treated  with  reagents,  and  are  said  to  be  of  about  the  consistence 
of  cartilage.  They  are  closely  set  together,  with  very  narrow  spaces  between 
them,  and  it  is  difficult  to  see  how  they  can  be  stretched  to  any  considerable 
degree  of  tension.  The  arch  is  longer  at  the  summit  than  at  the  base  of  the 
cochlea,  the  longest  rods,  at  the  summit,  measuring,  according  to  Pritchard, 
about  ^J-¥  of  an  inch  (125  /t),  and  the  shortest,  at  the  base,  about  -g^  of  an 
inch  (50  //.).  At  the  base  of  the  cochlea  the  two  sets  of  rods  are  about  equal 
in  length.  From  the  base  to  the  apex,  both  sets,  outer  and  inner,  progress- 
ively increase  in  length,  and  the  outer  rods  become  the  longer,  so  that  near 
the  apex  they  are  nearly  twice  as  long  as  the  inner.  The  anatomical  rela- 
tions between  the  pillars  and  the  terminal  filaments  of  the  auditory  nerves 
are  not  definitely  settled. 

In  addition  to  the  pillars  just  described,  various  cellular  elements  enter 
into  the  structure  of  the  organ  of  Corti.  The  most  important  of  these  are 
the  inner  and  the  outer  hair-cells.  These  are  16,400  to  20,000  in  number 
(Hensen,  Waldeyer).  The  inner  hair-cells  are  arranged  in  a  single  row,  and 
the  outer  hair-cells,  in  three  rows.  Nothing  definite  is  known  of  the  uses  of 
these  cells.  The  relations  of  these  parts  are  shown  in  Fig.  274.  It  is  sup- 
posed by  some  anatomists  that  the  filaments  of  the  auditory  nerves  terminate 
in  the  cells  above  described  ;  but  this  point  is  not  definitely  settled. 

USES    OF   DIFFERENT    PARTS   OF   THE   INTERNAL   EAR. 

The  precise  uses  of  the  different  parts  found  in  the  internal  ear  are  ob- 
scure, notwithstanding  the  careful  researches  that  have  been  made  into  the 
anatomy  and  the  physiology  of  the  labyrinth.  There  are  several  points, 
however,  bearing  upon  the  physiology  of  this  portion  of  the  auditory  appa- 
ratus, concerning  which  there  can  be  no  doubt : 

First,  it  is  certain  that  impressions  of  sound  are  received  by  the  terminal 
filaments  of  the  auditory  nerves  and  by  these  nerves  are  conveyed  to  the 
brain. 

Second,  the  uses  of  the  parts  composing  the  external  and  the  middle  ear 
are  chiefly  accessory.  The  sonorous  waves  are  collected  by  the  pavilion  and 
are  conveyed  by  the  external  meatus,  to  the  middle  ear ;  the  membrana  tym- 
pani  vibrates  under  their  influence ;  and  they  are  thus  collected,  repeated  and 
transmitted  to  the  internal  ear. 

Uses  of  the  Semicircular  Canals. — In  the  experiments  of  Flourens,  upon 
pigeons  and  rabbits  (1824),  it  was  shown  that  destruction  of  the  semicircular 
canals  had  apparently  no  effect  upon  the  sense  of  hearing,  while  destruction 
of  the  cochlea  upon  both  sides  produced  complete  deafness.  In  addition  it 
was  observed  that  destruction  of  the  semicircular  canals  on  both  sides  was 
followed  by  remarkable  disturbances  in  equilibration.  The  animals  could 
maintain  the  standing  position,  but  so  soon  as  they  made  any  movements, 
"  the  head  began  to  be  agitated ;  and  this  agitation  increasing  with  the  move- 
ments of  the  body,  walking  and  all  regular  movements  finally  became  impos- 
sible, in  nearly  the  same  way  as  when  equilibrium  and  stability  of  move- 


USES  OF  THE  PARTS  CONTAINED  IN  THE  COCHLEA.      763 

merits  are  lost  after  turning  several  times  or  violently  shaking  the  head." 
These  observations  of  Flourens,  at  least  as  far  as  regards  the  influence  of  the 
semicircular  canals  upon  equilibration,  have  been  confirmed  by  Goltz  and 
are  sustained  by  observations  upon  the  human  subject  in  the  condition 
known  as  Meniere's  disease.  As  far  as  can  be  judged  from  experimental 
data,  it  does  not  seem  probable  that  the  nerves  directly  concerned  in  audition 
are  distributed  to  any  considerable  extent  in  the  semicircular  canals.  In- 
deed the  uses  of  these  parts  is  exceedingly  obscure;  for  it  can  hardly  be 
admitted,  upon  purely  anatomical  grounds,  that  they  are  concerned  in  the 
discrimination  of  the  direction  of  sonorous  vibrations,  an  idea  which  has  been 
advanced  by  some  physiologists. 

Uxes  of  the  Parts  contained  in  the  Cochlea. — There  can  be  no  doubt  with 
regard  to  the  capital  point  in  the  physiology  of  the  cochlea ;  namely,  that 
those  branches  of  the  auditory  nerve  which  are  essential  to  the  sense  of  hear- 
ing and  which  receive  the  impressions  of  sound  are  distributed  mainly  in 
the  cochlea.  An  analysis  of  sonorous  impressions  shows  that  they  possess 
various  attributes,  such  as  intensity,  quality  and  pitch.  As  far  as  the  termi- 
nal filaments  of  the  auditory  nerve  are  concerned,  it  is  evident  that  the  in- 
tensity of  sound  is  appreciated  in  proportion  to  the  power  of  the  impression 
made  upon  these  nerves.  With  regard  to  quality  of  sound,  it  has  been  seen 
that  this  is  due  to  the  form  of  sonorous  vibrations,  and  that  musical  sounds 
usually  are  compound,  their  quality  depending  largely  upon  the  relative  power 
of  the  harmonics,  partial  tones  etc.  It  has  also  been  seen  that  consonating 
bodies  repeat  by  influence,  not  only  the  actual  pitch  of  tones,  but  their  quality. 
If  there  be  in  the  cochlea  an  anatomical  arrangement  of  rods  or  fibres  by 
which  the  sonorous  vibrations  conveyed  to  the  ear  by  the  atmosphere  are 
repeated,  there  is  reason  to  believe  that  the  quality  as  well  as  the  pitch  is  re- 
produced. 

The  arrangement  of  the  rods  which  enter  into  the  structure  of  the  organ 
of  Corti  has  afforded  a  theoretical  explanation  of  the  final  mechanism  of  the 
appreciation  of  pitch.  With  the  exception  of  the  internal  ear,  the  action  of 
different  portions  of  the  auditory  apparatus  is  simply  to  conduct  and  repeat 
sonorous  vibrations ;  and  the  sole  use  of  these  accessory  parts,  aside  from  the 
protection  of  the  organs,  is  to  convey  the  vibrations  to  the  terminal,  nervous 
filaments.  Whatever  be  the  uses  of  the  membrana  tympani  in  repeating 
sounds  by  influence,  it  is  certain  that  this  membrane  possesses  no  true,  audi- 
tory nerves,  and  that  the  auditory  nerves  only  are  capable  of  receiving  im- 
pressions of  sound.  Thus  hearing,  and  even  the  appreciation  of  pitch,  is 
not  necessarily  lost  after  destruction  of  the  membrana  tympani ;  and  if 
sonorous  vibrations  reach  the  auditory  nerves,  they  will  be  appreciated  and 
appreciated  correctly. 

In  view  of  the  arrangement  of  the  organ  of  Corti,  with  its  eleven  thousand 
or  more  rods  of  different  lengths  arranged  Avith  a  certain  degree  of  regularity, 
a  number  more  than  sufficient  to  represent  all  the  notes  of  the  musical  scale, 
it  is  not  surprising  that  they  should  be  regarded  as  capable  of  repeating  all 
the  notes  heard  in  music.  Helmholtz  formulated  this  idea  in  the  theory  that 


764  SPECIAL  SENSES. 

sounds  conveyed  to  the  cochlea  throw  into  vibration  only  those  elements  of 
the  organ  of  Corti  which  are  tuned,  so  to  speak,  in  unison  with  them.  Ac- 
cording to  this  hypothesis,  the  rods  of  Corti  constitute  a  harp  of  several 
thousand  strings,  played  upon,  as  it  were,  by  the  sonorous  vibrations.  The- 
ories analogous  to  the  one  proposed  by  Helmholtz,  but  of  course  lacking  the 
basis  of  exact  anatomical  and  physical  details  developed  by  modern  researches 
and  experiments,  were  advanced  by  Du  Verney  (1683)  and  by  Le  Cat  (1767). 

Viewing  the  question  anatomically,  it  is  by  no  means  certain  that  the  rods 
of  Corti  are  so  attached  and  stretched  that  they  are  capable  of  separate  and 
individual  vibrations.  It  has  not  been  demonstrated  that  certain  of  these 
rods  vibrate  under  the  influence  of  certain  notes  or  that  they  are  tuned  in 
accord  with  certain  notes.  Heusen  and  others  have  rejected  the  theory  of 
Helmholtz,  basing  their  opinions  mainly  upon  the  anatomical  arrangement 
of  the  rods  of  Corti.  Hensen  assumed  it  to  be  a  physical  impossibility  for 
the  different  rods  to  vibrate  individually,  and  he  regarded  it  as.  improbable 
that  the  rods  are  tuned  in  accord  with  different  musical  notes.  Similar  ob- 
jections apply  to  the  theory  that  different  transverse  fibres  in  the  membrana 
basilaris  vibrate  in  accord  with  particular  notes.  There  is,  indeed,  no  theory 
which  affords  an  entirely  satisfactory  explanation  of  the  mechanism  of  the 
final  appreciation  of  the  pitch  of  musical  sounds. 

It  is  not  absolutely  necessary  that  sonorous  vibrations  should  pass  to  the 
cochlea  through  the  external  ear  and  parts  in  the  middle  ear.  Sounds  may 
be  conducted  to  the  auditory  nerves  through  the  bones  of  the  head  or  through 
the  Eustachian  tube,  as  is  shown  by  the  simple  and  familiar  experiment  of 
placing  a  tuning-fork  in  contact  with  the  head  or  between  the  teeth,  the  ears 
being  closed. 

The  action  of  the  two  ears  does  not  seem  to  be  absolutely  necessary  to  the 
correct  appreciation  of  auditory  impressions ;  but  variations  in  the  force  of 
such  impressions,  made  upon  either  ear,  aid  in  determining  the  direction  of 
sounds,  although  errors  are  often  made  in  this  regard. 

The  estimate  of  the  distance  of  sounds  is  made  by  judging  of  the  intensity, 
in  connection  with  information  obtained  through  other  senses,  especially  the 
sense  of  sight.  The  power  of  estimating  distance  is  largely  influenced  by 
experience  and  education. 

Centres  for  Audition. — The  centres  for  audition  in  dogs  and  monkeys 
are  in  the  superior  temporo-sphenoidal  convolution  (Ferrier,  Munk).  In 
man  these  centres  are  in  the  first  (superior)  and  second  temporal  convolu- 
tions of  the  temporo-sphenoidal  lobe,  which  are  supplied  by  the  fourth  branch 
of  the  middle  cerebral  artery.  This  has  been  ascertained  by  pathological 
observations  as  well  as  by  experiments  on  the  lower  animals.  In  man  the 
action  of  these  centres  is  not  completely  crossed,  and  destruction  of  the  cen- 
tre upon  one  side  does  not  cause  complete  deafness  in  either  ear.  Complete 
destruction  of  the  centres  on  both  sides,  however,  produces  total  deafness. 
Injury  of  the  first  temporal  convolution  is  often  followed  by  the  condition 
known  as  word-deafness,  in  which  the  subject  hears  the  sound  of  words,  but 
these  sounds  convey  to  him  no  idea.  This  is  the  psychical,  auditory  centre, 


FEMALE  ORGANS  OF  GENERATION.          765 

and  it  is  confined  to  the  first  temporal  convolution  on  the  left  side  (Wer- 
nicke).  Word-deafness  is  analogous  to  the  condition  already  described 
under  the  name  of  word-blindness,  and  the  centre  usually  is  confined  to  the 
left  side  of  the  cerebrum.  It  has  been  suggested  by  Westphal  that  this 
centre  may  be  on  the  right  side  of  the  cerebrum,  in  left-handed  persons. 


CHAPTER  XXIV. 

ORGANS  AND  ELEMENTS  OF  GENERATION. 

General  considerations — Female  organs  of  generation — General  arrangement  of  the  female  organs — The 
ovaries— Graafian  follicles — The  parovarinrn — The  uterus— The  Fallopian  tubes— Structure  of  the  ovum 
— Discharge  of  the  ovum — Passage  of  ova  into  the  Fallopian  tubes — Puberty  and  menstruation — Changes 
in  the  Graafian  follicle  after  its  rupture  (corpus  luteum) — Male  organs  of  generation — The  testicles — 
Vesiculae  seminales — Prostate — Glands  of  the  urethra — Male  elements  of  generation — Spermatozoids. 

GENERATION  is  one  of  the  most  important  of  the  animal  functions,  and 
as  such  usually  is  treated  of  quite  fully  in  works  upon  physiology ;  but  a 
more  or  less  extended  account  of  this  function  is  also  to  be  found  in  every 
complete  treatise  on  anatomy  and  in  most  works  on  obstetrics.  While  the 
physiological  history  of  the  human  organism  would  not  be  complete  without 
touching  upon  generation  and  development,  it  does  not  seem  desirable  to 
give  a  very  full  description  of  these  processes,  in  which  there  would  neces- 
sarily be  a  repetition  of  what  is  always  to  be  found  in  works  upon  other 
subjects. 

The  question  of  so-called  spontaneous  generation  in  some  of  the  lower 
animals  was  formerly  much  discussed  by  physiologists.  This,  however,  is  now 
of  purely  historical  interest.  As  actual  knowledge  of  facts  has  accumulated, 
the  limits  of  what  was  thought  to  be  spontaneous  generation  have  become 
more  and  more  restricted ;  until  now  it  is  generally  admitted  that  sponta- 
neous generation  does  not  exist  in  the  history  of  animals.  The  entire  'ques- 
tion, therefore,  may  be  dismissed  with  this  simple  statement.  There  are, 
however,  certain  distinct  forms  of  generation ;  but  the  only  one  that  has  any 
considerable  importance  in  connection  with  human  physiology  is  generation 
of  new  beings  by  the  union  of  male  and  female  elements  in  the  fecundation  of 
the  ovum,  with  the  development  of  the  fecundated  ovum.  This  is  known  as 
sexual  generation.  The  two  elements  of  generation  are  developed  in  separate 
beings,  male  and  female,  and  these  elements  are  brought  together  normally 
in  what  is  known  as  sexual  connection,  or  copulation. 

FEMALE  ORGANS  OF  GENERATION. 

A  knowledge  of  certain  points  in  the  anatomy  of  the  female  organs  of 
generation  is  essential  to  the  comprehension  of  the  most  important  of  the 
processes  of  reproduction.  Following  a  fruitful  intercourse  of  the  sexes, 

50 


766  GENEEATION. 

the  function  of  generation,  as  regards  the  male,  ceases  with  the  comparatively 
simple  process  of  penetration  of  the  male  element  through  the  protective 
covering  of  the  ovum  and  its  fusion  with  the  female  element.  The  fecun- 
dated ovum  then  passes  through  certain  changes,  which  are  the  first  processes 
of  its  development,  forms  its  attachments  to  the  body  of  the  mother,  con- 
tinues its  development,  and  is  nourished  and  grows,  until  the  foetus  at  term 
is  brought  into  the  world.  It  will  not  be  necessary  to  describe  minutely  the 
anatomy  of  the  external  parts,  as  these  are  concerned  only  in  sexual  inter- 
course and  in  parturition ;  which  latter,  though  a  purely  physiological  pro- 
cess, forms  the  greatest  part  of  the  science  of  obstetrics,  is  considered  elabo- 
rately in  treatises  on  this  subject  and  usually  is  not  treated  of  to  any  great 
extent  in  works  upon  physiology. 

The  female  organs  of  generation  are  divided  anatomically  into  internal 
and  external.  The  external  organs  are  the  vulva,  the  adjacent  parts  and  the 
vagina.  The  internal  organs  are  the  uterus,  Fallopian  tubes  and  the  ovaries. 
The  ovaries  are  the  true,  female  organs,  in  which  alone  the  female  element 
can  be  produced.  The  Fallopian  tubes  and  the  uterus  are  accessory  in  their 
uses,  the  female  element,  the  ovum,  passing  through  the  Fallopian  tubes 
to  the  uterus,  where  it  forms  the  attachments  to  the  body  of  the  mother, 
which  are  essential  to  its  nourishment  and  full  development  after  fecunda- 
tion. 

The  vagina  has  a  direction,  slightly  curved  anteriorly,  which  is  nearly 
coincident  with  the  axis  of  the  outlet,  or  the  inferior  strait  of  the  pelvis. 
Projecting  into  the  vagina,  at  its  upper  extremity,  is  the  lower  part  of  the 
neck  of  the  uterus.  The  uterus  extends  from  the  vagina  nearly  to  the  brim 
of  the  pelvis.  It  is  situated  between  the  bladder  and  the  rectum,  and  has 
an  antero-posterior  inclination  when  the  bladder  is  moderately  distended, 
which  brings  its  axis  nearly  coincident  with  that  of  the  superior  strait  of  the 
pelvis.  With  the  body  erect,  the  angle  of  the  uterus  with  the  perpendicular 
is  about  forty-five  degrees. 

The  uterus  is  held  in  place  by  ligaments,  certain  of  which  are  formed  of 
folds  of  the  peritoneum.  The  anterior  ligament  is  reflected  from  the  ante- 
rior Surface  to  the  bladder;  the  posterior  ligament  extends  from  the  poste- 
rior surface  to  the  rectum ;  the  round  ligaments  extend  from  the  upper  angle 
of  the  uterus,  on  either  side,  between  the  folds  of  the  broad  ligament  and 
through  the  inguinal  canal,  to  the  symphysis  pubis ;  the  broad  ligaments  ex- 
tend from  the  sides  of  the  uterus  to  the  walls  of  the  pelvis. 

The  uterus  and  the  broad  ligaments  partially  divide  the  pelvis  into  two 
portions  ;  and  these  ligaments,  which  are  formed  of  a  double  fold  of  perito- 
neum, present  a  superior,  or  posterior  surface,  and  an  inferior,  or  anterior  sur- 
face. The  superior,  or  anterior  border  of  this  fold  is  occupied  by  the  Fallo- 
pian tubes,  the  peritoneum  constituting  their  outer  coat.  Laterally,  at  the 
free  extremities  of  the  tubes,  the  peritoneum  ceases,  and  there  is  an  actual 
opening  of  each  Fallopian  tube  into  the  peritoneal  cavity.  Attached  to  the 
broad  ligament  and  projecting  upon  its  posterior  surface,  is  the  ovary,  which 
is  connected  with  the  fibrous  tissue  between  the  two  layers  of  the  ligament. 


THE  OVARIES.  767 

At  the  hiliim  of  the  ovary,  as  will  be  seen  farther  on,  the  structure  of  the 
peritoneum  undergoes  a  marked  change. 

The  Ovaries. — The  ovaries,  attached  to  the  broad  ligament  and  project- 
ing from  its  posterior  surface,  lie  nearly  horizontally  in  the  pelvic  cavity,  on 


FIG.  275.—  Uterus,  Fallopian  tubes  and  ovaries ;  posterior  view  (Sappey). 

1,  ovaries  ;  2.  2,  Fallopian  tubes  :  3,  3,  flmbriated  extremity  of  the  left  Fallopian  tube,  seen  from  its  con- 
cavity ;  4,  opening  of  the  left  tube  ;  5,  fimbriated  extremity  of  the  right  tube,  posterior  view  ;  6,  6, 
fimbrias  which  attach  the  extremity  of  each  tube  to  the  ovary  ;  7,  7.  ligaments  of  the  ovary  ;  8,  8, 
9,  9,  broad  ligaments  ;  10,  uterus  ;  11,  cervix  uteri ;  12,  os  uteri ;  13, 13,  14,  vagina. 

either  side  of  the  uterus.  They  are  of  a  whitish  color,  and  their  form  is 
ovoid  and  flattened,  with  the  anterior  border,  sometimes  called  the  base, 
attached  to  the  broad  ligament.  By  closely  examining  their  mode  of  connec- 
tion with  the  broad  ligament,  it  is  seen  that  at  the  margin  of  the  attached 
surface  of  the  ovary,  the  posterior  layer  of  the  ligament  ceases,  and  that  the 
fibrous  stroma  of  the  medullary  portion  of  the  ovary  is  continuous  with  the 
fibrous  tissue  lying  between  the  two  layers. 

Each  ovary  is  about  an  inch  and  a  half  (38'1  mm.)  in  length,  half  an 
inch  (12-7  mm.)  in  thickness,  and  three-quarters  of  an  inch  (19'1  mm.)  in 
width  at  its  broadest  portion.  The  outer  extremity  is  somewhat  rounded 
and  is  attached  to  one  of  the  fimbriae  of  the  Fallopian  tube.  The  inner  ex- 
tremity is  more  pointed,  and  is  attached  to  the  side  of  the  uterus  by  means 
of  the  ligament  of  the  ovary.  This  ligament  is  shown  in  Fig.  275  (7,  7). 
It  is  a  rounded  cord,  composed  of  non-striated  muscular  fibres  spread  out 
upon  the  attached  extremity  of  the  ovary  and  the  posterior  surface  of  the 
uterus,  and  is  covered  by  peritoneum.  The  weight  of  each  ovary  is  sixty  to 
one  hundred  grains  (3'9  to  6'5  grammes),  and  these  organs  are  largest  in  the 
adult  virgin.  Its  attached  border  is  called  the  hilum ;  and  at  this  portion 
the  vessels  and  nerves  penetrate.  The  surface  is  marked  by  rounded,  trans- 
lucent elevations,  produced  by  distended  Graafian  follicles,  with  little  cica- 
trices indicating  the  situation  of  ruptured  follicles.  There  may  also  be 
seen,  between  the  distended  follicles,  corpora  lutea  in  various  stages  of 
atrophy. 


7G8  GENEEATION. 

After  the  peritoneum  has  reached  the  ovary,  its  fibrous  layer  becomes 
indistinct  and  fuses  with  the  fibrous  stroma  of  the  ovary  itself.  The  peri- 
toneal endothelium  here  undergoes  a  change,  and  the  cells  covering  the 
ovary  are  cylindrical.  This  change  in  the  structure  of  the  peritoneum  is 
abrupt  and  is  indicated  by  a  distinct  line  surrounding  the  hilum  of  the 
ovary.  There  seems  to  be  little  difference  between  the  epithelial  cells  cov- 
ering the  ovaries  and  those  lining  the  Fallopian  tubes,  except  that  the 
latter  are  provided  with  cilia. 

On  making  a  section  of  the  ovary,  it  is  readily  seen  by  the  naked  eye  that 
the  organ  is  composed  of  two  distinct  structures ;  a  cortical  substance,  for- 
merly called  the  tunica  albuginea,  which  is  about  ^  of  an  inch  (1  mm.)  in 
thickness,  and  a  medullary  substance  containing  a  large  number  of  blood- 
vessels. The  cortical  substance  alone  contains  the  Graafian  follicles.  The 
external  layer  of  this  is  denser  than  the  deeper  portion,  but  there  is  no 
distinct  fibrous  membrane  such  as  is  sometimes  described  under  the  name  of 
the  tunica  albuginea. 

The  cortical  substance  of  the  ovary  consists  of  connective  tissue  in  sev- 
eral layers,  the  fibres  of  which  are  continuous  with  the  looser  fibres  of  the 
medullary  portion.  In  the  substance  of  this  layer,  are  embedded  the  ova, 
enclosed  in  the  sacs  called  Graafian  follicles.  This  layer  contains  a  few 
blood-vessels,  coming  from  the  medullary  portion,  which  surround  the  fol- 
licles. 

The  medullary  portion  of  the  ovary  is  very  vascular  and  is  composed  of 
small  bands,  or  trabeculae  of  connective  tissue,  with  non-striated  muscular 
fibres.  The  blood-vessels,  which  penetrate  at  the  hilum,  are  large  and  con- 
voluted, especially  at  the  hilum  itself,  where  there  is  a  mass  of  convoluted 
veins,  forming  a  sort  of  vascular  bulb  (Rouget).  In  the  medullary  portion 
of  the  ovary,  which  is  sometimes  called  the  vascular  zone,  the  muscular  fibres 
follow  the  vessels,  in  the  form  of  muscular  sheaths. 

In  addition  to  the  blood-vessels,  the  ovary  receives  nerves  from  the  sper- 
matic plexus  of  the  sympathetic,  the  exact  mode  of  termination  of  which  has 
not  been  ascertained.  Lymphatics  have  also  been  demonstrated  at  the  hilum. 

Graafian  Follicles. — These  vesicles,  or  follicles,  were  described  and  figured 
by  DeGraaf,  in  1672,  and  are  known  by  his  name.  They  contain  the  ova, 
undergo  a  series  of  peculiar  changes,  enlarge,  approach  the  surface  of  the 
ovary,  and  finally  are  ruptured,  discharging  their  contents  into  the  fimbriated 
extremity  of  the  Fallopian  tube.  The  Graafian  follicles  are  developed  ex- 
clusively in  the  cortical  substance.  If  the  ovary  be  examined  at  any  period 
of  life,  no  follicles  are  found  in  the  medullary  substance ;  but  a  few  of  the 
larger  may  project  downward,  so  as  to  encroach  somewhat  upon  it,  being 
actually  of  a  diameter  greater  than  the  thickness  of  the  cortex.  The  entire 
number  of  follicles  of  all  sizes  in  each  ovary  is  about  36,000  (Henle).  Ac- 
cording to  the  table  of  measurements  given  by  Waldeyer,  the  primordial  fol- 
licles in  the  human  embryon,  at  the  seventh  month,  measure  -$fa  to  ^  of 
an  inch  (30  to  100  ft)  in  diameter,  and  the  primordial  ova,  y^o  to  TirW  of 
an  inch  (15  to  25  p.). 


GRAAFIAN  FOLLICLES.  769 

The  ovary  appears  very  early  in  embryonic  life,  in  the  form  of  a  cellular 
outgrowth  from  the  Wolffian  body.  Most  of  its  cells  are  small,  but  as  early 
as  the  fourth  or  fifth  day,  in  the  chick,  some  of  them  are  to  be  distinguished 
by  their  large  size,  their  rounded  form  and  the  presence  of  a  large  nucleus. 
These  cells  are  supposed  to  be  primordial  ova.  In  the  process  of  develop- 
ment of  the  ovary  some  of  the  peripheral  cells  penetrate  in  the  form  of  tubes 
(the  so-called  ovarian  tubes)  and  at  the  same  time,  delicate  processes,  formed 
of  connective  tissue  and  blood-vessels,  extend  from  the  fibrous  stroma  under- 
lying the  epithelium  and  enclose  collections  of  cells.  It  is  probable  that 
there  are*two  modes  of  formation  of  follicles ;  one,  by  the  penetration  of  epi- 
thelial tubes  from  the  surface,  which  become  constricted  and  divided  off  into 
closed  cavities,  and  the  other,  by  the  extension  of  fibrous  processes  from  be- 
low, which  enclose  little  collections  of  cells.  By  both  of  these  processes,  lit- 
tle cavities  are  formed,  which  contain  a  number  of  cells.  In  each  of  these 
cavities,  there  is  a  single,  large,  rounded  cell,  with  a  large  nucleus,  this  cell 
being  a  primordial  ovum ;  and  in  addition,  in  the  same  cavity,  there  are  other 
cells,  which  are  the  cells  of  the  Graafian  follicle.  The  exact  nature  of  the 
processes  just  described  has  been  studied  in  the  chick;  but  it  is  probable 
that  the  same  kind  of  development  occurs  in  mammalia  arid  in  the  human 
subject. 

From  birth  until  just  before  the  age  of  puberty,  the  cortical  substance  of 
the  ovary  contains  several  thousands  of  what  are  termed  primordial  follicles, 
enclosing  the  primordial  ova ;  and  it  is  probable  that  after  the  ovaries  are 
fully  developed  at  birth,  no  additional  ova  or  Graafian  follicles  make  their 
appearance.  The  prevailing  idea  is,  indeed,  that  the  great  majority  of  these 
never  arrive  at  maturity,  and  that  they  undergo  atrophy  at  various  stages 
of  their  development.  In  the  adult,  according  to  Waldeyer,  the  smallest 
Graafian  follicles  measure  -g-J-g-  to  -g^  of  an  inch  (30  to  40  /A),  and  the  small- 
est ova,  a  little  more  than  10*0()  of  an  inch  (26  /A).  The  primordial  ova  have 
the  form  of  rounded  cells,  each  with  a  large,  clear  nucleus  and  a  nucleolus. 
Other  structures  are  developed  in  and  surrounding  these  cells,  as  the  ova  ar- 
rive at  their  full  development. 

The  most  important  stage  in  the  development  of  the  ova  and  Graafian 
follicles  is  observed  at  about  the  period  of  puberty.  At  this  time  a  number 
of  follicles  (twelve,  twenty,  thirty  or  even  more)  enlarge,  so  that  all  sizes  are 
observed,  between  the  smallest  primordial  follicles,  -$fa  of  an  inch  (30  //,),  and 
the  largest,  nearly  £  an  inch  (12  mm.)  in  diameter.  In  follicles  that  have 
attained  any  considerable  size,  there  are  the  fully  developed  ova,  one  in  each 
follicle — except  in  very  rare  instances,  when  there  are  two — and  these  ova 
have  a  diameter  of  about  yf^  of  an  inch  (200  //,).  In  the  process  which  cul- 
minates in  the  discharge  of  the  ovum  into  the  fimbriated  extremity  of  the 
Fallopian  tube,  the  Graafian  follicle  gradually  enlarges,  becomes  distended 
with  liquid  and  finally  breaks  through  and  ruptures  upon  the  surface  of  the 
ovary. 

Fig.  276  shows  the  follicles  and  ova  of  various  sizes.  It  is  observed  that 
the  larger  follicles  contain  fully  formed  ova  and  have  a  proper,  fibrous  coat. 


770  GENERATION. 

The  ova  here  present  an  epithelial  covering  and  are  embedded  in  a  mass  of 
the  epithelial  lining  of  the  follicle,  the  membrana  granulosa,  this  mass  being 
called  the  discus  or  cumulus  proligerus. 

At  or  near  the  period  of  their  maturity  the  Graafian  follicles  present 
several  coats  and  are  filled  with  an  albuminous  liquid.     The  mature  follicles 


FIG.  276.— Portion  of  a  sagittal  section  of  the  ovary  of  an  old  bitch  (Waldeyer). 

a,  ovarian  epithelium  ;  6,  6,  ovarian  tubes  ;  c,  c,  younger  follicles  ;  rf,  older  follicle  :  e,  discus  proligerns, 
with  the  ovum  ;  /,  epithelium  of  a  second  ovum  in  the  same  follicle  ;  g,  fibrous  coat  of  the  follicle  ; 
h.  proper  coat  of  the  follicle ;  i,  epithelium  of  the  follicle  (membrana  granulosa) ;  k,  collapsed, 
atrophied  follicle  ;  I,  blood-vessels  ;  m,  m,  cell-tubes  of  the  parpvarium,  divided  longitudinally  and 
transversely  ;  y,  tubular  depression  of  the  ovarian  epithelium,  in  the  tissue  of  the  ovary  ;  z,  begin- 
ning of  the" ovarian  epithelium,  close  to  the  lower  border  of  the  ovary. 

project  just  beneath  the  surface  and  form  little,  rounded,  translucent  eleva- 
tions. The  smallest  follicles  are  near  the  surface,  and  as  they  enlarge,  at 
first  they  become  deeper,  as  is  seen  in  Fig.  276,  becoming  superficial  only  as 
they  approach  the  condition  of  fullest  distention. 

Taking  one  of  the  largest  follicles  as  an  example,  two  fibrous  layers  can 
be  distinguished ;  an  outer  layer,  of  ordinary  connective  tissue,  and  an  inner 
layer,  the  tunica  propria,  formed  of  the  same  kind  of  tissue,  with  the  differ- 
ence that  as  the  follicle  enlarges  the  inner  layer  becomes  vascular.  The 


THE  UTERUS. 


771 


vascular  tunica  propria  is  lined  by  cells  of  epithelium,  forming  the  so-called 
membrana  granulosa.  At  a  certain  point  in  this  membrane,  is  a  mass  of 
cells,  called  the  discus  or  cumulus  proligerus,  in  which  the  ovum  is  embedded. 
The  situation  of  the  discus  proligerus  is  not  invariable ;  sometimes  it  is  at 
the  most  superficial,  and  sometimes  it  is  at  the  deepest  part  of  the  Graafian 
follicle. 

The  liquid  of  the  Graafian  follicle  is  alkaline,  slightly  yellowish  and  not 
viscid.  It  contains  a  small  quantity  of  albuminoid  matter,  coagulable  by  heat, 
alcohol  and  acids.  This  liquid  is  supposed  to  be  secreted  by  the  cells  lining 
the  inner  membrane  of  the  follicle. 

The  Parovarium. — The  parovarium,  or  organ  of  Bosenmuller,  is  simply 
the  remains  of  the  "VVolffian  body,  lying  in  the  folds  of  the  broad  ligament, 
between  the  ovary  and  the  Fallopian  tube.  It  consists  of  twelve  to  fifteen 
tubes  of  fibrous  tissue,  lined  by  ciliated  epithelium.  It  has  no  physiological 
importance. 

The  Uterus. — The  form,  situation  and  relations  of  the  uterus  and  Fallo- 
pian tubes  have  already  been  indicated  and  are  shown  in  Fig.  275. 

The  uterus  is  a  pear-shaped  body,  somewhat  flattened  antero-posteriorly, 
presenting  a  f  undus,  a  body  and  a  neck.  At  its  lower  extremity,  is  an  open- 


FIG.  277 '.—  Virgin  uterus.    A. — anterior  view.    B. — median  section.    C. — transverse  section  (Sappey). 

A.  1.  body  ;  2.  2,  angles  ;  3,  cervix  ;  4,  site  of  the  os  internum  ;  5,  vaginal  portion  of  the  cervix  ;  6,  ex- 
ternal os  ;  7,  7,  vagina. 

B.  1,  1,  profile  of  the  anterior  surface  ;  2,  vesico-uterine  cul-de-sac  :  3.  3.  profile  of  the  posterior  surface; 

4,  body  ;  5,  neck  ;  6,  isthmus  :  7,  cavity  of  the  body  :  8.  cavity  of  the  cervix  ;  9,  os  internum  ;  10, 
anterior  lip  of  the  os  externum  ;  11,  posterior  lip  ;  12,  12,  vagina. 

C.  1,  cavity  of  the  body  :  2,  lateral  wall  ;  3,  superior  wall  :  4,  4,  cornua  ;  5,  os  internum  ;  6,  cavity  of  the 

cervix  ;  7,  arbor  vitse  of  the  cervix  ;  8,  os  externum  ;  9,  9,  vagina. 

ing  into  the  vagina,  called  the  os  externum.  At  the  upper  portion  of  the 
neck,  is  a  constriction,  which  indicates  the  situation  of  the  os  internum.  The 
form  of  the  uterus  is  shown  in  Fig.  277  (A).  It  usually  is  about  three  inches 
(76'2  mm.)  in  length,  two  inches  (5O8  mm.)  in  breadth  at  its  widest  portion, 
and  one  inch  (25-4  mm.)  in  thickness.  Its  weight  is  one  and  a  half  to  two 
and  a  half  ounces  (42'5  to  71  grammes).  It  is  somewhat  loosely  held  in  place 


772 


GENERATION. 


by  the  broad  and  round  ligaments  and  by  the  folds  of  the  peritoneum  in 
front  and  behind.  The  delicate  layer  of  peritoneum  which  forms  its  external 
covering  extends  behind  as  far  down  as  the  vagina,  where  it  is  reflected  back 
upon  the  rectum,  and  anteriorly,  a  little  below  the  upper  extremity  of  the 
neck  (os  internum),  where  it  is  reflected  upon  the  urinary  bladder.  At  the 
sides  of  the  uterus,  the  peritoneal  covering,  a  little  below  the  entrance  of  the 
Fallopian  tubes,  becomes  loosely  attached  and  leaves  a  line  for  the  penetra- 


Fio.  278.— Muscular  fibres  of  the  uterus  (Sappey). 

A,  fibres  of  the  uterus  of  the  foetus  at  term  ;  B,  of  a  woman  twenty  years  of  age  ;  C,  of  a  woman  just 

delivered. 

tion  of  the  vessels  and  nerves.  Fig.  277  (C),  giving  a  view  of  the  interior  of 
the  uterus,  shows  a  triangular  cavity,  with  two  cornua  corresponding  to  the 
openings  of  the  Fallopian  tubes,  and  very  thick  walls,  the  greatest  part  of 
which  is  composed  of  layers  and  bands  of  non-striated  muscular  fibres. 

The  muscular  walls  of  the  uterus  are  composed  of  non-striated  fibres  ar- 
ranged in  several  layers.  These  fibres  are  spindle-shaped  and  always  nucle- 
ated, the  nucleus  presenting  one  or  two  large  granules  which  have  been  taken 
for  nucleoli.  They  are  closely  bound  together,  so  that  they  are  isolated  with 
great  difficulty.  In  addition  to  an  amorphous,  adhesive  substance  between 
the  muscular  fibres,  there  are  many  rounded  and  spindle-shaped  cells  of  con- 
nective tissue,  and  a  few  elastic  fibres.  The  muscular  tissue  of  the  uterus  is 
remarkable  from  the  fact  that  the  fibres  enlarge  immensely  during  gestation, 
becoming  at  that  time  ten  or  fifteen  times  as  long  and  five  or  six  times  as 
broad  as  they  are  in  the  unimpregnated  state.  They  are  united  into  bun- 
dles or  fasciculi,  which  in  certain  of  the  layers  interlace  with  each  other  in 
every  direction.  The  fibres  are  divided  into  external,  middle  and  internal 
layers. 

The  external,  muscular  layer,  which  is  very  thin  but  distinct,  is  closely 


THE  UTERUS. 


(73 


attached  to  the  peritone- 
um. When  the  uterus  is 
somewhat  enlarged  after 
impregnation,  there  are  ob- 
served oblique  and  trans- 
verse, superficial  fibres 
passing  over  the  fundus 
and  the  anterior  and  pos- 
terior surfaces  to  the  sides. 
Here  they  are  prolonged 
upon  the  Fallopian  tubes, 
the  round  ligament  and 
the  ligament  of  the  ovary, 
and  they  also  extend  be- 
tween the  layers  of  the 
broad  ligament.  This  ex- 
ternal layer  is  so  thin  that 
it  can  not  be  very  efficient 
in  the  expulsive  contrac- 
tions OI  the  Uterus  ;  but 

from  its  connections  with 
1 

the    Fallopian     tubes    and 

the  ligaments,  it  is  useful 

in  holding  the  uterus  in  place. 


379.  —  Superficial  muscular  fibres  of  the  anterior  surface  of 
the  uterus 


a,  a,  round  ligaments  ;  6,  6,  Fallopian  tubes  ;  c,  c,  c,  e,  e,  transverse 
fibres  ;  d,  /,  longitudinal  fibres. 


It  does  not  extend  entirely  over  the  sides  of 
the  uterus. 

The  middle,  muscular  layer  is 
the  one  most  efficient  in  the  partu- 
rient contractions  of  the  uterus.  It 
is  composed  of  a  thick  and  intri- 
cate net-  work  of  fasciculi  interlac- 
ing with  each  other  in  every  direc- 
tion. 

The  inner,  muscular  layer  is  ar- 
ranged in  the  form  of  broad  rings, 
which  surround  the  Fallopian  tubes, 
become  larger  as  they  extend  over 
the  body  of  the  uterus  and  meet  at 
the  centre  of  the  organ,  near  the 
neck. 

The  mucous  membrane  of  the 
uterus  is  of  a  pale,  reddish  color  ; 
and  that  portion  lining  the  body  is 
smooth  and  is  so  closely  attached 
to  the  subjacent  structures  that  it 

FIG.  280.—  Inner  layer  of  muscular  fibres  of  the  uterus 

(Liegeois).  can  not  be  separated  to  any  great 

a,  a,  rings  around  the  openings  of  the  Fallopian  tubes  ;     _-_.+__  +  >,„  /]i««pptirm        TTiprPl's    in- 
6,  6,  circular  fibres  of  the  cervix.  extent   Dy  dlSSCCtlOn.       J.  11       ,   lb,  II 


774  GENERATION. 

deed,  no  proper  submucous,  areolar  tissue,  the  membrane  being  applied  di- 
rectly to  the  uterine  walls.  It  is  covered  by  a  single  layer  of  cylindrical  epi- 
thelial cells,  with  delicate  cilia,  the  movements  of  which  are  from  without 
inward,  toward  the  openings  of  the  Fallopian  tubes.  Examination  of  the 
surface  of  the  membrane  with  a  low  magnifying  power  shows  the  open- 
ings of  a  great  number  of  tubular  glands.  These  glands  usually  are  sim- 
ple, sometimes  branched,  dividing,  about  midway  between  the  opening  and 
the  lower  extremity,  into  two  and  very  rarely  into  three  secondary  tubules. 
Their  course  generally  is  tortuous,  so  that  their  length  frequently  exceeds 
the  thickness  of  the  mucous  membrane.  The  openings  of  these  tubes  are 
about  -5^5-  of  an  inch  (72  /i)  in  diameter.  Their  secretion,  which  forms  a 
thin  layer  of  mucus  on  the  surface  of  the  membrane  in  health,  is  grayish, 
viscid  and  feebly  alkaline.  The  tubes  themselves  have  very  thin,  structure- 
less walls  and  are  lined  with  cylindrical,  ciliated  epithelial  cells. 

The  changes  which  the  mucous  membrane  of  the  body  of  the  uterus 
undergoes  during  menstruation  are  remarkable.  Under  ordinary  conditions 
its  thickness  is  -fa  to  -fa  of  an  inch  (1  to  1*8  mm.) ;  but  it  measures  during 
the  menstrual  period  £  to  £  of  an  inch  (4'2  to  6'4  mm.).  • 

In  the  cervix  the  membrane  is  paler,  firmer  and  thicker  than  the  mem- 
brane of  the  body  of  the  uterus,  and  between  these  two  mucous  surfaces 
there  is  a  distinct  line  of  demarkation.  It  is  more  loosely  attached  to  the 
subjacent  tissue,  in  the  cervix,  and  the  anterior  and  posterior  surfaces  of 
the  neck  present  an  appearance  of  folds  radiating  from  the  median  line, 
forming  what  has  been  called  the  arbor  vitas  uteri,  or  plicse  palmatae. 
Throughout  the  entire  cervical  membrane,  are  mucous  glands,  and  in  addi- 
tion, in  the  lower  portion,  are  a  few  rounded,  semi-transparent,  closed  folli- 
cles, called  the  ovules  of  Naboth,  which  are  cystic  enlargements  of  obstructed 
follicles.  The  upper  half  of  the  cervical  membrane  is  smooth  but  the  lower 
half  presents  a  large  number  of  villi.  The  epithelium  of  the  cervix  presents 
great  variations  in  its  character  in  different  individuals.  Before  the  time  of 
puberty  the  entire  membrane  of  the  cervix  is  covered  with  ciliated  epithe- 
lium. After  puberty,  however,  the  epithelium  of  the  lower  portion  changes 
its  character,  and  there  are  cylindrical  cells  above,  with  squamous  cells  in 
the  inferior  portion.  The  latter  extend  upward  in  the  neck,  to  a  variable 
distance. 

The  blood-vessels  of  the  uterus  are  very  large  and  present  certain  impor- 
tant peculiarities  in  their  arrangement.  The  uterine  arteries  pass  between 
the  layers  of  the  broad  ligament,  to  the  neck,  and  then  ascend  by  the  sides 
of  the  uterus,  presenting  a  rich  plexus  of  vessels,  anastomosing  above  with 
branches  from  the  ovarian  arteries,  sending  branches  over  the  body  of  the 
uterus,  and  finally  penetrating  the  organ,  to  be  distributed  mainly  in  the 
middle  layer  of  muscular  fibres.  In  their  course  these  vessels  present  a  con- 
voluted arrangement  and  form  a  sort  of  mould  of  the  body  of  the  uterus. 
Eouget  has  called  this  the  erectile  tissue  of  the  internal  generative  organs. 
It  lacks,  however,  certain  of  the  characters  of  true,  erectile  tissue.  By 
placing  the  pelvis  in  a  bath  of  warm  water  and  injecting  what  he  called  the 


THE  FALLOPIAN  TUBES. 


775 


spongy  bodies  of  the  ovaries  and  uterus,  by  the  ovarian  veins,  he  produced  a 
distention  of  the  vessels  and  a  sort  of  erection,  the  uterus  executing  a  move- 
ment upward. 

In  the  muscular  walls  of  the  uterus,  are  large  veins,  the  walls  of  which 


Fio.  281.— Blood-vessels  of  the  uterus  and  ovaries ;  posterior  view  (Rouget). 

T,  T,  Fallopian  tubes  ;  O,  O,  ovaries  :  U,  uterus  ;  V,  vagina  ;  P,  pubis  ;  L,  anterior  round  ligament :  1, 
2,  muscular  fibres  of  the  vagina  ;  3,  4,  ligament  of  the  ovary  ;  5,  superior  round  ligament  ;  6,  ova- 
rian artery  ;  7,  ovarian  vein  ;  8,  uterine  artery  ;  9,  uterine  vein  ;  10,  11,  uterine  plexus  ;  12,  vaginal 
plexus. 

are  closely  adherent  to  the  uterine  tissue.  During  gestation  these  vessels 
become  enlarged,  forming  the  so-called  uterine  sinuses. 

Lymphatics  are  not  very  abundant  in  the  unimpregnated  uterus,  but  they 
become  largely  developed  during  gestation.  They  exist  in  a  superficial  and 
a  deep  layer,  the  deeper  vessels  being  connected  with  lymph-spaces  in  the 
muscular  walls  and  in  the  mucous  membrane. 

The  uterine  nerves  are  derived  from  the  inferior  hypogastric  and  the 
spermatic  plexuses,  and  the  third  and  fourth  sacral.  In  the  substance  of  the 
uterus  they  present  in  their  course  small  collections  of  ganglionic  cells,  and 
it  is  said  that  the  nerves  pass  finally  to  the  nucleoli  of  the  muscular  fibres 
(Frankenhaeuser). 

The  Fallopian  Tubes. — The  Fallopian  tubes,  or  oviducts,  lead  from  the 
ovaries  to  the  uterus.  They  are  shown  in  Fig.  275.  These  tubes  are  three 
to  four  inches  (7'6  to  10-1  centimetres)  long,  but  their  length  is  not  always 
equal  upon  the  two  sides.  They  lie  between  the  folds  of  the  broad  ligament, 
at  its  upper  border.  Opening  into  the  uterus  upon  either  side  at  the  cornua, 
they  present  a  small  orifice,  about  -£5  of  an  inch  (1  mm.)  in  diameter.  From 
the  cornua  they  take  a  somewhat  undulatory  course  outward,  gradually  in- 
creasing in  size,  so  that  they  are  rather  trumpet-shaped.  Near  the  ovary 


776 


GENERATION. 


they  turn  downward  and  backward.    The  extremity  next  the  ovary  is  marked 
by  ten  to  fifteen  fimbriae,  or  fringes,  which  have  given  this  the  name  of  the 


FIG.  382.— Section  through  the  right  Fallopian  tube  (Richard). 


fimbriated  extremity,  or  morsus  diaboli.  All  of  these  fringe-like  processes 
are  free  except  one  ;  and  this  one,  which  is  longer  than  the  others,  is  attached 
to  the  outer  angle  of  the  ovary  and  presents  a  little  gutter,  or  furrow,  extend- 
ing from  the  ovary  to  the  opening  of  the  tube.  At  this  extremity,  is  the 
abdominal  opening  of  the  tube,  which  is  two  or  three  times  larger  than  the 
uterine  opening.  Passing  from  the  uterus,  the  caliber  of  the  tube  gradually 
increases  as  the  tube  itself  enlarges,  and  there  is  an  abrupt  constriction  at 
the  abdominal  opening. 

Beneath  the  peritoneal  coat,  which  is  formed  by  the  layers  of  the  broad 
ligament,  is  a  layer  of  connective  tissue,  containing  a  rich  plexus  of  blood- 
vessels. This  constitutes  the  proper,  fibrous  coat  of  the  Fallopian  tubes. 

The  muscular  layer  is  composed  mainly  of  circular  fibres  of  the  non-stri- 
ated variety,  with  a  few  longitudinal  fibres  prolonged  over  the  tube  from  the 
external,  muscular  layer  of  the  uterus.  This  coat  is  quite  thick  and  sends 
bands  between  the  layers  of  the  broad  ligament,  to  the  ovary. 

The  mucous  membrane  of  the  tube  is  thrown  into  folds,  which  are  longi- 
tudinal and  transverse  near  the  uterus  and  are  more  complicated  at  the  dilated 
portion.  In  this  portion,  next  the  ovary,  embracing  about  the  outer  two- 
thirds,  the  folds  project  far  into  the  caliber  of  the  tube.  These  are  some- 
times simple,  but  more  frequently  they  present  secondary  folds,  often  meet- 
ing as  they  project  from  opposite  sides.  This  arrangement  gives  an  arbores- 
cent appearance  to  the  membrane  on  transverse  section  of  the  tube.  The 
mucous  membrane  is  covered  by  cylindrical  ciliated  epithelium,  the  move- 
ment of  the  cilia  being  from  the  ovary  toward  the  uterus.  The  membrane 
of  the  tubes  has  no  mucous  glands. 

It  is  not  necessary  to  give  a  minute  description  of  the  external  organs  of 
the  female.  Opening  by  the  vulva  externally,  and  terminating  at  the  neck 
of  the  uterus,  is  a  membranous  tube,  the  vagina.  This  lies  between  the  blad- 
der and  the  rectum.  It  has  a  curved  direction,  being  3£  to  3£  inches  (8  to  9 


//. 


•ismic  Zone;* 


proliger-us. 
Corona  radiata. 


terminal  Vesidt, 

wth  two  germinal  Spots. 


Cortina,  radiata 


ma  pdlucidc 


utoplasrfiic  Zone. 


tellirie  Space 


'•  Germinal   • 

( -with-  an  amoeboid 

'•germiiial  /'' 


Clear  Cuter  Zone. 


FIG.  2. 


FIG.  1. — Deutoplasm  -  forming  ovum  from  a  Graafian  follicle  of  a  woman  27  j'ears  old  (Nagel). 

FIG.  2. — Fresh  ovum  from  Graafian  follicle  of  a  woman  80  years  old ;   slightly  reduced  from 
the  original  figure  (Nagel). 


STEUCTURE  OF  THE  OVUM. 


777 


centimetres)  long  in  front,  and  3|  to  4  inches  (9  to  10  centimetres)  long  pos- 
teriorly (Sappey).  At  the  constricted  portion  of  the  outer  opening,  there  is 
a  muscle,  called  the  sphincter  vagina?,  and  the  tube  is  somewhat  narrowed 
at  its  upper  end,  where  it  embraces  the  cervix  uteri.  The  inner  surface  pre- 
sents a  mucous  membrane,  marked  by  transverse  rugse,-  with  papillae  and 
mucous  glands.  Its  surface  is  covered  with  flattened  epithelium.  The  vagina 
is  quite  extensible,  as  it  must  be  during  parturition,  to  allow  the  passage  of 
the  child.  It  pre- 
sents a  proper  coat 
of  dense,  fibrous  tis- 
sue, with  longitud- 
inal and  circular 
muscular  fibres  of 
the  non-striated  va- 
riety. Surrounding 
it,  is  a  rather  loose, 
so-called  erectile  tis- 
sue, which  is  most 
prominent  at  its 
lower  portion. 

The  parts  com- 
posing the  external 
organs  are  abund- 
antly supplied  with 
vessels  and  nerves. 

Tn  flip  plif  nria  wV>ir>V>  vein  of  the  clitoris  ;  I,  intermediary  plexus  ;  J,  vein  of  communication 

lb' w  J  with  the  obturator  vein  ;  K,  obturator  vein  ;  M,  labia  minora. 

corresponds    to  the 

penis  of  the  male,  and  on  either  side  of  the  vestibule,  there  is  a  true  erec- 
tile tissue. 

Structure  of  the  Ovum. — The  description  which  is  to  follow  is  based 
upon  recent  and  extended  researches  into  the  minute  anatomy  of  the 
healthy  human  ovum  (Nagel,  1888),  which  have  been  rendered  possible  by 
the  frequency  with  which,  within  the  past  few  years,  normal  ovaries  are 
removed  in  surgical  operations  : 

The  ovum  lies  in  the  Graafian  follicle,  embedded  in  the  mass  of  granu- 
lar cells  which  form  the  discus  proligerus.  Surrounding  the  ovum  are  cells 
similar  to  those  found  in  other  parts  of  the  membrana  granulosa,  and  two 
or  three  layers  of  columnar  cells,  the  latter  lying  next  the  zona  pellucida. 
These  columnar  cells  constitute  the  corona  radiata  (Bischoff).  The  ovum 
itself  presents  the  following  structures:  (1)  Zona  pellucida;  (2)  peri- 
vitelline  space ;  (3)  a  clear,  outer  zone  of  the  vitellus ;  (4)  protoplasmic 
zone  (formative  yelk) ;  (5)  deutoplasmic  zone  (nutritive  yelk) ;  (6)  ger- 
minal vesicle  (Purkinje) ;  germinal  spot  (Wagner).  The  extremely  thin 
membrane  within  the  zona  pellucida  and  immediately  surrounding  the 
vitellus,  described  under  the  name  of  vitelline  membrane  by  some  anato- 
mists, was  not  observed  by  Nagel  in  the  human  ovum. 


FIG.  283.— External  erectile  organs  of  the  female  CLiegeois). 
pubis  ;  B,  B,  ischium  ;  C,  clitoris  ;  D,  gland  of  the  clitoris  ;  E.  bulb  ;  F, 
constrictor  muscle  of  the  vulva  ;  G,  left  pillar  of  the  clitoris  ;  H,  dorsal 


778  GENEEATION. 

The  ovum  is  globular,  with  a  diameter  of  about  y^  of  an  inch  (165  to 
170  fji)  measured  from  the  outer  border  of  the  zona  pellucida. 

The  zona  pellucida  (zona  radiata,  or  vitelline  membrane)  is  y^Vo  to  j^Vo 
of  an  inch  (20  to  24  p.)  in  thickness.  It  is  a  strong  membrane  appearing 
in  the  form  of  a  clear  zone  in  the  mass  of  surrounding  cells.  It  is  marked 
by  striae,  which  are  thought  by  some  anatomists  to  indicate  the  presence  of 
small  pores  ;  but  the  large,  single  opening  called  a  micropyle,  which  is 
found  in  many  of  the  osseous  fishes  and  in  mollusks,  has  not  been  demon- 
strated in  the  human  ovum. 

Between  the  zona  pellucida  and  the  vitellus,  is  a  narrow  space,  about 
g-g-foT  of  an  inch  (1-3  /*)  in  diameter.  This  has  been  called  the  perivitelline 
space  (Nagel). 

The  vitellus  is  contained  in  the  zona  pellucida.  It  presents  a  clear,  outer 
zone  6o*6o  to  ^oVfr  °f  an  inch  (4  to  6  /x.)  in  diameter.  This  can  not  be  dis- 
tinguished from  the  protoplasmic  zone,  except  in  perfectly  fresh  ova.  It  is 
composed  of  clear  protoplasm  without  granules  and  represents  that  portion 
of  the  protoplasm  of  the  vitellus  which  is  not  at  any  time  converted  into 
deutoplasm  (Nagel).  Within  the  clear  zone,  is  the  protoplasmic  zone 
(formative  yelk).  This  presents  very  fine  granules,  and  the  zone  is  -^-gVo 
to  T?Vo  °f  an  incn  (10  to  21  p)  in  thickness.  Occupying  the  central  por- 
tion of  the  vitellus,  is  the  deutoplasm  (nutritive  yelk),  forming  a  mass  about 
j-J-^  of  an  inch  (82  to  87  /*)  in  diameter.  The  deutoplasm  presents  granules 
of  different  sizes  and  different  refractive  power.  Treated  with  eosin,  the 
protoplasm  becomes  rose-colored,  but  the  deutoplasm  is  unaffected.  As  the 
ovum  reaches  its  final  stage  of  development,  the  protoplasmic  zone,  as  far 
as  that  portion  which  forms  the  so-called  outer  zone,  is  gradually  changed 
into  deutoplasm.  In  Plate  II,  Fig.  1,  an  ovum  is  represented  in  which  this 
change  is  in  progress. 

The  germinal  vesicle  lies  always  in  the  protoplasmic  zone,  just  out- 
side of  the  deutoplasm.  As  the  mass  of  deutoplasm  extends,  the  germi- 
nal vesicle  is  pushed  toward  the  periphery  of  the  vitellus.  The  vesicle 
measures  about  joW  °^  an  inch  (25  to  27  p)  in  diameter. 
It  is  globular,  with  a  double  contour.  In  hardened  prepa- 
rations, it  presents  a  frame-work  of  fine  anastomosing 
fibres.  In  the  fully  developed  human  ovum,  no  amoeboid 
movements  have  as  yet  been  observed  in  the  germinal 

FIO.  yM.-prtawraiai    vesicle  (NaSe1)'     In  Plate  Il\  Fig'  2'  the  germinal  vesicle 
ovum  with  two  ger-    is  seen  lying  upon  and  not  within  the  deutoplasmic  zone. 

mtnal  vesicles  ana  i 


epttheii-    The  mature  ovum  presents  but  one  germinal  vesicle.     Two 

um  ;  from  the  ora-  .  A  ° 

ry  of  a  new-born    germinal  vesicles,  however,  are  sometimes  found  in  primor- 

child  (Nagel).  5  ' 

dial  ova  (see  Fig.  284). 

The  germinal  spot  (Wagner)  is  contained  in  the  germinal  vesicle.  Some 
vesicles  present  two  germinal  spots.  In  perfectly  fresh  ova,  the  germinal 
spots  have  been  observed  to  undergo  amoeboid  movements. 

Discharge  of  the  Ovum.  —  A  ripe  Graafian  follicle  measures  -§•  to  £  of  an 
inch  (10  to  12  mm.)  in  diameter,  and  presents  a  rounded  elevation,  contain- 


PASSAGE  OF  OVA  INTO  THE  FALLOPIAN  TUBES  779 

ing  a  plexus  of  blood-vessels,  upon  the  surface  of  the  ovary.  At  its  most 
prominent  portion,  is  an  ovoid  spot  in  which  the  membranes  are  entirely  free 
from  blood-vessels.  At  this  spot,  which  is  called  the  macula  folliculi,  the 
coverings  finally  give  way  and  the  contents  of  the  follicle  are  discharged. 
For  a  short  time  anterior  to  the  rupture  of  the  follicle,  important  changes 
have  been  going  on  in  its  structure.  In  the  first  place,  the  non-vascular  por- 
tion situated  at  the  very  surface  of  the  ovary  undergoes  fatty  degeneration, 
by  which  this  part  of  the  wall  gradually  becomes  weakened.  At  the  same 
time,  at  the  other  portions  of  the  follicle,  there  is  a  proliferation  of  cells 
which  project  into  the  interior,  and  an  extension,  into  the  interior,  of  blood- 
vessels in  the  form  of  loops.  These  changes,  with  an  increase  in  the  pressure 
of  liquid  and  the  fatty  degeneration  of  the  macula,  cause  the  follicle  to  burst ; 
and  with  the  liquid,  the  discus  proligerus  and  the  ovum  are  expelled.  The 
formation  of  a  cell-growth  in  the  interior  of  the  follicle  is  the  beginning  of 
the  corpus  luteum ;  and  this  occurs  some  time  before  the  discharge  of  the 
ovum  takes  place. 

The  time  at  which  the  follicle  ruptures,  particularly  with  reference  to  the 
menstrual  period,  is  not  definite ;  but  it  is  certain  that  while  sexual  excite- 
ment probably  hastens  the  discharge  of  an  ovum  by  producing  a  greater  or 
less  tendency  to  congestion  of  the  internal  organs,  ovulation  takes  place  in- 
dependently of  the  action  of  coition.  The  opportunities  for  determining 
this  fact  in  the  human  female  are  not  frequent ;  but  it  has  been  fully  dem- 
onstrated by  observations  upon  the  inferior  animals,  and  there  is  now  no 
doubt  with  regard  to  the  identity  of  the  phenomena  of  rut  and  of  menstru- 
ation. At  stated  periods  marked  by  the  phenomena  of  menstruation,  one 
Graafian  follicle — and  sometimes  more  than  one — becomes  distended  and 
usually  ruptures  and  discharges  its  contents  into  the  Fallopian  tubes.  This 
discharge  of  an  ovum  or  ova  may  occur  at  the  beginning,  at  the  end,  or  at 
any  time  during  the  continuance  of  the  menstrual  flow.  Upon  this  point  the 
observations  of  Coste  seem  entirely  conclusive.  In  a  woman  who  died  on  the 
first  day  of  menstruation,  he  found  a  recently  ruptured  follicle  ;  in  other  in- 
stances, at  a  more  advanced  period  and  toward  the  decline  of  the  menstrual 
flow,  he  found  evidences  that  the  rupture  had  occurred  later ;  in  the  case  of 
a  female  who  drowned  herself  four  or  five  days  after  the  cessation  of  the 
menses,  a  follicle  was  found  in  the  right  ovary,  so  distended  that  it  was  rupt- 
ured by  very  slight  pressure ;  and  other  instances  were  observed  in  which 
follicles  were  not  ruptured  during  the  menstrual  period. 

PASSAGE  OF  OVA  IXTO  THE  FALLOPIAN  TUBES. 

The  fact  that  the  ova  in  the  great  majority  of  instances  pass  into  the 
Fallopian  tubes  is  sufficiently  evident.  The  fact,  also,  that  ova  may  fall  into 
the  cavity  of  the  peritoneum  is  illustrated  by  the  occasional  occurrence  of 
extraiiterine  pregnancy,  a  rare  accident,  which  shows  that  in  all  probability 
the  failure  of  unimpregnated  ova  to  enter  the  tubes  is  exceptional.  As  regards 
the  mechanism  of  the  passage  of  the  ova  into  the  tubes,  however,  the  expla- 
nation is  difficult.  At  the  present  time  there  are  two  theories  with  regard 


780  GENERATION. 

to  this  process ;  one,  in  which  it  is  supposed  that  the  fimbriated  extremities 
of  the  Fallopian  tubes,  at  the  time  of  rupture  of  the  Graafian  follicles,  be- 
come adapted  to  the  surface  of  the  ovaries ;  and  the  other,  that  the  ova  are 
carried  to  the  openings  of  the  tubes  by  ciliary  currents.  Neither  of  these 
theories,  however,  is  susceptible  of  actual  demonstration ;  and  their  value  is  to 
be  judged  from  anatomical  facts.  It  is  not  difficult  to  understand,  taking 
into  account  the  situation  of  the  ovaries  and  the  relations  of  the  Fallopian 
tubes,  how  an  ovum  may  pass  into  the  tube,  without  invoking  the  aid  of 
muscular  action.  It  may  be  supposed,  for  example,  that  a  Graafian  follicle 
is  ruptured  when  the  fimbriated  extremity  of  the  tube  is  not  applied  to  the 
surface  of  the  ovary.  One  of  the  fimbriae,  longer  than  the  others,  is  at- 
tached to  the  outer  angle  of  the  ovary  and  presents  a  little  furrow,  or  gutter, 
leading  to  the  opening  of  the  tube.  This  furrow  is  lined  by  ciliated  epithe- 
lium, as  indeed,  is  the  mucous  membrane  of  all  of  the  fimbrias,  the  move- 
ments of  which  produce  a  current  in  the  direction  of  the  opening,  which 
would  apparently  be  sufficient  to  carry  the  ovum  into  the  tube.  At  the  same 
time  there  probably  is  a  constant  flow  of  liquid  over  the  ovarian  surface, 
directed  by  the  ciliary  current  toward  the  tube ;  and  when  the  liquid  of  the 
ruptured  follicle  is  discharged  this,  with  the  ovum,  takes  the  same  course 
(Becker).  This  probably  is  the  mechanism  of  the  passage  of  the  ova  into 
the  Fallopian  tubes ;  and  it  is  possible  that  the  fimbriated  extremity  may  be 
drawn  toward  the  ovarian  surface,  although  it  is  difficult  to  understand  how  it 
can  be  closely  applied  to  the  ovary  and  exert  any  considerable  pressure  upon 
the  distended  follicle.  It  is  proper  to  note,  also,  that  the  conditions  depend- 
ent upon  the  currents  of  liquid  directed  by  the  movements  of  cilia  are  con- 
stant and  could  influence  the  passage  of  an  ovum  at  whatever  time  it  might 
be  discharged,  while  a  muscular  action  would  be  more  or  less  intermittent. 

Puberty  and  Menstruation. — At  a  certain  period  of  life,  usually  between 
the  ages  of  thirteen  and  fifteen,  the  human  female  undergoes  a  remarkable 
change  and  arrives  at  what  is  termed  the  age  of  puberty.  At  this  time  there 
is  a  marked  increase  in  the  general  development  of  the  body  ;  the  limbs  be- 
come fuller  and  more  rounded  ;  a  growth  of  hair  makes  its  appearance  upon 
the  mons  Veneris ;  the  mammary  glands  increase  in  size  and  take  on  a  new 
stage  of  development ;  Graafian  follicles  enlarge,  and  one  or  more  approach 
the  condition  favorable  to  rupture  and  the  discharge  of  ova.  The  female 
becomes  capable  of  impregnation,  and  continues  so,  in  the  absence  of  patho- 
logical conditions,  until  the  cessation  of  the  menses. 

The  age  of  puberty  is  earlier  in  warm  than  in  cold  climates ;  and  many 
instances  are  on  record  in  which  the  menses  have  appeared  exceptionally 
much  before  the  usual  period.  Generally  at  the  age  of  forty  or  forty-five, 
the  menstrual  flow  becomes  irregular,  occasionally  losing  its  sanguineous 
character,  and  it  usually  ceases  at  about  the  age  of  fifty  years.  It  is  said  that 
sometimes  the  menses  return,  with  a  second  period  of  fecundity,  though  this 
is  rare.  According  to  most  writers,  while  climate  has  a  certain  influence 
over  the  time  of  cessation  as  Avell  as  the  first  appearance  of  the  menses,  this 
is  not  very  marked.  When  the  menses  appear  early  in  life,  they  usually 


PUBERTY   AND  MENSTRUATION.  781 

cease  at  a  correspondingly  early  period ;  but  this  is  by  no  means  constant. 
There  are,  also,  many  exceptions  to  the  ordinary  limits  to  the  period  of  fe- 
cundity. 

Although  there  is  a  periodical  condition  of  heat  in  the  lower  animals, 
connected  with  ovulation,  a  sanguineous  discharge  from  the  genital  organs 
is  not  often  observed.  It  is  only  in  monkeys  that  there  is  a  counterpart  of 
what  occurs  in  the  human  female  ;  and  observations  upon  these  animals  have 
shown  that  they  are  subject  to  a  monthly  discharge  of  blood,  at  this  time 
giving  evidence  of  unusual  salacity. 

In  the  human  female,  near  the  time  of  puberty,  there  is  sometimes  a  peri- 
odical, sero-mucous  discharge  from  the  genital  organs,  preceding,  for  a  few 
months,  the  regular  establishment  of  the  menstrual  flow.  Sometimes,  also, 
after  the  first  discharge  of  blood,  the  female  passes  several  months  without 
another  period,  when  the  second  flow  takes  place  and  the  menses  then  be- 
come regular.  In  a  condition  of  health  the  periods  recur  every  month, 
until  they  cease,  at  what  is  termed  the  change  of  life.  In  the  majority  of 
cases  the  flow  recurs  on  the  twenty-seventh  or  the  twenty-eighth  day ;  but 
sometimes  the  interval  is  thirty  days.  As  a  rule,  also,  utero-gestation,  lacta- 
tion, and  severe  diseases,  acute  and  chronic,  suspend  the  periods ;  but  this 
has  exceptions,  as  some  females  menstruate  regularly  during  pregnancy,  and 
it  is  not  very  uncommon  for  the  menses  to  appear  during  lactation. 

Eemoval  of  the  ovaries,  especially  when  this  occurs  before  the  age  of 
puberty,  usually  is  followed  by  arrest  of  the  menses.  It  is  a  well  known  fact 
that  animals  do  not  present  the  phenomena  of  heat,  after  extirpation  of  the 
ovaries.  Eaciborski  has  quoted  cases  of  this  operation  in  the  human  subject, 
in  which  the  menses  were  arrested ;  but  this  rule  does  not  appear  to  be  abso- 
lute, as  Storer  has  reported  at  least  one  case,  in  which  menstruation  contin- 
ued with  regularity  for  more  than  a  year  after  removal  of  both  ovaries. 
Thomas,  in  three  cases  of  removal  of  both  ovaries  from  menstruating 
women,  which  he  followed  for  five  and  a  half  months  to  two  years  and 
eleven  months  after  the  operation,  noted  no  return  of  menstruation ;  but  in 
one  case,  nearly  six  months  after  the  operation,  the  patient  had  "  a  bloody 
discharge  from  the  vagina  and  all  the  symptoms  accompanying  the  men- 
strual function."  Other  cases  of  this  kind  are  on  record. 

When  a  cow  gives  birth  to  twins,  one  a  male  and  the  other  apparently  a 
female,  the  latter  is  called  a  free-martin  and  generally  has  no  ovaries.  John 
Hunter,  in  his  paper  on  the  free-martin,  gave  a  full  description  of  this 
anomalous  animal  and  stated  that  it  does  not  breed  or  show  any  inclination 
for  the  bull.  In  an  examination  of  a  free-martin,  raised  and  killed  by  the 
late  Prof.  James  R.  Wood,  in  1868,  the  uterus  was  found  rudimentary  and 
there  were  no  ovaries  (Flint). 

A  menstrual  period  presents  three  stages :  first,  invasion ;  second,  a  san- 
guineous discharge ;  third,  cessation. 

The  stage  of  invasion  is  variable  in  different  females.  There  is  usually, 
anterior  to  the  establishment  of  the  flow,  more  or  less  of  a  feeling  of  general 
malaise,  a  sense  of  fullness  and  weight  in  the  pelvic  organs,  accompanied 
51 


782  GENERATION. 

with  a  greater  or  less  increase  in  the  quantity  of  vaginal  mucus,  which  be- 
comes brownish  or  rusty  in  color  and  has  a  peculiar  odor.  At  this  time, 
also,  the  breasts  become  slightly  enlarged.  This  stage  may  continue  for  one 
or  two  days,  although  in  many  instances  the  first  evidence  of  the  access  of  a 
period  is  a  discharge  of  blood. 

When  the  symptoms  above  indicated  occur,  the  general  sense  of  uneasi- 
ness usually  is  relieved  by  the  discharge  of  blood.  During  this,  the  second 
stage,  blood  flows  from  the  vagina  in  variable  quantity,  and  the  discharge 
continues  for  three  to  five  days.  With  regard  to  the  duration  of  the  flow 
there  are  great  variations  in  different  individuals.  Some  women  present 
a  flow  of  blood  for  only  one  or  two  days ;  while  in  others  the  flow  continues 
for  five  to  eight  days,  within  the  limits  of  health.  A  fair  average,  perhaps,  is 
four  days. 

It  is  difficult  to  arrive  at  even  an  approximation  of  the  total  quan- 
tity of  the  menstrual  flow.  Burdach  estimated  it  at  five  to  six  ounces  (about 
150  to  175  grammes).  According  to  Longet  this  estimate  is  rather  low,  the 
quantity  ordinarily  ranging  between  ten  and  twelve  ounces  (300  and  350 
grammes),  occasionally  amounting  to  seventeen  ounces  (500  grammes),  or 
even  more.  It  is  well  known  that  the  quantity  is  very  variable,  as  is  the 
duration  of  the  flow ;  and  the  difficulties  in  the  way  of  estimating  the  total 
discharge  are  evident. 

The  characters  of  the  menstrual  flow  are  sufficiently  simple.  Supposing 
the  discharge  to  continue  for  four  days,  on  the  first  day  the  quantity  is  com- 
paratively small ;  on  the  second  and  third  the  flow  is  at  its  height ;  and  the 
quantity  is  diminished  on  the  fourth  day.  During  this,  the  second  stage,  the 
fluid  has  the  appearance  of  pure,  arterial  blood,  not  coagulated,  and  mixed, 
as  has  been  shown  by  microscopical  examination,  with  epithelium  from  the 
vagina,  cylindrical  cells  from  the  uterus,  leucocytes  and  a  certain  quantity 
of  sero-mucous  secretion.  Chemical  examinations  of  the  fluid  have  not 
shown  any  marked  peculiarities,  except  that  the  quantity  of  fibrin  is  either 
not  estimated  or  is  given  as  much  less  than  in  ordinary  blood. 

The  mechanism  of  the  haemorrhage  is  probably  the  same  as  in  epistaxis. 
There  is  a  rupture  of  small  blood-vessels,  probably  capillaries,  and  blood  is 
thus  exuded  from  the  entire  surface  of  the  membrane  lining  the  uterus  and 
sometimes  from  the  membrane  of  the  Fallopian  tubes.  The  blood  is  then 
discharged  into  the  vagina  and  is  kept  fluid  by  the  vaginal  mucus.  The 
mucus  of  the  body  of  the  uterus  is  viscid  and  alkaline ;  the  mucus  secreted 
at  the  neck  is  gelatinous,  viscid  and  tenacious,  and  is  also  alkaline ;  the  vagi- 
nal mucus  is  decidedly  acid,  creamy  and  not  viscid,  containing  epithelium 
and  leucocytes. 

The  third  stage,  that  of  cessation  of  the  menses,  is  very  simple.  During 
the  latter  part  of  the  second  stage  the  flow  of  blood  gradually  diminishes. 
The  discharge  becomes  rusty,  then  lighter  in  color,  and  in  the  course  of 
about  twenty-four  hours,  it  assumes  the  characters  observed  in  the  intermen- 
strual  period. 

When  the  menstrual  flow  has  become  fully  established  there  is  no  very 


CORPUS  LUTEUM. 


783 


marked  general  disturbance,  except  a  sense  of  lassitude,  Which  may  become 
exaggerated  if  the  discharge  be  unusually  abundant.  It  has  been  noted, 
however,  by  Rabuteau,  that  during  the  menstrual  period  the  production  of 
urea  is  diminished  more  than  twenty  per  cent.,  that  the  pulse  becomes  slower 
and  that  the  temperature  falls  at  least  one  degree  Fahr.  (about  half  a  de- 
gree C.). 

If  the  mucous  membrane  of  the  uterus  be  examined  during  the  menstrual 
flow,  it  is  found  smeared  with  blood,  which  sometimes  extends  into  the  Fallo- 
pian tubes.  It  is  then  much  thicker  and  softer  than  during  the  intermen- 
strual  period.  Instead  of  measuring  about  ^  of  an  inch  (1-8  mm.)  in  thick- 
ness, as  it  does  under  ordinary  conditions,  its  thickness  is  ^  to  ^  of  an  inch 
(4-2  to  6-4  mm.).  It  becomes  more  loosely  attached  to  the  subjacent  parts, 
is  somewhat  rugous,  and  the  glands  are  very  much  enlarged.  At  the  same 
time  there  are  developed,  in  the  substance  of  the  membrane,  large  numbers 
of  spherical  and  fusiform  cells.  This  condition  probably  precedes  the  dis- 
charge of  blood  by  several  days,  during  which  time  the  membrane  is  gradu- 
ally preparing  for  the  reception  of  the  ovum.  There  is  also  a  fatty  degenera- 
tion of  the  different  elements  entering  into  the  structure  of  the  mucous 
membrane,  including  the  blood-vessels,  this  change  being  most  marked  at 
the  surface ;  and  it  is  on  account  of  the  weakened  condition  of  the  vascular 
walls  that  the  haemorrhage  takes  place.  A  short 
time  after  the  flow  has  ceased,  the  mucous  mem- 
brane returns  to  its  ordinary  condition.  There  is  a 
considerable  desquamation  of  epithelium  from  the 
uterus,  with  the  flow  of  blood,  during  the  menstrual 
period.  Sometimes,  in  normal  menstruation,  the 
epithelium  thrown  off  is  in  the  form  of  patches. 

Changes  in  the  Graafian  Follicles  after  their 
Rupture  (Corpus  Luteum). — After  the  discharge 
of  an  ovum,  its  Graafian  follicle  undergoes  certain 
retrograde  changes,  involving  the  formation  of  what 
is  called  the  corpus  luteum.  Even  when  the  dis- 
charged ovum  has  not  been  fecundated,  the  corpus 
luteum  persists  for  several  weeks,  so  that,  ovulation 
occurring  every  month,  several  of  these  bodies,  in 
various  stages  of  retrogression,  may  sometimes  be 
seen  in  the  ovaries. 

For  a  certain  time  anterior  to  the  discharge  of 

the  ovum,  there  is  a  cell-proliferation  from  the  2,  c^iu^um  at  the  fifth 
proper  coat  of  the  Graafian  follicle,  and  probably 
from  the  membrana  granulosa,  with  a  projection  of 
looped  blood-vessels  into  the  interior  of  the  follicle. 
This  is  the  first  formation  of  the  corpus  luteum. 
At  the  time  of  rupture  of  the  follicle,  the  ovum,  with  a  great  part  of  the 
membrana  granulosa,  is  discharged.  Usually,  at  the  time  of  rupture  of  the 
follicle,  there  is  a  discharge  of  blood  into  its  interior ;  but  this  is  not  invaria- 


Fio.  285.—  Sections  of  two  cor- 
pora lutea  ;  natural  size 
(Kcilliker). 

1,  corpus  luteum  eight  days  af- 
ter conception  :  a,  external 
coat  of  the  ovary  ;  b,  stroma 
of  the  ovary  ;  c,  convoluted 
wall  of  the  Graafian  follicle; 


voluted  wall  of  the  Graafian 
follicle  ;  e,  decolorized  clot ; 
/,  fibrous  envelope  of  the 
corpus  luteum. 


784:  GENERATION. 

ble,  although  there  is  always  a  gelatinous  exudation  more  or  less  colored 
with  blood.  At  the  same  time  the  follicular  wall  undergoes  hypertrophy, 
and  it  becomes  convoluted,  or  folded,  and  highly  vascular.  This  convoluted 
wall,  formed  by  the  proper  coat  of  the  follicle,  is  surrounded  by  the  fibrous 
tunic,  and  its  thickening  is  most  marked  at  the  deepest  portion  of  the  follicle. 
At  the  end  of  about  three  weeks,  the  body — which  is  now  called  the  corpus 
luteum,  on  account  of  its  yellowish  or  reddish-yellow  color — has  arrived  at 
its  maximum  of  development  and  measures  about  half  an  inch  (12'7  mm.)  in 
depth,  by  about  three-quarters  of  an  inch  (19'1  mm.)  in  length,  its  form  being 
ovoid.  The  convoluted  wall  then  contains  a  layer  of  large,  pale,  finely  granu- 
lar cells,  which  are  internal  and  are  supposed  to  be  the  remains  of  the  epithe- 
lium of  the  follicle.  The  great  mass  of  this  wall,  however,  is  composed  of 
large,  nucleated  cells,  containing  fatty  globules  and  granules  of  reddish  or 
yellowish  pigmentary  matter.  The  thickness  of  the  wall  is  about  one-eighth 
of  an  inch  (3-2  mm.)  at  its  deepest  portion. 

After  about  the  third  week  the  corpus  luteum  begins  to  contract;  its 
central  portion  and  the  convoluted  wall  become  paler ;  and  at  the  end  of 
seven  or  eight  weeks,  a  small  cicatrix  marks  the  point  of  rupture  of  the 
follicle. 

The  above  are  the  changes  which  occur  in  the  Graafian  follicles  after 
their  rupture  and  the  discharge  of  ova,  when  the  ova  have  not  been  fecun- 
dated ;  and  the  bodies  thus  produced  are  called  false  corpora  lutea,  as  distin- 
guished from  corpora  lutea  formed  after  conception,  which  latter  are  called 
true  corpora  lutea. 

Corpus  Luteum  of  Pregnancy. — When  a  discharged  ovum  has  been  fecun- 
dated, the  corpus  luteum  passes  through  its  various  stages  of  development 
and  retrogression  much  more  slowly  than  the  ordinary  corpus  luteum  of 
menstruation.  The  retrogression  begins  toward  the  end  of  the  third  month. 
"  During  the  fourth  month,  the  corpus  luteum  diminishes  by  nearly  a  third, 
and  toward  the  end  of  the  fifth,  it  ordinarily  is  reduced  one-half.  It  still 
forms,  however,  during  the  first  days  after  parturition,  and  in  the  greatest  num- 
ber of  cases,  a  tubercle  which  has  a  diameter  of  not  less  than  f  to  ^  of  an  inch 
(7'3  to  8'5  mm.).  The  tubercle  afterward  diminishes  quite  rapidly;  but  it 
is  nearly  a  month  before  it  is  reduced  to  the  condition  of  a  little,  hardened 
nucleus,  which  persists  more  or  less  as  the  last  vestige  of  a  process  so  slow  in 
arriving  at  its  final  term.  Nevertheless,  there  is  nothing  absolute  in  the 
retrograde  progress  of  this  phenomenon.  I  have  seen  women,  dead  at  the 
sixth  and  even  the  eighth  month  of  pregnancy,  present  corpora  lutea  as 
voluminous  as  others  at  the  fourth  month"  (Coste,  1849).  The  differences 
between  the  corpora  lutea  of  pregnancy  and  of  menstruation  were  accurately 
described  by  Dalton,  in  1851  and  1877. 

MALE  ORGANS  OF  GENERATION. 

The  chief  physiological  interest  attached  to  the  anatomy  of  the  male  or- 
gans of  generation  relates  to  the  testicles,  which  are  the  organs  in  which  the 
male  element  of  generation  is  developed.  As  regards  the  penis,  it  will  be 


THE  TESTICLES.  785 

necessary  to  do  little  more  than  describe  the  mechanism  of  erection  and  of 
the  ejaculation  of  semen. 

The  Testicles. — The  testicles  are  two  symmetrical  organs,  situated,  during 
a  certain  period  of  intrauterine  life,  in  the  abdominal  cavity,  but  finally  de- 
scending into  the  scrotum.  Immediately  beneath  the  skin  of  the  scrotum,  is 
a  loose,  reddish,  contractile  tissue,  called  the  dartos,  which  forms  two  distinct 
sacs,  one  enveloping  each  testicle,  the  inner  portion  of  these  sacs  fusing  in 
the  median  line,  to  form  a  septum.  Within  these  two  sacs  the  coverings  of 
each  testicle  are  distinct.  These  organs  are  suspended  in  the  scrotum,  by  the 
spermatic  cords,  the  left  usually  hanging  a  little  lower  than  the  right.  The 
coverings  for  each  testicle,  in  addition  to  those  just  mentioned,  are  the  inter- 
columnar  fascia,  the  cremaster  muscle,  the  iuf uudibuliform  fascia,  the  tunica 
vaginalis  and  the  proper,  fibrous  coat. 

The  tunica  vaginalis  is  a  shut  sac  of  serous  membrane,  covering  the  tes- 
ticle and  epididymis  and  reflected  from  the  posterior  border  of  the  testicle  to 
the  wall  of  the  scrotum,  lining  the  cavity  occupied  by  the  testicle  on  either 
side  and  also  extending  over  the  spermatic  cord.  This  tunic  is  really  a 
process  of  peritoneum,  which  has  become  shut  off  from  the  general  lining  of 
the  abdominal  cavity.  The  spermatic  cord  is  composed  of  the  vas  deferens, 
blood-vessels,  lymphatics  and  nerves,  with  the  coverings  already  described 
which  expand  and  surround  the  testicle. 

Beneath  the  tunica  vaginalis  are  the  testicles,  with  their  proper,  fibrous 
coat.  These  organs  are  ovoid,  and  flattened  laterally  and  posteriorly.  "  They 
are  an  inch  and  a  half  to  two  inches  (38-1  to  50-8  mm.)  long,  about  an  inch 
and  a  quarter  (3T8  mm.)  from  the  anterior  to  the  posterior  border,  and 
nearly  an  inch  (25 -4  mm.)  from  side  to  side.  The  weight  of  each  varies  from 
three-quarters  of  an  ounce  to  an  ounce  (21-2  to  28'3  grammes),  and  the  left 
is  often  a  little  the  larger  of  the  two  "  (Quain).  The  proper,  fibrous  coat 
is  everywhere  covered  by  the  closely  adherent  tunica  vaginalis,  except  at  the 
posterior  border,  where  the  vessels  enter  and  the  duct  passes  out.  At  the 
outer  edge  of  this  border,  is  the  epididymis,  formed  of  convoluted  tubes,  pre- 
senting a  superior  enlargement,  called  the  globus  major,  a  long  mass  running 
the  length  of  the  testicle,  called  the  body,  and  a  smaller,  inferior  enlarge- 
ment, called  the  globus  minor.  This  too  is  covered  with  the  tunica  vaginalis. 
Between  the  membrane  covering  the  testicle  and  epididymis  and  the  layer 
lining  the  scrotal  cavity,  is  a  small  quantity  of  serum,  just  enough  to  moisten 
the  serous  surfaces.  At  the  superior  portion  of  the  testicle  are  one  or  more 
small,  ovoid  bodies,  called  the  hydatids  of  Morgagni,  each  attached  to  the 
testicle,  by  short,  constricted  processes.  These  have  no  physiological  im- 
portance and  are  supposed  to  be  the  remains  of  fcetal  structures. 

The  proper,  fibrous  coat  of  the  testicle  is  called  the  tunica  albuginea.  It 
is  white,  dense,  inelastic,  measures  about  ^  of  an  inch  (1  mm.)  in  thickness, 
and  is  simply  for  the  protection  of  the  contained  structures.  Sections  of  the 
testicle,  made  in  various  directions,  show  an  incomplete,  vertical  process  of 
the  tunica  albuginea,  called  the  corpus  Highmorianum  or  the  mediastinum 
testis.  This  is  wedge-shaped,  about  £  of  an  inch  (4'2  mm.)  wide  at  its  su- 


786 


GENERATION. 


perior  and  thickest  portion,  is  pierced  by  a  number  of  openings,  and  lodges 
blood-vessels  and  seminiferous  tubes.  From  the  mediastinum,  delicate,  radi- 
ating processes  of  connective  tissue  pass  to  the  inner  surface  of  the  tunica 
albuginea,  dividing  the  substance  of  the  testicle  into  imperfect  lobules,  which 
lodge  the  seminiferous  tubes.  The  number  of  these  lobules  has  been  esti- 
mated at  one  hundred  and  fifty  to  two  hundred.  Their  shape  is  pyramidal, 
the  larger  extremities  presenting  toward  the  surface,  with  the  pointed  ex- 
tremities situated  at  the  mediastinum. 

Lining  the  tunica  albuginea  and  following  the  mediastinum  and  the 
processes  which  penetrate  the  testicle,  is  a  tunic,  composed  of  blood-ves- 
sels and  delicate,  connective  tissue,  called  the  tunica  vasculosa,  or  pia  mater 
testis. 

Lodged  in  the  cavities  formed  by  the  trabeculae  of  connective  tissue,  are 
the  seminiferous  tubes,  in  which  the  male  elements  of  generation  are  devel- 
oped. These  tubes  exist  to  the  number  of  about  eight  hundred  and  forty  in 

each  testicle  and  constitute  almost 
the  entire  substance  of  the  lobules. 
The  larger  lobules  contain  five  or  six 
tubes,  the  lobules  of  median  size, 
three  or  four,  and  the  smallest  en- 
close sometimes  but  a  single  tube. 
Each  tube  presents  a  convoluted 
mass,  which  can  be  disentangled  un- 
der water,  particularly  if  the  testicle 
be  macerated  for  several  months  in 
water  with  a  little  nitric  acid.  The 
entire  length  of  the  tube  when  thus 
unravelled  is  about  thirty  inches  (7'6 
decimetres),  and  its  diameter  is  -^-^ 
to  -j^-y  of  an  inch  (125  to  166  ju.).  It 
begins  by  two  to  seven  short,  blind 
extremities  and  sometimes  by  anas- 
tomosing loops.  The  caecal  diverti- 
cula  are  usually  found  in  the  exter- 
nal half  of  the  tube,  and  their  length 
is  -fa  to  £  of  an  inch  (2'1  to  3-2  mm.). 
The  anastomoses  are  sometimes  be- 
tween the  tubes  of  different  lobules, 
sometimes  between  tubes  in  the  same 
lobule  and  sometimes  between  dif- 
ferent points  in  the  same  tube.  As 
the  tubes  P^8  towar(l  the  posterior 
portion  of  the  testicle,  thsy  unite  into 
about  twenty  straight  canals,  called  the  vasa  recta,  about  -fa  of  an  inch  (0-33 
mm.)  in  diameter,  which  penetrate  the  mediastinum  testis.  In  the  mediasti- 
num the  tubes  form  a  close  net- work,  called  the  rete  testis ;  and  at  the  upper 


FIG.  286.— Testicle  and  epididymis  of  the  human  sub- 
ject (Arnold). 

a,  testicle ;  b.  6,  ft,  ft,  lobules  of  the  testicle  ;  c,  c,  vasa 
recta  ;  d,  d,  rete  testis ;  e,  e.  vasa  efferentia ; 
/i  /•  />  cones  of  the  globus  major  of  the  epididy- 
mis :  gr,  fir,  epididymis  ;  7i,  h,  vas  deferens  ;  i,  vas 
aberrans  ;  m,  m,  branches  of  the  spermatic  ar- 
tery, to  the  testicle  and  epididymis;  n,  n,  n,  ram- 
ification of  the  artery  upon  the  testicle  ;  o,  def- 
',  anastomosis  of  the  deferential 
ic  artery. 


VAS  DEFERENS.  787 

portion  of  the  posterior  border  they  pass  out  of  the  testicle,  by  twelve  to  fif- 
teen openings,  and  are  here  called  the  vasa  efferentia. 

Having  passed  out  of  the  testicle,  the  vasa  efferentia  form  a  series  of 
small,  conical  masses,  which  together  constitute  the  globus  major,  or  head  of 
the  epididymis.  Each  of  these  tubes  when  unravelled  is  six  to  eight  inches 
(15  to  20  centimetres)  long,  gradually  increasing  in  diameter,  until  they  all 
unite  into  a  single,  convoluted  tube,  which  forms  the  body  and  the  globus 
minor  of  the  epididymis.  This  single  tube  of  the  epididymis,  when  unrav- 
elled, is  about  twenty  feet  (6  metres)  in  length. 

The  walls  of  the  seminiferous  tubes  in  the  testicle  itself  are  composed  of 
connective  tissue  and  of  peculiar  structures  which  will  be  fully  described  in 
connection  with  the  processes  of  development  of  the  spermatozoids.  In  the 
rete  testis  it  is  uncertain  whether  the  tubes  have  a  special  fibrous  coat  or 
are  simple  channels  in  the  fibrous  structure.  They  are  here  lined  with 
pavement-epithelium.  In  the  vasa  efferentia  and  the  epididymis,  there  is  a 
fibrous  membrane,  with  longitudinal  and  circular  fibres  of  non-striated  mus- 
cular tissue  and  a  lining  of  ciliated  epithelium.  The  movements  of  the  cilia 
are  toward  the  vas  deferens.  In  the  lower  portion  of  the  epididymis  the  cilia 
are  absent.  The  tubular  structures  of  the  testicle,  the  epididymis  and  the 
beginning  of  the  vas  deferens  are  shown  in  Fig.  286. 

At  the  lower  portion  of  the  epididymis,  communicating  with  the  canal, 
there  usually  is  found  a  small  mass,  formed  of  a  convoluted  tube  of  variable 
length,  called  the  vas  aberrans  of  Haller  (/,  Fig.  286).  This  is  sometimes 
wanting. 

Vas  Deferens. — The  excretory  duct  of  the  testicle  extends  from  the  epi- 
didymis to  the  prostatic  portion  of  the  urethra  and  is  a  continuation  of  the 
single  tube  which  forms  the  body  and  globus  minor  of  the  epididymis.  It 
is  somewhat  tortuous  near  its  origin,  and  it  becomes  larger  at  the  base  of  the 
bladder,  just  before  it  is  joined  by  the  duct  of  the  seminal  vesicle.  Near  its 
point  of  junction  with  this  duct  it  becomes  narrower.  Its  entire  length  is 
nearly  two  feet  (about  6  decimetres). 

The  course  of  the  vas  deferens  is  in  the  spermatic  cord,  to  the  external 
abdominal  ring,  through  the  inguinal  canal,  to  the  internal  ring,  where  it 
leaves  the  blood-vessels,  passes  beneath  the  peritoneum,  to  the  side  of  the 
bladder,  then  along  the  base  of  the  bladder,  by  the  inner  side  of  the  seminal 
vesicle,  finally  joining  the  duct  of  the  seminal  vesicle,  the  common  tube 
forming  the  ejaculatory  duct,  which  opens  into  the  prostatic  portion  of  the 
urethra, 

The  walls  of  the  vas  deferens  are  thick,  abundantly  supplied  with  vessels 
and  nerves,  and  provided  with  an  external,  fibrous,  a  middle,  muscular,  and 
an  internal,  mucous  coat.  The  greater  part  of  that  portion  of  the  tube 
which  is  connected  with  the  bladder  is  dilated  and  sacculated.  The  fibrous 
coat  is  composed  of  strong,  connective  tissue.  The  muscular  coat  presents 
three  layers ;  an  external,  rather  thick  layer  of  longitudinal  fibres,  a  thin, 
middle  layer  of  circular  fibres,  and  a  thin,  internal  layer  of  longitudinal 
fibres,  all  of  the  non-striated  variety.  By  the  action  of  these  fibres  the  ves- 


788 


GENERATION. 


sel  may  be  made  to  undergo  energetic,  peristaltic  movements,  and  this  has 
followed  stimulation  of  that  portion  of  the  spinal  cord  corresponding  to  the 
fourth  lumbar  vertebra,  which  is  described  by  Budge  as  the  genito-spinal 
centre. 

The  mucous  membrane  of  the  vas  deferens  is  pale,  thrown  into  longitu- 
dinal folds  in  the  greatest  part  of  the  canal,  and  presents  a  number  of  addi- 

tional rugae  in  the  sacculated  portion, 
these  rugae  enclosing  little,  irregularly 
polygonal  spaces.  The  membrane  is 
covered  with  columnar  epithelium, 
which  is  not  ciliated.  In  the  sacculated 
portion  are  large  numbers  of  mucous 
glands. 

Attached  to  the  vas  deferens,  near 
the  head  of  the  epididymis,  is  a  little 
mass  of  convoluted  and  sacculated  tubes, 
called  the  organ  of  Giraldes,  or  the  cor- 
pus innominatnm.  The  body  is  fa  to  £ 
of  an  inch  (4-2  to  8'5  mm.)  long  and  -fa 
of  an  inch  (2'1  mm.)  broad.  Its  tubes 
are  lined  with  cells  of  pavement-epithe- 
lium, which  often  are  filled  with  fatty 
granules.  Generally  the  tubes  present 

-,     -,  -,.     -,  ...        •, 

only  blind  extremities,  but  some  of  them 
occasionally  communicate  with  the  tubes 
of  the  epididymis.  This  part  has  no 
physiological  importance.  It  was  re- 

garded by  Giraldes  as  the  remnant  of  the  Wolffian  body,  analogous  to  the 
parovarium. 

Vesiculm  Seminales.  —  Attached  to  the  base  of  the  bladder  and  situated 
externally  to  the  vasa  deferentia,  are  the  two  vesiculae  seminales.  These 
bodies  are  each  composed  of  a  coiled  and  sacculated  tube,  four  to  six  inches 
(10  to  15  centimetres)  in  length  when  unravelled,  and  somewhat  convoluted, 
in  the  natural  state,  into  an  ovoid  mass  which  is  firmly  bound  to  the  vesical 
wall.  The  structure  of  the  seminal  vesicles  is  not  very  unlike  that  of  the 
sacculated  portion  >of  the  vasa  deferentia.  They  have  an  external,  fibrous 
coat,  a  middle  coat  of  muscular  fibres,  and  a  mucous  lining.  Muscular  fibres 
pass  over  these  vesicles  from  the  bladder,  both  in  a  longitudinal  and  in  a  cir- 
cular direction,  and  serve  as  compressors,  by  the  action  of  which  their  con- 
tents may  be  discharged.  The  mucous  coat  is  pale,  finely  reticulated,  and 
covered  with  cells  of  polygonal  epithelium,  which  are  nucleated  and  contain 
brownish  granules.  The  vesiculae  seminales  undoubtedly  serve,  in  part  at 
least,  as  receptacles  for  the  seminal  fluid,  as  their  contents  often  present  a 
greater  or  less  number  of  spermatozoids.  Although  the  membrane  of  the 
vesicles  seems  to  produce  an  independent  secretion,  the  presence  of  mucous 
glands  has  not  been  demonstrated. 


:FiG.  287.—  Vas  deferens,  vesiculce  xeminales  and 

ry  ducts 


MALE  ELEMENTS  OF  GENERATION.  789 

The  ejaculatory  ducts  are  formed  by  the  union  of  the  vasa  deferentia  with 
the  ducts  of  the  vesicula3  seminales  on  either  side,  and  they  open  into  the 
prostatic  portion  of  the  urethra.  Except  that  their  coats  are  much  thinner, 
they  have  essentially  the  same  structure  as  the  vasa  deferentia. 

Prostate. — Surrounding  the  vesical  extremity  of  the  urethra,  including 
what  is  known  as  its  prostatic  portion,  is  the  prostate  gland,  or  body.  This 
organ,  except  as  it  secretes  a  fluid  which  forms  a  part  of  the  ejaculated  semen, 
has  chiefly  a  surgical  interest,  so  that  it  is  unnecessary  to  describe  minutely 
its  form  and  relations.  It  is  enveloped  in  a  very  dense,  fibrous  coat,  contains 
many  glandular  structures  opening  into  the  urethra,  and  presents  a  great  num- 
ber of  non-striated,  with  a  few  striated  muscular  fibres,  some  just  beneath  the 
fibrous  coat  and  others  penetrating  its  substance  and  surrounding  the  glands. 

The  glands  of  the  prostate  are  most  distinct  at  that  portion  which  lies 
behind  the  urethra.  In  the  posterior  portion  of  this  canal  are  found  about 
twenty  openings,  which  lead  to  tubes  ramifying  in  the  glandular  substance. 
These  tubes  are  formed  of  a  structureless  membrane  branching  as  it  pene- 
trates the  gland.  They  present  hemispherical  diverticula  in  their  course,  and 
terminate  in  dilated  extremities,  which  are  looped  and  coiled.  In  the  deeper 
portions  of  the  tubes,  the  epithelium  is  columnar  or  cubical,  becoming  tessel- 
lated near  their  openings,  and  sometimes  laminated. 

The  prostatic  fluid  probably  is  secreted  only  at  the  moment  of  ejaculation. 
Its  characters  will  be**  considered  in  connection  with  the  composition  of  the 
seminal  fluid.  According  to  Kraus  the  prostatic  fluid  has  an  important 
office  in  maintaining  the  vitality  of  the  spermatozoids.  "  The  spermatozoa, 
in  the  absence  of  the  prostatic  fluid,  can  not  live  in  the  mucous  membrane  of 
the  uterus  of  mammalia ;  but  with  its  aid  they  may  live  for  a  long  time  in 
the  uterine  mucus,  often  more  than  thirty-six  hours." 

Glands  of  the  Urethra. — In  front  of  the  prostate,  opening  into  the  bulb- 
ous portion  of  the  urethra,  are  two  small,  racemose  glands,  called  the  glands 
of  Mery  or  of  Cowper.  These  have  each  a  single  excretory  duct,  are  lined 
throughout  with  cylindrical  epithelium,  and  secrete  a  viscid,  mucus-like  fluid, 
which  forms  a  part  of  the  ejaculated  semen.  Sometimes  there  exists  only  a 
single  gland,  and  occasionally,  though  rarely,  both  are  absent.  Their  uses 
are  probably  not  very  important. 

The  glands  of  Littre,  found  throughout  the  entire  urethra  and  most 
abundant  on  its  anterior  surface,  are  simple  racemose  glands,  extending  be- 
neath the  mucous  membrane  into  the  muscular  structure,  presenting  here 
four  or  five  acini.  As  these  acini  are  surrounded  by  muscular  fibres,  it  is 
easy  to  understand  how  their  secretion  may  be  pressed  out  during  erection  of 
the  penis.  They  are  lined  throughout  with  columnar  or  conoidal  epithelium, 
and  secrete  a  clear  and  somewhat  viscid  mucus,  which  is  mixed  with  the 
ejaculated  semen. 

MALE  ELEMENTS  OF  GENERATIOX. 

The  spermatozoids  are  the  essential,  male  elements  of  generation,  and 
these  are  produced  in  the  substance  of  the  testicle;  by  a  process  analogous  to 


790  GENERATION. 

that  of  the  development  of  other  true,  anatomical  elements.  The  testicles 
can  not  be  regarded  strictly  as  glandular  organs.  They  are  analogous  to  the 
ovaries,  and  they  are  the  only  organs  in  which  spermatozoids  can  be  de- 
veloped, as  the  ovaries  are  the  only  organs  in  which  the  ovum  can  be  formed. 
If  the  testicles  be  absent,  the  power  of  fecundation  is  lost,  none  of  the  fluids 
secreted  by  the  accessory  organs  of  generation  being  able  to  perform  the  office 
of  the  true,  fecundating  elements. 

In  the  healthy  male,  at  the  climax  of  a  normal  venereal  orgasm,  11-6  to 
92*6  grains  (O75  to  6  grammes)  of  seminal  fluid  are  ejaculated  with  considera- 
ble force  from  the  urethra,  by  an  involuntary,  muscular  spasm  (Montegazza). 
This  fluid  requires  about  four  days  for  its  complete  restoration.  The  semen 
is  slightly  mucilaginous,  grayish  or  whitish,  streaked  with  lines  more  or  less 
opaque,  and  it  evidently  contains  various  kinds  of  mucus.  It  has  a  faint  and 
peculiar  odor,  sui  generis,  which  is  observed  only  in  the  ejaculated  fluid  and 
not  in  any  of  its  constituents  examined  separately.  It  is  a  little  heavier  than 
water  and  does  not  mix  with  it  or  dissolve.  After  ejaculation  it  becomes 
jelly-like  and  dries  into  a  peculiar,  hard  mass,  which  may  be  softened  by  the 
application  of  appropriate  liquids.  The  liquid  is  not  coagulated  by  heat  and 
does  not  contain  albumen.  Its  reaction  is  faintly  alkaline.  It  contains  in 
the  human  subject  100  to  120  parts  of  solid  matter  per  1,000. 

The  chemical  constitution  of  the  semen  has  not  been  very  thoroughly  in- 
vestigated and  does  not  present  the  same  physiological  importance  as  its 
anatomical  characters.  Aside  from  the  anatomical  elements  derived  from 
the  testicles  and  the  genital  passages,  it  presents  an  organic  substance 
(spermatine)  which  has  nearly  the  same  chemical  characters  as  ordinary 
mucine.  It  also  contains  a  considerable  quantity  of  phosphates.  During 
desiccation,  elongated,  rhomboidal  crystals  make  their  appearance,  frequently 
arranged  in  groups,  which  are  supposed  to  be  derived  from  the  prostatic  fluid 
and  to  consist  of  phosphoric  acid  combined  with  an  organic  base,  the  formula 
for  which,  united  with  hydrochloric  acid,  is  C8H3NHC1  (Schreiuer).  These 
are  sometimes  called  spermatic  crystals. 

In  the  dilated  portion  of  the  vasa  deferentia  the  mucous  glands  secrete  a 
fluid  which  is  the  first  that  is  added  to  the  spermatozoids  as  they  come  from 
the  testicles.  This  fluid  is  brownish  or  grayish.  It  contains  epithelium,  and 
small,  rounded  granulations,  which  are  dark  and  strongly  refractive.  The 
liquid  itself  is  very  slightly  viscid.  In  the  vesiculae  seminales  there  is  a  more 
abundant  secretion  of  the  grayish  fluid,  with  epithelium,  small,  colorless  con- 
cretions of  nitrogenized  matter,  called  by  Eobin,  sympexions,  and  a  few 
leucocytes.  The  glandular  structures  of  the  prostate  produce  a  creamy  secre- 
tion with  fine  granulations.  It  is  chiefly  to  the  admixture  of  this  fluid  that 
the  semen  owes  its  whitish  appearance.  Finally  as  the  semen  is  ejaculated, 
it  receives  the  viscid  secretion  of  the  glands  of  Cowper,  a  certain  quantity  of 
stringy  mucus  from  the  follicles  of  the  urethra,  with  perhaps  a  little  of  the 
urethral  epithelium. 

Anatomically  considered  the  seminal  fluid  contains  no  important  elements 
except  the  spermatozoidsj  the  various  secretions  just  mentioned  serving  sim- 


SPERMATOZOIDS. 


791 


FIG.  288. — Spermatozoids,  spermatic  crystals,  leuco- 
cytes etc.  (Peyer). 


ply  as  a  vehicle  for  the  introduction  of  these  bodies  into  the  generative 
passages  of  the  female. 

Spermatozoids. — In  August,  1G77,  a  German  student,  named  Von  Ham- 
men,  discovered  the  Spermatozoids  in  the  human  semen  and  exhibited  them 
to  Leeuwenhoek,  who  studied  them 
as  closely  as  was  possible  with  the  in- 
struments at  his  command.  For  a 
long  time  they  were  regarded  as  liv- 
ing animalcules,  although  now  they 
are  considered  simply  as  peculiar, 
anatomical  elements  endowed  with 
movements,  like  ciliated  epithelium. 
These  elements  are  developed  within 
the  seminiferous  tubes  ;  and  they 
differ,  not  so  much  in  their  mode  of 
development,  as  in  their  form,  in 
different  animals. 

The  fluid  taken  from  the  vesiculae 
seminales  of  an  adult  who  has  died 
suddenly  or  the  ejaculated  semen 
contains,  in  addition  to  the  various 

accidental  or  unimportant  anatomical  elements  that  have  been  mentioned,  in- 
numerable bodies,  resembling  animalcules,  which  present  a  flattened,  conoidal 
^  ^  head  and  a  long,  tapering,  filamentous  tail.  The  tail  is 

in  active  motion,  and  the  Spermatozoids  move  about  the 
field  of  view  with  considerable  rapidity  and  force,  pushing 
aside  little  corpuscles  or  granules  with  which  they  may 
come  in  contact.  Under  favorable  conditions,  particularly 
in  the  generative  passages  of  the  female,  the  movements 
may  continue  for  several  days. 

Microscropical  examination  does  not  reveal  any  very 
distinct  structure  in  the  substance  of  the  Spermatozoids. 
The  head  is  about  -j7Vo  of  an  inch  (5  /*)  long,  3-5*5-5-  of  an 
inch  (3  fj.)  broad,  and  wyj-oir  of  an  inch  (1  /u,)  in  thickness. 
The  tail  is  about  ^-^  of  an  inch  (50  p)  in  length.  La 
Yallette  St.  George  has  found  in  man  and  many  of  the  in- 
ferior animals  the  "  intermediate  segment "  described  first 
by  Schweigger-Seidel,  though  he  does  not  agree  with 
Schweigger-Seidel  that  this  portion  is  motionless.  The 
length  of  the  intermediate  segment  is  about  40^0  of  an 
inch  (6  /A).  It  usually  is  described  as  the  beginning  of  the 
^ '  an(^  tne  on^T  difference  between  this  and  other  por- 
tions  is  that  it  is  a  little  thicker.  At  the  extreme  end,  is 
i,  flat  view  ;  2,  side  a  short  and  excessively  fine  filament,  called  the  terminal 

view  ;  A  A,  head;  B  B,     „-, 
intermediate       seg-    nlament. 

termini  filament" D'         Water  speedily  arrests  the  movements  of  the  sperma- 


GENERATION. 


tozoids,  which  may  be  restored  by  the  addition  of  dense  saline  and  other 
solutions.  All  of  the  alkaline,  animal  fluids  of  moderate  viscidity  favor  the 
movements,  while  the  action  of  acid  or  of  very  dilute  solutions  is  unfavorable. 
The  movements  are  suspended  by  extreme  cold,  but  they  return  when  the 
ordinary  temperature  is  restored. 

Before  the  age  of  puberty  the  seminiferous  tubes  are  much  smaller  than 
in  the  adult,  and  they  contain  small,  transparent  cells,  which  in  their  form 
and  arrangement  resemble  epithelium.  As  puberty  approaches,  however, 
the  tubes  become  larger,  and  the  contents  change  their  character.  The  walls 
are  then  provided  with  spindle-shaped  cells  with  a  nucleated,  protoplasmic 
lining,  sending  prolongations  into  the  interior  of  the  tube.  These  prolonga- 
tions afterward  break  up  into  little,  rounded  bodies  called  spermatoblasts,  a 
part  of  each  one  of  which  becomes  the  head  of  a  spermatozoid  (Ebner). 
Between  the  prolongations,  are  the  so-called  spermatic  cells.  The  spermato- 
blasts send  out  each  one  a  short  process  which  forms  the  intermediate  seg- 


FIG.  290. — Spermatogenesis  ;  semi-diagrammatic  (Landois). 
I,  transverse  section  of  a  seminal  tubule  ;  A,  external  membrane  ;  B,  protoplasmic  lining  ;  c,  sperma- 

toblast ;  s,  seminal  cells. 
II,  projection  with  F,  spermatoblasts  ;  s,  seminal  cells. 

III,  spermatoblasts  with  spermatozoids  not  yet  detached. 

IV,  spermatoblasts  with  a  spermatozoid  detached. 

ment  of  the  spermatozoid,  and  from  this  a  long  filament  is  developed,  which 
forms  the  tail.  The  spermatozoid  is  detached  when  its  development  is  complete. 

The  spermatozoids  are  motionless  while  they  are  within  the  testicle,  the 
epididymis  or  the  vasa  deferentia,  apparently  on  account  of  the  density  of 
the  substance  in  which  they  are  embedded ;  for  movements  are  sometimes 
presented  when  the  contents  of  the  vasa  deferentia  are  examined  with  the 
addition  of  water  or  of  saline  solutions.  Once  in  the  vesiculae  seminales,  and 
for  a  certain  time  after  ejaculation,  the  spermatozoids  are  in  active  motion. 
When  the  spermatozoids  have  ceased  their  movements  they  are  incapable 
of  fecundating  the  ovum. 

The  semen,  thus  developed  and  mixed  with  the  various  secretions  before 
mentioned,  is  found  during  adult  life  and  sometimes  even  in  advanced  age, 
and  under  physiological  conditions  it  contains  innumerable  spermatozoids 
in  active  movement;  but  if  sexual  intercourse  be  frequently  repeated  at 
short  intervals,  the  ejaculated  fluid  becomes  more  and  more  transparent, 


FECUNDATION. 

homogeneous  and  scanty,  and  it  may  consist  of  a  small  quantity  of  secretion 
from  the  vesiculae  seminales  and  the  glands  opening  into  the  urethra,  with- 
out spermatozoids  and  consequently  deprived  of  fecundating  properties. 

In  old  men  the  seminal  vesicles  may  not  contain  spermatozoids ;  but  this 
is  not  always  the  case,  even  in  very  advanced  life.  Instances  are  constantly 
occurring  of  men  who  have  children  in  their  old  age,  in  which  the  paternity 
of  the  offspring  can  hardly  be  doubted.  Duplay,  in  1852,  examined  the 
semen  of  a  number  of  old  men,  and  found,  in  about  half  the  number,  sper- 
matozoids, normal  in  appearance  and  quantity,  though  in  some  the  vesicular 
seminales  contained  either  none  or  very  few.  Some  of  the  persons  in  whom 
the  spermatozoids  Avere  normal  were  between  seventy-three  and  eighty-two 
years  of  age.  These  observations  were  confirmed  by  Dieu,  who  found  sper- 
matozoids in  a  man  eighty-six  years  of  age.  The  contents  of  the  seminal 
vesicles,  in  these  cases,  were  examined  twenty-four  hours  after  death.  Some 
of  the  subjects  died  of  acute,  and  others,  of  chronic  diseases ;  but  the  mode 
of  death  did  not  present  any  differences  in  the  cases  classed  with  reference 
to  the  presence  of  spermatozoids.  As  the  result  of  his  own  and  of  other 
recorded  observations,  Dieu  concluded  that  the  power  of  fecundation  often 
persists  for  a  considerable  time  after  copulation  has  become  impossible  on 
account  simply  of  absence  of  the  power  of  erection. 


CHAPTER  XXV. 

FECUNDATION  AXD  DEVELOPMENT  OF  THE  OVUM. 

General  considerations— Fecundation— Changes  in  the  fecundated  ovum— Segmentation  of  the  vitellus— 
Primitive  trace— Blastodermic  layers— Formation  of  the  membranes— Amniotic  fluid— Umbilical  vesicle 
— Formation  of  the  allantois  and  the  permanent  chorion— Umbilical  cord— Membranse  deciduse Forma- 
tion of  the  placenta— Uses  of  the  placenta— Development  of  the  ovum— Development  of  the  cavities  and 
layers  of  the  trunk  in  the  chick— Vertebral  column— Development  of  the  skeleton— Development  of  the 
muscles— Development  of  the  skin— Development  of  the  nervous  system— Development  of  the  organs 
of  special  sense— Development  of  the  digestive  apparatus— Development  of  the  respiratory  apparatus- 
Development  of  the  face— Development  of  the  teeth— Development  of  the  genito-urinary  apparatus- 
Development  of  the  circulatory  apparatus— Description  of  the  foetal  circulation. 

As  far  as  the  male  is  concerned,  coitus  is  rendered  possible  by  erection  of 
the  penis.-  This  may  occur  before  puberty,  but  at  this  time  intercourse  can 
not  be  fruitful.  Coitus  may  be  impossible  in  old  age,  from  absence  of  the 
power  of  erection ;  but  spermatozoids  may  still  exist  in  the  vesiculae  seminales, 
and  fecundation  might  occur  if  the  seminal  fluid  could  be  discharged  into 
the  generative  passages  of  the  female.  Coitus  may  take  place  in  the  female 
before  the  age  of  puberty  or  after  the  final  cessation  of  the  menses,  but  inter- 
course can  not  then  be  fruitful.  There  are  many  instances  of  conception 
following  what  would  be  called  imperfect  intercourse,  as  in  cases  of  unrupt- 
ured  hymen,  deformities  of  the  male  organs,  etc.,  which  show  that  the  actual 


794  GENERATION. 

penetration  of  the  male  organ  is  not  essential,  and  that  fecundation  may 
occur  provided  the  seminal  fluid  find  its  way  into  even  the  lower  part  of  the 
vagina.  Conception  has  also  followed  intercourse  when  the  female  has  been 
insensible  or  entirely  passive.  Unlike  certain  of  the  lower  animals,  the  human 
subject  presents  no  distinct  periodicity  in  the  development  of  the  spermato- 
zoids ;  but  in  reiterated  connection,  an  orgasm  may  occur  when  the  ejaculated 
fluid  has  no  fecundating  properties. 

With  regard  to  the  mechanism  of  erection,  little  remains  to  be  said  after 
the  description  that  has  been  given  of  true,  erectile  tissue,  in  connection  with 
the  physiology  of  the  circulation.  The  cavernous  and  spongy  bodies  of  the 
penis  usually  are  taken  as  the  type  of  erectile  organs.  In  these  parts  the 
arteries  are  large,  contorted,  provided  with  unusually  thick,  muscular  coats, 
and  are  connected  with  the  veins  by  vessels  considerably  larger  than  the  true 
capillaries.  They  are  supported  by  a  strong,  fibrous  net- work  of  trabeculae, 
which  contains  non-striated  muscular  fibres ;  so  that  when  the  blood-vessels 
are  completely  filled  the  organ  becomes  enlarged  and  rigid.  Kesearches  with 
regard  to  the  nerves  of  erection  show  that  the  vessels  of  erectile  tissues  are 
distended  by  an  enlargement  of  the  arterioles  of  supply,  and  that  there  is  not 
simply  a  stasis  of  blood  produced  by  constriction  of  the  veins,  except  possi- 
bly for  a  short  time  during  the  period  of  greatest  excitement.  In  experi- 
ments upon  dogs  Eckhard  discovered  a  nerve  derived  from  the  sacral  plexus, 
stimulation  of  which  produced  an  increase  in  the  flow  of  blood  through  the 
penis,  attended  with  all  the  phenomena  of  erection.  This  nerve  arises  by 
two  roots,  at  the  sacral  plexus,  from  the  first  to  the  third  sacral  nerves,  and  is 
connected  with  the  genito-spinal  centre,  in  the  lower  part  of  the  lumbar  re- 
gion of  the  spinal  cord  (Budge).  In  the  experiments  referred  to,  by  a  com- 
parison of  the  quantity  of  venous  blood  coming  from  the  penis  before  and 
during  the  stimulation  of  the  nerve,  Eckhard  found  a  great  increase  during 
erection.  It  is  probable  that  in  addition  to  the  arterial  dilatation,  when  the 
penis  attains  its  maximum  of  rigidity  there  is  a  certain  degree  of  obstruc- 
tion to  the  outflow  of  blood,  by  compression  of  the  veins,  and  that  the  rigid- 
ity is  increased  by  contraction  of  the  trabecular  muscular  fibres  of  the 
corpora  cavernosa.  At  the  climax  of  an  orgasm,  the  semen  is  forcibly  dis- 
charged from  the  urethra,  by  spasmodic  contractions  of  the  vesiculaB  seminales 
and  the  ejaculatory  muscles.  Although  this  is  the  physiological  mechanism 
of  a  seminal  discharge,  friction  of  the  parts,  which  usually  precedes  ejacula- 
tion, is  not  absolutely  necessary,  as  is  shown  by  the  occurrence  of  orgasm 
during  sleep,  which  is  liable  to  take  place  in  healthy  men  after  prolonged 
continence. 

There  are  some  females,  in  whom  the  generative  function  is  performed, 
even  to  the  extent  of  bearing  children,  who  have  no  actual  knowledge  of  a 
true  venereal  orgasm ;  but  there  are  others  who  experience  an  orgasm  fully 
as  intense  as  that  which  accompanies  ejaculation  in  the  male.  There  is, 
therefore,  the  important  difference  in  the  sexes,  that  preliminary  excitement 
and  an  orgasm  are  necessary  to  the  performance  of  the  generative  act  in  the 
male,  but  are  not  essential  in  the  female.  Still  there  can  be  scarcely  a  doubt 


FECUNDATION.  795 

that  venereal  excitement  in  the  female  facilitates  conception,  other  condi- 
tions being  favorable.  When  excitement  occurs  in  the  female  there  is  en- 
gorgement of  the  true  erectile  tissues  and  possibly  of  the  convoluted  vessels 
surrounding  the  internal  organs.  The  neck  of  the  uterus  becomes  hardened 
and  slightly  elongated  (Wernich) ;  and  it  has  been  observed  by  Litzmann 
and  others,  that  there  occurs  a  sudden  opening  and  closing  of  the  os,  which 
exerts  more  or  less  suction  force.  These  conditions,  however,  are  not  essen- 
tial to  fecundation,  although  they  may  exert  a  favorable  influence  upon  the 
penetration  of  spermatozoids  and  may  at  certain  times  determine  the  rupture 
of  a  Graafian  follicle. 

The  spermatozoids,  once  within  the  cervix  uteri,  and  in  contact  with  the 
alkaline  mucus,  which  increases  the  activity  of  their  movements,  may  pass 
through  the  uterus  into  the  Fallopian  tubes,  and  even  to  the  surface'  of  the 
ovaries.  Precisely  how  their  passage  is  effected,  it  is  impossible  to  say.  It 
can  only  be  attributed  to  the  movements  of  the  spermatozoids  themselves,  to 
capillary  action,  and  to  a  possible  peristaltic  action  of  the  muscular  structures ; 
but  these  points  have  not  as  yet  been  subjects  of  positive  demonstration.  As 
regards  the  human  female,  it  is  impossible  to  give  a  definite  idea  of  the  time 
required  for  the  passage  of  the  spermatozoids  to  the  ovaries  or  for  the  de- 
scent of  the  ovum  into  the  uterus ;  and  it  is  readily  understood  how  these 
questions  hardly  admit  of  experimental  investigation.  It  is  known,  how- 
ever, that  spermatozoids  reach  the  ovaries,  and  they  have  been  seen  in  motion 
on  their  surface,  seven  or  eight  days  after  connection. 

Fecundation. — The  ordinary  situation  at  which  the  ovum  is  fecundated 
is  the  dilated,  or  external  portion  of  the  Fallopian  tube.  All  authorities  are 
agreed  that  fecundation  does  not  take  place  in  the  cavity  of  the  uterus.  In 
rabbits,  when  the  ovum  has  descended  into  the  uterus,  it  is  surrounded  with 
a  dense,  albuminous  coating  which  the  spermatozoids  can  not  penetrate 
(Coste).  It  is  possible  that  this  occurs  in  the  human  subject.  Cases  of 
abdominal  pregnancy  show  that  an  ovum  may  be  fecundated  on  the  ovary, 
as  soon  as  it  is  discharged  from  the  Graafian  follicle. 

The  question  of  the  duration  of  vitality  of  the  spermatozoids,  after  their 
passage  into  the  uterus,  has  an  important  bearing  upon  the  time  when  con- 
ception is  most  liable  to  follow  sexual  intercourse.  The  alkaline  mucus  of 
the  internal  organs  actually  favors  their  movements ;  the  movements  are  not 
arrested  by  contact  with  menstrual  blood ;  and,  indeed,  when  the  spermato- 
zoids are  mixed  with  the  uterine  mucus,  they  simply  change  their  medium, 
and  there  is  no  reason  to  believe  that  they  may  not  retain  their  vitality  as 
well  as  in  the  mucus  of  the  vesiculae  seminales.  It  seems  impossible,  there- 
fore, to  fix  .any  limit  to  the  vitality  of  these  anatomical  elements,  under  phys- 
iological conditions ;  and  it  is  not  certain  that  spermatozoids  may  not  remain 
in  the  Fallopian  tubes  and  around  the  ovary,  when  intercourse  has  taken 
place  immediately  after  a  menstrual  period,  until  the  ovulation  following. 
There  is  an  idea,  based  upon  rather  general  and  indefinite  observation,  that 
conception  is  most  likely  to  follow  an  intercourse  which  occurs  soon  after  a 
monthly  period ;  but  it  is  certain  that  it  may  occur  at  any  time.  It  is  prob- 


GENERATION. 


able  that  during  the  unusual  sexual  excitement  which  the  female  generally 
experiences  after  a  monthly  period,  the  action  of  the  internal  organs,  attend- 
ing and  following  coitus,  presents  the  most  favorable  conditions  for  the 
penetration  of  the  fecundating  elements. 

Union  of  the  Male  with  the  Female  Element  of  Generation. — In  the  ova 
of  certain  animals,  an  opening,  called  a  micropyle,  has  been  demonstrated  in 
the  vitelline  membrane  (Barry,  Keber).  This  has  been  seen  in  the  ova  of  rab- 
bits, although  its  existence  is  to  be  inferred,  only,  in  the  human  ovum.  The 
penetration  of  spermatozoids  has  been  observed  in  the  ova  of  various  animals, 
including  the  rabbit  (Newport,  Coste,  Bischoff,  Weil,  Hensen  and  others). 
Weil  has  seen  spermatozoids  wedged  in  the  substance  of  the  zona  pellucida, 
has  added  blood  to  a  specimen  under  observation,  and  has  restored  the  move- 
ments of  the  spermatozoids  while  in  this  position.  Hensen  has  seen  twenty 
or  more  spermatozoids  within  the  zona  pellucida  in  rabbits.  The  number  of 

spermatozoids  which  penetrate  the  ovum, 
according  to  the  most  recent  researches  on 
fecundation  in  rabbits,  does  not  seem  to  be 
important,  as  only  one  spermatozoid  forms 
a  direct  union  with  the  female  generative 
element.  It  is  assumed  that  the  processes 
observed  in  rabbits  nearly  represent  those 
which  take  place  in  the  human  subject. 

In  the  rabbit,  spermatozoids  begin  to 
pass  through  the  zona  pellucida  about  thir- 
teen hours  after  copulation  (Hensen).  By 
this  time  the  vitellus  usually  has  become 
somewhat  shrunken  and  more  or  less  de- 
formed. There  is  then  a  space,  filled  with 
a  clear  liquid,  between  the  vitellus  and  the  vitelline  membrane,  in  which  the 
spermatozoids  are  seen  in  active  movement.  The  vitelline  mass,  thus  sur- 
rounded with  liquid,  undergoes  usually  movements  of  rotation.  These  phe- 
nomena have  been  described  as  deformation  and  gyration  of  the  vitellus. 
At  about  this  time  the  germinal  vesicle,  according  to  the  older  writers,  dis- 
appears ;  but  it  has  been  lately  ascertained  that  this  body  is  concerned  in 
the  formation  of  the  polar  globule.  The  retraction  of  the  vitellus  and  the 
formation  of  the  polar  globule  are  independent  of  fecundation ;  but  the 
formation  of  the  polar  globule  is  a  process  immediately  preparatory  to  the 
union  of  the  male  with  the  female  generative  element,  and  may  properly 
be  described  in  connection  with  the  mechanism  of  fertilization  of  the  ovum. 
As  the  deutoplasmic  zone  extends  from  the  centre  toward  the  periphery 
of  the  ovum,  the  germinal  vesicle  is  pushed  outward  until  it  reaches  the 
surface  of  the  vitellus.  It  then  becomes  spindle-shaped  ;  and  the  granules 
of  the  vitellus  near  the  extremities  of  the  spindle  arrange  themselves  in  the 
form  of  stars,  forming  what  has  been  called  the  double  star,  or  diaster  (Fol). 
The  extremity  of  the  spindle  which  is  near  the  surface  projects  and  forms 
a  clear,  mammillated  eminence  upon  the  vitellus.  This  projection  becomes 


FIG.  291.—  Ovum  of  the  rabbit,  showing  pene- 
tration of  speiinatozoids  and  retraction 
of  the  mtellus  (Hensen). 


FECUNDATION.  797 

constricted  at  its  base,  and  is  finally  separated  in  the  form  of  a  globule.  A 
second  polar  globule  is  afterward  formed  in  the  same  way. 

That  portion  of  the  altered  germinal  vesicle  which  remains  embedded  in 
the  vitellus  is  called  the  female  pronucleus.  At  the  point  where  the  polar 
globules  are  separated,  a  single  spermatozoid  penetrates  the  vitellus.  The 
head  and  intermediate  segment  of  the  spermatozoid  become  surrounded  with 
a  star,  swell  up  and  form  the  male  pronucleus.  The  male  pronucleus  unites 
with  the  female  pronucleus,  and  fecundation  is  complete.  The  union  of  the 
male  with  the  female  pronucleus  forms  a  body  which  passes  downward  into 
the  substance  of  the  vitellus  and  is  called  the  vitelline  nucleus.  The  furrow 
which  marks  the  beginning  of  segmentation  of  the  vitellus  is  always  ob- 
served at  the  point  of  separation  of  the  polar  globules. 

Hereditary  Transmission,  Superfecundation  etc. — The  first  question 
which  naturally  arises  relates  to  the  conditions  which  determine  the  sex 
of  offspring.  Statistics  show  the  proportions  between  male  and  female 
births  ;  but  nothing  has  ever  been  done  in  the  way  of  procreating  male  or 
female  children  at  will.  According  to  Longet,  the  proportion  of  male  to 
female  births  is  about  104  to  105,  these  figures  presenting  certain  modifica- 
tions under  varying  conditions  of  climate,  season,  nutrition  etc.  It  has  been 
shown,  by  observations  upon  certain  of  the  inferior  animals,  that  the  pre- 
ponderance of  sex  in  births  bears  a  certain  relation  to  the  vigor  and  age  of 
the  parents  ;  and  that  old  and  feeble  females  fecundated  by  young  and  vig- 
orous males  produce  a  greater  number  of  males,  and  vice  versa  ;  but  no 
exact  laws  of  this  kind  have  been  found  applicable  to  the  human  subject. 

No  definite  rule  can  be  laid  down  with  regard  to  the  transmission  of 
mental  or  physical  peculiarities  to  offspring.  Sometimes  the  progeny  as- 
sumes more  the  character  of  the  male  than  of  the  female  parent,  and  some- 
times the  reverse  is  the  case,  without  any  reference  to  the  sex  of  the  child  ; 
sometimes  there  appears  to  be  no  such  relation  ;  and  occasionally  peculiari- 
ties are  observed,  derived  apparently  from  grandparents.  This  is  true  with 
regard  to  pathological  as  well  as  physiological  peculiarities,  as  in  the  inher- 
ited tendencies  to  certain  diseases,  malformations  etc. 

A  peculiar  and,  it  seems  to  be,  an  inexplicable  fact  is  that  previous  preg- 
nancies have  an  influence  upon  offspring.  This  is  well  known  to  breeders 
of  animals.  If  pure-blooded  mares  or  bitches  have  been  once  covered  by  an 
inferior  male,  in  subsequent  fecundations  the  young  are  likely  to  partake 
of  the  character  of  the  first  male,  even  if  they  be  afterward  bred  with  males 
of  unimpeachable  pedigree.  The  same  influence  is  observed  in  the  human 
subject.  A  woman  may  have,  by  a  second  husband,  children  who  resemble 
a  former  husband,  and  this  is  particularly  well  marked  in  certain  instances 
by  the  color  of  the  hair  and  eyes.  A  white  woman  who  has  had  children 
by  a  negro  may  subsequently  bear  children  to  a  white  man,  these  children 
presenting  some  of  the  unmistakable  peculiarities  of  the  negro  race. 

Superfecundation  of  course  does  not  come  in  the  category  of  influences 
just  mentioned.  It  is  not  infrequent  to  observe  twins,  when  two  males  have 
had  access  to  the  female,  which  are  entirely  distinct  from  each  other  in  their 
52 


798 


GENEEATION. 


physical  characters ;  a  fact  which  is  readily  explained  by  the  assumption  that 
two  ova  have  been  separately  fecundated.  This  view  is  entirely  sustained  by 
observation  and  experiment.  Many  cases  illustrating  this  point  are  on  record. 

The  following  communication,  with  a  photograph,  was  received  in  Janu- 
ary, 1869,  from  Dr.  John  H.  Janeway,  Assistant  Surgeon,  U.  S.  A.,  and  it 
illustrates  superfecundation  in  the  human  subject ;  or  at  least  that  was  the 
view  taken  by  the  negro  father  : 

"  Frances  Hunt,  a  freedwoman,  aged  thirty-five  years,  gave  birth  to 
twins,  February  4,  1867,  in  New  Kent  County,  Virginia.  One  of  these 
twins  was  black,  the  other  was  white.  Frances  is  a  mulatto.  The  black 


FIG.  292.—  Mulatto  mother  ivith  twins,  one  white  and  the  other  black  (from  a  photograph). 

child  is  much  darker  than  she  is.  Previous  to  the  parturition,  she  had 
given  birth  to  seven  children,  all  single  births.  She  was  living  at  the  time 
of  her  impregnation  in  the  family  of  a  white  man  as  house-servant,  sleep- 
ing with  a  black  man  at  night.  She  insists,  however,  that  she  never  had 
carnal  intercourse  with  a  white  man.  She -probably  does  this  because  the 
black  man  turned  her  out  of  his  house  when  he  saw  that  one  of  the  chil- 
dren was  white.  The  only  negro  feature  in  the  white  child  was  its  nose. 
There,  its  resemblance  to  its  mother  was  perfect.  Its  hair  was  long,  light 
and  silky.  Complexion  brilliant." 


CHANGES  IN  THE  FECUNDATED  OVUM.  799 

Keference  has  already  been  made  to  the  curious  fact  that  when  a  cow 
produces  twins,  one  male  and  the  other  female,  the  female,  which  is  called  a 
free-martin,  is  sterile  and  presents  an  imperfect  development  of  the  inter- 
nal organs  of  generation.  This  has  led  to  the  idea  that  possibly  the  same 
law  may  apply  to  the  human  subject,  in  cases  of  twins,  one  male  and  the 
other  female  ;  but  many  observations  are  recorded  in  gynaecological  works, 
showing  the  incorrectness  of  this  view. 

It  has  long  been  a  question  whether  impressions  made  upon  the  nervous 
system  of  the  mother  can  exert  an  influence  upon  the  foetus  in  ntero. 
While  many  authors  admit  that  violent  emotions  experienced  by  the  mother 
may  affect  the  nutrition  and  the  general  development  of  the  fo3tus,  some 
writers  of  authority  deny  that  the  imagination  can  have  any  influence  in 
producing  deformities.  The  remarkable  cases  recorded  as  instances  of  de- 
formity due  to  the  influence  of  the  maternal  mind  are  not  entirely  reliable  ; 
and  it  often  happens  that  when  a  child  is  born  with  a  deformity,  the  mother 
imagines  she  can  explain  it  by  some  impression  received  during  pregnancy, 
which  she  recalls  only  after  she  knows  that  the  child  is  deformed.  There 
is,  indeed,  no  satisfactory  evidence  that  the  maternal  mind  has  anything  to 
do  with  the  production  of  deformities  in  utero. 

CHANGES  IN  THE  FECUNDATED  OVUM. 

It  is  probable  that  the  ovum  is  fecundated  either  just  as  it  enters  the 
Fallopian  tube  or  in  the  dilated  portion,  near  the  ovary.  As  it  passes  down 
the  tube,  whether  it  be  or  be  not  fecundated,  it  becomes  covered  with  an 
albuminous  layer.  This  layer  probably  serves  to  protect  the  fecundated 
ovum,  and  when  the  spermatozoids  do  not  penetrate  the  vitelline  membrane 
near  the  ovary,  it  presents  an  obstacle  to  their  passage. 

After  fecundation  of  the  ovum,  at  least  in  many  of  the  lowest  forms  of 
animals,  the  appearance  of  the  vitellus  undergoes  a  remarkable  change,  by 
which  ova  that  are  about  to  pass  through  the  first  processes  of  development 
may  readily  be  distinguished  from  those  which  have  not  been  fecundated. 
This  change  consists  in  an  enlargement  of  the  granules  and  their  more 
complete  separation  from  the  clear  substance  of  the  vitellus.  The  granules 
then  refract  light  more  strongly  than  before,  so  that  the  fecundated  ova  are 
distinctly  brighter  than  the  others. 

Segmentation  of  the  Vitellus. — Soon  after  the  fecundation  of  the  ovum 
and  the  formation  of  the  vitelline  nucleus,  a  furrow  appears  at  the  point  of 
extrusion  of  the  polar  globules.  This  is  met  by  a  furrow  upon  the  opposite 
side,  and  the  vitellus  is  divided  into  two  globes.  One  of  the  globes  is 
slightly  larger  than  the  other,  and  presents  fewer  and  smaller  granules. 
The  larger  sphere  subsequently  forms,  by  its  division,  the  epiblastic  cells, 
and  the  smaller  sphere  forms  the  hypoblastic  cells.  Each  sphere  is  pro- 
vided with  a  distinct  nucleus.  The  two  spheres  resulting  from  the  first 
segmentation  of  the  vitellus  are  divided,  each  one  into  two,  making  four 
spheres.  These  spheres  are  again  divided  into  eight — four  epiblastic  and 
four  hypoblastic  spheres — each  with  a  nucleus  (Van  Beneden).  One  of  the 


800 


GENERATION. 


hypoblastic  spheres  now  passes  to  the  centre  of  the  ovum ;  and  the  four 
epiblastic  spheres,  which  are  at  the  periphery,  divide,  each  one  into  two, 
making  eight  epiblastic  and  four  hypoblastic  spheres.  When  this  has 
occurred,  the  epiblastic  spheres  are  smaller  and  more  transparent  than  the 
hypoblastic  spheres.  The  four  hypoblastic  spheres  now  divide  into  eight. 
The  epiblastic  spheres  then  divide  into  sixteen,  the  hypoblastic  spheres  in 
turn  divide,  and  this  goes  on  until  the  process  of  segmentation  is  com- 
pleted. In  the  rabbit,  this  occurs  usually  about  seventy  hours  after  impreg- 
nation (Van  Beneden).  As  segmentation  progresses,  the  epiblastic  cells  ex- 


FIG.  W3.— Formation  of  the  blastodermic  vesicle  (Van  Beneden). 

A,  B,  C,  D,  sections  of  ova  in  successive  i-iages  of  development  in  the  rabbit ;  zp,  zona  pellucida  ; 
ep,  epiblastic  cells  ;  hyp,  hypoblastic  cells. 

tend  over  the  hypoblastic  cells,  and  become  irregularly  polygonal  in  form. 
The  hypoblastic  cells  occupy  the  central  portion  of  the  ovum.  At  first 
there  is  a  circular  space  upon  the  ovum  where  the  epiblastic  cells  do  not 
cover  the  cells  of  the  hypoblast  (see  Fig.  293,  A)  ;  but  this  soon  becomes 
closed  by  an  extension  of  the  cells  of  the  epiblast  (see  Fig.  293,  B).  The 
hypoblastic  cells,  at  the  close  of  segmentation,  are  slightly  larger  than  the 
cells  of  the  epiblast  and  are  darker  and  more  rounded.  The  ovum  is  now 
called  the  morula,  on  account  of  its  fancied  resemblance  to  a  mulberry ; 
and  the  cells  of  which  it  is  composed  are  called  collectively  blastodermic 


CHANGES  IN  THE  FECUNDATED  OVUM.  801 

cells.  The  ovum  is  probably  in  this  condition  when  it  passes  from  the 
Fallopian  tube  into  the  uterus. 

Most  of  the  phenomena  of  segmentation  have  been  observed  in  the 
lower  forms  of  animals ;  but  there  can  be  no  doubt  that  analogous  pro- 
cesses take  place  in  the  human  ovum.  In  the  rabbit,  forty-five  and  a  half 
hours  after  copulation,  Weil  observed  an  ovum  with  sixteen  segmentations, 
situated  in  the  lower  third  of  the  Fallopian  tube.  He  observed  an  ovum, 
ninety-four  hours  after  copulation,  with  a  delicate  mosaic  appearance,  pre- 
senting a  small,  rounded  eminence  on  its  surface.  It  is  impossible  to  say 
how  long  the  process  of  segmentation  continues  in  the  human  ovum.  It  is 
stated  that  it  is  completed  in  rabbits  in  a  few  days,  and  in  dogs,  that  it 
occupies  more  than  eight  days  (Hermann). 

After  segmentation  has  been  completed,  a  cavity  filled  with  liquid 
appears  between  the  hypoblastic  and  epiblastic  cells,  except  at  that  portion 
which  has  last  been  covered  by  the  epiblast.  Here  the  cells  of  the  hypo- 
blast  are  in  contact  with  the  epiblast.  The  liquid  in  the  interior  of  the 
ovum  gradually  increases  in  quantity,  the  ovum  becomes  enlarged  to  the 
diameter  of  -fa  to  ^  of  an  inch  (0-5  to  1  mm.),  and  is  now  called  the 
blastodermic  vesicle.  The  epiblastic  cells  surround  the  blastodermic  ves- 
icle completely,  forming  a  single  layer  over  the  greater  portion ;  and  the 
hypoblastic  cells  form  a  lenticular  mass  attached  to  the  smaller  portion 
of  the  inner  surface  of  the  layer  of  epiblastic  cells  (see  Fig.  293,  c  and  D). 
It  is  at  this  portion  of  the  ovum  that  the  embryonic  spot  or  area  afterward 
appears. 

The  albuminous  covering  which  the  ovum  has  received  in  the  upper 
part  of  the  Fallopian  tube  gradually  liquefies  and  penetrates  the  vitel- 
line  membrane,  furnishing,  it  is  thought,  matter  for  the  nourishment 
and  development  of  the  vitellus.  In  the  Fallopian  tube,  indeed,  the 
adventitious  albuminous  covering  of  the  ovum  presents  an  analogy  to  the 
albuminous  coverings  which  the  eggs  of  oviparous  animals  receive  in 
the  oviducts ;  with  the  difference  that  this  albuminous  matter  is  almost 
the  sole  source  of  nourishment  in  the  latter  and  exists  in  large  quan- 
tity, while  in  viviparous  animals  the  quantity  is  small,  is  generally  con- 
sumed as  the  ovum  passes  into  the  uterus,  and  in  the  uterus  the  ovum 
forms  attachments  to  and  draws  its  nourishment  from  the  vascular  system 
of  the  mother. 

Primitive  Trace. — Soon  after  the  formation  of  the  blastodermic  vesicle, 
at  a  certain  point  on  its  surface  there  appears  a  rounded  elevation  or  heap 
of  smaller  cells,  forming  a  distinct  spot,  called  the  embryonic  spot.  As 
development  advances,  this  spot  becomes  elongated  and  oval.  It  is  then 
surrounded  by  a  clear,  oval  area,  called  the  area  pellucida,  and  the  area 
pellucida  is  itself  surrounded  by  a  zone  of  cells,  more  granular  and  darker 
than  the  rest  of  the  blastoderm,  called  the  area  opaca.  The  line  thus 
formed  and  surrounded  by  the  area  pellucida  is  called  the  primitive  trace. 
This  primitive  trace,  or  primitive  groove,  however,  is  a  temporary  structure. 
After  the  groove  is  formed,  there  appears,  in  front  of  but  not  continuous 


802 


GENEEATION. 


FIG.  294. — Primitive  trace  of  the  embryon  (Lie'geois). 
a,  primitive  trace ;  b,  area  pellucida ;  c,  area  opaca  ;  d,  blasto- 
dermic  cells  ;  e,  e,  villi  beginning  to  appear  on  the  vitelline 
membrane. 


with  it,  a  new  fold  and  a  groove  leading  from  it.  This  is  the  "  head-fold," 
and  the  groove  is  the  true  medullary  groove,  which  is  subsequently  devel- 
oped into  the  neural  canal. 
Blastodermic  Layers. — 
The  blastodermic  cells,  re- 
sulting originally  from  the 
segmentation  of  the  vitel- 
lus,  are  first  split  appar- 
ently into  two  layers,  the 
external,  or  epiblast,  and 
the  internal,  or  hypoblast. 
The  epiblast  is  developed 
into  the  epidermis  and  its 
appendages,  the  glands  of 
the  skin,  the  brain  and 
spinal  cord,  the  organs  of 
special  sense  and  possibly 
some  parts  of  the  genito- 
urinary apparatus.  The 
hypoblast  is  developed  into 
the  epithelium  lining  the 

mucous  membrane  and  glands  of  the  stomach  and  intestinal  canal.  There 
is  .a  thickening  of  both  of  these  layers  at  the  line  of  development  of 
the  cerebro-spinal  system,  with  a  furrow  that  is  finally  enclosed  by  an 
elevation  of  the  ridges  and  their  union  posteriorly,  forming  the  canal  for 
the  spinal  cord. 

As  the  spinal  canal  is  developed,  a  new  layer  of  cells  is  formed  between 
the  epiblast  and  the  hypoblast,  which  is  called  the  mesoblast.  The  meso- 
blast  itself  afterward  splits  into  two  layers.  All  the  parts  not  enumerated 
as  developed  from  the  epiblast  or  hypoblast  are  developed  from  the  two  lay- 
ers of  the  mesoblast.  The  outer  layer  of  the  mesoblast,  or  the  epiblastic 
mesoblast,  unites  with  the  epiblast,  and  the  two  membranes  together  form 
what  is  sometimes  called  the  somatopleure.  The  inner  layer  of  the  meso- 
blast, the  hypoblastic  mesoblast,  unites  with  the  hypoblast  to  form  what  is 
called  the  splanchnopleure.  The  cells  lining  the  vessels,  including  the 
lymphatics,  which  exist  in  a  single  layer,  are  called  endothelial  cells.  This 
name  is  also  applied  to  the  cells  lining  the  serous  membranes. 

FORMATION  OF  THE  MEMBRANES. 

In  the  mammalia  a  portion  of  the  blastoderm  is  developed  into  mem- 
branes by  which  a  communication  and  union  are  established  between  the 
ovum  and  the  mucous  membrane  of  the  uterus.  From  the  ovum  two  mem- 
branes are  developed  ;  one  non-vascular,  the  amnion,  and  another,  the  allan- 
tois,  which  is  vascular.  The  two  layers  of  decidua  are  formed  from  the 
mucous  membrane  of  the  uterus.  At  a  certain  part  of  the  uterus,  a  vascular 
connection  is  established  between  the  mucous  membrane  and  the  allantois, 


FORMATION  OF  THE  AMNION.  803 

and  the  union  of  these  two  structures  forms  the  placenta.  The  fcetal  portion 
of  the  placenta  is  connected  with  the  foetus,  by  the  vessels  of  the  umbilical 
cord,  and  the  maternal  portion  is  connected  with  the  great  uterine  sinuses. 

The  external  covering  of  the  ovum,  during  the  first  stage  of  its  develop- 
ment, is  the  vitelline  membrane.  As  the  ovum  is  received  into  the  uterus, 
the  vitelline  membrane  develops  upon  its  surface  little  villosities,  which  are 
non- vascular  and  are  formed  of  amorphous  matter  with  granules.  These  are 
the  first  villosities  of  the  ovum,  and  they  assist  in  fixing  the  egg  in  the  uter- 
ine cavity.  They  are  not  permanent,  they  do  not  become  developed  into  the 
vascular  villosities  of  the  chorion  and  they  disappear  as  the  true  membranes 
of  the  embryon  are  developed  from  the  blastodermic  layers.  The  vitelline 
membrane  disappears  soon  after  the  passage  of  the  ovum  into  the  uterus, 
when  it  is  replaced  by  the  amnion. 

Formation  of  the  Amnion. — As  the  ovum  advances  in  its  development,  it 
is  observed  that  a  portion  of  the  blastoderm  becomes  thickened,  forming  the 
epiblast,  the  two  layers  of  the  mesoblast  and  the  hypoblast.  At  about  the 
time  when  this  thickening  begins,  a  fold  of  the  epiblast  and  of  the  external 
layer  of  the  mesoblast  makes  its  appearance,  which  surrounds  the  thickened 
portion  and  is  most  prominent  at  the  cephalic  and  the  caudal  extremity  of 
the  furrow  for  the  neural  canal.  This  fold  increases  in  extent  as  develop- 
ment advances,  passes  over  the  dorsal  surface  of  the  embryon  and  finally 
meets  so  as  to  enclose  the  embryon  completely.  At  a  certain  period  of  the 
development  of  the  amnion,  this  membrane  consists  of  an  external  layer, 
formed  of  the  external  layer  of  the  fold,  and  an  internal  layer ;  and  the  point 
of  union  of  the  two  layers,  or  the  point  of  meeting  of  the  fold,  is  marked  by 
a  membranous  septum. 

The  two  amniotic  layers  are  formed  in  the  way  just  described,  and  a  com- 
plete separation  finally  takes  place,  by  a  disappearance  of  the  septum  formed 
by  the  meeting  of  the  folds  over  the  back  of  the  embryon.  This  process 
occupies  four  or  five  days,  in  the  human  ovum.  The  point  where  the  folds 
meet  is  called  the  amniotic  umbilicus.  When  the  amnion  is  thus  completely 
formed,  the  vitelline  membrane  has  been  encroached  upon  by  the  external 
amniotic  layer  and  disappears,  leaving  this  layer  of  the  amnion  as  the  external 
covering  of  the  ovum.  At  this  time  there  is  a  growth  of  villosities  upon  the 
surface  of  the  external  amniotic  layer,  which,  like  the  villosities  of  the  vitel- 
line membrane,  are  not  vascular. 

Soon  after  the  development  of  the  amnion  the  allantois  is  formed.  This 
membrane  is  vascular.  It  encroaches  upon  and  takes  the  place  of  the  external 
amniotic  membrane,  and  is  covered  with  hollow  villi,  which  take  the  place 
of  the  villi  of  the  amnion.  Over  a  certain  portion  of  the  membrane  the  villi 
are  permanent.  The  mode  of  development  of  the  amnion  is  illustrated  by 
the  diagrammatic  Fig.  295.  This  figure  illustrates  the  formation  of  the 
amnion,  the  umbilical  vesicle  and  the  allantois.  The  last  two  structures  are 
derived  from  the  hypoblast  and  the  internal  layer  of  the  mesoblast. 

When  the  allantois  has  become  the  chorion,  or  the  external  membrane  of 
the  ovum,  having  taken  the  place  of  the  external  layer  of  the  amnion,  the 


804 


GENEKATION. 


structures  of  the  ovum  are  the  following :  1.  The  chorion,  formed  of  the 
two  layers  of  the  allantois  and  penetrated  by  blood-vessels.     2.  The  umbili- 


FIG.  295.—  Five  diagrammatic  representations  of  the  formation  of  the  membranes  in  the  mammalia 

(Kolliker). 

1 :  a,  a',  epiblast ;  d,  vitelline  membrane  ;  d',  villi  on  the  vitelline  membrane  ;  t,  hypoblast ;  m,  m', 
mesoblast. 

2 :  a',  external  layer  of  the  amnion  ;  d,  d',  vitelline  membrane  ;  e,  embryon  ;  d  s,  umbilical  vesicle  ;  v  I, 
k  s,  s  s,  folds  of  the  amnion  ;  d  d,  m',  s  t,  hypoblast ;  d  d,  connection  of  the  embryon  with  the  um- 
bilical vesicle. 

3 :  d,  d',  vitelline  membrane  ;  v  I,  internal  amniotic  layer  ;  e,  embryon  ;  a  h,  amniotic  cavity  ;  sh,  sh, 
external  amniotic  layer  ;  a  m,  space  between  the  two  layers  of  the  amnion  ;  d  d,  hypoblast ;  d/,  s  t, 
i,  walls  of  the  umbilical  vesicle ;  d  g,  omphalo-mesenteric  canal ;  d  s,  cavity  of  the  umbilical  vesicle; 
a  I,  first  appearance  of  the  allantois. 

4 :  s  h,  external  layer  of  the  amnion  ;  s  z,  villi  of  the  external  layer  of  the  amnion,  which  has  now  be- 
come the  chorion,  the  vitelline  membrane  having  disappeared  ;  h  h,  a  m,  internal  layer  of  the  am- 
nion ;  e,  embryon  ;  o  h,  amniotic  cavity  ;  d  g,  omphalo-mesenteric  canal ;  d  s,  cavity  of  the  umbilical 
vesicle  ;  a  I,  allantois  ;  r,  space  between  the  two  layers  of  the  amnion. 

5  :  c  h,  s  h,  c  h,  a  I,  allantois  (which  has  now  become  the  chorion,  the  external  amniotic  layer  having  dis- 
appeared), with  its  villi ;  a  m,  amnion  ;  a  s,  amniotic  covering  of  the  umbilical  cord  ;  r,  space  between 
the  amnion  and  the  allantois  ;  ah,  amniotic  cavity  ;  ds,  umbilical  vesicle  ;  dg,  omphalo-mesenteric 
canal. 


PI.M 


FIG.  1. — Human  embryon,  at  the  ninth  week,  removed  from  the  membranes ;  three  times 

the  natural  size  (Erdl). 
FIG.  2. — Human  embryon,  at  the  twelfth  week,  inclosed  in  the  amnion;  natural  size  (Erdl). 


AMNIOTIC  FLUID.  805 

cal  cord,  which  connects  the  embryon  with  the  placental  portion  of  the 
chorion,  and  the  umbilical  vesicle,  formed  from  the  same  layers  as  the  allan- 
tois.  3.  The  amnion,  which  is  the  internal  layer  of  the  amniotic  fold,  per- 
sisting throughout  total  life.  4.  The  embryon  itself. 

During  the  early  stages  of  development  of  the  umbilical  vesicle  and  the 
allantois,  the  internal  amuiotic  layer,  or  the  true  amniotic  membrane,  is 
closely  applied  to  the  surface  of  the  embryon,  and  is  continuous  with  the  epi- 
dermis, at  the  umbilicus.  It  is  then  separated  from  the  allantois  by  a  layer 
of  gelatinous  matter ;  and  in  this  layer,  between  the  amnion  and  the  allan- 
tois, is  the  umbilical  vesicle.  At  this  time  the  umbilical  cord  is  short  and 
not  twisted.  As  development  advances,  however,  the  intermembranous  gelat- 
inous matter  gradually  disappears ;  the  cavity  of  the  amnion  is  enlarged  by 
the  production  of  a  liquid  between  its  internal  surface  and  the  embryon ;  and 
at  about  the  end  of  the  fourth  month,  the  amnion  comes  in  contact  with  the 
internal  surface  of  the  chorion.  At  this  time  the  embryon  floats  in  the 
amniotic  cavity,  surrounded  by  the  amniotic  fluid. 

The  amnion  forms  a  lining  membrane  for  the  chorion.  By  its  gradual 
enlargement  it  has  formed  a  covering  for  the  umbilical  cord ;  and  between 
it  and  the  cord,  is  the  atrophied  umbilical  vesicle.  The  amnion  then  resem- 
bles a  serous  membrane,  except  that  it  is  non-vascular.  It  is  lined  by  a 
single  layer  of  pale,  delicate  cells  of  pavement-epithelium,  which  contain  a 
few  fine,  fatty  granulations.  At  term  the  amnion  adheres  to  the  chorion, 
although  it  may  be  separated,  with  a  little  care,  as  a  distinct  membrane  and 
may  be  stripped  from  the  cord.  From  its  arrangement  and  from  the  absence 
of  blood-vessels,  it  is  evident  that  this  membrane  is  simply  for  the  protec- 
tion of  the  fcetus  and  is  not  directly  concerned  in  its  nutrition  and  devel- 
opment (see  Plate  III,  Fig.  2).  The  gelatinous  mass  referred  to  above,  situ- 
ated, during  the  early  periods  of  intrauteriue  life,  between  the  amnion  and 
the  chorion,  presents  a  semi-fluid  consistence,  with  very  delicate,  interlacing 
fibres  of  connective  tissue  and  fine,  grayish  granulations  scattered  through 
its  substance.  These  fibres  are  gradually  developed  as  the  quantity  of  gelat- 
inous matter  diminishes  and  the  amnion  approaches  the  chorion,  until 
finally  they  form  a  rather  soft,  reticulated  layer,  which  is  sometimes  called 
the  membrana  media. 

Amniotic  Fluid. — The  process  of  enlargement  of  the  amnion  shows  that 
the  amniotic  fluid  gradually  increases  in  quantity  as  the  development  of  the 
foetus  progresses.  At  term  the  entire  quantity  is  variable,  being  rarely  more 
than  two  pints  (about  one  litre)  or  less  than  one  pint  (about  half  a  litre). 
In  the  early  periods  of  utero-gestation  it  is  clear,  sliglitly  yellowish  or  green- 
ish, and  perfectly  liquid.  Toward  the  sixth  month  its  color  is  more  pro- 
nounced and  it  becomes  slightly  mucilaginous.  Its  reaction  usually  is  neutral 
or  faintly  alkaline,  though  sometimes  it  is  feebly  acid  in  the  latest  periods. 
It  sometimes  contains  a  small  quantity  of  albumin,  as  determined  by  heat 
and  nitric  acid ;  and  there  generally  is  a  gelatinous  precipitate  on  the  addi- 
tion of  acetic  acid.  The  following  table  gives  its  chemical  composition 
(Robin) : 


806  GENERATION. 

COMPOSITION   OF   THE   AMNIOTIC    FLUID. 

Water 991-00  to  975-00 

Albumin  and  mucine 0-82  "     10-77 

Urea 2-00  "       3*50 

Creatine  and  creatinine  (Scherer,  Robin  and  Verdeil) not  estimated 

Sodium  lactate  (Vogt,  Regnauld) a  trace 

Fatty  matters  (Rees,  Mack) 0-13  to      1-25 

Glucose  (Bernard) not  estimated 

Sodium  chloride  and  potassium  chloride 2-40  to      5-95 

Calcium  chloride a  trace 

Sodium  carbonate a  trace 

Sodium  sulphate a  trace 

Potassium  sulphate  (Rees) a  trace 

Calcareous  and  magnesian  phosphates  and  sulphates 1-14  to      1-72 

The  presence  of  certain  of  the  urinary  constituents  in  the  amniotic  fluid 
has  led  to  the  view  that  the  urine  of  the  foetus  is  discharged  in  greater  or  less 
quantity  into  the  amniotic  cavity.  Bernard,  who  is  cited  in  the  table  of  com- 
position of  the  amniotic  fluid  as  having  determined  the  presence  of  sugar, 
has  shown  that  in  animals  with  a  multiple  placenta,  the  amnion  has  a  glyco- 
genic  action  during  the  early  part  of  intrauterine  existence. 

With  regard  to  the  origin  of  the  amniotic  fluid,  it  is  impossible  to  say 
how  much  of  it  is  derived  from  the  general  surface  of  the  fcetus,  how  much 
from  the  urine,  and  how  much  from  the  amnion  itself,  by  transudation  from 
the  vascular  structures  beneath  this  membrane.  The  quantity  apparently  is 
too  great,  especially  in  the  early  months,  to  be  derived  entirely  from  the  urine 
of  the  foetus,  and  there  probably  is  an  exudation  from  the  general  surface  of 
the  foetus  and  from  the  membranes.  After  the  third  month  the  sebaceous 
secretion  from  the  skin  of  the  foetus  prevents  the  absorption  of  any  of  the 
liquid.  An  important  property  of  the  amniotic  fluid  is  that  of  resisting  pu- 
trefaction and  of  preserving  dead  tissues. 

Formation  of  the  Umbilical  Vesicle. — As  the  visceral  plates,  which  will 
be  described  hereafter,  close  over  the  front  of  the  embryon,  that  portion  of 
the  blastoderm  from  which  the  intestinal  canal  is  developed  presents  a  vesicle, 
which  is  cut  off  from  the  abdominal  cavity  but  which  still  communicates 
freely  with  the  intestine.  This  is  the  umbilical  vesicle.  On  its  surface,  is  a 
rich  plexus  of  blood-vessels ;  and  this  is  a  very  important  organ  in  birds  and 
in  many  of  the  lower  forms  of  animals.  In  the  human  subject  and  in  mam- 
mals, however,  the  umbilical  vesicle  is  not  so  important,  as  nutrition  is 
secured  by  means  of  vascular  connections  between  the  chorion  and  the  uterus. 
The  vesicle  becomes  gradually  removed  farther  and  farther  from  the  em- 
bryon, as  development  advances,  by  the  elongation  of  its  pedicle,  and  it  is 
compressed  between  the  amnion  and  the  chorion,  as  the  former  membrane 
becomes  distended. 

When  the  umbilical  vesicle  is  formed,  it  receives  two  arteries  from  the 
two  aortae,  and  the  blood  is  returned  to  the  embryon,  by  two  veins,  which 
open  into  the  vestibule  of  the  heart.  These  are  called  the  omphalo-mesen- 
teric  vessels.  At  about  the  fortieth  day  one  artery  and  one  vein  disappear, 


FORMATION  OF  THE  ALLANTOIS.  807 

and  soon  after,  all  vascular  connection  with  the  embryon  is  lost.  At  first 
there  is  a  canal  of  communication  with  the  intestine,  called  the  omphalo- 
mesenteric  canal.  This  is  gradually  obliterated,  and  it  closes,  between  the 
thirtieth  and  the  thirty-fifth  day.  The  point  of  communication  of  the  vesi- 
cle with  the  intestine  is  called  the  intestinal  umbilicus ;  and  early  in  the 
process  of  development,  there  is  here  a  hernia  of  a  loop  of  intestine.  The 
umbilical  vesicle  remains  as  a  tolerably  prominent  structure  as  late  as  the 
fourth  or  fifth  month,  but  it  may  often  be  -discovered  at  the  end  of  preg- 
nancy. 

The  umbilical  vesicle  presents  three  coats;  an  external,  smooth  mem- 
brane, formed  of  connective  tissue,  a  middle  layer  of  transparent,  polyhedric 
cells,  and  an  internal  layer  of  spheroidal  cells.  The  membrane,  composed  of 
these  layers,  encloses  a  pulpy  mass,  composed  of  a  liquid  containing  cells  and 
yellowish  granulations. 

Formation  of  the  Allantois  and  the  Permanent  Chorion. — During  the 
early  stages  of  development  of  the  umbilical  vesicle,  and  as  it  is  shut  off 
from  the  intestine,  there  appears  an  elevation  at  the  posterior  portion 
of  the  intestine,  which  rapidly  increases  in  extent,  until  it  forms  a  mem- 
brane of  two  layers,  which  is  situated  between  the  internal  and  the  external 
layers  of  the  amnion.  This  membrane  becomes  vascular  early  in  the  prog- 
ress of  its  development,  increases  in  size  quite  rapidly,  and  finally  it  com- 
pletely encloses  the  internal  layer  of  the  amnion  and  the  embryon,  the 
gelatinous  mass  already  described  being  situated  between  it  and  the  internal 
amniotic  layer  before  this  membrane  becomes  enlarged.  While  the  forma- 
tion of  the  two  layers  of  the  allantois  is  quite  distinct  in  certain  of  the  lower, 
forms  of  animals,  in  the  human  subject  and  in  mammals  it  is  not  so  easily 
observed ;  still  there  can  be  no  doubt  as  to  the  mechanism  of  its  formation, 
even  in  the  human  ovum.  Here,  however,  the  allantois  soon  becomes  a 
single  membrane,  the  two  original  layers  of  which  can  not  be  separated  from 
each  other.  The  process  of  the  development  of  the  allantois  is  shown  in  the 
diagrammatic  Fig.  295  (3,  4,  5). 

It  is  the  vascularity  of  the  allantois  which  causes  the  rapid  development 
by  which  it  invades  and  finally  supersedes  the  external  layer  of  the  amnion, 
becoming  the  permanent  chorion,  or  external  membrane  of  the  ovum.  At 
first  there  are  two  arteries  extending  into  this  membrane  from  the  lower  por- 
tion of  the  aorta,  and  two  veins.  The  two  arteries  persist  and  form  the  two 
arteries  of  the  umbilical  cord,  coming  from  the  internal  iliac  arteries  of  the 
foetus ;  and  one  vein,  the  umbilical  vein,  which  returns  the  blood  from  the 
placenta  to  the  foetus,  is  permanent.  These  vessels  are  connected  with  the 
permanent,  vascular  tufts  of  the  chorion. 

The  development  of  the  allantois  can  not  be  well  observed  in  human  ova 
before  the  fifteenth  or  the  twenty-fifth  day.  When  the  allantois  becomes  the 
permanent  chorion,  it  is  marked  by  a  large  number  of  hollow,  branching 
villi  over  its  entire  surface,  which  give  the  ovum  a  shaggy  appearance.  As 
the  ovum  enlarges,  over  a  certain  area  surrounding  the  point  of  attachment 
of  the  pedicle  which  connects  the  chorion  with  the  embryon,  the  villi  are 


808 


GENERATION. 


FIG.  296.— Human  embryon  at  the  third  week,  showing 
villi  covering  the  entire  chorion  (Haeckel). 


developed  more  rapidly  than  over  the  rest  of  the  surface.  Indeed,  as  the 
ovum  becomes  larger  and  larger,  the  villi  of  the  surface  outside  of  this  area 

become  more  and  more  scanty, 
lose  their  vascularity  and  finally 
disappear.  That  portion  of  the 
allantois  upon  which  the  villi  per- 
sist and  increase  in  length  and  in 
the  number  of  their  branches  is 
destined  to  form  connections  with 
the  mucous  membrane  of  the  ute- 
rus and  constitutes  the  foetal  por- 
tion of  the  placenta.  This  change 
begins  at  about  the  end  of  the  sec- 
ond month,  and  the  placenta  be- 
comes distinctly  limited  at  about 
the  end  of  the  third  month. 

It  must  be  remembered  that  as 
the  changes  go  on  which  result  in 
the  formation  of  the  permanent 
chorion  and  the  limitation  of  the 
foetal  portion  of  the  placenta,  the 

formation  of  the  umbilical  vesicle  and  the  enlargement  of  the  amnion  are 
also  progressing.  The  amnion  is  gradually  distended  by  the  increase  in  the 
quantity  of  amniotic  fluid.  It  reaches  the  internal  surface  of  the  chorion  at 
about  the  end  of  the  fourth  month,  extends  over  the  umbilical  cord  to  form 
its  external  covering,  including  the  cord  of  the  umbilical  vesicle,  and  the 
umbilical  vesicle  itself  lies  in  the  gelatinous  matter  between  the  two  mem- 
branes. 

At  about  the  beginning  of  the  fifth  month  the  ovum  is  constituted  as 
follows : 

The  foetus  floats  freely  in  the  amniotic  fluid,  attached  to  the  placenta  by 
the  umbilical  cord ;  the  chorion  presents  a  highly  vascular,  thickened  and 
villous  portion,  the  f oatal  portion  of  the  placenta ;  the  rest  of  the  chorion  is 
a  simple  membrane,  without  villi  and  without  blood-vessels;  the  amnion 
lines  the  internal  surface  of  the  chorion  and  also  forms  the  external  covering 
of  the  umbilical  cord  ;  the  umbilical-  vesicle  has  become  atrophied  and  has 
lost  its  vascularity ;  the  hernia  at  the  point  of  connection  of  the  umbilical 
vesicle  with  the  intestine  of  the  foatus  has  closed ;  and  finally  the  fcetus  has 
undergone  considerable  development. 

Umbilical  Cord. — From  the  description  given  of  the  mode  of  develop- 
ment of  the  chorion  and  the  amnion,  it  is  evident  that  the  umbilical  cord  is 
nothing  more  than  the  pedicle  which  connects  the  embryon  with  that  por- 
tion of  the  chorion  which  enters  into  the  structure  of  the  placenta.  It  is, 
indeed,  a  process  of  the  allantois,  in  which  the  vessels  eventually  become  the 
most  important  structures.  The  cord  is  distinct  at  about  the  end  of  the  first 
month ;  and  as  development  advances,  the  vessels  consist  of  two  arteries 


UMBILICAL  CORD.  809 

coming  from  the  body  of  the  f cetus,  which  are  twisted  usually  from  left  to 
right,  around  the  single  umbilical  vein.  In  addition  to  the  spiral  turns  of 
the  arteries  around  the  vein,  the  entire  cord  may  be  more  or  less  twisted, 
probably  from  the  movements  of  the  foetus. 

The  fully  developed  cord  extends  from  the  umbilicus  of  the  foetus  to  the 
central  portion  of  the  placenta,  in  which  its  insertion  usually  is  oblique ; 
although  it  may  be  inserted  at  other  points,  and  even  outside  of  the  border  of 
the  placenta,  its  vessels  penetrating  this  organ  from  the  side.  Its  usual 
length,  which  varies  very  considerably,  is  about  twenty  inches  (50-8  centi- 
metres). It  has  been  observed  as  long  as  sixty  (152-4  centimetres),  and  as 
short  as  seven  inches  (17'8  centimetres).  When  the  cord  is  very  long,  it 
sometimes  presents  knots,  or  it  may  be  wound  around  the  neck,  the  body  or 
any  of  the  members  of  the  f ostus  ;  and  this  can  be  accounted  for  only  by  the 
movements  of  the  foetus  in  utero. 

The  external  covering  of  the  cord  is  a  process  of  the  amnion ;  and  as  it 
extends  over  the  vessels,  it  includes  a  gelatinous  substance  (the  gelatine  of 
Wharton)  which  surrounds  the  vessels  and  protects  them  from  compression. 
This  gelatinous  substance  is  identical  with  the  so-called  membrana  inter- 
media, or  the  substance  included  between  the  amnion  and  the  chorion.  The 
entire  cord,  covered  with  the  gelatine  of  Wharton  and  the  amnion,  usually  is 
about  the  size  of  the  little  finger.  According  to  Robin,  the  umbilical  cord 
will  sustain  a  weight  of  about  twelve  pounds  (5-4  kilos).  As  the  amniotic 
fluid  accumulates  and  distends  the  amniotic  membrane,  this  membrane  be- 
comes more  and  more  closely  applied  to  the  cord.  The  pressure  extends 
from  the  placental  attachment  of  the  cord  toward  the  foetus,  and  it  gradu- 
ally forces  into  the  abdomen  of  the  fostus  the  loop  of  intestine,  which,  in  the 
early  periods  of  intrauterine  life,  forms  an  umbilical  hernia. 

The  vessels  of  the  cord,  the  arteries  as  well  as  the  vein,  are  provided 
with  valves.  These  are  simple  inversions  of  the  walls  of  the  vessels,  and 
they  do  not  exist  in  pairs  nor  do  they  seem  to  influence  the  current  of  blood. 
In  the  arteries  these  folds  are  situated  at  intervals  of  half  an  inch  to  two 
inches  (12-7  to  58'8  mm.),  and  they  are  more  abundant  where  the  vessels  are 
very  contorted.  In  the  vein  the  folds  are  most  abundant  near  the  placenta. 
They  are  very  irregularly  placed,  and  in  a  length  of  four  inches  (10  centi- 
metres), fifteen  folds  were  found  (Berger).  It  is  not  apparent  that  these 
valvular  folds  have  any  physiological  importance. 

As  the  allantois  is  developed,  it  presents,  in  the  early  stages  of  its  forma- 
tions, three  portions ;  an  external  portion,  which  becomes  the  chorion,  an 
internal  portion,  enclosed  in  the  body  of  the  ernbryon,  and  an  intermediate 
portion.  The  intermediate  portion  becomes  the  umbilical  cord.  As  the 
umbilicus  of  the  foetus  closes  around  the  cord,  it  shuts  off  a  portion  of  the 
allantois,  contained  in  the  abdominal  cavity,  which  becomes  the  urinary  blad- 
der ;  but  there  is  a  temporary  communication  between  the  internal  portion 
and  the  lower  portion  of  the  cord,  called  the  urachus.  This  generally  is 
obliterated  before  birth  and  is  reduced  to  the  condition  of  an  impervious 
cord ;  but  it  may  persist  during  intrauterine  life,  in  the  form  of  a  narrow 


810  GENEEATION. 

canal  extending  from  the  bladder  to  the  umbilicus,  which  is  closed  soon  after 
birth. 

Membranes  Deciduce. — In  addition  to  the  two  membranes  connected  with 
the  foetus,  there  are  two  membranes  formed  from  the  mucous  membrane  of 
the  uterus,  which  are  derived  from  the  mother  and  which  serve  still  farther 
to  protect  the  ovum.  The  chorion  is  for  the  protection  of  the  foetus ;  but  a 
portion  of  this  membrane — about  one-third  of  its  surface — becomes  closely 
united  with  a  corresponding  portion  of  the  uterine  mucous  membrane,  to 
form  the  placenta. 

As  the  fecundated  ovum  descends  into  the  uterus,  it  is  invested  with  a 
shaggy  covering,  which  is  either  the  permanent  chorion  or  one  of  the  mem- 
branes which  invests  the  ovum  previous  to  the  complete  development  of  the 
allantois.  At  this  time  the  mucous  membrane  of  the  uterus  has  undergone 
certain  changes  by  which  it  is  prepared  for  the  reception  of  the  ovum.  The 
changes  which  this  membrane  undergoes  in  menstruation  have  already  been 
described.  It  has  been  seen  that  during  an  ordinary  menstrual  period,  the 
membrane  is  increased  three  or  four  times  in  thickness  and  becomes  more  or 
less  rugous.  If  a  fecundated  ovum  descend  into  the  uterus,  the  changes  in 
the  mucous  membrane  progress.  The  glands  enlarge  and  the  mucous  mem- 
brane becomes  thicker,  so  that  at  the  end  of  the  first  month  it  measures 
about  two-fifths  of  an  inch  (10  mm.).  This  thickening  is  due  chiefly  to  de- 
velopment of  tissue  between  the  glands,  and  the  membrane  becomes  soft  and 
pulpy.  In  the  mean  time  the  ovum  has  effected  a  lodgement  between  the 
folds,  usually  at  the  f undus,  near  the  opening  of  one  of  the  Fallopian  tubes ; 
and  the  adjacent  parts  of  the  mucous  membrane  extend  over  the  ovum  so 
that  it  is  at  last  completely  enclosed.  This  occurs  at  the  twelfth  or  thirteenth 
day  (Reichert).  The  extension  of  the  mucous  membrane  which  covers  the 
ovum  becomes  the  decidua  reflexa ;  the  changed  mucous  membrane  which 
lines  the  uterus  becomes  the  decidua  vera ;  and  the  portion  of  the  mucous 
membrane  which  remains  at  the  site  of  the  placenta  becomes  the  decidua 
serotina.  The  vascular  villosities  of  the  chorion  probably  do  not,  as  was 
once  thought,  penetrate  the  uterine  tubules,  but  they  become  surrounded  by 
tissues  developed  between  these  tubules. 

As  development  advances,  the  decidua  vera  becomes  extended,  loses  its 
vessels  and  glands  and  is  reduced  to  the  condition  of  a  simple  membrane. 
The  cylindrical  epithelium  of  the  mucous  membrane  of  the  body  of  the  ute- 
rus, soon  after  fecundation,  becomes  exfoliated,  and  its  place  is  supplied  by 
flattened  cells.  This  change  is  effected  at  the  sixth  or  the  eighth  week.  The 
epithelium  of  the  cervix  retains  its  cylindrical  character,  but  most  of  the 
cells  lose  their  cilia.  The  decidua  reflexa,  which  is  thinner  than  the  decidua 
vera,  has  neither  blood-vessels,  glands  nor  epithelium. 

During  the  first  periods  of  iitero-gestation,  the  two  layers  of  decidua  are 
separated  by  a  small  quantity  of  an  albuminous  and  sometimes  a  sanguinolent 
fluid ;  but  this  disappears  at  about  the  end  of  the  fourth  month,  and  the 
membranes  then  come  in  contact  with  each  other.  They  soon  become  so 
closely  adherent  as  to  form  a  single  membrane,  which  is  in  contact  with  the 


FORMATION  OF  THE  PLACENTA. 


811 


chorion.  Sometimes,  at  full  term,  the  membranes  of  the  foetus  can  be  sepa- 
rated from  the  decidua ;  but  frequently  all  of  the  different  layers  are  closely 
adherent  to  each  other. 

The  changes  just  described  are  not  participated  in  by  the  mucous  mem- 
brane of  the  neck  of  the  uterus.  The  glands  in  this  situation  secrete  a  semi- 
solid,  transparent,  viscid  mucus,  which  closes  the  os  and  is  sometimes  called 
the  uterine  plug. 

Toward  the  fourth  month  a  very  delicate,  soft,  homogeneous  layer  ap- 
pears over  the  muscular  fibres  of  the  uterus,  beneath  the  decidua  vera,  which 
is  the  beginning  of  a  new  mucous  membrane.  This  is  developed  very  gradu- 
ally, and  the  membrane  is  completely  restored  about  two  months  after  partu- 
rition. 

Formation  of  the  Placenta. — At  about  the  end  of  the  second  month  the 
villi  of  the  chorion  become  enlarged  and  arborescent  over  that  part  which 
eventually  forms  the  foetal  portion  of  the  placenta.  They  are  then  highly 
vascular  and  are  embedded  in  the  soft  substance  of  the  hypertrophied  mucous 


FIG.  297.— Diagrammatic  figure,  shotting  the  placenta  and  deciduoE  (Liegeois). 

c,  embryon  ;  t,  intestine  ;  p,  pedicle  of  the  umbilical  vesicle  ;  o,  umbilical  vesicle  :  m,  m,  TO,  amnion  ; 
a',  chorion  ;  a,  lower  end  of  the  umbilical  cord  ;  q.  q,  vascular  tufts  of  the  chorion,  constituting  the 
foetal  portion  of  the  placenta  ;  n',  n,  maternal  portion  of  the  placenta  ;  n,  w,  decidua  vera  ;  «,  decid- 
ua reflexa. 

membrane.  At  the  same  time  the  villi  over  the  rest  of  the  chorion  are  ar- 
rested in  their  growth,  and  they  finally  disappear  during  the  third  month. 
The  blood-vessels  penetrate  the  villi  in  the  form  of  loops  at  about  the  fourth 
week ;  and  the  placenta  is  distinctly  marked  at  about  the  end  of  the  third 


812  GENERATION. 

month.  The  placenta  then  rapidly  assumes  the  anatomical  characters  ob- 
served after  it  may  be  said  to  be  fully  developed. 

The  fully  formed  placenta  occupies  about  one-third  of  the  uterine  mu- 
cous membrane,- and  generally  is  rounded  or  ovoid  in  form,  with  a  distinct 
border  connected  with  the  decidua  and  the  chorion.  It  is  seven  to  nine 
inches  (18  to  23  centimetres)  in  diameter,  a  little  more  than  an  inch  (2-5 
centimetres)  in  thickness  at  the  point  of  penetration  of  the  umbilical  cord, 
slightly  attenuated  toward  the  border,  and  weighs  fifteen  to  thirty  ounces 
(425  to  850  grammes).  Its  foetal  surface  is  covered  with  the  smooth,  amni- 
otic  membrane,  and  its  uterine  surface,  when  detached,  is  rough,  and 
divided  into  irregular  lobes,  or  cotyledons,  half  an  inch  to  an  inch  and  a 
half  (12-7  to  38-l  mm.)  in  diameter.  Between  these  lobes,  are  membranes, 
called  dissepiments,  which  penetrate  into  the  substance  of  the  placenta,  and 
at  its  border  extend  as  far  as  the  foetal  surface. 

Upon  the  uterine  surface  of  the  placenta,  is  a  thin,  soft  membrane,  the 
decidua  serotina.  This  is  composed  of  amorphous  matter,  a  large  number  of 
granulations,  and  colossal  cells  with  enlarged  and  multiple  nuclei.  A  portion 
of  this  membrane  is  not  thrown  off  with  the  placenta  in  parturition,  but  pro- 
cesses extend  into  the  placenta  and  closely  surround  the  foetal  tufts. 

The  two  arteries  of  'the  umbilical  cord  branch  upon  the  foetal  surface  of 
the  placenta,  beneath  the  amnion,  and  finally  penetrate  the  substance  of  the 
organ.  The  branches  of  the  veins,  which  are  about  sixteen  in  number,  con- 
verge toward  the  cord  and  unite  to  form  the  umbilical  vein.  Upon  the 
uterine  surface  of  the  placenta  are  oblique  openings  of  a  large  number  of 
veins  which  return  the  maternal  blood  to  the  uterine  sinuses.  There  are  also 
the  small,  spiral  arteries,  which  pass  into  the  substance  of  the  organ,  to  supply 
blood  to  the  maternal  portion.  These  are  the  "  curling  arteries,"  described 
by  John  Hunter.  If  the  umbilical  arteries  be  injected,  the  fluid  is  returned 
by  the  umbilical  vein,  having  passed  through  the  vascular  tufts  of  the  foetal 
portion  of  the  placenta. 

According  to  Winkler,  there  are  three  kinds  of  foetal  villi :  I.  Those 
which  terminate  just  beneath  the  chorion,  without  penetrating  the  vascular 
lacunae.  2.  Longer  villi,  which  hang  free  in  the  lacunae.  3.  Long,  branch- 
ing villi,  which  penetrate  more  deeply  into  the  placenta,  some  extending  as 
far  as  its  uterine  surface. 

The  great  vascular  spaces,  or  lacunae  of  the  maternal  portion  of  the  pla- 
centa, present  a  number  of  trabeculae,  which  extend  from  the  uterine  to  the 
foetal  surface ;  and  between  these  trabeculge,  are  exceedingly  delicate,  trans- 
verse and  oblique  secondary  trabecular  processes.  The  blood-vessels  of  the 
foetal  tufts  are  surrounded  with  a  gelatinous,  connective-tissue  structure,  and 
as  late  as  the  sixth  month  (Heinz)  are  covered  with  a  layer  of  chorionic  cells. 

The  mode  of  formation  of  the  vascular  spaces  in  the  placenta  has  been  a 
subject  of  much  discussion.  The  following,  however,  seems  to  be  the  most 
reasonable  view  with  regard  to  this  question  :  That  portion  of  the  uterine 
mucous  membrane  which  becomes  the  maternal  portion  of  the  placenta  ex- 
tends from  the  decidua  serotina  and  surrounds  the  villi,  which  are  embedded 


DEVELOPMENT  OF  THE  OVUM.  813 

in  its  substance.  As  the  arborescent  villi  extend,  they  encroach  upon  the 
blood-vessels  of  the  prolongations  from  the  serotina,  which  latter  become 
much  enlarged  and  finally  form  the  great  vascular  spaces  traversed  by  the 
trabeculae  mentioned  above.  At  term,  however,  according  to  Heinz  (1888), 
the  foetal  vessels  have  lost  their  covering  of  epithelium,  which  is  observed  in 
the  earlier  months  of  pregnancy.  Thus  the  most  important  parts  of  the 
placenta  are  formed  by  an  interlacement  of  the  villi  of  the  chorion  with  the 
altered  structures  of  the  mucous  membrane  of  the  uterus. 

In  the  human  subject  the  maternal  and  fcetal  portions  of  the  placenta 
are  so  closely  united  that  they  can  not  be  separated  from  each  other.  In 
parturition  the  curling  arteries  and  the  veins  on  the  uterine  surface  of  the 
placenta  are  torn  off,  and  the  placenta  then  consists  of  the  parts  just  de- 
scribed ;  the  torn  ends  of  the  vessels  attached  to  the  uterus  are  closed  by 
the  contractions  of  the  surrounding  muscular  fibres ;  and  the  blood  which 
is  discharged  is  derived  mainly  from  the  placenta  itself. 

Uses  of  the  Placenta. — The  placenta  is  the  respiratory,  excretory  and 
nutritive  organ  of  the  fcetus.  Its  action  as  a  respiratory  organ  has  already 
been  mentioned  in  connection  with  the  physiology  of  respiration.  It  cer- 
tainly serves  as  an  organ  for  the  elimination  of  carbon  dioxide,  and  probably 
also  for  other  products  of  excretion.  It  is  the  only  source  of  materials  for 
the  development  and  nutrition  of  the  fcetus.  It  is  thought  that  cells  de- 
rived from  the  serotina  elaborate  a  fluid  called  uterine  milk,  which  is  ab- 
sorbed by  the  fcetal  tufts.  This  fluid  has  been  collected  from  between  the 
fcetal  tufts  of  the  placenta  of  the  cow,  and  has  been  found  to  contain  fatty 
matter,  albuminous  matters  and  certain  salts,  but  no  sugar  or  caseine  (Gam- 
gee).  It  is  not  probable,  however,  that  such  a  fluid  exists  in  the  human 
placenta;  although  "uterine  milk"  of  the  ruminants  was  mentioned  dis- 
tinctly by  Haller,  and  was  alluded  to  by  even  earlier  writers. 

DEVELOPMENT  OF  THE  OVUM. 

The  product  of  generation  retains  the  name  of  ovum  until  the  form  of 
the  body  begins  to  be  apparent,  when  it  is  called  the  embryon.  At  the 
fourth  month,  about  the  time  of  quickening,  it  is  called  the  fcetus,  a  name 
which  it  retains  during  the  rest  of  intrauterine  life.  The  membranes  are 
appendages  developed  for  the  purposes  of  protection  and  nutrition ;  and  the 
embryon  itself,  in  the  mammalia,  is  developed  from  a  restricted  portion  of 
the  layers  of  cells  resulting  from  the  segmentation  of  the  vitellus. 

The  formation  of  the  blastoderm  ic  cells  and  the  appearance  of  the  groove 
which  is  subsequently  developed  into  the  neural  canal  have  already  been  de- 
scribed. At  this  portion  of  the  ovum,  there  is  a  thickening  of  the  blastoderm, 
which  then  presents  three  layers,  the  mesoblast,  the  thickest  and  most  impor- 
tant, being  developed  from  the  opposite  surfaces  of  the  epiblast  and  the  hypo- 
blast.  The  earliest  stages  of  development  have  been  studied  almost  exclu- 
sively in  the  chick ;  and  it  is  probable  that  the  appearances  here  observed 
nearly  represent  the  earlier  processes  of  development  in  the  human  subject. 

Development  of  the  Cavities  and  Layers  of  the  Trunk,  in  the  Chick.— As, 

63 


814 


GENERATION. 


an  introduction  to  a  description  of  the  development  of  special  organs  in  the 
human  subject  and  in  mammals,  it  will  be  found  very  useful  to  study  the 
first  stages  of  development  in  the  chick,  which  will  give  an  idea  of  the  ar- 
rangement of  the  different  blastodermic  layers  and  the  way  in  which  they 
are  developed  into  the  different  parts  of  the  trunk,  with  the  mode  of  forma- 
tion of  the  great  cavities.  The  figures  by  which  this  description  is  illustrated 
are  those  of  Briicke,  which  were  photographed  on  wood  from  diagrams  made 
from  actual  preparations  by  Seboth.  These  figures,  therefore,  can  hardly  be 
called  diagrammatic. 

Fig.  298  shows  one  of  the  earliest  stages  of  development  in  the  chick.     In 
this  figure,  the  upper  layer  of  dark  cells  (B,  B)  represents  the  epiblast.     The 


FIG.  298. 


lower  layer  of  dark  cells  (D,  D)  represents  the  hypoblast.  The  middle  layer 
of  lighter  cells  is  the  mesoblast,  which,  toward  the  periphery,  is  split  into  two 
layers.  This  figure  represents  a  transverse  section.  At  A,  is  a  transverse 
section  of  the  groove  which  is  subsequently  developed  into  the  canal  for  the 
spinal  cord.  Beneath  this  groove,  is  a  section  of  a  rounded  cord  (E),  the 
chorda  dorsalis.  The  openings  (G,  G)  represent  the  situation  of  the  two 
aorta}.  The  other  cavities  are  as  yet  indistinct  in  this  figure. 

Fig.  299  shows  the  same  structures  at  a  more  advanced  stage  of  develop- 
ment.    The  dorsal,  or  vertebral  plates,  which  bound  the  furrow  (A)  in  Fig. 


FIG.  299. 


298,  are  closed  above,  and  include  (A)  the  neural  canal.  The  chorda  dorsalis 
(E)  is  separated  from  the  cells  surrounding  it  in  Fig.  298.  The  epiblast 
(B,  B)  and  the  hypoblast  (D,  D)  present  certain  curves  which  follow  the 
arrangement  of  the  cells  of  the  mesoblast.  By  the  sides  of  the  boundaries 
of  the  neural  canal,  are  two  distinct  masses  of  cells  (C,  C),  which  are  devel- 
oped into  the  vertebrae.  Outside  of  these  masses  of  cells,  are  two  smaller 
collections  of  cells,  afterward  developed  into  the  "VVolffian  bodies.  Beneath 
those  two  masses,  are  two  large  cavities  (G,  G),  the  largest  cavities  shown  in 


DEVELOPMENT  OF  THE  OVUM.  815 

Fig.  299,  presenting  an  irregular  form,  which  are  sections  of  the  two  primi- 
tive aortae.  The  two  openings  (H,  H)  afterward  become  the  pleuro-peritoneal 
cavity. 

In  Fig.  300  the  parts  are  still  farther  developed.  The  neural  canal  is 
represented  (A)  nearly  the  same  as  in  Fig.  299,  with  the  chorda  dorsalis  (E) 
just  beneath  it.  A  groove,  or  gutter  (U) 
has  been  formed  in  front,  which  is  the 
groove  of  the  intestinal  canal.  This 
remains  open  at  this  time  and  is  lined 
by  the  hypoblast.  Just  above  D,  is  a 
single  opening  (G),  which  is  formed  by 
the  union  of  the  two  openings  (G,  G)  in 
Figs.  298  and  299 ;  and  this  is  the  ab- 
dominal aorta,  which  has  here  become 
single.  The  two  openings  (H,  H)  rep- 
resent a  section  of  the  pleuro-peritoneal 
cavity.  The  outer  wall  of  this  cavity  is 
the  outer  visceral  plate,  which  is  devel- 

FIG  300 

oped  into  the  muscular  walls  of  the  ab- 
domen. The  lower  and  inner  wall  is  the  inner  visceral  plate,  which  forms 
the  main  portion  of  the  intestinal  wall.  The  outer  wall  is  the  outer  layer  of 
the  mesoblast,  and  the  inner  wall  is  the  inner  layer  of  the  same  membrane. 
The  two  round  orifices  (I,  I)  are  sections  of  the  Wolffian  ducts.  The  space 
(#,  b)  is  the  amniotic  cavity. 

The  figures  just  described,  it  must  be  borne  in  mind,  represent  transverse 
sections  of  the  body  of  the  chick,  made  through  the  middle  portion  of  the 
abdomen.  The  posterior  parts,  it  is  seen,  are  developed  first,  the  situation  of 
the  vertebral  column  being  marked  soon  after  the  enclosure  of  the  neural 
canal,  by  the  vertebral  plates ;  and  at  about  the  same  time,  the  two  aortas 
make  their  appearance,  with  the  first  traces  of  the  pleuro-peritoneal  cavity. 
The  next  organs  in  the  order  of  development,  after  the  vascular  system,  are 
the  Wolffian  bodies.  The  intestinal  canal  is  then  a  simple  groove,  and  the 
embryon  is  entirely  open  in  front.  In  the  farther  process  of  development, 
the  visceral  plates  advance  and  close  over  the  abdominal  cavity,  as  the 
medullary  plates  have  closed  over  the  neural  canal.  Thus  there  is  formed  a 
closed  tube,  the  intestine,  lined  by  the  hypoblast,  the  walls  of  the  intestine 
being  formed  of  the  inner  layer  of  the  mesoblast.  This  brings  the  external 
layer  of  the  mesoblast  around  the  intestine,  to  form  the  muscular  walls  of  the 
abdomen,  the  cavity  (Fig.  300,  H,  H)  being  the  peritoneal  cavity,  and  the 
external  covering  being  the  epiblast.  At  this  time  the  Wolffian  bodies  lie 
next  the  spinal  column,  between  the  intestine  and  the  abdominal  walls,  with 
the  single,  abdominal  aorta  situated  behind  the  intestine. 

DEVELOPMENT  OF  THE  SKELETON,  MUSCULAR  SYSTEM  AND  SKIN. 

Chorda  Dorsalis. — One  of  the  earliest  structures  observed  in  the  develop- 
ing embryon  is  the  chorda  dorsalis,  or  notochord.  This  is  situated  beneath 


816 


GENEEATION. 


the  neural  canal  and  extends  the  entire  length  of  the  body.  It  is  formed  of 
a  cord  of  simple  cells,  and  marks  the  situation  of  the  vertebral  column,  though 
it  is  not  itself  developed  into  the  vertebras,  which  grow  around  it  and  encroach 
upon  its  substance  until  it  finally  disappears.  In  many  mammals  the  noto- 
chord  presents  a  slight  enlargement  at  the  cephalic  extremity,  which  extends 
to  the  auditory  vesicles  and  it  is  somewhat  diminished  in  size  at  the  caudal  ex- 
tremity. By  the  sides  of  this  cord  are  masses  of  cells  which  unite  in  front 
of  the  neural  canal  and  eventually  are  developed  into  the  vertebrae.  These  are 

called  protovertebrae,  or  somites,  and 
are  shown  in  Fig.  303  (C,  in  A  and  B). 
Twelve  pairs  of  protovertebrae  are 
shown  in  Fig.  303,  C.  In  the  chick, 
two  pairs  are  first  formed  in  the  up- 
per cervical  region,  on  the  second 
day.  They  rapidly  increase  in  .num- 
ber, from  above  downward,  until  at 
the  fourth  day  there  are  twenty-one 
or  twenty-two  pairs.  They  are  not 
formed  in  the  region  of  the  head  or 
at  the  lowest  part  of  the  vertebral 
column.  The  vertebrae,  as  they  are 
developed,  are  formed  of  temporary 
cartilaginous  structure,  gradually  ex- 
tending around  the  chorda  dorsalis, 


Fio.  301. — The  first  six  cervical  vertebrae  of  the  em- 
bryon  of  a  rabbit  one  inch  in  length  (Robin). 

a,  6,  cephalic  portion  of  the  notochord,  exposed  by 
the  removal  of  the  cartilage  ;  6,  portion  of  the 
chorda  dorsalis  slightly  enlarged,  which,  in  this 
embryon,  was  situated  between  the  atlas  and 
the  occipital  bone  :  c,  odontoid  process  ;  d, 
base  of  the  odontoid  process ;  e,  inferior,  or 
second  part  of  the  body  of  the  axis ;  /,  k,  en- 
largements of  the  chorda  dorsalis,  between  the 
vertebrae  ;  a,  cartilage  of  the  lateral  portion  of 
the  atlas ;  h.  lateral  portion  of  the  axis ;  t,  i, 
transverse  apophyses  of  vertebrae. 


FIG.  302. — Human  embryon,  about  one  month  old, 
showing  the  large  size  of  the  head  and  up- 
per parts  of  the  body,  the  twisted  form  of  the 
spinal  column,  the  rudimentary  condition  of 
the  upper  and  lower  extremities  and  the  rudi- 
mentary tail  at  the  end  of  the  spinal  column 
(Dalton). 


which  then  occupies  the  axis  of  the  spinal  column.  These  cartilages  are  not 
divided  at  the  lines  of  separation  of  the  protovertebrae,  but  the  protovertebrae 
fuse  together  and  the  cartilages  which  are  to  be  developed  into  the  bodies  of 
the  vertebras  are  so  divided  off,  that  one  cartilage  occupies  the  place  of  the 
adjacent  halves  of  two  protovertebrae.  Between  the  bodies  of  the  vertebrae, 
the  chorda  dorsalis  presents  regular  enlargements  surrounded  by  a  delicate 
membrane.  As  ossification  of  the  spinal  column  advances,  that  portion  of 


DEVELOPMENT  OF  THE  SKELETON.          817 

the  chorda  dorsalis  which  is  surrounded  by  the  bodies  of  the  vertebra?  disap- 
pears, leaving  the  enlargements  between  the  vertebrae  distinct.  These  en- 
largements, which  are  not  permanent,  are  gradually  invaded  by  fibrous  tis- 
sue, their  gelatinous  contents  disappear,  and  the  intervertebral  disks,  com- 
posed of  fibro-cartilaginous  structure,  remain.  These  disks  are  permanent 
between  the  cervical,  the  dorsal  and  the  lumbar  vertebras ;  but  they  eventu- 
ally disappear  from  between  the  different  parts  of  the  sacrum  and  coccyx,  as 
these  are  consolidated,  this  occurring,  in  the  human  subject,  between  the 
ninth  and  the  twelfth  years. 

Vertebral  Column,  etc. — In  Figs.  299  and  300  (C,  C),  are  seen  the  two 
masses  of  cells  (protovertebras)  situated  by  the  sides  of  the  neural  canal,  which 
are  destined  to  be  developed  into  the  vertebras.  These  cells  extend  around 
and  encroach  upon  the  chorda  dorsalis,  and  form  the  bodies  of  the  vertebras. 
They  also  extend  over  the  neural  canal,  closing  above,  and  their  processes  are 
called  the  medullary,  or  dorsal  plates.  Sometimes  the  dorsal  plates  fail  to 
close  at  a  certain  point  in  the  spinal  column,  and  this  constitutes  the  mal- 
formation known  as  spina  bifida.  From  the  sides  of  the  bodies  of  the  verte- 
bras, the  various  processes  of  these  bones  are  formed.  As  the  spinal  column 
is  developed,  its  lower  portion  presents  a  projection  beyond  the  pelvis,  which 
constitutes  a  temporary  caudal  appendage,  curved  toward  the  abdomen ;  but 
this  no  longer  projects  after  the  bones  of  the  pelvis  are  fully  developed.  At 
the  same  time  the  entire  vertebral  column  is  curved  toward  the  abdomen, 
and  it  is  twisted  upon  its  axis,  from  left  to  right,  so  that  the  anterior  face  of 
the  pelvis  presents  a  right  angle  to  the  upper  part  of  the  body ;  but  as  the 
inferior  extremities  and  the  pelvis  are  developed,  the  spine  becomes  straight. 
The  vertebras  make  their  appearance  first  in  the  middle  of  the  dorsal  region, 
from  which  point  they  rapidly  extend  upward  and  downward,  until  the  spinal 
column  is  complete. 

At  the  base  of  the  skull,  on  either  side  of  the  superior  prolongation  of  the 
chorda  dorsalis,  are  two  cartilaginous  processes,  which  are  developed  into  the 
so-called  cranial  vertebras.  In  this  cartilaginous  mass,  three  ossific  points 
appear,  one  behind  the  other.  The  posterior  point  of  ossification  is  for  the 
basilar  portion  of  the  occipital  bone,  which  is  developed  in  the  same  way  as 
one  of  the  vertebras ;  the  middle  point  is  for  the  posterior  portion  of  the 
sphenoid ;  and  the  anterior  point  is  for  the  anterior  portion  of  the  sphenoid. 
The  frontal  bone,  the  parietal  bone,  the  temporal  bone  and  a  portion  of  the 
occipital  bone  are  developed  from  the  connective  tissue,  without  the  inter- 
vention of  pre-existing  cartilaginous  structure.  At  the  time  when  the  verte- 
bras are  developed,  with  their  laminas  and  their  spinous  and  transverse  pro- 
cesses, the  ribs  extend  over  the  thorax,  and  the  clavicle,  scapula  and  sternum 
make  their  appearance. 

At  about  the  beginning  of  the  second  month,  four  papillary  prominences, 
which  are  the  first  traces  of  the  arms  and  legs,  appear  on  the  body  of  the 
embryon.  These  progressively  increase  in  length,  the  arms  appearing  near 
the  middle  of  the  embryon,  and  the  legs,  at  the  lower  portion.  Each  extrem- 
ity is  divided  into  three  portions,  the  arm,  forearm  and  hand,  for  the  upper 


818  GENERATION. 

extremities,  and  the  thigh,  leg  and  foot,  for  the  lower  extremities.  At  the 
end  of  each  extremity,  there  are,  finally,  divisions  into  the  fingers  and  toes, 
with  the  various  cartilages  and  bones  of  all  of  these  parts,  and  their  articula- 
tions. 

Very  early  in  intrauterine  life  the  skeleton  begins  to  ossify,  from  little 
bony  points  which  appear  in  the  cartilaginous  structure.  The  first  points 
appear  at  nearly  the  same  time — about  the  beginning  of  the  second  month — 
in  the  clavicle  and  the  upper  and  the  lower  jaw.  Similar  ossific  points, 
which  gradually  extend,  are  also  seen  in  other  parts,  the  head,  ribs,  pelvis, 
scapula,  metacarpus  and  metatarsus,  and  the  phalanges  of  the  fingers  and 
toes.  At  birth  the  carpus  is  entirely  cartilaginous,  and  it  does  not  begin  to 
ossify  until  the  second  year.  The  same  is  true  of  the  tarsus,  except  the 
calcaneum  and  astragalus,  which  ossify  just  before  birth.  The  pisiform 
bone  of  the  carpus  is  the  last  to  take  on  osseous  transformation,  this  occur- 
ring between  the  twelfth  and  the  fifteenth  years.  As  ossification  progresses, 
the  deposits  in  the  various  ossific  points  gradually  extend  until  they  reach 
the  joints,  which  remain  incrusted  with  the  permanent,  articular  cartilage. 

While  the  skeleton  is  thus  developing,  the  muscles  are  formed  from  the 
outer  layer  of  the  mesoblast,  and  the  visceral  plates  close  over  the  thorax 
and  abdomen  in  front,  leaving  an  opening  for  the  umbilical  cord.  The  vari- 
ous tissues  of  the  external  parts,  particularly  the  muscles,  begin  to  be  distinct 
at  the  end  of  the  second  month.  The  deep  layers  of  the  dorsal  muscles  are 
the  first  to  be  distinguished ;  then  successively,  the  long  muscles  of  the  neck, 
the  anterior  straight  muscles  of  the  head,  the  straight  and  transverse  mus- 
cles of  the  abdomen,  the  muscles  of  the  extremities,  the  superficial  muscles 
of  the  back,  the  oblique  muscles  of  the  abdomen  and  the  muscles  of  the  face. 

The  skin  appears  at  about  the  beginning  of  the  second  month,  when  it 
is  very  delicate  and  transparent.  At  the  end  of  the  second  month  the  epi- 
dermis may  be  distinguished.  The  sebaceous  follicles  are  developed  at  the 
third  month ;  and  at  about  the  fifth  month  the  surface  is  covered  with  their 
secretion  mixed  with  desquamated  epithelium.  This  cheesy  substance  con- 
stitutes the  vernix  caseosa.  At  the  third  month  the  nails  make  their  appear- 
ance, and  the  hairs  begin  to  grow  at  about  the  fifth  month.  The  sudoripa- 
rous glands  first  appear  at  about  the  fifth  month,  by  the  formation  of  flask- 
like  processes  of  the  true  skin,  which  are  gradually  elongated  and  convoluted, 
until  they  are  fully  developed  only  a  short  time  before  birth. 

DEVELOPMENT  OF  THE  NERVOUS  SYSTEM. 

It  has  been  seen,  in  studying  the  development  of  the  spinal  column,  how 
the  dorsal,  or  medullary  plates  close  over  the  groove  for  the  neural  canal. 
In  the  interior  of  this  canal,  the  cerebro-spinal  axis  is  developed,  by  cells 
which  gradually  encroach  upon  its  caliber,  until  there  remains  only  the  small, 
central  canal  of  the  spinal  cord,  communicating  with  the  ventricles  of  the 
brain.  As  the  nervous  tissue  is  developed  in  the  interior  of  the  neural  canal, 
there  is  a  separation  of  the  histological  elements  at  the  surface,  to  form  the 
membranes.  The  dura  mater  and  the  pia  mater  are  formed  first,  appearing 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM. 


819 


at  about  the  end  of  the  second  month,  while  the  arachnoid  is  not  distinct 
until  the  fifth  month.  The  nerves  are  not  produced  as  prolongations  from 
the  cord  into  the  various  tissues  nor  do  they  extend  from  the  tissues  to  the 
cord,  but  they  are  developed  in  each  tissue  by  a  separation  of  histological 
elements  from  the  cells  of  which  the  parts  are  originally  constituted.  The 
nerves  of  the  sympathetic  system  are  developed  in  the  same  way. 

The  mode  of  development  of  the  spinal  cord  is  thus  sufficiently  simple ; 
but  with  the  growth  of  the  embryon  dilatations  are  observed  at  the  superior 
and  at  the  inferior  extremities  of  the  neural  canal.  The  cord  is  nearly  uni- 
form in  size  in  the  dorsal  region,  marked  only  by  the  regular  enlargements 
at  the  sites  of  origin  of  the  spinal  nerves ;  but  there  soon  appears  an  ovoid 
dilatation  below,  which  forms  the  lumbar  enlargement,  from  which  the  nerves 
are  given  off  to  the  inferior  extremities,  and  the  brachial  enlargement  above, 
where  the  nerves  of  the  superior  extremities  take  their  origin.  At  the  same 
time  there  is  a  more  marked  dilatation  of  the  canal  at  its  cephalic  extremity. 
Here  a  single  enlargement  appears,  which  is  soon  divided  into  three  vesicles, 
called  the  anterior,  middle  and  posterior  cerebral  vesicles.  These  become 
more  and  more  distinct  as  development  advances.  The  formation  of  these 
parts  is  shown  in  Fig.  303.  This  figure,  in  C,  shows  the  projections,  on  either 
side,  of  the  vesicles  which  are 
eventually  developed  (o,  Fig. 
303,  C)  into  the  nervous  por- 
tions of  the  organ  of  vision. 

The  three  cerebral  vesicles 
now  undergo  farther  changes. 
The  superior,  or  the  first  prim- 
itive vesicle,  is  soon  divided 
into  two  secondary  vesicles,  the 
anterior  of  which  becomes  the 
cerebral  hemispheres,  and  the 
posterior,  the  optic  thalami, 
which  are  eventually  covered 
by  the  greater  relative  develop- 
ment of  the  hemispheres.  The 
middle,  or  second  primitive 
vesicle,  does  not  undergo  divis- 
ion and  is  developed  into  the 
tubercula  quadrigemina.  The 
posterior,  or  third  primitive  vesicle,  is  divided  into  two  secondary  vesicles, 
the  anterior  of  which  becomes  the  cerebellum,  and  the  posterior,  which  is 
covered  by  the  anterior,  the  medulla  oblongata  and  the  pons  Varolii.  While 
this  division  of  the  primitive  cerebral  vesicles  is  going  on,  the  entire  chain 
of  encephalic  ganglia  becomes  curved  from  behind  forward,  forming  three 
prominent  angles.  The  first  of  these  angles  or  prominences  (e,  Fig.  304, 
A,  B,  C),  counting  from  before  backward,  is  formed  by  a  projection  of  the 
.tubercula  quadrigemina,  which  at  this  time  constitute  the  most  projecting 


FIG.  303. — Development  of  the  nervous  system  of  the  chick 
(Longet,  after  Wagner). 

A,  the  two  primitive  halves  of  the  nervous  system,  twenty- 
four  hours  after  incubation  :  B,  the  same,  thirty-six  hours 
after :  C.  the  same,  at  a  more  advanced  stage,  c,  the 
protovertebree  ;  6,  posterior  dilatation  (the  lumbar  en- 
largement); d,  anterior  dilatation  of  the  neural  canal ; 
1.  2.  3,  anterior,  middle  and  inferior  cerebral  vesicles;  a, 
slight  flattening  of  the  anterior  cerebral  vesicle;  o,  for- 
mation of  the  ocular  vesicles. 


820  GENERATION. 

portion  of  the  encephalic  mass  ;  the  second  prominence  (c,  Fig.  304),  situated 
behind  the  tubercula  quadrigemina,  is  formed  by  the  projection  of  the  cere- 
bellum ;  the  third  (d,  Fig.  304,  A,  B,  C),  is  the  bend  of  the  superior  portion 
of  the  spinal  cord.  These  projections  and  the  early  formation  of  certain 
parts  of  the  encephalon  in  the  human  subject  are  illustrated  in  Fig.  304. 

The  cerebrum  is  developed  from  the  anterior  division  of  the  first  primitive 
cerebral  vesicle.  The  development  of  this  part  is  more  rapid  in  its  lateral 
portions  than  in  the  median  line,  which  divides  the  cerebrum  imperfectly 
into  two  lateral  halves,  forming  in  this  way  the  great  longitudinal  fissure.  At 

the  same  time,  by  the  rapid 
development  of  the  posterior 
portion,  it  extends  over  the 
optic  thalami,  the  corpora 
quadrigemina  and  the  cere- 
bellum. Until  the  end  of  the 
fourth  month,  the  hemi- 
spheres are  smooth  on  their 

FIG.  304.  —  Development  of  the  spinal  cord  and  brain  of  the 

human  subject  (Longet,  after  Tiedemann).  SUrf  aC6  ;    but  they  then   begin 

A,  brain  and  spinal  cord  of  an  embryon  of  seven  weeks  ;  lat-     ,  ,    i  •, 

eraiview.  to  present  large  depressions, 

B,  the  same,  from  an  embryon  farther  advanced  in  develop-     PIT        •    „  »  i  i        *  .v  „      • 

ment;  6,  spinal  cord;  d,  enlargement  of  the  spinal  cord,    lOllOWing  lOldS  OI  me  pia  ma- 
with  its  anterior  curvature;  c,  cerebellum  ;  e,  tubercula    j.         •nrV.ioVi     Qr-a   fVio    fifat-    /-./-.r> 
quadrigemina  ;  /,  optic  thalamus  ;    g,  cerebral    hemi-      'er>  Will 

C,  brawfand  spinal  cord  of  an  embryon  of  eleven  weeks  ;  6,    Volutions,     these       increasing 

spinal  cord;  d,  enlargement  of  the  spinal  cord,  with  its    -o-nj/qiv  in    rmmhpr    nnrJ 
anterior  curvature;  c,  cerebellum;  e,   tubercula  quadri-    «««**     *] 


e:  g'  cerebral  hemisPhere8;  °'°Ptic  nerve  of  the  plexity,    especially  after  the 

C',  the  same  parts  in  a  vertical  section  in  the  median  line,  from  OOVem-t-Vi  mrvntV»        TVio  at>r>tnm 

before  backward  ;  6,  membrane  of  the  spinal  cord,  turned  seventn  HlOnin. 

backward  :  d,  second  curvature  of  the  upper  portion  of  lnr>irliTm  ia  fl-»on  fnrmorl    \\v  an 
the  spinal  cord,  which  has  become  thickened  and  consti-  eu'  DJ  dn 

tutes  the  peduncles  of  the  cerebrum  ;  e.  tubercula  quadri-  plpva+irm     rvf    nprvniic     mai-fpr 
gemina  ;  /,  optic  thalami,  covered  by  the  hemispheres. 

from  the  base,  which  divides 

the  lower  portion  of  the  space  left  between  the  hemispheres  as  they  ascend, 
and  forms  the  two  lateral  ventricles.  At  the  base  of  these,  are  developed 
the  corpora  striata.  The  septum  lucidum  is  formed  of  two  laminge,  with  a 
small  space  between  them,  which  is  the  cavity  of  the  fifth  ventricle.  The 
posterior  division  of  this  first  primitive  vesicle  forms  the  optic  thalami. 
These  become  separated  in  front  into  two  lateral  halves,  but  they  remain 
connected  together  at  their  posterior  portion,  which  becomes  the  posterior 
commissure.  The  central  canal  of  the  cord  is  prolonged  upward  between 
the  optic  thalami,  and  forms  the  third  ventricle,  which  is  covered  by  the 
hemispheres. 

The  second,  or  middle  cerebral  vesicle,  becomes  filled  with  medullary 
substance,  extends  upward  and  forms  the  peduncles  of  the  cerebrum,  the 
upper  portion  being  divided  to  form  the  tubercula  quadrigemina. 

The  anterior  portion  of  the  third  primitive  vesicle  is  developed  into  the 
cerebellum,  the  convolutions  of  which  appear  at  about  the  fifth  month.  Its 
posterior  portion  forms  the  medulla  oblongata,  in  the  substance  of  which  is 
the  fourth  ventricle,  communicating  with  the  third  ventricle,  by  the  aque- 
duct of  Sylvius,  which  is  left  in  the  development  of  the  middle  vesicle.  At. 


DEVELOPMENT  OF  THE  NERVOUS  SYSTEM.  821 

about  the  fourth  month  there  is  a  deposition  of  nervous  matter  in  front  and 
above,  forming  the  pons  Varolii. 

In  Fig.  304  (C,  o),  it  is  seen  that  the  vesicles  for  the  organs  of  vision 
appear  very  early,  as  lateral  offshoots  of  the  anterior  cerebral  vesicle.  These 
gradually  increase  in  size  and  advance  anteriorly,  as  development  of  the  other 
parts  progresses.  The  eyes  are  situated  at  first  at  the  sides  of  the  head,  grad- 
ually approaching  the  anterior  portion.  At  the  extremity  of  each  of  these 
lateral  prolongations,  a  rounded  mass  appears,  which  becomes  the  globe  of  the 
eye.  The  superficial  portions  of  the  globe  are  developed  into  the  sclerotic 
and  the  cornea,  which  seem  to  be  formed  of  a  process  from  the  dura  mater. 
The  pedicle  attached  to  the  globe  becomes  the  optic  nerve.  The  iris  is  de- 
veloped at  about  the  seventh  week,  and  is  at  first  a  simple  membrane,  with- 
out any  central  opening.  As  the  pupil  appears,  it  is  closed  by  a  vascular 
membrane — which  probably  belongs  to  the  capsule  of  the  crystalline  lens — 
called  the  pupillary  membrane.  This  membrane  gradually  disappears,  by 
an  atrophy  extending  from  the  centre  to  the  periphery.  It  attains  its  max- 
imum of  development  at  the  sixth  month  and  disappears  at  the  seventh 
month.  The  vitreous  humor  is  formed  of  the  fluid  contents  of  the  optic 
vesicle.  The  crystalline  lens  is  regarded  as  a  product  of  the  epiblast.  At 
the  tenth  week  there  is  the  beginning  of  the  formation  of  the  eyelids. 
These  meet  at  about  the  fourth  month  and  adhere  together  by  their  edges. 
In  many  mammals  the  eyelids  remain  closed  for  a  few  days  after  birth; 
but  they  become  separated  in  the  human  subject  in  the  later  periods  of  f  cetal 
life. 

It  is  probable  that  the  vesicle  which  becomes  developed  into  the  internal 
ear  is  formed  independently;  at  least  cases  have  been  observed  in  which 
there  was  congenital  absence  of  the  auditory  nerves,  the  parts  of  the  internal 
ear  being  perfect.  Soon  after  the  formation  of  the  auditory  vesicle,  however, 
it  communicates  with  the  third  primitive  cerebral  vesicle,  the  filament  of 
communication  being  developed  into  the  auditory  nerve. 

The  auditory  vesicle,  which  appears  later  than  the  organ  of  vision,  is 
eventually  developed  into  the  vestibule.  The  next  formations  are  the  arches, 
or  diverticula,  which  constitute  the  semicircular  canals.  The  membranous 
labyrinth  appears  long  before  the  osseous  labyrinth ;  and  it  has  been  found 
perfectly  developed  at  three  months.  The  bones  of  the  middle  ear,  which 
have  no  connection,  in  their  development,  with  the  nervous  system,  but  which 
it  is  convenient  to  mention  here,  are  remarkable  for  their  early  appearance. 
They  appear  at  the  beginning  of  the  third  month  and  are  as  large  in  the 
foetus  at  term  as  in  the  adult.  A  remarkable  anatomical  point  with  relation 
to  these  structures  is  the  existence  of  a  cartilage,  attached  to  the  malleus  on 
either  side  and  extending  from  this  bone  along  the  inner  surface  of  the  lower 
jaw,  the  two  cartilages  meeting  and  uniting  in  the  median  line,  to  form  a 
single  cord.  "  This  cartilage  now  ossifies,  although,  in  the  commencement,  it 
forms  most  of  the  mass  of  the  bone ;  it  disappears  at  the  eighth  month " 
(Meckel).  This  structure  is  known  as  the  cartilage  of  Meckel. 

There  are  no  special  points  for  description  in  the  development  of  the 


822  GENEEATION. 

olfactory  lobes,  which  is  very  simple.  These  are  offshoots  from  the  first 
cerebral  vesicle,  appearing  at  the  inferior  and  anterior  part  of  the  cerebral 
hemispheres,  a  little  later  than  the  parts  connected  with  vision  and  audition. 
The  vesicles  themselves  become  filled  with  ganglionic  matter  and  constitute 
the  olfactory  bulbs,  their  pedicles  being  the  so-called  olfactory  nerves,  or 
olfactory  commissures. 

As  far  as  the  action  of  the  nervous  system  of  the  foetus  is  concerned,  it 
is  probable  that  it  is  restricted  mainly  to  reflex  phenomena  depending 
upon  the  spinal  cord,  and  that  perception  and  volition  hardly  exist.  It  is 
probable  that  many  reflex  movements  take  place  in  utero.  When  a  foetus  is 
removed  from  the  uterus  of  an  animal,  even  during  the  early  months  of 
pregnancy,  movements  of  respiration  occur ;  and  it  is  well  known  that  efforts 
of  respiration  sometimes  take  place  within  the  uterus.  These  are  due  to  the 
want  of  oxygen-carrying  blood  in  the  medulla  oblongata  when  the  placental 
circulation  is  interrupted. 

DEVELOPMENT  OF  THE  DIGESTIVE  APPARATUS. 

The  intestinal  canal  is  the  first  formation  of  the  digestive  system.  This 
is  at  first  open  in  the  greatest  part  of  its  extent,  presenting,  at  either  extrem- 
ity of  the  longitudinal  gutter,  in  front  of  the  spinal  column,  a  rounded,  blind 
extremity,  which  is  closed  over  in  front  for  a  short  distance.  The  closure  of 
the  visceral  plates  then  extends  laterally  and  from  the  two  extremities  of  the 
intestine,  until  only  the  opening  remains  for  the 
passage  of  the  umbilical  cord  and  the  pedicle  of  the 
umbilical  vesicle.  There  is  at  first  an  open  com- 
munication between  the  lower  part  of  the  intestinal 
tube  and  the  allantois,  which  forms  the  canal  known 
as  the  urachus ;  but  that  portion  of  this  communi- 
cation which  remains  enclosed  in  the  abdominal 
cavity  becomes  separated  from  the  urachus,  is  di- 
lated and  eventually  forms  the  urinary  bladder. 
When  the  bladder  is  first  shut  off,  it  communicates 
with  the  lower  portion  of  the  intestine,  which  is 

FIG.  305. — Foztalpig,  showing  a 

loop  of  intestine,  forming    called  the  cloaca ;   but  it  finally  loses  this  connec- 

an  umbilical  hernia  (Dal-       .  .  J 

ton).  tion  and  presents  a  special  opening,  the  urethra. 

As  development  advances,  the  intestine  grows 
rapidly  in  length  and  becomes  convoluted.  It  is 
held  loosely  to  the  spinal  column  by  the  mesentery, 

a  fold  of  the  peritoneum,  this  membrane  being  reflected  along  the  walls  of 
the  abdominal  cavity.  In  the  early  stages  of  development,  a  portion  of  the 
intestine  protrudes  at  the  umbilicus,  where  the  first  intestinal  convolution 
appears ;  and  sometimes  there  is  a  congenital  hernia  of  this  kind  at  birth, 
which  usually  disappears  under  the  influence  of  gentle  and  continued  press- 
ure. An  illustration  of  this  is  given  in  Fig.  305.  This  protrusion,  in  the 
normal  process  of  development,  is  gradually  returned  into  the  abdomen,  as 


DEVELOPMENT  OF  THE  DIGESTIVE  APPARATUS.  823 

the  cavity  of  the  pedicle  of  the  umbilical  vesicle  is  obliterated,  at  about  the 
tenth  week. 

At  the  upper  part  of  the  abdominal  cavity  the  alimentary  canal  presents 
two  lateral  projections,  or  pouches.  The  one  on  the  left  side,  as  it  increases 
in  size,  becomes  the  greater  pouch  of  the  stomach,  and  the  one  on  the  right 
side,  the  lesser  pouch. 

At  a  short  distance  below  the  attachment  of  the  pedicle  of  the  umbilical 
vesicle  to  the  intestine,  there  appears  a  rounded  diverticulum,  which  is 
eventually  developed  into  the  caecum.  The  caecum  gradually  recedes  from 
the  neighborhood  of  the  umbilicus,  which  is  its  original  situation,  and  finally 
becomes  fixed,  by  a  shortening  of  the  mesentery,  in  the  right  iliac  region. 
As  the  caecum  is  developed  it  presents  a  conical  appendage,  which  is  at  first 
as  large  as  the  small  intestine  and  is  relatively  longer  than  in  the  adult. 
During  the  fourth  week  this  appendage  becomes  relatively  smaller  and  more 
or  less  twisted,  forming  the  appendix  vermiformis.  At  the  second  month 
the  caecum  is  at  the  umbilicus,  and  the  large  intestine  extends  in  a  straight 
line  toward  the  anus ;  at  the  third  month  it  is  situated  at  about  the  middle 
of  the  abdomen  ;  and  it  gradually  descends,  until  it  reaches  the  right  iliac 
region  at  about  the  seventh  month.  Thus  at  the  second  month,  there  is 
only  a  descending  colon  ;  the  transverse  colon  is  formed  at  the  third  month ; 
and  the  ascending  colon,  at  the  fifth  month.  The  ileo-caecal  valve  appears 
at  the  third  month ;  the  rectum,  at  the  fourth  month ;  and  the  sigrnoid  flex- 
ure of  the  colon,  at  the  fifth  month.  During  this  time  the  large  intestine  in- 
creases more  rapidly  in  diameter  than  the  small  intestine,  while  the  latter 
develops  more  rapidly  in  its  length. 

In  the  early  stages  of  development  the  internal  surface  of  the  intestines  is 
smooth ;  but  villi  appear  upon  its  mucous  membrane  during  the  latter  half 
of  intrauterine  existence.  These  are  found  at  first  both  in  the  large  and 
the  small  intestine.  At  the  fourth  month  they  become  shorter  and  less 
abundant  in  the  large  intestine,  and  they  are  lost  at  about  the  eighth  month, 
when  the  projections  which  bound  the  sacculi  of  this  portion  of  the  intes- 
tinal canal  make  their  appearance.  The  valvulae  conniventes  appear,  in  the 
form  of  slightly  elevated,  transverse  folds,  in  the  upper  portion  of  the  small 
intestine.  The  villi  of  the  small  intestine  are  permanent. 

The  mesentery  is  first  formed  of  two  perpendicular  folds,  attached  to  the 
sides  of  the  spinal  column.  As  the  intestine  undergoes  development  a  por- 
tion of  the  peritoneal  membrane  extends  in  a  quadruple  fold  from  the  stom- 
ach to  the  colon,  to  form  the  great  omentum,  which  covers  the  small  intes- 
tine in  front. 

As  the  head  undergoes  development  a  large  cavity  appears,  which  is 
eventually  bounded  by  the  arches  that  are  destined  to  form  the  different 
parts  of  the  face.  This  is  the  pharynx.  It  is  entirely  independent,  in  its 
formation,  of  the  intestinal  canal,  the  latter  terminating  in  a  blind  extremity, 
at  the  stomach  ;  and  between  the  pharynx  and  the  stomach  there  is  at  first 
no  channel  of  communication.  The  anterior  portion  of  the  pharynx  pre- 
sents, during  the  sixth  week,  a  large  opening,  which  is  afterward  partially 


824  GENERATION. 

closed  in  the  formation  of  the  face.  The  rest  of  this  cavity  remains  closed 
until  a  communication  is  effected  with  the  oesophagus.  The  oesophagus 
appears  in  the  form  of  a  tube,  which  finally  opens  into  the  pharynx  above 
and  into  the  stomach  below.  At  this  time  there  is  really  no  thoracic  cavity, 
the  upper  part  of  the  stomach  is  very  near  the  pharynx,  the  oesophagus  is 
short,  the  rudimentary  lungs  appear  by  its  sides  and  the  heart  lies  just  in 
front.  As  the  thorax  is  developed,  however,  the  O3sophagus  becomes  longer, 
the  lungs  increase  in  size,  and  finally  the  diaphragm  shuts  off  its  cavity  from 
the  cavity  of  the  abdomen.  The  growth  of  the  diaphragm  is  from  its  pe- 
riphery to  the  central  portion,  which  latter  gives  passage  to  the  vessels  and 
the  O3sophagus.  When  this  closure  is  incomplete  there  is  the  malformation 
known  as  congenital  diaphragmatic  hernia. 

The  development  of  the  anus  is  very  simple.  At  first  the  intestine  ter- 
minates below  in  a  blind  extremity  ;  but  at  about  the  seventh  week  a  longi- 
tudinal slit  appears  below  the  external  organs  of  generation,  by  which  the 
rectum  opens.  This  is  the  anus.  It  is  not  very  unusual  to  observe  an  arrest 
in  the  development  of  this  opening,  the  intestine  terminating  in  a  blind  ex- 
tremity, a  short  distance  beneath  the  integument.  This  constitutes  the  mal- 
formation known  as  imperforate  anus,  a  deformity  which  usually  can  be 
relieved,  without  much  difficulty,  by  a  surgical  operation,  if  the  distance  be- 
tween the  rectum  and  the  skin  be  not  too  great.  The  opening  of  the  anus 
appears  about  a  week  after  the  opening  of  the  mouth,  at  or  about  the  seventh 
week. 

The  rudiments  of  the  liver  appear  very  early,  and,  indeed,  at  the  end  of 
the  first  month  this  organ  has  attained  a  large  size.  Two  projections,  or 
buds,  appear  on  either  side  of  the  intestine,  which  form  the  two  principal 
lobes  of  the  liver.  This  organ  is  at  first  symmetrical,  the  two  lobes  being  of 
nearly  the  same  size,  with  a  median  fissure.  One  of  these  prolongations 
from  the  intestine  becomes  perforated  and  forms  the  excretory  duct,  of  which 
the  gall-bladder,  with  its  duct,  is  an  appendage.  During  the  early  part  of 
foetal  life  the  liver  occupies  the  greatest  part  of  the  abdominal  cavity.  Its 
weight,  in  proportion  to  the  weight  of  the  body  at  different  ages,  is  as  fol- 
lows :  At  the  end  of  the  first  month,  1  to  3 ;  at  term,  1  to  18 ;  in  the  adult, 
1  to  36  (Burdach).  Its  structure  is  very  soft  during  the  first  months.  As 
development  advances  and  as  the  relative  size  of  the  liver  gradually  dimin- 
ishes, its  tissue  becomes  more  solid. 

The  pancreas  appears  at  the  left  side  of  the  duodenum,  by  the  formation 
of  two  ducts  leading  from  the  intestine,  which  branch  and  develop  glandu- 
lar structure  at  their  extremities.  The  spleen  is  developed,  about  the  same 
time,  at  the  greater  curvature  of  the  stomach,  and  becomes  distinct  during 
the  second  month. 

There  is  no  reason  to  believe  that  any  of  the  digestive  fluids  are  secreted 
during  intraiiterine  Kfe.  At  birth  the  intestine  contains  a  peculiar  sub- 
stance, called  meconium,  which  will  be  described  farther  on.  Cholesterine, 
an  important  constituent  of  the  bile,  is  found  in  large  quantity  in  the  me- 
conium. 


DEVELOPMENT  OF  THE  FACE.  825 

DEVELOPMENT  OF  THE  RESPIRATORY  SYSTEM. 

On  the  anterior  surface  of  the  membranous  tube  which  becomes  the 
oesophagus,  an  elevation  appears,  which  soon  presents  an  opening  into  the 
oesophagus,  the  projection  forming  at  this  time  a  single,  hollow  cul-de-sac. 
This  opening  becomes  the  rima  glottidis,  and  the  single  tube  with  which  it 
is  connected  is  developed  into  the  trachea.  At  the  lower  extremity  of  this 
tube,  a  bifurcation  appears,  termi- 
nating first  in  one  and  afterward 
in  several  culs-de-sac.  The  bi- 
furcated tube  constitutes,  after 
the  lungs  are  developed,  the  prim- 
itive bronchia,  at  the  extremities 
of  which  are  the  branches  of  the 
bronchial  tree.  As  the  bronchia 
branch  and  subdivide,  they  extend 

.  FIG.  306.— Formation  of  the  bronchial  ramifications 

downward     into      What  becomes  and  of  the  pulmonary  cells.— A,  B,  development  of 

n       ,1               .,         ,  ,,         ,,  the  lungs,  after  Rathke ;  C,  D,  histological  develop- 

eventually  the  Cavity  Of  the    tllO-  ment  of  the  lungs,  after  J.  Miiller  (Longet). 

rax.     The  pulmonary  vesicles  are 

developed  before  the  trachea  (Burdach).  The  lungs  contain  no  air  at  any 
period  of  intrauterine  life  and  receive  but  a  small  quantity  of  blood ;  but 
at  birth  they  become  distended  with  air,  are  increased  thereby  in  volume  and 
receive  all  the  blood  from  the  right  ventricle.  This  process  of  development 
is  illustrated  in  Fig.  306.  The  lungs  appear,  in  the  human  embryon,  during 
the  sixth  week.  The  two  portions  into  which  the  original  bud  is  bifurcated 
constitute  the  true  pulmonary  structure,  and  the  formation  of  the  trachea 
and  bronchial  tubes  occurs  afterward  and  is  secondary. 

DEVELOPMENT  OF  THE  FACE. 

The  anterior  portion  of  the  embryon  remains  open  in  front  long  after  the 
medullary  plates  have  met  at  the  back  and  enclosed  the  neural  canal.  The 
common  cavity  of  the  thorax  and  abdomen  is  closed  by  the  growth  of  the 
visceral  plates,  which  meet  in  front.  At  the  time  that  the  visceral  plates  are 
closing  over  the  thorax  and  abdomen,  four  distinct,  tongue-like  projections 
appear,  one  above  the  other,  by  the  sides  of  the  neck.  These  are  called  the 
visceral  arches,  and  the  slits  between  them  are  called  the  visceral  clefts.  The 
first  three  arches,  enumerating  them  from  above  downward,  correspond,  in 
their  origin,  to  the  three  primitive  cerebral  vesicles.  The  fourth  arch — which 
is  not  enumerated  by  some  authors,  who  recognize  but  three  arches — corre- 
sponds to  the  superior  cervical  vertebra?.  Of  these  four  arches,  the  first  is  the 
most  important,  as  its  development,  in  connection  with  that  of  the  frontal 
process,  forms  the  face  and  the  malleus  and  incus  of  the  middle  ear.  The 
second  arch  forms  the  lesser  cornua  of  the  hyoid  bone,  the  stapes  and  the 
styloid  ligament.  The  third  arch  forms  the  body  and  the  greater  cornua  of 
the  hyoid.  The  fourth  arch  forms  the  larynx.  The  first  cleft,  situated  be- 
tween the  first  and  the  second  arch,  is  finally  closed  in  front,  but  an  opening 


826 


GENERATION. 


remains  by  the  side,  which  forms,  externally,  the  external  auditory  meatus, 
and  internally,  the  tympanic  cavity  and  the  Eustachian  tube.  The  other 
clefts  become  obliterated  as  the  arches  advance  in  their  development. 

From  the  above  sketch,  it  is  seen  that  the  face  and  the  neck  are  formed 
by  the  advance  and  closure  in  front  of  projections  from  behind,  in  the  same 

way  as  the  cavities  of  the  thorax  and 
abdomen  are  closed ;  but  the  closure  of 
the  first  visceral  arch  is  complicated  by 
the  projection,  from  above  downward, 
of  the  frontal,  or  intermaxillary  process, 
and  by  the  formation  of  several  second- 
ary projections,  which  leave  certain 
permanent  openings,  forming  the 
mouth,  nose  etc. 

In  the  very  first  stages  of  develop- 
ment of  the  head  there  is  no  appear- 
ance of  the  face.  The  cephalic  extrem- 
ity consists  simply  of  the  cerebral  vesi- 
cles, the  surface  of  this  enlarged  por- 
tion of  the  embryon  being  covered,  in 
front  as  well  as  behind,  by  the  epiblast. 
During  the  sixth  week,  after  the  cavity 
of  the  pharynx  has  appeared,  the  mem- 
brane gives  way  in  front,  forming  a 
large  opening,  which  may  be  called  the 
first  opening  of  the  mouth.  At  this 
time,  however,  the  face  is  entirely  open 
in  front,  as  far  back  as  the  ears.  The 
first,  or  the  superior  visceral  arch,  now 
appears  as  a  projection  of  the  meso- 
blast,  extending  forward.  This  is  soon 
marked  by  two  secondary  projections, 

the  upper  projection  forming  the  superior  maxillary  portion  of  the  face,  and 
the  lower,  the  inferior  maxilla.  The  two  projections  which  form  the  lower 
jaw  soon  meet  in  the  median  line,  and  their  superior  margin  is  the  lower  lip. 
At  the  same  time  there  is  a  projection  from  above,  extending  between  the 
two  superior  projections,  which  is  called  the  frontal,  or  intermaxillary  pro- 
cess. This  extends  from  the  forehead — that  portion  which  covers  the  front 
of  the  cerebrum — downward.  The  superior  maxillary  projections  then  ad- 
vance forward,  gradually  passing  to  meet  the  frontal  process,  but  leaving  two 
small  openings  on  either  side  of  the  median  line,  which  are  the  openings  of 
the  nostrils.  The  upper  portion  of  the  frontal  process  thus  forms  the  nose ; 
but  below,  is  the  lower  end  of  this  process,  which  is  at  first  split  in  the  medi- 
an line,  projects  below  the  nose,  and  forms  the  incisor  process,  at  the  lower 
border  of  which  are  finally  developed  the  incisor  teeth.  As  the  superior  max- 
illary processes  advance  forward,  the  eyes  are  moved,  as  it  were,  from  the 


FIG.  307.— Mouth  of  a  human  embryon  of  twen- 
ty-flue to  twenty-eight  days ;  magnified  15 
diameters  (Coste). 

1,  median  or  frontal  process,  the  inferior  portion 
of  which  is  considerably  enlarged  ;  2,  right 
nostril :  3,  left  nostril ;  4,  4,  inferior  maxil- 
lary processes,  already  united  in  the  median 
line  ;  5,  5,  superior  maxillary  processes, 
which  have  become  quite  prominent  and 
have  descended  to  the  level  of  the  slope  of 
the  frontal  process  ;  6,  mouth  ;  7,  first  vis- 
ceral arch  ;  8,  second  visceral  arch  ;  9,  third 
visceral  arch  ;  10,  eye  ;  11,  ear. 


DEVELOPMENT  OF  THE  FACE. 


827 


sides  of  the  head  and  present  anteriorly,  until  finally  their  axes  become  parallel. 
These  processes  advance  from  the  two  sides,  come  to  the  sides  of  the  incisor 
process,  beneath  the  nose,  unite  with  the  incisor  process  on  either  side,  and 
their  lower  margin,  with  the  lower  margin  of  the  incisor  process,  forms  the 
upper  lip ;  but  before  this,  the  two  lateral  halves  of  the  incisor  process  have 
united  in  the  median  line.  At  the  bottom  of  the  cavity  of  the  mouth  a 
small  papilla  makes  its  appearance,  which  gradually  elongates  and  forms  the 
tongue. 

While  this  process  of  development  of  the  anterior  portion  of  the  first 
visceral  arch  is  going  on,  at  its  posterior  portion,  the  malleus  and  incus  are 
developing,  the  former  being  at  first  connected  with  the  cartilage  of  Meckel, 
which  extends  along  the  inner  surface  of  the  inferior  maxilla,  the  cartilages 
from  either  side  meeting  at  the  chin.  The  cleft  between  the  first  and  the 
second  visceral  arch  has  closed,  except  at  its  posterior  portion,  where  an 

opening  is  left  for  

the  external  audi- 
tory meatus,  the 
cavity  of  the  tym- 
panum and  the 
Eustachian  tube. 

At  the  same 
time  the  second  vis- 
ceral arch  advances 
and  forms  the 
stapes,  the  styloid 
ligament  and  the 
lesser  cornua  of  the 
hyoid  bone.  The 
third  arch  advances 
in  the  same  way ; 
and  the  arches  from 
the  two  sides  meet, 
become  united  in 
the  median  line  and 
form  the  body  and 
the  greater  cornua 
of  the  hyoid  bone. 
The  clefts  between 
the  second  and  the 
third  and  between 
the  third  and 
fourth  arches  are 
finally  obliterated. 

The  fourth  arch  forms  the  sides  of  the  neck  and  the  larynx,  the  arytenoid 
cartilages  being  developed  first.  In  front  of  the  larynx  and  just  behind  the 
tongue,  is  a  little  elevation,  which  is  developed  into  the  epiglottis.  The 


FIG.  308.— Mouth  of  a  human  em- 
bnjon  of  thirty-five  days  (Coste). 

1,  frontal  process,  widely  sloped  at 
its  inferior  portion  ;  2,  2,  inci- 
sor processes  produced  by  this 
sloping  ;  3,  3,  nostrils;  4.  lower 
lip  and  maxilla,  formed  by  the 
union  of  the  inferior  maxillary 
processes  ;  5,  5,  superior  max- 
illary processes,  contiguous  to 
the  incisor  process  ;  6,  mouth, 
still  confounded  with  the  nasal 
fossee  ;  7,  first  appearance  of 
the  closure  of  the  nasal  fossae  ; 
8,  8,  first  appearance  of  the  two 
halves  of  the  palatine  arch  ;  9, 
tongue  ;  10.  10,  eyes  ;  11,  12,  13, 
visceral  arches. 


Fio.  309.—  Mouth  of  an  embryon  of  for- 
ty days  (Coste.). 

1,  first  appearance  of  the  nose  ;  2, 2,  first 
appearance  of  the  alae  of  the  nose  ; 
3,  appearance  of  the  closure  beneath 
the  nose  ;  4,  middle,  or  median  por- 
tion of  the  upper  lip,  formed  by  the 
approach  and  union  of  the  two  in- 
cisor processes,  a  little  notch  in  the 
median  line  still  indicating  the  prim- 
itive separation  of  the  two  process- 
es; 5, 5,  superior  maxillary  process- 
es, forming  the  lateral  portions  of 
the  upper  lip  ;  6,  6,  groove  for  the 
development  of  the  lachrymal  sac 
and  the  nasal  canal ;  7,  lower  lip;  8, 
mouth  ;  9,  9,  the  two  lateral  halves 
of  the  palatine  arch,  already  nearly 
approximated  to  each  other  in  front, 
but  still  widely  separated  behind. 


828  GENERATION. 

openings  of  the  nostrils  appear  during  the  second  half  of  the  second  month. 
A  little  elevation,  the  nose,  appears  between  these  openings,  and  the  nasal 
cavity  begins  to  be  separated  from  the  mouth.  The  lips  are  distinct  during 
the  third  month,  and  the  tongue  first  appears  in  the  course  of  the  seventh 
week. 

When,  by  an  arrest  of  development,  the  superior  maxilla  on  one  side  fails 
to  unite  with  the  side  of  the  incisor  process,  there  is  the  very  common  de- 
formity known  as  single  harelip.  If  this  union  fail  on  both  sides,  there  is 
double  harelip,  when  the  incisor  process  usually  is  more  or  less  projecting. 
As  a  very  rare  deformity,  it  is  sometimes  observed  that  the  two  sides  of  the 
incisor  process  have  failed  to  unite  with  each  other,  leaving  a  fissure  in  the 
median  line. 

The  palatine  arch  is  developed  by  two  processes,  which  arise  on  either 
side,  from  the  incisor  process,  pass  backward  and  upward  and  finally  meet 
and  unite  in  the  median  line.  The  union  of  these  forms  the  plane  of  sepa- 
ration between  the  mouth  and  the  nares ;  and  want  of  fusion  of  these  pro- 
cesses, from  arrest  of  development,  produces  the  malformation  known  as 
cleft  palate,  in  which  the  fissure  is  always  in  the  median  line.  At  the  same 
time  a  vertical  process  forms  in  the  median  line,  between  the  palatine  arch 
and  the  roof  of  the  nasal  cavity,  which  separates  the  two  nares. 

Development  of  the  Teeth. — The  first  appearance  of  the  organs  for  the 
development  of  the  teeth  is  marked  by  the  formation  of  a  cellular  projection 
extending  the  entire  length  of  the  rounded  border  of  either  jaw,  which  forms 
a  rounded  band  above  and  dips  down  somewhat  into  the  subjacent  structure. 
This  band  is  readily  separated  by  maceration,  and  the  removal  of  the  portion 
that  dips  into  the  maxilla  leaves  a  groove.  This  band  extends  the  entire 
length  of  the  jaws,  without  interruption.  Its  superior  surface  is  rounded, 
and  that  portion  which  dips  into  the  subjacent  mucous  structure  is  wedge- 
shaped,  so  that  its  section  has  the  form  of  a  V. 

As  soon  as  this  primitive  band  is  formed,  which  occurs  at  the  sixth  or 
seventh  week,  a  flat  band  projects  from  its  internal  surface,  near  the  mucous 
structure,  which  is  called  the  epithelial  band.  This  also  extends  over  the 
entire  length  of  the  jaws.  It  is  thin,  flattened,  with  its  free  edge  curved 
inward  and  toward  the  jaw,  and  is  composed  at  first  of  a  central  layer  of 
polygonal  cells,  covered  by  a  layer  of  columnar  epithelium. 

At  certain  points — these  points  corresponding  to  the  situation  of  the  true, 
dental  bulbs — there  appear  rounded  enlargements  at  the  free  margin  of  the 
epithelial  band  just  described.  Each  one  of  these  is  developed  into  one  of 
the  structures  of  the  perfect  tooth.  The  mechanism  of  the  formation  of  this, 
which  is  called  the  enamel-organ,  and  of  the  dental  bulb  is  as  follows : 

A  rounded  enlargement  appears  at  the  margin  of  the  epithelial  band. 
This  soon  becomes  directed  downward — adapting  the  description  to  the  lower 
jaw — and  dips  into  the  mucous  structure,  being  at  first  connected  with  the 
epithelial  band,  by  a  narrow  pedicle,  which  soon  disappears,  leaving  the  en- 
largement enclosed  completely  in  a  follicle.  This  is  the  dental  follicle,  and 
it  has  no  connection  with  the  wedge-shaped  band  described  first.  While 


DEVELOPMENT  OF  THE  TEETH. 


829 


this  process  is  going  on,  a  conical  bulb  appears  at  the  bottom  of  the  follicle. 
The  enamel-organ,  formed  from  the  epithelial  band,  becomes  excavated,  or 
cup-shaped,  at  its  under  surface,  and  fits  over  the  dental  bulb,  becoming 
united  to  it. 

The  tooth  at  this  time  consists  of  the  dental  bulb,  with  the  enamel-organ 
closely  fitted  to  its  projecting  surface.     The  enamel-organ  is  developed  into 


Fia.  310.— Temporary  and  permanent  teeth  (Sappey). 


second  bicuspids  ;  11,  11,  first  molars. 

the  enamel ;  the  dental  bulb,  which  is  provided  with  vessels  and  nerves,  be- 
comes the  tooth-pulp ;  and  upon  the  surface  of  the  dental  bulb,  the  dentine 
is  developed  in  successive  layers.  The  cement  is  developed  by  successive 
layers,  upon  that  portion  of  the  dentine  which  forms  the  root  of  the  tooth. 
As  these  processes  go  on,  the  tooth  projects  more  and  more,  the  upper  •  part 
of  the  wall  of  the  follicle  gives  way  and  the  tooth  finally  appears  at  the  sur- 
face. 

The  permanent  teeth  are  developed  beneath  the  follicles  of  the  tempo- 
rary, or  milk-teeth.  The  first  appearance  is  a  prolongation  or  diverticulum 
from  the  enamel-organ  of  the  temporary  tooth,  which  dips  more  deeply  into 
the  mucous  structure.  This  becomes  the  enamel-organ  of  the  permanent 
tooth ;  and  the  successive  stages  of  development  of  the  dental  follicles  and 
the  dental  pulp  progress  in  the  same  way  as  in  the  temporary  teeth.  As 
the  permanent  teeth  increase  in  size,  they  gradually  encroach  upon  the  roots 
54 


830  GENERATION. 

of  the  temporary  teeth.  The  roots  of  the  latter  are  absorbed,  the  permanent 
teeth  advance  more  and  more  toward  the  surface,  and  the  crown  of  each  tem- 
porary tooth  is  finally  pushed  out.  The  number  of  the  temporary  teeth  is 
twenty,  and  there  are  thirty-two  permanent  teeth.  Thus  there  are  three 
permanent  teeth  on  either  side  of  both  jaws,  which  are  developed  de  novo  and 
are  not  preceded  by  temporary  structures. 

The  first  dental  follicles  usually  appear  in  regular  succession.  The  folli- 
cles for  the  internal  incisors  of  the  lower  jaw  appear  first,  this  occurring  at 
about  the  ninth  week.  All  of  the  follicles  for  the  temporary  teeth  are  com- 
pletely formed  at  about  the  eleventh  or  twelfth  week. 

The  temporary  teeth  appear  successively,  the  corresponding  teeth  appear- 
ing a  little  earlier  in  the  lower  jaw.  The  usual  order,  subject  to  certain  ex- 
ceptional variations,  is  as  follows  (Sappey) : 

The  four  central  incisors  appear  six  to  eight  months  after  birth. 

The  four  lateral  incisors  appear  seven  to  twelve  months  after  birth. 

The  four  anterior  molars  appear  twelve  to  eighteen  months  after  birth. 

The  four  canines  appear  sixteen  to  twenty-four  months  after  birth. 

The  four  posterior  molars  appear  twenty-four  to  thirty-six  months  after  birth. 

The  order  of  eruption  of  the  permanent  teeth  is  as  follows : 

The  two  central  incisors  of  the  lower  jaw  appear  between  the  sixth  and  the  eighth 
years. 

The  two  central  incisors  of  the  upper  jaw  appear  between  the  seventh  and  the  eighth 
years. 

The  four  lateral  incisors  appear  between  the  eighth  and  the  ninth  years. 

The  four  first  bicuspids  appear  between  the  ninth  and  the  tenth  years. 

The  four  canines  appear  between  the  tenth  and  the  eleventh  years. 

The  four  second  bicuspids  appear  between  the  twelfth  and  the  thirteenth  years. 

The  above  are  the  permanent  teeth  which  replace  the  temporary  teeth. 
The  permanent  teeth  which  are  developed  de  novo  appear  as  follows : 

The  first  molars  appear  between  the  sixth  and  the  seventh  years. 

The  second  molars  appear  between  the  twelfth  and  the  thirteenth  years. 

The  third  molars  appear  between  the  seventeenth  and  the  twenty-first  years. 

DEVELOPMENT  OF  THE  GENITO-URINARY  APPARATUS. 

The  genital  and  the  urinary  organs  are  developed  together  and  are  both 
preceded  by  the  appearance  of  two  large,  symmetrical  structures,  known  as 
the  Wolffian  bodies,  or  the  bodies  of  Oken.  These  are  sometimes  called  the 
false,  or  the  primordial  kidneys.  They  appear  at  about  the  thirtieth  day,  de- 
velop very  rapidly  on  either  side  of  the  spinal  column  and  are  so  large  as  to 
almost  fill  the  cavity  of  the  abdomen.  Fig.  311  shows  how  large  these  bodies 
are  in  the  early  life  of  the  embryon,  at  which  time  their  office  is  undoubtedly 
very  important. 

Very  soon  after  the  Wolffian  bodies  have  made  their  appearance,  there 
appear  at  their  inner  borders,  two  ovoid  bodies,  which  are  finally  developed 
into  the  testicles,  for  the  male,  or  the  ovaries,  for  the  female.  At  their  ex- 
ternal borders,  are  two  ducts  on  either  side,  one  of  which,  the  internal,  is 


DEVELOPMENT  OF  THE  GENITO-URINARY  APPARATUS.      831 

called  the  duct  of  the  "VVolffian  body.     This  finally  disappears  in  the  female, 

but  it  is  developed  into  the  vas  deferens  in  the  male.    The  other  duct,  which 

is  external  to  the  duct  of  the  Wolffian  body,  disappears  in  the  male,  but  it 

becomes   the  Fallopian   tube  in  the  female.     This   is 

known  as  the  duct  of   M tiller.     Behind  the  Wolffian 

bodies,  are  developed  the  kidneys  and  the  suprarenal 

capsules. 

As  the  development  of  the  Wolffian  bodies  attains 
its  maximum  their  structure  becomes  somewhat  com- 
plex. From  their  proper  ducts,  which  are  applied  di- 
rectly to  their  outer  borders,  tubes  make  their  appear- 
ance at  right  angles  to  the  ducts,  which  extend  into  the 
substance  of  the  bodies  and  become  somewhat  convo- 
luted  at  their  extremities.  These  tubes  communicate 
directly  with  the  ducts,  and  the  ducts  themselves  open  *»  heart ;  2,  anterior  ex- 

J  tremity ;     3,     posterior 

into  the  lower  part  of  the  intestinal  canal,  opposite  to       bSiremity '  4'  Wolfflan 
the   point  of   its   communication  with  the  allantois.    The  abdominal  wails  have 

been  cut  away,  in  order 

The  tubes  of  the  Wolffian  bodies  are  simple,  termiua-        to  show  the  position  of 

the  Wolfflan  bodies. 

ting  in  single,  somewhat  dilated,  blind  extremities,  are 
lined  with  epithelium,  and  are  penetrated  at  their  extremities,  by  blood-ves- 
sels, which  form  coils  or  convolutions  in  their  interior.  These  are  undoubt- 
edly organs  of  depuration  for  the  embryon  and  take  on  the  office  to  be  after- 
ward assumed  by  the  kidneys  ;  but  in  the  female  they  are  temporary  struct- 
ures, disappearing  as  development  advances,  and  having  nothing  to  do  with 
the  development  of  the  true,  urinary  organs. 

The  testicles  or  ovaries  are  developed  at  the  internal  and  anterior  surface 
of  the  Wolffian  bodies,  first  appearing  in  the  form  of  small,  ovoid  masses. 
Beginning  just  above  and  passing  along  the  external  borders  of  the  Wolffian 
bodies,  are  the  tubes  called  the  ducts  of  Mtiller.  These  at  first  open  into  the 
intestine,  near  the  point  of  entrance  of  the  Wolffian  ducts.  In  the  female 
their  upper  extremities  remain  free,  except  the  single  fimbria  which  is  con- 
nected with  the  ovary.  Their  inferior  extremities  unite  with  each  other, 
and  at  their  point  of  union  they  form  the  uterus.  When  this  union  is  in- 
complete there  is  the  malformation  known  as  double  uterus,  which  may  be 
associated  with  a  double  vagina.  The  Wolffian  bodies  and  their  ducts  disap- 
pear, in  the  female,  at  about  the  fiftieth  day.  A  portion  of  their  structure, 
however,  persists  in  the  form  of  a  collection  of  closed  tubes  constituting  the 
parovarium,  or  organ  of  Rosenmuller. 

In  the  female  the  ovaries  pass  down  no  farther  than  the  pelvic  cavity ; 
but  the  testicles,  which  are  at  first  in  the  abdomen  of  the  male,  finally  de- 
scend into  the  scrotum.  As  the  testicles  descend  they  carry  with  them  the 
Wolffian  duct,  that  portion  of  the  Wolffian  body  which  is  permanent  consti- 
tuting the  head  of  the  epididymis.  At  the  same  time  a  cord  appears,  at- 
tached to  the  lower  extremity  of  the  testicle  and  extending  to  the  symphysis 
pubis.  This  is  called  the  gubernaculum  testis.  It  is  at  first  muscular,  but 
the  muscular  fibres  disappear  during  the  later  periods  of  utero-gestation.  It 


832  GENERATION. 

is  not  known  that  its  muscular  structure  takes  any  part,  by  contractile  action, 
in  the  descenf  of  the  testicle  in  the  human  subject.  The  epididymis  and 
the  vas  deferens  are  formed  from  the  Wolffian  body  and  the  Wolffian  duct. 

At  about  the  end  of  the  seventh  month  the  testicle  has  reached  the  in- 
ternal abdominal  ring ;  and  at  this  time  a  double  tubular  process  of  perito- 
neum, covered  with  a  few  fibres  from  the  lower  portion  of  the  internal  oblique 
muscle  of  the  abdomen,  gradually  extends  into  the  scrotum.  The  testicle 
descends,  following  this  process  of  peritoneum,  which  latter  become  eventu- 
ally the  visceral  and  parietal  portions  of  the  tunica  vaginalis.  The  canal  of 
communication  between  the  abdominal  cavity  and  the  cavity  of  the  scrotum 
is  finally  closed,  and  the  tunica  vaginalis  is  separated  from  the  peritoneum. 
The  fibres  derived  from  the  internal  oblique  constitute  the  cremaster  muscle. 

At  the  eighth'  or  the  ninth  month  the  testicles  have  reached  the  external 
abdominal  ring  and  then  soon  descend  into  the  scrotum.  The  vas  deferens 
passes  from  the  testicle,  along  the  base  of  the  bladder,  to  open  into  the  pros- 
tatic  portion  of  the  urethra ;  and  as  development  advances,  two  sacculated 
diverticula  from  these  tubes  make  their  appearance,  which  are  attached  to 
the  bladder  and  constitute  the  vesiculae  seminales. 

As  the  ovaries  descend  to  their  permanent  situation  in  the  pelvic  cavity, 
there  appears,  attached  to  the  inner  extremity  of  each,  a  rounded  cord,  analo- 
,gous  to  the  gubernaculum  testis.  A  portion  of  this,  connecting  the  ovary 
with  the  uterus,  constitutes  the  ligament  of  the  ovary ;  and  the  inferior  por- 
tion forms  the  round  ligament  of  the  uterus,  which  passes  through  the  in- 
;guinal  canal  and  is  attached  to  the  symphysis  pubis. 

Development  of  the  Urinary  Apparatus. — Behind  the  Wolffian  bodies, 
and  developed  entirely  independently  of  them,  the  kidneys,  suprarenal  cap- 
sules and  ureters  make  their  appearance.  The  kidneys  are  developed  in  the 
form  of  little,  rounded  bodies,  composed  of  short,  blind  tubes,  all  converging 
toward  a  single  point,  which  is  the  hilum.  These  tubes  increase  in  length, 
branch,  become  convoluted  in  a  certain  portion  of  their  extent,  and  they 
finally  assume  the  structure  and  arrangement  of  the  renal  tubules,  with  their 
Malpighian  bodies,  blood-vessels  etc.  They  all  open  into  the  hilum.  At  the 
time  that  the  kidneys  are  undergoing  development  the  suprarenal  capsules 
are  formed  at  their  superior  extremities.  These  bodies,  the  uses  of  which  are 
unknown,  are  relatively  so  much  larger  in  the  foetus  than  in  the  adult  that 
they  have  been  supposed  to  be  peculiarly  important  in  intrauterine  life, 
though  nothing  definite  is  known  upon  this  point.  The  kidneys  are  rela- 
tively very  large  in  the  foetus.  Their  proportion  to  the  weight  of  the  body, 
in  the  foetus,  is  1  to  80,  and  in  the  adult,  1  to  240.  The  ureters  undoubtedly 
are  developed  as  tubular  processes  from  the  kidneys,  which  finally  extend  to 
open  into  the  bladder.  This  fact  is  shown  by  certain  cases  of  malformation, 
in  which  the  ureters  do  not  reach  the  bladder,  but  terminate  in  blind  ex- 
tremities. The  development  of  the  genito-urinary  apparatus  can  be  readily 
understood,  after  the  discription  just  given,  by  a  study  of  Fig.  312. 

Development  of  the  External  Organs  of  Generation. — The  external  organs 
of  generation  begin  to  be  developed  at  about  the  fifth  week.  At  the  infe- 


DEVELOPMENT  OF  THE  GENITO-URINARY  APPARATUS.      833 


FIG.  312. — Diagrammatic  representation  of  the  genitourinary  apparatus  (Henle). 

I,  embryonic  condition,  in  which  there  is  no  distinction  of  sex  ;  II.  female  form  ;  III,  male  form.  The 
dotted  lines  in  II  and  III  represent  the  situations  which  the  male  and  female  genital  organs  assume 
after  the  descent  of  the  ovaries  and  testicles.  The  small  letters  in  II  and  III  correspond  to  the  cap- 
ital letters  in  I. 

Fig.  312, 1.— A.  kidney  ;  B,  ureter  :  C,  bladder  ;  D,  urachus,  developed  into  the  median  ligament  of  the 
bladder  ;  E,  constriction  which  becomes  the  urethra  ;  F',  Wolfflan  body  ;  G,  Wolfflan  duct,  with  its 
opening  below,  G' ;  H,  duct  of  Miiller,  united  below,  from  the  two  sides,  into  a  single  tube,  J,  which 
presents  a  single  opening,  J',  between  the  openings  of  the  Wolfflan  ducts  :  K,  ovary  or  testicle  ;  L, 
gubernaculum  testis  or  round  ligament  of  the  uterus  ;  M,  genito-urinary  sinus ';  N,  O,  external 
genitalia. 

Fig.  312,  II  (female).— a,  kidney  ;  b,  ureter  ;  c.  bladder  ;  d,  urachus;  e.  urethra;  f,  remains  of  the  Wolf- 
flan  body  (parovarium);  g,  remnant  of  the  Wolfflan  duct  ;  h.  Fallopian  tube  ;  i,  uterus  ;  i',  vagina  ; 
k,  ovary  ;  1,  round  ligament  of  the  uterus ;  m,  extremity  of  the  urethra  :  n,  clitoris  ;  n',  corpus 
cavernosum  of  the  clitoris  ;  n",  bulb  of  the  vestibule  ;  o,  external  genital  opening  ;  p.  excretory 
duct  of  the  gland  of  Bartholinus. 

Fig.  312,  III  (male).— a,  kidney  :  b,  ureter  ;  c,  bladder  ;  d.  urachus  ;  e,  m.  urethra  ;  f,  epididymis  ;  g,  vas 
deferens  ;  g',  seminal  vesicle  ;  g",  ejaculatory  duct ;  h,  i,  remains  of  the  duct  of  Miiller  ;  k,  testicle; 
1,  gubernaculum  testis  ;  n,  n',  n",  urethra  and  penis  ;  o,  scrotum  ;  p,  gland  of  Cowper  ;  q,  prostate. 


834  GENERATION. 

rior  extremity  of  the  body  of  the  embryon  a  small,  ovoid  eminence  appears 
in  the  median  line,  at  the  lower  portion  of  which  there  is  a  longitudinal  slit, 
which  forms  the  common  opening  of  the  anus  and  the  genital  and  urinary 
passages.  This  is  the  cloaca.  There  is  soon  developed  internally  a  septum, 
which  separates  the  rectum  from  the  vagina,  the  urethra  of  the  female  open- 
ing above.  In  the  male  this  septum  is  developed  between  the  rectum  and  the 
urethra,  the  generative  and  the  urinary  passages  opening  together.  From 
this  median  prominence  two  lateral,  rounded  bodies  make  their  appearance. 
These  are  developed,  with  the  median  elevation,  into  the  glans  penis  and  cor- 
pora cavernosa  of  the  male  or  into  the  clitoris  and  the  labia  minora  of  the 
female.  In  the  male  these  two  lateral  prominences  unite  in  the  median  line 
and  enclose  the  spongy  portion  of  the  urethra.  When  there  is  a  want  of 
union  in  the  cavernous  bodies  in  the  male,  there  is  the  malformation  known 
as  hypospadias.  In  the  female  there  is  no  union  in  the  median  line,  and  an 
opening  remains  between  the  two  labia  minora.  The  scrotum  in  the  male  is 
analogous  to  the  labia  majora  of  the  female ;  the  distinction  being  that  the 
two  sides  of  the  scrotum  unite  in  the  median  line,  while  the  labia  majora 
remain  permanently  separated.  This  analogy  is  farther  illustrated  by  the 
anatomy  of  inguinal  hernia,  in  which  the  intestine  descends  into  the  labium, 
in  the  female,  and  into  the  scrotum,  in  the  male.  It  sometimes  occurs,  also, 
that  the  ovaries  descend,  very  much  as  the  testicles  pass  down  in  the  male, 
and  pass  through  the  external  abdominal  ring. 

DEVELOPMENT  OF  THE  CIRCULATORY  APPARATUS. 

The  blood  and  the  blood-vessels  are  developed  very  early  in  the  life  of  the 
ovum  and  make  their  appearance  nearly  as  soon  as  the  primitive  trace.  The 
mode  of  development  of  the  first  vessels  differs  from  that  of  vessels  formed 
later,  as  they  appear  tie  novo  in  the  blastodermic  layers,  while  afterward,  ves- 
sels are  formed  as  prolongations  of  pre-existing  tubes.  Soon  after  the  epi- 
blast  and  the  hypoblast  have  become  separated  from  each  other  and  the 
mesoblast  has  been  formed  at  the  thickened  portion  of  the  ovum,  which  is 
destined  to  be  developed  into  the  embryon,  certain  of  the  blastodermic  cells 
undergo  a  transformation  into  blood-corpuscles.  These  are  larger  than  the 
blood-corpuscles  of  the  adult  and  generally  are  nucleated.  At  about  the 
same  time — it  may  be  before  or  after  the  appearance  of  the  corpuscles,  for 
this  point  is  undetermined — certain  of  the  blastodermic  cells  fuse  with  each 
other  and  arrange  themselves  so  as  to  form  vessels.  Leucocytes  probably  are 
developed  in  the  same  way  as  the  red  corpuscles.  The  vessels  thus  formed 
constitute  the  area  vasculosa,  which  is  the  beginning  of  what  is  known  as 
the  first  circulation. 

According  to  His  and  Waldeyer,  the  cells  of  the  mesoblast  do  not  take 
part  in  the  formation  of  the  blood  and  blood-vessels,  as  indicated  above,  but 
cells  penetrate  at  the  edges,  between  the  epiblast  and  the  hypoblast,  and  these, 
which  are  called  parablastic  cells,  are  developed  into  blood-vessels  and  blood- 
corpuscles.  The  connective  tissue  is  also  supposed  to  be  developed  from 
parablastic  cells.  According  to  this  view — which,  however,  is  not  generally 


DEVELOPMENT  OF  THE  CIRCULATORY  APPARATUS. 


835 


adopted — the  parablastic  cells  are  to  be  distinguished  from  the  cslls  of  the 
mesoblast,  which  latter  are  called  archiblastic  cells.  According  to  Rind- 
fleisch  the  so-called  parablastic  cells  are  derived  from  the  area  opaca. 

The  First,  or  Vitelline  Circulation. — In  the  development  of  oviparous 
animals,  the  first,  or  vitelline  circulation  is  very  important ;  for  by  these  ves- 
sels the  contents  of  the  nutritive  yelk  are  taken  up  and  carried  to  the  em- 


FIG.  313. — Area  vasculosa  (Bisehoff). 
a,  a,  b,  sinus  terminalis ;  c,  omphalo-mesenteric  vein  ;  d,  heart ;  e,  /,  /,  posterior  vertebral  arteries. 

bryon,  constituting  the  only  source  of  material  for  its  nutrition  and  growth. 
In  mammals,  however,  nutritive  matter  is  absorbed  almostly  exclusive  from  the 
mother,  by  simple  endosmosis,  before  the  placental  circulation  is  established, 
and  by  the  placental  vessels,  at  a  later  period.  The  vitelline  circulation  is 
therefore  not  important,  and  the  vessels  dissappear  with  the  atrophy  of  tho 
umbilical  vesicle. 

The  area  vasculosa  in  mammals  consists  of  vessels  coming  from  the  body 
of  the  embryon,  forming  a  nearly  circular  plexus  in  the  substance  of  the  vi- 
tellus,  around  the  embryon.  The  vessels  of  this  plexus  open  into  a  sinus  at 
the  border  of  the  area,  called  the  sinus  terminalis. 

In  examining  the  ovum  when  the  area  vasculosa  is  first  formed,  the  em- 
bryon is  seen  lying  in  the  direction  of  the  diameter  of  the  nearly  circular 
plexus  of  blood-vessels.  The  plexus  surrounds  the  embryon,  except  at  the 
cephalic  extremity,  where  the  terminal  sinuses  of  the  two  sides  curve  down- 
ward toward  the  head,  to  empty  into  the  omphalo-mesenteric  veins.  As  the 
umbilical  vesicle  is  separated  from  the  body  of  the  embryon,  it  carries  the 
plexus  of  vessels  of  the  area  vasculosa  with  it,  the  vessels  of  communication 


836  GENEEATION. 

with  the  embryon  being  the  omphalo-mesenteric  arteries  and  veins.  As 
these  processes  are  going  on,  the  great,  central  vessel  of  the  embryon  becomes 
enlarged  and  twisted  upon  itself,  at  a  point  just  below  the  cephalic  enlarge- 
ment of  the  embryon,  between  the  inferior  extremity  of  the  pharynx  and  the 
superior  cul-de-sac  of  the  intestinal  canal.  The  excavation  which  receives 
this  vessel  is  called  the  fovea  cardiaca.  Simple,  undulatory  movements  take 
place  in  the  heart  of  the  chick  at  about  the  middle  of  the  second  day ;  but 
there  is  not  at  that  time  any  regular  circulation.  At  the  end  of  the  second 
day  or  the  beginning  of  the  third,  the  currents  of  the  circulation  are  estab- 
lished. The  time  of  the  first  appearance  of  the  circulation  in  the  human 
embryon  has  not  been  accurately  determined. 

In  the  arrangement  of  the  vessels  for  the  first  circulation  in  the  embryon, 
the  heart  is  situated  exactly  in  the  median  line  and  gives  off  two  arches  which 
curve  to  either  side  and  unite  into  a  single  central  trunk  at  the  spinal  column 
below.  These  are  the  two  aortae,  and  the  single  trunk  formed  by  their 
union  becomes  the  abdominal  aorta.  The  two  aortic  arches,  only  one  of 
which  is  permanent,  are  sometimes  called  the  inferior  vertebral  arteries.  These 
vessels  give  off  a  number  of  branches,  which  pass  into  the  area  vasculosa. 
Two  of  these  branches,  however,  are  larger  than  the  others,  pass  to  the  um- 
bilical vesicle  and  are  called  the  omphalo-mesenteric  arteries.  In  the  em- 
bryon of  mammals,  there  are  at  first  four  omphalo-mesenteric  veins,  two 
superior,  which  are  the  larger,  and  two  inferior ;  but  as  development  advances, 
the  two  inferior  veins  are  closed,  and  there  are  then  two  omphalo-mesen- 
teric arteries  and  two  omphalo-mesenteric  veins.  At  about  the  fortieth  day 
one  artery  and  one  vein  disappear,  leaving  one  omphalo-mesenteric  artery 
and  one  vein.  Soon  after,  as  the  circulation  becomes  established  in  the 
allantois,  the  vessels  of  the  umbilical  vesicle  and  the  omphalo-mesenteric 
vessels  are  obliterated,  and  the  first  circulation  is  superseded  by  the  second. 

As  the  septum  between  the  two  ventricles  makes  its  appearance,  that 
division  of  the  right  aortic  arch  which  constitutes  the  vascular  portion  of  one 
of  the  branchial  arches  disappears  and  loses  its  connection  with  the  abdom- 
inal aorta ;  a  branch,  however,  persists  during  the  whole  of  intrauterine  life 
and  constitutes  the  ductus  arteriosus,  and  another  branch  is  permanent, 
forming  the  pulmonary  artery. 

The  Second,  or  Placental  Circulation. — As  the  omphalo-mesenteric  ves- 
sels disappear  and  as  the  allantois  is  developed  to  form  the  chorion,  two 
vessels  (the  hypogastric  arteries)  are  given  off,  first  from  the  abdominal  aorta ; 
but  afterward,  as  the  vessels  going  to  the  lower  extremities  are  developed, 
the  branching  of  the  abdominal  aorta  is  such  that  the  vessels  become  con- 
nected with  the  internal  iliac  arteries.  The  hypogastric  arteries  pass  to  the 
chorion,  through  the  umbilical  cord,  and  constitute  the  two  umbilical  arteries. 
At  first  there  are  two  umbilical  veins ;  but  one  of  them  afterward  disap- 
pears, and  there  is  finally  but  one  vein  in  the  umbilical  cord.  It  is  in  this 
way — the  umbilical  arteries  carrying  the  blood  to  the  tufts  of  the  foetal  pla- 
centa, which  is  returned  by  the  umbilical  vein — that  the  placental  circulation 
is  established. 


DEVELOPMENT  OF  THE  CIRCULATOEY  APPARATUS.        837 


Corresponding  to  the  four  visceral  arches,  which  have  been  described  in 
connection  with  the  development  of  the  face,  are  four  vascular  arches.  One 
of  these  disappears,  and  the  remaining  three  undergo  certain  changes,  by 
which  they  are  converted  into  the  vessels  going  to  the  head  and  the  superior 
extremities.  The  anterior  arches  on  the  two  sides  are  converted  into  the 
carotids  and  subclavians ;  the  second,  on  the  left  side, 
is  converted  into  the  permanent  aorta,  and  the  right  is 
obliterated ;  the  third,  on  either  side,  is  converted  into 
the  right  and  left  pulmonary  arteries. 

The  changes  of  the  branchial  arches  are  illustrated 
in  the  diagrammatic  Fig.  314.  In  this  figure  the  three 
branchial  arches  that  remain  and  participate  in  the  de- 
velopment of  the  upper  portion  of  the  vascular  system 
are  1,  2,  3,  on  either  side.  The  two  anterior  (3,  3)  be- 
come the  carotids  (c,  c)  and  the  subclavians  (x,  s).  The 
second  (2,  2)  is  obliterated  on  the  right  side,  and  be- 
comes the  arch  of  the  aorta  on  the  left  side.  The  third 
(1,  1),  counting  from  above  downward,  is  converted  into 
the  pulmonary  arteries  of  the  two  sides.  Upon  the  left 
side  there  is  a  large,  anastomosing  vessel  (m),  between 
the  pulmonary  artery  of  that  side  and  the  arch  of  the 
aorta,  which  is  the  ductus  arteriosus.  The  anastomos- 
ing vessel  (cd),  between  the  right  pulmonary  artery  and 
the  aorta,  is  obliterated. 

The  mode  of  development  of  the  veins  is  very  sim- 
ple. Two  venous  trunks  make  their  appearance  by  the 
sides  of  the  spinal  column,  which  are  called  the  cardi- 
nal veins,  and  run  parallel  with  the  superior  vertebral 
arteries,  or  the  two  aortae,  emptying  finally  into  the  au- 
ricular portion  of  the  heart,  by  two  canals,  which  are 
called  the  canals  of  Cuvier.  These  veins  change  their 
relations  and  connections  as  the  first  circulation  is  re- 
placed by  the  second.  The  omphalo-mesenteric  vein  opens  into  the  heart, 
between  the  two  canals  of  Cuvier.  As  development  advances,  the  liver  is 
formed  in  the  course  of  this  vessel,  a  short  distance  below  the  heart,  and  the 
vein  ramifies  in  its  substance ;  so  that  the  blood  of  the  omphalo-mesenteric 
vein  passes  through  the  liver  before  it  goes  to  the  heart.  The  omphalo- 
mesenteric  vein  is  obliterated  as  the  umbilical  vein  makes  its  appearance. 
The  blood  from  the  umbilical  vein  is  at  first  emptied  directly  into  the  heart ; 
but  this  vessel  soon  establishes  the  same  relations  with  the  liver  as  the  om- 
phalo-mesenteric vein,  and  its  blood  passes  through  the  liver  before  it  reaches 
the  central  organ  of  the  circulation.  As  the  omphalo-mesenteric  vein  atro- 
phies, the  mesenteric  vein,  bringing  the  blood  from  the  intestinal  canal,  is 
developed,  and  this  penetrates  the  liver,  becoming  finally  the  portal  vein. 

As  the  lower  extremities  are  developed,  the  inferior  vena  cava  makes  its 
appearance,  between  the  two  inferior  cardinal  veins.     This  vessel  receives  an 


FIG.  314.  —  Transforma- 
tion of  the  system  of 
aortic  arches  into  per- 
manent arterial  trunks, 
in  the  mammalia  (.Von 
Baer). 

B,  aortic  bulb :  1,  2,  3,  4, 
5,  on  either  side,  the  five 
pairs  of  aortic  arches  ; 
5,  5,  the  earliest  in  their 
appearance  ;  1,  1,  the 
most  recent ;  r,  c,  the 
two  carotids,  still  unit- 
ed, which  are  separated 
at  a  later  period  ;  «,  8, 
the  two  subclavians,  the 
right  arising  from  the 
arteria  innominata  ;  a, 
a,  the  aorta  ;  p,  p,  the 
pulmonary  arteries;  ca, 
the  ductus  arteriosus  ; 
cd,  the  left  artieral  ca- 
nal, which  is  finally  ob- 
literated. 


838  GENERATION. 

Anastomosing  branch  from  the  umbilical  vein,  before  it  penetrates  the  liver, 
and  this  branch  is  the  ductus  venosus.  As  the  inferior  vena  cava  increases 
in  size,  it  communicates  below  with  the  two  inferior  cardinal  veins ;  and  that 
portion  of  the  two  inferior  cardinal  veins  which  remains  constitutes  the  two 
iliac  veins.  The  inferior  cardinal  veins,  between  that  portion  which  forms 
the  iliac  veins  and  the  heart,  finally  become  the  right  and  the  left  azygos 
veins. 

The  right  canal  of  Cuvier,  as  the  upper  extremities  are  developed,  en- 
larges and  becomes  the  vena  cava  descendens,  receiving  finally  all  the  blood 
from  the  head  and  the  superior  extremities.  The  left  canal  of  Cuvier  iinder- 
goes  atrophy  and  disappears.  The  upper  portion  of  the  superior  cardinal 
veins  is  developed  into  the  jugulars  and  subclavians  on  the  two  sides.  As 
the  lower  portion  of  the  left  cardinal  vein  and  the  left  canal  of  Cuvier 
atrophy,  a  venous  trunk  appears,  connecting  the  left  subclavian  with  the 
right  canal  of  Cuvier.  This  increases  in  size  and  becomes  the  left  vena 
innominata,  which  connects  the  left  subclavian  and  internal  jugular  with  the 
vena  cava  descendens. 

Development  of  the  Heart. — The  central  enlargement  of  the  vascular  sys- 
tem in  the  first  circulation,  which  becomes  the  heart,  is  twisted  upon  itself 
by  a  single  turn.  The  portion  connected  with  the  cephalic  extremity  of  the 
embryon  gives  origin  to  the  arterial  system,  and  the  portion  connected  with 
the  caudal  extremity  receives  the  blood  from  the  venous  system.  The  walls 
of  the  arterial  portion  of  the  heart  soon  become  thickened,  while  the  walls 
of  the  venous  portion  remain  comparatively  thin.  There  then  appears  a  con- 
striction, which  partly  separates  the  auricular  from  the  ventricular  portion. 
At  a  certain  period  of  development  the  heart  presents  a  single  auricle  and 
a  single  ventricle. 

The  division  of  the  heart  into  two  ventricles  appears  before  the  two  auri- 
cles are  separated.  This  is  effected  by  a  septum,  which  gradually  extends 
from  the  apex  of  the  heart  upward  toward  the  auricular  portion.  At  the 
seventh  week  there  is  a  large  opening  between  the  two  ventricles.  This 
gradually  closes  from  below  upward,  the  heart  becomes  more  pointed,  and 
the  separation  of  the  two  ventricles  is  complete  at  about  the  end  of  the  second 
month. 

At  about  the  end  of  the  second  month  a  septum  begins  to  be  formed 
between  the  auricles.  This  extends  from  the  base  of  the  heart,  toward  the 
ventricles,  but  it  leaves  an  opening  between  the  two  sides — the  foramen  ovale, 
or  the  foramen  of  Botal — which  persists  during  the  whole  of  foetal  life.  At 
the  anterior  edge  of  the  opening  of  the  vena  cava  ascendens  into  the  right 
auricle,  there  is  a  membranous  fold,  which  projects  into  the  auricle.  This 
is  the  valve  of  Eustachius,  and  it  divides  the  right  auricle  incompletely  into 
two  portions. 

During  the  sixth  week  the  heart  is  vertical  and  is  situated  in  the  median 
line,  with  the  aorta  arising  from  the  centre  of  its  base.  At  the  end  of  the 
second  month  it  is  raised  up  by  the  development  of  the  liver,  and  its  point 
presents  forward.  During  the  fourth  month  it  is  twisted  slightly  upon  its 


THE  FCETAL  CIRCULATION.  839 

axis,  and  the  point  presents  to  the  left.  At  this  time  the  auricular  portion 
is  larger  than  the  ventricles ;  but  the  auricles  diminish  in  their  relative  capac- 
ity during  the  latter  half  of  intrauterine  life.  The  pericardium  makes  its 
appearance  during  the  ninth  week. 

Early  in  intrauterine  life  the  relative  size  of  the  heart  is  very  great.  At 
the  second  mouth  its  weight,  in  proportion  to  the  weight  of  the  body,  is  as  1 
to  50.  This  proportion,  however,  gradually  diminishes,  until  at  birth  the 
ratio  is  as  1  to  120.  The  weight  in  the  adult  is  about  as  1  to  160.  During 
about  the  first  half  of  intrauterine  life  the  thickness  of  the  two  ventricles  is 
nearly  the  same ;  but  after  that  time  the  relative  thickness  of  the  left  ven- 
tricle gradually  increases. 

Peculiarities  of  the  Fcetal  Circulation. — Beginning  at  the  abdominal 
aorta,  the  blood  passes  into  the  two  primitive  iliacs,  and  thence  into  the  in- 
ternal iliacs.  From  the  two  internal  iliacs  the  two  hypogastric  arteries  arise, 
which  ascend  along  the  sides  of  the  bladder,  to  its  fundus,  pass  to  the  umbili- 
cus and  go  to  the  placenta,  forming  the  two  umbilical  arteries.  In  this  way 
the  blood  of  the  foetus  goes  to  the  placenta. 

The  umbilical  vein  enters  the  body  of  the  foetus  at  the  umbilicus ;  it 
passes  along  the  margin  of  the  suspensory  ligament,  to  the  under  surface  of 
the  liver ;  it  gives  off  one  branch  of  large  size,  and  one  or  two  smaller 
branches  to  the  left  lobe  ;  it  sends  a  branch  each  to  the  lobus  quadratus  and 
the  lobus  Spigelii;  and  the  vessel  reaches  the  transverse  fissure.  At  the 
transverse  fissure  it  divides  into  two  branches,  the  larger  of  which  joins  the 
portal  vein  and  enters  the  liver ;  and  the  smaller,  which  is  the  ductus  venosus, 
passes  to  the  vena  cava  ascendens,  at  the  point  where  it  receives  the  left 
hepatic  vein.  Thus  the  greater  part  of  the  blood  returned  to  the  foetus  from 
the  placenta  passes  through  the  liver,  a  relatively  small  quantity  being 
emptied  into  the  vena  cava,  by  the  ductus  venosus. 

The  vena  cava  ascendens,  containing  the  placental  blood  which  has  passed 
through  the  liver,  the  blood  conveyed  directly  from  the  umbilical  vein  by  the 
ductus  venosus  and  the  blood  from  the  lower  extremities,  passes  to  the  right 
auricle.  As  the  blood  enters  the  right  auricle  it  is  directed  by  the  Eustachian 
valve,  passing  behind  the  valve,  through  the  foramen  ovale,  into  the  left 
auricle.  At  the  same  time  the  blood  from  the  head  and  the  superior  ex- 
tremities passes  down,  by  the  vena  cava  descendens,  in  front  of  the  Eustachian 
valve,  through  the  right  auricle,  into  the  right  ventricle.  The  arrangement 
of  the  Eustachian  valve  is  such  that  the  right  auricle  simply  affords  a  pas- 
sage for  the  two  currents  of  blood ;  the  one,  from  the  vena  cava  ascendens, 
through  the  foramen  ovale,  passes  into  the  left  auricle  and  the  left  ventricle ; 
and  the  other,  from  the  vena  cava  descendens,  passes  through  the  right 
auriculo-ventricular  opening,  into  the  right  ventricle.  It  is  probable,  indeed, 
that  there  is  very  little  admixture  of  these  two  currents  of  blood  in  the  natu- 
ral course  of  the  total  circulation. 

The  blood  poured  into  the  left  auricle,  from  the  vena  cava  ascendens, 
through  the  foramen  ovale,  passes  from  the  left  auricle  into  the  left  ventricle. 
The  left  auricle  and  the  left  ventricle  also  receive  a  small  quantity  of  blood 


840 


GENERATION. 


from  the  lungs,  by  the  pulmonary  veins.     Thus  the  left  ventricle  is  filled. 
At  the  same  time  the  right  ventricle  is  filled  with  blood  which  has  passed 


Pulmonary  Art. 

Foramen  Ovale. 

Eustachian  Valve. 

Right  Auric.  -  Tent.  Opening. 


Hepatic  Vein. 

Branches  of  the 
Umbilical  Vein, 
to  (he  Liver. 


Bladder.  - 


Pulmonary  Art. 
Left  Auricle. 
Left  Auric.  -  Vent. 
Opening. 


"'  Ductus  Venosus. 


Internal  Iliac  Arteries. 
FIG.  315 — Diagram  of  thefcetal  circulation. 


through  the  right  auricle,  in  front  of  the  Eustachian  valve.     The  two  ventn- 
cles,  thus  distended,   then  contract  simultaneously.     The  blood  from  the 


THE  FCETAL  CIRCULATION.  841 

right  ventricle  passes  in  small  quantity  to  the  lungs,  the  greater  part  passing 
through  the  ductus  arteriosus,  into  the  descending  portion  of  the  arch  of 
the  aorta.  This  duct  is  half  an  inch  (12'7  mm.)  in  length,  and  about  the 
size  of  a  goose-quill.  The  blood  from  the  left  ventricle  passes  into  the  aorta 
and  goes  to  the  system.  The  vessels  of  the  head  and  superior  extremities 
being  given  off  from  the  aorta  before  it  receives  the  blood  from  the  ductus 
arteriosus,  these  parts  receive  almost  exclusively  the  pure  blood  from  the 
vena  cava  ascendens,  the  only  mixture  with  the  placental  blood  being  the 
blood  from  the  lower  extremities,  the  blood  from  the  portal  system  and  the 
small  quantity  of  blood  received  from  the  lungs.  After  the  aorta  has  received 
the  blood  from  the  ductus  arteriosus,  however,  it  is  mixed  blood ;  and  it  is 
this  which  supplies  the  trunk  and  lower  extremities. 

In  Fig.  315,  which  is  diagrammatic,  the  foetal  circulation  is  illustrated. 
In  endeavoring,  in  this  figure,  to  give  a  clear  idea  of  the  second  circulation, 
no  attempt  has  been  made  to  preserve  the  exact  relations  or  the  relative  size 
of  the  organs.  The  Eustachian  valve,  the  foramen  ovale  and  the  two  auric- 
ulo- ventricular  orifices  are  represented  by  dotted  lines.  The  liver  and  the 
bladder  are  also  represented  by  dotted  lines. 

The  Third,  or  Adult  Circulation. — When  the  child  is  born  the  placental 
circulation  is  suddenly  arrested.  After  a  short  time  the  sense  of  want  of  air 
becomes  sufficiently  intense  to  give  rise  to  an  inspiratory  effort,  and  the  first 
inspiration  is  made.  The  pulmonary  organs  are  then  for  the  first  time  dis- 
tended with  air,  the  pulmonary  arteries  carry  the  greatest  part  of  the  blood 
from  the  right  ventricle  to  the  lungs,  and  a  new  circulation  is  established. 
During  the  later  periods  of  foetal  life  the  heart  is  gradually  prepared  for  the 
new  currents  of  blood.  The  .foramen  ovale,  which  is  largest  at  the  sixth 
month,  after  that  time  is  partly  occluded  by  the  gradual  growth  of  a  valve, 
which  extends  from  below  upward  and  from  behind  forward,  upon  the  side 
of  the  left  auricle.  The  Eustachian  valve,  which  is  also  largest  at  the  sixth 
month,  gradually  atrophies  after  this  time,  and  at  full  term  it  has  nearly 
disappeared.  At  birth,  then,  the  Eustachian  valve  is  practically  absent ;  and 
after  pulmonary  respiration  becomes  established,  the  foramen  ovale  has  nearly 
closed.  The  arrangement  of  the  valve  of  the  foramen  ovale  is  such  that  at 
birth  a  small  quantity  of  blood  may  pass  from  the  right  to  the  left  auricle, 
but  none  can  pass  in  the  opposite  direction.  The  situation  of  the  Eustachian 
valve,  on  the  right  side  of  the  interauricular  septum,  is  marked  by  an  oval 
depression,  called  the  fossa  ovalis. 

As  a  congenital  malformation,  the  foramen  ovale  may  remain  open,  pro- 
ducing the  condition  known  as  cyanosis  neonatorum.  This  may  continue  into 
adult  life,  and  it  is  then  attended  with  more  or  less  disturbance  of  respiration 
and  difficulty  in  maintaining  the  normal  heat  of  the  body.  Usually  the  fora- 
men ovale  is  completely  closed  at  about  the  tenth  day  after  birth.  The  ductus 
arteriosus  begins  to  contract  at  birth,  and  it  is  occluded,  being  reduced  to 
the  condition  of  an  impervious  cord,  between  the  third  and  the  tenth  days. 

When  the  placental  circulation  is  arrested  at  birth,  the  hypogastric  arter- 
ies, the  umbilical  vein  and  the  ductus  venosus  contract,  and  they  become 


842  GENERATION. 

impervious  between  the  second  and  the  fourth  days.  The  hypogastric  arter- 
ies remain  pervious  at  their  lower  portion  and  constitute  the  superior  vesi- 
cal  arteries.  A  rounded  cord,  which  is  the  remnant  of  the  umbilical  vein, 
forms  the  round  ligament  of  the  liver.  A  slender  cord,  the  remnant  of  the 
ductus  venosus,  is  lodged  in  a  fissure  of  the  liver,  called  the  fissure  of  the 
ductus  venosus. 


CHAPTER  XXVI. 

FCETAL  LIFE-DEVELOPMENT  AFTER  BIRTH-DEATH. 

Enlargement  of  the  uterus  in  pregnancy— Duration  of  pregnancy — Size,  weight  and  position  of  the  foetus 
— The  foetus  at  different  stages  of  intrattterine  life— Multiple  pregnancy — Cause  of  the  first  contractions 
of  the  uterus,  in  normal  parturition — Involution  of  the  uterus — Meconium — Dextral  pre-eminence — De- 
velopment after  birth— Ages— Death — Cadaveric  rigidity  (rigor  mortis). 

As  the  development  of  the  ovum  advances,  the  uterus  is  enlarged  and  its 
walls  are  thickened.  The  form  of  the  organ,  also,  gradually  changes,  as  well 
as  its  position.  Immediately  after  birth  its  weight  is  about  a  pound  and  a 
half  (680  grammes)  while  the  virgin  uterus  weighs  less  than  two  ounces  (56-7 
grammes).  The  neck  of  the  uterus,  while  it  becomes  softer  and  more  patu- 
lous  during  pregnancy,  does  not  change  its  length,  even  in  the  very  latest 
periods  of  utero-gestation  (Taylor).  The  changes  in  the  walls  of  the  uterus 
during  pregnancy  are  very  important.  The  blood-vessels  become  much  en- 
larged, and  the  muscular  fibres  increase  immensely  in  size,  so  that  their  con- 
tractions are  very  powerful  when  the  foetus  is  expelled. 

It  is  evident  that  on  account  of  the  progressive  increase  in  the  size  of  the 
uterus  during  pregnancy,  it  can  not  remain  in  the  cavity  of  the  pelvis  dur- 
ing the  later  months.  During  the  first  three  months,  however,  when  it  is 
not  too  large  for  the  pelvis,  it  sinks  back  into  the  hollow  of  the  sacrum,  the 
fundus  being  directed  somewhat  backward,  with  the  neck  presenting  down- 
ward, forward  and  a  little  to  the  left.  After  this  time,  however,  the  in- 
creased size  of  the  organ  causes  it  to  extend  into  the  abdominal  cavity,  so 
that  its  fundus  eventually  reaches  the  epigastric  region.  Its  axis  then  has 
the  general  direction  of  the  axis  of  the  superior  strait  of  the  pelvis. 

The  enlargement  of  the  uterus  and  the  necessity  of  carrying  on  a  greatly 
increased  circulation  in  its  walls  during  pregnancy  are  attended  with  a  tem- 
porary hypertrophy  of  the  heart.  It  is  mainly  the  left  ventricle  which  is 
thickened  during  utero-gestation,  and  the  increase  in  the  weight  of  the  heart 
at  full  term  amounts  to  more  than  one-fifth.  After  delivery  the  weight  of 
the  heart  soon  returns  nearly  to  the  normal  standard. 

Duration  of  Pregnancy. — The  duration  of  pregnancy,  dating  from  a 
fruitful  intercourse,  must  be  considered  as  variable,  within  certain  limits. 
The  method  of  calculation  most  in  use  by  obstetricians  is  to  date  from  the 
end  of  the  last  menstrual  period.  Taking  into  account,  however,  the  various 


SIZE,  WEIGHT  AND  POSITION  OF  THE  FCETUS.  843 

cases  which  are  quoted  by  authors,  in  which  conception  has  been  supposed  to 
follow  a  single  coitus,  there  appears  to  be  a  range  of  variation  in  the  dura- 
tion of  pregnancy  of  not  less  than  40  days,  the  extremes  being  260  and  300 
days.  As  regards  the  practical  applications  of  calculations  of  the  probable 
duration  of  pregnancy  in  individual  oases,  the  fact  must  be  recognized  that 
the  period  is  variable.  Dating  from  the  end  of  the  last  menstrual  flow,  an 
average  of  278  days,  or  a  little  more  than  nine  calendar  months,  may  be 
adopted. 

Size,  Weight  and  Position  of  the  Foetus. — The  estimates  of  writers  with 
regard  to  the  size  and  weight  of  the  embryon  and  fetus  at  different  stages  of 
intraiiterine  life  present  very  wide  variations ;  still  it  is  important  to  have 
an  approximate  idea,  at  least,  upon  these  points,  and  the  estimates  by  Scan- 
zoni  are  given,  as  presenting  fair  averages. 

At  the  third  week  the  embryon  is  two  to  three  lines  (4-2  to  6-4  mm.)  in 
length.  This  is  about  the  earliest  period  at  which  measurements  have  been 
taken  in  the  normal  state. 

At  the  seventh  week  the  embryon  measures  about  nine  lines  (19-1  mm.). 
Points  of  ossification  have  appeared  in  the  clavicle  and  the  lower  jaw  ;  the 
Wolffian  bodies  are  large  ;  the  pedicle  of  the  umbilical  vesicle  is  very  much 
reduced  in  size ;  the  internal  organs  of  generation  have  just  appeared ;  the 
liver  is  of  large  size ;  the  lungs  present  several  lobules. 

At  the  eighth  week  the  embryon  is  ten  to  fifteen  lines  (21-2  to  31*8  mm.) . 
in  length.     The  lungs  begin  to  receive  a  small  quantity  of  blood  from  the 
pulmonary  arteries ;  the  external  organs  of  generation  have  appeared,  but  it 
is  difficult  to  determine  the  sex ;  the  abdominal  walls  have  closed  over  in 
front. 

At  the  third  month  the  embryon  is  two  to  two  and  a  half  inches  (50-8 
to  63-5  mm.)  long  and  weighs  about  one  ounce  (28'3  grammes).  The  amni- 
otic  fluid  is  then  more  abundant,  in  proportion  to  the  size  of  the  embryon, 
than  at  any  other  period ;  the  umbilical  cord  begins  to  be  twisted ;  the  vari- 
ous glandular  organs  of  the  abdomen  appear ;  the  pupillary  membrane  is 
formed ;  the  limitation  of  the  placenta  has  become  distinct.  At  this  time 
the  upper  part  of  the  embryon  is  relatively  much  larger  than  the  lower 
portion. 

At  the  end  of  the  fourth  month  the  embryon  becomes  the  foetus.  It  is 
then  four  to  five  inches  (10-1  to  12-7  centimetres)  long  and  weighs  about 
five  ounces  (141-7  grammes).  The  muscles  begin  to  show  contractility ; 
the  eyes,  mouth  and  nose  are  closed  ;  the  gall-bladder  is  just  developed  ;  the 
fontanelles  and  sutures  are  wide. 

At  the  fifth  month  the  foetus  is  nine  to  twelve  inches  (22'8  to  30'5  centi- 
metres) long  and  weighs  five  to  nine  ounces  (141-7  to  255-1  grammes).  The 
hairs  begin  to  appear  on  the  head ;  the  liver  begins  to  secrete  bile,  and  the 
meconium  appears  in  the  intestinal  canal ;  the  amnion  is  in  contact  with  the 
chorion. 

At  the  sixth  month  the  foetus  is  eleven  to  fourteen  inches  (27'9  to  35-5 
centimetres)  long  and  weighs  one  and  a  half  to  two  pounds  (680  to  907 


844  GENERATION. 

grammes).  If  the  foetus  be  delivered  at  this  time,  life  may  continue  for  a 
few  moments ;  the  bones  of  the  head  are  ossified,  but  the  f ontanelles  and 
sutures  are  still  wide ;  the  prepuce  has  appeared ;  the  testicles  have  not 
descended. 

At  the  seventh  month  the  foetus  is  fourteen  to  fifteen  inches  (35*5  to  38*1 
centimetres)  long  and  weighs  two  to  three  pounds  (907  to  1,361  grammes). 
The  hairs  are  longer  and  darker ;  the  pupillary  membrane  disappears,  under- 
going atrophy  from  the  centre  to  the  periphery ;  the  relative  quantity  of  the 
amniotic  fluid  is  diminished,  and  the  foetus  is  not  so  free  in  the  cavity  of  the 
uterus ;  the  foetus  is  now  viable. 

At  the  eighth  month,  the  foetus  is  fifteen  to  sixteen  inches  (38-1  to  40-9 
centimetres  long  and  weighs  three  to  four  pounds  (1,361  to  1,814  grammes). 
The  eyelids  are  opened  and  the  cornea  is  transparent ;  the  pupillary  membrane 
has  disappeared ;  the  left  testicle  has  descended  ;  the  umbilicus  is  at  about  the 
middle  of  the  body,  the  relative  size  of  the  lower  extremities  having  increased. 

At  the  ninth  month  the  foetus  is  about  seventeen  inches  (43*2  centimetres) 
long  and  weighs  five  to  six  pounds  (2-27  to  2-72  kilos).  Both  testicles  usu- 
ally have  descended,  but  the  tunica  vaginalis  still  communicates  with  the 
peritoneal  cavity. 

At  birth  the  infant  weighs  a  little  more  than  seven  pounds  (3-17  kilos), 
the  usual  range  being  between  four  and  ten  pounds  (1-81  and  4*53  kilos), 
although  these  limits  are  sometimes  exceeded. 

The  position  of  the  foetus,  in  the  great  majority  of  cases,  excluding  ab- 
normal presentations,  is  with  the  head  downward.  In  the  early  months  of 
pregnancy  the  foetus  floats  quite  freely  in  the  amniotic  fluid ;  and  it  is  prob- 
able that  the  natural  gravitation  of  the  head  and  of  the  upper  part  of  the 
foetus  is  the  determining  cause  of  the  ordinary  position  in  utero. 

The  shape  of  the  uterus  at  full  term  is  ovoid,  the  lower  portion  being  the 
narrower.  The  foetus  has  the  head  slightly  flexed  upon  the  sternum,  the 
arms  flexed  upon  the  chest  and  crossed,  the  spinal  column  curved  forward,  the 
thighs  flexed  upon  the  abdomen,  the  legs  slightly  flexed  and  usually  crossed 
in  front,  and  the  feet  flexed  upon  the  legs,  with  their  inner  margin  drawn 
toward  the  tibia.  This  is  the  position  in  which  the  foetus  is  best  adapted  to 
the  size  of  the  uterine  cavity,  and  in  which  the  expulsive  force  of  the  uterus 
can  be  most  favorably  exerted,  both  as  regards  the  foetus  and  the  generative 
passages  of  the  mother. 

Multiple  Pregnancy. — It  is  not  very  rare  to  observe  two  children  at  a 
birth,  and  cases  are  on  record  where  there  have  been  four  and  even  five, 
though  in  these  latter  instances  the  children  generally  survive  but  a  short 
time,  or  as  is  more  common,  atfortion  takes  place  during  the  first  months. 
Examples  of  three  at  a  birth  have  been  often  observed. 

In  cases  of  twins  it  is  an  interesting  question  to  determine  whether  the 
development  always  takes  place  from  two  ova  or  whether  a  single  ovum  may 
be  developed  into  two  beings.  In  the  majority  of  cases,  twins  are  of  the 
same  sex,  though  sometimes  they  are  male  and  female.  In  some  cases  there 
are  two  full  sets  of  membranes,  each  foetus  having  its  distinct  decidua,  pla- 


PARTURITION.  845 

centa  and  chorion ;  in  others  there  is  a  single  chorion  and  a  double  amnion ; 
but  in  some  both  foetuses  are  enclosed  in  the  same  amnion.  As  a  rule 
the  two  placentae  are  distinct ;  but  sometimes  there  is  a  vascular  com- 
munication between  them,  or  what  appears  to  be  a  single  placenta  may 
give  origin  to  two  umbilical  cords.  If  there  be  but  a  single  chorion  and 
amnion  and  a  single  placenta,  it  has  been  thought  that  the  two  beings  are 
developed  from  a  single  ovum ;  otherwise  it  would  be  necessary  to  assume 
that  there  were  originally  two  sets  of  membranes,  which  had  become  fused 
into  one.  The  instances  on  record  of  twins,  one  white  and  the  other  black, 
show  conclusively  that  two  ova  may  be  developed  in  the  uterus  at  the  same 
time.  While  there  can  be  no  doubt  upon  this  point,  the  question  of  the 
possibility  of  the  development  of  two  beings  from  a  single  ovum  remains  un- 
settled. 

As  pathological  conditions,  extrauterine  pregnancies  occur,  in  which  the 
fecundated  ovum,  forming  its  attachments  in  the  Fallopian  tube  (Fallopian 
pregnancy)  or  within  the  abdominal  cavity  (abdominal  pregnancy),  under- 
goes a  certain  degree  of  development.  The  uterus  usually  enlarges  in  these 
instances  and  forms  an  imperfect  decidua. 

Cause  of  the  First  Contractions  of  the  Uterus  in  Normal  Parturition. — 
The  cause  of  the  first  contraction  of  the  uterus  in  normal  parturition  is  un- 
doubtedly referable  to  some  change  in  the  attachment  of  its  contents,  which 
causes  the  foetus  and  its  membranes  to  act  as  a  foreign  body.  When  for  any 
reason  it  is  advisable  to  cause  the  uterus  to  expel  its  contents  before  the  full 
term  of  pregnancy,  the  most  physiological  method  of  bringing  on  the  con- 
tractions of  this  organ  is  to  cautiously  separate  a  portion  of  the  membranes, 
as  is  often  done  by  introducing  an  elastic  catheter  between  the  ovum  and  the 
uterine  wall.  A  certain  time  after  this  operation,  the  uterus  contracts  to 
expel  the  ovum,  which  then  acts  as  a  foreign  body. 

In  the  normal  state,  toward  the  end  of  pregnancy,  the  cells  of  the  decidua 
vera  and  of  that  portion  of  the  placenta  which  is  attached  to  the  uterus 
undergo  fatty  degeneration,  and  in  this  way  there  is  a  gradual  separation  of 
the  outer  membrane,  so  that  the  contents  of  the  uterus  gradually  lose  their 
anatomical  connection  with  the  mother.  W^hen  this  change  has  progressed 
to  a  certain  extent,  the  uterus  begins  to  contract ;  each  contraction  then 
separates  the  membranes  more  and  more,  the  most  dependent  part  pressing 
upon  the  os  internum ;  and  the  subsequent  contractions  are  due  to  reflex 
action.  The  first  "  pain  "  is  induced  by  the  presence  of  the  foetus  and  its 
membranes  as  a  foreign  body,  a  mechanism  similar  to  that  which  obtains 
when  premature  labor  has  been  brought  on  by  separation  of  the  membranes. 

According  to  Korner,  there  exists  in  the  spinal  cord,  at  the  site  of  the 
first  and  second  lumbar  vertebrae,  a  reflex  centre  for  parturition.  This,  like 
other  centres  in  the  cord,  is  subordinate  to  a  centre  which  is  situated  in  the 
medulla  oblongata. 

The  mechanism  of  parturition,  although  this  is  entirely  a  physiological 
process,  is  considered  elaborately  in  works  upon  obstetrics.  The  first  con- 
tractions of  the  uterus,  by  pressing  the  bag  of  waters  against  the  os  internum, 

55 


84:6  GENERATION. 

gradually  dilate  the  cervix ;  the  membranes  usually  rupture  when  the  os  is 
pretty  fully  dilated,  and  the  amniotic  fluid  is  discharged ;  the  head  then 
presses  upon  the  outlet ;  and  the  uterine  contractions  becoming  more  and 
more  vigorous  and  efficient,  the  child  is  brought  into  the  world,  this  being 
followed  by  the  expulsion  of  the  membranes  and  placenta.  There  then  fol- 
lows a  tonic  contraction  of  the  muscular  walls  of  the  uterus,  which  becomes 
a  hard,  globular  mass,  easily  felt  through  the  flaccid,  abdominal  walls.  The 
very  contractions  of  the  muscular  fibres  of  the  uterus  which  expel  the  foetus 
close  the  vessels  ruptured  by  the  separation  of  the  placenta  and  arrest  the 
haemorrhage  from  the  mother.  The  changes  which  then  take  place  in  the 
respiration  and  the  circulation  of  the  infant  have  been  considered  in  connec- 
tion with  the  development  of  the  circulatory  system. 

Involution  of  the  Uterus. — At  four  to  six  days,  and  seldom  later  than 
eight  days  after  parturition,  the  uterus  has  sensibly  advanced  in  the  process 
of  involution;  and  it  is  then  gradually  reduced  to  the  size  and  structure 
which  it  presents  during  the  non-pregnant  condition,  though  it  never  be- 
comes quite  as  small  as  in  the  virgin  state.  The  new  mucous  membrane, 
which  has  been  developing  during  the  latest  periods  of  pregnancy,  becomes 
perfect  at  about  the  end  of  the  second  month  after  delivery.  It  has  then 
united,  at  the  os  internum,  with  the  mucous  membrane  of  the  neck,  which 
has  not  participated  in  the  formation  of  the  decidua.  The  muscular  fibres, 
after  parturition,  present  granules  and  globules  of  fat  in  their  substance,  and 
are  gradually  reduced  in  size  as  the  uterus  becomes  smaller.  Their  involu- 
tion is  complete  at  about  the  end  of  the  second  month.  During  the  first 
month,  and  particularly  within  the  first  two  weeks  after  delivery,  there  is  a 
sero-sanguinolent  discharge  from  the  uterus,  which  is  due  to  disintegration 
of  the  blood  and  of  the  remains  of  the  membranes  in  its  cavity,  this  debris 
being  mixed  with  a  certain  quantity  of  sero-mucous  secretion.  This  dis- 
charge constitutes  the  lochia.  It  is  at  first  red  but  becomes  paler  as  it  is 
reduced  in  quantity  and  disappears. 

Meconium. — At  about  the  fifth  month  there  is  a  certain  quantity  of 
secretion  in  the  intestinal  canal,  which  becomes  more  abundant,  particularly 
in  the  large  intestine,  as  development  advances.  This  is  rather  light-colored 
or  grayish  in  the  upper  portion  of  the  small  intestine,  becoming  yellowish  in 
the  lower  portion,  and  it  is  of  a  dark-greenish  color  in  the  colon.  The  dark, 
pasty,  adhesive  matter,  which  is  discharged  from  the  rectum  soon  after  birth, 
is  called  the  meconium. 

The  meconium  appears  to  consist  of  a  thick,  mucous  secretion,  with 
abundant,  grayish  granules,  a  few  fatty  granules,  intestinal  epithelium,  and 
frequently  crystals  of  cholesterine.  The  color  seems  to  be  due  to  granula- 
tions of  the  coloring  matter  of  the  bile,  but  the  biliary  salts  can  not  be  de- 
tected in  the  meconium,  by  Pettenkofer's  test.  The  constituent  of  the  me- 
conium which  possesses  the  greatest  physiological  importance,  is  cholesterine. 
Although  but  few  crystals  of  cholesterine'  are  found  upon  microscopical 
examination,  the  simplest  processes  for  its  extraction  will  reveal  the  presence 
of  this  substance  in  large  quantity.  In  a  specimen  of  meconium  in  which  a 


DEXTRAL  PRE-EMINENCE. 


847 


FIG.  316.— Cholesterine  extracted  from  meconium. 


quantitative  examination  was  made,  the  proportion  of  cholesterine  was  6-245 
parts  per  1,000  (Flint).     The  meconium  contains  cholesteriiie  and  no  ster- 
corine,  the  stercorine,  in  the  adult, 
resulting  from  a  transformation  of 
cholesterine,  by  the  digestive  fluids, 
which  probably  are  not  secreted  dur- 
ing intraiiterine  life. 

None  of  the  secretions  concerned 
in  digestion  appear  to  be  produced 
in  utero,  and  it  is  also  probable  that 
the  true,  biliary  salts  are  not  formed 
at  that  time ;  but  the  processes  of 
disassimilation  and  excretion  are 
then  active,  and  the  cholesterine  of 
the  meconium  is  the  product  of  the 
excretory  action  of  the  liver.  The 
relations  of  cholesterine  as  an  ex- 
crementitious  product  have  already 
been  very  fully  discussed,  in  connection  with  the  bile  and  with  excre- 
tion. 

Dextral  Pre-eminence. — Most  persons  by  preference  use  the  right  arm, 
leg,  eye  etc.,  instead  of  the  left ;  but  exceptionally  some  use  the  left  in  pref- 
erence to  the  right.  There  can  be  no  doubt  with  regard  to  the  fact  of  a 
natural,  dextral  pre-eminence ;  and  also,  that  left-handedness  is  congenital, 
difficult  if  not  impossible  to  correct  entirely,  and  not  due  simply  to  habit. 
It  would  appear  that  there  must  be  some  condition  of  organization,  which 
produces  dextral  pre-eminence  in  the  great  majority  of  persons,  and  left- 
handedness,  as  an  exception ;  but  what  this  condition  is,  it  is  very  difficult 
to  determine.  An  explanation  which  was  offered  by  anatomists  is  that  the 
right  subclavian  artery  arises  nearer  the  heart  than  the  left,  that  the  right 
arm  is  therefore  better  supplied  with  arterial  blood,  develops  more  fully,  and 
therefore  is  generally  used  in  preference  to  the  left ;  but  the  exceptional  pre- 
dominance of  the  left  hand  can  not  be  explained  in  this  way. 

The  most  important  anatomical  and  pathological  facts  bearing  upon  the 
question  under  consideration  are  the  following :  Boyd  has  shown  that  the 
left  side  of  the  brain  almost  invariably  exceeds  the  right  in  weight,  by  about 
one-eighth  of  an  ounce  (3'5  grammes).  In  aphasia  the  lesion  is  almost  al- 
ways on  the  left  side  of  the  brain.  These  facts  point  to  a  predominance  of 
the  left  side  of  the  brain,  which  presides  over  the  movements  of  the  right 
side  of  the  body.  Again,  a  few  cases  of  aphasia  with  left  hemiplegia,  the 
lesion  being  on  the  right  side  of  the  brain,  have  been  reported  as  occurring 
in  left-handed  persons.  Ogle  gives  several  such  instances,  in  which  the 
brain-lesion  was  on  the  right  side.  In  two  left-handed  individuals,  the  brain 
was  examined  and  compared  with  the  brain  of  right-handed  persons.  It  was 
found  that  the  brain  was  more  complex  011  the  left  side  in  the  right-handed, 
and  on  the  right  side,  in  the  left-handed.  Bastian  has  found  the  gray  matter 


848  GENERATION. 

of  the  brain  generally  to  be  heavier  on  the  left  than  on  the  right  side.  With 
regard  to  the  cause  of  the  superior  development  of  the  left  side  of  the  brain, 
the  only  explanation  offered  is  the  fact  that  the  arteries  going  to  the  left  side 
usually  are  larger  than  those  on  the  right.  There  are  no  observations  with 
regard  to  the  comparative  size  of  the  arteries  upon  the  two  sides  in  left- 
handed  persons. 

Reasoning  from  the  facts  just  stated,  Ogle  has  assumed  that  dextral  pre- 
eminence depends  upon  a  natural  predominance  of  the  left  side  of  the  brain, 
the  reverse  obtaining  in  the  left-handed.  This  view  seems  to  afford  the 
most  rational  explanation  of  dextral  pre-eminence.  Generally  it  is  true  that 
the  members  on  the  right  side  are  stronger  than  the  left,  particularly  the 
arm ;  but  this  is  not  always  the  case,  even  in  the  right-handed,  although  the 
right  hand  is  more  conveniently  and  easily  used  than  the  left.  In  many 
feats  of  strength,  the  left  arm  appears  less  powerful  than  the  right,  because 
there  is  less  command  over  the  muscles.  As  regards  the  cause  of  the  superior 
development  of  the  left  side  of  the  brain,  it  must  be  admitted  that  the  ana- 
tomical explanation  is  not  entirely  satisfactory.  It  is  a  fact,  however,  that 
the  two  sides  of  the  brain  generally  are  not  exactly  equal  in  their  develop- 
ment, the  left  side  usually  being  superior  to  the  right,  and  that  the  muscles 
of  the  right  side  of  the  body  generally  are  used  in  preference  to  those  of  the 
left  side. 

DEVELOPMENT  AFTER  BIRTH — AGES  AND  DEATH. 

When  the  child  is  born,  the  organs  of  special  sense  and  the  intelligence 
are  dull ;  there  is  then  very  little  muscular  power ;  and  the  new  being,  for 
several  weeks,  does  little  more  than  eat  and  sleep.  The  natural  food  at  this 
time  is  the  milk  of  the  mother,  and  the  digestive  fluids  do  not  for  some  time 
possess  the  varied  solvent  properties  that  are  found  in  the  adult,  though  ob- 
servations upon  the  secretions  of  the  infant  are  few  and  rather  unsatisfac- 
tory. The  full  activity  of  pulmonary  respiration  is  gradually  and  slowly 
established.  Young  animals  appropriate  a  comparatively  small  quantity  of 
oxygen,  and  just  after  birth  they  present  a  much  greater  power  of  resist- 
ance to  asphyxia  than  the  adult.  The  power  of  maintaining  the  animal 
temperature  is  also  much  less  in  the  newly-born.  The  processes  of  ossification, 
development  of  the  teeth  etc.,  have  already  been  described.  The  hairs  are 
shed  and  replaced  by  a  new  growth  a  short  time  after  birth.  The  fonta- 
nelles  gradually  diminish  in  size  after  birth,  and  they  are  completely  closed 
at  the  age  of  about  four  years. 

The  period  of  life  which  dates  from  birth  to  the  age  of  two  years  is  called 
infancy.  At  the  age  of  two  years  the  transition  takes  place  from  infancy 
to  childhood.  The  child  is  then  able  to  walk  without  assistance,  the  food  is 
more  varied  and  the  digestive  operations  are  more  complex.  The  special 
senses  and  the  intelligence  become  more  acute,  and  the  being  begins  to  learn 
how  to  express  ideas  in  language.  The  child  gradually  develops,  and  the 
milk-teeth  are  replaced  by  the  permanent  teeth.  At  puberty,  which  begins 
between  the  fourteenth  and  the  seventeenth  years — a  little  earlier  in  the 


CADAVERIC  RIGIDITY.  849 

female — the  development  of  the  generative  organs  is  attended  with  important 
physical  and  moral  changes. 

The  different  ages  recognized  by  physiologists  are  the  following :  Infancy, 
from  birth  to  the  age  of  five  years ;  adolescence,  or  youth,  to  the  twenty-fifth 
year;  adult  age,  to  the  thirty-fifth  year;  middle  life,  to  the  fiftieth  year;  old 
age,  to  the  sixtieth  year ;  and  then,  extreme  old  age.  A  man  may  be  re- 
garded at  his  maximum  of  intellectual  and  physical  development  at  about  the 
age  of  thirty-five,  and  he  begins  to  decline  after  the  sixtieth  year,  although 
this  rule,  as  regards  intellectual  vigor,  has  many  exceptions. 

As  regards  nutrition,  it  may  be  stated  in  general  terms  that  the  appro- 
priation of  new  matter  is  a  little  superior  to  disassimilation,  to  about  the 
age  of  twenty-five  years ;  between  twenty-five  and  forty-five  these  two  pro- 
cesses are  nearly  equal ;  and  at  a  later  period  the  nutrition  does  not  com- 
pletely supply  the  physiological  waste  of  the  tissues,  the  proportion  of  organic 
to  inorganic  matter  gradually  diminishes,  and  death  follows,  as  an  inevitable 
consequence  of  life.  In  old  age  the  muscular  movements  gradually  become 
feeble ;  the  bones  contain  an  excess  of  inorganic  matter ;  the  ligaments  be- 
come stiff ;  the  special  senses  generally  are  somewhat  obtuse ;  and  there  is  a 
diminished  capacity  for  mental  labor,  with  more  or  less  loss  of  memory 
and  of  intellectual  vigor.  It  is  a  curious  fact  that  remote  events  are  more 
clearly  and  easily  recalled  to  the  mind  in  old  age  than  those  of  recent  occur- 
rence ;  and,  indeed,  early  impressions  and  prejudices  then  appear  to  be  un- 
usually strong. 

It  frequently  happens  in  old  age  that  some  organ  essential  to  life  gives 
way,  and  that  this  is  the  immediate  cause  of  death,  or  that  an  old  person  is 
stricken  down  by  some  disease  to  which  his  age  renders  him  peculiarly  liable. 
It  is  so  infrequent  to  observe  a  perfectly  physiological  life,  continuing 
throughout  the  successive  ages  of  man,  that  it  is  almost  impossible  to  present 
a  picture  of  physiological  death ;  but  it  sometimes  occurs  that  there  is  a 
gradual  fading  away  of  vitality  in  old  persons,  who  die  without  being  affected 
with  any  special  disease.  It  is  also  difficult  to  fix  the  natural  period  of  human 
life.  Some  persons  die,  apparently  of  old  age,  at  seventy,  and  it  is  rare  that 
life  is  preserved  beyond  one  hundred  years.  The  tissues  usually  die  succes- 
sively and  not  simultaneously,  nearly  all  of  them  being  dependent  upon  the 
circulating,  oxygen-carrying  blood,  for  the  maintenance  of  their  physiological 
properties.  It  has  been  demonstrated,  indeed,  that  the  properties  of  tissues 
may  be  restored  for  a  time,  after  apparent  death,  by  the  injection  of  blood 
into  their  vessels. 

After  death  there  often  is  a  discharge  of  the  contents  of  the  rectum  and 
bladder,  and  parturition,  even,  has  been  known  to  take  place.  The  appear- 
ance which  indicates  growth  of  the  beard  after  death  is  probably  due  to 
shrinking  of  the  skin  and,  perhaps,  contraction  of  the  smooth  muscular  fibres 
attached  to  the  hair- follicles.  The  most  important  phenomenon,  however, 
which  is  observed  before  putrefaction  begins,  is  a  general  rigidity  of  the  mus- 
cular system. 

Cadaveric  Rigidity  (Rigor  Mortis). — At  a  variable  time  after  death,  usu- 


850  GENEKATION. 

ally  five  to  seven  hours,  all  of  the  muscles  of  the  body,  involuntary  as  well  as 
voluntary,  become  rigid,  and  can  be  stretched  only  by  the  application  of  con- 
siderable force.  Sometimes,  especially  after  long-continued  and  exhausting 
diseases,  this  rigidity  appears  as  soon  as  a  quarter  of  an  hour  after  death.  In 
the  case  of  persons  killed  suddenly  while  in  full  health,  it  may  not  be  devel- 
oped until  twenty  or  thirty  hours  after  death,  and  it  then  continues  for  six 
or  seven  days.  Its  average  duration  is  twenty-four  to  thirty-six  hours ;  and 
as  a  rule  it  is  more  marked  and  lasts  longer  the  later  it  appears.  In  warm 
weather  cadaveric  rigidity  appears  early  and  continues  for  a  short  time. 
When  the  contraction  is  overcome  by  force,  after  the  rigidity  has  been  com- 
pletely established  and  has  continued  for  some  time,  it  does  not  reappear. 
The  rigidity  of  the  muscular  system  extends  to  the  muscular  coats  of  the 
arteries  and  lymphatics.  During  what  may  be  called  the  first  stage  the 
muscles  are  still  excitable ;  but  when  the  rigidity  is  complete  their  excita- 
bility is  lost  and  can  not  be  restored.  Cadaveric  rigidity  is  always  preceded 
by  loss  of  excitability  of  the  motor  nerves. 

The  rigidity  first  appears  in  the  muscles  which  move  the  lower  jaw.  Then 
it  is  noted  in  the  muscles  of  the  trunk  and  neck,  extends  to  the  arms,  and 
finally  to  the  legs,  disappearing  in  the  same  order  of  succession.  The  stiffen- 
ing of  the  muscles  is  due  to  a  coagulation  of  their  substance,  analogous  to 
the  coagulation  of  the  blood,  and  probably  is  attended  with  some  shortening 
of  the  fibres;  at  all  events,  the  fingers  and  thumbs  generally  are  flexed. 
That  the  rigidity  is  not  due  to  coagulation  of  the  blood,  is  shown  by  the  fact 
that  it  occurs  in  animals  dead  from  hsemorrhage. 

According  to  John  Hunter  the  blood  does  not  coagulate  nor  do  the  mus- 
cles become  rigid  in  animals  killed  by  lightning  or  hunted  to  death  ;  but  it  is  a 
question  in  these  instances  whether  the  rigidity  does  not  begin  very  soon  after 
death  and  continue  for  a  brief  period,  so  that  it  may  escape  observation.  As 
a  rule  rigidity  is  less  marked  in  very  old  and  in  very  young  persons  than  in 
the  adult.  It  occurs  in  paralyzed  muscles,  provided  they  have  not  under- 
gone extensive  fatty  degeneration. 

Under  ordinary  conditions  of  heat  and  moisture,  as  the  rigidity  of  the 
muscular  system  disappears  the  processes  of  putrefaction  begin.  The  vari- 
ous tissues — with  the  exception  of  certain  parts,  such  as  the  bones  and  teeth, 
which  contain  a  large  proportion  of  inorganic  matter — gradually  decompose, 
forming  water,  carbon  dioxide,  ammonia  etc.,  which  pass  into  the  earth  and 
the  atmosphere.  The  products  of  decomposition  of  the  organism  are  then  in 
a  condition  in  which  they  may  be  appropriated  by  the  vegetable  kingdom. 


INDEX. 


Absorption 272 

by  blood-vessels 272 

by  the  mucous  membrane  of  the  mouth. . .  272 

by  the  stomach 272 

by  the  intestinal  mucous  membrane 273 

by  lacteals 285 

—  by  parts  not  connected  with  the  digestive 
system 286 

—  by  the  skin 286 

by  the  respiratory  surface 287 

—  by  closed  cavities,  reservoirs  of  glands  etc.  288 

of  fats  and  insoluble  substances 288 

variations  and  modifications  of 290 

—  of  fluids  of  greater  density  than  the  blood.  290 

of  curare,  venoms  etc 290 

of  substances  which  disorganize  the  tissues  291 

—  influence  of  the  condition  of  the  blood  and 

of  the  vessels  upon 291 

influence  of  the  nervous  system  upon 291 

—  passage  of  liquids  through  membranes  (see 
Endosmosis) 292 

Accelerator  nerves  of  the  heart 55 

Accommodation  of  the  eye  for  different  degrees 
of  illumination 702 

—  for  different  distances 708 

Addison's  disease 421 

Adipose  tissue 442 

Adolescence 849 

Adult  age 849 

^Esthcsiometer 656 

After-images 716 

Ages  (infancy,  childhood,  youth,  adult  age,  mid- 
dle age  and  old  age) 848 

Agminated  glands  of  the  small  intestine 239 

Agraphia 621 

Air,  composition  of 135 

in  the  veins  (see  Veins) 98 

proper  allowance  of,  in  hospitals,  prisons 

etc ..  137 


Air-cells  of  the  lungs 114 

Air-swallowing 210 

Albumin 170 

Albuminates 227 

Albuminates  in  the  blood 23 

Albuminoids,  characters  of 170,  437 

—  in  the  body 437 

Albuminose  (peptones) 226 

Alcohol,  action  of,  in  alimentation  and  nutri- 
tion    . .  175 


PAGE 

Alcohol,  elimination  of 176 

influence  of,  upon  endurance,  the  power  of 

resistance  to  cold,  etc  177,  450 

formation  of,  in  the  body 440 

heat-value  of 454 

Alcoholic  beverages,  influence  of,  upon  the  ex- 
halation of  carbon  dioxide 144 

Aliment  (see  Food) 169 

Alimentation ^. 164 

Allantois,  formation  of . . .  . .  807 


villosities  of 807 

Alternate  paralysis 551 

Amoeboid  movements 460 

Ammonia,  exhalation  of,  by  the  lungs 149 

Amnion,  formation  of 803 

villosities  of 803 

enlargement  of 805 

Amniotic  fluid 805 

origin  of 806 

—  antiseptic  properties  of 806 

Amniotic  umbilicus 803 

Amphioxus  lanceolatus,  an  animal  without  a 

brain 617 

Amylopsine 246 

Andersch,  ganglion  of 665 

Anelectrotonus 535 

Angle  alpha  of  the  eye 691 

Animal  heat 444 

—  quantity  of  heat  produced  by  the  body, 
estimated  in  heat-units 444 

—  limits  of  variation  in  the  normal  tempera- 
ture in  man 446 

—  variations  of,  with  external  temperature. .  446 
variations  of,  in  different  parts  of  the  body  447 

—  variations  of,  at  different  periods  of  life. . .  448 
variations  of,  at  different  times  of  the  day, 

etc 448 

• relations  of  defective  nutrition  to 449 

—  in  inanition 449 

influence  of  alcohol  upon 449 

influence  of  exercise  etc.  upon 450 

influence  of  mental  exertion  upon 451 

—  influence  of  the  nervous  system  upon.  451,  641 
— —  centres  of 451 

—  mechanism  of  the  production  of 452 

relations  of  non-nitrogenized  and  nitrogen- 

ized  food  to  454 

—  equalization  of  456 

Antihelix  of  the  ear...  ..730 


INDEX. 


PAGE 

Ano-spinal  centre 270 

Antiperistaltic  movements  of  the  small  intestine  255 

Antiscorbutics 184 

Antitragus  of  the  ear 730 

Anns 201 

—  sphincter  of . . .  * 261,  2G9 

—  development  of 824 

—  imperforate 824 

Aorta,  development  of 836 

Aortse,  primitive 836 

Aortic  valves  '37 

Aphasia 621 

—  in  left  hemiplegia  in  left-handed  persons. 

C22,  847 

Appendices  epiploicse 260 

Appendix  vermif ormis 258 

—  development  of 823 

Appetite  for  food 165 

—  influence  of  climate  and  season  upon 165 

Aqueous  humor  of  the  eye 688 

Arachnoid 587 

—  first  appearance  of 819 

Arantius,  corpuscles  of 37 

Arbor  vitas  uteri 774 

Archiblastic  cells 835 

Arctic  regions,  diet  in 184 

Area  opaca  of  the  ovum 801 

Area  pellucida  of  the  ovum 801 

Area  vasculosa  of  the  ovum 835 

Arms,  development  of 817 

Arnold's  ganglion 638 

Arrowroot 171 

Arsenious  hydride,  effects  of 136 

Arteries,  physiological  anatomy  of 60 

—  course  of  the  blood  in 64 

—  elasticity  of 64 

—  gradual  diminution  of  the  intennittency  of 
the  current  in 64 

—  contractility  of 65 

—  influence  of  the  resiliency  of,  upon  the  cir- 
culation   65,  66 

influence  of  the  contractility  of  the  small 

vessels  upon  the  distribution  of  blood  in  the 
tissues 65,  66 

—  locomotion  of,  and  production  of  the  pulse    66 

—  tonicity  of 70 

variations  in  the  diameter  of,  at  different 

times  of  the  day 71 

—  pressure  of  blood  in 71 

—  pressure  in  different  vessels 73 

—  influence  of  respiration  upon  the  pressure 

of  blood  in 74 

—  influence  of  muscular  effort  upon  the  press- 
ure of  blood  in 74 

influence  of  haemorrhage  upon  the  pressure 

of  blood  in 75 

—  rapidity  of  the  flow  of  blood  in 76 

—  reason  why  they  are  found  empty  after 
death 107 

development  of 837 

Articular  cartilage 315,  487 

Arytenoid  muscle 490 

Asphyxia,  influence  of,  upon  the  circulation.  51,  85 

—  arrest  of  the  action  of  the  heart  in 51 

—  power  of  resistance  to,  in  the  newly-born. 

138,  162 


PACE 

Asphyxia,  phenomena  of 162 

influence  of  various  conditions  of  the  sys- 
tem upon  the  power  of  resistance  to 164 

Associated  movements    524 

Astigmatism 704 

Atmosphere,  composition  of 135 

Attollens  aurem 731 

Attrahens  aurem 731 

Audition,  general  considerations 728 

topographical  anatomy  of  the  parts  con- 
nected with 730 

—  physics  of  sound  (see  Sound) 737 

centres  for 764 

Auditory  meatus,  external 731 

development  of 826 

internal 729,  736 

Auditory  nerves,  physiological  anatomy  of 729 

—  general  properties  of 729 

Faradization  of 730 

—  development  of 821 

Auditory  vesicles 821 

Auerbach's  plexus 257 

Auricles  of  the  heart 32 

Auriculo- ventricular  valves,  action  of 43 

Axis-cylinder 508 

Azygos  uvulse 204 

Azygos  veins,  development  of 838 

Beats,  a  cause  of  discord 747 

Bellini,  tubes  of 361 

Berlin,  columns  of 359 

Besoin  de  respirer 157 

Bile,  action  of,  in  digestion 251 

—  color,  reaction  and  specific  gravity  of 252 

variations  in  the  flow  of 252 

—  influence  of,  upon  the  fasces  and  upon  the 
peristaltic  movements  of  the  intestine 253 

—  influence  of,  upon  the  digestion  and  ab- 
sorption of  fats 253 

—  absorption  of  the  salts  of,  by  the  intestinal 
canal 254 

mechanism  of  the  secretion  and  discharge 

of 399 

—  quantity  of 401 

—  properties  and  composition  of 401 

— tests  for 404 

Biliary  fistula 252 

nutrition  in  a  case  of 252 

Biliary  salts  402 

Bilirubin 404 

Biliverdine 404 

Binocular  vision 712 

fusion  of  colors 716 

Bitters,  influence  of,  upon  the  appetite 166 

"  Black-hole  "  of  Calcutta 163 

Bladder,  urinary,  physiological  anatomy  of 370 

—  first  appearance  of 822 

Blastodermic  cells 800 

Blastodermic  layers 802 

Blepharoptosis 542 

Blind  spot  of  the  retina 699 

Blood,  general  considerations 1 

extra-vascular  tissues 1 

—  effects  of  abstraction  and  subsequent  re- 
turn of 1 

transfusion  of 2 


INDEX. 


853 


Blood,  quantity  of 2 

—  opacity  of 3 

odor  of,  and  development  of  odor  of,  by 

sulphuric  acid 3 

taste  of 3 

reaction  of 4 

specific  gravity  of 4 

temperature  of 4 

color  of 4 

variations  in  the  color  of,  in  the  vascular 

system 4 

—  color  of,  in  veins  coming  from  glands 5 

—  anatomical  elements  (corpuscles)  of 5 

—  red  corpuscles  of 6 

—  relations  of  the  size  of  the  red  corpuscles 

of,  to  muscular  activity  in  different  animals. .  8 

enumeration  of  red  corpuscles  of 8 

post-mortem  changes  in  the  red  corpuscles 

of 9 

—  structure  of  the  red  corpuscles  of 10 

—  development  of  the  red  corpuscles  of . .  10,  834 

—  relations  of  leucocytes  to  the  development 

of  the  red  corpuscles  of 10 

—  theory  of  destruction  of  the  red  corpuscles 

of,  for  the  production  of  pigment 11 

relations  of  the  spleen  to  the  blood-cor- 
puscles   11,418 

—  uses  of  the  red  corpuscles  of 11 

—  capacity  of  the  red  corpuscles  of,  for  the 
absorption  of  oxygen,  as  compared  with  the 
plasma 12,  151 

—  action  of  the  red  corpuscles  of,  as  respira- 
tory organs  12,  151 

—  leucocytes,  or  white  corpuscles  of 12 

—  situations  in  which  leucocytes  are  found . .  12 

—  appearance  and  characters  of  leucocytes . .  13 

—  variations  in  the  proportion  of  leucocytes  13 

—  development  of  leucocytes 14 

proportion  of  leucocytes  in  the  blood  of 

the  splenic  veins 14 

uses  of  leucocytes  of 15 

plaques 15 

—  composition  of  the  red  corpuscles  of 18 

—  composition  of  the  blood-plasma 1? 

—  coloring  matter  of 17 

uses  of  water  in 20 

uses  of  sodium  chloride  in 21 

—  uses  of  other  inorganic  salts  in 21 

—  organic  saline  constituents  of 21 

—  organic  non-nitrogenized  constituents  of..  21 

—  excrementitious  constituents  of 21 

—  fats  and  sugars  in 21 

—  organic  nitrogenized  constituents  of 22 

—  plasmine,  fibrin,  metalbumen  and  serine  in  22 

—  peptones  in 23 

—  coloring  matter  of  the  plasma  of 23 

coagulation  of 23 

albuminates  in 23 

conditions  which  modify  coagulation  of, 

out  of  the  body 25 

—  coagulation  of,  in  the  organism 25 

coagulation  of,  in  animals  killed  by  light- 
ning or  hunted  to  death 25,  850 

—  office  of  the  coagulation  of,  in  the  arrest  of 
haemorrhage 26 

cause  of  the  coagulation  of 27 


Blood,  action  of  leucocytes  in  coagulation  of . .     27 

non-coagulation  of,  when  drawn   by  the 

leech 28 

— —  fibrillation  of  fibrin  in  coagulation  of 28 

—  non-coagulation  of,  in  the  renal  and  he- 
patic veins  and  in  the  capillaries 29 

circulation  of  (tee  Circulation) 29 

—  changes  in,  in  respiration  (see  Respiration;  135 
difference  in  color  between  arterial  and 

venous 150 

—  absorption  of  oxygen  by  the  red  corpuscles 

of 12,  151 

gases  of 151 

condition  of  the  gases  in 155 

—  general  differences  in  the  composition  of 
arterial  and  venous 154,  155 

sources  of  carbon  dioxide  of 157 

Blood-corpuscles,  development  of,  in  the  ovum  834 
Blood-vessels,  first  formation  of,  in  the  blasto- 

dermic  layers 834 

Bones,  anatomy  of 481 

—  regeneration  of,  by  transplantation  of  peri- 
osteum    485 

Bone-corpuscles 483 

Botal,  foramen  of 838,  841 

Bowman,  capsule  of 362 

Brain,  circulation  in 101,  £88 

—  contraction  and  expansion  of,  with  the  acts 

of  respiration 102,  583 

peculiarity  of  the  small  vessels  of 275,  588 

—  lymphatics  of 275,  588 

—  variations  in  the  quantity  of  blood  in 588 

ganglia  of 601 

—  weight  of  different  parts  of 602 

—  difference  in  the  weight  of,  in  the  sexes. . .  603 
differences  in  the  weight  of,  at  different 

ages 60) 

specific  gravity  of 603 

fissures  and  convolutions  of 604 

basal  ganglia  of 606 

directions  of  the  fibres  in 610 

rolling  and  turning  movements  following 

injury  of  certain  parts  of 633 

—  development  of 820 

Branchial  arches 837 

Bread 185 

Breschet,  perilymph  and  endolymph  of  759 

Bronchia Ill 

mucous  glands  of 113 

—  development  of 825 

Bronchial  arteries 115 

Brunner,  glands  of 235 

Buccal  glands 197 

Bulb  (see  medulla  oblongata) 627 

Burdach,  columns  of 593 

Butter 186,  336 

Cadaveric  rigidity ., 850 

Caecum 258 

—  development  of 823 

Caffeine 180 

Calcium  oxalate  in  the  urine 383 

Calcium  phosphate,  uses  of,  in  alimentation —  175 

Calcutta,  "  black  hole  "of 163 

Canals  of  Cuvier 837 

Cane-sugar 171 


854 


INDEX. 


PAGE 

Capillaries,  circulation  in  78 

—  physiological  anatomy  of 79 

stomata  in  the  walls  of 79 

size  of  79 

capacity  of  the  system  of 81 

course  of  blood  in 81 

—  study  of  the  circulation  in,  with  the  micro- 
scope     81 

"still  layer"  in 83 

circulation  in,  in  the  lungs 84 

—  pressure  of  blood  in 84 

—  rapidity  of  the  flow  of  blood  in 83 

—  relations  of  the  circulation  in,  to  respira- 
tion   85 

causes  of  the  circulation  in 86 

—  influence  of  temperature  upon 87 

Capriline 336 

Caprine 336 

Caprolne 336 

Capsicum 181 

Caput  coli 258 

Carbohydrates 170,  439 

Carbon,  quantity  of,  necessary  to  nutrition 183 

Carbonates  in  the  body 435,  436 

Carbon  dioxide,  small  proportion  of,  in  the  air  135 
relations  of  the  consumption  of  oxygen  to 

the  production  of 146 

—  exhalation  of,  in  respiration  (see  Kespira- 
tion) 140 

—  sources  of,  in  the  expired  air 148 

—  analysis  of  the  blood  for 151 

—  proportion  of,  in  the  blood.  154 

condition  of,  in  the  blood 155 

—  action  of  sodium  phosphate  upon  the  capa- 
city of  absorption  of,  by  the  blood 155 

—  sources  of,  in  the  blood 157 

effects  of  accumulation  of,  in  the  atmos- 
phere   163 

Carbon  monoxide,  effects  of 136,  164 

use  of,  in  analysis  of  the  blood  for  oxygen  152 

Cardiac  nerve-centres 55,  632 

Cardinal  veins 837 

Cardiograph 41 

Cardiometer 72 

Carotids,  development  of —  : 837 

Cartilage 486 

—  of  Meckel 821,  827 

Caruncula  lacrynmlis 727 

Caseine 170,  335 

vegetable 170 

Casper  Hauser,  case  of 714 

Catelectrotonus 535 

Cauda  equina 589 

Cellulose 172 

Cement  of  the  teeth..  190 

Cephalo-rachidian  fluid 101,  588 

Cerebellum,  weight  of 623 

—  physiological  anatomy  of 623 

course  of  the  fibres  in C24 

—  extirpation  of,  in  animals 624 

—  influence  of,  upon  muscular  co-ordination  625 
recovery  of  co-ordinating  power  after  re- 
moval of  a  portion  of 625 

—  pathological  facts  bearing  upon  the  uses  of  625 
connection  of,  with  the  generative  func- 
tion....    626 


PAGE 

Cerebellum,  development  of 819,  820 

Cerebral  localization 612 

Cerebral  vesicles,  formation  of 819 

Cerebrine 520 

Cerebro-spinal  axis,  general  arrangement  of 586 

Cerebro-spinal  fluid 101,  588 

Cerebrum,  weight  of 602 

cortical  substance  of 603 

fissures  and  convolutions  of 604 

612 
C13 
615 
616 
GIG 
C17 
017 


—  general  properties  of. . 

motor  cortical  zone  of. 

motor  centres  in. . . 


sensory  centres  in 

general  uses  of 

extirpation  of,  in  animals 

—  absence  of,  in  the  amphioxus  lanceolatus.. 
comparative  development  of,  in  the  lower 

animals 

—  comparative  development  of,  in  different 
races  of  men  and  in  different  individuals 

—  pathological  facts  bearing  upon  the  uses  of 
in  idiots 

—  centre  in,  for  the  expression  of  ideas  in 
language 

—  development  of 819, 

—  development  of  the  convolutions  of 

development  of  the  ventricles  of 

Cerumen 

Ceruminous  glands 

Chick,  development  of 

Childhood 

Chlorides  in  the  body 432, 

Chocolate 

Cholesterine 

transformation  of,  into  stercorine 266, 

—  in  the  bile 

origin  of  

elimination  of,  by  the  liver 

—  proportion  of,  in  the  blood  in  cases  of  grave 
and  of  simple  icterus 

—  proportion  of,  in  the  blood  in  cases  of  cir- 
rhosis   

—  poisoning  by  injection  of,  into  the  blood. . 

Cholestersemia 

Chondrine 439, 

Chondroplasts 

Chorda  dorsalis 

Chorda  tympani 

—  influence  of,  upon  gustation 554, 

Chords  in  music 

Chorion  of  the  ovum,  formation  of 

—  disappearance  of  villi  from  a  portion  of  808, 

Choroid 

Chromatic  aberration 

Chyle,  properties  and  composition  of 299, 

coagulation  of 

—  comparison  of  constituents  of,  with  those 
of  lymph .   

—  microscopical  characters  of 

—  movements  of  (see  Lymph) 

Cilia 

Cilia  (eyelashes) 

Ciliary  ganglion 

Ciliary  movements 

Ciliary  muscle 

Ciliary  nerves  (short) 


618 

619 
620 
620 

621 
820 
820 
820 
326 
322 
814 
848 
437 
180 
266 
407 
403 
406 
40S 

407 
407 


486 
815 
552 
664 
745 
803 
811 
676 
696 
301 
300 

302 
302 
303 
461 
724 
637 
461 
677 
543 


INDEX. 


855 


PAGE 

Ciliary  processes 677 

Cilio-spinal  centres 707 

Circulation  of  the  blood 29 

discovery  of 29 

action  of  the  heart  in  (see  Heart) 32 

effects  of  section  of  the  pneumogastrics 

upon 56 

effects  of  Faradizing  the  pneumogastrics 

or  their  branches  upon 56 

— .  reflex  influence  upon,  through  the  pneu- 
mogastrics      56 

—  in  the  arteries  (see  Arteries) CO 

depressor  nerve  of 75,  580 

—  in  the  capillaries  (see  Capillaries) 78 

—  in  the  veins  (see  Veins) 87 

in  the  cranial  cavity 101 

—  in  erectile  tissues 102 

derivative 103 

—  pulmonary 103 

—  in  the  walls  of  the  heart 104 

—  passage  of  the  blood-corpuscles  through  the 
walls  of  the  vessels 104 

—  general  rapidity  of 105 

—  relations  of  the  frequency  of  the  heart's  ac- 
tion to  the  rapidity  of 106 

—  phenomena  of,  after  death 107 

—  first  appearance  of,  in  the  ovum 835 

—  foetal  (see  Foetal  circulation) 839 

Circulatory  apparatus,  development  of 834 

Circumflexus,  or  tensor  palati  muscle 735 

Claustrtiin , 607 

Cleft  palate 838 

Climate,  influence  of,  upon  the  diet 184 

Clitoris 777 

Cloaca 822,  834 

Clot  of  blood  (see  Blood) 24 

Coagulation  of  the  blood  (see  Blood) 23 

Coccyx,  consolidation  of 817 

Cochlea,  bony 736 

—  membranous 756 

—  membrana  basilaris  of 757 

—  membrana  tectoria  (membrane  of  Corti)  of  757 

—  membrane  of  Reissner  of 757 

—  scala  tympani  and  scala  vestibuli  of 758 

—  the  true  membranous 758 

—  limbus  laminae  spiralis  of 759 

—  quadrilateral  canal  of 759 

—  distribution  of  the  nerves  in 759 

—  uses  of,  in  audition 763 

Cocoa 180 

Coffee 178 

—  composition  of 179 

—  influence  of,  upon  nutrition 179 

Coitus 793 

—  influence  of,  upon  the  rupture  of  the  Graa- 
fian  follicles 779 

—  action  of  the  male  in 704 

—  action  of  the  female  in 794 

—  action  of  the  cervix  and  os  uteri  in 795 

Colloids 438 

Colon 258 

—  development  of 823 

Color-blindness 723 

Colors 692 

—  perception  of 723 

Colostrum 338 


PAGE 

Colostrum,  relations  of  the  subsequent  secre- 
tion of  milk  to  the  quantity  of 339 

Colostrum-corpuscles 338 

Complemental  air 131 

Concha  of  the  ear 730 

Condiments 181 

Conjunctiva 725 

Connective  tissue 468 

—  development  of 834 

Consonance 747 

Consonants 503 

Contractility 472 

Co-ordination  of  muscular  movements,  connec- 
tion of  the  posterior  white  columns  of  the 
spinal  cord  with 596 

connection  of  the  cerebellum  with  (see  Cere- 
bellum)   625 

Cornea 675 

—  development  of 821 

Corona  radiata  of  the  ovum 777 

Corpora  striata 606 

—  development  of 820 

Corpus  Highmorianum 785 

Corpus  innominatum  (organ  of  Giraldes), 788 

Corpus  luteum 783 

trigonum 371 


Corpn 


Correlation  and  conservation  of  forces. 

Corti,  ganglion  of 

organ  of 

uses  of  the  organ  of 

Cotugno,  humor  of 

Coughing 

Cowper,  glands  of 

Cranial  nerves 

classification  of.  

Cranium,  circulation  in 

development  of 

Cream 

Creatine 

Creatinine 

Cremaster  muscle 

Cresol,  in  the  faeces 

Cretinism 


Crico-arytenoid  muscles. 

— —  posterior 

later 


nil . 


Crico-thyroid  muscles 

Crura  cerebri 

Crusta 

Crystalline  (organic  substance  of  the  lens) 

Crystalline  lens 

suspensory  ligament  of 

refraction  by 

changes  of,  in  accommodation 

development  of 

Cumulus  proligerus 770, 

Curling  arteries  of  the  placenta. .   

Cuticle  (see  Skin) 

Cutis  vera  (see  Skin) 

Cuvier,  canals  of 

Cyanosis  neonatorum 

Cystine 

Cytoblastions 


457 
7GO 
760 
763 
7'59 
129 
789 
539 
540 
101 
817 
334 
382 
383 
785 
264 
422 
489 
489 
490 
490 
608 
609 
439 
085 
687 
703 
709 
821 
777 
812 
344 
343 
&37 
841 
384 
344 


Dacryoline 728 

Dartos  ...  . .  785 


856 


INDEX. 


PAGE 

Death 444,632,  849 

—  phenomena  in  the  circulatory  system  after.  107 
discharge  of  contents  of  the  bladder  and 

rectum  after 849 

—  apparent  growth  of  the  beard  after 849 

—  parturition  after 849 

Decidua  vera 810 

—  reflexa 810 

serotina 810 

Deciduse,  formation  of 810 

Defalcation 268 

centre  for 270,  601 

Degeneration,  secondary,  in  the  cord. .  592,  593,  594 

Deglutition Ill,  202 

—  influence  of  the  saliva  upon 201 

action  of  the  tongue  in 206 

physiological  anatomy  of  the  parts  con- 
cerned in 206 

mechanism  of 206 

first  period  of 206 

in  cases  of  absence  of  the  tongue 206 

second  period  of 207 

action  of  the  constrictors  of  the  pharynx 

in  the  second  period  of 207 

protection  of  the  posterior  nares  during. . .  207 

protection  of  the  opening  of  the  larynx 

during 208 

action  of  the  epiglottis  in Ill,  208 

influence  of  the  sensibility  of  the  top  of 

the  larynx  in  protecting  the  opening  during..  208 

third  period  of 209 

action  of  the  oesophagus  in 209 

length  of  time  occupied  in 209 

character  of  the  movements  of 210 

in  the  inverted  posture 210 

of  air 210 

influence  of  the  small  root  of  the  fifth 

nerve  upon 550 

—  influence  of  the  spinal  accessory  nerves 
upon 560 

—  influence  of  the  snblingual  nerves  upon.. .  563 

—  influence  of  the  trifacial  upon   569 

—  influence  of  the  superior  laryngeal  branch- 
es of  the  pneumogastrics  upon 569,  579 

Demours,  membrane  of 675 

Dentals  (division  of  consonants) 503 

Dentine   189 

Depressor  nerve  of  the  circulation 75,  580 

Derivative  circulation 103 

Descemet.  membrane  of 675 

Deutoplasm 778 

Dextral  pre-eminence 847 

Dextrine 172,  201 

Diabetes,  artificial ,   411 

Diapedesis 104 

Diaphragm,  action  of.  in  inspiration 118 

development  of 824 

Diaphragmatic  hernia,  congenital 824 

Diaster 790 

Dicrotism  of  the  pulse 69 

Diet  (see  Food) 169 

—  regulation  of,  in  hospitals,  etc 183 

—  influence    of,   upon    the    development  of 
power  and  endurance 183 

—  variations  in,  in  different  climates 184 

in  arctic  regions 184 


FAGS 

Digestion 183 

action  of  the  saliva  in  (see  Saliva) . . : 200 

action  of  the  gastric  juice  in  (see  Gastric 

juice) 222 

duration  of,  in  the  stomach 228 

conditions  which  influence 229 

in  the  small  intestine 233 

action  of  the  intestinal  juice  in  (see  Intes- 
tinal juice) 242 

—  action  of  the  pancreatic  juice  in  (see  Pan- 
creatic juice) 247 

action  of  the  bile  in  (see  Bile) 251 

Digestive  fluids  in  the  foetus 824 

Dilator  tubce  muscle 735 

Diphthongs 501 

Disasisimilation  (see  Urine,  Fasces,  Sweat  and 

Excretion) 428 

Discords 746 

Discus  proligerus 770,  777 

Dorsal  plates 814 

Dreams .648 

Drinking,  mechanism  of 188 

Ductless  glands 413 

Ductus  arteriosus '. 836,841 

closure  of 841 

venostis &38,  842 

Duodenum 233 

glands  of 235 

Dura  mater 587 

—  first  appearance  of 818 

Ear,  glands  of 322,  731 

—  uses  of  the  hairs  at  the  opening  of 353 

—  disease  of  the  semicircular  canals  of . .  626,  763 

Ear,  external 730 

muscles  of 731 

uses  of 748 

Ear,  middle,  general  arrangement  of 731 

arrangement  of  the  ossicles  of 733,  753 

—  uses  of  different  parts  of 748 

—  development  of 821,  825 

Ear,  internal,  physiological  anatomy  of 755 

—  liquids  of 759 

distribution  of  the  nerves  in 759 

hair-cells  of 762 

—  uses  of  different  parts  of 763 

—  development  of 821 

Eggs 180 

Ejaculatory  ducts 789 

Elastic  tissue 462 

Elastine 439 

Electricity,  action  of,  upon  the  nerves 529 

action  of  descending  and  ascending  cur- 
rents of,  upon  the  nerves  (law  of  contraction)  532 

—  action  of  a  constant  current  of,  upon  the 
nerves 532,  535 

Electrotonns 535 

—  of  muscles 537 

Embryon 802 

time  when  it  becomes  the  foetus 813 

—  size,  weight,  and  development  of,  at  dif- 
ferent periods  of  utero-gestation 843 

Embryonic  spot 801 

Emulsification  of  fats 174 

Enamel  of  the  teeth 189 

Enamel-organ 828 


INDEX. 


85T 


PAGE 

Encephalon  (see  Brain) 601 

development  of 820 

End-bulbs 515 

Endocardium 32 

Endolymph  of  the  labyrinth 759 

Endosmometer 293 

Endosmosis 292 

Endothelium 802 

Epiblast 801,  814 

Epidermis  (see  Skin) 344 

first  appearance  of 818 

Epididymis 785,  787 

development  of,   from  a  portion  of   the 

Wolfflan  body 832 

Epiglottis,  uses  of,  in  deglutition Ill,  208 

—  cases  of  loss  of Ill,  208 

action  of,  in  deglutition Ill 

— •  removal  of,  from  the  lower  animals Ill 

— •  cases  of  loss  of,  in  the  human  subject Ill 

development  of 827 

Epithelium,  glandular 310 

pavement,  mucous  membranes  covered 

with 316 

columnar,  or  conoidal,  mucous  membranes 

covered  with 317 

•  ciliated,  mucous  membranes  covered  with.  317 

—  mixed,  mucous  membranes  covered  with. .  318 
influence    of,    upon    the    absorption    of 

venoms 320 

Equilibrium  of  the  body  in  nutrition 439,  453 

Erectile  organs,  structure  of 102,  794 

—  tissues,  circulation  in 102,  794 

Erection,  mechanism  of 794 

Erection  of  the  penis 794 

—  nerve  of 794 

Erection-centre 601,  794 

Eructation 232 

Eustachian  tube 734 

muscular  action  in  dilatation  of 735 

—  development  of 826 

Eustachian  valve 34,  838,  841 

—  disappearance  of 34,  841 

Excrementitious   matters,    mechanism   of  the 

production  of  (see  Excretion) 341 

Excretine 264 

Excretion,  distinction  of,  from  secretion. 

307,  311,  341 

—  mechanism  of 311,  341 

—  general  considerations 341 

Excretoleic  acid 264 

Excretory  action  of  the  liver 405 

Exercise,  influence  of,  upon  the  development  of 

parts 443 

Exosmosis 292 

Expiration 123 

—  action  of  the  elasticity  of  the  parenchyma 

of  the  lungs  in 123 

action  of  the  elasticity  of  the  thoracic  walls 

in    123 

—  table  of  muscles  of 124 

action  of  the  abdominal  muscles  in 125 

—  relations  of,  to  inspiration 128 

—  duration  of  128 

Expression,  nerve  of  (see  Facial  nerve) 550 

External  capsule 607 

Eye,  physiological  anatomy  of 674 


PAGE 

Eye,  chambers  of  688 

—  summary  of  the  anatomy  of  the  globe  of. .  689 
refraction  in  ((see  Vision) 690 

—  considered  as  an  optical  instrument 691 

—  simple  schematic 703 

movements  of 718 

muscles  of 718 

—  protrusion  and  retraction  of,  by  muscular 

action 719 

action  of  the  recti  muscles  of 720 

—  action  of  the  oblique  muscles  of 720 

associated  action  of  the  muscles  of 721 

parts  for  the  protection  of 723 

—  development  of 821 

Eyebrows 353,  724 

Eyelashes 353,  724 

Eyelids / 724 

—  glands  of 323,  724 

muscles  of 725 

—  development  of 821 

—  time  of  separation  of,  in  the  foetus 821 

Face,  development  of 825 

Facial  angle 619 

Facial  nerve 550 

—  decussation  of  the  roots  of 550 

—  general  properties  of 553 

uses  of  the  branches  of,  given  off  within 

the  aqueduct  of  Fallopius 553 

—  influence  of,  upon  the  movements  of  the 
palate  and  uvula 554 

uses  of  the  external  branches  of 555 

- influence  of,  upon  mastication,  through  the 

buccinator  muscle 557 

Faeces,  influence  of  the  bile  upon 253 

—  constituents  of 264 

—  bacteria  of 264 

Fallopian  pregnancy 845 

Fallopian  tubes 775 

development  of,  from  the  ducts  of  Muller.  831 

Falsetto-register 497 

Fats,  composition  of 173,  174 

—  saponification  of 174 

emulsification  of ^ 174 

—  absorption  of  (gee  Absorption) 288 

relations  of,  to  nutrition 440 

—  formation  and  deposition  of 440 

anatomy  of  adipose  tissue 442 

Fatty  degeneration 441 

Fatty  diarrhoea,  cases  of 250 

Fauces,  pillars  of 203 

isthmus  of 203 

Fecundation,  situation  of 795,  799 

—  time  when  it  is  most  likely  to  occur 795 

mechanism  of 796 

Fecundity,  limits  of,  as  regards  age 780 

Fenestra  ovalis 732,  736 

Fenestra  rotunda 732,  736 

Ferrcin,  pyramids  of 359,  361 

Fibrin 22 

—  of  the  clot 24 

—  formation  of,  by  decomposition  of  plas- 
mine 27 

fibrillation  of,  in  coagulation 29 

Fibrin-factors 27 

Fibrin-ferment .27 


858 


INDEX. 


PAGE 

Fibrinogen 23,  27 

Fibrinoplastic  matter 23,  27 

Fibro-cartilage 487 

Fifth  cranial  nerve,  small  root  of  (see  Mastica- 
tion, nerve  of)  547 

large  root  of 564 

—  physiological  anatomy  of 564 

—  branches  of 505 

—  properties  and  uses  of 568 

—  operation  for  the  division  of,  within  the 
cranial  cavity 568 

• immediate  effects  of  division  of 568 

—  influence  of,  upon  deglutition 569 

remote  effects  of  division  of 570 

—  different  remote  effects  of  division  of,  be- 
fore and  behind  the  ganglion  of  Gasser 571 

—  relations  of,  to  the  sympathetic  system  ...  571 

—  cases  of  paralysis  of,  in  the  human  sub- 
ject    572 

Filum  terminale 589 

Flavors 663 

Foetal  circulation 839 

change  of,  into  the  adult  circulation 841 

Foetus,  blood-corpuscles  of 10 

—  respiratory  efforts  by 161,  822 

urine  of 390 

determination  of  the  sex  of 797 

influence  of  the  maternal  mind  upon  the 

development  of 799 

—  at  the  fifth  month 808 

—  time  when  this  name  is  applied  to  thu  prod- 
uct of  fecundation 813 

reflex  movements  in   822 

—  respiratory  efforts  by 822 

digestive  fluids  in 824 

—  size,  weight,  and  development  of,  at  differ- 
ent periods  of  utero-gestation 843 

when  viable 844 

weight  of,  at  term 844 

—  position  of,  in  the  uterus 844 

Food,  definition  of 169 

classification  of 169 

—  nitrogenized  constituents  of 169 

animal .  .^ 170 

vegetable 170 

non-nitrogenized  constituents  of 170 

inorganic  constituents  of 174 

— r  quantity  and  variety  of,  necessary  to  nu- 
trition   181,  182 

regulation  of,  in  hospitals,  etc 183 

influence  of,  upon  the  capacity  for  labor. .  183 

necessity  of  a  varied  diet. 184 

—  influence  of  climate  and  season  upon  the 
quantity  of 184' 

influence  upon  nutrition  of  single  articles 

of,  when  taken  alone 187 

heat- value  of 453 

Foot-pound 444,  458 

Foramen  ovale 33,  838,  841 

—  closure  of 841 

Force,  relations  of  heat  to 457 

Fourth  ventricle 629 

Fovea  cardiaca 836 

centralis 681 

Free-martin 781,  799 

Fromann,  lines  of 508 


PAGE 

Frontal  process,   in  the  development  of   the 
face 826 

Galactose 336 

Gall-bladder 399 

—  development  of 824 

Gases  of  the  blood 151 

—  in  the  blood  in  different  parts  of  the  system  154 

Gases  in  the  body 429 

Gasser,  ganglion  of 565 

Gasterase 221 

Gastric  fistula  in  the  lower  animals 217 

—  in  the  human  subject 216 

Gastric  juice 216 

mode  of  collecting 217 

secretion  of 218 

—  artificial .  218 

—  modifications  of  the  secretion  of 219 

—  quantity  of 219 

properties  and  composition  of 219 

—  antiseptic  properties  of 220,  226 

—  table  of  composition  of 220 

organic  constituent  of 221 

source  of  the  acidity  of 221 

ordinary  saline  constituents  of 221 

—  action  of,  In  digestion 222 

Gelatine 439 

French  committee  on 187 

Gelatine  of  Wharton   809 

Generation 765 

—  spontaneous 765 

sexual 765 

766 

..  784 


female  organs  of 

male  organs  of 

—  development  of  the  internal  organs  of 

development  of  the  external  organs  of 

Gcniculate  ganglion 

Genito-spinal  centre 373, 

Genito-urinary  apparatus,  development  of 

Germinal  spot 

Germinal  vesicle 

—  disappearance  of 

Giraldes,  organ  of 

Glands,  excitability  of 

—  color  of  the  blood  in  the  veins  of 5, 

comparative  quantity  of  blood  in,  during 

activity  and  repose 5, 

elimination  of  foreign  substances  by 

anatomical  classification  of 

ductless,  or  blood-glands 

terminations  of  nerves  in 

Glandular  epithelium 

Glisson,  capsule  of 392, 

Globuline 

Glosso-labio-laryngeal  paralysis 

Glosso-pharyngeal  nerves 

—  general  properties  of 


—  relations  of,  to  gustation 

Glottis,  movements  of,  in  respiration 

—  development  of , 

Glucose  (see  Sugars) 

Gluten 

Glutine 

Glycocholic  acid  and  sodium  glycocholate 

Glycogen,  mechanism  of  the  formation  of,  by 

the  liver  (see  Liver) 408, 


834 
552 
794 
830 
778 
778 
7% 
788 
310 
311 

311 
311 
313 
413 
512 
310 
393 
16 
564 
665 
667 
667 
111 
825 
171 
185 
186 
402 

409 


INDEX. 


859 


Glycogen,  mode  of  extraction  of 409 

Goblet  cells 214 

Goll,  columns  of 593 

Goose-flesh 344 

Graaflan  follicles 768 

situation  of  the  ovum  in 771 

rupture  of 769,  779 

Grape-sugar 171 

Gubernaculum  testis 831 

Gums 1?2 

Gustation,  relations  of,  to  olfaction 662 

general  considerations  of 663 

nerves  of 664 

—  uses  of  the  chorda  tympani  in 664 

—  uses  of  the  glosso-pharyngeal  nerve  in 067 

—  physiological  anatomy  of  the  organ  of CCS 

centre  for 670 

Gutturals  (division  of  consonants) 503 


Haemadynamometcr 

Hsemaglobine 17, 

absorption  of  oxygen  by 


Haematine 

Ha?matocrystalline 

Hffimatosine 

Hsematosis 

Haemophilia 

Hasmorrhagic  diathesis 

Hair-cells  of  the  internal  ear 

Hairs,  physiological  anatomy  of 

growth  of 

development  of 

shedding  of,  in  the  infant 

sudden  blanching  of 

uses  of 

first  appearance  of 

Haller,  vas  aberrans  of 

Hamulus  of  the  cochlea 

Harelip 

Harmonics,  or  overtones 

Harmony 

Hauser,  Caspar,  case  of 

Haversian  canals 

Haversian  rods 

Head-fold  of  the  neural  canal 

Hearing  (see  Audition) 

Heart,  description  of  the  action  of,  by  Har- 


175 

17 

17 

17 

17 

150 

333 

20 

762 

348 

352 

352 

353 

352 

353 

818 

787 

757 

828 

743 

745 

714 

482 

482 

802 

728 


vey. 


general  description  of  the  action  of 31 

physiological  anatomy  of 32 

comparative  capacity  of  the  right  and  the 

left  ventricle  of 34 

quantity  of  blood  discharged  by  each  ven- 
tricular systole  of 34 

muscular  tissue  of 35 

•  comparative  thickness  of  the  ventricles  of  35 

valves  of 36 

movements  of 37 

action  of  the  auricles  of 38 

action  of  the  ventricles  of 38 

locomotion  of 39 

twisting  of 39 

hardening  of 39 

shortening  and  elongation  of 39 

—  impulse  of 40 

succession  of  the  movements  of . .     .  40 


PAGE 

Heart,  relative  time  occupied  by  the  auricular 

and  the  ventricular  contractions  of 43 

force  of • 42 

action  of  the  valves  of 43,  44 

sounds  of 44 

—  frequency  of  the  action  of  (see  Pulse) 48 

influence  of  respiration  upon  the  action  of    51 

arrest  of  the  action  of,  in  asphyxia 51 

cause  of  the  rhythmical  contractions  of . . .     52 

arrest  of  the  action  of,  by  tying  the  coro- 
nary arteries .   . .   53,  58 

—  contractions  of,  produced  by  stimulation 
during  its  repose 53 

—  influence  of  the  blood  in  its  cavities  upon 
the  contractions  of 53 

—  influence  of  the  density  of   its  contents 
upon  the  contractions  of 5.') 

ganglia  in  the  substance  of 54 

accelerator  nerves  of 55 

nerve  centre  of 55,  632 

—  influence  of  the  sympathetic  nerves  upon..  E5 

direct  inhibition  of 56 

reflex  inhibition  of 57 

—  want  of  action  of  digitalis  upon,  after  sec- 
tion of  the  pneumogastrics 56 

—  effects  of  Faradization  of  the  pneumogas- 
trics upon 56 

influence  of  the  pnenmogastrics upon...  56,  57 

—  influence  of  the  spinal  accessory  nerves 
upon 56,  560 

—  palpitation  of 57 

—  influence  of  mental  emotions  upon 57 

summary  of  causes  of  arrest  of  the  action  of  58 

death  from  distention  of 58 

—  death  from  a  blow  upon  the  epigastrium  . .  59 
relations  of  the  force  of,  to  the  frequency 

of  its  pulsations 75,  107 

circulation  in  the  walls  of 104 

—  time  required  for  the  passage  of  the  entire 
mass  of  blood  through 106 

relation  of  the  frequency  of  the  action  of, 

to  the  rapidity  of  the  circulation 106 

temperature  of  the  blood  in  the  two  sides 

of 4,  448 

development  of 830,  838 

relative  size  of,  in  the  foetus  and  at  differ- 

*ent  periods  of  life 839 

enlargement  of,  in  pregnancy 842 

Heart-clots.. 25 

Heat,  animal  (see  Animal  heat) 444 

Heat-centres 451 

Heat-units   444,  458 

Helix  of  the  ear 730 

Hemialbumose. 227 

Hemianopsia 722 

Henle,  tubes  of 362 

sheath  of .510 

Hereditary  transmission 797 

Hernia  at  the  umbilicus,  in  the  foetus.  807,  8C9,  822 

diaphragmatic 824 

Hibernation,  consumption  of  oxygen  in 139 

cholesterine  in  the  fasces  in 267 

Hiccough 130 

Hippuric  acid  and  its  compounds 381 

Homer,  muscle  of 724 

Horopter 713 


8GO 


INDEX. 


Hunger 165 

scat  of  the  sense  of 100 

—  after  section  of  both  pneumogastric  nerves  167 

—  after  section  of  the  hypoglossal  and  lingual 
nerves 107 

Hydatids  of  Morgagni 785 

Hydrogen,  effects*  of  confining  an  animal  in  a 

mixture  of  with  oxygen 139 

Hydrogen  monosulphide,  poisonous  effects  of. .  136 

Hyoid  bone,  development  of 825,  827 

Hypermetropia 695 

Hypnagogic  hallucinations 048 

Hypoblast 801,  814 

Hypogastric  arteries 839 

closure  of 842 

Hypoglossal  nerve  (see  Sublingual  nerve) 561 

Hypospadias 834 

Hypoxanthine 384 

Ileo-csecal  valve 259 

—  development  of 823 

Ileum 234 

Iliac  veins,  development  of 838 

Imbibition 291 

Imperf orate  anus 824 

Inanition,  influence  of,  upon  the  exhalation  of 

carbon  dioxide 144 

influence  of  age  upon  the  power  of  resist- 
ance to 165 

—  phenomena  attending 166 

—  duration  of  life  in 168 

Incisor  process,  in  the  development  of  the  face  826 
Incus 733 

—  development  of 825 

Indol,  production  of,  by  action  of  trypsine  on 

albuminoids 249,  267 

in  the  fasces 264 

Induced  muscular  contraction 534 

Inelastic  fibrous  tissue 469 

Infancy 848 

secretion  of  milk  in 340 

Inf racostales,  action  of,  in  expiration 125 

Innominate  vein,  development  of 838 

Inorganic  alimentary  substances 174 

Inorganic  constituents  of  the  body 429 

Inspiration 116 

table  of  muscles  of 147 

auxiliary  muscles  of 121 

relations  of,  to  expiration 128 

duration  of 128 

Insula 606,  621 

Intellectual  faculties 616 

Intercostal  muscles  120 

action  of,  in  inspiration 120 

action  of,  in  expiration 124 

Intermaxillary  process,  in  the  development  of 

the  face 826 

Internal  capsule 607 

Intestinal  canal,  fermentation  in 202 

—  first  appearance  of 822 

Intestinal  digestion 233 

Intestinal  fistula,  case  of,  in  the  human  subject  242 

Intestinal  juice 240 

Intestinal  villi 237 

—  development  of 823 

Intestine,  small,  physiological  anatomy  of 233 


PAGE 

Intestine,  movements  of 255 

uses  of  the  gases  in 256,  271 

—  influence  of  the  circulation  upon  the  move- 
ments of 256 

—  influence  of  the  nervous  system  upon  the 
movements  of 257 

distribution  of  the  pneumogastric  to 257 

—  influence  of  the  pneumogastric  upon 257 

development  of 823 

Intestine,  large,  physiological  anatomy  of 257 

—  digestion  and  absorption  in 262 

contents  of  (see  Faeces) 263 

movements  of 267 

gases  of 270 

—  development  of 823 

Inuline 172 

Involuntary  muscular  tissue  and  movements. . .  404 

Involution  of  the  uterus 840 

Iris,  influence  of   the   motor   oculi  communis 

upon 543,  706 

anatomy  of  679 

movements  of 705 

—  direct  action  of  light  upon 706 

—  action  of  the  nervous  system  upon 706 

—  influence  of  the  sympathetic  nerves  upon..  707 

—  consensual  contraction  of 707 

—  influence  of  the  cilio-spinal  centre  upon . . .  707 

—  changes  of,  in  accommodation 710 

movements  of,  in  converging  the  axes  of 

vision 706,  710 

voluntary  contraction  of 711 

—  development  of 821 

Iron,  uses  of,  in  the  organism 175 

in  milk  and  eggs 175 

Irradiation  in  the  spinal  cord 598 

in  vision 717 

Island  of  Reil 600,  621 

Jacobson,  nerve  of 665 

Jacob's  membrane 681 

Jaws,  physiological  anatomy  of 192 

articulations  of 192 

Jejunum 234 

Jugular  veins,  development  of 838 

Juice-canals 274 

Keratine 439 

Kidneys,  effects  of  destruction  of  the  nerves 
of 313,  369 

—  physiological  anatomy  of 358 

distribution  of  blood-vessels  in 364 

lymphatics  of 360 

nerves  of 366 

—  extirpation  of 366 

—  extirpation  of,  upon  one  side 368 

alternate  action  of,  upon  the  two  sides 369 

—  development  of 832 

Kinetic  energy 458 

Krause,  corpuscles  of 515 

Labia  majora,  development  of 834 

Labia  minora,  smegma  of 325 

Labial  glands 197 

Labials  (division  of  consonants) 503 

Labyrinth,  bony 735 

membranous 755 

liquids  of 759 


INDEX. 


861 


PAGE 

Labyrinth,  distribution  of  the  nerves  in 759 

development  of 821 

Lachrymal  apparatus 726 

—  glands 726 

fluid 727 

—  points 727 

sac  and  ducts 727 

Lachrymine 728 

Lactates  in  the  blood 21 

—  in  the  nrine 382 

Lactation,  modifications  of  (see  Milk) 331 

Lacteals,  in  the  intestinal  villi 238 

discovery  of 273 

•  course  of 279 

structure  of 281 

—  absorption  by 285 

Lactoproteine 335 

Lactose 171,  33G 

Lancet-fish,  an  animal  without  a  brain 617 

Language 501 

centre  for  the  expression  of  ideas  in C21 

Laryngoscopy 491 

Larynx,  physiological  anatomy  of 110 

action  of,  in  respiration.  Ill 

muscles  of 489 

action  of,  in  phonation, 491 

—  development  of 825,  827 

Laughing 130 

Laxntor  tympani 733 

Lecithene 21 

Lef  t-handedness  (see  Dextral  pre-eminence) . . .  847 

Legs,  development  of 817 

Lenses,  refraction  by 693 

—  correction  of 697 

Lenticular  ganglion 637 

Leucine  in  the  urine 384 

—  production  of,  by  the  action  of  trypsine  on 
albuminoids 249 

Leucocytes  (see  Blood) 12 

relations  of,   to  the  development  of  the 

blood-corpuscles 10 

—  development  of 14,  834 

—  passage  of,  through  the  walls  of  the  blood- 
vessels    104 

—  in  the  lymph 274,  298 

Leucocy thaemia 14,  418 

Levator  anguli  scapulae,  action  of,  in  respira- 
tion    122 

Levator  palati .-  204 

Levator  palpebrce  superioris 725 

Levatores  costarurn,  action  of,  in  respiration. . .  121 

Lichenine 172 

Lieberkuhn,  follicles  of 236 

Life,  definition  of,  etc 427 

—  duration  of ,  in  man 849 

Ligamentum  denticulatum 588 

Ligamentum  iridis  pectinatum 676 

Light,  theory  of  the  propagation  of 692 

velocity  of 692 

—  decomposition  of 693 

Lingual  glands 198 

Lips,  development  of 826 

Liquids  (division  of  consonants)  503 

Littre,  glands  of 789 

Liver,  circulation  in  the  veins  of 97 

—  formation  of  urea  in 377,  400 

56 


PAQB 

Liver,  physiological  anatomy  of 392 

structure  of  a  lobule  of 395 

arrangement  of  the  bile-ducts  in  the  lobules 

of 396 

—  anatomy  of  the  excretory  biliary  passages 

of 397 

racemose  glands  attached  to  the  ducts  of. .  397 

—  vasa  aberrantia  of 398 

—  gall-bladder,  hepatic,  cystic,  and  common 
ducts  of 398 

nerves  and  lymphatics  of 399 

excretory  action  of 405 

formation  of  glycogen  by 408 

—  ferment  produced  by,  which  is  capable  of 
changing  glycogen  into  sugar 410 

—  action  of,  upon  foreign  and  poisonous  sub- 
stances    413 

development  of 824 

proportionate  weight  of,  at  different  peri- 
ods of  life 824 

Lobule  of  the  ear 731 

Lochia 846 

Locomotion,  passive  organs  of 481 

Locomotor  ataxia 596,  654 

Locus  niger. 609 

Lungs,  capillary  circulation  in 84 

circulation  through 103 

—  parenchyma  of 113 

air-cells  of 114 

—  action  of  the  elasticity  of  the  parenchyma 

of,  in  expiration 123 

—  capacity  of 130 

—  vital  capacity  of 133 

—  absorption  by  the  respiratory  surface 287 

—  development  of 825 

Luxus-consumption 438 

Lymph  294 

—  quantity  of 295 

properties  and  composition  of 295 

coagulation  of 295 

corpuscular  elements  of 274,  298 

origin  and  uses  of 299 

—  comparison  of  constituents  of,  with  those 

of  chyle 302 

movements  of 303 

Lymphatic  glands 279,  283 

uses  of 285 

Lymphatic  trunk,  right 279 

Lymphatics,  discovery  of 273 

—  descriptive  anatomy  of 273 

relations  of,  to  connective  tissue 274 

valves  of 276,  282 

structure  of 281 

Lymph-corpuscles 274,  298 

Lymph-spaces 274 

Macula  folliculi 779 

Macula  lutea 681 

Malleus 733 

development  of 825 

Malpighi,  pyramids  of 359 

Malpighian  bodies  of  the  kidney 361,  362 

—  capsule  of  the  spleen 414 

bodies  of  the  spleen 415 

Maltose 201 

Mammary  glands 327 


862 


INDEX. 


PAQR 

Mammary  secretion  (see  Milk) 327 

Manege,  movements  of 634 

Mannite 172 

Mariotte,  experiment  of 699 

Marrow 484 

Mastication 189 

table  of  muscles  of 193 

—  action  of  the  muscles  of,  which  depress  the 

lower  jaw 193 

-• — -action  of  the  muscles  which  elevate  the 
lower  jaw  and  move  it  laterally  and  antero- 

posteriorly   194 

action  of  the  tongue,  lips  and  cheeks  in. . .  194 

action  of  the  orbicularis  oris  and  buccina- 
tor in 194 

uses  of  the  sensibility  of  the  teeth  to  hard 

and  soft  substances  in 195 

— •  influence  of,  upon  the  flow  of  the  parotid 

saliva 196 

nerve  of 547 

—  properties  and  uses  of  the  nerve  of 549 

influence  of  division  of  the  nerve  of,  upon 

the  teeth,  in  the  rabbit 549 

influence  of,  upon  deglutition 550 

Mastoid  cells • 734 

Maxilla,  inferior,  development  of 826 

—  superior,  development  of 826 

Maxillary  bones,  physiological  anatomy  of 192 

articulations  of 192 

Meats 185 

Meckel,  cartilage  of 821,  827 

Meckel's  ganglion 638 

Meconium 824,  846 

Medulla  oblongata,  physiological  anatomy  of . .  627 

—  general  properties  of 630 

uses  of 630 

connection  of,  with  respiration 158,  631 

development  of 819,  820 

Medullocells 484 

Meibomian  glands 333,  724 

secretion 326 

Meissner,  corpuscles  of 514 

Meissner's  plexus 257 

Melody 741 

Membrana  f  usca 676 

Membranes  of  the  f oetus,  formation  of 802 

Meniere's  disease 626,  763 

Menstruation •. 781 

— —  supposed  appearance  of,  after  extirpation 

of  the  ovaries 781 

duration  of 782 

characters  of  the  flow  in 782 

diminution  in  the  excretion  of  urea  in 783 

Mery,  glands  of 789 

Mesenteric  vein,  development  of 837 

Mesentery 233 

development  of 823 

Mesoblast 802,  814 

Mesocsecum 259 

Mesocolon 260 

Metabolism 428 

Metalbumin 22 

Micropyle 778,  796 

Micturition 372 

Milk 186,  333 

mechanism  of  the  secretion  of 330 


Milk,  modifications  of .    331 

—  quantity  of 332 

—  general  properties  of 333 

coagulation  of 333,  336 

—  microscopical  characters  of 334 

—  composition  of 334 

comparison  of,  from  the  cow  and  from  the 

human  subject 336 

fermentation  of 336 

variations  in  the  composition  of 337 

—  relations  of  the  quantity  of,  to  the  previous 
secretion  of  colostrum 339 

of  the  infant 340 

Milk-globules 334 

Milk-sugar 171,  336 

Mind 616 

Mitral  valve 37 

Modiolus  of  the  cochlea 757 

Molar  glands 197 

Monoplegias 615 

Morgagni,  liquid  of 686 

—  hydatids  of 785 

Morsus  diaboli 776 

Morula 800 

Motor  cortical  zone 613 

Motor  nerves,  disappearance  of  excitability  of.  521 

action  of 523 

Motor  oculi  communis 541 

influence  of,  upon  the  iris 543 

Motor  oculi  externus 546 

Mouth,  first  appearance  of 826 

Movements 460 

of  amorphous  contractile  substance  (amoe- 
boid)    460 

ciliary 461 

due  to  elasticity 462 

muscular 464 

associated 524 

Mucilages 172 

Mucine 319 

Mucinogen 310 

Mucous  membranes 316 

Mucus,  mechanism  of  the  secretion  of 318 

composition  and  varieties  of 319 

—  influence  of,  upon  the  absorption  of  ven- 
oms    320 

Muller,  capsule  of 362 

— duct  of 831 

Muscles,  connection  of,  with  the  tendons 470 

voluntary,  terminations  of  nerves  in 511 

involuntary,  terminations  of  nerves  in 512 

Muscular  atrophy,  progressive . . . » 645 

Muscular  current 479 

Muscular  effort 480 

Muscular  movements  (see  Movements) 464 

Muscular  sense 654 

Muscular  system,  development  of 818 

Muscular  tissue,  involuntary 464 

contraction  of 465 

voluntary 466 

—  development  of,  by  exercise 467 

—  blood-vessels  and  lymphatics  of 470 

chemical  composition  of 470 

reactions  of 471 

—  physiological  properties  of .  471 

elasticity  of 471 


INDEX. 


863 


PAGE 

Muscular  tissue,  tonicity  of 471 

sensibility  of 472 

contractility  of 472 

changes  in  the  form  of,  during  contraction  475 

duration  of  contraction  of,  under  artificial 

excitation 476 

single  contraction  of 476 

tetanic  contraction  of 477 

—  sound  produced  by  contraction  of 477 

—  fatigue  of 478 

—  electric  phenomena  in 479 

negative  variation  of 480 

Musical  sounds  (see  Sound) 739 

Mustache,  uses  of 353 

Mustard  181 

Mutes  (division  of  consonants) 503 

Myeline 507 

Myelocy tes 520 

Myeloplaxes 484 

Myolemma 467 

Myopia 695 

Myosine 439,  470 

Myxcedema 422 

Naboth,  ovules  of 774 

Nails,  physiological  anatomy  of 345 

connections  of,  with  the  skin 347 

growth  of 347 

—  development  of 347 

—  first  appearance  of 818 

Nares,  development  of 828 

Nasal  duct 727 

Nasal  fossae 658 

action  of,  in  phonation 495 

Nasals  (division  of  consonants) 503 

Nasmyth's  membrane 189 

Negative  variation  of  the  muscular  current 480 

of  the  nerve-current 537 

Nerve-cells 517 

striation  of,  by  the  action  of  silver  nitrate.  519 

connections  of,  with  the  fibres  and  with 

each  other 519 

Nerve-centres,  structure  of 517 

accessory  anatomical  elements  of 519 

connective  tissue  of  (neuroglia) 520 

blood-vessels  of 520 

—  lymphatics  of  (peri vascular  canals) 520 

Nerve-current 535 

Nerve-fibres 507 

—  mednllated 507 

axis-cylinder  of 508 

—  striation  of,  by  the  action  of  silver  nitrate.  508 

non-medullated 509 

gelatinous,  or  fibres  of  Remak 509 

Nerves,  structure  of 507 

blood-vessels  of 511 

branching  and  course  of 511 

terminations  of,  in  the  voluntary  muscles.  511 

terminations  of,  in  the  involuntary  mus- 
cles    512 

terminations  of,  in  glands 512 

sensory,  terminations  of 513,  516 

degeneration  and  regeneration  of 521 

trophic  centres  for 521 

reunion  of 522 

motor  and  sensory 522,  526 


PAGE 

Nerves,  motor,  action  of 523 

sensory,  action  of 525 

—  physiological  differences   between  motor 

and  sensory 526 

artificial  union  of  motor  with  sensory 526 

excitability    of    (see   Nervous    excitabil- 


ity). 


527 

—  action  of  electricity  upon  (see  Electricity) .  529 

process  of  dying  of 533 

galvanic  current  from  the  exterior  to  the 

cut  surface  of 535 

spinal 538 

cranial  (see  Cranial  nerves) 539 

—  development  of 819 

Nervi  nervorum 511 

Nervous  conduction,  rapidity  of 527 

Nervous  excitability 527 

Nervous  system,  divisions  of 505 

physiological  anatomy  of  the  tissue  of 507 

development  of 818 

—  action  of,  in  the  f retus 822 

Nervous  tissue,  composition  of 520 

Neural  canal 814 

head-fold  of 802 

Neurilemma 507 

Neuroglia  of  the  nerve-centres 520 

—  of  the  spinal  cord 591 

Neutral  point 536 

Nitrogen,  proportion  of,  in  the  air 135 

exhalation  of,  in  respiration 150 

—  quantity  of,  necessary  to  nutrition  182 

Nitrogen  monoxide,  effects  of  respiration  of . . .  136 

Nitrogenized  alimentary  substances 169 

Non-nitrogenized  alimentary  substances 170 

action  of,  in  nutrition 439 

Nose,  uses  of  the  hairs  in 353 

—  development  of 826,  828 

Notochord \ 815 

Nutrition,  quantity  and  variety  of  food  neces- 
sary to 181,  182 

general  considerations 426 

action  of  inorganic  substances  in 428,  429 

substances    consumed   by   the    organism 

in 437 

action  of  nitrogenized  substances  in 438 

action  of  non-nitrogenized  substances  in. .  439 

modifications  of,  by  various  conditions 442 

O'Beirne,  sphincter  of 269 

Obesity 441 

Obliquus  externus,  action  of,  in  expiration 125 

internus,  action  of,  in  expiration 125 

Odors 661 

(Esophagus,  structure  of 205 

action  of,  in  deglutition 209 

alternate  contraction  and  relaxation  of —  209 

—  development  of 824 

Oils  (see  Fats) 173 

Oken,  bodies  of 814,  830 

Old  age 849 

Oleine 1?4 

Olfaction,  mechanism  of 661 

relations  of,  to  the  sense  of  taste 662 

Olfactory  cells 660 

Olfactory  centre 662 

Olfactory  ganglia,  or  bulbs 660 


364 


INDEX. 


Olfactory  commissures  and  nerves,  development 

of 822 

Olfactory  nerves 659 

—  properties  and  uses  of 660 

Omentum 260 

—  development  of 823 

Omphalo-mesenteric  canal 807 

Omphalo-mesenteric  vessels 836 

Ophthalmic  ganglion 637 

Optic  commissure 672 

Optic  nerves,  physiological  anatomy  of 671 

—  decussation  of 672 

—  general  properties  of 673 

—  development  of 821 

Optic  thalami 607 

—  development  of 819.  820 

Osmosis 292 

Osseine  (bone-corpuscles) 439 

Ossicles  of  the  ear 733 

—  mechanism  of  the  action  of 753 

Ossification  of  the  skeleton 818 

time  of,  for  various  bones 818 

Osteoplasts 483 

Otic  ganglion 638 

Otoliths 756 

Ovaries 767 

Graafian  follicles  of 768 

—  development  of •. . . .  769 

Overtones 743 

Ovules  of  Naboth 774 

Ovum,  primordial 768 

Ovum,  situation  of,  in  the  Graafian  follicle 771 

—  structure  of 777 

—  discharge  of,  from  the  Graafian  follicle 778 

—  influence  of  copulation  upon  the  discharge 

of 779 

relations  of  the  discharge  of,  to  menstru- 
ation    779 

—  passage  of,  into  the  Fallopian  tube 779 

—  coating  of,  with  albumen,  in  the  Fallopian 
tube 795,  799 

—  union  of  spermatozoids  with 796 

—  primitive  trace  on 801 

—  development  of 813 

Oxygen,  absorption  of,  by  the  blood-corpuscles 

12,  151 

—  proportion  of,  in  the  air 135 

—  minimum  proportion  of,  in  the  air,  capable 

of  supporting  life 138 

—  effects  of  respiration  of  pure 136 

—  consumption  of  (see  Respiration) 133 

relations  of  the  consumption  of,  to  the  ex- 
halation of  carbon  dioxide 146 

analysis  of  the  blood  for 152 

—  proportion  of,  in  the  blood 154 

Oxyhoemaglobine 17,  155 

Pacini,  corpuscles  of 513 

Palatals  (division  of  consonants) 503 

Palate 203 

muscles  of 204 

—  development  of 828 

Palmitine 174 

Pancreas,  physiological  anatomy  of 243 

development  of 824 

Pancreatic  juice 244 


PAGE 

Pancreatic  juice,  mode  of  secretion  of 244 

properties  and  composition  of 245 

—  quantity  of 247 

—  alterations  of 247 

action  of,  in  digestion 247 

action  of,  upon  starches  and  sugars 247 

action  of,  upon  nitrogenized  substances. . .  248 

action  of,  upon  fats 250 

Pancreatic  secretion,  centre  for 341 

Pancreatine 246 

Panniculus  adiposus 343,  442 

Parablastic  cells 834 

Paracentral  lobule 614 

Paraglobuline 23,    27 

Paralytic  secretion  by  glands 313 

Parotid  saliva  (see  Saliva) 195 

Parovarium 771,  831 

Parturition,  cause  of  the  first  contractions  of 

the  uterus  in 845 

centre  for 001,  845 

arrest  of  hemorrhage  after 846 

after  death 849 

Par  vagum  nerve  '(see  Pneumogastric) 573 

Patheticus 545 

Pavement-epithelium  (squamous  epithelium). . .  316 
Pectoralis  major,  action  of  the  inferior  portion 

of,  in  respiration 122 

Pectoralis  minor,  action  of,  in  respiration 122 

Pectose 172 

Penis,  erection  of 794 

development  of 834 

Pepper 181 

Pepsine 221 

Pepsinogen 310 

Peptones 224,  226 

in  the  blood 23 

Pericardial  secretion 32 

Pericardium 32 

Perilymph  of  the  labyrinth •. 759 

Perimeter 712 

Perimysium 468 

Perivitelline  space 778 

Periosteum 485 

Peristaltic  movements  of  the  small  intestine. . .  255 

influence  of  the  bile  upon 253 

influence  of  the  nervous  system  upon 257 

Peritoneal  cavity,  first  appearance  of 815,  824 

Perivascular  canals 275,  588 

Personal  equation 529 

Perspiration  (see  Sweat) 353 

Petit,  canal  of 687 

Pettenkofer's  test  for  bile 405 

Peyer,  patches  of 239 

Pharyngeal  glands 198 

Pharynx,  physiological  anatomy  of 202 

muscles  of 204 

mucous  membrane  of 204 

—  action  of  the  muscles  of,  in  deglutition 207 

—  action  of,  in  phonation 495 

—  development  of : 823 

Phenol,  production  of,  by  the  action  of  tryp-  ' 

sine  on  albuminoids 249,  267 

in  the  faeces 264 

Phonation  (see  Voice) 491 

Phonograph 504 

Phosphates  in  the  body 433,  436 


INDEX. 


865 


PAGE 

Phrenic  nerve 119 

Pia  mater 587 

—  first  appearance  of 818 

Pia  mater  testis 786 

Pineal  gland 425 

Pinna  of  the  ear 730 

Pituitary  body 425 

Pituitary  membrane 658 

Placenta,  first  appearance  of 811 

—  development  and  structure  of 812 

uses  of 813 

Placental  circulation 836 

Plasma  of  the  blood  (see  Blood) 17 

Plasmine 22 

Pleuro-peritoneal  cavity,  first  appearance  of  ...  815 
Pnenmogastric  nerves,  influence  of,  upon  the 

action  of  the  heart 56 

want  of  action  of  digitalis  upon  the  heart 

after  section  of 56 

—  effects  of  Faradization  of,  upon  the  circu- 
lation   56,  57 

direct  influence  of,  upon  the  heart 56,  57 

—  influence  of,  upon  the  movements  of  the 
email  intestine 257 

—  physiological  anatomy  of 573 

branches  of 574 

difference  in  the  distribution  of  the  nerves 

of  the  two  sides,  to  the  abdominal  organs 577 

—  general  properties  of  the  roots  of 577 

properties  and  uses  of  the  auricular  branch 

of 578 

—  properties   and   uses   of   the   pharyngeal 
branch  of 578 

properties  and  uses  of  the  superior  laryn- 

geal  branch  of 578 

properties  and  uses  of  the  inferior,  or  re- 
current laryngeal  branch  of 579 

influence  of  the  inferior  laryngeal  branch 

of,  upon  the  movements  of  the  larynx 579 

properties  and  uses  of  the  cardiac  branches 

of 580 

effects  of  section  of,  upon  the  circulation. 

56,  580 

—  properties   and   uses    of    the   pulmonary 
branches  of 581 

effects  of  section  of,  upon  the  respiratory 

movements 581 

condition  of  the  lungs  after  death  follow- 
ing section  of 581 

effects  of  Faradization  of,  upon  respira- 
tion    582 

—  properties   and   uses  of   the  cesophageal 
branches  of 583 

—  effects  of  division  of,  upon  the  oesophagus.  583 
properties   and    uses    of    the   abdominal 

branches  of 583 

—  influence  of,  upon  the  liver 583 

—  influence  of,  upon  the  stomach 230,  584 

distribution  of,  to  the  intestinal  canal 585 

want  of  action  of  purgatives,  after  section 

of 585 

Polar  globule  of  the  vitellus 796 

Pons  Varolii 609 

uses  of 610 

development  of 819,  821 

Portal  vein,  distribution  of  (see  Liver) 393 


PACK 

Portal  vein,  development  of 837 

Potatoes 186 

Potential  energy 457 

Pregnancy,  influence  of,  upon  lactation 331 

influence  of,  upon  menstruation 781 

—  influence  of,  upon  the  corpus  luteum 784 

—  influence  of,  upon  subsequent  offspring. .  797 
—  enlargement  of  the  uterus  in 842 

—  enlargement  of  the  heart  in 842 

duration  of 842 

—  multiple 844 

extrauterine 845 

Fallopian 845 

abdominal 845 

Prehension  of  solids  and  liquids.' 188 

Prepuce,  smegma  of 325 

Presbyopia 695 

Primitive  trace  of  the  embryon 801 

Progressive  muscular  atrophy 645 

Pronucleus,  male  and  female 797 

Propeptone 227 

Prostate 789 

Protagon 520 

Proteids 437 

Proteine 170,  438 

Protoplasm 460 

Protovertebrae 816 

Ptosis  (see  Blepharoptosis) 542 

Pytaline 200 

Puberty 780 

Pulmonary  artery,  pressure  of  blood  in 104 

—  development  of 836 

Pulmonary  circulation 103 

Pulmonic  semilunar  valves 37 

safety-valve  action  of 44 

Pulp-cavity  of  the  teeth 190 

Pulse,  frequency  of,  at  different  ages 48 

in  the  sexes 48 

influence  of  digestion  upon  the  frequency 

of 49 

influence  of  muscular  exertion  upon  the 

frequency  of 49 

comparative  frequency  of,  in  sitting  and 

standing 49 

—  influence  of  sleep  upon  the  frequency  of . .    50 
influence  of   temperature  upon  the   fre- 
quency of 50 

—  production  of,  and  locomotion  of  the  arte- 
ries      66 

—  investigation  of,  by  the  finger 66  . 

gradual  delay  of,  receding  from  the  heart.    67 

—  pathological  varieties  of 67 

form  of 67 

movements  of,  in  the  foot  when  the  legs 

are  crossed 67 

traces  of 68 

dicrotism  of 69 

influence  of  temperature  upon  the  form  of.    70 

in  the  veins 94,  100 

relation  of  the  frequency  of,  to  the  respira- 
tory acts 127 

Pupil 679 

Pupillary  membrane 680,  821 

Purkinje,  vesicle  of 778 

Putrefaction  of  the  body  after  death 850 

Pyloric  muscle 212 


866 


INDEX. 


PAGE 

Quadrilateral  canal  of  the  cochlea 759 

Quickening 813 

Rnnvier,  nodes  of 508 

Reaction-time 620 

Receptaculura  chyli 273 

Rectum,  physiological  anatomy  of 258,  261 

—  sphincter  of 269 

—  development  of 823 

Recurrent  sensibility 523 

Reflex  action,  time  occupied  by 529 

definition  of 598 

—  of  the  spinal  cord 598 

—  exaggeration  of,  by  poisoning  with  strych- 
nine    599 

abolition  of,  by  anaesthetics 599 

examples  of 599 

inhibition  of 600 

—  operating    through  the  sympathetic  sys- 
tem   643 

in  the  foetus 822 

Reflexes,  superficial  and  deep 600 

Refraction 690 

Regurgitation  from  the  stomach 232 

Reil,  island  of 606,  621 

Reissner,  membrane  of 757 

Remak,  fibres  of 509 

Reproduction  (see  Generation) 765 

Reserve  air 131 

Residual  air 131 

Resonators  of  Helmholtz 744 

Respiration,  influence  of,  upon  the  action  of  the 

heart 51 

movements  of  the  brain  with 102 

general  considerations  and  definition  of. . .  108 

essential  conditions  in 109 

—  physiological  anatomy  of  the  organs  of  ...  110 

movements  of 115 

action  of  the  ribs  in 116,  120 

—  table  of  muscles  of,  used  in  inspiration ...  117 

—  auxiliary  muscles  of,  used  in  inspiration  . .  121 

table  of  muscles  of,  used  in  expiration . . .  124 

action  of  the  abdominal  muscles  in  125 

types  of 126 

difference  in  types  of,  in  the  sexes  and  at 

different  ages 126 

—  frequency  of  the  movements  of 127 

relations  of  the  frequency  of  the  movements 

of,  to  the  pulse 127 

• influence  of  age  upon  the  frequency  of  the 

movements  of 127 

—  relations  of  inspiration  and  expiration  to 
each  other  in 128 

sounds  of 128,  129 

—  extreme  breathing  capacity  in 133 

—  relations  in  volume  of  the  expired  to  the  in- 
spired air  in 133 

diffusion  of  air  in 134 

—  of  pure  oxygen 136 

—  consumption  of  oxygen  in 136 

—  variations  in  the  consumption  of  oxygen 
in,  with  muscular  activity,  external  tempera- 
ture and  digestion 138 

quantity  of  oxygen  consumed  per  hour  in .  138 

variations  in  the  consumption  of  oxygen 

in,  with  age 138 


Respiration,  variations  in  the  consumption  of 
oxygen  in,  sleeping  and  waking 139 

variations  in  the  consumption  of  oxygen 

in,  in  lean  and  fat  animals 139 

effects  upon  the  consumption  of  oxygen 

in,  of  increasing  its  proportion  in  the  air. . ... .  139 

—  effects  upon  the  consumption  of  oxygen  in, 
of  confining  an  animal  in  a  mixture  of  oxy- 
gen and  hydrogen 139 

— —  changes  in  the  air  passing  through  the  lungs  140 

elevation  in  temperature  in  the  air  in  pass- 
ing through  the  lungs  in 140 

exhalation  of  carbon  dioxide  in 140 

variations  in  the  exhalation  of  carbon  di- 
oxide with  the  frequency  and  extent  of  the 
acts  of 140,  141 

quantity  of  carbon  dioxide  exhaled  per 

hour  in 142 

—  influence  of  age  upon  the  exhalation  of  car- 
bon dioxide  in 142 

—  influence  of  sex  upon  the  exhalation  of  car- 
bon dioxide  in 143 

influence  of  digestion  upon  the  exhalation 

of  carbon  dioxide  in 143 

—  influence  of  inanition  upon  the  exhalation 

of  carbon  dioxide  in 144 

influence  of  diet  upon  the  exhalation  of 

carbon  dioxide  in 144 

influence  of  alcoholic  beverages,  tea,  and 

coffee  upon  the  exhalation  of  carbon  dioxide 

in 144 

influence  of  exercise  upon  the  exhalation 

of  carbon  dioxide  in 142,  145 

influence  of  sleep  upon  the  exhalation  of 

carbon  dioxide  in 145 

—  relations  of  the  consumption  of  oxygen  to 
the  production  of  carbon  dioxide  in 146 

influence  of  moisture  and  temperature  upon 

the  exhalation  of  carbon  dioxide  in 146 

influence  of  season  upon  the  exhalation  of 

carbon  dioxide  in 146 

relations  between  the  quantity  of  oxygen 

consumed  and  the  quantity  of  carbon  dioxide 

exhaled  in 146 

sources  of  the  carbon  dioxide  exhaled  in..  148 

exhalation  of  watery  vapor  in 148 

exhalation   of   ammonia,   organic   matter 

etc.,  in 149 

exhalation  of  nitrogen  in 150 

changes  in  the  blood  in 150 

mechanism  of  the  interchange  of  gases  be- 
tween the  blood  and  the  air  in 156 

relations  of,  to  nutrition 156 

cutaneous 161 

—  in  a  confined  space 163 

connection  of  the  medulla  oblongata  with 

158,  631 

Respiratory  centres 631 

Respiratory  efforts  before  birth 161,  822 

Respiratory  excitants 144 

Respiratory  movements,  character  of,  and  cause 

of  these  movements 157 

Respiratory  movements  of  the  glottis .  Ill 

Respiratory  non-exciters 144 

Respiratory  sense 157,  631 

Resultant  tones . .  745 


INDEX. 


867 


PAGE 

Rete  testis 786 

Retina,  physiological  anatomy  of 680 

sensibility  of  the  layer  of  rods  and  cones  of  C98 

shadows  of  the  vessels  of G98 

—  relative  sensibility  of  the  different  parts  of  700 
— -  corresponding  points  in 713 

Retrahens  aurem 731 

Rhodopsine 700 

Ribs 116 

Right-handedness  (see  Dextral  pre-eminence). . .  847 

Rigor  mortis  (see  Cadaveric  rigidity) 850 

Rima  glottidis Ill 

Rolling  movements  following  injury  of  certain 

parts  of  the  encephalon  etc 633 

Rosenmuller,  organ  of 771,  831 

Rut,  identity  of,  with  menstruation 781 

Ruysch,  tunic  of 677 

Saccharose 171 

Saccule  of  the  internal  ear 756 

Sacro-lumbalis,  action  of.  in  expiration 126 

Sacrum,  consolidation  of 817 

Saliva 195 

—  parotid 195 

secretion  of 196 

relations  of  the  flow  of,  to  mastication 196 

—  alternation  in  the  secretion  of,  upon  the 
two  sides  196 

submaxillary 196 

—  influence  of  sapid  substances  upon  the  se- 
cretion of 197 

sublingual 197 

influence  of  sapid  substances  upon  the  se- 
cretion of 197 

fluids  from  the  smaller  glands  of  the  mouth, 

tongue,  and  pharynx 197 

mixed 198 

•  influence  of  matters  introduced  into  the 

stomach  through  a  gastric  fistula  upon  the 
secretion  of 199 

—  quantity  of 199 

—  reaction  of 199 

—  quantity  of,  secreted  during  the  intervals 

of  mastication 199 

general  properties  and  composition  of 199 

table  of  the  composition  of 200 

uses  of 200 

—  influence  of,  upon  deglutition 201 

mechanical  uses  of 201 

Salivary  glands . .  195 

Salivary  secretion,  centre  for 341 

Saponiflcation 174 

Sarcolactates 382 

Sarcolemma 467 

Savors 663 

Scala  tympani  of  the  cochlea 758 

Scala  vestibuli  of  the  cochlea 758 

Scalene  muscles,  action  of,  in  respiration 119 

Scarpa,  humor  of. 759 

Schlemm,  canal  of 680 

Schneiderian  mucous  membrane  658 

Schsvann,  sheath  of 507 

—  white  substance  of 507 

Sclerotic  coat  of  the  eye 675 

—  development  of •. 821 

Scrotum 785 


PAGE 

Scrotum,  development  of 834 

Sebaceous  glands 320 

—  first  appearance  of 818 

Sebaceous  matter 324 

Secreted  fluids,  classification  of 307 

Secretion,  general  considerations 306,  311 

mechanism  of 307 

distinction  of ,  from  excretion 307,  311,  341 

mechanism  of,  as  distinguished  from  ex- 
cretion  308 

—  influence  of  the  composition  and  pressure 

of  the  blood  upon 311 

influence  of  the  nervous  system  upon 312 

paralytic 313 

centres  presiding  over 340 

Segmentation  of  the  vitellus 799 

Semen 790 

—  quantity  of 790 

mucous  secretions  mixed  with 790 

in  advanced  age 793 

ejaculation  of 794 

penetration  of,  into  the  uterus 795 

passage  of,  through  the  Fallopian  tubes . . .  795 

time  occupied  by  passage  of,  to  the  ova- 
ries   795 

Semicircular  canals,  bony 736 

membranous 756 

uses  of 762 

influence  of,  upon  equilibration 762 

disease  of  (M^niere's  disease) 626,  763 

development  of 821 

Semilunar  valves,  pulmonic 37 

aortic 37 

safety-valve  function  of 44 

Seminal  vesicles 788 

Seminiferous  tubes 786,  787 

Semi-vowels 503 

Sensation  in  amputated  members  etc 525 

Sensory  nerves,  disappearance  of  the  physio- 
logical properties  of 521 

reappearance  of  sensation  in 522 

action  of 525 

Septum  lucidum,  development  of 820 

Serine 23 

Seroline 265 

Serotina,  cells  of 812 

Serous  cavities 275,  315 

Serous  fluids 315 

Serratus  magnus,  action  of,  in  respiration 122 

Serratus  posticus  superior,  action  of,  in  respira- 
tion    122 

Serum  of  the  blood  (see  Blood) 24 

Sex,  determination  of,  in  the  foetus 797 

Sexual  intercourse  (see  Coitus) 793 

Sighing 130 

Sight  (see  Vision) 671 

Sinus  terminalis  of  the  area  vasculosa 835 

Sinuses  of  Valsalva 37 

Skatol,  production  of,  by  action  of  trypsine  on 

albuminoids 249,  267 

in  the  faeces 264 

Skeleton,  development  of 817 

ossification  of 818 

Skin,  respiration  by 161 

—  effects  of  an  impermeable  coating  applied 
to....  ....  162 


868 


INDEX. 


PAGE 

Skin,  absorption  by 286 

—  physiological  anatomy  of 342 

quantity  of  exhalation  from 356 

—  action  of,  in  the  equalization  of  the  ani- 
mal heat  357,  456 

—  tactile  papillae  of 515 

development  of 818 

Skull,  development  of 817 

Sleep 647 

condition  of  the  brain  and  nervous  system 

in 649 

650 
652 


—  produced  by  pressure  on  the  carotids 

conditions  of  various  functions  in 651, 

Smegma  of  the  prepuce  and  of  the  labia  mi- 

nora 325 

Smell  (see  Olfaction) 658 

Sneezing 129 

Snoring 128 

Sobbing 130 

Sodium  chloride,  uses  of,  in  the  blood 21 

uses  of  in  alimentation 175 

as  a  condiment 181 

Solitary  glands  of  the  intestine 239 

Somatopleure 802 

Somites 816 

Sommering,  yellow  spot  of 681 

Sound,  physics  of 737 

reflection  of 739 

refraction  of 739 

shadows  of 739 

rapidity  of  transmission  of 739 

noisy  and  musical 739 

pitch  of 740 

range  of,  in  music 740 

musical  scale  of 740 

—  quality  of 742 

harmonics,  or  overtones  of 743 

resultant  tones  of 745 

summation  tones  of 745 

harmony  of 745 

chords  of 746 

discords  of 746 

beats  in 747 

tones  by  influence  in  (consonance) 747 

Sounds  of  the  heart 44 

Speech,  mechanism  of 501 

Speech-centre 621 

Spermatic  crystals 790 

Spermatine 790 

Spermatoblasts 792 

Spermatozoids 791 

—  duration  of  the  vitality  of,  in  the  female 
generative  passages 791,  795 

development  of 792 

in  advanced  age 793 

penetration  of,  through  the  vitelline  mem- 
brane   793 

Spheno-palatine  ganglion 638 

Sphymograph 68 

Sphincter  of  the  anus 261,  209 

of  the  rectum 269 

—  of  the  bladder 371 

Spices 181 

Spina  biflda 817 

Spinal  accessory  nerve 557 

physiological  anatomy  of 557 


PAGE 

Spinal  accessory  nerve,  properties  and  uses  of..  559 
uses  of  the  internal  branch  of 559 

—  influence  of,  upon  phonation 560 

—  influence  of,  upon  deglutition 560 

influence  of,  upon  the  heart  56,  560 

uses  of  the  external,  or  muscular  branch 

of,  going  to  the  sterno-cleido-mastoid    and 

trapczius  muscles 561 

Spinal  column,  development  of 817 

twisting  of,  in  the  enibryon 817 

Spinal  cord,  rate  of  conduction  by 528 

—  physiological  anatomy  of 586,  589 

direction  of  the  fibres  in 593 

—  general  properties  of 594 

motor  paths  in 595 

sensory  paths  in 595 

hypersesthesia  due  to  injury  of  portions  of.  596 

—  uses  of,  in  connection  with  muscular  co- 
ordination   * 596 

nerve-centres  in 597 

reflex  action  of 598 

—  development  of 819 

Spinal  nerves 538 

motor  and  sensory  roots  of 522,  538 

Splanchnopleure 802 

Spleen,  relations  of,  to  the  blood-corpuscles. 

11,  418 

proportion  of  leucocytes  in  the  blood  of 

the  veins  of - 14,  418 

• physiological  anatomy  of 413 

—  blood-vessels,  nerves,  and  lymphatics  of. .  415 

chemical  constitution  of 416 

variations  in  the  volume  of 417 

—  extirpation  of 417 

uses  of 418 

—  development  of 824 

Stapedius  muscle 734 

Stapes 733 

—  development  of 827 

Starch 171 

Steapsine 246,  250 

Stearine 174 

Steno,  duct  of 195 

Stercorine 265 

Stereoscope 716 

Sterno-mastoideus,  action  of,  in  respiration 122 

St.  Martin,  case  of 216 

Stomach,  physiological  anatomy  of 211 

—  glands 214 

closed  follicles  of 216 

secretion  of  (see  Gastric  juice) 216 

changes  in  the  appearance  of  the  mucous 

membrane  of,  during  the  secretion  of  gastric 

juice 218 

extracts  of  the  mucous  membrane  of 218 

duration  of  digestion  in 228 

—  digestibility  of  different  aliments  in 229 

influence  of  the  pneumogastrics  upon 230 

influence  of  the  nervous  system  upon 230 

—  movements  of 230 

—  regurgitation  of  food  from 232 

gases  of 232 

—  development  of 823 

Strabismus,  external 542 

internal 547 

Styloid  ligament,  development  of 827 


INDEX. 


869 


Subclavian  arterie%,  development  of 837 

Subclavian  veins,  development  of 838 

Sublingnal  nerves,  physiological  anatomy  of . . .  502 
properties  and  uses  of 5(i2 

—  effects  of  section  of,  upon  deglutition 583 

Sublingual  saliva  (see  Saliva) 197 

Submaxillary  ganglion 638 

Submaxillary  saliva  (see  Saliva) 196 

Sucking,  mechanism  of 188 

Sudoriparous  glands  (see  Sweat) 353 

first  appearance  of 818 

Suffocation,  sense  of 160 

Sugars 170 

Sugar  of  milk 336 

—  production  of,  by  the  liver  (see  Liver) 408 

— •  character  of,  produced  by  the  liver 410 

Sulphates  in  the  body 437 

Sulphocyanide  in  the  saliva 195 

Summation  tones 745 

Superfecundation 797 

Suprarenal  capsules,  weight  of,  compared  with 

the  kidneys,  in  foetus  and  adult 419 

structure  of 419 

chemical  reactions  of 421 

—  extirpation  of 421 

—  development  of 832 

Sweat 353 

—  mechanism  of  the  secretion  of 355 

influence  of  the  nervous  system  upon  the 

secretion  of 355 

quantity  of 356 

properties  and  composition  of 357 

equalization  of  animal  heat  by 357 

peculiarities  of,  in  certain  parts 358 

Sweat-centres 356 

Sweat-glands . 353 

Sympathetic  system 635 

—  general  arrangement  of 635 

—  cranial  ganglia  of 637 

cervical  ganglia  of 638 

thoracic  ganglia  of 639 

abdominal  and  pelvic  ganglia  of 639 

—  general  properties  of 640 

• —  direct  experiments  upon 641 

influence  of  division  of  nerves  of,  upon 

animal  heat 641 

—  influence  of,  upon  the  circulation 641 

—  influence  of,  upon  secretion 642 

—  influence  of,  upon  the  urine 642 

—  influence  of,  upon  the  intestines 642 

—  reflex  phenomena  in  643 

—  development  of 819 

Sympexions 790 

Synovial  bursa; 315 

Synovial  fluid 316 

Synovial  fringes 315 

Synovial  membranes 315 

Synovial  sheaths 316 

Sy novine 316 

Tactile  centre 658 

Tactile  corpuscles 514,  657 

Taste  (see  Gustation) 663 

—  influence  of  the  chorda  tympani  upon.  554,  664 

—  nerves  of 664 

—  action  of  the  glosso-pharyngeal  nerve  in  .    667 


PAOB 

Taste-beakers 669 

Taste-cells 670 

Taste-centre 670 

Taste-pores 670 

Tastes  and  flavors 663 

Taurine  in  the  urine 384 

Taurocholic  acid  and  sodium  taurocholate 402 

Tea 179 

—  composition  of 180 

Tears 727 

Teeth,  physiological  anatomy  of 189 

—  uses  of  the  sensibility  of,  to  hard  sub- 
stances, in  mastication 195 

Teeth,  temporary,  development  of 828 

—  order  of  eruption  of 830 

permanent,  development  of 829 

order  of  eruption  of 830 

Temperature  of  the  body 446 

sense  of 657 

Temporo-maxillary  articulation 192 

Tendons,  connection  of,  with  the  muscles 470 

Tenon,  capsule  of 674 

Tensor  palati 204,  735 

Tensor  tympani , 733,  751 

Testicles 785 

—  first  appearance  of 831 

descent  of 831 

gubernaculum  of 1 . .  831 

Tegmentum 609 

Tetanus 477 

Theine 180 

Theobromine 180 

Thirst 167 

—  effects  of  haemorrhage  upon 107 

seat  of  sense  of 168 

relief  of,  by  absorption  of  water  by  the 

skin 287 

Thoracic  duct 273 

—  fistula  into 294 

Thorax,  form  of 116 

—  action  of  the  elasticity  of  the  walls  of,  in 
expiration 123 

Thraenine 728 

Thymus  gland 423 

Thyro-arytenoid  muscles 491 

Thyroid  gland,  structure  of 421 

—  chemical  constitution  of 422 

—  extirpation  of 422 

Tidal  air 131 

Titillation ; 654 

Tongue,  action  of,  in  sucking 188 

action  of,  in  mastication 194 

—  glands  of 198 

action  of,  in  deglutition 206 

action  of,  in  phonation 495 

—  papillae  of 668 

—  development  of 827 

Tonsils 198,  203 

Touch,  sense  of 655 

—  variations  in  the  sense  of,  in  different  parts  655 

extraordinary  development  of  the  sense  of  655 

table  of  variations  in  the  sense  of,  in  differ- 
ent parts 656 

—  centre  for 658 

Trachea Ill 

—  development  of 825 


870 


INDEX. 


PAGE 

Trachealis  muscle 113 

Tragus  of  the  ear 730 

Transfusion  of  blood 2 

Transudations 308 

Transversalis,  action  of,  in  expiration 120 

Trapezius,  action  of  the  superior  portion  of,  in 

respiration 122 

Triangularis  sterni,  action  of,  in  expiration 125 

Tricuspid  valve 36 

saf ty-valve  action  of 44 

Trifacial,  or  trigeminal  nerve  (see  Fifth  cranial 

nerve,  large  root  of) 564 

Trigone 371 

Trioleine 174 

Tripalmitine 174 

Triphthongs 501 

Tristearine 174 

Trophic  centres  and  nerves 645 

Trypsine 246,  249 

Trypsinogen 310 

Tuber  annulare  (see  Pons  Varolii) 609 

Tubercula  quadrigemina  608 

development  of 819,  820 

Turck,  columns  of 592 

Twins,  one  white  and  the  other  black 798 

one  male  and  the  other  female 781,  799 

question  of  development  of,  from  a  single 

ovum  or  from  two  ova 844 

Tympanic  membrane,  physiological  anatomy 

of 732,748 

cone  of  light  in 750 

uses  of 750 

Tympanum 732 

development  of 820 

Tyrosine,  production  of,  by  the  action  of  tryp- 

sine  on  albuminoids 249 

in  the  urine 384 

Tyson,  glands  of 322 

Umbilical  arteries  and  vein 807,  808 

Umbilical  cord 808,  836 

valves  in  the  vessels  of 809 

Umbilical  hernia  in  the  foetus 807,  809,  822 

Umbilical  vein,  closure  of 841 

Umbilical  vesicle 800 

Umbilicus,  amniotic 803 

intestinal 807 

Urachus 809,  822 

Urea 376 

—  where  found  in  the  economy 376 

artificial  formation  of 376 

origin  of 377 

—  formation  of,  in  the  liver 377,  400 

—  theory  of  production  of,  from  uric  acid, 
creatine  etc 377 

—  influence   of   ingesta   upon   the   elimina- 
tion of 377 

—  influence  of  muscular  exercise  upon  the 
elimination  of 378 

quantity  of  daily  excretion  of 380 

Ureters,  physiological  anatomy  of 369 

Urethra 372 

glands  of 789 

Uric  acid  and  its  compounds 380 

Urinary  apparatus,  development  of 832 

Urine,  mechanism  of  the  production  of 366 


Urine,  influence  of  blood-pressur£,  the  nervous 

system  etc.,  upon  the  secretion  of 368 

— —  effects  of  destruction  of  the  nerves  of  the 

kidneys  upon  the  secretion  of 313,  369 

alternate  action  of  the  kidneys  in  the  secre- 
tion of 369 

mechanism  of  the  discharge  of 371 

properties  and  composition  of 373 

table  of  constituents  of 375 

fatty  matters  in 385 

inorganic  constituents  of 385 

coloring- matter  and  mucus  of 388 

gases  of 388 

variations  in  the  composition  of 389 

variations  of,  with  age  and  sex  390 

of  the  foetus 390 

variations  of,  at  different  seasons  and  at 

different  periods  of  the  day 391 

influence  of  mental  exertion  upon 391 

Urochrome 388 

Uterine  plug  of  mucus 811 

Uterus 766 

—  situation  and  position  of 766 

ligaments  of 766 

physiological  anatomy  of 771 

blood-vessels  of 774 

changes  in  the  mucous  membrane  of,  dur- 
ing menstruation 774,  783 

formation  of  the  membrane  deciduse  from 

the  mucous  membrane  of 810 

secretion  of  mucus  by  the  cervix  of,  in 

pregnancy 811 

first  appearance  of  the  new  mucous  mem- 
brane of,  in  pregnancy 811,  846 

development  of 831 

double 831 

enlargement  of,  in  pregnancy 842 

cause  of  the  first  contraction  of,  in  normal 

parturition 845 

involution  of 846 

—  restoration  of  the  mucous  membrane  of, 
after  parturition 846 

Utricle  of  the  internal  ear 756 

Uvea 679 

Uvula 203 

Uvula  vesicse 371 

Vagina 766,  776 

—  double &31 

Valsalva,  sinuses  of 37 

humor  of 759 

Valsalva's  method  for  protection  of  the  mem- 

braua  tympani  from  concussion 753 

Valve,  tricuspid 36 

—  pulmonic 37 

mitral 37 

aortic 37 

Valves  of  the  veins,  discovery  of 30 

—  uses  of. 31,  98 

Valves  of  the  heart,  action  of 43 

Valves  of  the  lymphatics 276,  282 

Valvulas  conniventes 235 

—  development  of 823 

Vas  def  erens 787 

movements  of,  produced  by  galvanization 

of  the  lumbar  portion  of  the  spinal  cord 788 


INDEX. 


871 


PAGE 

Vas  deferens,  development  of,  from  the  Wolf- 

fian  duct 831 

Vasa  vasorum 63,  89 

Vasa  vorticosa 677 

Vascular  arches,  in  the  embryon 837 

Vaso-dilator  nerves 645 

Vaso-mhibitory  nerves 645 

Vaso-motor  centres  and  nerves 642 

Vaso-motor  reflex  phenomena 643 

Vater,  corpuscles  of 513 

Veins,  variations-  in  the  color  of  the  blood  in. . .      4 

—  renal,  color  of  the  blood  in 4 

discovery  of  valves  of 30 

uses  of  the  valves  of 31,  98 

circulation  in 87 

—  capacity  of,  as  compared  with  that  of  the 
arteries 87 

anastomoses  of. ...   89,  99 

—  structure  and  properties  of  89 

vasa  vasorum  of 89 

strength  of  the  walls  of 90 

elasticity  and  contractility  of 91 

valves  of 91 

those  in  which  there  are  no  valves 92 

course  of  the  blood  in 93 

—  pulse  in 94 

—  pressure  of  blood  in 94 

—  rapidity  of  the  flow  of  blood  in 95 

. causes  of  the  circulation  in 95 

—  obstacles  to  the  flow  of  blood  in 95,  100 

influence  of  muscular  contraction  upon  the 

flow  of  blood  in 96 

—  influence  of  the  force  of  aspiration  from 
the  thorax  upon  the  circulation  in 90 

—  of  the  liver,  circulation  in 97 

—  relations  of  respiration  to  the  circulation 

in 97,  100 

entrance  of  air  into 98 

—  influence  of  gravity  upon  the  circulation 

in 98,  101 

influence  of  a  suction  force  exerted  by  larg- 
er upon  smaller  vessels  upon  the  circulation  in    98 

—  regurgitant  pulse  in 100 

—  development  of 837 

Velum  pendulum  palati 203 

Vena  innominata,  development  of 838 

Venae  cavae,  development  of 837 

Venereal  sense 658 

Venoms,  absorption  of 320 

Ventilation  of  hospitals,  prisons  etc 137 

Ventricles  of  the  heart 34 

—  comparative  capacity  of  right  and  left 34 

—  comparative  thickness  of  right  and  left 35 

—  shortening  and  elongation  of 39 

Verheyn,  stars  of 365 

Vermiform  appendix 258 

Vernix  caseosa 325,  818 

Vertebrae,  first  appearance  of 817 

Vertebral  arteries,  development  of 836 

Vertebral  plates ...  814 

Vesiculae  seminales 788 

development  of 832 

Vestibule  of  the  ear 736,  755 

Villi  of  the  small  intestine 237 

—  development  of 823 

Vinegar 181 


PAGE 

Visceral  arches 825 

Visceral  clefts 825 

Visceral  plates 815 

Vision,  physiological  anatomy  of  the  organs  of  671 

—  area  of 691 

—  laws  of  refraction,  dispersion  etc.,  in 692 

refraction  by  lenses  in 693 

—  myopic 695 

—  hypermetropic 695 

—  presbyopic 695 

formation  of  images  in 698 

—  demonstration  of  the  fact  that  the  layer  of 
rods  and  cones  is  the  seat  of  impressions  in. .  698 

area  of  distinct. . .  . .  699 


blind  spot  in  the  retina  in 699 

—  accommodation  of,  to  different  degrees  of 
illumination 702 

—  mechanism  of  refraction  in 702 

—  astigmatic 704 

movements  of  the  iris  in 705 

—  accommodation  of,  for  different  distances.  708 

through  a  small  orifice,  like  a  pinhole 711 

erect,  although  the  images  on  the  retina  are 

inverted. '. 711 

—  field  of 711 

binocular 712 

—  double 712 

—  corresponding  points  on  the  retina  in 713 

—  horopter  of 714 

—  monocular 714 

—  binocular  field  of 714 

estimation  of  distance,  the  form  and  so- 
lidity of  objects,  etc.,  in 715 

with  the  stereoscope 716 

binocular  fusion  of  colors  in 716 

duration  of  luminous  impressions  in  (after 

images) 716 

fusion  of  colors  in 717 

irradiation  in 717 

accidental  areolse  in 718 

centres  for 722 

—  perception  of  colors  in 723 

—  development  of  the  organs  of 821 

Visual  purple  and  visual  yellow 700 

Vital  capacity  of  the  lungs 133 

variations  in,  with  stature 133 

Vital  point 632 

Vitelline  circulation 835 

Vitelline  membrane  of  the  ovnm 778 

disappearance  of,  after  fecundation 803 

—  villosities  of 803 

Vitelline  nucleus 797 

Vitellus 778 

deformation  and  gyration  of 796 

—  formation  of  the  polar  globule  of 796 

formation  of  the  nucleus  of 797 

—  bright  appearance  of,  after  fecundation. . .  799 

—  segmentation  of 799 

Vitreous  humor 688 

—  development  of  821 

Vocal  chords   110,  488 

—  action  of,  in  phonation 491 

Vocal  registers , 496 

Voice  and  speech 488 

Voice,  mechanism  of  the  production  of 491 

action  of  the  vocal  chords  in.. .  . .  491 


872 


INDEX. 


PAGE 

Voice,  varieties  of . .  493 

—  in  boys 493 

range  of 494 

action  of  the  intrinsic  muscles  of  the  larynx 

in 494 

—  action  of  the  accessory  organs  of 495 

action  of  the  trachea  in 495 

—  action  of  the  larynx  and  epiglottis  in 495 

—  action  of  the  pharynx  in 495 

action  of  the  mouth  in 495 

action  of  the  nasal  fossae  in 495 

action  of  the  tongue  in 495 

—  action  of  the  velum  palati  in 496 

different  registers  of 496 

influence  of   the   spinal   accessory  nerve 

upon 560 

Voltaic  alternation 534 

Vomiting,  mechanism  of 232 

Vowels 501 

Vowel-sounds,  mechanism  of 502 

Wagner,  corpuscles  of 514 

—  spot  of 778 

Wallerian  method 521 

Water,  uses  of,  in  the  blood 20,  430 


Water,  as  a  product  of  excretion 389,  455 

uses  of,  in  alimentation  etc 431 

table  of  quantities  of,  in  different  tissues. .  431 

origin  and  discharge  of 431 

Watery  vapor,  exhalation  of,  by  the  lungs 148 

Weight,  appreciation  of 654 

Wharton,  duct  of 196 

gelatine  of 809 

Whispering 503 

Wolfflan  bodies 814,  830 

—  structure  of 831 

—  time  of  disapearance  of,  in  the  female.  ...  831 
Wolfflan  ducts 831 

—  development  of  the  vasa  deferentia  from. .  831 

Word-blindness 621 

Wrisberg,  nerve  of 550 


Xanthine . 


Yawning 130 

Yellow  spot  of  SOmmerring 681 

Youth 849 

Zona  pellucida  (zona  radiata) 778 

Zone  of  Zinn 677,  687 

Zymogen k 215,  310 


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